GPU based acceleration of first principles calculation
International Nuclear Information System (INIS)
Tomono, H; Tsumuraya, K; Aoki, M; Iitaka, T
2010-01-01
We present a Graphics Processing Unit (GPU) accelerated simulations of first principles electronic structure calculations. The FFT, which is the most time-consuming part, is about 10 times accelerated. As the result, the total computation time of a first principles calculation is reduced to 15 percent of that of the CPU.
First-principles calculations of mobility
Krishnaswamy, Karthik
First-principles calculations can be a powerful predictive tool for studying, modeling and understanding the fundamental scattering mechanisms impacting carrier transport in materials. In the past, calculations have provided important qualitative insights, but numerical accuracy has been limited due to computational challenges. In this talk, we will discuss some of the challenges involved in calculating electron-phonon scattering and carrier mobility, and outline approaches to overcome them. Topics will include the limitations of models for electron-phonon interaction, the importance of grid sampling, and the use of Gaussian smearing to replace energy-conserving delta functions. Using prototypical examples of oxides that are of technological importance-SrTiO3, BaSnO3, Ga2O3, and WO3-we will demonstrate computational approaches to overcome these challenges and improve the accuracy. One approach that leads to a distinct improvement in the accuracy is the use of analytic functions for the band dispersion, which allows for an exact solution of the energy-conserving delta function. For select cases, we also discuss direct quantitative comparisons with experimental results. The computational approaches and methodologies discussed in the talk are general and applicable to other materials, and greatly improve the numerical accuracy of the calculated transport properties, such as carrier mobility, conductivity and Seebeck coefficient. This work was performed in collaboration with B. Himmetoglu, Y. Kang, W. Wang, A. Janotti and C. G. Van de Walle, and supported by the LEAST Center, the ONR EXEDE MURI, and NSF.
First-principles calculations of novel materials
Sun, Jifeng
Computational material simulation is becoming more and more important as a branch of material science. Depending on the scale of the systems, there are many simulation methods, i.e. first-principles calculation (or ab-initio), molecular dynamics, mesoscale methods and continuum methods. Among them, first-principles calculation, which involves density functional theory (DFT) and based on quantum mechanics, has become to be a reliable tool in condensed matter physics. DFT is a single-electron approximation in solving the many-body problems. Intrinsically speaking, both DFT and ab-initio belong to the first-principles calculation since the theoretical background of ab-initio is Hartree-Fock (HF) approximation and both are aimed at solving the Schrodinger equation of the many-body system using the self-consistent field (SCF) method and calculating the ground state properties. The difference is that DFT introduces parameters either from experiments or from other molecular dynamic (MD) calculations to approximate the expressions of the exchange-correlation terms. The exchange term is accurately calculated but the correlation term is neglected in HF. In this dissertation, DFT based first-principles calculations were performed for all the novel materials and interesting materials introduced. Specifically, the DFT theory together with the rationale behind related properties (e.g. electronic, optical, defect, thermoelectric, magnetic) are introduced in Chapter 2. Starting from Chapter 3 to Chapter 5, several representative materials were studied. In particular, a new semiconducting oxytelluride, Ba2TeO is studied in Chapter 3. Our calculations indicate a direct semiconducting character with a band gap value of 2.43 eV, which agrees well with the optical experiment (˜ 2.93 eV). Moreover, the optical and defects properties of Ba2TeO are also systematically investigated with a view to understanding its potential as an optoelectronic or transparent conducting material. We find
THERMODYNAMIC MODELING AND FIRST-PRINCIPLES CALCULATIONS
Energy Technology Data Exchange (ETDEWEB)
Turchi, P; Abrikosov, I; Burton, B; Fries, S; Grimvall, G; Kaufman, L; Korzhavyi, P; Manga, R; Ohno, M; Pisch, A; Scott, A; Zhang, W
2005-12-15
The increased application of quantum mechanical-based methodologies to the study of alloy stability has required a re-assessment of the field. The focus is mainly on inorganic materials in the solid state. In a first part, after a brief overview of the so-called ab initio methods with their approximations, constraints, and limitations, recommendations are made for a good usage of first-principles codes with a set of qualifiers. Examples are given to illustrate the power and the limitations of ab initio codes. However, despite the ''success'' of these methodologies, thermodynamics of complex multi-component alloys, as used in engineering applications, requires a more versatile approach presently afforded within CALPHAD. Hence, in a second part, the links that presently exist between ab initio methodologies, experiments, and CALPHAD approach are examined with illustrations. Finally, the issues of dynamical instability and of the role of lattice vibrations that still constitute the subject of ample discussions within the CALPHAD community are revisited in the light of the current knowledge with a set of recommendations.
First principles calculations for analysis martensitic transformations
International Nuclear Information System (INIS)
Harmon, B.N.; Zhao, G.L.; Ho, K.M.; Chan, C.T.; Ye, Y.Y.; Ding, Y.; Zhang, B.L.
1993-01-01
The change in crystal energy is calculated for atomic displacements corresponding to phonons, elastic shears, and lattice transformations. Anomalies in the phonon dispersion curves of NiAl and NiTi are analyzed and recent calculations for TiPd alloys are presented
Ammonia synthesis from first principles calculations
DEFF Research Database (Denmark)
Honkala, Johanna Karoliina; Hellman, Anders; Remediakis, Ioannis
2005-01-01
. When the size distribution of ruthenium particles measured by transmission electron microscopy was used as the [ink between the catalyst material and the theoretical treatment, the calculated rate was within a factor of 3 to 20 of the experimental rate. This offers hope for computer-based methods......The rate of ammonia synthesis over a nanoparticle ruthenium catalyst can be calculated directly on the basis of a quantum chemical treatment of the problem using density functional theory. We compared the results to measured rates over a ruthenium catalyst supported on magnesium aluminum spinet...
First-principle calculations of structural, electronic, optical, elastic ...
Indian Academy of Sciences (India)
S CHEDDADI
2017-11-28
Nov 28, 2017 ... First-principle calculations on the structural, electronic, optical, elastic and thermal properties of the chalcopyrite ... The Kohn–Sham equations were solved using the ... RMTKmax = 7 was used for all the investigated systems,.
First principles calculation of two dimensional antimony and antimony arsenide
Energy Technology Data Exchange (ETDEWEB)
Pillai, Sharad Babu, E-mail: sbpillai001@gmail.com; Narayan, Som; Jha, Prafulla K. [Department. of Physics, Faculty of Science, The M. S. University of Baroda, Vadodara-390002 (India); Dabhi, Shweta D. [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar-364001 (India)
2016-05-23
This work focuses on the strain dependence of the electronic properties of two dimensional antimony (Sb) material and its alloy with As (SbAs) using density functional theory based first principles calculations. Both systems show indirect bandgap semiconducting character which can be transformed into a direct bandgap material with the application of relatively small strain.
First principles calculations of structural, electronic and thermal ...
Indian Academy of Sciences (India)
Home; Journals; Bulletin of Materials Science; Volume 37; Issue 5. First principles calculations of structural, electronic and thermal properties of lead chalcogenides PbS, PbSe and PbTe compounds. N Boukhris H Meradji S Amara Korba S Drablia S Ghemid F El Haj Hassan. Volume 37 Issue 5 August 2014 pp 1159-1166 ...
First-principle calculations of the structural, electronic ...
Indian Academy of Sciences (India)
First-principle calculations were performed to study the structural, electronic, thermodynamic and thermal properties of ... functional theory (DFT) combined with the quasi-harmonic .... is consistent with Vegard's law which assumes that the lat- tice constant varies .... reflects a charge-transfer effect which is due to the different.
Parallelization for first principles electronic state calculation program
International Nuclear Information System (INIS)
Watanabe, Hiroshi; Oguchi, Tamio.
1997-03-01
In this report we study the parallelization for First principles electronic state calculation program. The target machines are NEC SX-4 for shared memory type parallelization and FUJITSU VPP300 for distributed memory type parallelization. The features of each parallel machine are surveyed, and the parallelization methods suitable for each are proposed. It is shown that 1.60 times acceleration is achieved with 2 CPU parallelization by SX-4 and 4.97 times acceleration is achieved with 12 PE parallelization by VPP 300. (author)
The first principle calculation of two-dimensional Dirac materials
Lu, Jin
2017-12-01
As the size of integrated device becoming increasingly small, from the last century, semiconductor industry is facing the enormous challenge to break the Moore’s law. The development of calculation, communication and automatic control have emergent expectation of new materials at the aspect of semiconductor industrial technology and science. In spite of silicon device, searching the alternative material with outstanding electronic properties has always been a research point. As the discovery of graphene, the research of two-dimensional Dirac material starts to express new vitality. This essay studied the development calculation of 2D material’s mobility and introduce some detailed information of some approximation method of the first principle calculation.
Prospects for first-principle calculations of scintillator properties
International Nuclear Information System (INIS)
Derenzo, Stephen E.; Weber, Marvin J.
1999-01-01
Several scintillation processes can be modeled from first principles using quantum chemistry cluster calculations and recently available high-performance computers. These processes include the formation of excitons and trapping centers, the diffusion of ionization energy (electrons and holes) through a host crystal, and the efficient capture of these carriers by an activator atom to form a luminous, non-quenched excited state. As examples of such calculations, results are presented for (1) hole transport in the known scintillator host crystal CsI, (2) hole trapping in the non-scintillator PbF 2 , (3) hole transport in the experimentally unexplored PbF 4 , and (4) the electronic nature of excited states of CsI : Tl and CsI : Na
Predicting catalysis: Understanding ammonia synthesis from first-principles calculations
DEFF Research Database (Denmark)
Hellmann, A.; Baerends, E.J.; Biczysko, M.
2006-01-01
. Furthermore, our studies provide new insight into several related fields, for instance, gas-phase and electrochemical ammonia synthesis. The success of predicting the outcome of a catalytic reaction from first-principles calculations supports our point of view that, in the future, theory will be a fully......Here, we give a full account of a large collaborative effort toward an atomic-scale understanding of modern industrial ammonia production over ruthenium catalysts. We show that overall rates of ammonia production can be determined by applying various levels of theory (including transition state...... for any given point along an industrial reactor, and the kinetic results can be integrated over the catalyst bed to determine the industrial reactor yield. We find that, given the present uncertainties, the rate of ammonia production is well-determined directly from our atomic-scale calculations...
First principles calculations of interstitial and lamellar rhenium nitrides
Energy Technology Data Exchange (ETDEWEB)
Soto, G., E-mail: gerardo@cnyn.unam.mx [Universidad Nacional Autonoma de Mexico, Centro de Nanociencias y Nanotecnologia, Km 107 Carretera Tijuana-Ensenada, Ensenada Baja California (Mexico); Tiznado, H.; Reyes, A.; Cruz, W. de la [Universidad Nacional Autonoma de Mexico, Centro de Nanociencias y Nanotecnologia, Km 107 Carretera Tijuana-Ensenada, Ensenada Baja California (Mexico)
2012-02-15
Highlights: Black-Right-Pointing-Pointer The possible structures of rhenium nitride as a function of composition are analyzed. Black-Right-Pointing-Pointer The alloying energy is favorable for rhenium nitride in lamellar arrangements. Black-Right-Pointing-Pointer The structures produced by magnetron sputtering are metastable variations. Black-Right-Pointing-Pointer The structures produced by high-pressure high-temperature are stable configurations. Black-Right-Pointing-Pointer The lamellar structures are a new category of interstitial dissolutions. - Abstract: We report here a systematic first principles study of two classes of variable-composition rhenium nitride: i, interstitial rhenium nitride as a solid solution and ii, rhenium nitride in lamellar structures. The compounds in class i are cubic and hexagonal close-packed rhenium phases, with nitrogen in the octahedral and tetrahedral interstices of the metal, and they are formed without changes to the structure, except for slight distortions of the unit cells. In the compounds in class ii, by contrast, the nitrogen inclusion provokes stacking faults in the parent metal structure. These faults create trigonal-prismatic sites where the nitrogen residence is energetically favored. This second class of compounds produces lamellar structures, where the nitrogen lamellas are inserted among multiple rhenium layers. The Re{sub 3}N and Re{sub 2}N phases produced recently by high-temperature and high-pressure synthesis belong to this class. The ratio of the nitrogen layers to the rhenium layers is given by the composition. While the first principle calculations point to higher stability for the lamellar structures as opposed to the interstitial phases, the experimental evidence presented here demonstrates that the interstitial classes are synthesizable by plasma methods. We conclude that rhenium nitrides possess polymorphism and that the two-dimensional lamellar structures might represent an emerging class of materials
First principles calculations of interstitial and lamellar rhenium nitrides
International Nuclear Information System (INIS)
Soto, G.; Tiznado, H.; Reyes, A.; Cruz, W. de la
2012-01-01
Highlights: ► The possible structures of rhenium nitride as a function of composition are analyzed. ► The alloying energy is favorable for rhenium nitride in lamellar arrangements. ► The structures produced by magnetron sputtering are metastable variations. ► The structures produced by high-pressure high-temperature are stable configurations. ► The lamellar structures are a new category of interstitial dissolutions. - Abstract: We report here a systematic first principles study of two classes of variable-composition rhenium nitride: i, interstitial rhenium nitride as a solid solution and ii, rhenium nitride in lamellar structures. The compounds in class i are cubic and hexagonal close-packed rhenium phases, with nitrogen in the octahedral and tetrahedral interstices of the metal, and they are formed without changes to the structure, except for slight distortions of the unit cells. In the compounds in class ii, by contrast, the nitrogen inclusion provokes stacking faults in the parent metal structure. These faults create trigonal-prismatic sites where the nitrogen residence is energetically favored. This second class of compounds produces lamellar structures, where the nitrogen lamellas are inserted among multiple rhenium layers. The Re 3 N and Re 2 N phases produced recently by high-temperature and high-pressure synthesis belong to this class. The ratio of the nitrogen layers to the rhenium layers is given by the composition. While the first principle calculations point to higher stability for the lamellar structures as opposed to the interstitial phases, the experimental evidence presented here demonstrates that the interstitial classes are synthesizable by plasma methods. We conclude that rhenium nitrides possess polymorphism and that the two-dimensional lamellar structures might represent an emerging class of materials within binary nitride chemistry.
Accurate line intensities of methane from first-principles calculations
Nikitin, Andrei V.; Rey, Michael; Tyuterev, Vladimir G.
2017-10-01
In this work, we report first-principle theoretical predictions of methane spectral line intensities that are competitive with (and complementary to) the best laboratory measurements. A detailed comparison with the most accurate data shows that discrepancies in integrated polyad intensities are in the range of 0.4%-2.3%. This corresponds to estimations of the best available accuracy in laboratory Fourier Transform spectra measurements for this quantity. For relatively isolated strong lines the individual intensity deviations are in the same range. A comparison with the most precise laser measurements of the multiplet intensities in the 2ν3 band gives an agreement within the experimental error margins (about 1%). This is achieved for the first time for five-atomic molecules. In the Supplementary Material we provide the lists of theoretical intensities at 269 K for over 5000 strongest transitions in the range below 6166 cm-1. The advantage of the described method is that this offers a possibility to generate fully assigned exhaustive line lists at various temperature conditions. Extensive calculations up to 12,000 cm-1 including high-T predictions will be made freely available through the TheoReTS information system (http://theorets.univ-reims.fr, http://theorets.tsu.ru) that contains ab initio born line lists and provides a user-friendly graphical interface for a fast simulation of the absorption cross-sections and radiance.
Reliability evaluation of thermophysical properties from first-principles calculations.
Palumbo, Mauro; Fries, Suzana G; Dal Corso, Andrea; Kürmann, Fritz; Hickel, Tilmann; Neugebauer, Jürg
2014-08-20
Thermophysical properties, such as heat capacity, bulk modulus and thermal expansion, are of great importance for many technological applications and are traditionally determined experimentally. With the rapid development of computational methods, however, first-principles computed temperature-dependent data are nowadays accessible. We evaluate various computational realizations of such data in comparison to the experimental scatter. The work is focussed on the impact of different first-principles codes (QUANTUM ESPRESSO and VASP), pseudopotentials (ultrasoft and projector augmented wave) as well as phonon determination methods (linear response and direct force constant method) on these properties. Based on the analysis of data for two pure elements, Cr and Ni, consequences for the reliability of temperature-dependent first-principles data in computational thermodynamics are discussed.
Thermopower switching by magnetic field: first-principles calculations
DEFF Research Database (Denmark)
Maslyuk, Volodymyr V.; Achilles, Steven; Sandratskii, Leonid
2013-01-01
We present first-principles studies of the thermopower of the organometallic V4Bz5 molecule attached between Co electrodes with noncollinear magnetization directions. Different regimes in the formation of the noncollinear magnetic state of the molecule lead to a remarkable nonmonotonous dependence...
First principle calculations for improving desorption temperature in ...
Indian Academy of Sciences (India)
5Institute of Nanomaterials and Nanotechnology, MAScIR, Rabat 10000, Morocco. 6Hassan II Academy of Science and Technology, Rabat 10000, Morocco. 7Institut Néel, CNRS-UJF, 38042 Grenoble cedex 9, France. MS received 26 June 2013; revised 25 December 2013. Abstract. Using ab initio calculations, we predict ...
Hydrogen storage on graphene: First-principle calculations
Boukhvalov, D.W.; Katsnelson, M.I.; Lichtenstein, A.I.
2007-01-01
Density functional calculations of electronic structure, total energy, structural distortions, and magnetism for hydrogenated single-layer, bilayer, and multi-layer graphene are performed. It is found that hydrogen-induced magnetism can survives only at very low concentrations of hydrogen
Photoabsorption in sodium clusters: first principles configuration interaction calculations
Priya, Pradip Kumar; Rai, Deepak Kumar; Shukla, Alok
2017-05-01
We present systematic and comprehensive correlated-electron calculations of the linear photoabsorption spectra of small neutral closed- and open-shell sodium clusters (Nan, n = 2 - 6), as well as closed-shell cation clusters (Nan+, n = 3, 5). We have employed the configuration interaction (CI) methodology at the full CI (FCI) and quadruple CI (QCI) levels to compute the ground, and the low-lying excited states of the clusters. For most clusters, besides the minimum energy structures, we also consider their energetically close isomers. The photoabsorption spectra were computed under the electric-dipole approximation, employing the dipole-matrix elements connecting the ground state with the excited states of each isomer. Our calculations were tested rigorously for convergence with respect to the basis set, as well as with respect to the size of the active orbital space employed in the CI calculations. These calculations reveal that as far as electron-correlation effects are concerned, core excitations play an important role in determining the optimized ground state geometries of various clusters, thereby requiring all-electron correlated calculations. But, when it comes to low-lying optical excitations, only valence electron correlation effects play an important role, and excellent agreement with the experimental results is obtained within the frozen-core approximation. For the case of Na6, the largest cluster studied in this work, we also discuss the possibility of occurrence of plasmonic resonance in the optical absorption spectrum. Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjd/e2017-70728-3
First principle calculations of charge ordering in manganites
International Nuclear Information System (INIS)
Baldomir, D.; Pardo, V.; Castro, J.; Iglesias, M.; Arias, J.E.; Rivas, J.
2007-01-01
Electronic structure calculations were performed on the compound La 0.5 Ca 0.5 MnO 3 to study the relationship between the magnetic ordering, the charge ordering and the geometry of the compound. Charge ordering is intimately related to the magnetic ordering. An antiferromagnetic ordering induces charge disproportionation via a Jahn-Teller distortion. A full disproportionation in Mn 3+ /Mn 4+ occurs for the experimental geometry and allows to predict the experimentally found antiferromagnetic insulating state
First Principles Calculations of Electronic Excitations in 2D Materials
DEFF Research Database (Denmark)
Rasmussen, Filip Anselm
electronic transport, optical and chemical properties. On the other hand it has shown to be a great starting point for a systematic pertubation theory approach to obtain the so-called quasiparticle spectrum. In the GW approximation one considers the considers the potential from a charged excitation...... as if it is being screened by the electrons in the material. This method has been very successful for calculating quasiparticle energies of bulk materials but results have been more varying for 2D materials. The reason is that the 2D confined electrons are less able to screen the added charge and some...
Accurate first principles calculation of many-body interactions
International Nuclear Information System (INIS)
Tawa, G.J.; Moskowitz, J.W.; Schmidt, K.E.
1991-01-01
This paper reports on the electronic structure Schrodinger equation that is solved for the van der Waals complexes spin-polarized H 2 and H 3 , and the closed-shell systems He 2 and He 3 by Monte Carlo methods. Two types of calculations are performed, variational Monte Carlo, which gives an upper bound to the eigenvalue of the Schrodinger equation, and Green's function Monte Carlo, which can solve the Schrodinger equation exactly within statistical sampling errors. The simulations are carried out on an ETA-10 supercomputer, and already existing computer codes were extensively modified to ensure highly efficient coding. A major component of the computations was the development of highly optimized many-electron wave functions. The results from the variational Monte Carlo simulations are reported for both the two- and three-body interaction energies
First principle calculations of alkali hydride electronic structures
International Nuclear Information System (INIS)
Novakovic, N; Radisavljevic, I; Colognesi, D; Ostojic, S; Ivanovic, N
2007-01-01
Electronic structure, volume optimization, bulk moduli, elastic constants, and frequencies of the transversal optical vibrations in LiH, NaH, KH, RbH, and CsH are calculated using the full potential augmented plane wave method, extended with local orbitals, and the full potential linearized augmented plane wave method. The obtained results show some common features in the electronic structure of these compounds, but also clear differences, which cannot be explained using simple empirical trends. The differences are particularly prominent in the electronic distributions and interactions in various crystallographic planes. In the light of these findings we have elaborated some selected experimental results and discussed several theoretical approaches frequently used for the description of various alkali hydride properties
Zhao, Hongxia; Yang, Yong; Shu, Xin; Wang, Yanwei; Ran, Qianping
2018-04-09
First-principle calculations, especially by the density functional theory (DFT) methods, are becoming a power technique to study molecular structure and properties of organic/inorganic interfaces. This review introduces some recent examples on the study of adsorption models of organic molecules or oligomers on mineral surfaces and interfacial properties obtained from first-principles calculations. The aim of this contribution is to inspire scientists to benefit from first-principle calculations and to apply the similar strategies when studying and tailoring interfacial properties at the atomistic scale, especially for those interested in the design and development of new molecules and new products. Copyright © 2017. Published by Elsevier B.V.
Thermodynamic modeling of the Sc-Zn system coupled with first-principles calculation
Directory of Open Access Journals (Sweden)
Tang C.
2012-01-01
Full Text Available The Sc-Zn system has been critically reviewed and assessed by means of CALPHAD (CALculation of PHAse Diagram approach. By means of first-principles calculation, the enthalpies of formation at 0 K for the ScZn, ScZn2, Sc17Zn58, Sc3Zn17 and ScZn12 have been computed with the desire to assist thermodynamic modeling. A set of self-consistent thermodynamic parameters for the Sc-Zn system is then obtained. The calculated phase diagram and thermodynamic properties agree well with the experimental data and first-principles calculations, respectively.
Thermodynamic assessment of the Sn–Sr system supported by first-principles calculations
International Nuclear Information System (INIS)
Zhao, Jingrui; Du, Yong; Zhang, Lijun; Wang, Aijun; Zhou, Liangcai; Zhao, Dongdong; Liang, Jianlie
2012-01-01
Highlights: ► All the literature data of Sn–Sr system is critically reviewed. ► First-principles calculation of enthalpy of formation is carried out for each compound. ► Thermodynamic parameters for Sn–Sr system are obtained by CALPHAD method. ► A hybrid approach of CALPHAD and first-principles calculations is recommended. - Abstract: A hybrid approach of CALPHAD and first-principles calculations was employed to perform a thermodynamic modeling of the Sn–Sr system. The experimental phase diagram and thermodynamic data available in the literature were critically reviewed. The enthalpies of formation for the 6 stoichiometric compounds (i.e. Sr 2 Sn, Sr 5 Sn 3 , SrSn, Sr 3 Sn 5 , SrSn 3 and SrSn 4 ) at 0 K were computed by means of first-principles calculations. These data were used as the experimental values in the optimization module PARROT in the subsequent CALPHAD assessment to provide thermodynamic parameters with sound physical meaning. A set of self-consistent thermodynamic parameters was finally obtained by considering reliable literature data and the first-principles computed results. Comprehensive comparisons between the calculated and measured quantities indicate that all the reliable experimental information can be satisfactorily accounted for by the present thermodynamic description.
Forecast of Piezoelectric Properties of Crystalline Materials from First Principles Calculation
International Nuclear Information System (INIS)
Zheng Yanqing; Shi Erwei; Chen Jianjun; Zhang Tao; Song Lixin
2006-01-01
In this paper, forecast of piezoelectric tensors are presented. Piezo crystals including quartz, quartz-like crystals, known and novel crystals of langasite-type structure are treated with density-functional perturb theory (DFPT) using plane-wave pseudopotentials method, within the local density approximation (LDA) to the exchange-correlation functional. Compared with experimental results, the ab initio calculation results have quantitative or semi-quantitative accuracy. It is shown that first principles calculation opens a door to the search and design of new piezoelectric material. Further application of first principles calculation to forecast the whole piezoelectric properties are also discussed
Miyazato, Itsuki; Tanaka, Yuzuru; Takahashi, Keisuke
2018-02-01
Two-dimensional (2D) magnets are explored in terms of data science and first principle calculations. Machine learning determines four descriptors for predicting the magnetic moments of 2D materials within reported 216 2D materials data. With the trained machine, 254 2D materials are predicted to have high magnetic moments. First principle calculations are performed to evaluate the predicted 254 2D materials where eight undiscovered stable 2D materials with high magnetic moments are revealed. The approach taken in this work indicates that undiscovered materials can be surfaced by utilizing data science and materials data, leading to an innovative way of discovering hidden materials.
First Principles Calculations for X-ray Resonant Spectra and Elastic Properties
International Nuclear Information System (INIS)
Yongbin Lee
2006-01-01
In this thesis, we discuss applications of first principles methods to x-ray resonant spectra and elastic properties calculation. We start with brief reviews about theoretical background of first principles methods, such as density functional theory, local density approximation (LDA), LDA+U, and the linear augmented plane wave (LAPW) method to solve Kohn-Sham equations. After that we discuss x-ray resonant scattering (XRMS), x-ray magnetic circular dichroism (XMCD) and the branching problem in the heavy rare earths Ledges. In the last chapter we discuss the elastic properties of the second hardest material AlMgB 14
Yang, Hua; Mi, Wenbo; Bai, Haili; Cheng, Yingchun
2012-01-01
Electronic structure and optical properties of α-FeMO 3 systems (M = Sc, Ti, V, Cr, Cu, Cd or In) have been investigated using first principles calculations. All of the FeMO 3 systems have a large net magnetic moment. The ground state of pure α-Fe 2
First-principles calculation of the magnetic properties of paramagnetic fcc iron
International Nuclear Information System (INIS)
Johnson, D.D.; Gyorffy, B.L.; Pinski, F.J.; Staunton, J.; Stocks, G.M.
1985-01-01
Using the disordered local moment picture of itinerant magnetism, we present calculations of the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state. These calculations are based on the parameter-free, first principles approach of local spin density functional theory and the coherent potential approximation is used to treat the disorder associated with the random orientation of the local moments
Zhang, J.; Liu, H. J.; Cheng, L.; Wei, J.; Liang, J. H.; Fan, D. D.; Jiang, P. H.; Shi, J.
2017-01-01
Phosphorene has attracted tremendous interest recently due to its intriguing electronic properties. However, the thermal transport properties of phosphorene, especially for its allotropes, are still not well-understood. In this work, we calculate the thermal conductivities of five phosphorene allotropes ({\\alpha}-, \\b{eta}-, {\\gamma}-, {\\delta}- and {\\zeta}-phase) by using phonon Boltzmann transport theory combined with first-principles calculations. It is found that the {\\alpha}-phosphorene ...
International Nuclear Information System (INIS)
Mizoguchi, Teruyasu
2011-01-01
In this review, following two topics are introduced: 1) experimental and theoretical electron energy loss (EEL) near edge structures (ELNES) and X-ray absorption near edge structures (XANES), and 2) atomic and electronic structure analysis of ceramic interface by combing spectroscopy, microscopy, and first principles calculation. In the ELNES/XANES calculation, it is concluded that inclusion of core-hole effect in the calculation is essential. By combining high energy resolution observation and theoretical calculation, detailed analysis of the electronic structure is achieved. In addition, overlap population (OP) diagram is used to interpret the spectrum. In the case of AlN, sharp and intense first peak of N-K edge is found to reflect narrow dispersion of the conduction band bottom. By applying ELNES and the OP diagram to Cu/Al 2 O 3 heterointerface, it is revealed that intensity of prepeak in O-K edge is inverse proportional to interface strength. The relationships between atomic structure and defect energetics at SrTiO 3 grain boundary are also investigated, and reveal that the formation behavior of Ti vacancy is sensitive to the structural distortion. In addition, by using state-of-the-art spectroscopy, microscopy, and first principles calculations, atomic scale visualization of fluorine dopant in LaFeOAs and first principles calculation of HfO 2 phase transformation are demonstrated. (author)
First principles calculations for interaction of tyrosine with (ZnO)3 cluster
Singh, Satvinder; Singh, Gurinder; Kaura, Aman; Tripathi, S. K.
2018-04-01
First Principles Calculations have been performed to study interactions of Phenol ring of Tyrosine (C6H5OH) with (ZnO)3 atomic cluster. All the calculations have been performed under the Density Functional Theory (DFT) framework. Structural and electronic properties of (ZnO)3/C6H5OH have been studied. Gaussian basis set approach has been adopted for the calculations. A ring type most stable (ZnO)3 atomic cluster has been modeled, analyzed and used for the calculations. The compatibility of the results with previous studies has been presented here.
Defects in boron carbide: First-principles calculations and CALPHAD modeling
International Nuclear Information System (INIS)
Saengdeejing, Arkapol; Saal, James E.; Manga, Venkateswara Rao; Liu Zikui
2012-01-01
The energetics of defects in B 4+x C boron carbide and β-boron are studied through first-principles calculations, the supercell phonon approach and the Debye–Grüneisen model. It is found that suitable sublattice models for β-boron and B 4+x C are B 101 (B,C) 4 and B 11 (B,C) (B,C,Va) (B,Va) (B,C,Va), respectively. The thermodynamic properties of B 4+x C, β-boron, liquid and graphite are modeled using the CALPHAD approach based on the thermochemical data from first-principles calculations and experimental phase equilibrium data in the literature. The concentrations of various defects are then predicted as a function of carbon composition and temperature.
Anomalous doping effect in black phosphorene from first-principles calculations
Yu, Weiyang; Zhu, Zhili; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu
2014-01-01
Using first-principles density functional theory calculations, we investigate the geometries, electronic structures, and thermodynamic stabilities of substitutionally doped phosphorene sheets with group III, IV, V, and VI elements. We find that the electronic properties of phosphorene are drastically modified by the number of valence electrons in dopant atoms. The dopants with even number of valence electrons enable the doped phosphorenes to have a metallic feature, while the dopants with odd...
Canning, Andrew
2013-03-01
Inorganic scintillation phosphors (scintillators) are extensively employed as radiation detector materials in many fields of applied and fundamental research such as medical imaging, high energy physics, astrophysics, oil exploration and nuclear materials detection for homeland security and other applications. The ideal scintillator for gamma ray detection must have exceptional performance in terms of stopping power, luminosity, proportionality, speed, and cost. Recently, trivalent lanthanide dopants such as Ce and Eu have received greater attention for fast and bright scintillators as the optical 5d to 4f transition is relatively fast. However, crystal growth and production costs remain challenging for these new materials so there is still a need for new higher performing scintillators that meet the needs of the different application areas. First principles calculations can provide a useful insight into the chemical and electronic properties of such materials and hence can aid in the search for better new scintillators. In the past there has been little first-principles work done on scintillator materials in part because it means modeling f electrons in lanthanides as well as complex excited state and scattering processes. In this talk I will give an overview of the scintillation process and show how first-principles calculations can be applied to such systems to gain a better understanding of the physics involved. I will also present work on a high-throughput first principles approach to select new scintillator materials for fabrication as well as present more detailed calculations to study trapping process etc. that can limit their brightness. This work in collaboration with experimental groups has lead to the discovery of some new bright scintillators. Work supported by the U.S. Department of Homeland Security and carried out under U.S. Department of Energy Contract no. DE-AC02-05CH11231 at Lawrence Berkeley National Laboratory.
Absolute Hydration Free Energy of Proton from First Principles Electronic Structure Calculations
International Nuclear Information System (INIS)
Zhan, Chang-Guo; Dixon, David A.
2001-01-01
The absolute hydration free energy of the proton, DGhyd298(H+), is one of the fundamental quantities for the thermodynamics of aqueous systems. Its exact value remains unknown despite extensive experimental and computational efforts. We report a first-principles determination of DGhyd298(H+) by using the latest developments in electronic structure theory and massively parallel computers. DGhyd298(H+) is accurately predicted to be -262.4 kcal/mol based on high-level, first-principles solvation-included electronic structure calculations. The absolute hydration free energies of other cations can be obtained by using appropriate available thermodynamic data in combination with this value. The high accuracy of the predicted absolute hydration free energy of proton is confirmed by applying the same protocol to predict DGhyd298(Li+)
Elastic properties of cubic perovskite BaRuO{sub 3} from first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Han Deming; Liu Xiaojuan; Lv Shuhui; Li Hongping [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Meng Jian, E-mail: jmeng@ciac.jl.c [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China)
2010-08-01
We present first-principles investigations on the structural and elastic properties of the cubic perovskite BaRuO{sub 3} using density-functional theory within both local density approximation (LDA) and generalized gradient approximation (GGA). Basic physical properties, such as lattice constant, shear modulus, elastic constants (C{sub ij}) are calculated. The calculated energy band structures show that the cubic perovskite BaRuO{sub 3} is metallic. We have also predicted the Young's modulus (Y), Poisson's ratio ({upsilon}), and Anisotropy factor (A).
First-principles calculations of a high-pressure synthesized compound PtC
International Nuclear Information System (INIS)
Li Linyan; Yu Wen; Jin Changqing
2005-01-01
The first-principles density-functional method is used to study the recently high-pressure synthesized compound PtC. It is confirmed by our calculations that platinum carbide has a zinc-blende ground-state phase at zero pressure and that the rock-salt structure is a high-pressure phase. The theoretical transition pressure from zinc-blende to rock-salt structure is determined to be 52 GPa. Furthermore, our calculation shows the possibility that the PtC experimentally synthesized under high pressure conditions might undergo a transition from rock-salt to zinc-blende structure after a pressure quench to ambient conditions
Anisotropic elastic and thermal properties of titanium borides by first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Sun, Liang; Gao, Yimin [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China); Xiao, Bing [Department of Physics and Quantum Theory Group, School of Science and Engineering, Tulane University, New Orleans, LA 70118 (United States); Li, Yefei, E-mail: yefeili@126.com [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China); Wang, Guoliang [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China)
2013-12-05
Highlights: •Elastic properties of titanium borides are calculated by first principles calculation. •Thermodynamical stability of titanium borides is analyzed. •Heat capacity and thermal expansion coefficient for titanium borides are calculated and compared. •Grüneisen parameters of titanium borides are calculated. -- Abstract: The anisotropic elastic and thermal expansions of the titanium borides (TiB{sub 2}, Ti{sub 3}B{sub 4}, TiB{sub P}nma and TiB{sub F}m3{sup ¯}m) are calculated from first-principles using density functional theory. All borides show different anisotropic elastic properties; the bulk, shear and Young’s moduli are consistent with those determined experimentally. The temperature dependence of thermal expansions is mainly caused by the restoration of thermal energy due to phonon excitations at low temperature. When the temperature is higher than 500 K, the volumetric coefficient is increased linearly by increasing temperature. Meanwhile, the heat capacities of titanium borides are obtained based on the knowledge of thermal expansion coefficient and the elasticity, the calculations are in good agreement with the experiments.
International Nuclear Information System (INIS)
Iwata, K.; Matsumiya, T.; Sawada, H.; Kawakami, K.
2003-01-01
The method is presented to predict the activity coefficients and the interaction parameters of the solute elements in infinite dilute Si solutions by the use of first-principles calculations based on density functional theory. In this method, the regular solution model is assumed. The calculated activity coefficients in solid Si are converted to those in molten Si by the use of the solid-liquid partition coefficients. Furthermore, the interaction parameters in solid Si solutions are calculated and compared with reported experimental values of those in liquid Si solutions. The results show that the calculated activity coefficients and interaction parameters of Al, Fe, Ti and Pb in Si solutions are in good agreement with the tendency of the experiments. However, the calculations have some quantitative discrepancy from the experiments. It is expected that consideration of the excess entropy would reduce this discrepancy
Pressure induced structural phase transition of OsB2: First-principles calculations
International Nuclear Information System (INIS)
Ren Fengzhu; Wang Yuanxu; Lo, V.C.
2010-01-01
Orthorhombic OsB 2 was synthesized at 1000 deg. C and its compressibility was measured by using the high-pressure X-ray diffraction in a Diacell diamond anvil cell from ambient pressure to 32 GPa [R.W. Cumberland, et al. (2005)]. First-principles calculations were performed to study the possibility of the phase transition of OsB 2 . An analysis of the calculated enthalpy shows that orthorhombic OsB 2 can transfer to the hexagonal phase at 10.8 GPa. The calculated results with the quasi-harmonic approximation indicate that this phase transition pressure is little affected by the thermal effect. The calculated phonon band structure shows that the hexagonal P 6 3 /mmc structure (high-pressure phase) is stable for OsB 2 . We expect the phase transition can be further confirmed by the experimental work. - Abstract: Graphical Abstract Legend (TOC Figure): Table of Contents Figure Pressure induced structural phase transition from the orthorhombic structure to the hexagonal one for OsB 2 takes place under 10.8 GPa (0 K), 10.35 GPa (300, 1000 K) by the first-principles predictions.
First Principles Calculations of Oxygen Adsorption on the UN(001) Surface
International Nuclear Information System (INIS)
Zhukovskii, Yuri F.; Bocharov, Dmitry; Kotomin, Eugene Alexej; Evarestov, Robert; Bandura, A.V.
2009-01-01
Fabrication, handling and disposal of nuclear fuel materials require comprehensive knowledge of their surface morphology and reactivity. Due to unavoidable contact with air components (even at low partial pressures), UN samples contain considerable amount of oxygen impurities affecting fuel properties. In this study we focus on reactivity of the energetically most stable (001) substrate of uranium nitride towards the atomic oxygen as one of initial stages for further UN oxidation. The basic properties of O atoms adsorbed on the UN(001) surface are simulated here combining the two first principles calculation methods based on the plane wave basis set and that of the localized orbitals.
Stability, electronic and thermodynamic properties of aluminene from first-principles calculations
International Nuclear Information System (INIS)
Yuan, Junhui; Yu, Niannian; Xue, Kanhao; Miao, Xiangshui
2017-01-01
Highlights: • We have predicted two NEW stable phases of atomic layer aluminum, buckled and 8-Pmmn aluminene. • We have revealed the electronic structures and bonding characteristics of aluminene. • Thermodynamic properties of aluminene were investigated based on phonon properties. - Abstract: Using first-principles calculations based on density functional theory (DFT), we have investigated the structure stability and electronic properties of both buckled and 8-Pmmn phase aluminene. Phonon dispersion analysis reveals that the buckled and 8-Pmmn aluminene are dynamically stable. The band structure shows that both the buckled and 8-Pmmn aluminene exhibit metallic behavior. Finally, the thermodynamic properties are investigated based on phonon properties.
First principles calculation on the adsorption of water on lithium-montmorillonite (Li-MMT)
International Nuclear Information System (INIS)
Wungu, Triati Dewi Kencana; Agusta, Mohammad Kemal; Saputro, Adhitya Gandaryus; Kasai, Hideaki; Dipojono, Hermawan Kresno
2012-01-01
The interaction of water molecules and lithium-montmorillonite (Li-MMT) is theoretically investigated using density functional theory (DFT) based first principles calculation. The mechanism of water adsorption at two different water concentrations on Li-MMT as well as their structural and electronic properties are investigated. It is found that the adsorption stability in Li-MMT is higher in higher water concentration. It is also found that an adsorbed water molecule on Li-MMT causes the Li to protrude from the MMT surface, so it is expected that Li may be mobile on H 2 O/Li-MMT.
First principles calculation on the adsorption of water on lithium-montmorillonite (Li-MMT).
Wungu, Triati Dewi Kencana; Agusta, Mohammad Kemal; Saputro, Adhitya Gandaryus; Dipojono, Hermawan Kresno; Kasai, Hideaki
2012-11-28
The interaction of water molecules and lithium-montmorillonite (Li-MMT) is theoretically investigated using density functional theory (DFT) based first principles calculation. The mechanism of water adsorption at two different water concentrations on Li-MMT as well as their structural and electronic properties are investigated. It is found that the adsorption stability in Li-MMT is higher in higher water concentration. It is also found that an adsorbed water molecule on Li-MMT causes the Li to protrude from the MMT surface, so it is expected that Li may be mobile on H(2)O/Li-MMT.
Site-specific electronic structure analysis by channeling EELS and first-principles calculations.
Tatsumi, Kazuyoshi; Muto, Shunsuke; Yamamoto, Yu; Ikeno, Hirokazu; Yoshioka, Satoru; Tanaka, Isao
2006-01-01
Site-specific electronic structures were investigated by electron energy loss spectroscopy (EELS) under electron channeling conditions. The Al-K and Mn-L(2,3) electron energy loss near-edge structure (ELNES) of, respectively, NiAl2O4 and Mn3O4 were measured. Deconvolution of the raw spectra with the instrumental resolution function restored the blunt and hidden fine features, which allowed us to interpret the experimental spectral features by comparing with theoretical spectra obtained by first-principles calculations. The present method successfully revealed the electronic structures specific to the differently coordinated cationic sites.
First-principles calculation of the structural stability of 6d transition metals
International Nuclear Information System (INIS)
Oestlin, A.; Vitos, L.
2011-01-01
The phase stability of the 6d transition metals (elements 103-111) is investigated using first-principles electronic-structure calculations. Comparison with the lighter transition metals reveals that the structural sequence trend is broken at the end of the 6d series. To account for this anomalous behavior, the effect of relativity on the lattice stability is scrutinized, taking different approximations into consideration. It is found that the mass-velocity and Darwin terms give important contributions to the electronic structure, leading to changes in the interstitial charge density and, thus, in the structural energy difference.
Stability, electronic and thermodynamic properties of aluminene from first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Yuan, Junhui [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Yu, Niannian [School of Science, Wuhan University of Technology, Wuhan, Hubei 430070 (China); Xue, Kanhao, E-mail: xkh@hust.edu.cn [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Miao, Xiangshui [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)
2017-07-01
Highlights: • We have predicted two NEW stable phases of atomic layer aluminum, buckled and 8-Pmmn aluminene. • We have revealed the electronic structures and bonding characteristics of aluminene. • Thermodynamic properties of aluminene were investigated based on phonon properties. - Abstract: Using first-principles calculations based on density functional theory (DFT), we have investigated the structure stability and electronic properties of both buckled and 8-Pmmn phase aluminene. Phonon dispersion analysis reveals that the buckled and 8-Pmmn aluminene are dynamically stable. The band structure shows that both the buckled and 8-Pmmn aluminene exhibit metallic behavior. Finally, the thermodynamic properties are investigated based on phonon properties.
First-principle calculation of refractive indices of BAlN and BGaN
Alqatari, Feras; Li, Kuang-Hui; Liu, Kaikai; Li, Xiaohang
2018-01-01
The refractive indices of BAlN and BGaN ternary alloys are being investigated using first-principle calculation. The hybrid density functional theory is applied to determine the refractive indices of different alloys. A peculiar bowing effect in the static refractive indices and crossovers of different refractive index curves are found. We speculate that the explanation to these phenomena lies in the interband transitions of electrons where each band bows at a different rate from the other. An average of these bowing effects may result in the bowing of refractive indices.
Piezoelectric, Mechanical and Acoustic Properties of KNaNbOF5 from First-Principles Calculations
Directory of Open Access Journals (Sweden)
Han Han
2015-12-01
Full Text Available Recently, a noncentrosymmetric crystal, KNaNbOF5, has attracted attention due to its potential to present piezoelectric properties. Although α- and β-KNaNbOF5 are similar in their stoichiometries, their structural frameworks, and their synthetic routes, the two phases exhibit very different properties. This paper presents, from first-principles calculations, comparative studies of the structural, electronic, piezoelectric, and elastic properties of the α and the β phase of the material. Based on the Christoffel equation, the slowness surface of the acoustic waves is obtained to describe its acoustic prosperities. These results may benefit further applications of KNaNbOF5.
First-principle calculation of refractive indices of BAlN and BGaN
Alqatari, Feras
2018-03-27
The refractive indices of BAlN and BGaN ternary alloys are being investigated using first-principle calculation. The hybrid density functional theory is applied to determine the refractive indices of different alloys. A peculiar bowing effect in the static refractive indices and crossovers of different refractive index curves are found. We speculate that the explanation to these phenomena lies in the interband transitions of electrons where each band bows at a different rate from the other. An average of these bowing effects may result in the bowing of refractive indices.
First-principles calculations on thermodynamic properties of BaTiO3 rhombohedral phase.
Bandura, Andrei V; Evarestov, Robert A
2012-07-05
The calculations based on the linear combination of atomic orbitals have been performed for the low-temperature phase of BaTiO(3) crystal. Structural and electronic properties, as well as phonon frequencies were obtained using hybrid PBE0 exchange-correlation functional. The calculated frequencies and total energies at different volumes have been used to determine the equation of state and thermal contribution to the Helmholtz free energy within the quasiharmonic approximation. For the first time, the bulk modulus, volume thermal expansion coefficient, heat capacity, and Grüneisen parameters in BaTiO(3) rhombohedral phase have been estimated at zero pressure and temperatures form 0 to 200 K, based on the results of first-principles calculations. Empirical equation has been proposed to reproduce the temperature dependence of the calculated quantities. The agreement between the theoretical and experimental thermodynamic properties was found to be satisfactory. Copyright © 2012 Wiley Periodicals, Inc.
Directory of Open Access Journals (Sweden)
Bidai K.
2017-06-01
Full Text Available First-principles density functional theory calculations have been performed to investigate the structural, elastic and thermodynamic properties of rubidium telluride in cubic anti-fluorite (anti-CaF2-type structure. The calculated ground-state properties of Rb2Te compound such as equilibrium lattice parameter and bulk moduli are investigated by generalized gradient approximation (GGA-PBE that are based on the optimization of total energy. The elastic constants, Young’s and shear modulus, Poisson ratio, have also been calculated. Our results are in reasonable agreement with the available theoretical and experimental data. The pressure dependence of elastic constant and thermodynamic quantities under high pressure are also calculated and discussed.
First-principle calculations on the structural and electronic properties of hard C11N4
International Nuclear Information System (INIS)
Li, Dongxu; Shi, Jiancheng; Lai, Mengling; Li, Rongkai; Yu, Dongli
2014-01-01
A graphite-like C 11 N 4 model was built by stacking graphene and a C 3 N 4 triazine layer and simulated by first principle calculations, which transfers to a diamond-like structure under high pressure. The structural, mechanical, and electronic properties of both materials were calculated. The elastic constants of both materials satisfy the Born-criterion. Furthermore, no imaginary frequencies were observed in phonon calculations. The diamond-like C 11 N 4 is semiconducting and consists of polyhedral and hollow C–N cages. The Vickers hardness of diamond-like C 11 N 4 was calculated to be 58 GPa. The phase transformation from graphite-like to diamond-like C 11 N 4 is proposed to occur at approximately 27.2 GPa based on the pressure-dependent enthalpy
Pressure induced structural phase transition of OsB 2: First-principles calculations
Ren, Fengzhu; Wang, Yuanxu; Lo, V. C.
2010-04-01
Orthorhombic OsB 2 was synthesized at 1000 °C and its compressibility was measured by using the high-pressure X-ray diffraction in a Diacell diamond anvil cell from ambient pressure to 32 GPa [R.W. Cumberland, et al. (2005)]. First-principles calculations were performed to study the possibility of the phase transition of OsB 2. An analysis of the calculated enthalpy shows that orthorhombic OsB 2 can transfer to the hexagonal phase at 10.8 GPa. The calculated results with the quasi-harmonic approximation indicate that this phase transition pressure is little affected by the thermal effect. The calculated phonon band structure shows that the hexagonal P 6 3/ mmc structure (high-pressure phase) is stable for OsB 2. We expect the phase transition can be further confirmed by the experimental work.
DEFF Research Database (Denmark)
Mattsson, T.R.; Wahnström, G.; Bengtsson, L.
1997-01-01
First-principles density-functional calculations of hydrogen adsorption on the Ni (001) surface have been performed in order to get a better understanding of adsorption and diffusion of hydrogen on metal surfaces. We find good agreement with experiments for the adsorption energy, binding distance...
Directory of Open Access Journals (Sweden)
Xuan L Liu
Full Text Available The phase relations and thermodynamic properties of the condensed Al-Co-Cr ternary alloy system are investigated using first-principles calculations based on density functional theory (DFT and phase-equilibria experiments that led to X-ray diffraction (XRD and electron probe micro-analysis (EPMA measurements. A thermodynamic description is developed by means of the calculations of phase diagrams (CALPHAD method using experimental and computational data from the present work and the literature. Emphasis is placed on modeling the bcc-A2, B2, fcc-γ, and tetragonal-σ phases in the temperature range of 1173 to 1623 K. Liquid, bcc-A2 and fcc-γ phases are modeled using substitutional solution descriptions. First-principles special quasirandom structures (SQS calculations predict a large bcc-A2 (disordered/B2 (ordered miscibility gap, in agreement with experiments. A partitioning model is then used for the A2/B2 phase to effectively describe the order-disorder transitions. The critically assessed thermodynamic description describes all phase equilibria data well. A2/B2 transitions are also shown to agree well with previous experimental findings.
Elastic and thermal properties of silicon compounds from first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Hou, Haijun; Zhu, H.J. [Yancheng Institute of Technology (China). School of Materials Engineering; Cheng, W.H. [Yancheng Institute of Technology (China). Dept. of Light Chemical Engineering; Xie, L.H. [Sichuan Normal Univ., Chengdu (China). Inst. of Solid State Physics and School of Physics and Electronic Engineering
2016-11-01
The structural and elastic properties of V-Si (V{sub 3}Si, VSi{sub 2}, V{sub 5}Si{sub 3}, and V{sub 6}Si{sub 5}) compounds are studied by using first-principles method. The calculated equilibrium lattice parameters and formation enthalpy are in good agreement with the available experimental data and other theoretical results. The calculated results indicate that the V-Si compounds are mechanically stable. Elastic properties including bulk modulus, shear modulus, Young's modulus, and Poisson's ratio are also obtained. The elastic anisotropies of V-Si compounds are investigated via the three-dimensional (3D) figures of directional dependences of reciprocals of Young's modulus. Finally, based on the quasi-harmonic Debye model, the internal energy, Helmholtz free energy, entropy, heat capacity, thermal expansion coefficient, Grueneisen parameter, and Debye temperature of V-Si compounds have been calculated.
Whether FeTe is superconductor: Insights from first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Li, Jian; Huang, GuiQin, E-mail: huangguiqin@njnu.edu.cn; Zhu, XingFeng
2013-09-15
Highlights: • The ground state of FeTe is in the double stripe antiferromagnetic phase. • The nesting of electron and hole at the Fermi surface is not present in FeTe. • The spin–lattice interaction can lead to the phonon softening. • The electron–phonon coupling constant λ is enhanced due to spin–phonon coupling. • Whether FeTe can be superconductor? Some discussions are made. -- Abstract: We present a first-principles pseudopotential study on the electronic structure, phonon structure and the electron–phonon interaction of stoichiometric FeTe in both the nonmagnetic and double stripe antiferromagnetic phases. Our electronic structure calculations show that the nesting effect of Fermi surface is not present in stoichiometric FeTe after considering the magnetic interaction. Comparing the phonon behavior in the double stripe antiferromagnetic phase with that in the nonmagnetic phase, we find that the spin–lattice interaction can lead to the phonon softening and increase electron–phonon coupling constant λ by about 33%, which is similar to other iron-based superconductors in the single stripe antiferromagnetic phase. We suggest that the phonon softening may have no clear contact with the specific magnetic order in the ground state. Finally, we make some discussion about whether FeTe can be superconductor combining our first-principles calculations.
Magnetism, microstructure and First Principles calculations of atomized and annealed Ni3Al
International Nuclear Information System (INIS)
García-Escorial, A.; Crespo, P.; Hernando, A.; Lieblich, M.; Marín, P.; Velasco, V.; Ynduráin, F.
2014-01-01
Highlights: • The microstructure and order of as-atomized Ni 3 Al powder change with annealing. • The change of the magnetic properties shows the influence of the chemical order. • First Principles calculations show the effect of the density of states to the order. - Abstract: In this work Ni 3 Al powder particles obtained by atomization were characterized magnetically and microstructurally in as-atomized state and after annealing. Upon annealing the X-ray diffraction patterns show a noticeable increase of the signal of the ordered phase γ′-Ni 3 Al, L1 2 , phase and the microstructure evolves from a lamellar and dendrite to a large grain microstructure. The Curie temperature of the as-atomized powder particles is 85 K and decreases after annealing down to 50 K. First Principles calculations were carried out to correlate the experimental observations with local order of Ni and Al atoms and illustrate the importance of the local order in the density of states at the Fermi level, showing how the magnetic moment depends on the Ni and Al atomic position
Magnetism, microstructure and First Principles calculations of atomized and annealed Ni{sub 3}Al
Energy Technology Data Exchange (ETDEWEB)
García-Escorial, A., E-mail: age@cenim.csic.es [CENIM-CSIC, Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); Crespo, P.; Hernando, A. [Instituto de Magnetismo Aplicado, IMA-UCM, P.O. Box 155, 28230 Madrid (Spain); Lieblich, M. [CENIM-CSIC, Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); Marín, P.; Velasco, V. [Instituto de Magnetismo Aplicado, IMA-UCM, P.O. Box 155, 28230 Madrid (Spain); Ynduráin, F. [Dpto. de Física de la Materia Condensada, UAM, Cantoblanco, 28049 Madrid (Spain)
2014-12-05
Highlights: • The microstructure and order of as-atomized Ni{sub 3}Al powder change with annealing. • The change of the magnetic properties shows the influence of the chemical order. • First Principles calculations show the effect of the density of states to the order. - Abstract: In this work Ni{sub 3}Al powder particles obtained by atomization were characterized magnetically and microstructurally in as-atomized state and after annealing. Upon annealing the X-ray diffraction patterns show a noticeable increase of the signal of the ordered phase γ′-Ni{sub 3}Al, L1{sub 2}, phase and the microstructure evolves from a lamellar and dendrite to a large grain microstructure. The Curie temperature of the as-atomized powder particles is 85 K and decreases after annealing down to 50 K. First Principles calculations were carried out to correlate the experimental observations with local order of Ni and Al atoms and illustrate the importance of the local order in the density of states at the Fermi level, showing how the magnetic moment depends on the Ni and Al atomic position.
The elastic and thermodynamic properties of ZrMo2 from first principles calculations
International Nuclear Information System (INIS)
Liu, Xian-Kun; Zhou, Wei; Zheng, Zhou; Peng, Shu-Ming
2014-01-01
Highlights: • Elastic and thermodynamic properties of ZrMo 2 under high temperature and pressure are calculated by first principles. • Mechanical stability is testified from elastic constants at zero pressure. • Phonon scattering of ZrMo 2 under different temperature are obtained. - Abstract: The elastic and thermodynamic properties of ZrMo 2 under high temperature and pressure are investigated by first-principles calculations based on pseudopotential plane-wave density functional theory (DFT) within the generalized gradient approximation (GGA) and quasi-harmonic Debye model. The calculated lattice parameters are in good agreement with the available experimental data. The calculated elastic constants of ZrMo 2 increase monotonically with increasing pressure, and the relationship between the elastic constants and pressure show that ZrMo 2 satisfies the mechanical stability criteria under applied pressure (0–65 GPa). The related mechanical properties such as bulk modulus (B), shear modulus (G), Young’s modulus (E), and Poisson’s ratio (v) are also studied for polycrystalline of ZrMo 2 . The calculated B/G value shows that ZrMo 2 behaves in a ductile manner, and higher pressure can significantly improve the ductility of ZrMo 2 . The pressure and temperature dependencies of the relative volume, the bulk modulus, the elastic constants, the heat capacity and the thermal expansion coefficient, as well as the Grüneisen parameters are obtained and discussed by the quasi-harmonic Debye model in the ranges of 0–1800 K and 0–65 GPa
Adsorption of methanol molecule on graphene: Experimental results and first-principles calculations
Zhao, X. W.; Tian, Y. L.; Yue, W. W.; Chen, M. N.; Hu, G. C.; Ren, J. F.; Yuan, X. B.
2018-04-01
Adsorption properties of methanol molecule on graphene surface are studied both theoretically and experimentally. The adsorption geometrical structures, adsorption energies, band structures, density of states and the effective masses are obtained by means of first-principles calculations. It is found that the electronic characteristics and conductivity of graphene are sensitive to the methanol molecule adsorption. After adsorption of methanol molecule, bandgap appears. With the increasing of the adsorption distance, the bandgap, adsorption energy and effective mass of the adsorption system decreased, hence the resistivity of the system decreases gradually, these results are consistent with the experimental results. All these calculations and experiments indicate that the graphene-based sensors have a wide range of applications in detecting particular molecules.
Thermodynamic description of the Al-Cu-Yb ternary system supported by first-principles calculations
Directory of Open Access Journals (Sweden)
Huang G.
2016-01-01
Full Text Available Phase relationships of the ternary Al-Cu-Yb system have been assessed using a combination of CALPHAD method and first principles calculations. A self-consistent thermodynamic parameter was established based on the experimental and theoretical information. Most of the binary intermetallic phases, except Al3Yb, Al2Yb, Cu2Yb and Cu5Yb, were assumed to be zero solubility in the ternary system. Based on the experimental data, eight ternary intermetallic compounds were taken into consideration in this system. Among them, three were treated as line compounds with large homogeneity ranges for Al and Cu. The others were treated as stoichiometric compounds. The calculated phase diagrams were in agreement with available experimental and theoretical data.
Lattice dynamics and thermal conductivity of lithium fluoride via first-principles calculations
Liang, Ting; Chen, Wen-Qi; Hu, Cui-E.; Chen, Xiang-Rong; Chen, Qi-Feng
2018-04-01
The lattice thermal conductivity of lithium fluoride (LiF) is accurately computed from a first-principles approach based on an iterative solution of the Boltzmann transport equation. Real-space finite-difference supercell approach is employed to generate the second- and third-order interatomic force constants. The related physical quantities of LiF are calculated by the second- and third- order potential interactions at 30 K-1000 K. The calculated lattice thermal conductivity 13.89 W/(m K) for LiF at room temperature agrees well with the experimental value, demonstrating that the parameter-free approach can furnish precise descriptions of the lattice thermal conductivity for this material. Besides, the Born effective charges, dielectric constants and phonon spectrum of LiF accord well with the existing data. The lattice thermal conductivities for the iterative solution of BTE are also presented.
Structural and electronic properties of LaPd2As2 superconductor: First-principle calculations
Singh, Birender; Kumar, Pradeep
2017-05-01
In present work we have studied electronic and structural properties of superconducting LaPd2As2 compound having collapsed tetragonal structure using first-principle calculations. The band structure calculations show that the LaPd2As2 is metallic consistent with the reported experimental observation, and the density of states plots clearly shows that at the Fermi level major contribution to density of states arises from Pd 4d and As 4p states, unlike the Fe-based superconductors where major contribution at the Fermi level comes from Fe 3d states. The estimated value of electron-phonon coupling is found to be 0.37, which gives the upper bound of superconducting transition temperature of 5K, suggesting the conventional nature of this superconductor.
Elasticity, electronic properties and hardness of MoC investigated by first principles calculations
International Nuclear Information System (INIS)
Liu, YangZhen; Jiang, YeHua; Feng, Jing; Zhou, Rong
2013-01-01
The crystal structure, cohesive energy, formation enthalpy, mechanical anisotropy, electronic properties and hardness of α−MoC, β−MoC and γ−MoC are investigated by the first-principles calculations. The elastic constants and the bulk moduli, shear moduli, Young's moduli are calculated. The Young's modulus values of α−MoC, β−MoC and γ−MoC are 395.6 GPa, 551.2 GPa and 399.5 GPa, respectively. The surface constructions of Young's moduli identify the mechanical anisotropy of molybdenum carbide, and the results show that anisotropy of α−MoC is stronger than others. The electronic structure indicates that the bonding behaviors of MoC are the combinations of covalent and metallic bonds. The hardness of β−MoC is obviously higher than those of α−MoC and γ−MoC
Zhang, J; Liu, H J; Cheng, L; Wei, J; Liang, J H; Fan, D D; Jiang, P H; Shi, J
2017-07-04
Phosphorene has attracted tremendous interest recently due to its intriguing electronic properties. However, the thermal transport properties of phosphorene, especially for its allotropes, are still not well-understood. In this work, we calculate the thermal conductivities of five phosphorene allotropes (α-, β-, γ-, δ- and ζ-phase) by using phonon Boltzmann transport theory combined with first-principles calculations. It is found that the α-phosphorene exhibits considerable anisotropic thermal transport, while it is less obvious in the other four phosphorene allotropes. The highest thermal conductivity is found in the β-phosphorene, followed by the δ-, γ- and ζ-phase. The much lower thermal conductivity of the ζ-phase can be attributed to its relatively complex atomic configuration. It is expected that the rich thermal transport properties of phosphorene allotropes can have potential applications in the thermoelectrics and thermal management.
Anomalous doping effect in black phosphorene using first-principles calculations.
Yu, Weiyang; Zhu, Zhili; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu
2015-07-07
Using first-principles density functional theory calculations, we investigate the geometries, electronic structures, and thermodynamic stabilities of substitutionally doped phosphorene sheets with group III, IV, V, and VI elements. We find that the electronic properties of phosphorene are drastically modified by the number of valence electrons in dopant atoms. The dopants with an even number of valence electrons enable the doped phosphorenes to have a metallic feature, while the dopants with an odd number of valence electrons retain a semiconducting feature. This even-odd oscillating behavior is attributed to the peculiar bonding characteristics of phosphorene and the strong hybridization of sp orbitals between dopants and phosphorene. Furthermore, the calculated formation energies of various substitutional dopants in phosphorene show that such doped systems can be thermodynamically stable. These results propose an intriguing route to tune the transport properties of electronic and photoelectronic devices based on phosphorene.
A theoretical study of blue phosphorene nanoribbons based on first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Xie, Jiafeng; Si, M. S., E-mail: sims@lzu.edu.cn; Yang, D. Z.; Zhang, Z. Y.; Xue, D. S. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China)
2014-08-21
Based on first-principles calculations, we present a quantum confinement mechanism for the band gaps of blue phosphorene nanoribbons (BPNRs) as a function of their widths. The BPNRs considered have either armchair or zigzag shaped edges on both sides with hydrogen saturation. Both the two types of nanoribbons are shown to be indirect semiconductors. An enhanced energy gap of around 1 eV can be realized when the ribbon's width decreases to ∼10 Å. The underlying physics is ascribed to the quantum confinement effect. More importantly, the parameters to describe quantum confinement are obtained by fitting the calculated band gaps with respect to their widths. The results show that the quantum confinement in armchair nanoribbons is stronger than that in zigzag ones. This study provides an efficient approach to tune the band gap in BPNRs.
International Nuclear Information System (INIS)
Noh, Seunghyo; Kwak, Dohyun; Lee, Juseung; Kang, Joonhee; Han, Byungchan
2014-01-01
We utilized first-principles density-functional-theory (DFT) calculations to evaluate the thermodynamic feasibility of a pyroprocessing methodology for reducing the volume of high-level radioactive materials and recycling spent nuclear fuels. The thermodynamic properties of transuranium elements (Pu, Np and Cm) were obtained in electrochemical equilibrium with a LiCl-KCl molten salt as ionic phases and as adsorbates on a W(110) surface. To accomplish the goal, we rigorously calculated the double layer interface structures on an atomic resolution, on the thermodynamically most stable configurations on W(110) surfaces and the chemical activities of the transuranium elements for various coverages of those elements. Our results indicated that the electrodeposition process was very sensitive to the atomic level structures of Cl ions at the double-layer interface. Our studies are easily expandable to general electrochemical applications involving strong redox reactions of transition metals in non-aqueous solutions.
Thermodynamics and elastic properties of Ir from first-principle calculations
International Nuclear Information System (INIS)
Li Qiang; Huang Duohui; Cao Qilong; Wang Fanhou
2013-01-01
Within the framework of the quasiharmonic approximation, the thermodynamics and elastic properties, including phonon dispersion curves, equation of state, linear thermal expansion coefficient and temperature-dependent entropy, enthalpy, heat capacity, elastic constants, bulk modulus, shear modulus, Young's modulus of Ir have been studied using first-principles projector-augmented wave method. The results revealed that the predicted phonon dispersion curves of Ir are in agreement with the experimental measurements by neutron diffractions. Considering the thermal electronic contribution to Helmholtz free energy, the calculated entropy, enthalpy, heat capacity and linear thermal expansion co- efficient from the first-principle are consistent well with the experimental data. At 2600 K, the electronic heat capacity accounts for 17% of the total heat capacity at constant pressure, thus the thermal electronic contribution to Helmholtz free energy is very important. The predicted elastic constants, bulk modulus, shear modulus and Young's modulus at room temperature are also in agreement with the available measurements and increase with the increasing temperature. (authors)
Mechanical properties of layered oxysulfide CaZnOS from first principle calculations
Energy Technology Data Exchange (ETDEWEB)
Zhang, Zhi-Jun [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of); Feng, Ang [Key Laboratory of Transparent Opto-Functional Inorganic Materials of Chinese Academy of Sciences, Shanghai Institute of Ceramics, Shanghai, 200050 (China); Zhang, Shao-Lin; Zhang, Wei-Bin [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of); Yang, Woochul, E-mail: wyang@dongguk.edu [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of)
2016-06-15
Elastic and tensile properties of mixed-anion oxysulfide CaZnOS have been theoretically investigated by first principle method of density functional theory (DFT). Elastic constants were obtained by stress–strain relationships, and bulk structure parameters including bulk modulus, shear modulus, as well as Poisson's ratio were then calculated using Voigt-Reuses-Hill (VRH) approximation. The results of shear anisotropic factors, compressibility anisotropic factor and directional Young's modulus showed that CaZnOS is almost elastically isotropic in {001} planes and maintains elastic anisotropy in {100} or {010} planes. Chemical bond anisotropy shown by Mulliken atomic charges and bond overlap populations is responsible for the elastic anisotropy behavior aforementioned. Moreover, theoretical uniaxial and biaxial tensile results showed the crystal collapsed at strain more than 12%, except in the biaxial extension where CaZnOS collapsed at strain of 7%. - Highlights: • Elastic and theoretical tensile properties of CaZnOS have been investigated by first principle method. • CaZnOS is elastically isotropic in {001} planes and maintains elastic anisotropy in {100} or {010} planes. • Mulliken atomic charges and bond overlap populations are responsible for the elastic anisotropy behavior.
Sundararaman, Ravishankar; Letchworth-Weaver, Kendra; Schwarz, Kathleen A.
2018-04-01
Reliable first-principles calculations of electrochemical processes require accurate prediction of the interfacial capacitance, a challenge for current computationally efficient continuum solvation methodologies. We develop a model for the double layer of a metallic electrode that reproduces the features of the experimental capacitance of Ag(100) in a non-adsorbing, aqueous electrolyte, including a broad hump in the capacitance near the potential of zero charge and a dip in the capacitance under conditions of low ionic strength. Using this model, we identify the necessary characteristics of a solvation model suitable for first-principles electrochemistry of metal surfaces in non-adsorbing, aqueous electrolytes: dielectric and ionic nonlinearity, and a dielectric-only region at the interface. The dielectric nonlinearity, caused by the saturation of dipole rotational response in water, creates the capacitance hump, while ionic nonlinearity, caused by the compactness of the diffuse layer, generates the capacitance dip seen at low ionic strength. We show that none of the previously developed solvation models simultaneously meet all these criteria. We design the nonlinear electrochemical soft-sphere solvation model which both captures the capacitance features observed experimentally and serves as a general-purpose continuum solvation model.
First principles calculation of material properties of group IV elements and III-V compounds
Malone, Brad Dean
This thesis presents first principles calculations on the properties of group IV elements and group III-V compounds. It includes investigations into what structure a material is likely to form in, and given that structure, what are its electronic, optical, and lattice dynamical properties as well as what are the properties of defects that might be introduced into the sample. The thesis is divided as follows: • Chapter 1 contains some of the conceptual foundations used in the present work. These involve the major approximations which allow us to approach the problem of systems with huge numbers of interacting electrons and atomic cores. • Then, in Chapter 2, we discuss one of the major limitations to the DFT formalism introduced in Chapter 1, namely its inability to predict the quasiparticle spectra of materials and in particular the band gap of a semiconductor. We introduce a Green's function approach to the electron self-energy Sigma known as the GW approximation and use it to compute the quasiparticle band structures of a number of group IV and III-V semiconductors. • In Chapter 3 we present a first-principles study of a number of high-pressure metastable phases of Si with tetrahedral bonding. The phases studied include all experimentally determined phases that result from decompression from the metallic beta-Sn phase, specifically the BC8 (Si-III), hexagonal diamond (Si-IV), and R8 (Si-XII). In addition to these, we also study the hypothetical ST12 structure found upon decompression from beta-Sn in germanium. • Our attention is then turned to the first principles calculations of optical properties in Chapter 4. The Bethe-Salpeter equation is then solved to obtain the optical spectrum of this material including electron-hole interactions. The calculated optical spectrum is compared with experimental data for other forms of silicon commonly used in photovoltaic devices, namely the cubic, polycrystalline, and amorphous forms. • In Chapter 5 we present
SU-E-T-191: First Principle Calculation of Quantum Yield in Photodynamic Therapy
Energy Technology Data Exchange (ETDEWEB)
Abolfath, R; Guo, F; Chen, Z; Nath, R [Yale New Haven Hospital, New Haven, CT (United States)
2014-06-01
Purpose: We present a first-principle method to calculate the spin transfer efficiency in oxygen induced by any photon fields especially in MeV energy range. The optical pumping is mediated through photosensitizers, e.g., porphyrin and/or ensemble of quantum dots. Methods: Under normal conditions, oxygen molecules are in the relatively non-reactive triplet state. In the presence of certain photosensitizer compounds such as porphyrins, electromagnetic radiation of specific wavelengths can excite oxygen to highly reactive singlet state. With selective uptake of photosensitizers by certain malignant cells, photon irradiation of phosensitized tumors can lead to selective killing of cancer cells. This is the basis of photodynamic therapy (PDT). Despite several attempts, PDT has not been clinically successful except in limited superficial cancers. Many parameters such as photon energy, conjugation with quantum dots etc. can be potentially combined with PDT in order to extend the role of PDT in cancer management. The key quantity for this optimization is the spin transfer efficiency in oxygen by any photon field. The first principle calculation model presented here, is an attempt to fill this need. We employ stochastic density matrix description of the quantum jumps and the rate equation methods in quantum optics based on Markov/Poisson processes and calculate time evolution of the population of the optically pumped singlet oxygen. Results: The results demonstrate the feasibility of our model in showing the dependence of the optical yield in generating spin-singlet oxygen on the experimental conditions. The adjustable variables can be tuned to maximize the population of the singlet oxygen hence the efficacy of the photodynamic therapy. Conclusion: The present model can be employed to fit and analyze the experimental data and possibly to assist researchers in optimizing the experimental conditions in photodynamic therapy.
Yang, Hua
2012-01-01
Electronic structure and optical properties of α-FeMO 3 systems (M = Sc, Ti, V, Cr, Cu, Cd or In) have been investigated using first principles calculations. All of the FeMO 3 systems have a large net magnetic moment. The ground state of pure α-Fe 2O 3 is an antiferromagnetic insulator. For M = Cu or Cd, the systems are half-metallic. Strong absorption in the visible region can be observed in the Cu and Cd-doped systems. Systems with M = Sc, Ti, V, Cr or In are not half-metallic and are insulators. The strongest peaks shift toward shorter wavelengths in the absorption spectra. It is concluded that transition metal doping can modify the electronic structure and optical properties of α-FeMO 3 systems. This journal is © 2012 The Royal Society of Chemistry.
Aqueous Stability of Alkali Superionic Conductors from First-Principles Calculations
International Nuclear Information System (INIS)
Radhakrishnan, Balachandran; Ong, Shyue Ping
2016-01-01
Ceramic alkali superionic conductor solid electrolytes (SICEs) play a prominent role in the development of rechargeable alkali-ion batteries, ranging from replacement of organic electrolytes to being used as separators in aqueous batteries. The aqueous stability of SICEs is an important property in determining their applicability in various roles. In this work, we analyze the aqueous stability of twelve well-known Li-ion and Na-ion SICEs using Pourbaix diagrams constructed from first-principles calculations. We also introduce a quantitative free-energy measure to compare the aqueous stability of SICEs under different environments. Our results show that though oxides are, in general, more stable in aqueous environments than sulfides and halide-containing chemistries, the cations present play a crucial role in determining whether solid phases are formed within the voltage and pH ranges of interest.
Near-infrared radiation absorption properties of covellite (CuS using first-principles calculations
Directory of Open Access Journals (Sweden)
Lihua Xiao
2016-08-01
Full Text Available First-principles density functional theory was used to investigate the electronic structure, optical properties and the origin of the near-infrared (NIR absorption of covellite (CuS. The calculated lattice constant and optical properties are found to be in reasonable agreement with experimental and theoretical findings. The electronic structure reveals that the valence and conduction bands of covellite are determined by the Cu 3d and S 3p states. By analyzing its optical properties, we can fully understand the potential of covellite (CuS as a NIR absorbing material. Our results show that covellite (CuS exhibits NIR absorption due to its metal-like plasma oscillation in the NIR range.
Effects of hydrogen on Mn-doped GaN: A first principles calculation
International Nuclear Information System (INIS)
Wu, M.S.; Xu, B.; Liu, G.; Lei, X.L.; Ouyang, C.Y.
2013-01-01
First-principles calculations based on spin density functional theory are performed to study the effects of H on the structural, electronic and magnetic properties of the Mn-doped GaN dilute magnetic semiconductors. Our results show that the interstitial H atom prefers to bond with N atom rather than Mn atom, which means that H favors to form the N–H complex rather than Mn–H complex in the Mn-doped GaN. After introducing one H atom in the system, the total magnetic moment of the Mn-doped GaN increases by 25%, from 4.0μ B to 5.0μ B . The physics mechanism of the increase of magnetic moment after hydrogenation in Mn-doped GaN is discussed
DEFF Research Database (Denmark)
Jones, Glenn; Jakobsen, Jon Geest; Shim, Signe Sarah
2008-01-01
This paper presents a detailed analysis of the steam reforming process front first-principles calculations, supported by insight from experimental investigations. In the present work we employ recently recognised scaling relationships for adsorption energies of simple molecules adsorbed at pure...... metal Surfaces to develop an overview of the steam reforming process catalyzed by a range of transition metal surfaces. By combining scaling relationships with thermodynamic and kinetic analysis, we show that it is possible to determine the reactivity trends of the pure metals for methane steam...... in situ TEM measurements under a hydrogen atmosphere. The overall agreement between theory and experiment (at 773 K, 1 bar pressure and 10% conversion) is found to be excellent with Ru and Rh being the most active pure transition metals for methane steam reforming, while Ni, Ir, Pt, and Pd...
Electronic structures of N- and C-doped NiO from first-principles calculations
International Nuclear Information System (INIS)
Long, Run; English, Niall J.; Mooney, Damian A.
2010-01-01
The large intrinsic band gap of NiO has hindered severely its potential application under visible-light irradiation. In this Letter, we have performed first-principles calculations on the electronic properties of N- and C-doped NiO to ascertain if its band gap may be narrowed theoretically. It was found that impurity bands driven by N 2p or C 2p states appear in the band gap of NiO and that some of these locate at the conduction band minimum, which leads to a significant band gap narrowing. Our results show that N-doped NiO may serve as a potential photocatalyst relative to C-doped NiO, due to the presence of some recombination centres in C-doped NiO.
Nanoparticle shapes by using Wulff constructions and first-principles calculations
Directory of Open Access Journals (Sweden)
Georgios D. Barmparis
2015-02-01
Full Text Available Background: The majority of complex and advanced materials contain nanoparticles. The properties of these materials depend crucially on the size and shape of these nanoparticles. Wulff construction offers a simple method of predicting the equilibrium shape of nanoparticles given the surface energies of the material.Results: We review the mathematical formulation and the main applications of Wulff construction during the last two decades. We then focus to three recent extensions: active sites of metal nanoparticles for heterogeneous catalysis, ligand-protected nanoparticles generated as colloidal suspensions and nanoparticles of complex metal hydrides for hydrogen storage.Conclusion: Wulff construction, in particular when linked to first-principles calculations, is a powerful tool for the analysis and prediction of the shapes of nanoparticles and tailor the properties of shape-inducing species.
Nano-sized graphene flakes: insights from experimental synthesis and first principles calculations.
Lin, Pin-Chun; Chen, Yi-Rui; Hsu, Kuei-Ting; Lin, Tzu-Neng; Tung, Kuo-Lun; Shen, Ji-Lin; Liu, Wei-Ren
2017-03-01
In this study, we proposed a cost-effective method for preparing graphene nano-flakes (GNFs) derived from carbon nanotubes (CNTs) via three steps (pressing, homogenization and sonication exfoliation processes). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), laser scattering, as well as ultraviolet-visible and photoluminescence (PL) measurements were carried out. The results indicated that the size of as-synthesized GNFs was approximately 40-50 nm. Furthermore, we also used first principles calculations to understand the transformation from CNTs to GNFs from the viewpoints of the edge formation energies of GNFs in different shapes and sizes. The corresponding photoluminescence measurements of GNFs were carried out in this work.
Phase Transition and Thermodynamics of Ruthenium Diboride via First-Principles Calculations
International Nuclear Information System (INIS)
Fen, Luo; Yan, Cheng; Xiang-Rong, Chen; Guang-Fu, Ji
2009-01-01
The pressure induced phase transitions of RuB 2 from the OsB 2 -type structure to the ReB 2 -type structure are investigated by first-principles calculations based on the plane-wave basis set with the generalized gradient approximation for exchange and correlation. It is found that the phase transition occurs at 18.6 GPa. We predict the phase transition from the OsB 2 -type RuB 2 to the ReB 2 -type RuB 2 at high temperatures for the first time. The dependences of the heat capacity, thermal expansion coefficient, and the Grüneisen parameter on pressure and temperature for OsB 2 -type RuB 2 and ReB 2 -type RuB 2 are also investigated
International Nuclear Information System (INIS)
Yan Han; Gan Zhiyin; Song Xiaohui; Chen Zhaohui; Xu Jingping; Liu Sheng
2009-01-01
First-principles calculations of magnesium adsorption at the Ga-terminated and N-terminated {0 0 0 1} basal plane wurtzite gallium nitride surfaces have been carried out to explain the atomic-scale insight into the initial adsorption processes of magnesium doping in gallium nitride. The results reveal that magnesium adsorption on N-terminated surfaces is preferred than that on Ga-terminated surfaces. Furthermore, the surface diffusivity of magnesium atom on the N-terminated surface is much lower than that on the Ga-terminated surface, which is due to both the larger average adsorption energies and the lower adsorption distance on N-terminated surface than that on Ga-terminated surface. The results indicate that the p-type doping on the Ga-terminated surface will be better distributed than that on the N-terminated surface.
Puligheddu, Marcello; Gygi, Francois; Galli, Giulia
The prediction of the thermal properties of solids and liquids is central to numerous problems in condensed matter physics and materials science, including the study of thermal management of opto-electronic and energy conversion devices. We present a method to compute the thermal conductivity of solids by performing ab initio molecular dynamics at non equilibrium conditions. Our formulation is based on a generalization of the approach to equilibrium technique, using sinusoidal temperature gradients, and it only requires calculations of first principles trajectories and atomic forces. We discuss results and computational requirements for a representative, simple oxide, MgO, and compare with experiments and data obtained with classical potentials. This work was supported by MICCoM as part of the Computational Materials Science Program funded by the U.S. Department of Energy (DOE), Office of Science , Basic Energy Sciences (BES), Materials Sciences and Engineering Division under Grant DOE/BES 5J-30.
First principles and phonon calculations of ZrCo and ZrCo-H systems
International Nuclear Information System (INIS)
Chattaraj, D.; Parida, S.C.; Dash, Smruti; Majumder, C.
2012-01-01
The intermetallic ZrCo is a potential material for the storage and release of hydrogen isotopes because of its high gravimetric capacity and its low hydrogen equilibrium pressure. This intermetallic is a proposed material for the safe storage, supply and delivery of hydrogen isotope in the ITER project. To investigate the suitability of ZrCo as a getter material for the storage of hydrogen isotope it is essential to know in detail the structure-property relationships in both ZrCo and its hydride. Hence, in this study, we have investigated the structural, electronic, vibrational and thermodynamic properties of ZrCo and ZrCoH 3 using the first principles and phonon calculations
International Nuclear Information System (INIS)
Bondi, Robert J.; Desjarlais, Michael P.; Thompson, Aidan P.; Brennecka, Geoff L.; Marinella, Matthew J.
2013-01-01
We apply first-principles density-functional theory (DFT) calculations, ab-initio molecular dynamics, and the Kubo-Greenwood formula to predict electrical conductivity in Ta 2 O x (0 ≤ x ≤ 5) as a function of composition, phase, and temperature, where additional focus is given to various oxidation states of the O monovacancy (V O n ; n = 0,1+,2+). In the crystalline phase, our DFT calculations suggest that V O 0 prefers equatorial O sites, while V O 1+ and V O 2+ are energetically preferred in the O cap sites of TaO 7 polyhedra. Our calculations of DC conductivity at 300 K agree well with experimental measurements taken on Ta 2 O x thin films (0.18 ≤ x ≤ 4.72) and bulk Ta 2 O 5 powder-sintered pellets, although simulation accuracy can be improved for the most insulating, stoichiometric compositions. Our conductivity calculations and further interrogation of the O-deficient Ta 2 O 5 electronic structure provide further theoretical basis to substantiate V O 0 as a donor dopant in Ta 2 O 5 . Furthermore, this dopant-like behavior is specific to the neutral case and not observed in either the 1+ or 2+ oxidation states, which suggests that reduction and oxidation reactions may effectively act as donor activation and deactivation mechanisms, respectively, for V O n in Ta 2 O 5
The first-principles calculations for the elastic properties of Zr2Al under compression
International Nuclear Information System (INIS)
Yuan Xiaoli; Wei Dongqing; Chen Xiangrong; Zhang Qingming; Gong Zizheng
2011-01-01
Graphical abstract: The calculated elastic constants C ij as a function of pressure P. Display Omitted Research highlights: → It is found that the five independent elastic constants increase monotonically with pressure. C 11 and C 33 vary rapidly as pressure increases, C 13 and C 12 becomes moderate. However, C 44 increases comparatively slowly with pressure. Figure shows excellent satisfaction of the calculated elastic constants of Zr 2 Al to these equations and hence in our calculation, the Zr 2 Al is mechanically stable at pressure up to 100 GPa. - Abstract: The first-principles calculations were applied to investigate the structural, elastic constants of Zr 2 Al alloy with increasing pressure. These properties are based on the plane wave pseudopotential density functional theory (DFT) method within the generalized gradient approximation (GGA) for exchange and correlation. The result of the heat of formation of Zr 2 Al crystal investigated is in excellent consistent with results from other study. The anisotropy, the shear modulus, and Young's modulus for the ideal polycrystalline Zr 2 Al are also studied. It is found that (higher) pressure can significantly improve the ductility of Zr 2 Al. Moreover, the elastic constants of Zr 2 Al increase monotonically and the anisotropies decrease with the increasing pressure. Finally, it is observed that Zr d electrons are mainly contributed to the density of states at the Fermi level.
Energy Technology Data Exchange (ETDEWEB)
Yamaguchi, Kizashi [Institute for Nano Science Design Center, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan and TOYOTA Physical and Chemical Research Institute, Nagakute, Aichi, 480-1192 (Japan); Nishihara, Satomichi; Saito, Toru; Yamanaka, Shusuke; Kitagawa, Yasutaka; Kawakami, Takashi; Yamada, Satoru; Isobe, Hiroshi; Okumura, Mitsutaka [Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan)
2015-01-22
First principle calculations of effective exchange integrals (J) in the Heisenberg model for diradical species were performed by both symmetry-adapted (SA) multi-reference (MR) and broken-symmetry (BS) single reference (SR) methods. Mukherjee-type (Mk) state specific (SS) MR coupled-cluster (CC) calculations by the use of natural orbital (NO) references of ROHF, UHF, UDFT and CASSCF solutions were carried out to elucidate J values for di- and poly-radical species. Spin-unrestricted Hartree Fock (UHF) based coupled-cluster (CC) computations were also performed to these species. Comparison between UHF-NO(UNO)-MkMRCC and BS UHF-CC computational results indicated that spin-contamination of UHF-CC solutions still remains at the SD level. In order to eliminate the spin contamination, approximate spin-projection (AP) scheme was applied for UCC, and the AP procedure indeed corrected the error to yield good agreement with MkMRCC in energy. The CC double with spin-unrestricted Brueckner's orbital (UBD) was furthermore employed for these species, showing that spin-contamination involved in UHF solutions is largely suppressed, and therefore AP scheme for UBCCD removed easily the rest of spin-contamination. We also performed spin-unrestricted pure- and hybrid-density functional theory (UDFT) calculations of diradical and polyradical species. Three different computational schemes for total spin angular momentums were examined for the AP correction of the hybrid (H) UDFT. HUDFT calculations followed by AP, HUDFT(AP), yielded the S-T gaps that were qualitatively in good agreement with those of MkMRCCSD, UHF-CC(AP) and UB-CC(AP). Thus a systematic comparison among MkMRCCSD, UCC(AP) UBD(AP) and UDFT(AP) was performed concerning with the first principle calculations of J values in di- and poly-radical species. It was found that BS (AP) methods reproduce MkMRCCSD results, indicating their applicability to large exchange coupled systems.
Electronic Structure of Cu(tmdt2 Studied with First-Principles Calculations
Directory of Open Access Journals (Sweden)
Kiyoyuki Terakura
2012-08-01
Full Text Available We have studied the electronic structure of Cu(tmdt2, a material related to single-component molecular conductors, by first-principles calculations. The total energy calculations for several different magnetic configurations show that there is strong antiferromagnetic (AFM exchange coupling along the crystal a-axis. The electronic structures are analyzed in terms of the molecular orbitals near the Fermi level of isolated Cu(tmdt2 molecule. This analysis reveals that the system is characterized by the half-filled pdσ(− band whose intermolecular hopping integrals have strong one-dimensionality along the crystal a-axis. As the exchange splitting of the band is larger than the band width, the basic mechanism of the AFM exchange coupling is the superexchange. It will also be shown that two more ligand orbitals which are fairly insensitive to magnetism are located near the Fermi level. Because of the presence of these orbitals, the present calculation predicts that Cu(tmdt2 is metallic even in its AFM state, being inconsistent with the available experiment. Some comments will be made on the difference between Cu(tmdt2 and Cu(dmdt2.
First-principles calculation on dilute magnetic alloys in zinc blend crystal structure
International Nuclear Information System (INIS)
Ullah, Hamid; Inayat, Kalsoom; Khan, S.A; Mohammad, S.; Ali, A.; Alahmed, Z.A.; Reshak, A.H.
2015-01-01
Ab-initio calculations are performed to investigate the structural, electronic and magnetic properties of spin-polarized diluted magnetic alloys in zinc blende structure. The first-principles study is carried out on Mn doped III–V semiconductors. The calculated band structures, electronic properties and magnetic properties of Ga 1−x Mn x X (X=P, As) compounds reveal that Ga 0.75 Mn 0.25 P is half metallic turned to be metallic with increasing x to 0.5 and 0.75, whereas substitute P by As cause to maintain the half-metallicity nature in both of Ga 0.75 Mn 0.25 As and Ga 0.5 Mn 0.5 As and tune Ga 0.25 Mn 0.75 As to be metallic. Calculated total magnetic moments and the robustness of half-metallicity of Ga 0.75 Mn 0.25 P, Ga 0.75 Mn 0.25 As and Ga 0.5 Mn 0.5 As with respect to the variation in lattice parameters are also discussed. The predicted theoretical evidence shows that some Mn-doped III–V semiconductors can be effectively used in spintronic devices
First-principles cluster variation calculations of tetragonal-cubic transition in ZrO2
International Nuclear Information System (INIS)
Mohri, Tetsuo; Chen, Ying; Kiyokane, Naoya
2013-01-01
Highlights: ► Cluster variation method is extended to study displacive transition. ► Electronic structure total energy calculations are performed on ZrO2. ► Tetragonal-cubic transition is studied within the framework of order -disorder transition. -- Abstract: It is attempted to extend the basic idea of continuous displacement cluster variation method (CDCVM) to the study of a displacive phase transition. As a preliminary study, we focus on cubic to tetragonal transition in ZrO 2 in which oxygen atoms on the cubic lattice are displaced alternatively in the opposite direction (upward and downward) along the tetragonal axis. Within the CDCVM, displaced atoms are regarded as different atomic species, and two distinguished atoms, A-oxygen (upward shifting) and B-oxygen (downward shifting), are introduced in the description of the free energy. FLAPW electronic structure total energy calculations are performed to extract effective interaction energies among displaced oxygen atoms, and by combing them with CDCVM, the transition temperature is calculated from the first-principles
First-principles calculations of the electronic and structural properties of GaSb
Energy Technology Data Exchange (ETDEWEB)
Castaño-González, E.-E. [Universidad del Norte, Grupo de Investigación en Física Aplicada, Departamento de Física (Colombia); Seña, N. [Universidad Nacional de Colombia-Colombia, Departamento de Física, Grupo de Materiales Nanoestructurados y sus Aplicaciones (Colombia); Mendoza-Estrada, V.; González-Hernández, R., E-mail: rhernandezj@uninorte.edu.co [Universidad del Norte, Grupo de Investigación en Física Aplicada, Departamento de Física (Colombia); Dussan, A. [Universidad Nacional de Colombia-Colombia, Departamento de Física, Grupo de Materiales Nanoestructurados y sus Aplicaciones (Colombia); Mesa, F., E-mail: fredy.mesa@urosario.edu.co [Universidad del Rosario, Grupo NanoTech, Facultad de Ciencias Naturales y Matemáticas (Colombia)
2016-10-15
In this paper, we carried out first-principles calculations in order to investigate the structural and electronic properties of the binary compound gallium antimonide (GaSb). This theoretical study was carried out using the Density Functional Theory within the plane-wave pseudopotential method. The effects of exchange and correlation (XC) were treated using the functional Local Density Approximation (LDA), generalized gradient approximation (GGA): Perdew–Burke–Ernzerhof (PBE), Perdew-Burke-Ernzerhof revised for solids (PBEsol), Perdew-Wang91 (PW91), revised Perdew–Burke–Ernzerhof (rPBE), Armiento–Mattson 2005 (AM05) and meta-generalized gradient approximation (meta-GGA): Tao–Perdew–Staroverov–Scuseria (TPSS) and revised Tao–Perdew–Staroverov–Scuseria (RTPSS) and modified Becke-Johnson (MBJ). We calculated the densities of state (DOS) and band structure with different XC potentials identified and compared them with the theoretical and experimental results reported in the literature. It was discovered that functional: LDA, PBEsol, AM05 and RTPSS provide the best results to calculate the lattice parameters (a) and bulk modulus (B{sub 0}); while for the cohesive energy (E{sub coh}), functional: AM05, RTPSS and PW91 are closer to the values obtained experimentally. The MBJ, Rtpss and AM05 values found for the band gap energy is slightly underestimated with those values reported experimentally.
First-principles calculations on Mg/Al2CO interfaces
International Nuclear Information System (INIS)
Wang, F.; Li, K.; Zhou, N.G.
2013-01-01
The electronic structure, work of adhesion, and interfacial energy of the Mg(0 0 0 2)/Al 2 CO(0 0 0 1) interface were studied with the first-principles calculations to clarify the heterogeneous nucleation potential of Al 2 CO particles in Mg melt. AlO-terminated Al 2 CO(0 0 0 1) slabs with seven atomic layers were adopted for interfacial model geometries. Results show that the “Over O” stacking interface is more stable than the “Over Al” stacking interface due to the larger interfacial adhesion and stronger mixed ionic/metallic bond formed across the interface. The calculated interfacial energies of Mg/Al 2 CO depend on the value of Δμ Al + Δμ C , proving Al 2 CO particles can exist stably in Mg–Al alloys melt and become effective nucleation substrate for α-Mg grain under certain conditions. The above calculation and corresponding analysis provide strong theoretical support to the Al 2 CO nucleus hypothesis from interfacial atomic structure and atomic bonding energy considerations.
International Nuclear Information System (INIS)
Hua Manyu; Li Yimin; Long Chunguang; Li Xia
2012-01-01
The structural, electronic and elastic properties of potassium hexatitanate (K 2 Ti 6 O 13 ) whisker were investigated using first-principles calculations. The calculated cell parameters of K 2 Ti 6 O 13 including lattice constants and atomic positions are in good agreement with the experimental data. The obtained formation enthalpy (-61.1535 eV/atom) and cohesive energy (-137.4502 eV/atom) are both negative, showing its high structural stability. Further analysis of the electronic structures shows that the potassium hexatitanate is a wide-band semiconductor. Within K 2 Ti 6 O 13 crystal, the Ti---O bonding interactions are stronger than that of K---O, while no apparent K---Ti bonding interactions can be observed. The structural stability of K 2 Ti 6 O 13 was closely associated with the covalent bond interactions between Ti (d) and O (p) orbits. Further calculations on elastic properties show that K 2 Ti 6 O 13 is a high stiffness and brittle material with small anisotropy in shear and compression.
Effects of Al substitution in Nd2Fe17 studied by first-principles calculations
International Nuclear Information System (INIS)
Huang, M.; Ching, W.Y.
1994-01-01
We have studied the effect of Al substitution in Nd 2 Fe 17 compound by means of first-principles calculations. We first obtain the site-decomposed potentials for Fe from self-consistent calculation on Y 2 Fe 17 and the atomiclike potentials in the crystalline environment for Al and Nd. Calculations are carried out for a single Al substituting one Fe at four different Fe sites (6c), (9d), (18f ), and (18h), two Al substituting two Fe (18h), and four Al substituting three Fe (18h) and one Fe (18f ). Our results show that the Al moment is oppositely polarized to Fe. The average moment per Fe atom actually increases for Al substituting Fe (18h) and Fe (18f ) is about the same for Al substituting Fe (6c), and is drastically reduced when replacing Fe (9d). Experimentally, Al is shown to be excluded from the (9d) sites because of the small Wigner--Seitz volume. When two Fe atoms are replaced by two Al atoms, the total moment is only slightly less than when only one Fe atom is replaced, and the M s per Fe site actually increases, in agreement with the Moessbauer data. These results are analyzed in terms of the local atomic geometry and the charge transfer effect from the neighboring Fe to Al
First principles calculation of thermodynamic properties of NaAlSi ternary
International Nuclear Information System (INIS)
Qin Jining; Lu Weijie; Zhang Di; Fan Tongxiang
2012-01-01
PbFCl-type NaAlSi ternary is a corrosion compound found in aluminum, which is used as a sealing material in sodium sulfur battery. To understand and control the corrosion process, it is important to predict its quantitative properties. In this study, a first-principles calculation has been carried out to calculate its equilibrium lattice parameters, bulk modulus and pressure derivative of bulk modulus by both all-electron full-potential linear augmented plane wave scheme and pseudopotential plane wave scheme within the generalized gradient approximation. The theoretical results show good agreement with the available experimental data. The thermodynamic properties, including the specific heat capacity and entropy with pressure up to 9 GPa, have been investigated for the first time by coupling of density functional perturbation theory and quasiharmonic approximation. The volume and linear thermal expansion coefficients were estimated and the results show that the linear thermal expansion on c-axis is nearly twice as large as that on a-axis within the calculated temperature.
First-principles calculation on electronic properties of zinc oxide by zinc–air system
Directory of Open Access Journals (Sweden)
Ahmad Azmin Mohamad
2017-07-01
Full Text Available First-principles calculations are performed to study the electronic properties of zinc oxide (ZnO formed on an anode after discharging a Zn–air system. Prior to calculation, the ZnO is characterised by X-ray diffraction using Rietveld refinement. Diffracted patterns proved the formation of single phase ZnO, while Rietveld analysis shows that the ZnO has a hexagonal wurtzite structure with lattice parameters, a = 3.244 and c = 5.199 Å. Geometry optimisation of the hexagonal wurtzite structure of the ZnO is performed using various exchange–correlation energy functionals. The local density approximation functional method is used to explain the structure, electronic band structure and density of state properties of hexagonal ZnO. The calculated energy band gap was 0.75 eV while the density of states reveals that the O 2p (the top valence band and Zn 4s (the bottom conduction band states domination.
First-principles calculation on dilute magnetic alloys in zinc blend crystal structure
Energy Technology Data Exchange (ETDEWEB)
Ullah, Hamid, E-mail: hamidullah@yahoo.com [Department of Physics, Government Post Graduate Jahanzeb College, Saidu Sharif Swat (Pakistan); Inayat, Kalsoom [Department of Physics, Government Post Graduate Jahanzeb College, Saidu Sharif Swat (Pakistan); Khan, S.A; Mohammad, S. [Department of Physics, Materials Modeling Laboratory, Hazara University, Mansehra 21300 (Pakistan); Ali, A. [Department of Advanced Materials Science & Engineering, Hanseo University, Seosan-si, Chungnam-do 356-706 (Korea, Republic of); Alahmed, Z.A. [Department of Physics and Astronomy, King Saud University, Riyadh 11451 (Saudi Arabia); Reshak, A.H. [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia)
2015-07-01
Ab-initio calculations are performed to investigate the structural, electronic and magnetic properties of spin-polarized diluted magnetic alloys in zinc blende structure. The first-principles study is carried out on Mn doped III–V semiconductors. The calculated band structures, electronic properties and magnetic properties of Ga{sub 1−x}Mn{sub x}X (X=P, As) compounds reveal that Ga{sub 0.75}Mn{sub 0.25}P is half metallic turned to be metallic with increasing x to 0.5 and 0.75, whereas substitute P by As cause to maintain the half-metallicity nature in both of Ga{sub 0.75}Mn{sub 0.25}As and Ga{sub 0.5}Mn{sub 0.5}As and tune Ga{sub 0.25}Mn{sub 0.75}As to be metallic. Calculated total magnetic moments and the robustness of half-metallicity of Ga{sub 0.75}Mn{sub 0.25}P, Ga{sub 0.75}Mn{sub 0.25}As and Ga{sub 0.5}Mn{sub 0.5}As with respect to the variation in lattice parameters are also discussed. The predicted theoretical evidence shows that some Mn-doped III–V semiconductors can be effectively used in spintronic devices.
First-principles calculations of BC{sub 4}N nanostructures: stability and electronic structure
Energy Technology Data Exchange (ETDEWEB)
Freitas, A.; Azevedo, S. [Universidade Federal da Paraiba, CCEN, Departamento de Fisica, Joao Pessoa, PB (Brazil); Machado, M. [Universidade Federal de Pelotas, Departamento de Fisica, Pelotas, RS (Brazil); Kaschny, J.R. [Instituto Federal da Bahia-Campus Vitoria da Conquista, Vitoria da Conquista, BA (Brazil)
2012-07-15
In this work, we apply first-principles methods to investigate the stability and electronic structure of BC{sub 4}N nanostructures which were constructed from hexagonal graphite layers where substitutional nitrogen and boron atoms are placed at specific sites. These layers were rolled up to form zigzag and armchair nanotubes, with diameters varying from 7 to 12 A, or cut and bent to form nanocones, with 60 and 120 disclination angles. The calculation results indicate that the most stable structures are the ones which maximize the number of B-N and C-C bonds. It is found that the zigzag nanotubes are more stable than the armchair ones, where the strain energy decreases with increasing tube diameter D, following a 1/D {sup 2} law. The results show that the 60 disclination nanocones are the most stable ones. Additionally, the calculated electronic properties indicate a semiconducting behavior for all calculated structures, which is intermediate to the typical behaviors found for hexagonal boron nitride and graphene. (orig.)
BaTiO3-based nanolayers and nanotubes: first-principles calculations.
Evarestov, Robert A; Bandura, Andrei V; Kuruch, Dmitrii D
2013-01-30
The first-principles calculations using hybrid exchange-correlation functional and localized atomic basis set are performed for BaTiO(3) (BTO) nanolayers and nanotubes (NTs) with the structure optimization. Both the cubic and the ferroelectric BTO phases are used for the nanolayers and NTs modeling. It follows from the calculations that nanolayers of the different ferroelectric BTO phases have the practically identical surface energies and are more stable than nanolayers of the cubic phase. Thin nanosheets composed of three or more dense layers of (0 1 0) and (0 1 1[overline]) faces preserve the ferroelectric displacements inherent to the initial bulk phase. The structure and stability of BTO single-wall NTs depends on the original bulk crystal phase and a wall thickness. The majority of the considered NTs with the low formation and strain energies has the mirror plane perpendicular to the tube axis and therefore cannot exhibit ferroelectricity. The NTs folded from (0 1 1[overline]) layers may show antiferroelectric arrangement of Ti-O bonds. Comparison of stability of the BTO-based and SrTiO(3)-based NTs shows that the former are more stable than the latter. Copyright © 2012 Wiley Periodicals, Inc.
First-principles thermodynamic calculations of diffusion characteristics of impurities in γ-iron
International Nuclear Information System (INIS)
Tsuru, T.; Kaji, Y.
2013-01-01
Because solute impurities have an effect on embrittlement through segregation under irradiation, solute stability and the influence of irradiation on the diffusion characteristics of impurities become prominent due to several acceleration effects of high irradiance circumstances in irradiated materials. In this study, the diffusion characteristics of several impurities in non-magnetic fcc iron are investigated using first-principles density functional theory (DFT) calculations. In accordance with classical diffusion and transition state theories, we nonempirically evaluated the contribution to properties of the binding energy between vacancy and each impurity and the migration enthalpy. The migration energy was calculated using the nudged elastic band method with DFT. The vacancy formation energy, including the entropic contributions to free energies in γ-iron, was evaluated by considering vibrational phonon frequencies based on frozen phonons employing the harmonic approximation for the lattice dynamics. Consequently, we confirmed that the binding energy between large-radius impurities and vacancies is larger than that with an equivalent size of the solvent element, and that the migration enthalpies of these impurities are quite small compared with self diffusion. This finding may indicate that the electronic binding states at the saddle point have a large influence on the migration of impurities
First-principles calculations of the interaction between hydrogen and 3d alloying atom in nickel
Energy Technology Data Exchange (ETDEWEB)
Liu, Wenguan, E-mail: liuwenguan@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Chinese Academy of Sciences, Shanghai 201800 (China); Qian, Yuan; Zhang, Dongxun [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Chinese Academy of Sciences, Shanghai 201800 (China); Liu, Wei, E-mail: liuwei@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Chinese Academy of Sciences, Shanghai 201800 (China); Han, Han [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Chinese Academy of Sciences, Shanghai 201800 (China)
2015-10-15
Knowledge of the behavior of hydrogen (H) in Ni-based alloy is essential for the prediction of Tritium behavior in Molten Salt Reactor. First-principles calculations were performed to investigate the interaction between H and 3d transition metal (TM) alloying atom in Ni-based alloy. H prefers the octahedral interstitial site to the tetrahedral interstitial site energetically. Most of the 3d TM elements (except Zn) attract H. The attraction to H in the Ni–TM–H system can be mainly attributed to the differences in electronegativity. With the large electronegativity, H and Ni gain electrons from the other TM elements, resulting in the enhanced Ni–H bonds which are the source of the attraction to H in the Ni–TM–H system. The obviously covalent-like Cr–H and Co–H bindings are also beneficial to the attraction to H. On the other hand, the repulsion to H in the Ni–Zn–H system is due to the stable electronic configuration of Zn. We mainly utilize the results calculated in 32-atom supercell which corresponds to the case of a relatively high concentration of hydrogen. Our results are in good agreement with the experimental ones.
Moon, Juhyuk
2012-06-04
The structure and elasticity of tricalcium aluminate (C 3A) have been experimentally and theoretically studied. From high-pressure X-ray diffraction experiments, the bulk modulus of 102(6) and 110(3) GPa were obtained by fitting second- and third-order finite strain equation of state, respectively. First-principles calculations with a generalized gradient approximation gave an isotropic bulk modulus of 102.1 GPa and an isothermal bulk modulus of 106.0 GPa. The static calculations using the exchange-correlation functional show an excellent agreement with the experimental measurements. Based on the agreement, accurate elastic constants and other elastic moduli were computed. The slight difference of behavior at high pressure can be explained by the infiltration of pressure-transmitting silicone oil into structural holes in C 3A. The computed elastic and mechanical properties will be useful in understanding structural and mechanical properties of cementitious materials, particularly with the increasing interest in the advanced applications at the nanoscale. © 2012 The American Ceramic Society.
A first principle calculation of anisotropic elastic, mechanical and electronic properties of TiB
Zhang, Junqin; Zhao, Bin; Ma, Huihui; Wei, Qun; Yang, Yintang
2018-04-01
The structural, mechanical and electronic properties of the NaCl-type structure TiB are theoretically calculated based on the first principles. The density of states of TiB shows obvious density peaks at -0.70eV. Furthermore, there exists a pseudogap at 0.71eV to the right of the Fermi level. The calculated structural and mechanical parameters (i.e., bulk modulus, shear modulus, Young's modulus, Poisson's ratio and universal elastic anisotropy index) were in good agreement both with the previously reported experimental values and theoretical results at zero pressure. The mechanical stability criterion proves that TiB at zero pressure is mechanistically stable and exhibits ductility. The universal anisotropic index and the 3D graphics of Young's modulus are also given in this paper, which indicates that TiB is anisotropy under zero pressure. Moreover, the effects of applied pressures on the structural, mechanical and anisotropic elastic of TiB were studied in the range from 0 to 100GPa. It was found that ductility and anisotropy of TiB were enhanced with the increase of pressure.
Multipole moments of water molecules in clusters and ice Ih from first principles calculations
International Nuclear Information System (INIS)
Batista, E.R.; Xantheas, S.S.; Jonsson, H.
1999-01-01
We have calculated molecular multipole moments for water molecules in clusters and in ice Ih by partitioning the charge density obtained from first principles calculations. Various schemes for dividing the electronic charge density among the water molecules were used. They include Bader close-quote s zero flux surfaces and Voronoi partitioning schemes. A comparison was also made with an induction model including dipole, dipole-quadrupole, quadrupole-quadrupole polarizability and first hyperpolarizability as well as fixed octopole and hexadecapole moments. We have found that the different density partitioning schemes lead to widely different values for the molecular multipoles, illustrating how poorly defined molecular multipoles are in clusters and condensed environments. For instance, the magnitude of the molecular dipole moment in ice Ih ranges between 2.3 D and 3.1 D depending on the partitioning scheme used. Within each scheme, though, the value for the molecular dipole moment in ice is larger than in the hexamer. The magnitude of the molecular dipole moment in the clusters shows a monotonic increase from the gas phase value to the one in ice Ih, with the molecular dipole moment in the water ring hexamer being smaller than the one in ice Ih for all the partitioning schemes used. copyright 1999 American Institute of Physics
Moon, Juhyuk; Yoon, Seyoon; Wentzcovitch, Renata M.; Clark, Simon M.; Monteiro, Paulo J.M.
2012-01-01
The structure and elasticity of tricalcium aluminate (C 3A) have been experimentally and theoretically studied. From high-pressure X-ray diffraction experiments, the bulk modulus of 102(6) and 110(3) GPa were obtained by fitting second- and third-order finite strain equation of state, respectively. First-principles calculations with a generalized gradient approximation gave an isotropic bulk modulus of 102.1 GPa and an isothermal bulk modulus of 106.0 GPa. The static calculations using the exchange-correlation functional show an excellent agreement with the experimental measurements. Based on the agreement, accurate elastic constants and other elastic moduli were computed. The slight difference of behavior at high pressure can be explained by the infiltration of pressure-transmitting silicone oil into structural holes in C 3A. The computed elastic and mechanical properties will be useful in understanding structural and mechanical properties of cementitious materials, particularly with the increasing interest in the advanced applications at the nanoscale. © 2012 The American Ceramic Society.
Energy Technology Data Exchange (ETDEWEB)
Bondi, Robert J., E-mail: rjbondi@sandia.gov; Desjarlais, Michael P.; Thompson, Aidan P.; Brennecka, Geoff L.; Marinella, Matthew J. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
2013-11-28
We apply first-principles density-functional theory (DFT) calculations, ab-initio molecular dynamics, and the Kubo-Greenwood formula to predict electrical conductivity in Ta{sub 2}O{sub x} (0 ≤ x ≤ 5) as a function of composition, phase, and temperature, where additional focus is given to various oxidation states of the O monovacancy (V{sub O}{sup n}; n = 0,1+,2+). In the crystalline phase, our DFT calculations suggest that V{sub O}{sup 0} prefers equatorial O sites, while V{sub O}{sup 1+} and V{sub O}{sup 2+} are energetically preferred in the O cap sites of TaO{sub 7} polyhedra. Our calculations of DC conductivity at 300 K agree well with experimental measurements taken on Ta{sub 2}O{sub x} thin films (0.18 ≤ x ≤ 4.72) and bulk Ta{sub 2}O{sub 5} powder-sintered pellets, although simulation accuracy can be improved for the most insulating, stoichiometric compositions. Our conductivity calculations and further interrogation of the O-deficient Ta{sub 2}O{sub 5} electronic structure provide further theoretical basis to substantiate V{sub O}{sup 0} as a donor dopant in Ta{sub 2}O{sub 5}. Furthermore, this dopant-like behavior is specific to the neutral case and not observed in either the 1+ or 2+ oxidation states, which suggests that reduction and oxidation reactions may effectively act as donor activation and deactivation mechanisms, respectively, for V{sub O}{sup n} in Ta{sub 2}O{sub 5}.
Mapping energetics of atom probe evaporation events through first principles calculations.
Peralta, Joaquín; Broderick, Scott R; Rajan, Krishna
2013-09-01
The purpose of this work is to use atomistic modeling to determine accurate inputs into the atom probe tomography (APT) reconstruction process. One of these inputs is evaporation field; however, a challenge occurs because single ions and dimers have different evaporation fields. We have calculated the evaporation field of Al and Sc ions and Al-Al and Al-Sc dimers from an L1₂-Al₃Sc surface using ab initio calculations and with a high electric field applied to the surface. The evaporation field is defined as the electric field at which the energy barrier size is calculated as zero, corresponding to the minimum field that atoms from the surface can break their bonds and evaporate from the surface. The evaporation field of the surface atoms are ranked from least to greatest as: Al-Al dimer, Al ion, Sc ion, and Al-Sc dimer. The first principles results were compared with experimental data in the form of an ion evaporation map, which maps multi-ion evaporations. From the ion evaporation map of L1₂-Al₃Sc, we extract relative evaporation fields and identify that an Al-Al dimer has a lower evaporation field than an Al-Sc dimer. Additionally, comparatively an Al-Al surface dimer is more likely to evaporate as a dimer, while an Al-Sc surface dimer is more likely to evaporate as single ions. These conclusions from the experiment agree with the ab initio calculations, validating the use of this approach for modeling APT energetics. Copyright © 2013 Elsevier B.V. All rights reserved.
Structural and electronic phase transitions of ThS2 from first-principles calculations
International Nuclear Information System (INIS)
Guo, Yongliang; Wang, Changying; Qiu, Wujie; Ke, Xuezhi
2016-01-01
Performed a systematic study using first-principles methods of the pressure-induced structural and electronic phase transitions in ThS_2, which may play an important role in the next generation nuclear energy fuel technology.
Point defects in hexagonal germanium carbide monolayer: A first-principles calculation
International Nuclear Information System (INIS)
Ersan, Fatih; Gökçe, Aytaç Gürhan; Aktürk, Ethem
2016-01-01
Highlights: • Semiconductor GeC turns into metal by introducing a carbon vacancy. • Semiconductor GeC becomes half-metal by a single Ge vacancy. • Band gap value of GeC system can be tuned in the range of 0.308–1.738 eV by antisite or Stone–Wales defects. - Abstract: On the basis of first-principles plane-wave calculations, we investigated the electronic and magnetic properties of various point defects including single Ge and C vacancies, Ge + C divacancy, Ge↔C antisites and the Stone–Wales (SW) defects in a GeC monolayer. We found that various periodic vacancy defects in GeC single layer give rise to crucial effects on the electronic and magnetic properties. The band gaps of GeC monolayer vary significantly from 0.308 eV to 1.738 eV due to the presence of antisites and Stone–Wales defects. While nonmagnetic ground state of semiconducting GeC turns into metal by introducing a carbon vacancy, it becomes half-metal by a single Ge vacancy with high magnetization (4 μ_B) value per supercell. All the vacancy types have zero net magnetic moments, except single Ge vacancy.
Point defects in hexagonal germanium carbide monolayer: A first-principles calculation
Energy Technology Data Exchange (ETDEWEB)
Ersan, Fatih [Department of Physics, Adnan Menderes University, 09100 Aydın (Turkey); Gökçe, Aytaç Gürhan [Department of Physics, Adnan Menderes University, 09100 Aydın (Turkey); Department of Physics, Dokuz Eylül University, 35160 İzmir (Turkey); Aktürk, Ethem, E-mail: ethem.akturk@adu.edu.tr [Department of Physics, Adnan Menderes University, 09100 Aydın (Turkey); Nanotechnology Application and Research Center, Adnan Menderes University, 09100 Aydın (Turkey)
2016-12-15
Highlights: • Semiconductor GeC turns into metal by introducing a carbon vacancy. • Semiconductor GeC becomes half-metal by a single Ge vacancy. • Band gap value of GeC system can be tuned in the range of 0.308–1.738 eV by antisite or Stone–Wales defects. - Abstract: On the basis of first-principles plane-wave calculations, we investigated the electronic and magnetic properties of various point defects including single Ge and C vacancies, Ge + C divacancy, Ge↔C antisites and the Stone–Wales (SW) defects in a GeC monolayer. We found that various periodic vacancy defects in GeC single layer give rise to crucial effects on the electronic and magnetic properties. The band gaps of GeC monolayer vary significantly from 0.308 eV to 1.738 eV due to the presence of antisites and Stone–Wales defects. While nonmagnetic ground state of semiconducting GeC turns into metal by introducing a carbon vacancy, it becomes half-metal by a single Ge vacancy with high magnetization (4 μ{sub B}) value per supercell. All the vacancy types have zero net magnetic moments, except single Ge vacancy.
Nagura, Takuya; Kawachi, Shingo; Chokawa, Kenta; Shirakawa, Hiroki; Araidai, Masaaki; Kageshima, Hiroyuki; Endoh, Tetsuo; Shiraishi, Kenji
2018-04-01
It is expected that the off-state leakage current of MOSFETs can be reduced by employing vertical body channel MOSFETs (V-MOSFETs). However, in fabricating these devices, the structure of the Si pillars sometimes cannot be maintained during oxidation, since Si atoms sometimes disappear from the Si/oxide interface (Si missing). Thus, in this study, we used first-principles calculations based on the density functional theory, and investigated the Si emission behavior at the various interfaces on the basis of the Si emission model including its atomistic structure and dependence on Si crystal orientation. The results show that the order in which Si atoms are more likely to be emitted during thermal oxidation is (111) > (110) > (310) > (100). Moreover, the emission of Si atoms is enhanced as the compressive strain increases. Therefore, the emission of Si atoms occurs more easily in V-MOSFETs than in planar MOSFETs. To reduce Si missing in V-MOSFETs, oxidation processes that induce less strain, such as wet or pyrogenic oxidation, are necessary.
First-principle calculations of optical properties of monolayer arsenene and antimonene allotropes
Energy Technology Data Exchange (ETDEWEB)
Xu, Yuanfeng; Peng, Bo; Zhang, Hao; Zhang, Rongjun; Zhu, Heyuan [Shanghai Ultra-precision Optical Manufacturing Engineering Research Center and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, Fudan University, Shanghai 200433 (China); Shao, Hezhu [Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China)
2017-04-15
Recently a stable monolayer of antimony in buckled honeycomb structure called antimonene was successfully grown on 3D topological insulator Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3}, which displays novel semiconducting properties. By first-principle calculations, we systematically investigate the electronic and optical properties of α- and β-allotropes of monolayer arsenene/antimonene. The obtained electronic structures reveal that the direct band gap of α-arsenene/antimonene is much smaller than the indirect band gap of their β-counterpart, respectively. Significant absorption is observed in α-antimonene, which can be used as a broad saturable absorber. For β-arsenene/antimonene, the reflectivity is low and the absorption is negligible in the visible region when the polarization along the out-plane direction, indicating that β-arsenene/antimonene are polarizationally transparent materials. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Density functional studies: First principles and semiempirical calculations of clusters and surfaces
International Nuclear Information System (INIS)
Sinnott, S.B.
1993-01-01
In the research presented here, various theoretical electronic structure techniques are utilized to analyze widely different systems from silicon clusters to transition metal solids and surfaces. For the silicon clusters, first principles density functional methods are used to investigate Si N for N = 2-8. The goal is to understand the different types of bonding that can occur in such small clusters where the coordination of the atoms differs substantially from that of the stable bulk tetrahedral bonding. Such uncoordinated structures can provide a good test of more approximate theories that can be used eventually to model silicon surfaces, of obvious technological importance. For the transition metal systems, non-self-consistent electronic structure methods are used to provide an understanding of the driving force for surface relaxations. An in-depth analysis of the results is presented and the physical basis of surface relaxation within the theory is discussed. In addition, the limitations inherent in calculations of metal surface relaxation are addressed. Finally, in an effort to increase understanding of approximate methods, a novel non-self-consistent density functional electronic structure method is developed that is ∼1000 times faster computationally than more sophisticated methods. This new method is tested for a variety of systems including diatomics, mixed clusters, surfaces and bulk lattices. The strengths and weaknesses of the new theory are discussed in detail, leading to greater understanding of non-self-consistent density functional theories as a whole
The electronic properties of phosphorus-doped GaN nanowires from first-principle calculations
International Nuclear Information System (INIS)
Fu, Nannan; Li, Enling; Cui, Zhen; Ma, Deming; Wang, Wei; Zhang, Yulong; Song, Sha; Lin, Jie
2014-01-01
Highlights: • The P impurities tend to enrich at the surface of GaN nanowires. • The lattice parameters of GaN nanowires are changed by the P impurity. • Donor impurity level appears when the P impurity substitutes for the Ga atom. • The band gap decreases slightly when the P impurity substitutes for the N atom. - Abstract: The electronic properties of phosphorus-doped unsaturated and saturated gallium nitride (GaN) nanowires have been investigated from first-principles using the ultrasoft pseudopotential method. The results of these calculations indicate that the P impurities are enriched at the surface of gallium nitride nanowires, and that the structural symmetry of GaN nanowires is broken due to changes in the lattice parameters. When the P impurity substitutes for the Ga atom, the width of band gap increases at the Γ point, a donor impurity level appears in the band gap, and the P impurity and adjacent N atoms exists covalent interaction. Moreover, when the P impurity substitutes for the N atom, the width of the band gap decreases slightly at the Γ point, there is no obvious impurity level in the band gap, and P–Ga covalent bonds are formed, including those composed of ionic bonds. These conclusions indicate that the incorporation of P impurities can improve the field emission performance of GaN nanowires, which is consistent with the experimental results
Magnetic and electronic properties of Cu1-xFexO from first principles calculations
Yang, Hua; Cheng, Yingchun; Chen, Guifeng; Mi, Wenbo; Bai, Haili
2013-01-01
Magnetic and electronic properties of Cu1-xFexO systems with x = 6.25% and 12.5% have been investigated using first principles calculations. The ground state of CuO is an antiferromagnetic insulator. At x = 6.25%, Cu1-xFexO systems with Fe on 2 and 4 substitution positions are half-metallic due to the strong hybridization among Fe, the nearest O and Cu atoms, which may come from the double exchange coupling between Fe2+-O2--Cu2+. At x = 12.5%, Cu 1-xFexO system with Fe on 9-11 position has a strong spin polarization near the Fermi level and the system energy is lowest when the doped two Fe atoms form ferromagnetic configuration. This indicates the two doped Fe atoms prefer to form ferromagnetic configuration in Fe2+-O 2--Cu2+-O2--Fe2+ chains. While in the Fe on 7-11 position, the spin-down Fe-11 3d states have a large spin polarization near the Fermi level when the two doped Fe atoms form antiferromagnetic configuration. It is concluded that the transition metal doping can modify the magnetism and electronic structures of Cu 1-xFexO systems. This journal is © The Royal Society of Chemistry 2013.
Xiong, Hui-Hui; Gan, Lei; Tong, Zhi-Fang; Zhang, Heng-Hua; Zhou, Yang
2018-05-01
The nucleation potential of transition metal (TM) carbides formed in steel can be predicted by the behavior of iron adsorption on their surface. Therefore, Fe adsorption on the (001) surface of (A1-xmx)C (A = Nb, Ti, m = Mo, V) was investigated by the first-principles method to reveal the initialization of Fe nucleation. The Mulliken population and partial density of state (PDOS) were also calculated and analyzed in this work. The results show that Fe adsorption depends on the composition and configuration of the composite carbides. The adsorption energy (Wads) of Fe on most of (A1-xmx)C is larger than that of Fe on pure TiC or NbC. The maximum Wads is found for Fe on (Nb0.5Mo0.5)C complex carbide, indicating that this carbide has the high nucleation capacity at early stage. The Fe adsorption could be improved by the segregation of Cr and Mn atoms on the surfaces of (Nb0.5Mo0.5)C and (Ti0.5Mo0.5)C. The PDOS analysis of (Cr, Mn)-doped systems further explains the strong interactions between Fe and Cr or Mn atoms.
Ma, Xia-Xia; Li, Ze-Sheng
2018-01-01
Oxygen molecule has a negative effect on perovskite solar cells, which has been investigated experimentally. However, detailed theoretical research is still rare. This study presents a microscopic view to reveal the interaction mechanism between O2 and perovskite based on the first-principles calculation. The results show that O2 is adsorbed on the (100) surface of MAPbI3 perovskite mainly by Van der Waals force. O2 adsorption makes the MAPbI3 surface generate a small number of positive charges, which leads to the increase of the work function of the MAPbI3 surface. This is in agreement with the experimental measurement. And increased work function of MAPbI3 surface is not beneficial to electron transfer from perovskite to electronic extraction layer (such as TiO2). Comparison of the density of states (DOS) of the clean (100) surface and the adsorbed system shows that an in-gap state belonging to O2 appears, which can explain the phenomenon observed from experiments that electron transfers from the surface of perovskite to O2 to form superoxide. The theoretical power conversion efficiency of the system with and without O2 adsorption is evaluated, and it turns out that the power conversion efficiency of the system with O2 adsorption is slightly lower than that of the system without O2 adsorption. This result indicates that avoiding the introduction of O2 molecules between perovskite and electronic extraction layer is beneficial to the perovskite solar cell.
Quantum effect enhanced magnetism of C-doped phosphorene nanoribbons: first-principles calculations.
Cai, Xiaolin; Niu, Chunyao; He, Yuan-Yao; Wang, Jianjun; Zhu, Zhili; Zhang, Liwei; Jia, Yu
2017-10-25
Manipulating magnetism of low-dimensional materials is of great importance for their practical applications. Here, using first-principles calculations, we report a systematic investigation of the magnetic properties of C-doped H saturated zigzag phosphorene nanoribbons (H-ZPNRs), which are rather different from those of 2D periodic systems due to the quantum size effect. First of all, we observed a greatly enhanced magnetic moment locating mainly on the C atom and also slightly on its surrounding P atoms. Our results also indicated a strong dependence of the magnetic moment of the C atom on its location, which decays from the edge to the center site of the nanoribbons with an odd-even oscillating behavior originating from Friedel oscillation in low-dimensional materials. As for the C atom on a specific location, its magnetic moment decreases gradually with increasing width of H-ZPNRs, degenerating to the 2D case. What is more, we found that both the magnitude and the oscillating behavior of the magnetic moment on the C atom can be tuned by the edge saturation atoms. In addition, the case of two C atoms co-doping H-ZPNRs was also studied, showing non-magnetic (NM), ferromagnetic (FM) and antiferromagnetic (AFM) states depending on the locations of the two C atoms. Our findings suggest a plausible route for manipulating magnetism of the sp element doped H-ZPNRs, which are expected to have potential applications in spintronics.
Piezoelectricity in K1−xNaxNbO3: First-principles calculation
International Nuclear Information System (INIS)
Li Qiang; Zhang Rui; Lv Tian-Quan; Zheng Li-Mei
2015-01-01
The piezoelectric properties of K 1−x Na x NbO 3 are studied by using first-principles calculations within virtual crystal approximation. To understand the critical factors for the high piezoelectric response in K 1−x Na x NbO 3 , the total energy, piezoelectric coefficient, elastic property, density of state, Born effective charge, and energy barrier on polarization rotation paths are systematically investigated. The morphotropic phase boundary in K 1−x Na x NbO 3 is predicted to occur at x = 0.521, which is in good agreement with the available experimental data. At the morphotropic phase boundary, the longitudinal piezoelectric coefficient d 33 of orthorhombic K 0.5 Na 0.5 NbO 3 reaches a maximum value. The rotated maximum of is found to be along the 50° direction away from the spontaneous polarization (close to the [001] direction). The moderate bulk and shear modulus are conducive to improving the piezoelectric response. By analyzing the energy barrier on polarization rotation paths, it is found that the polarization rotation of orthorhombic K 0.5 Na 0.5 NbO 3 becomes easier compared with orthorhombic KNbO 3 , which proves that the high piezoelectric response is attributed to the flattening of the free energy at compositions close to the morphotropic phase boundary. (paper)
The electronic properties of phosphorus-doped GaN nanowires from first-principle calculations
Energy Technology Data Exchange (ETDEWEB)
Fu, Nannan; Li, Enling, E-mail: Lienling@xaut.edu.cn; Cui, Zhen; Ma, Deming; Wang, Wei; Zhang, Yulong; Song, Sha; Lin, Jie
2014-05-01
Highlights: • The P impurities tend to enrich at the surface of GaN nanowires. • The lattice parameters of GaN nanowires are changed by the P impurity. • Donor impurity level appears when the P impurity substitutes for the Ga atom. • The band gap decreases slightly when the P impurity substitutes for the N atom. - Abstract: The electronic properties of phosphorus-doped unsaturated and saturated gallium nitride (GaN) nanowires have been investigated from first-principles using the ultrasoft pseudopotential method. The results of these calculations indicate that the P impurities are enriched at the surface of gallium nitride nanowires, and that the structural symmetry of GaN nanowires is broken due to changes in the lattice parameters. When the P impurity substitutes for the Ga atom, the width of band gap increases at the Γ point, a donor impurity level appears in the band gap, and the P impurity and adjacent N atoms exists covalent interaction. Moreover, when the P impurity substitutes for the N atom, the width of the band gap decreases slightly at the Γ point, there is no obvious impurity level in the band gap, and P–Ga covalent bonds are formed, including those composed of ionic bonds. These conclusions indicate that the incorporation of P impurities can improve the field emission performance of GaN nanowires, which is consistent with the experimental results.
First-principles calculation of electronic energy level alignment at electrochemical interfaces
Energy Technology Data Exchange (ETDEWEB)
Azar, Yavar T.; Payami, Mahmoud, E-mail: mpayami@aeoi.org.ir
2017-08-01
Highlights: • Using DFT calculation, level shifts of TiO{sub 2} and ZnO at the interfaces with MeCN and DMF are determined. • Level shifts are obtained using potential difference between the surfaces of asymmetric slabs. • Solvent molecules give an up-shift to the levels that varies with coverage. • MD simulations show that at room temperatures the surface is not fully covered by the solvent molecules. - Abstract: Energy level alignment at solid–solvent interfaces is an important step in determining the properties of electrochemical systems. The positions of conduction and valence band edges of a semiconductor are affected by its environment. In this study, using first-principles DFT calculation, we have determined the level shifts of the semiconductors TiO{sub 2} and ZnO at the interfaces with MeCN and DMF solvent molecules. The level shifts of semiconductor are obtained using the potential difference between the clean and exposed surfaces of asymmetric slabs. In this work, neglecting the effects of present ions in the electrolyte solution, we have shown that the solvent molecules give rise to an up-shift for the levels, and the amount of this shift varies with coverage. It is also shown that the shapes of density of states do not change sensibly near the gap. Molecular dynamics simulations of the interface have shown that at room temperatures the semiconductor surface is not fully covered by the solvent molecules, and one must use intermediate values in an static calculations.
Mechanical, electronic, and optical properties of β-B{sub 6}O. First-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Yang, Ruike; Ma, Shaowei; Wei, Qun [Xidian Univ., Shaanxi (China). School of Physics and Optoelectronic Engineering; Du, Zheng [National Supercomputing Center in Shenzhen, Shenzhen (China)
2017-07-01
The mechanical, electronic, and optical properties of β-B{sub 6}O are calculated by first-principles. The structural optimization and all properties are calculated by the method of generalized gradient approximation - Perdew, Burke and Ernzerhof (PBE). The hardness of β-B{sub 6}O is 39 GPa under a pressure of 0 GPa, which indicates that it belongs to a hard material. The band gap is indirect with a value of 1.836 eV, showing that β-B{sub 6}O is a semiconductor. The research of the electron localization function shows that the bonds of β-B{sub 6}O are covalent bonds, which can increase the stability of the compound. The phonon dispersion curves present the dynamical stability of β-B{sub 6}O under pressures of 0 and 50 GPa. The optical properties of β-B{sub 6}O are also calculated. In the energy range from 0 to 18 eV, β-B{sub 6}O presents high reflectivity; it has a strong absorption in the energy range from 3 to 18 eV. The refractive index results show that light propagates through the β-B{sub 6}O in a difficult manner in the energy range from 6.9 to 16.5 eV. In addition, the energy of the plasma frequency for β-B{sub 6}O is 16.6 eV and the peak value of the loss function is 13.6. These properties provide the basis for the development and application of β-B{sub 6}O.
First principles calculation of mixing enthalpy of β-Ti with transition elements
International Nuclear Information System (INIS)
Chandran, Mahesh; Subramanian, P.R.; Gigliotti, Michael F.
2013-01-01
Highlights: ► Compares the accuracy of SQS with parametric method to determine ΔH for binary alloys which has not been done before. ► Trends in ΔH for β-Ti–X alloys where X is 3d-, 4d- and 5d-transition series are presented. ► The design space for new β-Ti alloys is determined by combining ΔH with Hume-Rothery rules. - Abstract: The mixing enthalpy ΔH mix (x) of body-centered cubic (BCC) β-Ti with transition elements was calculated using first-principles methods based on density functional theory (DFT). The solid solution effect was treated by two different approaches, viz. special quasi-random structures (SQS) and the parametric method. The SQS-N method uses direct DFT to calculate energy of structures containing N atoms which approximate the correlation of an ideal solid solution up to some distance, whereas the parametric method employs a polynomial representation for ΔH mix (x) and the coefficients are calculated using DFT. Comparison of the two methods shows fair agreement for most alloys though differences as high as 40% can also be seen among some of the alloys. The trends in ΔF mix (x), obtained by adding entropy contribution from ideal solution model to ΔH mix (x) for 3d-, 4d- and 5d-transition series were analyzed in terms of e/a, the ratio of number of valence electrons to atoms. The early transition elements, between Group 4–7, was found to have very small ΔF mix (x) over a wide range of concentration. Stability of the alloys is analyzed by combining ΔF mix (x) with Hume-Rothery rules.
Calculations of thermodynamic properties of PuO{sub 2} by the first-principles and lattice vibration
Energy Technology Data Exchange (ETDEWEB)
Minamoto, Satoshi [Energy and Industrial Systems Department, ITOCHU Techno-Solutions Corporation, Kasumigaseki 3-chome, Chiyoda-ku, Tokyo 100-6080 (Japan)], E-mail: satoshi.minamoto@ctc-g.co.jp; Kato, Masato [Japan Atomic Energy Agency, 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki 319-1194 (Japan); Konashi, Kenji [Institute for Materials Research, Tohoku University, 2145-2 Narita-chou, Oarai-chou, Ibaraki 311-1313 (Japan); Kawazoe, Yoshiyuki [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)
2009-03-15
Plutonium dioxide (PuO{sub 2}) is a key compound of mixed oxide fuel (MOX fuel). To predict the thermal properties of PuO{sub 2} at high temperature, it is important to understand the properties of MOX fuel. In this study, thermodynamic properties of PuO{sub 2} were evaluated by coupling of first-principles and lattice dynamics calculation. Cohesive energy was estimated from first-principles calculations, and the contribution of lattice vibration to total energy was evaluated by phonon calculations. Thermodynamic properties such as volume thermal expansion, bulk modulus and specific heat of PuO{sub 2} were investigated up to 1500 K.
Calculations of thermodynamic properties of PuO2 by the first-principles and lattice vibration
International Nuclear Information System (INIS)
Minamoto, Satoshi; Kato, Masato; Konashi, Kenji; Kawazoe, Yoshiyuki
2009-01-01
Plutonium dioxide (PuO 2 ) is a key compound of mixed oxide fuel (MOX fuel). To predict the thermal properties of PuO 2 at high temperature, it is important to understand the properties of MOX fuel. In this study, thermodynamic properties of PuO 2 were evaluated by coupling of first-principles and lattice dynamics calculation. Cohesive energy was estimated from first-principles calculations, and the contribution of lattice vibration to total energy was evaluated by phonon calculations. Thermodynamic properties such as volume thermal expansion, bulk modulus and specific heat of PuO 2 were investigated up to 1500 K
Review of high pressure phases of calcium by first-principles calculations
International Nuclear Information System (INIS)
Ishikawa, T; Tsuchiya, T; Nagara, H; Suzuki, N; Tsuchiya, J
2010-01-01
We review high pressure phases of calcium which have obtained by recent experimental and first-principles studies. In this study, we investigated the face-centered cubic (fcc) structure, the body-centered cubic (bcc) structure, the simple cubic (sc) structure, a tetragonal P4 3 2 1 2 [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmca [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmcm [Teweldeberhan A M and Bonev S A 2008 Phys. Rev. B 78 140101(R)], an orthorhombic Pnma [Yao Y et al. 2008 Phys. Rev. B 78 054506] and a tetragonal I4/mcm [Arapan S et al. 2008 Proc. Natl. Acad. Sci. USA 105 20627]. We compared the enthalpies among the structures up to 200 GPa and theoretically determined the phase diagram of calcium. The sequence of the structural transitions is fcc (0- 3.5 GPa) → bcc (3.5 - 35.7 GPa) → Cmcm (35.7- 52GPa) → P4 3 2 1 2 (52-109 GPa) → Cmca (109-117.4GPa) → Pnma (117.4-134.6GPa) → I4mcm(134.6 GPa -). The sc phase is experimentally observed in the pressure range from 32 to 113 GPa but, in our calculation, there is no pressure region where the sc phase is the most stable. In addition, we found that the enthalpy of the hexagonal close-packed (hcp) structure is lower than that of I4/mcm above 495 GPa.
Review of high pressure phases of calcium by first-principles calculations
Ishikawa, T.; Nagara, H.; Suzuki, N.; Tsuchiya, J.; Tsuchiya, T.
2010-03-01
We review high pressure phases of calcium which have obtained by recent experimental and first-principles studies. In this study, we investigated the face-centered cubic (fcc) structure, the body-centered cubic (bcc) structure, the simple cubic (sc) structure, a tetragonal P43212 [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmca [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmcm [Teweldeberhan A M and Bonev S A 2008 Phys. Rev. B 78 140101(R)], an orthorhombic Pnma [Yao Y et al. 2008 Phys. Rev. B 78 054506] and a tetragonal I4/mcm(00) [Arapan S et al. 2008 Proc. Natl. Acad. Sci. USA 105 20627]. We compared the enthalpies among the structures up to 200 GPa and theoretically determined the phase diagram of calcium. The sequence of the structural transitions is fcc (0- 3.5 GPa) → bcc (3.5 - 35.7 GPa) → Cmcm (35.7- 52GPa) → P43212 (52-109 GPa) → Cmca (109-117.4GPa) → Pnma (117.4-134.6GPa) → I4/mcm(00) (134.6 GPa -). The sc phase is experimentally observed in the pressure range from 32 to 113 GPa but, in our calculation, there is no pressure region where the sc phase is the most stable. In addition, we found that the enthalpy of the hexagonal close-packed (hcp) structure is lower than that of I4/mcm(00) above 495 GPa.
First-principles calculation of adsorption of shale gas on CaCO3 (100) surfaces.
Luo, Qiang; Pan, Yikun; Guo, Ping; Wang, Zhouhua; Wei, Na; Sun, Pengfei; Liu, Yuxiao
2017-06-16
To demonstrate the adsorption strength of shale gas to calcium carbonate in shale matrix, the adsorption of shale gas on CaCO3 (100) surfaces was studied using the first-principles method, which is based on the density functional theory (DFT). The structures and electronic properties of CH4, C2H6, CO2 and N2 molecules were calculated by the generalized gradient approximation (GGA), for a coverage of 1 monolayer (ML). Under the same conditions, the density of states (DOS) of CaCO3 (100) surfaces before and after the adsorption of shale gas molecules at high-symmetry adsorption sites were compared. The results showed that the adsorption energies of CH4, C2H6, CO2 and N2 on CaCO3 (100) surfaces were between 0.2683 eV and -0.7388 eV. When a CH4 molecule was adsorbed at a hollow site and its 2 hydrogen atoms were parallel to the long diagonal (H3) on the CaCO3 (100) surface, it had the most stable adsorption, and the adsorption energy was only -0.4160 eV. The change of adsorption energy of CH4 was no more than 0.0535 eV. Compared with the DOS distribution of CH4 before adsorption, it shifted to the left overall after adsorption. At the same time, the partial density of states (PDOS) curves of CaCO3 (100) surfaces before and after adsorption basically overlapped. This work showed that the adsorption effect of shale gas on calcium carbonate is very weak, and the adsorption is physisorption at the molecular level.
EPR parameters of E centers inν-SiO2 from first-principles calculations
International Nuclear Information System (INIS)
Giacomazzi, Luigi; Martin-Samos, L.; Boukenter, A.; Ouerdane, Y.; Girard, S.; Richard, N.
2014-01-01
A first-principles investigation of E' centers in vitreous silica (ν-SiO 2 ) based on calculations of the electron paramagnetic resonance (EPR) parameters is presented. The EPR parameters are obtained by exploiting the gauge including projector augmented wave method as implemented in the QUANTUM-ESPRESSO package. First, we analyze the EPR parameters of a large number of Si 2 dimers. The g tensor of the Si 2 dimers is shown to possess an average rhombic symmetry and larger g principal values with respect to those observed, e.g., for the E 'γ center in silica. Furthermore, the g principal values clearly show a linear trend with the Si-Si dimer length. Our results suggest that the Si 2 dimers could correspond to an unidentified paramagnetic center, though occasionally the calculated g principal values of the Si 2 dimer might be compatible with those found experimentally for the E' δ center. Next, we generate non dimer configurations by a procedure involving structural relaxations in the subsequent positively charged states. In particular, puckered, un-puckered, doubly puckered, and forward-oriented configurations are generated. The distributions of the calculated EPR parameters of the puckered and un-puckered configurations further support the assignment of the E' γ center to an unpaired spin localized at a threefold coordinated silicon dangling bond. Moreover, by analyzing Fermi contacts and g tensors of the puckered and forward-oriented configurations, we suggest the assignment of the E' α center to the latter type of configurations. This work also suggests that the differences in the EPR parameters of E' α and E' γ centers mainly arise from the strained geometry of the silicon dangling bond. In the forward-oriented configurations, one Si-O bond is about 0.2 Angstroms longer than the remaining two, whereas in the silicon dangling bond of the puckered and un-puckered configurations, all three bonds have a length of ≅1
International Nuclear Information System (INIS)
Eisenbach, Markus; Perera, Meewanage Dilina N.; Landau, David P; Nicholson, Don M.; Yin, Junqi; Brown, Greg
2015-01-01
We present a unified approach to describe the combined behavior of the atomic and magnetic degrees of freedom in magnetic materials. Using Monte Carlo simulations directly combined with first principles the Curie temperature can be obtained ab initio in good agreement with experimental values. The large scale constrained first principles calculations have been used to construct effective potentials for both the atomic and magnetic degrees of freedom that allow the unified study of influence of phonon-magnon coupling on the thermodynamics and dynamics of magnetic systems. The MC calculations predict the specific heat of iron in near perfect agreement with experimental results from 300K to above Tc and allow the identification of the importance of the magnon-phonon interaction at the phase-transition. Further Molecular Dynamics and Spin Dynamics calculations elucidate the dynamics of this coupling and open the potential for quantitative and predictive descriptions of dynamic structure factors in magnetic materials using first principles-derived simulations.
First-Principles Calculation of Lithium Adsorption and Diffusion on Silicene
International Nuclear Information System (INIS)
Huang Juan; Chen Hong-Jin; Wu Mu-Sheng; Liu Gang; Ouyang Chu-Ying; Xu Bo
2013-01-01
The adsorption and diffusion of lithium on silicene are studied by using the first-principles method. It is found that the adsorption energy of Li adsorbing on silicene is significantly larger than that of Li adsorbing on graphene. With the increasing concentration of adsorbed Li atoms, the adsorption energy also increases. The diffusion barrier of Li on silicene is relatively low, which is insensitive to the concentration of adsorbed atoms
van Setten, Michiel J.; de Wijs, Gilles A.; Brocks, G.
2008-01-01
Alanates and boranates are intensively studied because of their potential use as hydrogen storage materials. In this paper, we present a first-principles study of the electronic structure and the energetics of beryllium boranate BeBH42. From total energy calculations, we show that—in contrast to the
Ruthenia-based electrochemical supercapacitors: insights from first-principles calculations.
Ozoliņš, Vidvuds; Zhou, Fei; Asta, Mark
2013-05-21
Electrochemical supercapacitors (ECs) have important applications in areas wherethe need for fast charging rates and high energy density intersect, including in hybrid and electric vehicles, consumer electronics, solar cell based devices, and other technologies. In contrast to carbon-based supercapacitors, where energy is stored in the electrochemical double-layer at the electrode/electrolyte interface, ECs involve reversible faradaic ion intercalation into the electrode material. However, this intercalation does not lead to phase change. As a result, ECs can be charged and discharged for thousands of cycles without loss of capacity. ECs based on hydrous ruthenia, RuO2·xH2O, exhibit some of the highest specific capacitances attained in real devices. Although RuO2 is too expensive for widespread practical use, chemists have long used it as a model material for investigating the fundamental mechanisms of electrochemical supercapacitance and heterogeneous catalysis. In this Account, we discuss progress in first-principles density-functional theory (DFT) based studies of the electronic structure, thermodynamics, and kinetics of hydrous and anhydrous RuO2. We find that DFT correctly reproduces the metallic character of the RuO2 band structure. In addition, electron-proton double-insertion into bulk RuO2 leads to the formation of a polar covalent O-H bond with a fractional increase of the Ru charge in delocalized d-band states by only 0.3 electrons. This is in slight conflict with the common assumption of a Ru valence change from Ru(4+) to Ru(3+). Using the prototype electrostatic ground state (PEGS) search method, we predict a crystalline RuOOH compound with a formation energy of only 0.15 eV per proton. The calculated voltage for the onset of bulk proton insertion in the dilute limit is only 0.1 V with respect to the reversible hydrogen electrode (RHE), in reasonable agreement with the 0.4 V threshold for a large diffusion-limited contribution measured experimentally
Tunable redox potential of nonmetal doped monolayer MoS{sub 2}: First principle calculations
Energy Technology Data Exchange (ETDEWEB)
Lu, S. [Center for Coordination Bond Engineering, China Jiliang University (China); Li, C., E-mail: canli1983@gmail.com [Center for Coordination Bond Engineering, China Jiliang University (China); School of Materials Science and Engineering, China Jiliang University (China); Zhao, Y.F.; Gong, Y.Y.; Niu, L.Y.; Liu, X.J. [Center for Coordination Bond Engineering, China Jiliang University (China)
2016-10-30
Graphical abstract: Both E{sub CBM} and E{sub VBM} values are affected by the chemical valences of dopants, which also affect the redox potentials of specimens. Compared to the pristine monolayer MoS{sub 2}, the nonmetal ions with odd chemical valences [monovalent (H{sup +}, F{sup –}, Cl{sup –}, Br{sup –} and I{sup –}), trivalent (N{sup 3–}, P{sup 3–} and As{sup 3–}) and pentavalence (B{sup 5–})] enhance the oxidation potential and reduce the reduction potential of specimens, but the nonmetal ions with even chemical valences [divalent (O{sup 2–}, Se{sup 2–} and Te{sup 2–}) and quadravalent (C{sup 4–} and Si{sup 4–})] have the opposite effects on the redox potentials. Display Omitted - Highlights: • The newly formed chemical bonds affect the electronic distribution around the dopants and the nearby Mo atoms. • Compared to pristine monolayer MoS{sub 2}, the nonmetal ions with odd (even) chemical valences enhance (reduce) the oxidation potential and reduce (enhance) the reduction potential of specimens. • The lone pair electrons in nonmetal ions with odd chemical valences extra interact with the Mo ions which reduces the E{sub CBM} and E{sub VBM} values of specimens. - Abstract: Doping is an effective method to alter the electronic behavior of materials by forming new chemical bonds and bringing bond relaxation. With this aid of first principle calculations, the crystal configuration and electronic properties of monolayer MoS{sub 2} have been modulated by the nonmetal (NM) dopants (H, B, C, N, O, F, Si, P, Cl, As, Se, Br, Te and I), and the thermodynamic stability depending on the preparation conditions (Mo-rich and S-rich conditions) were discussed. Results shown that, the NM dopants substituted preferentially for S under Mo-rich condition, the electronic distribution around the dopants and the nearby Mo atoms are changed by the new formed Mo-NM bonds and bands relaxation. Compared to pristine monolayer MoS{sub 2}, the NM ions with odd
Effect of contact deformation on contact electrification: a first-principles calculation
International Nuclear Information System (INIS)
Zhang, Yuanyue; Shao, Tianmin
2013-01-01
The effect of contact deformation on contact electrification of metallic materials was studied by the first-principles method. The results of charge population and the densities of states of the deformed contact models demonstrated that the magnitude of the transferred charge increased with deformation. The mechanism of the effect of deformation was investigated by studying the electronic properties of the deformed surface slabs. The results showed that crystal deformation led to a change in the electrostatic potential of the metal, where the number of nearly free electrons and unoccupied orbitals for charge transfer increased, and their energy barrier decreased. (paper)
Liu, Lili
2014-06-01
Based on the quasiharmonic approach from first-principles phonon calculations, the volume versus temperature relations for Al, Ni and Cu are obtained. Using the equilibrium volumes at temperature T, the temperature dependences of generalized planar fault energies have also been calculated by first-principles calculations. It is found that the generalized planar fault energies reduce slightly with increasing temperature. Based on the calculated generalized planar fault energies, the twinnabilities of Al, Ni and Cu are discussed with the three typical criteria for crack tip twinning, grain boundary twinning and inherent twinning at different temperatures. The twinnabilities of Al, Ni and Cu also decrease slightly with increasing temperature. Ni and Cu have the inherent twinnabilities. But, Al does not exhibit inherent twinnability. These results are in agreement with the previous theoretical studies at 0 K and experimental observations at ambient temperature. © 2014 Elsevier B.V. All rights reserved.
Liu, Lili; Wang, Rui; Wu, Xiaozhi; Gan, Liyong; Wei, Qunyi
2014-01-01
Based on the quasiharmonic approach from first-principles phonon calculations, the volume versus temperature relations for Al, Ni and Cu are obtained. Using the equilibrium volumes at temperature T, the temperature dependences of generalized planar fault energies have also been calculated by first-principles calculations. It is found that the generalized planar fault energies reduce slightly with increasing temperature. Based on the calculated generalized planar fault energies, the twinnabilities of Al, Ni and Cu are discussed with the three typical criteria for crack tip twinning, grain boundary twinning and inherent twinning at different temperatures. The twinnabilities of Al, Ni and Cu also decrease slightly with increasing temperature. Ni and Cu have the inherent twinnabilities. But, Al does not exhibit inherent twinnability. These results are in agreement with the previous theoretical studies at 0 K and experimental observations at ambient temperature. © 2014 Elsevier B.V. All rights reserved.
Properties of half-Heusler compounds TaIrGe by using first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Wei, JunHong [Henan Normal University, College of Physics and Information Engineering, Xinxiang, Henan (China); Henan Institute of Science and Technology, School of Mechanical and Electrical Engineering, Xinxiang, Henan (China); Wang, Guangtao [Henan Normal University, College of Physics and Information Engineering, Xinxiang, Henan (China)
2017-05-15
The electronic structures, optical and thermoelectric properties of ternary half-Heusler compound TaIrGe were investigated by using the first-principles and Boltzmann transport theory. Spin-orbit coupling (SOC) removed the degeneracy of VBM, and then decreased the Seebeck coefficients and power factor. From the compressive to tensile strain, the band gap gradually increases from 0.96 to 1.11 eV, accompanied by the absorption coefficient peak red-shift. The effective mass (m{sup *}{sub DOS}) of VBM and CBM gradually increases from the compressive to tensile strain, which enhances the Seebeck coefficient and power factor. Our results indicate that the electronic structures, optical and thermoelectric properties of TaIrGe can be effectively tuned by the strain and TaIrGe can be used as an important photoelectric and thermoelectric material in the future. (orig.)
Shi, Tingting
In this dissertation, a series of earth-abundant photovoltaic materials including lead halide perovskites, copper based compounds, and silicon are investigated via density functional theory (DFT). Firstly, we study the unique optoelectronic properties of perovskite CH3NH3PbI3 and CH3NH3PbBr 3. First-principle calculations show that CH3NH3PbI 3 perovskite solar cells exhibit remarkable optoelectronic properties that account for the high open circuit voltage (Voc) and long electron-hole diffusion lengths. Our results reveal that for intrinsic doping, dominant point defects produce only shallow levels. Therefore lead halide perovskites are expected to exhibit intrinsic low non-radiative recombination rates. The conductivity of perovskites can be tuned from p-type to n-type by controlling the growth conditions. For extrinsic defects, the p-type perovskites can be achieved by doping group-IA, -IB, or -VIA elements, such as Na, K, Rb, Cu, and O at I-rich growth conditions. We further show that despite a large band gap of 2.2 eV, the dominant defects in CH3 NH3PbBr3 also create only shallow levels. The photovoltaic properties of CH3NH3PbBr3 - based perovskite absorbers can be tuned via defect engineering. Highly conductive p-type CH3NH3PbBr3 can be synthesized under Br-rich growth conditions. Such CH3NH3PbBr 3 may be potential low-cost hole transporting materials for lead halide perovskite solar cells. All these unique defect properties of perovskites are largely due to the strong Pb lone-pair s orbital and I p (Br p) orbital antibonding coupling and the high ionicity of CH3NH3PbX3 (X=I, Br). Secondly, we study the optoelectronic properties of Cu-V-VI earth abundant compounds. These low cost thin films may have the good electronic and optical properties. We have studied the structural, electronic and optical properties of Cu3-V-VI4 compounds. After testing four different crystal structures, enargite, wurtzite-PMCA, famatinite and zinc-blend-PMCA, we find that Cu3PS4 and
Energy Technology Data Exchange (ETDEWEB)
Lu, Xingxu [School of Materials Science and Engineering, Central South University, Changsha, Hunan 410083 (China); State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Liu, Shuhong, E-mail: shhliu@csu.edu.cn [State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Sino-German Cooperation Group “Microstructure in Al alloys”, Central South University, Changsha, Hunan 410083 (China); Cheng, Kaiming; Tang, Ying [State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Ou, Pengfei [School of Materials Science and Engineering, Central South University, Changsha, Hunan 410083 (China); State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Nash, Philip [Thermal Processing Technology Center, Illinois Institute of Technology (IIT), 10 West 32nd Street, Chicago, IL 60616 (United States); Sundman, Bo [INSTN, CEA Saclay, 91191 Gif-Sur-Yvette Cedex (France); Du, Yong [State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Sino-German Cooperation Group “Microstructure in Al alloys”, Central South University, Changsha, Hunan 410083 (China); Zheng, Feng [School of Materials Science and Engineering, Central South University, Changsha, Hunan 410083 (China)
2015-05-20
Highlights: • Heat contents of Co{sub 2}Hf and CoHf{sub 2} were measured by drop calorimetry. • Enthalpy of formation for Co{sub 23}Hf{sub 6} was computed via first-principles calculations. • Co–Hf system was assessed by means of CALPHAD approach. • Order–disorder model is used to describe B2 (CoHf) and A2 (βHf). • Glass forming range of the Co–Hf amorphous alloys was predicted. - Abstract: Phase equilibria and thermodynamic properties of the Co–Hf system were investigated via calorimetric measurements, first-principles calculations and thermodynamic modeling. Heat contents of Co{sub 2}Hf and CoHf{sub 2} were measured by drop calorimetry from 300 to 1200 °C. The enthalpy of formation for Co{sub 23}Hf{sub 6} at 0 K was computed via first-principles calculations. Based on the experimental measurements and first-principles calculations from the present work and the literature, the Co–Hf system was assessed by means of CALPHAD (CALculation of PHAse Diagram) approach. The excess Gibbs energy of solution phases was modeled with Redlich–Kister polynomial. Sublattice models were employed to describe the homogeneity ranges of Co{sub 2}Hf, CoHf and CoHf{sub 2}. The order–disorder transition between B2 (CoHf) and A2 (βHf) phases was taken into account in the current optimization. Using the optimized parameters, glass forming range (GFR) of the Co–Hf amorphous alloys was predicted to be 15–75 at.% Hf, which is in satisfactory agreement with the experimental observation.
Half-metallic ferromagnetism in Fe-doped Zn3P2 from first-principles calculations
International Nuclear Information System (INIS)
Jaiganesh, G.; Jaya, S. Mathi
2014-01-01
Using the first-principles calculations based on the density functional theory, we have studied the magnetism and electronic structure of Fe-doped Zinc Phosphide (Zn 3 P 2 ). Our results show that the half-metallic ground state and ferromagnetic stability for the small Fe concentrations considered in our study. The stability of the doped material has been studied by calculating the heat of formation and analyzing the minimum total energies in nonmagnetic and ferromagnetic phases. A large value of the magnetic moment is obtained from our calculations and our calculation suggests that the Fe-doped Zn 3 P 2 may be a useful material in semiconductor spintronics
Folegati, P.; Makkonen, I.; Ferragut, R.; Puska, Martti J.
2007-01-01
Electron-positron momentum distributions measured by the coincidence Doppler broadening method can be used in the chemical analysis of the annihilation environment, typically a vacancy-impurity complex in a solid. In the present work, we study possibilities for a quantitative analysis, i.e., for distinguishing the average numbers of different atomic species around the defect. First-principles electronic structure calculations self-consistently determining electron and positron densities and i...
Energy Technology Data Exchange (ETDEWEB)
Zhang, G. P., E-mail: gpzhang@indstate.edu [Department of Physics, Indiana State University, Terre Haute, Indiana 47809 (United States); Si, M. S. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); George, Thomas F. [Office of the Chancellor and Center for Nanoscience, Departments of Chemistry and Biochemistry and Physics and Astronomy, University of Missouri-St. Louis, St. Louis, Missouri 63121 (United States)
2015-05-07
When a laser pulse excites a ferromagnet, its spin undergoes a dramatic change. The initial demagnetization process is very fast. Experimentally, it is found that the demagnetization time is related to the spin moment in the sample. In this study, we employ the first-principles method to directly simulate such a process. We use the fixed spin moment method to change the spin moment in ferromagnetic nickel, and then we employ the Liouville equation to couple the laser pulse to the system. We find that in general the dependence of demagnetization time on the spin moment is nonlinear: It decreases with the spin moment up to a point, after which an increase with the spin moment is observed, followed by a second decrease. To understand this, we employ an extended Heisenberg model, which includes both the exchange interaction and spin-orbit coupling. The model directly links the demagnetization rate to the spin moment itself and demonstrates analytically that the spin relaxes more slowly with a small spin moment. A future experimental test of our predictions is needed.
Half-metallic ferromagnetism in Fe, Co and Ni doped BaS: First principles calculations
Maurya, Savita; Sharma, Ramesh; Bhamu, K. C.
2018-04-01
The first principle investigation of structural, electronic, magnetic and optical properties of Ba1-xTMxS (x = 0.25) have been done using FPLAW method within the density functional theory (DFT) using generalized gradient approximation (GGA) for exchange correlation potential using two different functionals which are the PBE-sol and the modified Becke and Johnson local (spin) density approximation (mBJLDA). It was found that mBJLDA functional offer better account for the electronic structure of the Fe, Co and Ni-doped BaS. It was also observed that Fe/Co/Ni d, S p and Ba d states play a major role in determining the electronic properties of this alloy system. Investigation results shows that Ba0.75(Fe/Co/Ni)0.25S is ferromagnetic with magnetic moment of 3.72 µB, 2.73908 µB and 1.74324 µB at Fe, Co and Ni sites respectively. Complex dielectric constant ɛ(ω) and normal incidence reflectivity R(ω) are also been investigate for broad range of photon energies. These results are compared with the some reported existing experimental values.
First-principles calculation of transport property in nano-devices under an external magnetic field
International Nuclear Information System (INIS)
Chen Jingzhe; Zhang Jin; Han Rushan
2008-01-01
The mesoscopic quantum interference phenomenon (QIP) can be observed and behaves as the oscillation of conductance in nano-devices when the external magnetic field changes. Excluding the factor of impurities or defects, specific QIP is determined by the sample geometry. We have improved a first-principles method based on the matrix Green's function and the density functional theory to simulate the transport behaviour of such systems under a magnetic field. We have studied two kinds of QIP: universal conductance fluctuation (UCF) and Aharonov–Bohm effect (A–B effect). We find that the amplitude of UCF is much smaller than the previous theoretical prediction. We have discussed the origin of difference and concluded that due to the failure of ergodic hypothesis, the ensemble statistics is not applicable, and the conductance fluctuation is determined by the flux-dependent density of states (DOSs). We have also studied the relation between the UCF and the structure of sample. For a specific structure, an atomic circle, the A–B effect is observed and the origin of the oscillation is also discussed
Tang, Yu; Cheng, Feng; Li, Decong; Deng, Shuping; Chen, Zhong; Sun, Luqi; Liu, Wenting; Shen, Lanxian; Deng, Shukang
2018-06-01
SnSe is a promising thermoelectric material with a record high dimensionless figure of merit ZT at high temperature ∼923 K. However, the ZT values for low-Temperature Pnma phase SnSe are just 0.1-0.9. Here, we use First-principle combine with Boltzmann transport theory methods to study the effect of tensile and compressible strain on the thermoelectric transport properties. The power factor of SnSe with -4% strain have a large boost along b and c directions of 7.7 and 3.9 μW cm-1 K-2, respectively, which are 2.5 and 2 times as large as those pristine SnSe. The charge density distributions reveal that the overlap of wave function has significant change due to the changed bond lengths and bond angles under different strain, which lead to the change of band gap and band dispersion. Our work provides a new effective strategy to enhance the thermoelectric properties of materials.
International Nuclear Information System (INIS)
Itakura, Mitsuhiro; Kaburaki, Hideo; Yamaguchi, Masatake; Endo, Tatsuro; Higuchi, Kenji; Ogata, Shigenobu; Kimizuka, Hajime
2012-01-01
Effect of hydrogen atoms on the mobility of a screw dislocation in BCC iron has been evaluated using the first-principles calculation. The stable position of a hydrogen atom is found to be near the screw dislocation core and inside the core respectively when the dislocation is at the easy-core or hard-core configuration in BCC iron. The intrinsically unstable hard-core configuration of the screw dislocation is stabilized when a hydrogen atom is trapped inside the core. On the basis of this first-principles result, an elastic string model of a dislocation is developed to predict the kink motion in the presence of a hydrogen atom. It is found that a double-kink formation is facilitated when a hydrogen atom is located near a dislocation line, however, a kink motion is retarded when a hydrogen atom is behind the kink. (author)
DEFF Research Database (Denmark)
Strange, Mikkel; Thygesen, Kristian Sommer
2011-01-01
-electron interactions are described by th=e many-body GW approximation. The conductance follows an exponential length dependence: Gn = Gc exp(-βn). The main difference from standard density functional theory (DFT) calculations is a significant reduction of the contact conductance, Gc, due to an improved alignment......The calculation of the electronic conductance of nanoscale junctions from first principles is a long-standing problem in the field of charge transport. Here we demonstrate excellent agreement with experiments for the transport properties of the gold/alkanediamine benchmark system when electron...
Polar phonons in β-Ga2O3 studied by IR reflectance spectroscopy and first-principle calculations
Azuhata, Takashi; Shimada, Kazuhiro
2017-08-01
IR reflectance spectra of β-Ga2O3 are measured in the range from 400 to 1100 cm-1 using the (\\bar{2}01) and (010) planes for pure transverse Au- and Bu-mode phonons, respectively. The spectra measured using the (010) plane depend remarkably on the polarization direction of the incident light because of the monoclinic symmetry. Reflectance spectra simulated using parameters obtained from first-principle calculations are in good agreement with the experimental spectra. By adjusting the calculated phonon parameters so as to reproduce the experimental spectra, the polar phonon parameters were determined for six modes above 400 cm-1.
International Nuclear Information System (INIS)
Asta, M.; Foiles, S.M.; Quong, A.A.
1998-01-01
The configurational thermodynamic properties of fcc-based Al-Sc alloys and coherent Al/Al 3 Sc interphase-boundary interfaces have been calculated from first principles. The computational approach used in this study combines the results of pseudopotential total-energy calculations with a cluster-expansion description of the alloy energetics. Bulk and interface configurational-thermodynamic properties are computed using a low-temperature-expansion technique. Calculated values of the {100} and {111} Al/Al 3 Sc interfacial energies at zero temperature are, respectively, 192 and 226mJ/m 2 . The temperature dependence of the calculated interfacial free energies is found to be very weak for {100} and more appreciable for {111} orientations; the primary effect of configurational disordering at finite temperature is to reduce the degree of crystallographic anisotropy associated with calculated interfacial free energies. The first-principles-computed solid-solubility limits for Sc in bulk fcc Al are found to be underestimated significantly in comparison with experimental measurements. It is argued that this discrepancy can be largely attributed to nonconfigurational contributions to the entropy which have been neglected in the present thermodynamic calculations. copyright 1998 The American Physical Society
Cesium under pressure: First-principles calculation of the bcc-to-fcc phase transition
Carlesi, S.; Franchini, A.; Bortolani, V.; Martinelli, S.
1999-05-01
In this paper we present the ab initio calculation of the structural properties of cesium under pressure. The calculation of the total energy is done in the local-density approximation of density-functional theory, using a nonlocal pseudopotential including the nonlinear core corrections proposed by Louie et al. The calculation of the pressure-volume diagram for both bcc and fcc structures allows us to prove that the transition from bcc to fcc structure is a first-order transition.
First principle calculation of structure and lattice dynamics of Lu2Si2O7
Directory of Open Access Journals (Sweden)
Nazipov D.V.
2017-01-01
Full Text Available Ab initio calculations of crystal structure and Raman spectra has been performed for single crystal of lutetium pyrosilicate Lu2Si2O7. The types of fundamental vibrations, their frequencies and intensities in the Raman spectrum has been obtained for two polarizations. Calculations were made in the framework of density functional theory (DFT with hybrid functionals. The isotopic substitution was calculated for all inequivalent ions in cell. The results in a good agreement with experimental data.
Inelastic Transport through Molecules: Comparing First-Principles Calculations to Experiments
DEFF Research Database (Denmark)
Paulsson, Magnus; Frederiksen, Thomas; Brandbyge, Mads
2006-01-01
We present calculations of the elastic and inelastic conductance through three different hydrocarbon molecules connected to gold electrodes. Our method is based on a combination of the nonequilibrium Green's function method with density functional theory. Vibrational effects in these molecular...
First-principles calculations of the vacancy formation energy in transition and noble metals
DEFF Research Database (Denmark)
Korzhavyi, P.A.; Abrikosov, Igor A.; Johansson, Börje
1999-01-01
approach and include electrostatic multipole corrections to the atomic sphere approximation. The results are in excellent agreement with available full-potential calculations and with the vacancy formation energies obtained in positron annihilation measurements. The variation of the vacancy formation...
DEFF Research Database (Denmark)
Vanin, Marco; Gath, Jesper; Thygesen, Kristian Sommer
2010-01-01
The stability of graphene nanoribbons in the presence of typical atmospheric molecules is systematically investigated by means of density-functional theory. We calculate the edge formation free energy of five different edge configurations passivated by H, H-2, O, O-2, N-2, CO, CO2, and H2O...
Variations in first principles calculated defect energies in GaAs and ...
Indian Academy of Sciences (India)
Keywords. Ab initio calculations; semi-insulating GaAs; point defects. ... We are focusing on gallium arsenide. .... gallium vacancy in S & L, P et al and N & Z will exist in triple ... gallium antisite defect that include relaxation, a negative. U-effect is ...
First-principles calculations of Moessbauer hyperfine parameters for solids and large molecules
Energy Technology Data Exchange (ETDEWEB)
Guenzburger, Diana [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil); Ellis, D.E. [Northwestern Univ., Evanston, IL (United States). Dept. of Physics; Zeng, Z. [Academia Sinica, Hefei, AH (China). Inst. of Solid-State Physics
1997-10-01
Electronic structure calculations based on Density Functional theory were performed for solids and large molecules. The solids were represented by clusters of 60-100 atoms embedded in the potential of the external crystal. Magnetic moments and Moessbauer hyperfine parameters were derived. (author) 22 refs., 8 figs., 1 tab.
First-principles calculations of Moessbauer hyperfine parameters for solids and large molecules
International Nuclear Information System (INIS)
Guenzburger, Diana; Ellis, D.E.; Zeng, Z.
1997-10-01
Electronic structure calculations based on Density Functional theory were performed for solids and large molecules. The solids were represented by clusters of 60-100 atoms embedded in the potential of the external crystal. Magnetic moments and Moessbauer hyperfine parameters were derived. (author)
Yang, Xiao-Yong; Lu, Yong; Zheng, Fa-Wei; Zhang, Ping
2015-11-01
Mechanical, electronic, and thermodynamic properties of zirconium carbide have been systematically studied using the ab initio calculations. The calculated equilibrium lattice parameter, bulk modulus, and elastic constants are all well consistent with the experimental data. The electronic band structure indicates that the mixture of C 2p and Zr 4d and 4p orbitals around the Fermi level makes a large covalent contribution to the chemical bonds between the C and Zr atoms. The Bader charge analysis suggests that there are about 1.71 electrons transferred from each Zr atom to its nearest C atom. Therefore, the Zr-C bond displays a mixed ionic/covalent character. The calculated phonon dispersions of ZrC are stable, coinciding with the experimental measurement. A drastic expansion in the volume of ZrC is seen with increasing temperature, while the bulk modulus decreases linearly. Based on the calculated phonon dispersion curves and within the quasi-harmonic approximation, the temperature dependence of the heat capacities is obtained, which gives a good description compared with the available experimental data. Project supported by the National Natural Science Foundation of China (Grant No. 51071032).
DEFF Research Database (Denmark)
Greeley, Jeffrey Philip; Nørskov, Jens Kehlet
2007-01-01
A simple procedure is introduced to use periodic Density Functional Theory calculations to estimate trends in the thermodynamics of surface alloy dissolution in acidic media. With this approach, the dissolution potentials for solute metal atoms embedded in the surface layer of various host metals...
First-principle calculation of SP 3 hybridization and bonding in ...
African Journals Online (AJOL)
electrons in the diamond-structure semiconductor crystals has been calculated for the k = 0 state. This charge density represents the electronic distribution in the direct lattice of the crystals. Normally, the charge density in a condensed matter such as crystals is obtained from extremely complicated functions. However, in this ...
Gd impurities effect on Co2CrSi alloy: first-principle calculations
Indian Academy of Sciences (India)
2018-02-02
Feb 2, 2018 ... the minority-spin gap is filled and half-metallicity is lost when Gd substitutes Co atoms. Keywords. ... compound NiMnSb in 1983 [1], intensive research on half- metallic materials has .... Our E value is close to that calculated for ...
Explanation of ferromagnetism origin in C-doped ZnO by first principle calculations
International Nuclear Information System (INIS)
El Amiri, A.; Lassri, H.; Hlil, E.K.; Abid, M.
2015-01-01
By ab-initio calculations, we systematically study possible source of ferromagnetism C-doped ZnO compound. The electronic structure and magnetic properties of C-doped ZnO with / without ZnO host and C defects were investigated using the Korringa–Kohn–Rostoker (KKR) method combined with coherent potential approximation (CPA). We show that Zn vacancy and presence of C defects (substitutional, interstitial or combination of both) induce the ferromagnetism in C-doped ZnO. From density of state (DOS) analysis, we show that p–p interaction between C atoms and/or C and O atoms is the mechanism of ferromagnetic coupling in C-doped ZnO. - Highlights: • We study the effect of ZnO host and C defects on ferromagnetism in C-doped ZnO. • Details of KKR method calculations performed to investigate both magnetic and electronic structures. • Magnetic moments, total and partial DOS for C-doped ZnO are well calculated and discussed. • Based on DOS calculations we interpret a origin of ferromagnetism in C-doped ZnO. • Mechanism of ferromagnetic coupling is well proposed
Explanation of ferromagnetism origin in C-doped ZnO by first principle calculations
Energy Technology Data Exchange (ETDEWEB)
El Amiri, A., E-mail: aelamiri@casablanca.ma [Laboratoire de Physique Fondamentale et Appliquée (LPFA), Faculté des Sciences Ain Chock, Université Hassan II, B.P. 5366 Mâarif, Casablanca, Maroc (Morocco); Lassri, H. [Laboratoire de Physique des Matériaux, Micro-électronique, Automatique et Thermique (LPMMAT). Faculté des Sciences Ain Chock, Université Hassan II, B.P. 5366 Mâarif, Casablanca, Maroc (Morocco); Hlil, E.K. [Institut Néel, CNRS et Université Joseph Fourier, BP 166, 38042 Grenoble (France); Abid, M. [Laboratoire de Physique Fondamentale et Appliquée (LPFA), Faculté des Sciences Ain Chock, Université Hassan II, B.P. 5366 Mâarif, Casablanca, Maroc (Morocco)
2015-01-15
By ab-initio calculations, we systematically study possible source of ferromagnetism C-doped ZnO compound. The electronic structure and magnetic properties of C-doped ZnO with / without ZnO host and C defects were investigated using the Korringa–Kohn–Rostoker (KKR) method combined with coherent potential approximation (CPA). We show that Zn vacancy and presence of C defects (substitutional, interstitial or combination of both) induce the ferromagnetism in C-doped ZnO. From density of state (DOS) analysis, we show that p–p interaction between C atoms and/or C and O atoms is the mechanism of ferromagnetic coupling in C-doped ZnO. - Highlights: • We study the effect of ZnO host and C defects on ferromagnetism in C-doped ZnO. • Details of KKR method calculations performed to investigate both magnetic and electronic structures. • Magnetic moments, total and partial DOS for C-doped ZnO are well calculated and discussed. • Based on DOS calculations we interpret a origin of ferromagnetism in C-doped ZnO. • Mechanism of ferromagnetic coupling is well proposed.
The phase diagram of solid hydrogen at high pressure: A challenge for first principles calculations
Azadi, Sam; Foulkes, Matthew
2015-03-01
We present comprehensive results for the high-pressure phase diagram of solid hydrogen. We focus on the energetically most favorable molecular and atomic crystal structures. To obtain the ground-state static enthalpy and phase diagram, we use semi-local and hybrid density functional theory (DFT) as well as diffusion quantum Monte Carlo (DMC) methods. The closure of the band gap with increasing pressure is investigated utilizing quasi-particle many-body calculations within the GW approximation. The dynamical phase diagram is calculated by adding proton zero-point energies (ZPE) to static enthalpies. Density functional perturbation theory is employed to calculate the proton ZPE and the infra-red and Raman spectra. Our results clearly demonstrate the failure of DFT-based methods to provide an accurate static phase diagram, especially when comparing insulating and metallic phases. Our dynamical phase diagram obtained using fully many-body DMC calculations shows that the molecular-to-atomic phase transition happens at the experimentally accessible pressure of 374 GPa. We claim that going beyond mean-field schemes to obtain derivatives of the total energy and optimize crystal structures at the many-body level is crucial. This work was supported by the UK engineering and physics science research council under Grant EP/I030190/1, and made use of computing facilities provided by HECTOR, and by the Imperial College London high performance computing centre.
First principles electron-correlated calculations of optical absorption in magnesium clusters★
Shinde, Ravindra; Shukla, Alok
2017-11-01
In this paper, we report large-scale configuration interaction (CI) calculations of linear optical absorption spectra of various isomers of magnesium clusters Mgn (n = 2-5), corresponding to valence transitions. Geometry optimization of several low-lying isomers of each cluster was carried out using coupled-cluster singles doubles (CCSD) approach, and these geometries were subsequently employed to perform ground and excited state calculations using either the full-CI (FCI) or the multi-reference singles-doubles configuration interaction (MRSDCI) approach, within the frozen-core approximation. Our calculated photoabsorption spectrum of magnesium dimer (Mg2) is in excellent agreement with the experiments both for peak positions, and intensities. Owing to the sufficiently inclusive electron-correlation effects, these results can serve as benchmarks against which future experiments, as well as calculations performed using other theoretical approaches, can be tested. Supplementary material in the form of one pdf fille available from the Journal web page at http://https://doi.org/10.1140/epjd/e2017-80356-6.
International Nuclear Information System (INIS)
Kubobuchi, Kei; Imai, Hideto
2015-01-01
Redox reaction behaviors of a lithium ion secondary battery were investigated by K-edge in-situ XANES and L-edge XANES measurements combined with ab initio XANES simulation. During the charge process, the shape of K-edge XANES spectra was found to change, suggesting contribution of Mn 3d electron to charge and discharge. The detailed analysis based on first-principles electronic structure calculation and ab initio XANES simulation, however, indicated that valence change of Mn is little and rather O largely contribute to the reaction. (author)
Directory of Open Access Journals (Sweden)
Ruikuan Xie
2017-11-01
Full Text Available First-principle calculations of the electronic structure and magnetic interaction of C-Gd co-doped GaN nanowires have been performed. The room-temperature ferromagnetism in GaN:Gd nanowires is observed after the substitution of N atoms by C atoms. A p-d coupling is considered as the reason of the observed ferromagnetism. The striking feature is that such coupling is effected greatly by the position where the C atoms dope in. As the C-Gd distance increases this coupling decreases and the system won’t gain enough energy to stabilize the ferromagnetism.
Wang, Wei; Sun, Jiafa; Li, Bin; He, Junqi
2017-09-01
First-principles pseudopotential calculations on phonon and electronic properties of β -pyrochlore superconductor KOs2O6 are performed. The imaginary soft-phonon modes with a special double-well potential for the lowest Eu(1) mode and the second lowest T1u(1) mode are reported, which indicates the dynamical instability in KOs2O6. However, the double wells are too small to induce a structural phase transformation in KOs2O6. The strong anharmonicity especially for K T2g(1) phonon mode is got, which is approved to be from the strong electron-phonon coupling that supports the superconductivity in KOs2O6.
Directory of Open Access Journals (Sweden)
Fuda Guo
2016-01-01
Full Text Available The phase stability, mechanical, electronic, and thermodynamic properties of In-Zr compounds have been explored using the first-principles calculation based on density functional theory (DFT. The calculated formation enthalpies show that these compounds are all thermodynamically stable. Information on electronic structure indicates that they possess metallic characteristics and there is a common hybridization between In-p and Zr-d states near the Fermi level. Elastic properties have been taken into consideration. The calculated results on the ratio of the bulk to shear modulus (B/G validate that InZr3 has the strongest deformation resistance. The increase of indium content results in the breakout of a linear decrease of the bulk modulus and Young’s modulus. The calculated theoretical hardness of α-In3Zr is higher than the other In-Zr compounds.
First-principle calculations on the structural and electronic properties of hard C{sub 11}N{sub 4}
Energy Technology Data Exchange (ETDEWEB)
Li, Dongxu, E-mail: lidongxu@hqu.edu.cn [College of Materials Science and Engineering, Huaqiao University, Xiamen 361021 (China); Shi, Jiancheng; Lai, Mengling; Li, Rongkai [College of Materials Science and Engineering, Huaqiao University, Xiamen 361021 (China); Yu, Dongli [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China)
2014-09-15
A graphite-like C{sub 11}N{sub 4} model was built by stacking graphene and a C{sub 3}N{sub 4} triazine layer and simulated by first principle calculations, which transfers to a diamond-like structure under high pressure. The structural, mechanical, and electronic properties of both materials were calculated. The elastic constants of both materials satisfy the Born-criterion. Furthermore, no imaginary frequencies were observed in phonon calculations. The diamond-like C{sub 11}N{sub 4} is semiconducting and consists of polyhedral and hollow C–N cages. The Vickers hardness of diamond-like C{sub 11}N{sub 4} was calculated to be 58 GPa. The phase transformation from graphite-like to diamond-like C{sub 11}N{sub 4} is proposed to occur at approximately 27.2 GPa based on the pressure-dependent enthalpy.
First-principles calculations on double-walled inorganic nanotubes with hexagonal chiralities
International Nuclear Information System (INIS)
Zhukovskii, Yuri F; Evarestov, Robert A; Bandura, Andrei V; Losev, Maxim V
2011-01-01
The two sets of commensurate double-walled boron nitride and titania hexagonally-structured nanotubes (DW BN and TiO 2 NTs) possessing either armchair- or zigzag-type chiralities have been considered, i.e., (n 1 ,n 1 )-(n 2 ,n 2 ) or (n 1 ,0)-(n 2 ,0), respectively. For symmetry analysis of these nanotubes, the line symmetry groups for one-periodic (1D) nanostructures with rotohelical symmetry have been applied. To analyze the structural and electronic properties of hexagonal DW NTs, a series of large-scale ab initio DFT-LCAO calculations have been performed using the hybrid Hartree-Fock/Kohn-Sham exchange-correlation functional PBE0 (as implemented in CRYSTAL-09 code). To establish the optimal inter-shell distances within DW NTs corresponding to the minima of calculated total energy, the chiral indices n 1 and n 2 of the constituent single-walled (SW) nanotubes have been successively varied.
Schottky barrier at graphene/metal oxide interfaces: insight from first-principles calculations
Cheng, Kai; Han, Nannan; Su, Yan; Zhang, Junfeng; Zhao, Jijun
2017-02-01
Anode materials play an important role in determining the performance of lithium ion batteries. In experiment, graphene (GR)/metal oxide (MO) composites possess excellent electrochemical properties and are promising anode materials. Here we perform density functional theory calculations to explore the interfacial interaction between GR and MO. Our result reveals generally weak physical interactions between GR and several MOs (including Cu2O, NiO). The Schottky barrier height (SBH) in these metal/semiconductor heterostructures are computed using the macroscopically averaged electrostatic potential method, and the role of interfacial dipole is discussed. The calculated SBHs below 1 eV suggest low contact resistance; thus these GR/MO composites are favorable anode materials for better lithium ion batteries.
Schottky barrier at graphene/metal oxide interfaces: insight from first-principles calculations.
Cheng, Kai; Han, Nannan; Su, Yan; Zhang, Junfeng; Zhao, Jijun
2017-02-06
Anode materials play an important role in determining the performance of lithium ion batteries. In experiment, graphene (GR)/metal oxide (MO) composites possess excellent electrochemical properties and are promising anode materials. Here we perform density functional theory calculations to explore the interfacial interaction between GR and MO. Our result reveals generally weak physical interactions between GR and several MOs (including Cu2O, NiO). The Schottky barrier height (SBH) in these metal/semiconductor heterostructures are computed using the macroscopically averaged electrostatic potential method, and the role of interfacial dipole is discussed. The calculated SBHs below 1 eV suggest low contact resistance; thus these GR/MO composites are favorable anode materials for better lithium ion batteries.
First principles calculations using density matrix divide-and-conquer within the SIESTA methodology
International Nuclear Information System (INIS)
Cankurtaran, B O; Gale, J D; Ford, M J
2008-01-01
The density matrix divide-and-conquer technique for the solution of Kohn-Sham density functional theory has been implemented within the framework of the SIESTA methodology. Implementation details are provided where the focus is on the scaling of the computation time and memory use, in both serial and parallel versions. We demonstrate the linear-scaling capabilities of the technique by providing ground state calculations of moderately large insulating, semiconducting and (near-) metallic systems. This linear-scaling technique has made it feasible to calculate the ground state properties of quantum systems consisting of tens of thousands of atoms with relatively modest computing resources. A comparison with the existing order-N functional minimization (Kim-Mauri-Galli) method is made between the insulating and semiconducting systems
Issues in first-principles calculations for defects in semiconductors and oxides
International Nuclear Information System (INIS)
Nieminen, Risto M
2009-01-01
Recent advances in density-functional theory (DFT) calculations of defect electronic properties in semiconductors and insulators are discussed. In particular, two issues are addressed: the band-gap underestimation of standard density-functional methods with its harmful consequences for the positioning of defect-related levels in the band-gap region, and the slow convergence of calculated defect properties when the periodic supercell approach is used. Systematic remedies for both of these deficiencies are now available, and are being implemented in the context of popular DFT codes. This should help in improving the parameter-free accuracy and thus the predictive power of the methods to enable unambiguous explanation of defect-related experimental observations. These include not only the various fingerprint spectroscopies for defects but also their thermochemistry and dynamics, i.e. the temperature-dependent concentration and diffusivities of defects under various doping conditions and in different stoichiometries
Czech Academy of Sciences Publication Activity Database
Vackář, Jiří; Šipr, Ondřej; Šimůnek, Antonín
2008-01-01
Roč. 77, č. 4 (2008), 045112/1-045112/6 ISSN 1098-0121 R&D Projects: GA AV ČR IAA100100514; GA AV ČR(CZ) IAA100100637 Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z10100521 Keywords : core levels * ab-initio calculations * electronic states * ground state properties Subject RIV: BE - Theoretical Physics Impact factor: 3.322, year: 2008
First-principles calculated decomposition pathways for LiBH4 nanoclusters
Huang, Zhi-Quan; Chen, Wei-Chih; Chuang, Feng-Chuan; Majzoub, Eric H.; Ozoliņš, Vidvuds
2016-05-01
We analyze thermodynamic stability and decomposition pathways of LiBH4 nanoclusters using grand-canonical free-energy minimization based on total energies and vibrational frequencies obtained from density-functional theory (DFT) calculations. We consider (LiBH4)n nanoclusters with n = 2 to 12 as reactants, while the possible products include (Li)n, (B)n, (LiB)n, (LiH)n, and Li2BnHn; off-stoichiometric LinBnHm (m ≤ 4n) clusters were considered for n = 2, 3, and 6. Cluster ground-state configurations have been predicted using prototype electrostatic ground-state (PEGS) and genetic algorithm (GA) based structural optimizations. Free-energy calculations show hydrogen release pathways markedly differ from those in bulk LiBH4. While experiments have found that the bulk material decomposes into LiH and B, with Li2B12H12 as a kinetically inhibited intermediate phase, (LiBH4)n nanoclusters with n ≤ 12 are predicted to decompose into mixed LinBn clusters via a series of intermediate clusters of LinBnHm (m ≤ 4n). The calculated pressure-composition isotherms and temperature-pressure isobars exhibit sloping plateaus due to finite size effects on reaction thermodynamics. Generally, decomposition temperatures of free-standing clusters are found to increase with decreasing cluster size due to thermodynamic destabilization of reaction products.
International Nuclear Information System (INIS)
Akdim, Brahim; Pachter, Ruth; Naik, Rajesh R.
2015-01-01
In this letter, we report on the evaluation of diphenylalanine (FF), dityrosine (YY), and phenylalanine-tryptophan (FW) self-assembled peptide nanotube structures for electronics and photonics applications. Realistic bulk peptide nanotube material models were used in density functional theory calculations to mimic the well-ordered tubular nanostructures. Importantly, validated functionals were applied, specifically by using a London dispersion correction to model intertube interactions and a range-separated hybrid functional for accurate bandgap calculations. Bandgaps were found consistent with available experimental data for FF, and also corroborate the higher conductance reported for FW in comparison to FF peptide nanotubes. Interestingly, the predicted bandgap for the YY tubular nanostructure was found to be slightly higher than that of FW, suggesting higher conductance as well. In addition, the band structure calculations along the high symmetry line of nanotube axis revealed a direct bandgap for FF. The results enhance our understanding of the electronic properties of these material systems and will pave the way into their application in devices
Takahashi, Masae; Ishikawa, Yoichi; Ito, Hiromasa
2013-03-01
A weak hydrogen bond (WHB) such as CH-O is very important for the structure, function, and dynamics in a chemical and biological system WHB stretching vibration is in a terahertz (THz) frequency region Very recently, the reasonable performance of dispersion-corrected first-principles to WHB has been proven. In this lecture, we report dispersion-corrected first-principles calculation of the vibrational absorption of some organic crystals, and low-temperature THz spectral measurement, in order to clarify WHB stretching vibration. The THz frequency calculation of a WHB crystal has extremely improved by dispersion correction. Moreover, the discrepancy in frequency between an experiment and calculation and is 10 1/cm or less. Dispersion correction is especially effective for intermolecular mode. The very sharp peak appearing at 4 K is assigned to the intermolecular translational mode that corresponds to WHB stretching vibration. It is difficult to detect and control the WHB formation in a crystal because the binding energy is very small. With the help of the latest intense development of experimental and theoretical technique and its careful use, we reveal solid-state WHB stretching vibration as evidence for the WHB formation that differs in respective WHB networks The research was supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan (Grant No. 22550003).
Mehmood, Faisal; Pachter, Ruth; Murphy, Neil R.; Johnson, Walter E.
2015-11-01
Prediction of the frequency-dependent dielectric function of thin films poses computational challenges, and at the same time experimental characterization by spectroscopic ellipsometry remains difficult to interpret because of changes in stoichiometry and surface morphology, temperature, thickness of the film, or substrate. In this work, we report calculations for titanium nitride (TiN), a promising material for plasmonic applications because of less loss and other practical advantages compared to noble metals. We investigated structural, electronic, and optical properties of stoichiometric bulk TiN, as well as of the TiN(100), TiN(110), and TiN(111) outermost surfaces. Density functional theory (DFT) and many-body GW methods (Green's (G) function-based approximation with screened Coulomb interaction (W)) were used, ranging from G0W0, GW0 to partially self-consistent sc-GW0, as well as the GW-BSE (Bethe-Salpeter equation) and time-dependent DFT (TDDFT) methods for prediction of the optical properties. Structural parameters and the band structure for bulk TiN were shown to be consistent with previous work. Calculated dielectric functions, plasma frequencies, reflectivity, and the electron energy loss spectrum demonstrated consistency with experiment at the GW0-BSE level. Deviations from experimental data are expected due to varying experimental conditions. Comparison of our results to spectroscopic ellipsometry data for realistic nanostructures has shown that although TDDFT may provide a computationally feasible level of theory in evaluation of the dielectric function, application is subject to validation with GW-BSE calculations.
International Nuclear Information System (INIS)
Mehmood, Faisal; Pachter, Ruth; Murphy, Neil R.; Johnson, Walter E.
2015-01-01
Prediction of the frequency-dependent dielectric function of thin films poses computational challenges, and at the same time experimental characterization by spectroscopic ellipsometry remains difficult to interpret because of changes in stoichiometry and surface morphology, temperature, thickness of the film, or substrate. In this work, we report calculations for titanium nitride (TiN), a promising material for plasmonic applications because of less loss and other practical advantages compared to noble metals. We investigated structural, electronic, and optical properties of stoichiometric bulk TiN, as well as of the TiN(100), TiN(110), and TiN(111) outermost surfaces. Density functional theory (DFT) and many-body GW methods (Green's (G) function-based approximation with screened Coulomb interaction (W)) were used, ranging from G 0 W 0 , GW 0 to partially self-consistent sc-GW 0 , as well as the GW-BSE (Bethe-Salpeter equation) and time-dependent DFT (TDDFT) methods for prediction of the optical properties. Structural parameters and the band structure for bulk TiN were shown to be consistent with previous work. Calculated dielectric functions, plasma frequencies, reflectivity, and the electron energy loss spectrum demonstrated consistency with experiment at the GW 0 -BSE level. Deviations from experimental data are expected due to varying experimental conditions. Comparison of our results to spectroscopic ellipsometry data for realistic nanostructures has shown that although TDDFT may provide a computationally feasible level of theory in evaluation of the dielectric function, application is subject to validation with GW-BSE calculations
X-Ray Absorption Spectra of Water from First Principles Calculations
International Nuclear Information System (INIS)
Prendergast, David; Galli, Giulia
2006-01-01
We present a series of ab initio calculations of the x-ray absorption cross section (XAS) of ice and liquid water at ambient conditions. Our results show that all available experimental data and theoretical results are consistent with the standard model of the liquid as comprising molecules with approximately four hydrogen bonds. Our simulations of ice XAS including the lowest lying excitonic state are in excellent agreement with experiment and those of a quasitetrahedral model of water are in reasonable agreement with recent measurements. Hence we propose that the standard, quasitetrahedral model of water, although approximate, represents a reasonably accurate description of the local structure of the liquid
First-principles calculations for elastic properties of OsB{sub 2} under pressure
Energy Technology Data Exchange (ETDEWEB)
Yang Junwei [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); Chen Xiangrong, E-mail: x.r.chen@tom.co [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016 (China); Luo Fen [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); Ji Guangfu [Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, Chinese Academy of Engineering Physics, Mianyang 621900 (China)
2009-11-01
The structure, elastic properties and elastic anisotropy of orthorhombic OsB{sub 2} are investigated by density functional theory method with the ultrasoft pseudopotential scheme in the frame of the generalized gradient approximation (GGA) as well as local density approximation (LDA). The obtained structural parameters, elastic constants, elastic anisotropy and Debye temperature for OsB{sub 2} under pressure are consistent with the available experimental data and other theoretical results. It is found that the elastic constants, bulk modulus and Debye temperature of OsB{sub 2} tend to increase with increasing pressure. It is predicted that OsB{sub 2} is not a superhard material from our calculations.
First-principles calculations for elastic properties of OsB2 under pressure
International Nuclear Information System (INIS)
Yang Junwei; Chen Xiangrong; Luo Fen; Ji Guangfu
2009-01-01
The structure, elastic properties and elastic anisotropy of orthorhombic OsB 2 are investigated by density functional theory method with the ultrasoft pseudopotential scheme in the frame of the generalized gradient approximation (GGA) as well as local density approximation (LDA). The obtained structural parameters, elastic constants, elastic anisotropy and Debye temperature for OsB 2 under pressure are consistent with the available experimental data and other theoretical results. It is found that the elastic constants, bulk modulus and Debye temperature of OsB 2 tend to increase with increasing pressure. It is predicted that OsB 2 is not a superhard material from our calculations.
First-principles calculations for elastic properties of OsB 2 under pressure
Yang, Jun-Wei; Chen, Xiang-Rong; Luo, Fen; Ji, Guang-Fu
2009-11-01
The structure, elastic properties and elastic anisotropy of orthorhombic OsB 2 are investigated by density functional theory method with the ultrasoft pseudopotential scheme in the frame of the generalized gradient approximation (GGA) as well as local density approximation (LDA). The obtained structural parameters, elastic constants, elastic anisotropy and Debye temperature for OsB 2 under pressure are consistent with the available experimental data and other theoretical results. It is found that the elastic constants, bulk modulus and Debye temperature of OsB 2 tend to increase with increasing pressure. It is predicted that OsB 2 is not a superhard material from our calculations.
First-principles calculations on double-walled inorganic nanotubes with hexagonal chiralities
Energy Technology Data Exchange (ETDEWEB)
Zhukovskii, Yuri F [Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., LV-1063, Riga (Latvia); Evarestov, Robert A; Bandura, Andrei V; Losev, Maxim V, E-mail: quantzh@latnet.lv [Department of Quantum Chemistry, St. Petersburg State University, 26 Universitetsky Ave., 198504, Petrodvorets (Russian Federation)
2011-06-23
The two sets of commensurate double-walled boron nitride and titania hexagonally-structured nanotubes (DW BN and TiO{sub 2} NTs) possessing either armchair- or zigzag-type chiralities have been considered, i.e., (n{sub 1},n{sub 1})-(n{sub 2},n{sub 2}) or (n{sub 1},0)-(n{sub 2},0), respectively. For symmetry analysis of these nanotubes, the line symmetry groups for one-periodic (1D) nanostructures with rotohelical symmetry have been applied. To analyze the structural and electronic properties of hexagonal DW NTs, a series of large-scale ab initio DFT-LCAO calculations have been performed using the hybrid Hartree-Fock/Kohn-Sham exchange-correlation functional PBE0 (as implemented in CRYSTAL-09 code). To establish the optimal inter-shell distances within DW NTs corresponding to the minima of calculated total energy, the chiral indices n{sub 1} and n{sub 2} of the constituent single-walled (SW) nanotubes have been successively varied.
Energy Technology Data Exchange (ETDEWEB)
Errico, L.A.; Fabricius, G.; Renteria, M. [Departamento de Fisica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata (Argentina)
2004-08-01
We report an ab-initio comparative study of the electric-field-gradient tensor (EFG) and structural relaxations introduced by acceptor (Cd) and donor (Ta) impurities when they replace cations in a series of binary oxides: TiO{sub 2}, SnO{sub 2}, and In{sub 2}O{sub 3}. Calculations were performed with the Full-Potential Linearized-Augmented Plane Waves method that allows us to treat the electronic structure and the atomic relaxations in a fully self-consistent way. We considered different charge states for each impurity and studied the dependence on these charge states of the electronic properties and the structural relaxations. Our results are compared with available data coming from PAC experiments and previous calculations, allowing us to obtain a new insight on the role that metal impurities play in oxide semiconductors. It is clear from our results that simple models can not describe the measured EFGs at impurities in oxides even approximately. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
First-principles calculation of electronic transport in low-dimensional disordered superconductors
Conduit, G. J.; Meir, Y.
2011-08-01
We present a novel formulation to calculate transport through disordered superconductors connected between two metallic leads. An exact analytical expression for the current is derived and applied to a superconducting sample described by the negative-U Hubbard model. A Monte Carlo algorithm that includes thermal phase and amplitude fluctuations of the superconducting order parameter is employed, and a new efficient algorithm is described. This improved routine allows access to relatively large systems, which we demonstrate by applying it to several cases, including superconductor-normal interfaces and Josephson junctions. Moreover, we can link the phenomenological parameters describing these effects to the underlying microscopic variables. The effects of decoherence and dephasing are shown to be included in the formulation, which allows the unambiguous characterization of the Kosterlitz-Thouless transition in two-dimensional systems and the calculation of the finite resistance due to vortex excitations in quasi-one-dimensional systems. Effects of magnetic fields can be easily included in the formalism, and are demonstrated for the Little-Parks effect in superconducting cylinders. Furthermore, the formalism enables us to map the local super and normal currents, and the accompanying electrical potentials, which we use to pinpoint and visualize the emergence of resistance across the superconductor-insulator transition.
International Nuclear Information System (INIS)
Hao Xianfeng; Wu Zhijian; Xu Yuanhui; Zhou Defeng; Liu Xiaojuan; Meng Jian
2007-01-01
We investigate the cohesive energy, heat of formation, elastic constant and electronic band structure of transition metal diborides TMB 2 (TM = Hf, Ta, W, Re, Os and Ir, Pt) in the Pmmn space group using the ab initio pseudopotential total energy method. Our calculations indicate that there is a relationship between elastic constant and valence electron concentration (VEC): the bulk modulus and shear modulus achieve their maximum when the VEC is in the range of 6.8-7.2. In addition, trends in the elastic constant are well explained in terms of electronic band structure analysis, e.g., occupation of valence electrons in states near the Fermi level, which determines the cohesive energy and elastic properties. The maximum in bulk modulus and shear modulus is attributed to the nearly complete filling of TM d-B p bonding states without filling the antibonding states. On the basis of the observed relationship, we predict that alloying W and Re in the orthorhombic structure OsB 2 might be harder than alloying the Ir element. Indeed, the further calculations confirmed this expectation
Energy Technology Data Exchange (ETDEWEB)
Hao Xianfeng [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Wu Zhijian [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Xu Yuanhui [School of Biological Engineering, Changchun University of Technology, Changchun 130012 (China); Zhou Defeng [School of Biological Engineering, Changchun University of Technology, Changchun 130012 (China); Liu Xiaojuan [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Meng Jian [Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China)
2007-05-16
We investigate the cohesive energy, heat of formation, elastic constant and electronic band structure of transition metal diborides TMB{sub 2} (TM = Hf, Ta, W, Re, Os and Ir, Pt) in the Pmmn space group using the ab initio pseudopotential total energy method. Our calculations indicate that there is a relationship between elastic constant and valence electron concentration (VEC): the bulk modulus and shear modulus achieve their maximum when the VEC is in the range of 6.8-7.2. In addition, trends in the elastic constant are well explained in terms of electronic band structure analysis, e.g., occupation of valence electrons in states near the Fermi level, which determines the cohesive energy and elastic properties. The maximum in bulk modulus and shear modulus is attributed to the nearly complete filling of TM d-B p bonding states without filling the antibonding states. On the basis of the observed relationship, we predict that alloying W and Re in the orthorhombic structure OsB{sub 2} might be harder than alloying the Ir element. Indeed, the further calculations confirmed this expectation.
First principles calculations for liquids and solids using maximally localized Wannier functions
Swartz, Charles W., VI
The field of condensed matter computational physics has seen an explosion of applicability over the last 50+ years. Since the very first calculations with ENIAC and MANIAC the field has continued to pushed the boundaries of what is possible; from the first large-scale molecular dynamics simulation, to the implementation of Density Functional Theory and large scale Car-Parrinello molecular dynamics, to million-core turbulence calculations by Standford. These milestones represent not only technological advances but theoretical breakthroughs and algorithmic improvements as well. The work in this thesis was completed in the hopes of furthering such advancement, even by a small fraction. Here we will focus mainly on the calculation of electronic and structural properties of solids and liquids, where we shall implement a wide range of novel approaches that are both computational efficient and physically enlightening. To this end we routinely will work with maximally localized Wannier functions (MLWFs) which have recently seen a revival in mainstream scientific literature. MLWFs present us with interesting opportunity to calculate a localized orbital within the planewave formalism of atomistic simulations. Such a localization will prove to be invaluable in the construction of layer-based superlattice models, linear scaling hybrid functional schemes and model quasiparticle calculations. In the first application of MLWF we will look at modeling functional piezoelectricity in superlattices. Based on the locality principle of insulating superlattices, we apply the method of Wu et al to the piezoelectric strains of individual layers under iifixed displacement field. For a superlattice of arbitrary stacking sequence an accurate model is acquired for predicting piezoelectricity. By applying the model in the superlattices where ferroelectric and antiferrodistortive modes are in competition, functional piezoelectricity can be achieved. A strong nonlinear effect is observed and can
Chandran, Mahesh; Lee, S. C.; Shim, Jae-Hyeok
2018-02-01
A disordered configuration of atoms in a multicomponent solid solution presents a computational challenge for first-principles calculations using density functional theory (DFT). The challenge is in identifying the few probable (low energy) configurations from a large configurational space before DFT calculation can be performed. The search for these probable configurations is possible if the configurational energy E({\\boldsymbol{σ }}) can be calculated accurately and rapidly (with a negligibly small computational cost). In this paper, we demonstrate such a possibility by constructing a machine learning (ML) model for E({\\boldsymbol{σ }}) trained with DFT-calculated energies. The feature vector for the ML model is formed by concatenating histograms of pair and triplet (only equilateral triangle) correlation functions, {g}(2)(r) and {g}(3)(r,r,r), respectively. These functions are a quantitative ‘fingerprint’ of the spatial arrangement of atoms, familiar in the field of amorphous materials and liquids. The ML model is used to generate an accurate distribution P(E({\\boldsymbol{σ }})) by rapidly spanning a large number of configurations. The P(E) contains full configurational information of the solid solution and can be selectively sampled to choose a few configurations for targeted DFT calculations. This new framework is employed to estimate (100) interface energy ({σ }{{IE}}) between γ and γ \\prime at 700 °C in Alloy 617, a Ni-based superalloy, with composition reduced to five components. The estimated {σ }{{IE}} ≈ 25.95 mJ m-2 is in good agreement with the value inferred by the precipitation model fit to experimental data. The proposed new ML-based ab initio framework can be applied to calculate the parameters and properties of alloys with any number of components, thus widening the reach of first-principles calculation to realistic compositions of industrially relevant materials and alloys.
Ford, Denise Christine
Insights to the fundamental processes that occur during the manufacturing of niobium superconducting radio-frequency (SRF) cavities are provided via analyses of density functional theory calculations and Raman, infrared, and nuclear magnetic resonance (NMR) spectra. I show that during electropolishing fluorine is bound and released by the reaction of the acid components in the solution: HF + H2SO4 HFSO3 + H2O. This result implies that new recipes can possibly be developed on the principle of controlled release of fluorine by a chemical reaction. I also show that NMR or Raman spectroscopy can be used to monitor the free fluorine when polishing with the standard electropolishing recipe. Density functional theory was applied to calculate the properties of common processing impurities---hydrogen, oxygen, nitrogen, and carbon---in the niobium. These impurities lower the superconducting transition temperature of niobium, and hydride precipitates are at best weakly superconducting. I modeled several of the niobium hydride phases relevant to SRF cavities, and explain the phase changes in the niobium hydrogen system based on the charge transfer between niobium and hydrogen and the strain field inside of the niobium. I also present evidence for a niobium lattice vacancy serving as a nucleation center for hydride phase formation. In considering the other chemical impurities in niobium, I show that the absorption of oxygen into a niobium lattice vacancy is preferred over the absorption of hydrogen, which indicates that oxygen can block these phase nucleation centers. I also show that dissolved oxygen atoms can trap dissolved hydrogen atoms to prevent niobium hydride phase formation. Nitrogen and carbon were studied in less depth, but behaved similarly to oxygen. Based on these results and a literature survey, I propose a mechanism for the success of the low-temperature anneal applied to niobium SRF cavities. Finally, I present the beginning of a model to describe magnetic
Energy Technology Data Exchange (ETDEWEB)
Ford, Denise Christine [Northwestern Univ., Evanston, IL (United States)
2013-03-01
Insights to the fundamental processes that occur during the manufacturing of niobium superconducting radio-frequency (SRF) cavities are provided via analyses of density functional theory calculations and Raman, infrared, and nuclear magnetic resonance (NMR) spectra. I show that during electropolishing fluorine is bound and released by the reaction of the acid components in the solution: HF + H_{2}SO_{4} <-> HFSO_{3} + H_{2}O. This result implies that new recipes can possibly be developed on the principle of controlled release of fluorine by a chemical reaction. I also show that NMR or Raman spectroscopy can be used to monitor the free fluorine when polishing with the standard electropolishing recipe. Density functional theory was applied to calculate the properties of common processing impurities – hydrogen, oxygen, nitrogen, and carbon – in the niobium. These impurities lower the superconducting transition temperature of niobium, and hydride precipitates are at best weakly superconducting. I modeled several of the niobium hydride phases relevant to SRF cavities, and explain the phase changes in the niobium hydrogen system based on the charge transfer between niobium and hydrogen and the strain field inside of the niobium. I also present evidence for a niobium lattice vacancy serving as a nucleation center for hydride phase formation. In considering the other chemical impurities in niobium, I show that the absorption of oxygen into a niobium lattice vacancy is preferred over the absorption of hydrogen, which indicates that oxygen can block these phase nucleation centers. I also show that dissolved oxygen atoms can trap dissolved hydrogen atoms to prevent niobium hydride phase formation. Nitrogen and carbon were studied in less depth, but behaved similarly to oxygen. Based on these results and a literature survey, I propose a mechanism for the success of the low-temperature anneal applied to niobium SRF cavities. Finally, I
Investigating the adsorption of H2O on ZnO nanoclusters by first principle calculations
Al-Sunaidi, Abdullah A.
2011-04-01
The interaction of a single H2O molecule on selected ZnO nanoclusters is investigated by carrying out calculations based on the density-functional theory at the hybrid-GGA (B97-2) level. These clusters have ring, drum, tube and bubble shapes and their physical properties like the binding energy and the band gap energy depend strongly on the shape and size of the cluster. Depending on the stability of the cluster, H2O show both chemisorption and dissociation on the surfaces of the clusters. We analyzed the effect of H2O adsorption on the properties of clusters of size n = 12 via the density of state, HOMO-LUMO orbitals and the changes in the IR frequencies. © 2011 Elsevier B.V. All rights reserved.
First-principles calculations of the magnetic properties of (Cd,Mn)Te nanocrystals
Echeverría-Arrondo, C.; Pérez-Conde, J.; Ayuela, A.
2009-04-01
We investigate the electronic and magnetic properties of Mn-doped CdTe nanocrystals (NCs) with ˜2nm in diameter which can be experimentally synthesized with Mn atoms inside. Using the density-functional theory, we consider two doping cases: NCs containing one or two Mn impurities. Although the Mnd peaks carry five up electrons in the dot, the local magnetic moment on the Mn site is 4.65μB . It is smaller than 5μB because of the sp-d hybridization between the localized 3d electrons of the Mn atoms and the s - and p -type valence states of the host compound. The sp-d hybridization induces small magnetic moments on the Mn-nearest-neighbor Te sites, antiparallel to the Mn moment affecting the p -type valence states of the undoped dot, as usual for a kinetic-mediated exchange magnetic coupling. Furthermore, we calculate the parameters standing for the sp-d exchange interactions. Conduction N0α and valence N0β are close to the experimental bulk values when the Mn impurities occupy bulklike NCs’ central positions, and they tend to zero close to the surface. This behavior is further explained by an analysis of valence-band-edge states showing that symmetry breaking splits the states and in consequence reduces the exchange. For two Mn atoms in several positions, the valence edge states show a further departure from an interpretation based in a perturbative treatment. We also calculate the d-d exchange interactions |Jdd| between Mn spins. The largest |Jdd| value is also for Mn atoms on bulklike central sites; in comparison with the experimental d-d exchange constant in bulk Cd0.95Mn0.05Te , it is four times smaller.
An approach to first principles electronic structure calculation by symbolic-numeric computation
Directory of Open Access Journals (Sweden)
Akihito Kikuchi
2013-04-01
Full Text Available There is a wide variety of electronic structure calculation cooperating with symbolic computation. The main purpose of the latter is to play an auxiliary role (but not without importance to the former. In the field of quantum physics [1-9], researchers sometimes have to handle complicated mathematical expressions, whose derivation seems almost beyond human power. Thus one resorts to the intensive use of computers, namely, symbolic computation [10-16]. Examples of this can be seen in various topics: atomic energy levels, molecular dynamics, molecular energy and spectra, collision and scattering, lattice spin models and so on [16]. How to obtain molecular integrals analytically or how to manipulate complex formulas in many body interactions, is one such problem. In the former, when one uses special atomic basis for a specific purpose, to express the integrals by the combination of already known analytic functions, may sometimes be very difficult. In the latter, one must rearrange a number of creation and annihilation operators in a suitable order and calculate the analytical expectation value. It is usual that a quantitative and massive computation follows a symbolic one; for the convenience of the numerical computation, it is necessary to reduce a complicated analytic expression into a tractable and computable form. This is the main motive for the introduction of the symbolic computation as a forerunner of the numerical one and their collaboration has won considerable successes. The present work should be classified as one such trial. Meanwhile, the use of symbolic computation in the present work is not limited to indirect and auxiliary part to the numerical computation. The present work can be applicable to a direct and quantitative estimation of the electronic structure, skipping conventional computational methods.
First principles calculation of L21+A2 coherent equilibria in the Fe-Al-Ti system
International Nuclear Information System (INIS)
Alonso, Paula R.; Gargano, Pablo H.; Ramirez-Caballero, Gustavo E.; Balbuena, Perla B.; Rubiolo, Gerardo H.
2009-01-01
By combining first-principles density functional total energy calculations and statistical mechanics the ground state and the phase equilibria at finite temperatures of the ternary system Fe-Al-Ti have been investigated. Total energy calculations have been performed by means of the Wien 2k code to establish the ground state energetic. A cluster expansion method was therewith used to describe solid solutions. At several chosen finite temperatures the cluster variation method in the irregular tetrahedron approximation was employed in order to calculate the iron rich ternary bcc equilibria. It is confirmed that there are two kinds of phase separations of the bcc phase, A2+L2 1 and B2+L2 1 .
Shi, Guangsha
Solar electricity is a reliable and environmentally friendly method of sustainable energy production and a realistic alternative to conventional fossil fuels. Moreover, thermoelectric energy conversion is a promising technology for solid-state refrigeration and efficient waste-heat recovery. Predicting and optimizing new photovoltaic and thermoelectric materials composed of Earth-abundant elements that exceed the current state of the art, and understanding how nanoscale structuring and ordering improves their energy conversion efficiency pose a challenge for materials scientists. I approach this challenge by developing and applying predictive high-performance computing methods to guide research and development of new materials for energy-conversion applications. Advances in computer-simulation algorithms and high-performance computing resources promise to speed up the development of new compounds with desirable properties and significantly shorten the time delay between the discovery of new materials and their commercial deployment. I present my calculated results on the extraordinary properties of nanostructured semiconductor materials, including strong visible-light absorbance in nanoporous silicon and few-layer SnSe and GeSe. These findings highlight the capability of nanoscale structuring and ordering to improve the performance of Earth-abundant materials compared to their bulk counterparts for solar-cell applications. I also successfully identified the dominant mechanisms contributing to free-carrier absorption in n-type silicon. My findings help evaluate the impact of the energy loss from this absorption mechanism in doped silicon and are thus important for the design of silicon solar cells. In addition, I calculated the thermoelectric transport properties of p-type SnSe, a bulk material with a record thermoelectric figure of merit. I predicted the optimal temperatures and free-carrier concentrations for thermoelectric energy conversion, as well the
Structure reconstruction of TiO2-based multi-wall nanotubes: first-principles calculations.
Bandura, A V; Evarestov, R A; Lukyanov, S I
2014-07-28
A new method of theoretical modelling of polyhedral single-walled nanotubes based on the consolidation of walls in the rolled-up multi-walled nanotubes is proposed. Molecular mechanics and ab initio quantum mechanics methods are applied to investigate the merging of walls in nanotubes constructed from the different phases of titania. The combination of two methods allows us to simulate the structures which are difficult to find only by ab initio calculations. For nanotube folding we have used (1) the 3-plane fluorite TiO2 layer; (2) the anatase (101) 6-plane layer; (3) the rutile (110) 6-plane layer; and (4) the 6-plane layer with lepidocrocite morphology. The symmetry of the resulting single-walled nanotubes is significantly lower than the symmetry of initial coaxial cylindrical double- or triple-walled nanotubes. These merged nanotubes acquire higher stability in comparison with the initial multi-walled nanotubes. The wall thickness of the merged nanotubes exceeds 1 nm and approaches the corresponding parameter of the experimental patterns. The present investigation demonstrates that the merged nanotubes can integrate the two different crystalline phases in one and the same wall structure.
First-principles calculations on the four phases of BaTiO3.
Evarestov, Robert A; Bandura, Andrei V
2012-04-30
The calculations based on linear combination of atomic orbitals basis functions as implemented in CRYSTAL09 computer code have been performed for cubic, tetragonal, orthorhombic, and rhombohedral modifications of BaTiO(3) crystal. Structural and electronic properties as well as phonon frequencies were obtained using local density approximation, generalized gradient approximation, and hybrid exchange-correlation density functional theory (DFT) functionals for four stable phases of BaTiO(3). A comparison was made between the results of different DFT techniques. It is concluded that the hybrid PBE0 [J. P. Perdew, K. Burke, M. Ernzerhof, J. Chem. Phys. 1996, 105, 9982.] functional is able to predict correctly the structural stability and phonon properties both for cubic and ferroelectric phases of BaTiO(3). The comparative phonon symmetry analysis in BaTiO(3) four phases has been made basing on the site symmetry and irreducible representation indexes for the first time. Copyright © 2012 Wiley Periodicals, Inc.
First-principles calculations: The elemental transition metals and their compounds
International Nuclear Information System (INIS)
Watson, R.E.; Fernando, G.W.; Weinert, M.; Davenport, J.W.
1991-01-01
If done with sufficient care, present day a priori theory yields calculated enthalpies of formation whose agreement with experiment (when such data is available) is of the order of the experimental scatter. Comparisons will be made for the Pt-Ti systems for which such data exist and for which one crystal structure involves atomics sites of low symmetry. Two other cases will be considered for which there is no direct experimental heats data. The first of these will be the structural stabilities of the 4d elemental metals. Such structural stabilities have been an issue of contention between electronic structure theorists and those who construct phase diagrams for some twenty-five years. The second involves the energetics of forming metal adlayers and artificial multilayers. The distortion energies associated with the requirement that adlayers (or multilayers) conform to some given substrate are often the controlling factors in the fabrication of multilayer materials. This contribution is best understood by invoking a combination of elemental structural promotion energies plus elastic distortions from these structures. As will be seen, the fabrication of multilayers also involves a term not normally encountered in bulk phase diagram considerations, namely the difference in surface energies of the two multilayer constituents. 22 refs., 4 figs
First-principles calculations of heat capacities of ultrafast laser-excited electrons in metals
International Nuclear Information System (INIS)
Bévillon, E.; Colombier, J.P.; Recoules, V.; Stoian, R.
2015-01-01
Ultrafast laser excitation can induce fast increases of the electronic subsystem temperature. The subsequent electronic evolutions in terms of band structure and energy distribution can determine the change of several thermodynamic properties, including one essential for energy deposition; the electronic heat capacity. Using density functional calculations performed at finite electronic temperatures, the electronic heat capacities dependent on electronic temperatures are obtained for a series of metals, including free electron like, transition and noble metals. The effect of exchange and correlation functionals and the presence of semicore electrons on electronic heat capacities are first evaluated and found to be negligible in most cases. Then, we tested the validity of the free electron approaches, varying the number of free electrons per atom. This shows that only simple metals can be correctly fitted with these approaches. For transition metals, the presence of localized d electrons produces a strong deviation toward high energies of the electronic heat capacities, implying that more energy is needed to thermally excite them, compared to free sp electrons. This is attributed to collective excitation effects strengthened by a change of the electronic screening at high temperature
First principles calculation of lithium-phosphorus co-doped diamond
Directory of Open Access Journals (Sweden)
Q.Y. Shao
2013-03-01
Full Text Available We calculate the density of states (DOS and the Mulliken population of the diamond and the co-doped diamonds with different concentrations of lithium (Li and phosphorus (P by the method of the density functional theory, and analyze the bonding situations of the Li-P co-doped diamond thin films and the impacts of the Li-P co-doping on the diamond conductivities. The results show that the Li-P atoms can promote the split of the diamond energy band near the Fermi level, and improve the electron conductivities of the Li-P co-doped diamond thin films, or even make the Li-P co-doped diamond from semiconductor to conductor. The affection of Li-P co-doping concentration on the orbital charge distributions, bond lengths and bond populations is analyzed. The Li atom may promote the split of the energy band near the Fermi level and also may favorably regulate the diamond lattice distortion and expansion caused by the P atom.
Ford, Denise C.; Cooley, Lance D.; Seidman, David N.
2013-09-01
Niobium hydride is suspected to be a major contributor to degradation of the quality factor of niobium superconducting radio-frequency (SRF) cavities. In this study, we connect the fundamental properties of hydrogen in niobium to SRF cavity performance and processing. We modeled several of the niobium hydride phases relevant to SRF cavities and present their thermodynamic, electronic, and geometric properties determined from calculations based on density functional theory. We find that the absorption of hydrogen from the gas phase into niobium is exothermic and hydrogen becomes somewhat anionic. The absorption of hydrogen by niobium lattice vacancies is strongly preferred over absorption into interstitial sites. A single vacancy can accommodate six hydrogen atoms in the symmetrically equivalent lowest energy sites and additional hydrogen in the nearby interstitial sites affected by the strain field: this indicates that a vacancy can serve as a nucleation center for hydride phase formation. Small hydride precipitates may then occur near lattice vacancies upon cooling. Vacancy clusters and extended defects should also be enriched in hydrogen, potentially resulting in extended hydride phase regions upon cooling. We also assess the phase changes in the niobium-hydrogen system based on charge transfer between niobium and hydrogen, the strain field associated with interstitial hydrogen, and the geometry of the hydride phases. The results of this study stress the importance of not only the hydrogen content in niobium, but also the recovery state of niobium for the performance of SRF cavities.
International Nuclear Information System (INIS)
Ford, Denise C; Cooley, Lance D; Seidman, David N
2013-01-01
Niobium hydride is suspected to be a major contributor to degradation of the quality factor of niobium superconducting radio-frequency (SRF) cavities. In this study, we connect the fundamental properties of hydrogen in niobium to SRF cavity performance and processing. We modeled several of the niobium hydride phases relevant to SRF cavities and present their thermodynamic, electronic, and geometric properties determined from calculations based on density functional theory. We find that the absorption of hydrogen from the gas phase into niobium is exothermic and hydrogen becomes somewhat anionic. The absorption of hydrogen by niobium lattice vacancies is strongly preferred over absorption into interstitial sites. A single vacancy can accommodate six hydrogen atoms in the symmetrically equivalent lowest energy sites and additional hydrogen in the nearby interstitial sites affected by the strain field: this indicates that a vacancy can serve as a nucleation center for hydride phase formation. Small hydride precipitates may then occur near lattice vacancies upon cooling. Vacancy clusters and extended defects should also be enriched in hydrogen, potentially resulting in extended hydride phase regions upon cooling. We also assess the phase changes in the niobium–hydrogen system based on charge transfer between niobium and hydrogen, the strain field associated with interstitial hydrogen, and the geometry of the hydride phases. The results of this study stress the importance of not only the hydrogen content in niobium, but also the recovery state of niobium for the performance of SRF cavities. (paper)
Gui, Gui; Li, Jin; Zhong, Jianxin
2009-10-01
We reply to the Comment by Farjam and Rafii-Tabar [Phys. Rev. B 80, 167401 (2009)] on our paper [Phys. Rev. B 78, 075435 (2008)]. We show that the gap opening found in our paper is due to the use of a small number of k points in the calculation which prevents revealing the sharp contact of the two bands near K or R . Once a large number of k points is used, the density-functional theory (DFT) VASP codes give the same conclusion as obtained by Farjam and Rafii-Tabar by using the QUANTUM-ESPRESSO codes, namely, there is no gap opening in the band structure of graphene under small planar strain. We also point out that all other results in our paper remain correct, except for the conclusion of the gap opening. The results demonstrate the importance of using a large number of k points for determining the gap width of the band structure of graphene under strain as well as the validity of the DFT VASP codes for the system.
First-principles calculations of the indigo encapsulation and adsorption by MgO nanotubes
Energy Technology Data Exchange (ETDEWEB)
Sánchez-Ochoa, F., E-mail: fsanchez@ifuap.buap.mx; Cocoletzi, Gregorio H. [Instituto de Física “Ing. Luis Rivera Terrazas,” Benemérita Universidad Autónoma de Puebla, Av. San Claudio y Blvd. 18 Sur, Col. San Manuel, C.P. 72570 Puebla, Pue (Mexico); Canto, Gabriel I. [Departamento de Materiales y Corrosión, Centro de Investigación en Corrosión, Universidad Autónoma de Campeche, Col. Buenavista, C.P. 24039 San Francisco de Campeche, Campeche (Mexico); Takeuchi, Noboru [Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Km 107 Carretera Tijuana-Ensenada, CP. 22800 Ensenada, B.C (Mexico)
2014-06-07
We have performed ab-initio calculations to investigate the structural and electronic properties of (m,m) chiral magnesium oxide nanotubes, (m,m)MgONTs, to explore the encapsulation, inclusion, and adsorption of dyes (organic molecules) such as Indigo (IND). Studies start by determining the structural parameters of the MgO nanotubes with different diameters and the IND. The indigo encapsulation into the MgONT is studied considering four (m,m) chiralities which yield 4 different NT diameters. In the endohedral functionalization, the indigo is within the NT at a tilt angle as in previous theoretical studies of organic molecules inside carbon and boron-nitride nanotubes. Results show that the encapsulation is a strong exothermic process with the m = 6 case exhibiting the largest encapsulation energy. It is also explored the indigo adsorption on the NT surface in the parallel and perpendicular configurations. The perpendicular configuration of the IND adsorption on the (8,8)MgONT exhibits the largest energy. The indigo inclusion within the NTs meets a potential barrier when m < 6, however this barrier diminishes as the index increases. Additionally, we have determined the total density of states (DOS), partial DOS, electron charge redistributions, and the highest occupied molecular orbital–lowest unoccupied molecular orbital levels for the NTs with m = 6. Very strong binding energies and electron charge transfer from the IND to NTs is present in the atomic structures.
First-principles calculations: The elemental transition metals and their compounds
Energy Technology Data Exchange (ETDEWEB)
Watson, R.E.; Fernando, G.W.; Weinert, M.; Davenport, J.W.
1991-01-01
If done with sufficient care, present day a priori theory yields calculated enthalpies of formation whose agreement with experiment (when such data is available) is of the order of the experimental scatter. Comparisons will be made for the Pt-Ti systems for which such data exist and for which one crystal structure involves atomics sites of low symmetry. Two other cases will be considered for which there is no direct experimental heats data. The first of these will be the structural stabilities of the 4d elemental metals. Such structural stabilities have been an issue of contention between electronic structure theorists and those who construct phase diagrams for some twenty-five years. The second involves the energetics of forming metal adlayers and artificial multilayers. The distortion energies associated with the requirement that adlayers (or multilayers) conform to some given substrate are often the controlling factors in the fabrication of multilayer materials. This contribution is best understood by invoking a combination of elemental structural promotion energies plus elastic distortions from these structures. As will be seen, the fabrication of multilayers also involves a term not normally encountered in bulk phase diagram considerations, namely the difference in surface energies of the two multilayer constituents. 22 refs., 4 figs.
Magnetism of CrO overlayers on Fe(001)bcc surface: first principles calculations
Félix-Medina, Raúl Enrique; Leyva-Lucero, Manuel Andrés; Meza-Aguilar, Salvador; Demangeat, Claude
2018-04-01
Riva et al. [Surf. Sci. 621, 55 (2014)] as well as Calloni et al. [J. Phys.: Condens. Matter 26, 445001 (2014)] have studied the oxydation of Cr films deposited on Fe(001)bcc through low-energy electron diffraction, Auger electron spectroscopy and scanning tunneling microscopy. In the present work we perform a density functional approach within Quantum Expresso code in order to study structural and magnetic properties of CrO overlayers on Fe(001)bcc. The calculations are performed using DFT+U. The investigated systems include O/Cr/Fe(001)bcc, Cr/O/Fe(001)bcc, Cr0.25O0.75/Fe(001)bcc, as well as the O coverage Ox/Cr/Fe(001)bcc (x = 0.25; 0.50). We have found that the ordered CrO overlayer presents an antiferromagnetic coupling between Cr and Fe atoms. The O atoms are located closer to the Fe atoms of the surface than the Cr atoms. The ground state of the systems O/Cr/Fe(001)bcc and Cr/O/Fe(001)bcc corresponds to the O/Cr/Fe(001)bcc system with a magnetic coupling c(2 × 2). The effect of the O monolayer on Cr/Fe(001)bcc changes the ground state from p(1 × 1) ↓ to c(2 × 2) and produces an enhancement of the magnetic moments. The Ox overlayer on Cr/Fe(001)bcc produces an enhancement of the Cr magnetic moments.
Combined Raman spectroscopy and first-principles calculation for essential oil of Lemongrass
Faria, Rozilaine A. P. G.; Picanço, Nágela F. M.; Campo, Gladís S. D. L.; Faria, Jorge L. B.; Instituto de Física/UFMT Collaboration; Instituto Federal de Mato Grosso/IFMT Team
2014-03-01
The essential oils have increased food's industry interest by the presence of antioxidant and antimicrobial. Many of them have antimicrobial and antioxidant, antibacterial and antifungal activities. But, due to the concentrations required to be added in the food matrix, the sensory quality of the food is changed. The production and composition of essential oil extracted from plants depend on the plant-environment interactions, the harvest season, phenophase and physiological state of the vegetal. Cymbopogom citratus (Lemongrass) has a good yield in essential oil with neral (citral A), geranial (citral B) and myrcene, reaching 90% of the oil composition. In our experimental work, the essential oil of lemongrass was obtained by hydrodistillation in Clevenger apparatus for 4 hours. The compound was further analyzed by Raman scattering in a spectrometer HR 800, with excitation at 633nm, in the range 80-3400 cm-1. The spectrum obtained was compared with DFT calculations of molecules of the oil components. Our results show the vibrational signatures of the main functional groups and suggest a simple, but very useful, methodology to quantify the proportions of these components in the oil composition, showing good agreement with Raman data. CNPq/Capes/Fapemat.
International Nuclear Information System (INIS)
Choo, R.T.C.; Szekely, J.; David, S.A.
1992-01-01
By combining a mathematical model of the welding arc and of the weld pool, calculations are presented here to describe the free surface temperature of weld pools for spot welding operations. The novel aspects of the treatment include the calculation of the heat and current fluxes falling on the free weld pool surface from first principles, a realistic allowance for heat losses due to vaporization, and a realistic allowance for the temperature dependence of the surface tension. The most important finding reported in this article is that the free surface temperature of weld pools appears to be limited by Marangoni convection, rather than heat losses due to vaporization. Furthermore, it was found that once thermocapillary flow can produce high enough surface velocities (>25 cm/s), the precise nature of the relationship between temperature and surface tension will become less important
International Nuclear Information System (INIS)
Emel'yanenko, Vladimir N.; Verevkin, Sergey P.; Heintz, Andreas
2011-01-01
The standard molar enthalpy of formation Δ f H m o (l) of the ionic liquid N-butyl-3-methylpyridinium dicyanamide has been determined at 298.15 K by means of combustion calorimetry. Vaporization of the ionic liquid into the nitrogen stream in order to obtain vaporization enthalpy has been attempted, but no vaporization was achieved. First-principles calculations of the enthalpy of formation in the gaseous phase have been performed for the ionic species using the G3MP2 theory. The combination of traditional combustion calorimetry with modern high-level quantum-chemical calculations allows estimation of the molar enthalpy of vaporization of the ionic liquid under study.
International Nuclear Information System (INIS)
Song, T.; Ma, Q.; Sun, X.W.; Liu, Z.J.; Fu, Z.J.; Wei, X.P.; Wang, T.; Tian, J.H.
2016-01-01
The phase transition, electronic band structure, and equation of state (EOS) of cubic TcN are investigated by first-principles pseudopotential method based on density-functional theory. The calculated enthalpies show that TcN has a transformation between zincblende and rocksalt phases and the pressure determined by the relative enthalpy is 32 GPa. The calculated band structure indicates the metallic feature and it might make cubic TcN a better candidate for hard materials. Particular attention is paid to the predictions of volume, bulk modulus and its pressure derivative which play a central role in the formulation of approximate EOSs using the quasi-harmonic Debye model. - Highlights: • The phase transition pressure and electronic band structure for cubic TcN are determined. • Particular attention is paid to investigate the equation of state parameters for cubic TcN. • The thermodynamic properties up to 80 GPa and 3000 K are successfully predicted.
Murray, Eamonn; Fahy, Stephen
2014-03-01
Using first principles electronic structure methods, we calculate the induced force on the Eg (zone centre transverse optical) phonon mode in bismuth immediately after absorption of polarized light. When radiation with polarization perpendicular to the c-axis is absorbed in bismuth, the distribution of excited electrons and holes breaks the three-fold rotational symmetry and leads to a net force on the atoms in the direction perpendicular to the axis. We calculate the initial excited electronic distribution as a function of photon energy and polarization and find the resulting transverse and longitudinal forces experienced by the atoms. Using the measured, temperature-dependent rate of decay of the transverse force[2], we predict the approximate amplitude of induced atomic motion in the Eg mode as a function of temperature and optical fluence. This work is supported by Science Foundation Ireland and a Marie Curie International Incoming Fellowship.
International Nuclear Information System (INIS)
Xie, Z.L.; Dy, K.S.; Wu, S.Y.
1997-01-01
A real-space scheme has been developed for a first-principles calculation of electronic structures and total energies of atomic clusters. The scheme is based on the combination of the tight-binding linear muffin-tin orbital (TBLMTO) method and the method of real-space Green close-quote s function. With this approach, the local electronic density of states can be conveniently determined from the real-space Green close-quote s function. Furthermore, the full electron density of a cluster can be directly calculated in real space. The scheme has been shown to be very efficient due to the incorporation of the method of real-space Green close-quote s function and Delley close-quote s method of evaluating multicenter integrals. copyright 1996 The American Physical Society
International Nuclear Information System (INIS)
Gao, Zhiyong; Chen, Baishu; Meng, Xianglong; Cai, Wei
2013-01-01
Highlights: •Site preference and phase stability of NiMnGaTi are studied by first-principles. •The Ti atoms prefer to occupy the Ga sites in the Ni 2 MnGa austenitic phase. •The phase stability becomes worse when Ga is replaced by Ti. •The phase stability is discussed based on the densities of states. -- Abstract: The effects of Ti content on martensitic transformation and phase stability of Ni 50 Mn 25 Ga 25−x Ti x shape memory alloys were investigated from first-principles calculations based on density functional theory. The formation energy results indicate that the added Ti preferentially occupies the Ga sites in Ni 2 MnGa alloy due to the lowest formation energy. The total energy difference between austenite and martensite increases with Ti alloying, being relevant to the experimentally reported changes in martensitic transformation temperature. The phase stability of Ni 50 Mn 25 Ga 25−x Ti x austenite decreases with increasing Ti content, which results from the reduced Ni 3d–Mn 3d hybridization when Ga is replaced by Ti
Fox, Stephen J; Pittock, Chris; Tautermann, Christofer S; Fox, Thomas; Christ, Clara; Malcolm, N O J; Essex, Jonathan W; Skylaris, Chris-Kriton
2013-08-15
Schemes of increasing sophistication for obtaining free energies of binding have been developed over the years, where configurational sampling is used to include the all-important entropic contributions to the free energies. However, the quality of the results will also depend on the accuracy with which the intermolecular interactions are computed at each molecular configuration. In this context, the energy change associated with the rearrangement of electrons (electronic polarization and charge transfer) upon binding is a very important effect. Classical molecular mechanics force fields do not take this effect into account explicitly, and polarizable force fields and semiempirical quantum or hybrid quantum-classical (QM/MM) calculations are increasingly employed (at higher computational cost) to compute intermolecular interactions in free-energy schemes. In this work, we investigate the use of large-scale quantum mechanical calculations from first-principles as a way of fully taking into account electronic effects in free-energy calculations. We employ a one-step free-energy perturbation (FEP) scheme from a molecular mechanical (MM) potential to a quantum mechanical (QM) potential as a correction to thermodynamic integration calculations within the MM potential. We use this approach to calculate relative free energies of hydration of small aromatic molecules. Our quantum calculations are performed on multiple configurations from classical molecular dynamics simulations. The quantum energy of each configuration is obtained from density functional theory calculations with a near-complete psinc basis set on over 600 atoms using the ONETEP program.
First-principles calculations of two cubic fluoropervskite compounds: RbFeF3 and RbNiF3
International Nuclear Information System (INIS)
Mubarak, A.A.; Al-Omari, Saleh
2015-01-01
We present first-principles calculations of the structural, elastic, electronic, magnetic and optical properties for RbFeF 3 and RbNiF 3 . The full-potential linear augmented plan wave (FP-LAPW) method within the density functional theory was utilized to perform the present calculations. We employed the generalized gradient approximation as exchange-correlation potential. It was found that the calculated analytical lattice parameters agree with previous studies. The analysis of elastic constants showed that the present compounds are elastically stable and anisotropic. Moreover, both compounds are classified as a ductile compound. The calculations of the band structure and density functional theory revealed that the RbFeF 3 compound has a half-metallic behavior while the RbNiF 3 compound has a semiconductor behavior with indirect (M–Γ) band gap. The ferromagnetic behavior was studied for both compounds. The optical properties were calculated for the radiation of up to 40 eV. A beneficial optics technology is predicted as revealed from the optical spectra. - Highlights: • RbFeF 3 and RbNiCl 3 compounds are elastically stable. • RbFeF 3 and RbNiCl 3 compounds are classified as a ductile compound. • The RbFeF 3 compound has a half-metallic behavior while the RbNiF 3 compound has a semiconductor behavior. • The optical properties were calculated for the radiation of up to 40 eV
First-principles calculations of the II-VI semiconductor β-HgS: Metal or semiconductor
International Nuclear Information System (INIS)
Delin, A.
2002-06-01
Relativistic all-electron full-potential first-principles calculations have been performed in order to study the symmetry of the energy levels around the valence band maximum in the zinc blende II-VI semiconductors β-HgS, HgSe, and HgTe. It is demonstrated that in general, an inverted band-structure does not necessarily lead to a zero fundamental energy gap for systems with zinc blende symmetry. Specifically, β-HgS is found to have at the same time an inverted band structure, and a small, slightly indirect, fundamental energy gap. Possibly, the energy levels around the valence band maximum order differently in each of these systems. (author)
International Nuclear Information System (INIS)
Xu, Shao-Gang; Liao, Ji-Hai; Zhao, Yu-Jun; Yang, Xiao-Bao
2015-01-01
The unique electronic property induced diversified structure of boron (B) cluster has attracted much interest from experimentalists and theorists. B 30–40 were reported to be planar fragments of triangular lattice with proper concentrations of vacancies recently. Here, we have performed high-throughput screening for possible B clusters through the first-principles calculations, including various shapes and distributions of vacancies. As a result, we have determined the structures of B n clusters with n = 30–51 and found a stable planar cluster of B 49 with a double-hexagon vacancy. Considering the 8-electron rule and the electron delocalization, a concise model for the distribution of the 2c–2e and 3c–2e bonds has been proposed to explain the stability of B planar clusters, as well as the reported B cages
Aghajani, M.; Hadipour, H.; Akhavan, M.
2018-05-01
Pressure dependence of the onsite Coulomb interactions of the BaFe2As2 has been studied by employing the constrained random phase approximation within first-principle calculations. Analyzing total and projected density of states, a pseudogap is found for dxy band at the energy roughly 0.25 eV higher than the Fermi level. Also, by applying pressure the spectral weight of the dxy orbital vanishes while other orbitals remain metallic. The different screening channels, as discussed in four different models, affect significantly on the Hubbard U while the Hund J remains almost unchanged. The average onsite bare and partially and fully screened Coulomb interactions increase with different rates upon compression. These different rates can be explained by competition between the electronic screening and reduction of bond lengths.
Seko, Atsuto; Togo, Atsushi; Hayashi, Hiroyuki; Tsuda, Koji; Chaput, Laurent; Tanaka, Isao
2015-11-01
Compounds of low lattice thermal conductivity (LTC) are essential for seeking thermoelectric materials with high conversion efficiency. Some strategies have been used to decrease LTC. However, such trials have yielded successes only within a limited exploration space. Here, we report the virtual screening of a library containing 54 779 compounds. Our strategy is to search the library through Bayesian optimization using for the initial data the LTC obtained from first-principles anharmonic lattice-dynamics calculations for a set of 101 compounds. We discovered 221 materials with very low LTC. Two of them even have an electronic band gap <1 eV , which makes them exceptional candidates for thermoelectric applications. In addition to those newly discovered thermoelectric materials, the present strategy is believed to be powerful for many other applications in which the chemistry of materials is required to be optimized.
Lu, Dao-Bang; Song, Yu-Ling
2018-03-01
Based on density functional theory, we perform first-principles investigations to study the optical properties of the O-, F- and H-terminated SiC nanoribbons with armchair edges (ASiCNRs). By irradiating with an external electromagnetic field, we calculate the dielectric function, reflection spectra, energy loss coefficient and the real part of the conductance. It is demonstrated that the optical constants are sensitive to the low-energy range, different terminal atoms do not make much difference in the shape of the curves of the optical constants for the same-width ASiCNR, and the optical constants of wider nanoribbons usually have higher peaks than that of the narrower ones in low energy range. We hope that our study helps in experimental technology of fabricating high-quality SiC-based nanoscale photoelectric device.
Role of anion doping on electronic structure and magnetism of GdN by first principles calculations
Zhang, Xuejing; Mi, Wenbo; Guo, Zaibing; Cheng, Yingchun; Chen, Guifeng; Bai, Haili
2014-01-01
We have investigated the electronic structure and magnetism of anion doped GdN1-yXy (X = B, C, O, F, P, S and As) systems by first-principles calculations based on density functional theory. GdN 1-yXy systems doped by O, C, F, P, and S atoms are more stable than those doped by B and As atoms because of relatively high binding energies. The anion doping and the N defect states modify the density of states at the Fermi level, resulting in a decrease in spin polarization and a slight increase in the magnetic moment at the Gd and N sites. © 2014 The Royal Society of Chemistry.
International Nuclear Information System (INIS)
Spanos, G.; Geltmacher, A.B.; Lewis, A.C.; Bingert, J.F.; Mehl, M.; Papaconstantopoulos, D.; Mishin, Y.; Gupta, A.; Matic, P.
2007-01-01
This paper provides a brief overview of a multidisciplinary effort at the Naval Research Laboratory aimed at developing a computationally-based methodology to assist in the design of advanced Naval steels. This program uses multiple computational techniques ranging from the atomistic length scale to continuum response. First-principles electronic structure calculations using density functional theory were employed, semi-empirical angular dependent potentials were developed based on the embedded atom method, and these potentials were used as input into Monte-Carlo and molecular dynamics simulations. Experimental techniques have also been applied to a super-austenitic stainless steel (AL6XN) to provide experimental input, guidance, verification, and enhancements to the models. These experimental methods include optical microscopy, scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, and serial sectioning in conjunction with computer-based three-dimensional reconstruction and quantitative analyses. The experimental results are also used as critical input into mesoscale finite element models of materials response
Sadasivam, Sridhar; Ye, Ning; Feser, Joseph P.; Charles, James; Miao, Kai; Kubis, Tillmann; Fisher, Timothy S.
2017-02-01
Heat transfer across metal-semiconductor interfaces involves multiple fundamental transport mechanisms such as elastic and inelastic phonon scattering, and electron-phonon coupling within the metal and across the interface. The relative contributions of these different transport mechanisms to the interface conductance remains unclear in the current literature. In this work, we use a combination of first-principles calculations under the density functional theory framework and heat transport simulations using the atomistic Green's function (AGF) method to quantitatively predict the contribution of the different scattering mechanisms to the thermal interface conductance of epitaxial CoSi2-Si interfaces. An important development in the present work is the direct computation of interfacial bonding from density functional perturbation theory (DFPT) and hence the avoidance of commonly used "mixing rules" to obtain the cross-interface force constants from bulk material force constants. Another important algorithmic development is the integration of the recursive Green's function (RGF) method with Büttiker probe scattering that enables computationally efficient simulations of inelastic phonon scattering and its contribution to the thermal interface conductance. First-principles calculations of electron-phonon coupling reveal that cross-interface energy transfer between metal electrons and atomic vibrations in the semiconductor is mediated by delocalized acoustic phonon modes that extend on both sides of the interface, and phonon modes that are localized inside the semiconductor region of the interface exhibit negligible coupling with electrons in the metal. We also provide a direct comparison between simulation predictions and experimental measurements of thermal interface conductance of epitaxial CoSi2-Si interfaces using the time-domain thermoreflectance technique. Importantly, the experimental results, performed across a wide temperature range, only agree well with
First-principles calculations of two cubic fluoropervskite compounds: RbFeF3 and RbNiF3
Mubarak, A. A.; Al-Omari, Saleh
2015-05-01
We present first-principles calculations of the structural, elastic, electronic, magnetic and optical properties for RbFeF3 and RbNiF3. The full-potential linear augmented plan wave (FP-LAPW) method within the density functional theory was utilized to perform the present calculations. We employed the generalized gradient approximation as exchange-correlation potential. It was found that the calculated analytical lattice parameters agree with previous studies. The analysis of elastic constants showed that the present compounds are elastically stable and anisotropic. Moreover, both compounds are classified as a ductile compound. The calculations of the band structure and density functional theory revealed that the RbFeF3 compound has a half-metallic behavior while the RbNiF3 compound has a semiconductor behavior with indirect (M-Γ) band gap. The ferromagnetic behavior was studied for both compounds. The optical properties were calculated for the radiation of up to 40 eV. A beneficial optics technology is predicted as revealed from the optical spectra.
International Nuclear Information System (INIS)
Soni, Himadri R.; Mankad, Venu; Gupta, Sanjeev K.; Jha, Prafulla K.
2012-01-01
Highlights: ► We present spin dependent bandstructure, structural and magnetic moment of FeN/CoN. ► The PDC, PHDOS, spin effect on phonons suggests ZB is preferred at ambient pressure. ► Spin calculation offers an opportunity to understand the role of spin on phonons. - Abstract: Using first principles density functional theoretical calculations, the present paper reports a systematic nonspin and spin polarized total energy calculations of the lattice dynamical and a number of other properties such as band structure, structural and magnetic moment of two mononitrides FeN and CoN. The phonon dispersion curves and phonon density of states in the case of FeN and CoN have been determined for the first time and discussed. The structural and dynamical calculations suggest that the zinc blende structure is preferred at ambient pressure for both compounds. The rocksalt FeN has a nonzero magnetic moment while for FeN in zinc blende phase, it is either zero or very small. The zinc blende phase for both compounds is nonmagnetic. The spin calculation offers an intensive opportunity to understand the role of spin on the phonon properties of two mononitrides. Majority of the modes are sensitive to the effect of spin due to the modification of lattice constant. In this work we reveal that spin modifies the interionic interactions and local structure and leads to a flexible lattice which can be used for the functional materials design.
Energy Technology Data Exchange (ETDEWEB)
He, Yang [Department of Materials Science and Engineering, China University of Petroleum (Beijing), Beijing 102249 (China); Beijing Key Laboratory of Failure, Corrosion and Protection of Oil/gas Facilities, China University of Petroleum (Beijing), Beijing 102249 (China); Chen, Changfeng, E-mail: chen_c_f@163.com [Department of Materials Science and Engineering, China University of Petroleum (Beijing), Beijing 102249 (China); Beijing Key Laboratory of Failure, Corrosion and Protection of Oil/gas Facilities, China University of Petroleum (Beijing), Beijing 102249 (China); Yu, Haobo [Department of Materials Science and Engineering, China University of Petroleum (Beijing), Beijing 102249 (China); Beijing Key Laboratory of Failure, Corrosion and Protection of Oil/gas Facilities, China University of Petroleum (Beijing), Beijing 102249 (China); Lu, Guiwu [Department of Materials Science and Engineering, China University of Petroleum (Beijing), Beijing 102249 (China)
2017-01-15
Highlights: • The structures of water compact layer on Pt(111) at different temperature were calculated. • The feature of chemical bond between water molecules and Pt (111) surface was discussed with temperature increased. • Temperature dependence of electrical strengths and capacitances of compact layer on Pt (111) surface was calculated. - Abstract: Formation of the double-layer electric field and capacitance of the water-metal interface is of significant interest in physicochemical processes. In this study, we perform first- principles molecular dynamics simulations on the water/Pt(111) interface to investigate the temperature dependence of the compact layer electric field and capacitance based on the calculated charge densities. On the Pt (111) surface, water molecules form ice-like structures that exhibit more disorder along the height direction with increasing temperature. The O−H bonds of more water molecules point toward the Pt surface to form Pt−H covalent bonds with increasing temperature, which weaken the corresponding O−H bonds. In addition, our calculated capacitance at 300 K is 15.2 mF/cm{sup 2}, which is in good agreement with the experimental results. As the temperature increases from 10 to 450 K, the field strength and capacitance of the compact layer on Pt (111) first increase and then decrease slightly, which is significant for understanding the water/Pt interface from atomic level.
Li, Xiaolong; Zhou, Zhaobo; Hu, Riming; Zhou, Xiaolong; Yu, Jie; Liu, Manmen
2018-04-01
The Phase stability, electronic structure, elastic properties and hardness of Ru-Ir alloys with different B concentration were investigated by first principles calculations. The calculated formation enthaplies and cohesive energies show that these compounds are all thermodynamically stable. Information on electronic structure indicates that they possess metallic characteristic and Ru-Ir-B alloys were composed of the Ru-B and Ir-B covalent bond. The elastic properties were calculated, which included bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio and hardness. The calculated results reveal that the plastic of Ru-Ir-B alloys increase with the increase of the content of B atoms, but the hardness of Ru-Ir-B alloys have no substantial progress with the increase of the content of B atoms. However, it is interesting that the hardness of the Ru-Ir-B compound was improved obviously as the B content was higher than 18 atoms because of a phase structure transition.
International Nuclear Information System (INIS)
Liu Qijun; Liu Zhengtang; Feng Liping; Tian Hao
2010-01-01
We have performed ab-initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study structural parameters, mechanical, electronic, chemical bonding and optical properties of cubic BaHfO 3 . The calculated lattice parameter and independent elastic constants are in good agreement with previous theoretical and experimental work. The bulk, shear and Young's modulus, Poisson coefficient, compressibility and Lame constants are obtained using Voigt-Reuss-Hill method and the Debye temperature is estimated using Debye-Grueneisen model, which are consistent with previous results. Electronic and chemical bonding properties have been studied from the calculations of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions of cubic BaHfO 3 , the complex dielectric function, refractive index, extinction coefficient, reflectivity, absorption efficient, loss function and complex conductivity function are calculated. Then, we have explained the origins of spectral peaks on the basis of the theory of crystal-field and molecular-orbital bonding.
First-principles calculations of a half-metallic ferromagnet zinc blende Zn1−xVxTe
International Nuclear Information System (INIS)
El Amine Monir, M.; Baltache, H.; Khenata, R.; Murtaza, G.; Azam, Sikander; Bouhemadou, A.; Al-Douri, Y.; Bin Omran, S.; Ali, Roshan
2015-01-01
First-principles calculations have been used to study the structural, elastic, electronic, magnetic and thermal properties of zinc blende Zn 1−x V x Te for x=0, 0.25, 0.50, 0.75 and 1 using the full-potential linearized augmented plane wave method (FP-LAPW) based on spin-polarized density functional theory (DFT). The electronic exchange-correlation potential is approached using the spin generalized gradient approximation (spin-GGA). The structural properties of the Zn 1−x V x Te alloys (x=0, 0.25, 0.50, 0.75 and 1) are given for the lattice constants and the bulk moduli and their pressure derivatives. The elastic constants C 11 , C 12 and C 44 are calculated using numerical first-principles calculations implemented in the WIEN2k package. An analysis of the band structures and the densities of states reveals that Zn 0.50 V 0.50 Te and Zn 0.75 V 0.25 Te exhibit a half-metallic character, while Zn 0.25 V 0.75 Te is nearly half-metallic. The band structure calculations are used to estimate the spin-polarized splitting energies Δ x (d) and Δ x (pd) produced by the V(3d)-doped and s(p)–d exchange constants N 0α (conduction band) and N 0β (valence band). The p–d hybridization reduces the magnetic moment of V from its atomic charge value of 3µ B and creates small local magnetic moments on the nonmagnetic Zn and Te sites. Finally, we present the thermal effect on the macroscopic properties of these alloys, such as the thermal expansion coefficient, heat capacity and Debye temperature, based on the quasi-harmonic Debye model. - Highlights: • Some physical properties of Vanadium doped ZnTe have been investigated. • Structural parameters for the parent compounds compare well with the available data. • The elastic and thermal properties are studied for the first time
First-principles X-ray absorption dose calculation for time-dependent mass and optical density.
Berejnov, Viatcheslav; Rubinstein, Boris; Melo, Lis G A; Hitchcock, Adam P
2018-05-01
A dose integral of time-dependent X-ray absorption under conditions of variable photon energy and changing sample mass is derived from first principles starting with the Beer-Lambert (BL) absorption model. For a given photon energy the BL dose integral D(e, t) reduces to the product of an effective time integral T(t) and a dose rate R(e). Two approximations of the time-dependent optical density, i.e. exponential A(t) = c + aexp(-bt) for first-order kinetics and hyperbolic A(t) = c + a/(b + t) for second-order kinetics, were considered for BL dose evaluation. For both models three methods of evaluating the effective time integral are considered: analytical integration, approximation by a function, and calculation of the asymptotic behaviour at large times. Data for poly(methyl methacrylate) and perfluorosulfonic acid polymers measured by scanning transmission soft X-ray microscopy were used to test the BL dose calculation. It was found that a previous method to calculate time-dependent dose underestimates the dose in mass loss situations, depending on the applied exposure time. All these methods here show that the BL dose is proportional to the exposure time D(e, t) ≃ K(e)t.
First-principles calculation of the structure and electronic properties of Fe-substituted Bi2Ti2O7
Huang, Jin-Dou; Zhang, Zhenyi; Lin, Feng; Dong, Bin
2017-12-01
We performed first-principles calculations to investigate the formation energy, geometry structure, and electronic property of Fe-doped Bi2Ti2O7 systems with different Fe doping content. The calculated formation energies indicate that the substitutional configurations of Fe-doping Bi2Ti2O7 are easy to obtain under O-rich growth condition, but their thermodynamic stability decreases with the increase of Fe content. The calculated spin-resolved density of states and band structures indicate that the introduction of Fe into Bi2Ti2O7 brings high spin polarization. The spin-down impurity levels in Fe x Bi2-x Ti2O7 and spin-up impurity levels in Fe x Bi2Ti2-x O7 systems locate in the bottom of conduction band and narrow the band gap significantly, thus leading to the absorption of visible light. Interestingly, the impurity states in Fe x Bi2-x Ti2O7 are the efficient separation center of photogenerated electron and hole, and less affected by Fe doping content, in comparison, the levels of impurity band in Fe x Bi2Ti2-x O7 systems are largely effected by the Fe doping content, and high Fe doping content is the key factor to improve the separating rate of photogenerated electron and hole.
International Nuclear Information System (INIS)
Liu Ya-Hui; Chong Xiao-Yu; Jiang Ye-Hua; Feng Jing
2017-01-01
The stability, electronic structures, and mechanical properties of the Fe–Mn–Al system were determined by first-principles calculations. The formation enthalpy and cohesive energy of these Fe–Mn–Al alloys are negative and show that the alloys are thermodynamically stable. Fe 3 Al, with the lowest formation enthalpy, is the most stable compound in the Fe–Mn–Al system. The partial density of states, total density of states, and electron density distribution maps of the Fe– Mn–Al alloys were analyzed. The bonding characteristics of these Fe–Mn–Al alloys are mainly combinations of covalent bonding and metallic bonds. The stress-strain method and Voigt–Reuss–Hill approximation were used to calculate the elastic constants and moduli, respectively. Fe 2.5 Mn 0.5 Al has the highest bulk modulus, 234.5 GPa. Fe 1.5 Mn 1.5 Al has the highest shear modulus and Young’s modulus, with values of 98.8 GPa and 259.2 GPa, respectively. These Fe–Mn–Al alloys display disparate anisotropies due to the calculated different shape of the three-dimensional curved surface of the Young’s modulus and anisotropic index. Moreover, the anisotropic sound velocities and Debye temperatures of these Fe–Mn–Al alloys were explored. (paper)
Energy Technology Data Exchange (ETDEWEB)
Li, Li [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Civil Aviation Flight Univ. of China, Guanghan (China). Dept. of Physics; Zeng, Zhao-Yi [Chongqing Normal Univ., Chongqing (China). College of Physics and Electronic Engineering; Liang, Ting; Tang, Mei; Cheng, Yan [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics
2017-07-01
The influence of pressure on the elastic and mechanical properties of the hexagonal transition-metal dichalcogenide WS{sub 2} is investigated using the first-principles calculations. With the increase in pressure, the lattice parameters and the volume of WS{sub 2} decrease, which is exactly in agreement with the available experimental data and other calculated results. The elastic constants C{sub ij}, bulk modulus B, shear modulus G, Young's modulus E, and Poisson's ratio σ of WS{sub 2} also increase with pressure. At last, for the first time, the band gaps of energy, the partial density of states, and the total density of states under three different pressures are obtained and analysed. It is found that the band gap of WS{sub 2} decreases from 0.843 to 0 eV when the external pressure varies from 0 to 20 GPa, which implies that WS{sub 2} may transform from semiconductors to semimetal phase at a pressure about 20 GPa.
Energy Technology Data Exchange (ETDEWEB)
Wu Yurong, E-mail: winwyr@126.com [College of Electromechanical Engineering, Hunan University of Science and Technology, Xiantang 411201 (China); Hu Wangyu [Department of Applied Physics, Hunan University, Changsha 410082 (China); Xu Longshan [Department of Materials Science and Engineering, Xiamen University of Technology, Xiamen 361024 (China)
2012-09-15
First-principles calculations were preformed to study the site preference behavior and elastic properties of 3d (Ti-Cu) transition-metal elements in B2 ductility YAg alloy. In YAg, Ti is found to occupy the Y sublattice whereas V, Cr, Co, Fe, Ni and Cu tend to substitute for Ag sublattice. Due to the addition of 3d transition metals, the lattice parameters of YAg is decreased in the order: V
First-principles calculations of vacancy formation in In-free photovoltaic semiconductor Cu2ZnSnSe4
International Nuclear Information System (INIS)
Maeda, Tsuyoshi; Nakamura, Satoshi; Wada, Takahiro
2011-01-01
To quantitatively evaluate the formation energies of Cu, Zn, Sn, and Se vacancies in kesterite-type Cu 2 ZnSnSe 4 (CZTSe), first-principles pseudopotential calculations using plane-wave basis functions were performed. The formation energies of neutral Cu, Zn, Sn and Se vacancies were calculated as a function of the atomic chemical potentials of constituent elements. The obtained results were as follows: (1) the formation energy of Cu vacancy was generally smaller than those of the other Zn, Sn and Se vacancies, (2) under the Cu-poor and Zn-rich condition, the formation energy of Cu vacancy was particularly low, (3) the formation energy of Zn vacancy greatly depended on the chemical potentials of the constituent elements and under the Zn-poor and Se-rich condition, the formation energy of Zn vacancy was smaller than that of Cu vacancy, and (4) the formation energy of Sn vacancy did not greatly depend on the chemical potentials of the constituent elements and was much larger than those of Cu, Zn, and Se vacancies. These results indicate that Cu vacancy is easily formed under Cu-poor and Zn-rich conditions, but Zn vacancy is easily formed under the Zn-poor and Se-rich conditions.
International Nuclear Information System (INIS)
Emel'yanenko, Vladimir N.; Zaitsau, Dzmitry H.; Verevkin, Sergey P.; Heintz, Andreas
2011-01-01
Highlights: → We studied the ionic liquid 1-ethanol-3-methylimidazolium dicyanamide. → Combustion calorimetry was used to derive enthalpy of formation in the liquid state. → Composite G3(MP2) method used to compute enthalpy of formation in the gaseous phase. → Enthalpy of vaporization was derived as the difference. → The liquid phase enthalpy of formation presumably obey the group additivity rules. - Abstract: The standard molar enthalpy of formation Δ f H m o (l) of the ionic liquid 1-ethanol-3-methylimidazolium dicyanamide has been determined at 298.15 K by means of combustion calorimetry. First-principles calculations of the enthalpy of formation in the gaseous phase have been performed for the ionic species using the composite G3(MP2) method. The combination of combustion calorimetry with the high-level quantum-chemical calculations allows to estimate the molar enthalpy of vaporization of the ionic liquid under study. It has been established, that the liquid phase enthalpy of formation of this ionic liquid presumably obeys the group additivity rules.
First-principles calculations of K-shell X-ray absorption spectra for warm dense nitrogen
International Nuclear Information System (INIS)
Li, Zi; Zhang, Shen; Kang, Wei; Wang, Cong; Zhang, Ping
2016-01-01
X-ray absorption spectrum is a powerful tool for atomic structure detection on warm dense matter. Here, we perform first-principles molecular dynamics and X-ray absorption spectrum calculations on warm dense nitrogen along a Hugoniot curve. From the molecular dynamics trajectory, the detailed atomic structures are examined for each thermodynamical condition. The K-shell X-ray absorption spectrum is calculated, and its changes with temperature and pressure along the Hugoniot curve are discussed. The warm dense nitrogen systems may contain isolated nitrogen atoms, N 2 molecules, and nitrogen clusters, which show quite different contributions to the total X-ray spectrum due to their different electron density of states. The changes of X-ray spectrum along the Hugoniot curve are caused by the different nitrogen structures induced by the temperature and the pressure. Some clear signatures on X-ray spectrum for different thermodynamical conditions are pointed out, which may provide useful data for future X-ray experiments.
Zhang, Yu; Tang, Fu-Ling; Xue, Hong-Tao; Lu, Wen-Jiang; Liu, Jiang-Fei; Huang, Min
2015-02-01
Using first-principles plane-wave calculations within density functional theory, we theoretically studied the atomic structure, bonding energy and electronic properties of the perfect Mo (110)/MoSe2 (100) interface with a lattice mismatch less than 4.2%. Compared with the perfect structure, the interface is somewhat relaxed, and its atomic positions and bond lengths change slightly. The calculated interface bonding energy is about -1.2 J/m2, indicating that this interface is very stable. The MoSe2 layer on the interface has some interface states near the Fermi level, the interface states are mainly caused by Mo 4d orbitals, while the Se atom almost have no contribution. On the interface, Mo-5s and Se-4p orbitals hybridize at about -6.5 to -5.0 eV, and Mo-4d and Se-4p orbitals hybridize at about -5.0 to -1.0 eV. These hybridizations greatly improve the bonding ability of Mo and Se atom in the interface. By Bader charge analysis, we find electron redistribution near the interface which promotes the bonding of the Mo and MoSe2 layer.
Løken, Andreas; Haugsrud, Reidar; Bjørheim, Tor S
2016-11-16
Differentiating chemical and thermal expansion is virtually impossible to achieve experimentally. While thermal expansion stems from a softening of the phonon spectra, chemical expansion depends on the chemical composition of the material. In the present contribution, we, for the first time, completely decouple thermal and chemical expansion through first principles phonon calculations on BaCeO 3 , providing new fundamental insights to lattice expansion. We assess the influence of defects on thermal expansion, and how this in turn affects the interpretation of chemical expansion and defect thermodynamics. The calculations reveal that the linear thermal expansion coefficient is lowered by the introduction of oxygen vacancies being 10.6 × 10 -6 K -1 at 300 K relative to 12.2 × 10 -6 K -1 for both the protonated and defect-free bulk lattice. We further demonstrate that the chemical expansion coefficient upon hydration varies with temperature, ranging from 0.070 to 0.115 per mole oxygen vacancy. Ultimately, we find that, due to differences in the thermal expansion coefficients under dry and wet conditions, the chemical expansion coefficients determined experimentally are grossly underestimated - around 55% lower in the case of 10 mol% acceptor doped BaCeO 3 . Lastly, we evaluate the effect of these volume changes on the vibrational thermodynamics.
Sun, Dongqiang; Wang, Yongxin; Zhang, Xinyi; Zhang, Minyu; Niu, Yanfei
2016-12-01
First-principles calculations based on density functional theory was used to investigate the structural, thermodynamic and elastic properties of precipitations, θ″, θ‧ and θ, in Al-Cu alloys. The values of lattice constants accord with experimental results well. The structural stability of θ is the best, followed by θ‧ and θ″. In addition, due to the highest bulk modulus, shear modulus and Young's modulus, θ possesses the best reinforcement effect in precipitation hardening process considered only from mechanical properties of perfect crystal. According to the values of B/G, Poisson's ratio and C11-C12, θ‧ has the worst ductility, while θ″ has the best ductility, the ductility of θ is in the middle. The ideal tensile strength of θ″, θ‧ and θ calculated along [100] and [001] directions are 20.87 GPa, 23.11 GPa and 24.70 GPa respectively. The analysis of electronic structure suggests that three precipitations all exhibit metallic character, and number of bonding electrons and bonding strength are the nature of different thermodynamic and elastic properties for θ″, θ‧ and θ.
International Nuclear Information System (INIS)
Dridi, Z.; Bouhafs, B.; Ruterana, P.; Aourag, H.
2002-01-01
First-principles calculations have been used to study the effect of vacancies on the structural and electronic properties in substoichiometric TiC x and TiN x . The effect of vacancies on equilibrium volumes, bulk moduli, electronic band structures and density of states of the substoichiometric phases was studied using a full-potential linear augmented plane-wave method. A model structure of eight-atom supercells with ordered vacancies within the carbon and nitrogen sublattices is used. We find that the lattice parameters of the studied stoichiometries in both TiC x and TiN x are smaller than that of ideal stoichiometric TiC and TiN. Our results for the variation of the lattice parameters and the bulk moduli for TiC x are found to be in good agreement with experiment. The variation of the energy gaps with the atomic concentration ratio shows that these compounds present the same trends. Results for TiC x are compared to a recent full-potential calculation with relaxed 16-atom supercells
Modeling of amorphous SiCxO6/5 by classical molecular dynamics and first principles calculations
Liao, Ningbo; Zhang, Miao; Zhou, Hongming; Xue, Wei
2017-02-01
Polymer-derived silicon oxycarbide (SiCO) presents excellent performance for high temperature and lithium-ion battery applications. Current experiments have provided some information on nano-structure of SiCO, while it is very challenging for experiments to take further insight into the molecular structure and its relationship with properties of materials. In this work, molecular dynamics (MD) based on empirical potential and first principle calculation were combined to investigate amorphous SiCxO6/5 ceramics. The amorphous structures of SiCO containing silicon-centered mix bond tetrahedrons and free carbon were successfully reproduced. The calculated radial distribution, angular distribution and Young’s modulus were validated by current experimental data, and more details on molecular structure were discussed. The change in the slope of Young’s modulus is related to the glass transition temperature of the material. The proposed modeling approach can be used to predict the properties of SiCO with different compositions.
Energy Technology Data Exchange (ETDEWEB)
Liu, Qi-Jun, E-mail: qijunliu@home.swjtu.edu.cn [School of Physical Science and Technology, Southwest Jiaotong University, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Chengdu 610031 (China); Bond and Band Engineering Group, Sichuan Provincial Key Laboratory (for Universities) of High Pressure Science and Technology, Southwest Jiaotong University, Chengdu 610031 (China); Qin, Han; Jiao, Zhen; Liu, Fu-Sheng [School of Physical Science and Technology, Southwest Jiaotong University, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Chengdu 610031 (China); Bond and Band Engineering Group, Sichuan Provincial Key Laboratory (for Universities) of High Pressure Science and Technology, Southwest Jiaotong University, Chengdu 610031 (China); Liu, Zheng-Tang [State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072 (China)
2016-09-01
First-principles calculations of the structural, elastic, mechanical and electronic properties of ilmenite-type ZnSnO{sub 3} under pressure have been investigated in the present paper. Our calculated lattice constants at zero pressure are in agreement with the published theoretical and experimental data. The elastic constants at zero and high pressure have been obtained, which are used to discuss the mechanical stability of ilmenite-type ZnSnO{sub 3}. The mechanical properties such as bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio under pressure have been studied. Electronic properties show that ilmenite-type ZnSnO{sub 3} is shown to be a direct bandgap of 1.063 (GGA-PW91)/3.977 (PBE0) eV. The bandgap increases with the increasing pressure. Moreover, the partial density of states has been analyzed to explain the increased bandgap. - Highlights: • Physical properties of ilmenite-type ZnSnO{sub 3} under pressure have been investigated. • Ilmenite-type ZnSnO{sub 3} behaves in a ductile manner. • Ilmenite-type ZnSnO{sub 3} is a direct bandgap compound with 3.977 eV. • Bandgap of Ilmenite-type ZnSnO{sub 3} increases with the increasing pressure.
The electronic structures and ferromagnetism of Fe-doped GaSb: The first-principle calculation study
Lin, Xue-ling; Niu, Cao-ping; Pan, Feng-chun; Chen, Huan-ming; Wang, Xu-ming
2017-09-01
The electronic structures and the magnetic properties of Fe doped GaSb have been investigated by the first-principles calculation based on the framework of the generalized gradient approximation (GGA) and GGA+U schemes. The calculated results indicated that Fe atoms tend to form the anti-ferromagnetic (AFM) coupling with the nearest-neighbor positions preferentially. Compared with the anti-ferromagnetic coupling, the ferromagnetic interactions occurred at the second nearest-neighbor and third nearest-neighbor sites have a bigger superiority energetically. The effect of strong electron correlation at Fe-d orbit taking on the magnetic properties predicted by GGA+U approach demonstrated that the ferromagnetic (FM) coupling between the Fe ions is even stronger in consideration of the strong electron correlation effect. The ferromagnetism in Fe doped GaSb system predicted by our investigation implied that the doping of Fe into GaSb can be as a vital routine for manufacturing the FM semiconductors with higher Curie temperature.
International Nuclear Information System (INIS)
Wang, Y.; Chen, W.; Chen, X.; Liu, H.Y.; Ding, Z.H.; Ma, Y.M.; Wang, X.D.; Cao, Q.P.; Jiang, J.Z.
2012-01-01
Highlights: ► Changes from NaCl-, WC- to anti-NiAs-type structures are for 4d and 5d metal monoborides. ► Vickers hardnesses of monoborides are relatively low. ► B-vacancies cause the difference in lattice parameters for IrB and PtB. ► Nonstoichiometric IrB and PtB phases synthesized. - Abstract: The crystal structures, stability, electronic and elastic properties of 4d and 5d transition metal monoborides have been studied by first principles calculations. It is found that NaCl-type ZrB, NbB, MoB, HfB, TaB and WB, WC-type TcB, RuB, ReB, OsB and IrB, and anti-NiAs-type RhB and PdB are thermodynamically stable at zero pressure. They all are metallic. The Vickers hardnesses of these monoborides are relatively low as compared with monocarbides and mononitrides. It is clarified that the presence of B-vacancies is the origin for the difference of lattice parameters between theoretical and experimental results for WC-type IrB and anti-NiAs-type PtB while IrB and PtB with stoichiometry from calculations are revealed to be mechanically unstable and dynamically unstable, respectively.
Energy Technology Data Exchange (ETDEWEB)
Wang, Y.; Chen, W. [International Center for New-Structured Materials (ICNSM), Zhejiang University, and Laboratory of New-Structured Materials, State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Chen, X.; Liu, H.Y. [State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012 (China); Ding, Z.H.; Ma, Y.M. [State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130012 (China); Wang, X.D.; Cao, Q.P. [International Center for New-Structured Materials (ICNSM), Zhejiang University, and Laboratory of New-Structured Materials, State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Jiang, J.Z., E-mail: jiangjz@zju.edu.cn [International Center for New-Structured Materials (ICNSM), Zhejiang University, and Laboratory of New-Structured Materials, State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China)
2012-10-15
Highlights: Black-Right-Pointing-Pointer Changes from NaCl-, WC- to anti-NiAs-type structures are for 4d and 5d metal monoborides. Black-Right-Pointing-Pointer Vickers hardnesses of monoborides are relatively low. Black-Right-Pointing-Pointer B-vacancies cause the difference in lattice parameters for IrB and PtB. Black-Right-Pointing-Pointer Nonstoichiometric IrB and PtB phases synthesized. - Abstract: The crystal structures, stability, electronic and elastic properties of 4d and 5d transition metal monoborides have been studied by first principles calculations. It is found that NaCl-type ZrB, NbB, MoB, HfB, TaB and WB, WC-type TcB, RuB, ReB, OsB and IrB, and anti-NiAs-type RhB and PdB are thermodynamically stable at zero pressure. They all are metallic. The Vickers hardnesses of these monoborides are relatively low as compared with monocarbides and mononitrides. It is clarified that the presence of B-vacancies is the origin for the difference of lattice parameters between theoretical and experimental results for WC-type IrB and anti-NiAs-type PtB while IrB and PtB with stoichiometry from calculations are revealed to be mechanically unstable and dynamically unstable, respectively.
Energy Technology Data Exchange (ETDEWEB)
Li, Ji-Hong [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Longdong Univ., Qingyang (China). College of Physics and Electronic Engineering; Zhu, Xu-Hui [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Cheng, Yan [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Sichuan Univ., Chengdu (China). Key Laboratory of High Energy Density Physics and Technology of Ministry of Education; Ji, Guang-Fu [Chinese Academy of Engineering Physics, Mianyang (China). National Key Laboratory of Shock Wave and Detonation Physics
2015-07-01
Based on the first-principles density functional theory calculations combined with the quasi-harmonic Debye model, the pressure dependencies of the structural, elastic, electronic and thermal properties of Li{sub 2}AgSb were systematically investigated. The calculated lattice parameters and unit cell volume of Li{sub 2}AgSb at the ground state were in good agreement with the available experimental data. The obtained elastic constants, the bulk modulus and the shear modulus revealed that Li{sub 2}AgSb is mechanically stable and behaves in a ductile manner under the applied pressure. The elasticity-relevant properties, the Young's modulus and the Poisson's ratio showed that pressure can enhance the stiffness of Li{sub 2}AgSb and that Li{sub 2}AgSb is mechanically stable up to 20 GPa. The characteristics of the band structure and the partial density of states of Li{sub 2}AgSb were analysed, showing that Li{sub 2}AgSb is a semiconductor with a direct band gap of 217 meV at 0 GPa and that the increasing pressure can make the band structure of Li{sub 2}AgSb become an indirect one. Studies have shown that, unlike temperature, pressure has little effect on the heat capacity and the thermal expansion coefficient of Li{sub 2}AgSb.
International Nuclear Information System (INIS)
Thore, A.; Dahlqvist, M.; Alling, B.; Rosén, J.
2014-01-01
In this paper, we report the by first-principles predicted properties of the recently discovered magnetic MAX phase Mn 2 GaC. The electronic band structure and vibrational dispersion relation, as well as the electronic and vibrational density of states, have been calculated. The band structure close to the Fermi level indicates anisotropy with respect to electrical conductivity, while the distribution of the electronic and vibrational states for both Mn and Ga depend on the chosen relative orientation of the Mn spins across the Ga sheets in the Mn–Ga–Mn trilayers. In addition, the elastic properties have been calculated, and from the five elastic constants, the Voigt bulk modulus is determined to be 157 GPa, the Voigt shear modulus 93 GPa, and the Young's modulus 233 GPa. Furthermore, Mn 2 GaC is found relatively elastically isotropic, with a compression anisotropy factor of 0.97, and shear anisotropy factors of 0.9 and 1, respectively. The Poisson's ratio is 0.25. Evaluated elastic properties are compared to theoretical and experimental results for M 2 AC phases where M = Ti, V, Cr, Zr, Nb, Ta, and A = Al, S, Ge, In, Sn.
International Nuclear Information System (INIS)
Lordi, V; Aberg, D; Erhart, P; Wu, K J
2007-01-01
The development of high resolution, room temperature semiconductor radiation detectors requires the introduction of materials with increased carrier mobility-lifetime (μτ) product, while having a band gap in the 1.4-2.2 eV range. AlSb is a promising material for this application. However, systematic improvements in the material quality are necessary to achieve an adequate μτ product. We are using a combination of simulation and experiment to develop a fundamental understanding of the factors which affect detector material quality. First principles calculations are used to study the microscopic mechanisms of mobility degradation from point defects and to calculate the intrinsic limit of mobility from phonon scattering. We use density functional theory (DFT) to calculate the formation energies of native and impurity point defects, to determine their equilibrium concentrations as a function of temperature and charge state. Perturbation theory via the Born approximation is coupled with Boltzmann transport theory to calculate the contribution toward mobility degradation of each type of point defect, using DFT-computed carrier scattering rates. A comparison is made to measured carrier concentrations and mobilities from AlSb crystals grown in our lab. We find our predictions in good quantitative agreement with experiment, allowing optimized annealing conditions to be deduced. A major result is the determination of oxygen impurity as a severe mobility killer, despite the ability of oxygen to compensation dope AlSb and reduce the net carrier concentration. In this case, increased resistivity is not a good indicator of improved material performance, due to the concomitant sharp reduction in μτ
Strong enhancement of piezoelectric constants in ScxAl1−xN: First-principles calculations
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Hiroyoshi Momida
2016-06-01
Full Text Available We theoretically investigate the piezoelectricity of ScxAl1−xN in the entire range of x by first-principles calculations. We find that the piezoelectric constants of wurtzite-type ScxAl1−xN significantly enhance as x increases from 0 to 0.75. However, the energy stability analyses between structure phases show that the cubic-type phases become more stable than the wurtzite-type phases at x of approximately 0.5 and higher, interfering with the ability of wurtzite-type ScxAl1−xN to realize the maximum piezoelectricity. Moreover, our study on element combination dependences on piezoelectricity in A0.5B0.5N (A = Sc, Y, La and B = Al, Ga, In indicates that Sc, Y, and La have the strongest effect on the enhancement of piezoelectric constants in AlN, GaN, and InN, respectively.
Directory of Open Access Journals (Sweden)
Soleyman Majidi
Full Text Available In this work, we investigated the electronic and structural properties of various defects including single Sn and C vacancies, double vacancy of the Sn and C atoms, anti-sites, position exchange and the Stone–Wales (SW defects in SnC nanosheets by using density-functional theory (DFT. We found that various vacancy defects in the SnC monolayer can change the electronic and structural properties. Our results show that the SnC is an indirect band gap compound, with the band gap of 2.10 eV. The system turns into metal for both structure of the single Sn and C vacancies. However, for the double vacancy contained Sn and C atoms, the structure remains semiconductor with the direct band gap of 0.37 eV at the G point. We also found that for anti-site defects, the structure remains semiconductor and for the exchange defect, the structure becomes indirect semiconductor with the K-G point and the band gap of 0.74 eV. Finally, the structure of SW defect remains semiconductor with the direct band gap at K point with band gap of 0.54 eV. Keywords: SnC nanosheets, Density-functional theory, First-principles calculations, Electronic density of states, Band gap
First-principles calculation on oxygen ion migration in alkaline-earth doped La2GeO5
International Nuclear Information System (INIS)
Thuy Linh, Tran Phan; Sakaue, Mamoru; Aspera, Susan Meñez; Alaydrus, Musa; Wungu, Triati Dewi Kencana; Hoang Linh, Nguyen; Kasai, Hideaki; Mohri, Takahiro; Ishihara, Tatsumi
2014-01-01
By using first-principles calculations based on the density functional theory, we investigated the doping effects of alkaline-earth metals (Ba, Sr and Ca) in monoclinic lanthanum germanate La 2 GeO 5 on its oxygen ion conduction. Although the lattice parameters of the doped systems changed due to the ionic radii mismatch, the crystal structures remained monoclinic. The contribution of each atomic orbital to electronic densities of states was evaluated from the partial densities of states and partial charge densities. It was confirmed that the materials behaved as ionic crystals comprising of cations of La and dopants and anions of oxygen and covalently formed GeO 4 . The doping effect on the activation barrier for oxygen hopping to the most stable oxygen vacancy site was investigated by the climbing-image nudged elastic band method. By tracing the charge density change during the hopping, it was confirmed that the oxygen motion is governed by covalent interactions. The obtained activation barriers showed excellent quantitative agreements with an experiment for the Ca- and Sr-doped systems in low temperatures as well as the qualitative trend, including the Ba-doped system. (paper)
Liu, Gang; Zhou, Jian; Wang, Hui
2017-06-14
Based on Grüneisen's theory, the elastic properties and thermal expansion of bulk SnSe with the Pnma phase are investigated by using first-principles calculations. Our numerical results indicate that the linear thermal expansion coefficient along the a direction is smaller than the one along the b direction, while the one along the c direction shows a significant negative value, even at high temperature. The numerical results are in good accordance with experimental results. In addition, generalized and macroscopic Grüneisen parameters are also presented. It is also found that SnSe possesses negative Possion's ratio. The contributions of different phonon modes to NTE along the c direction are investigated, and it is found that the two modes which make the most important contributions to NTE are transverse vibrations perpendicular to the c direction. Finally, we analyze the relation of elastic constants to negative thermal expansion, and demonstrate that negative thermal expansion can also occur even with all positive macroscopic Grüneisen parameters.
Study on the intrinsic defects in ZnO by combing first-principle and thermodynamic calculations
Ma, Changmin; Liu, Tingyu; Chang, Qiuxiang
2015-11-01
In this paper, the intrinsic point defects in ZnO crystal have been studied by the approach that integrates first-principles, thermodynamic calculations and the contributions of vibrational entropy. With temperature increasing and oxygen partial pressure decreasing, the formation energies of oxygen vacancy (VO), zinc interstitial (Zni) and zinc anti-site (ZnO) are decreasing, while it increases for zinc vacancy (VZn), oxygen interstitial (Oi) and oxygen anti-site (OZn). They are more sensitive to temperature than oxygen partial pressure. There are two interesting phenomena. First, VO or VZn have the lowest formation energies for whole Fermi level at special environment condition (such as at T = 300K, about PO2 = 10-10atm or T = 1500K, about PO2 = 104atm) and intrinsic p-type doping of ZnO is possible by VZn at these special conditions. Second, VO as donors have lowest formation energy for all Fermi level at high temperature and low oxygen partial pressure (T = 1500K, PO2 = 10-10atm). According to our analysis, the VO could produce n-type doping in ZnO at these special conditions and change p-type ZnO to n-type ZnO at condition from low temperature and high oxygen partial pressure to high temperature and low oxygen partial pressure.
International Nuclear Information System (INIS)
Hsu, Hsiao-Hsuan; Cheng, Chun-Hu; Chiou, Shan-Haw; Huang, Chiung-Hui; Liu, Chia-Mei; Lin, Yu-Li; Chao, Wen-Hsuan; Yang, Ping-Hsing; Chang, Chun-Yen; Cheng, Chin-Pao
2014-01-01
Highlights: • The diffusion behavior was originated from high-vapor-pressure Te atom. • Te out-diffusion is main driving force to cause inter-diffusion effect. • Mid-band Ta and TaN with favored ohmic-like contact showed small diffusion tail. • Strong Ta-N bonding and high total energy suppressed interfacial layer formation. -- Abstract: This study involved developing robust diffusion barrier for n-type antimony telluride (SbTe) thermoelectric devices. Compared to conventional Ni barrier, the mid-band metals of Ta and TaN with favored ohmic-like contact exhibited smaller diffusion tail because of structurally stable interface on SbTe, which have been supported by first-principles calculations and demonstrated by experimental results. Furthermore, the TaN barrier has strong ionic Ta–N bonding and a high total energy of −4.7 eV/atom that could effectively suppress the formation of SbTe-compounds interfacial layer
Andrés, Juan; Gracia, Lourdes; Gouveia, Amanda Fernandes; Ferrer, Mateus Meneghetti; Longo, Elson
2015-10-09
Morphology is a key property of materials. Owing to their precise structure and morphology, crystals and nanocrystals provide excellent model systems for joint experimental and theoretical investigations into surface-related properties. Faceted polyhedral crystals and nanocrystals expose well-defined crystallographic planes depending on the synthesis method, which allow for thoughtful investigations into structure-reactivity relationships under practical conditions. This feature article introduces recent work, based on the combined use of experimental findings and first-principles calculations, to provide deeper knowledge of the electronic, structural, and energetic properties controlling the morphology and the transformation mechanisms of different metals and metal oxides: Ag, anatase TiO2, BaZrO3, and α-Ag2WO4. According to the Wulff theorem, the equilibrium shapes of these systems are obtained from the values of their respective surface energies. These investigations are useful to gain further understanding of how to achieve morphological control of complex three-dimensional crystals by tuning the ratio of the surface energy values of the different facets. This strategy allows the prediction of possible morphologies for a crystal and/or nanocrystal by controlling the relative values of surface energies.
Energy Technology Data Exchange (ETDEWEB)
Cai, Linlin; Tian, Yanli; Yuan, Xiaobo; Hu, Guichao; Ren, Junfeng, E-mail: renjf@sdnu.edu.cn
2016-12-15
Highlights: • Thiophene molecule could be spin polarized when adsorbed at Co(001), Fe(100), and Ni(111) surfaces. • The biggest spin polarization will be obtained when the thiophene molecule adsorbed at the Fe(100) surface. • The spin polarization is originated from the interfacial orbital hybridizations between the 3d orbital of ferromagnetic electrodes and the 2p orbital of the thiophene molecule. - Abstract: First principles calculations are adopted to study the spin polarization properties of thiophene molecule which adsorbed at the Co, Fe, and Ni electrode surfaces. The density of states, spin-polarized density distributions as well as the differential charge density distributions are obtained. It is found that the p orbital of the thiophene molecule will interact with the d orbital of the ferromagnetic electrodes, which will generate new spin coupling states and lead to obvious spin polarization in the thiophene molecule. Different electrodes induce different spin polarization properties, and in which the Fe electrode will bring the biggest spin polarization of the thiophene molecule. People can selectively and efficiently inject spin polarized electrons into molecules by choosing suitable ferromagnetic electrodes in organic spintronic devices.
International Nuclear Information System (INIS)
Chen, Zhi-Yuan; Xu, Bin; Gao, G.Y.
2013-01-01
The structural, electronic and magnetic properties of zinc-blende TiBi are investigated by using the first-principles full-potential linearized augmented plane-wave method. It is found that zinc-blende TiBi exhibits half-metallic ferromagnetism with the energy gap of 1.39 eV in the minority-spin channel. The calculated total magnetic moment of 1.00 µ B per formula unit mainly originates from the Ti atom. We also show that the half-metallicity of zinc-blende TiBi can be maintained up to 3% compression and 5% expansion of lattice constant with respect to the equilibrium lattice, and zinc-blende TiBi is still half-metallic when the spin–orbit coupling is considered. The robust half-metallicity and low magnetic moment make zinc-blende TiBi a potential candidate for spintronic applications. - Highlights: • Half-metallic ferromagnetism in zinc-blende TiBi. • Zinc-blende TiBi has low magnetic moment of 1.00 µ B /f.u. • Spin–orbit coupling does not destroy the half-metallicity of zinc-blende TiBi
First principles total energy calculations of the structural and electronic properties of ScxGa1-xN
International Nuclear Information System (INIS)
Moreno-Armenta, Maria Guadalupe; Mancera, Luis; Takeuchi, Noboru
2003-01-01
Using first principles total energy calculations within the the full-potential linearized augmented plane wave (FP-LAPW) method, we have investigated the structural and electronic properties of Sc x Ga 1-x N, with Sc concentrations varying from 0% up to 100%. In particular we have studied the relative stability of several configurations of Sc x Ga 1-x N in wurtzite-like structures (the ground state configuration of GaN), or in rocksalt-like structures (the ground state configuration of ScN). It is found that for Sc concentrations less than ∼65%, the favored structure is a wurtzite-like one, while for Sc concentrations greater than ∼65%, the favored structure is a NaCl-like structure. It is also found that for the wurtzite-like crystals, the fundamental gap is large and direct. For the rocksalt crystals the fundamental gap is small and indirect, but with an additional larger direct gap. In agreement with the experiments of Little and Kordesch [Appl. Phys. Lett. 78, 2891 (2001)] we found a decrease of the band gap with the increase of the Sc concentration. (Abstract Copyright [2003], Wiley Periodicals, Inc.)
Energy Technology Data Exchange (ETDEWEB)
Han, Yong; Evans, James W. [Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA and Ames Laboratory—U.S. Department of Energy, Iowa State University, Ames, Iowa 50011 (United States)
2015-10-28
Large-scale first-principles density functional theory calculations are performed to investigate the adsorption and diffusion of Ru adatoms on monolayer graphene (G) supported on Ru(0001). The G sheet exhibits a periodic moiré-cell superstructure due to lattice mismatch. Within a moiré cell, there are three distinct regions: fcc, hcp, and mound, in which the C{sub 6}-ring center is above a fcc site, a hcp site, and a surface Ru atom of Ru(0001), respectively. The adsorption energy of a Ru adatom is evaluated at specific sites in these distinct regions. We find the strongest binding at an adsorption site above a C atom in the fcc region, next strongest in the hcp region, then the fcc-hcp boundary (ridge) between these regions, and the weakest binding in the mound region. Behavior is similar to that observed from small-unit-cell calculations of Habenicht et al. [Top. Catal. 57, 69 (2014)], which differ from previous large-scale calculations. We determine the minimum-energy path for local diffusion near the center of the fcc region and obtain a local diffusion barrier of ∼0.48 eV. We also estimate a significantly lower local diffusion barrier in the ridge region. These barriers and information on the adsorption energy variation facilitate development of a realistic model for the global potential energy surface for Ru adatoms. This in turn enables simulation studies elucidating diffusion-mediated directed-assembly of Ru nanoclusters during deposition of Ru on G/Ru(0001)
International Nuclear Information System (INIS)
Ganeshan, S.; Hector, L.G.; Liu, Z.-K.
2011-01-01
Research highlights: → Implemented the eight frequency model for impurity diffusion in hexagonal metals. → Model inputs were energetics/vibrational properties from first princples. → Predicted diffusion coefficients for Al, Ca, Zn and Sn impurity diffusion in Mg. → Successful prediction of partial correlation factors and jump frequencies. → Good agreement between calculated and experimental results. - Abstract: Diffusion in dilute Mg-X alloys, where X denotes Al, Zn, Sn and Ca impurities, was investigated with first-principles density functional theory in the local density approximation. Impurity diffusion coefficients were computed as a function of temperature using the 8-frequency model which provided the relevant impurity and solvent (Mg) jump frequencies and correlation factors. Minimum energy pathways for impurity diffusion and associated saddle point structures were computed with the climbing image nudged elastic band method. Vibrational properties were obtained with the supercell (direct) method for lattice dynamics. Calculated diffusion coefficients were compared with available experimental data. For diffusion between basal planes, we find D Mg-Ca > D Mg-Zn > D Mg-Sn > D Mg-Al, where D is the diffusion coefficient. For diffusion within a basal plane, the same trend holds except that D Mg-Zn overlaps with D Mg-Al at high temperatures and D Mg-Sn at low temperatures. These trends were explored with charge density contours in selected planes of each Mg-X alloy, the variation of the activation energy for diffusion with the atomic radius of each impurity and the electronic density of states. The theoretical methodology developed herein can be applied to impurity diffusion in other hexagonal materials.
International Nuclear Information System (INIS)
Mohanta, S.K.; Mishra, S.N.; Srivastava, S.K.
2014-01-01
We present first principles calculations of electronic structure and magnetic properties of dilute transition metal (3d, 4d and 5d) impurities in a Gd host. The calculations have been performed within the density functional theory using the full potential linearized augmented plane wave technique and the GGA+U method. The spin and orbital contributions to the magnetic moment and the hyperfine fields have been computed. We find large magnetic moments for 3d (Ti–Co), 4d (Nb–Ru) and 5d (Ta–Os) impurities with magnitudes significantly different from the values estimated from earlier mean field calculation [J. Magn. Magn. Mater. 320 (2008) e446–e449]. The exchange interaction between the impurity and host Gd moments is found to be positive for early 3d elements (Sc–V) while in all other cases an anti-ferromagnetic coupling is observed. The trends for the magnetic moment and hyperfine field of d-impurities in Gd show qualitative difference with respect to their behavior in Fe, Co and Ni. The calculated total hyperfine field, in most cases, shows excellent agreement with the experimental results. A detailed analysis of the Fermi contact hyperfine field has been made, revealing striking differences for impurities having less or more than half filled d-shell. The impurity induced perturbations in host moments and the change in the global magnetization of the unit cell have also been computed. The variation within each of the d-series is found to correlate with the d–d hybridization strength between the impurity and host atoms. - Highlights: • Detailed study of transition metal impurities in ferromagnetic Gd has been carried out. • The trends in impurity magnetic moment are qualitatively different from Fe, Co and Ni. • The variation within each of the d-series is found to correlate with the d–d hybridization strength between the impurity and host atoms. • Experimental trend in a hyperfine field has been reproduced successfully
Theoretical investigations on the α-LiAlO{sub 2} properties via first-principles calculation
Energy Technology Data Exchange (ETDEWEB)
Ma, Sheng-Gui [Institute of Atomic and Molecular Physics, Sichuan University, 610065, Chengdu (China); Gao, Tao, E-mail: gaotao@scu.edu.cn [Institute of Atomic and Molecular Physics, Sichuan University, 610065, Chengdu (China); Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu, 610064 (China); Li, Shi-Chang; Ma, Xi-Jun; Shen, Yan-Hong [Institute of Atomic and Molecular Physics, Sichuan University, 610065, Chengdu (China); Lu, Tie-Cheng, E-mail: lutiecheng@scu.edu.cn [Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu, 610064 (China); College of Physical Science and Technology, Sichuan University, Chengdu 610065 (China)
2016-12-15
Highlights: • Our calculation indicates that the α-LiAlO{sub 2} is an indirect band gap insulator of 6.319 eV. • The mechanical properties of α-LiAlO{sub 2} are predicted. • The complete phonon frequencies of α-LiAlO{sub 2} at gamma point for the infrared and Raman modes are assigned which to distinguish the α-LiAlO{sub 2} and γ-LiAlO{sub 2} in ITER and in MCFC. - Abstract: The physical properties including the structural, electronic, mechanical, lattice dynamical and thermodynamic properties of α-LiAlO{sub 2} are investigated using first-principles calculation. It is found that α-LiAlO{sub 2} is an insulator with an indirect gap of 6.319 eV according to band structure and density of states. The elastic constants are obtained and the results indicate that α-LiAlO{sub 2} is mechanically stable. The mechanical properties including bulk modulus (B), shear modulus (G), Young’s modulus (E), Poisson’s ratio (υ) are predicted with the value of 147.0 GPa, 105.2 GPa, 254.8 GPa and 0.211, respectively. The phonon dispersion curves and the phonon density of states are also calculated. The calculated phonon frequencies for the Raman-active and the infrared-active modes considering the LO-TO splitting are assigned. The two Raman active frequencies are 407.0 cm{sup −1} of E{sub g} mode and 628.8 cm{sup −1} of A{sub 1g} mode, and show satisfactory agreement with experiment. The thermodynamic functions such as ΔF, ΔE, C{sub V} and S is predicted by using the phonon density of states. These results provide valuable information for further insight into the properties of α-LiAlO{sub 2} in atomic scales, which is strategically important in ITER and in molten carbonate fuel cells (MCFC).
Energy Technology Data Exchange (ETDEWEB)
Zhang, Z.Y. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Si, M.S., E-mail: sims@lzu.edu.cn [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Peng, S.L. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Zhang, F. [Key Lab of Photovoltaic Materials of Henan Province, Henan University, Kaifeng 475001 (China); Wang, Y.H.; Xue, D.S. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China)
2015-11-15
Blue phosphorene (BP) was theoretically predicted to be thermally stable recently. Considering its similar in-layer hexagonal lattice to MoS{sub 2}, MoS{sub 2} could be an appropriate substrate to grow BP in experiments. In this work, the van der Waals (vdW) heterostructures are constructed by stacking BP on top of MoS{sub 2}. The thermal stability and electronic structures are evaluated based on first principles calculations with vdW-corrected exchange-correlation functional. The formation of the heterostructures is demonstrated to be exothermic and the most stable stacking configuration is confirmed. The heterostructures BP/MoS{sub 2} preserve both the properties of BP and MoS{sub 2} but exhibit relatively narrower bandgaps due to the interlayer coupling effect. The band structures can be further engineered by applying external electric fields. An indirect–direct bandgap transition in bilayer BP/MoS{sub 2} is demonstrated to be controlled by the symmetry property of the built-in electric dipole fields. - Graphical abstract: An indirect-direct band gap transition occurs in van der Waals heterostructure of MoS{sub 2}/BP under external electric fields which is demonstrated to be controlled by the symmetry of the built-in electric dipole fields. - Highlights: • The stacking of heterostructures of BP/MoS{sub 2} is demonstrated to be exothermic. • This suggests that it is possible to grow BP using MoS{sub 2} as the substrate. • The band structures of the heterostructures are exploited. • It realizes an indirect–direct gap transition under external electric fields. • The symmetry of the built-in electric dipole fields controls such gap transition.
Liu, Huan; Zhang, Jian-Min
2018-05-01
The structural, electronic, and magnetic properties of (ZnO)12 clusters doped with Cr atoms have been investigated by using spin-polarized first-principles calculations. The exohedral a3 isomer is favorable than endohedral a2 isomer. The isomer a1 and a5 respectively have the narrowest and biggest gap between highest unoccupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO) of 0.473 and 1.291 eV among these five monodoped isomers. The magnetic moment may be related to the local environment around the Cr atom that the a2 isomer whose total magnetic moment is 6 μB while the other monodoped isomers which all isomers have nearly total magnetic moments 4 μB . For Cr-doped (ZnO)12 on a1 or a3 isomer, the DOS of spin-up channel cross the Fermi level EF showing a finite magnitude near the Fermi level which might be useful for half metallic character. For the bidoped cases, the exohedral isomers are found to be most favorable. Including all bipoed isomers of substitutional, exohedral and endohedral bidoped clusters, the total magnetic moment of the ferromagnetic (antiferromagnetic) state is 8 (0) μB and the HOMO-LUMO gap of antiferromagnetic state is slightly larger than that of ferromagnetic state. The magnetic coupling between the Cr atoms in bidoped configurations is mainly governed by the competition between direct Cr and Cr atoms antiferromagnetic interaction and the ferromagnetic interaction between two Cr atoms via O atom due to strong p-d hybridization. Most importantly, we show that the exohedral bidoped (ZnO)12 clusters favor the ferromagnetic state, which may have the future applications in spin-dependent magneto-optical and magneto-electrical devices.
Energy Technology Data Exchange (ETDEWEB)
Aoki, M., E-mail: cmaoki@mail.ecc.u-tokyo.ac.jp; Masuda, S.
2015-10-01
Understanding and controlling local electronic structures at organic–metal interfaces are crucial for fabricating novel organic-based electronics, as in the case of heterojunctions in semiconductor devices. Here, we report recent studies of valence electronic states at organic–metal interfaces (especially those near the Fermi level of a metal substrate) by the combined analysis of ultraviolet photoemission spectroscopy (UPS), metastable atom electron spectroscopy (MAES), and first-principles calculations. New electronic states in the HOMO (highest occupied molecular orbital)–LUMO (lowest unoccupied molecular orbital) gap formed at an organic–metal interface are classified as a chemisorption-induced gap state (CIGS) and a complex-based gap state (CBGS). The CIGS is further characterized by an asymptotic feature of the metal wave function in the chemisorbed species. The CIGSs in alkanethiolates on Pt(1 1 1) and C{sub 60} on Pt(1 1 1) can be regarded as damping and propagating types, respectively. The CBGSs in K-doped dibenzopentacene (DBP) are composed of DBP-derived MOs and K sp states and distributed over the complex film. No metallic structures were found in the K{sub 1}DBP and K{sub 3}DBP phases, suggesting that they are Mott–Hubbard insulators due to strong electron correlation. The local electronic structures of a pentacene film bridged by Au electrodes under bias voltages were examined by an FET-like specimen. The pentacene-derived bands were steeply shifted at the positively biased electrode, reflecting the p-type character of the film.
First-principles calculations of structural, electronic and optical properties of CdxZn1-xS alloys
Noor, Naveed Ahmed; Ikram, Nazma; Ali, Sana Zulfiqar; Nazir, Safdar; Alay-E-Abbas, Syed Muhammad; Shaukat, Ali
2010-01-01
Structural, electronic and optical properties of ternary alloy system CdxZn1-xS have been studied using first-principles approach based on density functional theory. Electronic structure, density of states and energy band gap values for CdxZn1-xS
A theoretical study of perovskite CsXCl3 (X=Pb, Cd) within first principles calculations
Energy Technology Data Exchange (ETDEWEB)
Ilyas, Bahaa M., E-mail: bahaastring@gmail.com [Department of Physics, University Of Dohuk (Iraq); Elias, Badal H. [Laboratory of Theoretical Physics, Department of Physics, Faculty of Sciences, University of Dohuk (Iraq)
2017-04-01
the optical properties, both the static refractive index and dielectric constant are found to be related proportionally to the indirect band gap of CsCdCl{sub 3}. The refractive index, extinction coefficient, complex dielectric function, energy loss function, optical conductivity, reflectivity and absorption coefficient for 0–25 eV incident photon energies have been predicted. The phonon properties were investigated using response functions to predict the phonon lattice dispersion and the density of states. The thermal effect on the heat capacities, entropy, enthalpy and Free energy were predicted and compared using both the quasi-harmonic Debye model and response functions, the latter provided far better results. To the best of the authors' knowledge, most of the studied properties have not been experimentally reported so far. Generally, the computed results for both CsCdCl{sub 3} and CsPbCl{sub 3} are very satisfactory and show good agreement with other calculations.
International Nuclear Information System (INIS)
Rohlfing, Michael; Tiago, M.L.; Louie, Steven G.
2000-01-01
Experimental and theoretical studies have shown that excitonic effects play an important role in the optical properties of conjugated polymers. The optical absorption spectrum of trans-polyacetylene, for example, can be understood as completely dominated by the formation of exciton bound states. We review a recently developed first-principles method for computing the excitonic effects and optical spectrum, with no adjustable parameters. This theory is used to study the absorption spectrum of two conjugated polymers: trans-polyacetylene and poly-phenylene-vinylene(PPV)
Energy Technology Data Exchange (ETDEWEB)
Rohlfing, Michael; Tiago, M.L.; Louie, Steven G.
2000-03-20
Experimental and theoretical studies have shown that excitonic effects play an important role in the optical properties of conjugated polymers. The optical absorption spectrum of trans-polyacetylene, for example, can be understood as completely dominated by the formation of exciton bound states. We review a recently developed first-principles method for computing the excitonic effects and optical spectrum, with no adjustable parameters. This theory is used to study the absorption spectrum of two conjugated polymers: trans-polyacetylene and poly-phenylene-vinylene(PPV).
Ising-type anisotropy and spin state transitions in GdBaCo2O5.5 from first-principles calculations
International Nuclear Information System (INIS)
Pardo, V.; Baldomir, D.; Castro, J.; Iglesias, M.; Arias, J.E.
2007-01-01
Ising-type behaviour of GdBaCo 2 O 5.5 is analyzed from first principles calculations of the electronic structure of the material. The variations in its magnetic anisotropy properties in the different possible magnetic configurations is analyzed. A possible metallic phase is studied and an analysis of the electronic structure of the Co 3+ ions in that phase is presented
International Nuclear Information System (INIS)
Higuchi, Yuji; Ishikawa, Takeshi; Ozawa, Nobuki; Chazeau, Laurent; Cavaillé, Jean-Yves; Kubo, Momoji
2015-01-01
Highlights: • We study the different dynamics of dissociation and recombination processes. • Hydrogen at the chain ends collides each other in the recombination process. • Dissociation and recombination processes take different pathway. - Abstract: We investigate the different dynamics of the stress-induced dissociation and recombination reactions in a model of polyethylene by a first-principles molecular dynamics simulation at the B3LYP/6-31g(d) level. The dissociation under external forces acting on the chemical reaction site at 300 K follows the same pathway as the one calculated by the static first-principles method because it has a similar activation barrier to that of the static first-principles calculation. On the other hand, in the recombination process, thermal fluctuations causes collisions between hydrogen atoms at the chain ends. Furthermore, when external forces do not directly act on the chemical reaction site, two different dissociation processes are observed. On the other hand, recombination process is not observed due to rarely contact of the radical carbon. These results indicate that dissociation and recombination dynamics are very different, showing the importance of the dynamic calculation.
International Nuclear Information System (INIS)
Paglia, G.; Buckely, C.E.; O'Connor, B.H.; Van Riessen, A.; Rohl, A.L.; Gale, J.D.
2002-01-01
Full text: Because of its hardness, abrasion resistance, mechanical strength, corrosion resistance, and good electrical insulation, alumina (AI 2 O 3 ) is a material of high technological and industrial significance. Alumina exists in a variety of metastable structures including the γ, η, θ, K, and χ aluminas, as well as its stable α alumina phase. The crystal structure of the γ-phase in alumina has attracted considerable attention over the past 40 years, with various reports attributing either a cubic or tetragonal structure to this phase. Consensus on the definitive structure of γ-alumina (γ-AI 2 O 3 ) has yet to be reached. Rapid advancement has occurred in the field of computational materials science in recent times. Huge advances in computing power during this period have made ft possible to apply the laws of quantum mechanics to the study of macroscopic properties of real materials at the atomic level. Predicting the properties of materials by theoretical means complements the traditional experimental approaches. This research is directed at determining the structure of γ-Al 2 O 3 using theoretical first principles and empirical computational techniques combined with experimental methods. The purpose of this presentation is to discuss the problems associated with determining the structure of γ-AI 2 O 3 and to outline the methodology being applied to solve it. Copyright (2002) Australian X-ray Analytical Association Inc
First-principles calculations of structural, electronic and optical properties of CdxZn1-xS alloys
Noor, Naveed Ahmed
2010-10-01
Structural, electronic and optical properties of ternary alloy system CdxZn1-xS have been studied using first-principles approach based on density functional theory. Electronic structure, density of states and energy band gap values for CdxZn1-xS are estimated in the range 0 ≤ x ≤ 1 using both the standard local density approximation (LDA) as well as the generalized gradient approximations (GGA) of Wu-Cohen (WC) for the exchange-correlation potential. It is observed that the direct band gap EgΓ-Γ of CdxZn1-xS decreases nonlinearly with the compositional parameter x, as observed experimentally. It is also found that Cd s and d, S p and Zn d states play a major role in determining the electronic properties of this alloy system. Furthermore, results for complex dielectric constant ε(ω), refractive index n(ω), normal-incidence reflectivity R(ω), absorption coefficient α(ω) and optical conductivity σ(ω) are also described in a wide range of the incident photon energy and compared with the existing experimental data. © 2010 Elsevier B.V. All rights reserved.
International Nuclear Information System (INIS)
Yaita, Tsuyoshi; Kobayashi, Toru; Ikeda, Takashi; Matsumura, Daiju; Machida, Masahiko; Okumura, Masahiko; Nakamura, Hiroki
2014-01-01
The radioactive Cs released from Fukushima Dai-ichi Nuclear Power Plant accident is one of the important sources to increase air dose rate in environment, and thus the local and Japanese governments are still promoting the decontamination project in the contaminated area in Fukushima. On this backgrounds, in this study, 'the comprehensive researches', i.e., the elucidation of Cs speciation through the structural and electronic structural studies in clay minerals for supporting to develop the promising volume reduction methods of soil wastes (we will not touch the chemical treatment, wet classification, incineration, and alkaline fusion methods in this article) and the evaluation of Cs stability in soil wastes over mid- to long-term period, and the field investigation for elucidation of seasonal variation of bottom soil of agricultural reservoir in litate village on considering the features of local soil in Fukushima, have been performed. In this article, we introduce a part of the results obtaining by the synchrotron based X-ray analysis and the first principle molecular dynamics simulation methods. (author)
Saidi, F.; Sebaa, N.; Mahmoudi, A.; Aourag, H.; Merad, G.; Dergal, M.
2018-06-01
We performed first-principle calculations to investigate structural, phase stability, electronic and mechanical properties for the Laves phases YM2 (M = Mn, Fe, Co) with C15, C14 and C36 structures. We used the density functional theory within the framework of both pseudo-potentials and plane wave basis using VASP (Vienna Ab Initio Software Package). The calculated equilibrium structural parameters are in accordance with available theoretical values. Mechanical properties were calculated, discussed, and analyzed with data mining approach in terms of structure stability. The results reveal that YCo2 is harder than YFe2 and YMn2.
Nakayama, Masanobu; Kotobuki, Masashi; Munakata, Hirokazu; Nogami, Masayuki; Kanamura, Kiyoshi
2012-07-28
The research and development of rechargeable all-ceramic lithium batteries are vital to realize their considerable advantages over existing commercial lithium ion batteries in terms of size, energy density, and safety. A key part of such effort is the development of solid-state electrolyte materials with high Li(+) conductivity and good electrochemical stability; lithium-containing oxides with a garnet-type structure are known to satisfy the requirements to achieve both features. Using first-principles density functional theory (DFT), we investigated the electrochemical stability of garnet-type Li(x)La(3)M(2)O(12) (M = Ti, Zr, Nb, Ta, Sb, Bi; x = 5 or 7) materials against Li metal. We found that the electrochemical stability of such materials depends on their composition and structure. The electrochemical stability against Li metal was improved when a cation M was chosen with a low effective nuclear charge, that is, with a high screening constant for an unoccupied orbital. In fact, both our computational and experimental results show that Li(7)La(3)Zr(2)O(12) and Li(5)La(3)Ta(2)O(12) are inert to Li metal. In addition, the linkage of MO(6) octahedra in the crystal structure affects the electrochemical stability. For example, perovskite-type La(1/3)TaO(3) was found, both experimentally and computationally, to react with Li metal owing to the corner-sharing MO(6) octahedral network of La(1/3)TaO(3), even though it has the same constituent elements as garnet-type Li(5)La(3)Ta(2)O(12) (which is inert to Li metal and features isolated TaO(6) octahedra).
Energy Technology Data Exchange (ETDEWEB)
Migaou, Amani; Guiltat, Mathilde; Payen, Kevin; Landa, Georges; Hémeryck, Anne, E-mail: anne.hemeryck@laas.fr [LAAS-CNRS, Université de Toulouse, CNRS, UPS, Toulouse (France); Sarpi, Brice; Daineche, Rachid; Vizzini, Sébastien [Aix Marseille University, IM2NP, Fac Sci St. Jérôme, F-13397 Marseille (France)
2016-05-21
First principles calculations, scanning tunneling microscopy, and Auger spectroscopy experiments of the adsorption of Mg on Ag(111) substrate are conducted. This detailed study reveals that an atomic scale controlled deposition of a metallic Mg monolayer perfectly wets the silver substrate without any alloy formation at the interface at room temperature. A liquid-like behavior of the Mg species on the Ag substrate is highlighted as no dot formation is observed when coverage increases. Finally a layer-by-layer growth mode of Mg on Ag(111) can be predicted, thanks to density functional theory calculations as observed experimentally.
Novita, Mega; Nagoshi, Hikari; Sudo, Akiho; Ogasawara, Kazuyoshi
2018-01-01
In this study, we performed an investigation on α-Al2O3: V3+ material, or the so-called color change sapphire, based on first-principles calculations without referring to any experimental parameter. The molecular orbital (MO) structure was estimated by the one-electron MO calculations using the discrete variational-Xα (DV-Xα) method. Next, the absorption spectra were estimated by the many-electron calculations using the discrete variational multi-electron (DVME) method. The effect of lattice relaxation on the crystal structures was estimated based on the first-principles band structure calculations. We performed geometry optimizations on the pure α-Al2O3 and with the impurity V3+ ion using Cambridge Serial Total Energy Package (CASTEP) code. The effect of energy corrections such as configuration dependence correction and correlation correction was also investigated in detail. The results revealed that the structural change on the α-Al2O3: V3+ resulted from the geometry optimization improved the calculated absorption spectra. By a combination of both the lattice relaxation-effect and the energy correction-effect improve the agreement to the experiment fact.
International Nuclear Information System (INIS)
Wang Huanyou; Xu Hui; Wang Xianchun; Jiang Chunzhi
2009-01-01
The density function perturbation theory (DFPT) is employed to study the lattice dynamics and thermodynamic properties (with quasiharmonic approximation) of zinc-blende BN. First we discuss the structural properties and compare the phonon spectrum with available Raman scattering experiments. Thereafter using the calculated phonon dispersions we obtain the PTV equation of state from the free energy. Our results for the above properties are generally speaking in good agreement with experiments and with similar theoretical calculations. Owing to the anharmonic effect at high temperature, the calculated linear thermal expansion coefficients (CTE) are low to experimental data.
CSIR Research Space (South Africa)
Nyangiwe, Nangamso N
2017-10-01
Full Text Available with natural organic matter (NOMs) and ENPs inherent physicochemical properties. Herein, density functional theory (DFT), classical lattice dynamics (CLD), and quantum mechanical calculations based on frontier molecular orbital (FMO) theory were applied...
Energy Technology Data Exchange (ETDEWEB)
Masrour, R., E-mail: rachidmasrour@hotmail.com [Laboratory of Materials, Processes, Environment and Quality, Cady Ayyed University, National School of Applied Sciences, 63 46000 Safi (Morocco); LMPHE (URAC 12), Faculty of Science, Mohammed V-Agdal University, Rabat (Morocco); Hlil, E.K. [Institut Néel, CNRS et Université Joseph Fourier, BP 166, F-38042 Grenoble cedex 9 (France); Hamedoun, M. [Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Benyoussef, A. [LMPHE (URAC 12), Faculty of Science, Mohammed V-Agdal University, Rabat (Morocco); Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Hassan II Academy of Science and Technology, Rabat (Morocco)
2014-04-01
Self-consistent ab initio calculations, based on Density Functional Theory (DFT) approach and using Full Potential Linear Augmented Plane Wave (FLAPW) method within GGA+U approximation, are performed to investigate both electronic and magnetic properties of the GdS layers. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Gd layers. Magnetic moment considered to lie along (001) axes are computed. Obtained data from ab initio calculations are used as input for the High Temperature Series Expansions (HTSEs) calculations to compute other magnetic parameters. Using the Heisenberg model, the exchange interactions between the magnetic atoms Gd–Gd in the same layer and between the magnetic atoms in the adjacent bilayers are estimated. This estimate is obtained using the antiferromagnetic and ferromagnetic energies computed by abinitio calculations for GdS layers. The High Temperature Series Expansions (HTSEs) of the magnetic susceptibility of GdS with antiferromagnetic moment (m{sub Gd}) is given up to sixth order series versus of (J{sub 11}(Gd–Gd)/k{sub B}T). The Néel temperature T{sub N} is obtained by mean field theory and by HTSEs of the magnetic susceptibility series using the Padé approximant method. The critical exponent γ associated with the magnetic susceptibility is calculated for GdS layers. - Highlights: • Electronic and magnetic properties of GdS are investigated using the ab initio calculations. • Obtained data from abinitio calculations are used as input for HTSEs to compute other magnetic parameters. • Néel temperature and critical exponent are deduced using HTSE method.
International Nuclear Information System (INIS)
Masrour, R.; Hlil, E.K.; Hamedoun, M.; Benyoussef, A.
2014-01-01
Self-consistent ab initio calculations, based on Density Functional Theory (DFT) approach and using Full Potential Linear Augmented Plane Wave (FLAPW) method within GGA+U approximation, are performed to investigate both electronic and magnetic properties of the GdS layers. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Gd layers. Magnetic moment considered to lie along (001) axes are computed. Obtained data from ab initio calculations are used as input for the High Temperature Series Expansions (HTSEs) calculations to compute other magnetic parameters. Using the Heisenberg model, the exchange interactions between the magnetic atoms Gd–Gd in the same layer and between the magnetic atoms in the adjacent bilayers are estimated. This estimate is obtained using the antiferromagnetic and ferromagnetic energies computed by abinitio calculations for GdS layers. The High Temperature Series Expansions (HTSEs) of the magnetic susceptibility of GdS with antiferromagnetic moment (m Gd ) is given up to sixth order series versus of (J 11 (Gd–Gd)/k B T). The Néel temperature T N is obtained by mean field theory and by HTSEs of the magnetic susceptibility series using the Padé approximant method. The critical exponent γ associated with the magnetic susceptibility is calculated for GdS layers. - Highlights: • Electronic and magnetic properties of GdS are investigated using the ab initio calculations. • Obtained data from abinitio calculations are used as input for HTSEs to compute other magnetic parameters. • Néel temperature and critical exponent are deduced using HTSE method
International Nuclear Information System (INIS)
Kumar, V.; Tripathy, S.K.
2014-01-01
Highlights: • Optical properties of ZnSiP 2 studied under different pressure for stable structure. • Birefringence has been calculated at different wavelengths. • Lattice constants, ħω p , bulk modulus and its derivative have been calculated. • C ij , Y, υ and Zener anisotropic factor have also been estimated. • Our calculated values are relative more close to the experimental values. -- Abstract: The plane wave pseudo-potential method within density functional theory (DFT) has been used to investigate the structural, electronic, optical and elastic properties of ZnSiP 2 chalcopyrite semiconductor. The lattice constants are calculated from the optimized unit cells and compare with the experimental value. The band structure, total density of states (TDOS) and partial density of states (PDOS) have been discussed. The energy gap has been calculated along the Γ direction found to be 1.383 eV, which shows that ZnSiP 2 is pseudo-direct in nature. We have also analyzed the frequency dependent dielectric constant ε(ω) and calculated the birefringence (Δn). The optical properties under three different hydrostatic pressures of 0 GPa, 10 GPa and 20 GPa have been described for the first time in the energy range 0–20 eV. The values of bulk modulus (B), pressure derivative of bulk modulus (B ∗ ), elastic constants (C ij ), Young’s modulus (Y), anisotropic factor (A) and Poisson’s ratio (ν) have been calculated. The calculated values of all above parameters are compared with the available experimental values and the values reported by different workers. A fairly good agreement has been found between them
Energy Technology Data Exchange (ETDEWEB)
Xiong Wei; Du Yong; Wang Jiong; Zhang Wei-Wei [State Key Lab. of Powder Metallurgy, Central South Univ., Changsha (China); Hu Rong-Xiang; Nash, P. [Thermal Processing Technology Center, Illinois Inst. of Tech., Chicago (United States); Lu Xiao-Gang [Thermo-Calc AB, Stockholm Technology Park, Stockholm (Sweden)
2008-06-15
An extensive thermodynamic investigation of the Al-Ni-Si system is carried out via an integrated approach of calculation of phase diagrams, first-principles calculations, and key experiments. Eighteen decisive alloys are prepared in order to verify the existence of the previously reported ternary compounds and to provide new phase equilibrium data. Phase compositions, microstructure, and phase transition temperatures are determined using the combined techniques of X-ray diffraction, scanning electron microscopy, energy dispersion X-ray analysis, and differential thermal analysis. The order/disorder transition between disordered bccA2 and ordered bccB2 phases as well as that between disordered fccA1 and ordered L1{sub 2} phase are described using a two-sublattice model. A self-consistent parameter set is finally obtained by considering the huge amount of experimental data including 13 vertical sections and 5 isothermal sections from both the literature and the present experiments. Almost all of the reliable phase diagram data can be well described by the present modeling. The reliability of the calculated thermodynamic properties for ternary phases is verified through enthalpy measurement employing drop calorimetry and first-principles calculations. The thermodynamic parameters obtained can also successfully predict most of the thermodynamic properties and describe the solidification path for the selected as-cast alloy Al{sub 6}Ni{sub 55}Si{sub 39}. (orig.)
Patterson, C H
2012-09-07
Surface phonons, conductivities, and loss functions are calculated for reconstructed (2×1), p(2×2) and c(4×2) clean Si(001) surfaces, and (2×1) H and D covered Si(001) surfaces. Surface conductivities perpendicular to the surface are significantly smaller than conductivities parallel to the surface. The surface loss function is compared to high resolution electron energy loss measurements. There is good agreement between calculated loss functions and experiment for H and D covered surfaces. However, agreement between experimental data from different groups and between theory and experiment is poor for clean Si(001) surfaces. Formalisms for calculating electron energy loss spectra are reviewed and the mechanism of electron energy losses to surface vibrations is discussed.
International Nuclear Information System (INIS)
Singh, Janpreet; Singh, Satvinder; Tripathi, S. K.; Singh, Gurinder; Kaura, Aman
2016-01-01
The atomic arrangements and chemical bonding of stable Ge_4Sb_2Te_7 (GeTe rich), a phase-change material, have been investigated by means of ab initio total energy calculations. To study the atomic arrangement, GeTe block is considered into -TeSbTeSbTe- block and -Te-Te- layer in the stacking I and II respectively. The stacking I is energetically more stable than the stacking II. The reason for more stability of the stacking I has been explained. The chemical bonding has been studied with the electronic charge density distribution around the atomic bonds. The quantity of electronic charge loosed or gained by atoms has been calculated using the Bader charge analysis. The metallic character has been studied using band structures calculations. The band gap for the stacking I and II is 0.463 and 0.219 eV respectively.
DEFF Research Database (Denmark)
Hansen, Martin Hangaard; Stern, Lucas-Alexandre; Feng, Ligang
2015-01-01
We present insights into the mechanism and the active site for hydrogen evolution on nickel phosphide (Ni2P). Ni2P was recently discovered to be a very active non-precious hydrogen evolution catalyst. Current literature attributes the activity of Ni2P to a particular site on the (0001) facet....... In the present study, using Density Functional Theory (DFT) calculations, we show that several widely available low index crystal facets on Ni2P have better properties for a high catalytic activity. DFT calculations were used to identify moderately bonding nickel bridge sites and nickel hollow sites for hydrogen...... adsorption and to calculate barriers for the Tafel pathway. The investigated surfaces in this study were the (10 (1) over bar0), ((1) over bar(1) over bar 20), (11 (2) over bar0), (11 (2) over bar1) and (0001) facets of the hexagonal Ni2P crystal. In addition to the DFT results, we present experiments on Ni2...
Determination of diffusion coefficients of oxygen atoms in ZrO2 using first-principles calculations
International Nuclear Information System (INIS)
Segi, Takashi; Okuda, Takanari
2014-01-01
Density functional theory and nudged elastic band calculations were performed in order to determine the diffusion coefficient for oxygen from monoclinic ZrO 2 . The calculated values for monoclinic ZrO 2 at 1000 K and 1500 K were 5.88 × 10 -16 cm 2 s -1 and 2.91 × 10 -11 cm 2 s -1 , respectively, and agreed with previously determined experimental values. In addition, the results of the nudged elastic band calculations suggest that interstitial oxygen sites exist between stable oxygen sites, and if oxygen atoms occupy these sites, stable structures with values for the lattice angle β of greater than 80.53° may be obtained. (author)
Energy Technology Data Exchange (ETDEWEB)
Serikov, V.V. [Institute of Metal Physics UB RAS, S. Kovalevskaya str. 18, 620990 Ekaterinburg (Russian Federation); Kleinerman, N.M., E-mail: kleinerman@imp.uran.ru [Institute of Metal Physics UB RAS, S. Kovalevskaya str. 18, 620990 Ekaterinburg (Russian Federation); Vershinin, A.V.; Mushnikov, N.V.; Protasov, A.V.; Stashkova, L.A. [Institute of Metal Physics UB RAS, S. Kovalevskaya str. 18, 620990 Ekaterinburg (Russian Federation); Gorbatov, O.I. [Institute of Metal Physics UB RAS, S. Kovalevskaya str. 18, 620990 Ekaterinburg (Russian Federation); Department of Materials Science and Engineering, KTH Royal Institute of Technology, SE - 100 44 Stockholm (Sweden); Ruban, A.V. [Department of Materials Science and Engineering, KTH Royal Institute of Technology, SE - 100 44 Stockholm (Sweden); Gornostyrev, Yu.N. [Institute of Metal Physics UB RAS, S. Kovalevskaya str. 18, 620990 Ekaterinburg (Russian Federation)
2014-11-25
Highlights: • Structure features of the formation of quasibinary solid solutions Fe–Co–Ga and Fe–Cr–Ga are found. • The first-principles calculation of mixing and solubility energies for Ga in an Fe–X alloy are given. • Ga handicaps the processes of phase separation in the Fe–Cr system and ordering in the Fe–Co system. • Preference of Ga entering in the neighborhood of a second element can help study multielement alloys. - Abstract: Investigation of Ga influence on the structure of Fe–Cr and Fe–Co alloys was performed with the use of Mössbauer spectroscopy and X-ray diffraction methods. The experimental results are compared with results of first-principles calculations of the mixing and solubility energies for Ga in an Fe–X (X = Co, Cr) alloy both in ferromagnetic and paramagnetic states. It is shown that Ga mainly goes into the solid solutions of the base alloys. In the alloys of the Fe–Cr system, doping with Ga handicaps the decomposition of solid solutions, observed in the binary alloys, and increases its stability. In the alloys with Co, Ga also favors the uniformity of solid solutions. The results of the first-principles calculations testify in favor of a preferable dissolution of Ga in the FeCo regions of a multicomponent structure rather than FeCr regions, both types of regions being in the ferromagnetic state at the temperature of annealing. The analysis of Mössbauer experiments gives some grounds to conclude that if, owing to liquation, clusterization, or initial stages of phase separation, there exist regions enriched in iron, some amount of Ga atoms prefer to enter the nearest surroundings of iron atoms, thus forming binary Fe–Ga regions (or phases)
International Nuclear Information System (INIS)
Acatrinei, Alice I; Browne, D; Losovyj, Y B; Young, D P; Moldovan, M; Chan, Julia Y; Sprunger, P T; Kurtz, Richard L
2003-01-01
In this work we present valence band studies of LaSb 2 using angle-resolved photoelectron spectroscopy with synchrotron radiation and compare these data with band structure calculations. Valence band spectra reveal that Sb 5p states are dominant near the Fermi level and are hybridized with the La 5d states just below. The calculations show a fair agreement with the experimentally determined valence band spectra, allowing an identification of the observed features. We measured some dispersion for kbar, especially for Sb 5p states; no significant dispersion was found for k || . (letter to the editor)
International Nuclear Information System (INIS)
Yao Qiang; Zhu Yuhong; Wang Yan
2011-01-01
Ultrasoft pseudopotential within a generalized gradient approximation was employed to study the structural stability, electronic structure, and elastic properties of ternary Co 3 (Ga,W) precipitate. The Young's and shear moduli of the polycrystals containing the Co 3 (Ga,W) precipitate were calculated using the Voigt-Reuss-Hill averaging scheme. Results show that the stable ternary Co 3 (Ga,W) compound has the L1 2 structure, and is ductile in nature. The structural stability of the Co 3 (Ga,W) compound is discussed together with the calculated electronic structure.
Electronic structure of BaFe2As2 as obtained from DFT/ASW first-principles calculations
Schwingenschlö gl, Udo; Di Paola, Cono
2010-01-01
We use ab-initio calculations based on the augmented spherical wave method within density functional theory to study the magnetic ordering and Fermi surface of BaFe2As2, the parent compound of the hole-doped iron pnictide superconductors (K,Ba)Fe2As
Fang, C.M.; Wijs, G.A. de
2004-01-01
The phonon spectrum Of C3N4 with defect zincblende-type structure (deltaC(3)N(4)) was calculated by density functional theory (DFT) techniques. The results permit an assessment of important mechanical and thermodynamical properties such as the bulk modulus, lattice specific heat, vibration energy,
Valiev, R R; Cherepanov, V N; Baryshnikov, G V; Sundholm, D
2018-02-28
A method for calculating the rate constants for internal-conversion (k IC ) and intersystem-crossing (k ISC ) processes within the adiabatic and Franck-Condon (FC) approximations is proposed. The applicability of the method is demonstrated by calculation of k IC and k ISC for a set of organic and organometallic compounds with experimentally known spectroscopic properties. The studied molecules were pyrromethene-567 dye, psoralene, hetero[8]circulenes, free-base porphyrin, naphthalene, and larger polyacenes. We also studied fac-Alq 3 and fac-Ir(ppy) 3 , which are important molecules in organic light emitting diodes (OLEDs). The excitation energies were calculated at the multi-configuration quasi-degenerate second-order perturbation theory (XMC-QDPT2) level, which is found to yield excitation energies in good agreement with experimental data. Spin-orbit coupling matrix elements, non-adiabatic coupling matrix elements, Huang-Rhys factors, and vibrational energies were calculated at the time-dependent density functional theory (TDDFT) and complete active space self-consistent field (CASSCF) levels. The computed fluorescence quantum yields for the pyrromethene-567 dye, psoralene, hetero[8]circulenes, fac-Alq 3 and fac-Ir(ppy) 3 agree well with experimental data, whereas for the free-base porphyrin, naphthalene, and the polyacenes, the obtained quantum yields significantly differ from the experimental values, because the FC and adiabatic approximations are not accurate for these molecules.
Specific heat of MgB2 in a one- and a two-band model from first-principles calculations
International Nuclear Information System (INIS)
Golubov, A.A.; Dolgov, O.V.; Jepsen, O.; Kong, Y.; Andersen, O.K.; Gibson, B.J.; Ahn, K.; Kremer, R.K.; Kortus, J.
2002-01-01
The heat capacity anomaly at the transition to superconductivity of the layered superconductor MgB 2 is compared to first-principles calculations with the Coulomb repulsion, μ*, as the only parameter which is fixed to give the measured T c . We solve the Eliashberg equations for both an isotropic one-band model and a two-band model with different superconducting gaps on the π-band anσd-band Fermi surfaces. The agreement with experiments is considerably better for the two-band model than for the one-band model. (author)
Choi, Woo Seok; Jeen, Hyoungjeen; Lee, Jun Hee; Seo, S. S. Ambrose; Cooper, Valentino R.; Rabe, Karin M.; Lee, Ho Nyung
2013-01-01
Using real-time spectroscopic ellipsometry, we directly observed a reversible lattice and electronic structure evolution in SrCoOx (x = 2.5 - 3) epitaxial thin films. Drastically different electronic ground states, which are extremely susceptible to the oxygen content x, are found in the two topotactic phases, i.e. the brownmillerite SrCoO2.5 and the perovskite SrCoO3. First principles calculations confirmed substantial differences in the electronic structure, including a metal-insulator tran...
Hendrickx, Marc F A; Clima, S; Chibotaru, L F; Ceulemans, A
2005-10-06
An ab initio multiconfigurational approach has been used to calculate the ligand-field spectrum and magnetic properties of the title cyano-bridged dinuclear molybdenum complex. The rather large magnetic coupling parameter J for a single cyano bridge, as derived experimentally for this complex by susceptibility measurements, is confirmed to a high degree of accuracy by our CASPT2 calculations. Its electronic structure is rationalized in terms of spin-spin coupling between the two constituent hexacyano-monomolybdate complexes. An in-depth analysis on the basis of Anderson's kinetic exchange theory provides a qualitative picture of the calculated CASSCF antiferromagnetic ground-state eigenvector in the Mo dimer. Dynamic electron correlations as incorporated into our first-principles calculations by means of the CASPT2 method are essential to obtain quantitative agreement between theory and experiment.
Energy Technology Data Exchange (ETDEWEB)
Nyawere, P.W.O., E-mail: otienop98@yahoo.ca [Computational Materials Science Group, Department of Physics, University of Eldoret, P.O. Box 1125-30100 Eldoret (Kenya); Department of Computing, Kabarak University, P.O. - Private Bag - 20157 Kabarak (Kenya); The Abdus Salam International Centre for Theoretical Physics, Trieste (Italy); Makau, N.W., E-mail: wanimak@yahoo.com [Computational Materials Science Group, Department of Physics, University of Eldoret, P.O. Box 1125-30100 Eldoret (Kenya); Amolo, G.O., E-mail: georgeamolo862@gmail.com [Computational Materials Science Group, Department of Physics, University of Eldoret, P.O. Box 1125-30100 Eldoret (Kenya)
2014-02-01
All the elastic constants of cubic, orthorhombic and hexagonal phases of BaF{sub 2} have been calculated using first principles methods. We have employed density-functional theory within generalized gradient approximation (GGA) using a plane-wave pseudopotentials method and a plane-wave basis set. The calculated elastic constant values for a cubic phase compare well with recent theoretical and experimental calculations. The bulk modulus derived from the elastic constant calculations of orthorhombic phase of BaF{sub 2} is 94.5 GPa and those of hexagonal phase is 161 GPa. These values are in good agreement with experimental data available. Stability of these phases of BaF{sub 2} is also estimated in different crystallographic directions.
Energy Technology Data Exchange (ETDEWEB)
Prasad, K. Ganga; Niranjan, Manish K.; Asthana, Saket [Department of Physics, Indian Institute of Technology Hyderabad, India, 502205 (India)
2016-05-06
We report the electronic structure of the AgMO{sub 3}(M=Nb, Ta) within the frame work of density functional theory and calculations are performed within the generalized gradient approximation (GGA) by using ultrasoft pseudopotentials. The calculated equilibrium lattice parameters and volumes are extracted from fitting of Birch third order equation of state and which are reasonable agreement with the available experimental results. The density of states,band structure of Ag(Nb,Ta)O{sub 3} reveals that the valance bands mostly occupied with O-2p and O-2s states and whereas conduction band occupied with Nb (Ta) 4d(5d) states including less contribution from Ag 5s states.
Polyakov, Igor V.; Khrenova, Maria G.; Moskovsky, Alexander A.; Shabanov, Boris M.; Nemukhin, Alexander V.
2018-04-01
Modeling electronic excitation of bacteriochlorophyll (BChl) molecules in light-harvesting (LH) antennae from photosynthetic centers presents a challenge for the quantum theory. We report on a quantum chemical study of the ring of 32 BChl molecules from the bacterial core complex LH1-RC. Diagonal and off-diagonal elements of the excitonic Hamiltonian matrices are estimated in quantum chemical calculations of relevant fragments using the TD-DFT and CIS approaches. The deviation of the computed excitation energy of this BChl system from the experimental data related to the Qy band maximum of this LH1-RC complex is about 0.2 eV. We demonstrate that corrections due to improvement in modeling of an individual BChl molecule and due to contributions from the protein environment are in the range of the obtained discrepancy between theory and experiment. Differences between results of the excitonic model and direct quantum chemical calculations of BChl aggregates fall in the same range.
Electronic structure of BaFe2As2 as obtained from DFT/ASW first-principles calculations
Schwingenschlögl, Udo
2010-07-02
We use ab-initio calculations based on the augmented spherical wave method within density functional theory to study the magnetic ordering and Fermi surface of BaFe2As2, the parent compound of the hole-doped iron pnictide superconductors (K,Ba)Fe2As2, for the tetragonal I4/mmm as well as the orthorhombic Fmmm structure. In comparison to full potential linear augmented plane wave calculations, we obtain significantly smaller magnetic energies. This finding is remarkable, since the augmented spherical wave method, in general, is known for a most reliable description of magnetism. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Energy Technology Data Exchange (ETDEWEB)
Masrour, R., E-mail: rachidmasrour@hotmail.com [Laboratory of Materials, Processes, Environment and Quality, Cady Ayyed University, National School of Applied Sciences, 63 46000, Safi (Morocco); LMPHE (URAC 12), Faculty of Science, Mohammed V-Agdal University, Rabat (Morocco); Hlil, E.K. [Institut Néel, CNRS et Université Joseph Fourier, BP 166, F-38042 Grenoble Cedex 9 (France); Hamedoun, M. [Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Benyoussef, A. [LMPHE (URAC 12), Faculty of Science, Mohammed V-Agdal University, Rabat (Morocco); Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Hassan II Academy of Science and Technology, Rabat (Morocco); Boutahar, A.; Lassri, H. [LPMMAT, Université Hassan II-Casablanca, Faculté des Sciences, BP 5366 Maârif (Morocco)
2015-11-01
The self-consistent ab initio calculations, based on DFT (Density Functional Theory) approach and using FLAPW (Full potential Linear Augmented Plane Wave) method, are performed to investigate both electronic and magnetic properties of the Mn{sub 2}Au. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Mn plans. Magnetic moment considered to lie along (110) axes are computed. Obtained data from ab initio calculations are used as input for the high temperature series expansions (HTSEs) calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Mn–Mn in Mn{sub 2}Au are given by using the experiment results and the mean field theory. The High Temperature Series Expansions (HTSEs) of the magnetic susceptibility with the magnetic moments in Mn{sub 2}Au (m{sub Mn}) is given up to tenth order series in, 1/k{sub B}T. The Néel temperature T{sub N} is obtained by HTSEs combined with the Padé approximant method. The critical exponent associated with the magnetic susceptibility is deduced as well. - Highlights: • The both electronic and magnetic properties of the Mn{sub 2}Au are studied. • The exchange interactions between the magnetic atoms Mn–Mn in Mn{sub 2}Au are given. • The Néel temperature T{sub N} of Mn{sub 2}Au is obtained by HTSEs method. • The critical exponent associated with the magnetic susceptibility is deduced.
Künneth, Christopher; Kölbl, Simon; Wagner, Hans Edwin; Häublein, Volker; Kersch, Alfred; Alt, Hans Christian
2018-04-01
Molecular-like carbon-nitrogen complexes in GaAs are investigated both experimentally and theoretically. Two characteristic high-frequency stretching modes at 1973 and 2060 cm-1, detected by Fourier transform infrared absorption (FTIR) spectroscopy, appear in carbon- and nitrogen-implanted and annealed layers. From isotopic substitution, it is deduced that the chemical composition of the underlying complexes is CN2 and C2N, respectively. Piezospectroscopic FTIR measurements reveal that both centers have tetragonal symmetry. For density functional theory (DFT) calculations, linear entities are substituted for the As anion, with the axis oriented along the 〈1 0 0 〉 direction, in accordance with the experimentally ascertained symmetry. The DFT calculations support the stability of linear N-C-N and C-C-N complexes in the GaAs host crystal in the charge states ranging from + 3 to -3. The valence bonds of the complexes are analyzed using molecular-like orbitals from DFT. It turns out that internal bonds and bonds to the lattice are essentially independent of the charge state. The calculated vibrational mode frequencies are close to the experimental values and reproduce precisely the isotopic mass splitting from FTIR experiments. Finally, the formation energies show that under thermodynamic equilibrium CN2 is more stable than C2N.
International Nuclear Information System (INIS)
Minamoto, Satoshi; Kato, Masato; Konashi, Kenji
2010-01-01
A combination of a first-principles calculation, lattice dynamics and CALPHAD (CALculation of PHAse Diagrams) modeling is proven as a powerful tool so as to evaluate the Gibbs free energy and a phase equilibrium between compounds including large amount of vacancies. In this work, non-stoichiometric PuO 2-x (dioxide) and Pu 2 O 3 (sesquioxide) has been studied. An electron cohesive energy was evaluated from a first-principles calculations to estimate total energy of the compounds and a vacancy formation energy, and the theory of statistical mechanics was applied to evaluate enthalpy/entropy change due to oxygen vacancies for the non-stoichiometry of the PuO 2 (i.e. PuO 2-x ). Then a vacancy-vacancy interaction energy was determined by fitting to the experimental data of a quantity of non-stoichiometry of the PuO 2 compounds as a function of oxygen potentials at large deviation from stoichiometry. The resulting Gibbs free energy yields phase boundary between the phases with good agreement with to the experimental data.
Energy Technology Data Exchange (ETDEWEB)
Minamoto, Satoshi [ITOCHU Techno-Solutions Corporation, Kasumigaseki 3, Chiyoda-ku, Tokyo, Energy and Industrial Systems Department (Japan); Kato, Masato [Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki (Japan); Konashi, Kenji, E-mail: satoshi.minamoto@ctc-g.co.jp, E-mail: masato.kato@jaea.go.jp, E-mail: konashi@imr.tohoku-u.ac.jp [Institute for Materials Research, Tohoku University, Oarai-chou, Ibaraki (Japan)
2010-03-15
A combination of a first-principles calculation, lattice dynamics and CALPHAD (CALculation of PHAse Diagrams) modeling is proven as a powerful tool so as to evaluate the Gibbs free energy and a phase equilibrium between compounds including large amount of vacancies. In this work, non-stoichiometric PuO{sub 2-x} (dioxide) and Pu{sub 2}O{sub 3} (sesquioxide) has been studied. An electron cohesive energy was evaluated from a first-principles calculations to estimate total energy of the compounds and a vacancy formation energy, and the theory of statistical mechanics was applied to evaluate enthalpy/entropy change due to oxygen vacancies for the non-stoichiometry of the PuO{sub 2} (i.e. PuO{sub 2-x}). Then a vacancy-vacancy interaction energy was determined by fitting to the experimental data of a quantity of non-stoichiometry of the PuO{sub 2} compounds as a function of oxygen potentials at large deviation from stoichiometry. The resulting Gibbs free energy yields phase boundary between the phases with good agreement with to the experimental data.
Directory of Open Access Journals (Sweden)
Xiaofan Ma
Full Text Available In this manuscript, the effects of intrinsic defects on the electronic and optical properties of aluminum-doped β-Ga2O3 are investigated with first-principles calculations. Four types of defect complexes have been considered: AlGa2O3VO (Al-doped β-Ga2O3 with O vacancy, AlGa2O3VGa (Al-doped β-Ga2O3 with Ga vacancy, AlGa2O3Gai (Al-doped β-Ga2O3 with Ga interstitial and AlGa2O3Oi (Al-doped β-Ga2O3 with O interstitial. The calculation results show that the incorporation of Al into β-Ga2O3 leads to the tendency of forming O interstitial defects. And the bandgap of AlGa2O3 is 4.975 eV, which is a little larger than that of intrinsic β-Ga2O3. When O vacancies exist, a defect energy level is introduced to the forbidden band as a deep donor level, while no defective energy levels occur in the forbidden band with O interstitials. After Al-doped, a slightly blue-shift appears in the intrinsic absorption edge, and an additional absorption peak occurs with O vacancy located in 3.69 eV. Keywords: First-principle calculation, Intrinsic defects, Bandgap, Absorption peak
Chiodo, S.; Gotsis, H. J.; Russo, N.; Sicilia, E.
2006-07-01
Recently it has been reported that osmium diboride has an unusually large bulk modulus combined with high hardness, and consequently is a most interesting candidate as an ultra-incompressible and hard material. The electronic and structural properties of the transition metal diborides OsB 2 and RuB 2 have been calculated within the local density approximation (LDA). It is shown that the high hardness is the result of covalent bonding between transition metal d states and boron p states in the orthorhombic structure.
García-Toral, Dolores; González-Melchor, Minerva; Rivas-Silva, Juan F; Meneses-Juárez, Efraín; Cano-Ordaz, José; H Cocoletzi, Gregorio
2018-06-07
Classical molecular dynamics (MD) and density functional theory (DFT) calculations are developed to investigate the dopamine and caffeine encapsulation within boron nitride (BN) nanotubes (NT) with (14,0) chirality. Classical MD studies are done at canonical and isobaric-isothermal conditions at 298 K and 1 bar in explicit water. Results reveal that both molecules are attracted by the nanotube; however, only dopamine is able to enter the nanotube, whereas caffeine moves in its vicinity, suggesting that both species can be transported: the first by encapsulation and the second by drag. Findings are analyzed using the dielectric behavior, pair correlation functions, diffusion of the species, and energy contributions. The DFT calculations are performed according to the BLYP approach and applying the atomic base of the divided valence 6-31g(d) orbitals. The geometry optimization uses the minimum-energy criterion, accounting for the total charge neutrality and multiplicity of 1. Adsorption energies in the dopamine encapsulation indicate physisorption, which induces the highly occupied molecular orbital-lower unoccupied molecular orbital gap reduction yielding a semiconductor behavior. The charge redistribution polarizes the BNNT/dopamine and BNNT/caffeine structures. The work function decrease and the chemical potential values suggest the proper transport properties in these systems, which may allow their use in nanobiomedicine.
Wen, Jun-Qing; Zhang, Jian-Min; Chen, Guo-Xiang; Wu, Hua; Yang, Xu
2018-04-01
The density functional theory calculations using general gradient approximation (GGA) applying Perdew-Burke-Ernzerhof (PBE) as correlation functional have been systematically performed to research the formation energy, the electronic structures, band structures, total and partial DOS, and optical properties of Nd doping ZnO with the content from 6.25% to 12.5%. The formation energies are negative for both models, which show that two structures are energetically stable. Nd doping ZnO crystal is found to be a direct band gap semiconductor and Fermi level shifts upward into conduction band, which show the properties of n-type semiconductor. Band structures are more compact after Nd doping ZnO, implying that Nd doping induces the strong interaction between different atoms. Nd doping ZnO crystal presents occupied states at near Fermi level, which mainly comes from the Nd 4f orbital. The calculated optical properties imply that Nd doping causes a red-shift of absorption peaks, and enhances the absorption of the visible light.
Mehmood, Faisal; Pachter, Ruth; Murphy, Neil R.; Johnson, Walter E.; Ramana, Chintalapalle V.
2016-12-01
In this work, we investigated theoretically the role of oxygen vacancies on the electronic and optical properties of cubic, γ-monoclinic, and tetragonal phases of tungsten oxide (WO3) thin films. Following the examination of structural properties and stability of the bulk tungsten oxide polymorphs, we analyzed band structures and optical properties, applying density functional theory (DFT) and GW (Green's (G) function approximation with screened Coulomb interaction (W)) methods. Careful benchmarking of calculated band gaps demonstrated the importance of using a range-separated functional, where results for the pristine room temperature γ-monoclinic structure indicated agreement with experiment. Further, modulation of the band gap for WO3 structures with oxygen vacancies was quantified. Dielectric functions for cubic WO3, calculated at both the single-particle, essentially time-dependent DFT, as well as many-body GW-Bethe-Salpeter equation levels, indicated agreement with experimental data for pristine WO3. Interestingly, we found that introducing oxygen vacancies caused appearance of lower energy absorptions. A smaller refractive index was indicated in the defective WO3 structures. These predictions could lead to further experiments aimed at tuning the optical properties of WO3 by introducing oxygen vacancies, particularly for the lower energy spectral region.
International Nuclear Information System (INIS)
Yun-Jiang, Wang; Chong-Yu, Wang
2009-01-01
A model system consisting of Ni[001](100)/Ni 3 Al[001](100) multi-layers are studied using the density functional theory in order to explore the elastic properties of single crystal Ni-based superalloys. Simulation results are consistent with the experimental observation that rafted Ni-base superalloys virtually possess a cubic symmetry. The convergence of the elastic properties with respect to the thickness of the multilayers are tested by a series of multilayers from 2γ'+2γ to 10γ'+10γ atomic layers. The elastic properties are found to vary little with the increase of the multilayer's thickness. A Ni/Ni 3 Al multilayer with 10γ'+10γ atomic layers (3.54 nm) can be used to simulate the mechanical properties of Ni-base model superalloys. Our calculated elastic constants, bulk modulus, orientation-dependent shear modulus and Young's modulus, as well as the Zener anisotropy factor are all compatible with the measured results of Ni-base model superalloys R1 and the advanced commercial superalloys TMS-26, CMSX-4 at a low temperature. The mechanical properties as a function of the γ' phase volume fraction are calculated by varying the proportion of the γ and γ' phase in the multilayers. Besides, the mechanical properties of two-phase Ni/Ni 3 Al multilayer can be well predicted by the Voigt–Reuss–Hill rule of mixtures. (classical areas of phenomenology)
Middleton, Kirsten; Zhang, Guoping; George, Thomas F.
2012-02-01
Memantine is currently used as a treatment for mild to severe Alzheimer's disease, although its functionality is complicated. Using various density functional theory calculations and basis sets, we first examine memantine alone and then add ions which are present in the human body. This provides clues as to how the compound may react in the calcium ion channel, where it is believed to treat the disease. In order to understand the difference between calcium and magnesium ions interacting with memantine, we compute the electron affinity of each complex. We find that memantine is more strongly attracted to magnesium ions than calcium ions within the channel. By observing the HOMO-LUMO gap within memantine in comparison to adamantane, we find that memantine is more excitable than the anti-flu drug. We believe these factors to affect the efficiency of memantine as a treatment of Alzheimer's disease.
Dilmi, S.; Saib, S.; Bouarissa, N.
2018-06-01
Structural, electronic, electron-phonon coupling and superconducting properties of the intermetallic compound LuC2 are investigated by means of ab initio pseudopotential plane wave method within the generalized gradient approximation. The calculated equilibrium lattice parameters yielded a very good accord with experiment. There is no imaginary phonon frequency in the whole Brillouin zone supporting thus the dynamical stability in the material of interest. The average electron-phonon coupling parameter is found to be 0.59 indicating thus a weak-coupling BCS superconductor. Using a reasonable value of μ* = 0.12 for the effective Coulomb repulsion parameter, the superconducting critical temperature Tc is found to be 3.324 which is in excellent agreement with the experimental value of 3.33 K. The effect of the spin-orbit coupling on the superconducting properties of the material of interest has been examined and found to be weak.
Kokott, Sebastian; Levchenko, Sergey V.; Rinke, Patrick; Scheffler, Matthias
2018-03-01
We present a density functional theory (DFT) based supercell approach for modeling small polarons with proper account for the long-range elastic response of the material. Our analysis of the supercell dependence of the polaron properties (e.g., atomic structure, binding energy, and the polaron level) reveals long-range electrostatic effects and the electron–phonon (el–ph) interaction as the two main contributors. We develop a correction scheme for DFT polaron calculations that significantly reduces the dependence of polaron properties on the DFT exchange-correlation functional and the size of the supercell in the limit of strong el–ph coupling. Using our correction approach, we present accurate all-electron full-potential DFT results for small polarons in rocksalt MgO and rutile TiO2.
Hémeryck, Anne; Motta, Alessandro; Swiatowska, Jolanta; Pereira-Nabais, Catarina; Marcus, Philippe; Costa, Dominique
2013-07-14
Epoxy-amines are used as structural adhesives deposited on Ti. The amine adhesion to a Ti surface depends highly on the surface state (oxidation, hydroxylation). Amines may adsorb above preadsorbed water molecules or substitute them to bind directly to surface Ti(4+) Lewis acid sites. The adsorption of a model amine molecule, diaminoethane (DAE), on a model surface, hydrated TiO2-anatase (101) surface, is investigated using Density Functional Theory including Dispersive forces (DFT-D) calculations. DAE adsorption and water substitution by DAE are exothermic processes and turn nearly isoenergetic at high coverage with adsorption-substitution energies around -0.3 eV (including dispersion forces and ZPE). Complementary ab initio molecular dynamics studies also suggest that the formation of an amine-water interaction induces water desorption from the surface at room temperature, a preliminary step towards the amine-Ti bond formation. An atomistic thermodynamic approach is developed to evaluate the interfacial free energy balance of both processes (adsorption and substitution). The main contributions to the energetic balance are dispersive interactions between molecules and the surface on the exergonic side, translational and rotational entropic contributions on the endergonic one. The substitution process is stabilized by 0.55 eV versus the adsorption one when free solvation, rotational and vibrational energies are considered. The main contribution to this free energy gain is due to water solvation. The calculations suggest that in toluene solvent with a water concentration of 10(-4) M or less, a full DAE layer replaces a preadsorbed water layer for a threshold concentration of DAE ≥ 0.1 M.
Li, X. D.; Li, K.; Wei, C. H.; Han, W. D.; Zhou, N. G.
2018-06-01
The structural, electronic, elastic, and thermodynamic properties of CaSi, Ca2Si, and CaSi2 are systematically investigated by using first-principles calculations method based on density functional theory (DFT). The calculated formation enthalpies and cohesive energies show that CaSi2 possesses the greatest structural stability and CaSi has the strongest alloying ability. The structural stability of the three phases is compared according to electronic structures. Further analysis on electronic structures indicates that the bonding of these phases exhibits the combinations of metallic, covalent, and ionic bonds. The elastic constants are calculated, and the bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and anisotropy factor of polycrystalline materials are deduced. Additionally, the thermodynamic properties were theoretically predicted and discussed.
International Nuclear Information System (INIS)
Minamoto, Satoshi; Kato, Masato; Konashi, Kenji
2011-01-01
Combination of an oxygen vacancy formation energy calculated using first-principles approach and the configurational entropy change treated within the framework of statistical mechanics gives an expression of the Gibbs free energy at large deviation from stoichiometry of plutonium oxide PuO 2 . An oxygen vacancy formation energy 4.20 eV derived from our previously first-principles calculation was used to evaluate the Gibbs free energy change due to oxygen vacancies in the crystal. The oxygen partial pressures then can be evaluated from the change of the free energy with two fitting parameters (a vacancy-vacancy interaction energy and vibration entropy change due to induced vacancies). Derived thermodynamic expression for the free energy based on the SGTE thermodynamic data for the stoichiometric PuO 2 and the Pu 2 O 3 compounds was further incorporated into the CALPHAD modeling, then phase equilibrium between the stoichiometric Pu 2 O 3 and non-stoichiometric PuO 2-x were reproduced.
Energy Technology Data Exchange (ETDEWEB)
Minamoto, Satoshi, E-mail: satoshi.minamoto@ctc-g.co.jp [ITOCHU Techno-Solutions Corporation, Kasumigaseki, 2-5, Kasumigaseki 3-chome, Chiyoda-ku, Tokyo 100-6080 (Japan); Kato, Masato [Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki (Japan); Konashi, Kenji [Institute for Materials Research, Tohoku University, Oarai-chou, Ibaraki (Japan)
2011-05-31
Combination of an oxygen vacancy formation energy calculated using first-principles approach and the configurational entropy change treated within the framework of statistical mechanics gives an expression of the Gibbs free energy at large deviation from stoichiometry of plutonium oxide PuO{sub 2}. An oxygen vacancy formation energy 4.20 eV derived from our previously first-principles calculation was used to evaluate the Gibbs free energy change due to oxygen vacancies in the crystal. The oxygen partial pressures then can be evaluated from the change of the free energy with two fitting parameters (a vacancy-vacancy interaction energy and vibration entropy change due to induced vacancies). Derived thermodynamic expression for the free energy based on the SGTE thermodynamic data for the stoichiometric PuO{sub 2} and the Pu{sub 2}O{sub 3} compounds was further incorporated into the CALPHAD modeling, then phase equilibrium between the stoichiometric Pu{sub 2}O{sub 3} and non-stoichiometric PuO{sub 2-x} were reproduced.
Bachorz, Rafał A; Klopper, Wim; Gutowski, Maciej; Li, Xiang; Bowen, Kit H
2008-08-07
The photoelectron spectrum (PES) of the uracil anion is reported and discussed from the perspective of quantum chemical calculations of the vertical detachment energies (VDEs) of the anions of various tautomers of uracil. The PES peak maximum is found at an electron binding energy of 2.4 eV, and the width of the main feature suggests that the parent anions are in a valence rather than a dipole-bound state. The canonical tautomer as well as four tautomers that result from proton transfer from an NH group to a C atom were investigated computationally. At the Hartree-Fock and second-order Moller-Plesset perturbation theory levels, the adiabatic electron affinity (AEA) and the VDE have been converged to the limit of a complete basis set to within +/-1 meV. Post-MP2 electron-correlation effects have been determined at the coupled-cluster level of theory including single, double, and noniterative triple excitations. The quantum chemical calculations suggest that the most stable valence anion of uracil is the anion of a tautomer that results from a proton transfer from N1H to C5. It is characterized by an AEA of 135 meV and a VDE of 1.38 eV. The peak maximum is as much as 1 eV larger, however, and the photoelectron intensity is only very weak at 1.38 eV. The PES does not lend support either to the valence anion of the canonical tautomer, which is the second most stable anion, and whose VDE is computed at about 0.60 eV. Agreement between the peak maximum and the computed VDE is only found for the third most stable tautomer, which shows an AEA of approximately -0.1 eV and a VDE of 2.58 eV. This tautomer results from a proton transfer from N3H to C5. The results illustrate that the characteristics of biomolecular anions are highly dependent on their tautomeric form. If indeed the third most stable anion is observed in the experiment, then it remains an open question why and how this species is formed under the given conditions.
Energy Technology Data Exchange (ETDEWEB)
Watanabe, Shinta, E-mail: s-watanabe@nucl.nagoya-u.ac.jp, E-mail: j-onoe@nucl.nagoya-u.ac.jp; Sawada, Yuki; Nakaya, Masato; Yoshino, Masahito; Nagasaki, Takanori; Onoe, Jun, E-mail: s-watanabe@nucl.nagoya-u.ac.jp, E-mail: j-onoe@nucl.nagoya-u.ac.jp [Department of Materials, Physics and Energy Engineering, Graduated School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan); Kameyama, Tatsuya; Torimoto, Tsukasa [Department of Crystalline Materials Science, Graduated School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan); Inaba, Yusuke; Takahashi, Hideharu; Takeshita, Kenji [Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2-12-1-N1-16 O-okayama, Meguro-ku, Tokyo 152-8550 (Japan)
2016-06-21
We have investigated the electronic structures and optical properties of Fe, Co, and Ni ferrocyanide nanoparticles using first-principles relativistic many-electron calculations. The overall features of the theoretical absorption spectra for Fe, Ni, and Co ferrocyanides calculated using a first-principles many-electron method well reproduced the experimental one. The origins of the experimental absorption spectra were clarified by performing a configuration analysis based on the many-electron wave functions. For Fe ferrocyanide, the experimental absorption peaks originated from not only the charge-transfer transitions from Fe{sup 2+} to Fe{sup 3+} but also the 3d-3d intra-transitions of Fe{sup 3+} ions. In addition, the spin crossover transition of Fe{sup 3+} predicted by the many-electron calculations was about 0.24 eV. For Co ferrocyanide, the experimental absorption peaks were mainly attributed to the 3d-3d intra-transitions of Fe{sup 2+} ions. In contrast to the Fe and Co ferrocyanides, Ni ferrocyanide showed that the absorption peaks originated from the 3d-3d intra-transitions of Ni{sup 3+} ions in a low-energy region, while from both the 3d-3d intra-transitions of Fe{sup 2+} ions and the charge-transfer transitions from Fe{sup 2+} to Ni{sup 3+} in a high-energy region. These results were quite different from those of density-functional theory (DFT) calculations. The discrepancy between the results of DFT calculations and those of many-electron calculations suggested that the intra- and inter-atomic transitions of transition metal ions are significantly affected by the many-body effects of strongly correlated 3d electrons.
First-principles calculations of (Y, Ti, O) cluster formation in body centred cubic iron-chromium
International Nuclear Information System (INIS)
Claisse, Antoine; Olsson, Pär
2013-01-01
In the present work, the ab initio parametrization necessary for a Monte Carlo study of the (Y, Ti, O) clusters in a FeCr matrix is done. The cohesive, binding and migration energies of all the solutes have been calculated in the dilute limit in the framework of density functional theory. The special case of the strong interaction between an Y atom and a vacancy has been considered. In the dilute limit, Cr is transparent with respect to Y, Ti, O or vacancies. On the contrary, Y binds O strongly in 2NN configuration while not in 1NN. Ti binds O in 1NN and 2NN configurations. A vacancy binds strongly with Y and O in 1NN position which is resulting in a low diffusion coefficient for Y. The peculiar case of the binding attraction between two interstitial oxygen atoms has been studied and is believed to be the main reason for the planar (2D) symmetry of the cluster nuclei. A preferential cluster shape is determined for the early nucleation stage, up to 12 atoms
International Nuclear Information System (INIS)
Bastos, M.; Camps, I.
2013-01-01
Absorption of Pb on a zigzag (10, 0) carbon nanotube (CNT) surface, pure and functionalized with carboxyl (-COOH) and hydroxyl (-OH) groups was investigated using the density functional theory. Binding energy calculations were performed and indicated that adsorption of the Pb metal on the surface of the three nanotubes were stable, through a chemisorption. Therefore, CNTs are a feasible active material for filters that retain such metal. After Pb adsorption, the CNT and COOH-CNT conductivity changed, from semiconductor to half-metallic for CNT and from semiconductor to metallic for COOH-CNT, which can serve as a signal for Pb sensor. In all three cases adsorption produced a change in nanotube magnetism, which can also serve as a sensitive signal for chemical sensors. After adsorption of Pb, the changes in binding energy, charge transfer, conductance and magnetism may lead to the different response in the CNTs-based sensors. Thus, it is expected that these results could provide helpful information for the design and fabrication of the Pb sensing devices.
Energy Technology Data Exchange (ETDEWEB)
Faye, Omar, E-mail: omf071@mail.usask.ca [Department of Mechanical Engineering, College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, S7N 5A9 Saskatchewan (Canada); Department of Condensed Matter Physics, Cheikh Anta Diop University, Dakar (Senegal); Szpunar, Jerzy A; Szpunar, Barbara [Department of Mechanical Engineering, College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, S7N 5A9 Saskatchewan (Canada); Beye, Aboubaker Chedikh [Department of Condensed Matter Physics, Cheikh Anta Diop University, Dakar (Senegal)
2017-01-15
Highlights: • H{sub 2} adsorption in single and double-sided Pd-G(3x3) and the effect of NH radical on graphene were studied. • Strong interaction of Pd and graphene in double-sided Pd-G(3x3) than that in the single-sided Pd-G(3x3). • The storage capacity was 3.622 wt% with a binding energy of 0.658 eV/H2. • The increase of NH radicals on Pd-G(3x3) enhanced the binding of Pd atoms on the graphene sheet. • We predicted that 2NH-dopant at the opposite site of Pd atoms prevents the desorption of Pd atom from graphene sheet. - Abstract: We conducted a detailed theoretical investigation of the structural and electronic properties of single and double sided Pd-functionalized graphene and NH-doped Pd-functionalized graphene, which are shown to be efficient materials for hydrogen storage. Nitrene radical dopant was an effective addition required for enhancing the Pd binding on the graphene sheet as well as the storage of hydrogen. We found that up to eight H{sub 2} molecules could be adsorbed by double-sided Pd-functionalized graphene at 0 K with an average binding energy in the range 1.315–0.567 eVA gravimetric hydrogen density of 3.622 wt% was reached in the Pd-functionalized graphene on both sides. The binding mechanism of H{sub 2} molecules came not only the polarization mechanism between Pd and H atoms but also from the binding of the Pd atoms on the graphene sheet and the orbital hybridization. The most crucial part of our work is measuring the effect of nitrene radical on the H{sub 2} adsorption on Pd-functionalized graphene. Our calculations predicted that the addition of NH radicals on Pd-functionalized graphene enhance the binding of H{sub 2} molecules, which helps also to avoid the desorption of Pd(H{sub 2}){sub n} (n = 1–5) complexes from graphene sheet. Our results also predict Pd-functionalized NH-doped graphene is a potential hydrogen storage medium for on-board applications.
International Nuclear Information System (INIS)
Faye, Omar; Szpunar, Jerzy A; Szpunar, Barbara; Beye, Aboubaker Chedikh
2017-01-01
Highlights: • H_2 adsorption in single and double-sided Pd-G(3x3) and the effect of NH radical on graphene were studied. • Strong interaction of Pd and graphene in double-sided Pd-G(3x3) than that in the single-sided Pd-G(3x3). • The storage capacity was 3.622 wt% with a binding energy of 0.658 eV/H2. • The increase of NH radicals on Pd-G(3x3) enhanced the binding of Pd atoms on the graphene sheet. • We predicted that 2NH-dopant at the opposite site of Pd atoms prevents the desorption of Pd atom from graphene sheet. - Abstract: We conducted a detailed theoretical investigation of the structural and electronic properties of single and double sided Pd-functionalized graphene and NH-doped Pd-functionalized graphene, which are shown to be efficient materials for hydrogen storage. Nitrene radical dopant was an effective addition required for enhancing the Pd binding on the graphene sheet as well as the storage of hydrogen. We found that up to eight H_2 molecules could be adsorbed by double-sided Pd-functionalized graphene at 0 K with an average binding energy in the range 1.315–0.567 eVA gravimetric hydrogen density of 3.622 wt% was reached in the Pd-functionalized graphene on both sides. The binding mechanism of H_2 molecules came not only the polarization mechanism between Pd and H atoms but also from the binding of the Pd atoms on the graphene sheet and the orbital hybridization. The most crucial part of our work is measuring the effect of nitrene radical on the H_2 adsorption on Pd-functionalized graphene. Our calculations predicted that the addition of NH radicals on Pd-functionalized graphene enhance the binding of H_2 molecules, which helps also to avoid the desorption of Pd(H_2)_n (n = 1–5) complexes from graphene sheet. Our results also predict Pd-functionalized NH-doped graphene is a potential hydrogen storage medium for on-board applications.
Das, Tridip
temperature and oxygen partial pressure, for multiple LSF compositions and phases using a combined thermodynamics and DFT approach. A detailed oxygen vacancy migration barrier calculation gave the oxygen ionic diffusivity and conductivity. Oxygen vacancy also causes chemical strain, which was treated as a scalar in the literature. However, in many materials, it should be a tensor, which is anisotropic. We illustrate this effect on CeO2, in which it explained a puzzling experiment, which shows significant amplification of measured strain on applied bias in non-stoichiometric Gd doped ceria. The presence of highly localized 4f valence orbital in Ce causes charge disproportionation on the formation of neutral oxygen vacancy, producing anisotropic chemical strain in ceria with cubic symmetry. Understanding of delta and X and anisotropic chemical strain in the lattice has led to the design of better MIEC via element doping and strain engineering of the lattice.
Choi, Garam; Lee, Won Bo
Metal alloys, especially Al-based, are commonly-used materials for various industrial applications. In this paper, the Al-Cu alloys with varying the Al-Cu ratio were investigated based on the first-principle calculation using density functional theory. And the electronic transport properties of the Al-Cu alloys were carried out using Boltzmann transport theory. From the results, the transport properties decrease with Cu-containing ratio at the temperature from moderate to high, but with non-linearity. It is inferred by various scattering effects from the calculation results with relaxation time approximation. For the Al-Cu alloy system, where it is hard to find the reliable experimental data for various alloys, it supports understanding and expectation for the thermal electrical properties from the theoretical prediction. Theoretical and computational soft matters laboratory.
International Nuclear Information System (INIS)
Shein, I.R.; Ivanovskii, A.L.
2014-01-01
Highlights: • α and β polymorphs of BaZn 2 As 2 as a parent phase of the new DMSs are examined. • Structural, elastic, electronic properties are evaluated from first principles. • Inter-atomic bonding picture is discussed. -- Abstract: Very recently, on the example of hole- and spin-doped BaZn 2 As 2 , quite an unexpected area of potential applications of 122-like phases was proposed as a promising platform for searching the new diluted magnetic semiconductors (DMSs) (2013; K. Zhao, et al, Nature Commun. 4:1442). Herein, by means of the first-principles calculations, we have examined in detail the basic structural, elastic, electronic properties and the peculiarities of the inter-atomic bonding in α and β polymorphs of 122-like BaZn 2 As 2 – a parent phase of the new DMSs. Our characterization of these materials covers the optimized structural parameters, the main elastic parameters (elastic constants, bulk, shear, and Young’s moduli, Poisson’s ratio, anisotropy indexes, and Pugh’s criterion), as well as electronic bands and densities of electronic states
Aizawa, H.; Kuroki, K.; Yasuzuka, S.; Yamada, J.
2012-11-01
We perform a first-principles band calculation for a group of quasi-two-dimensional organic conductors β-(BDA-TTP)2MF6 (M = P, As, Sb and Ta). The ab-initio calculation shows that the density of states is correlated with the bandwidth of the singly occupied (highest) molecular orbital, while it is not necessarily correlated with the unit-cell volume. The direction of the major axis of the cross section of the Fermi surface lies in the Γ-B-direction, which differs from that obtained by the extended Hückel calculation. Then, we construct a tight-binding model which accurately reproduces the ab-initio band structure. The obtained transfer energies give a smaller dimerization than in the extended Hückel band. As to the difference in the anisotropy of the Fermi surface, the transfer energies along the inter-stacking direction are smaller than those obtained in the extended Hückel calculation. Assuming spin-fluctuation-mediated superconductivity, we apply random phase approximation to a two-band Hubbard model. This two-band Hubbard model is composed of the tight-binding model derived from the first-principles band structure and an on-site (intra-molecule) repulsive interaction taken as a variable parameter. The obtained superconducting gap changes sign four times along the Fermi surface like in a d-wave gap, and the nodal direction is different from that obtained in the extended Hückel model. Anion dependence of Tc is qualitatively consistent with the experimental observation.
International Nuclear Information System (INIS)
Aizawa, H; Kuroki, K; Yasuzuka, S; Yamada, J
2012-01-01
We perform a first-principles band calculation for a group of quasi-two-dimensional organic conductors β-(BDA-TTP) 2 MF 6 (M = P, As, Sb and Ta). The ab-initio calculation shows that the density of states is correlated with the bandwidth of the singly occupied (highest) molecular orbital, while it is not necessarily correlated with the unit-cell volume. The direction of the major axis of the cross section of the Fermi surface lies in the Γ–B-direction, which differs from that obtained by the extended Hückel calculation. Then, we construct a tight-binding model which accurately reproduces the ab-initio band structure. The obtained transfer energies give a smaller dimerization than in the extended Hückel band. As to the difference in the anisotropy of the Fermi surface, the transfer energies along the inter-stacking direction are smaller than those obtained in the extended Hückel calculation. Assuming spin-fluctuation-mediated superconductivity, we apply random phase approximation to a two-band Hubbard model. This two-band Hubbard model is composed of the tight-binding model derived from the first-principles band structure and an on-site (intra-molecule) repulsive interaction taken as a variable parameter. The obtained superconducting gap changes sign four times along the Fermi surface like in a d-wave gap, and the nodal direction is different from that obtained in the extended Hückel model. Anion dependence of T c is qualitatively consistent with the experimental observation. (paper)
Energy Technology Data Exchange (ETDEWEB)
Wan, Dongyun; Xiong, Ping; Chen, Lanli [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Shi, Siqi, E-mail: sqshi@shu.edu.cn [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Ishaq, Ahmad [National Center for Physics, Quaid-I-Azam University, Islamabad 44000 (Pakistan); Luo, Hongjie [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Gao, Yanfeng, E-mail: yfgao@shu.edu.cn [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China)
2017-03-01
Graphical abstract: VO{sub 2}(B) thin films with high TCR and suitable resistance were first achieved by W doping. The mechanism for performance improvement was studied by first-principles calculations. The two-dimensional octahedral structure of VO{sub 2}(B) favors the strain control with W-doping for achieving a large TCR, which overcomes the contradiction between the high conductivity and large TCR generated by dopants in VO{sub 2}(M). - Highlights: • High performance W-doped VO{sub 2}(B) thin films were first achieved by co-sputtering. • Mechanism for performance improvement was studied by first-principles calculations. • The two-dimensional octahedral structure of VO{sub 2} (B) favors the strain control. • Achieved VO{sub 2} films possess high thermal sensitivity (TCR: −3.9%/K & R{sub 0}: 32.7 kΩ). - Abstract: VO{sub 2}(B) is currently a preferred phase structure for the application as bolometer material, which, however, suffers from low temperature-coefficient-of-resistance (TCR) values and large resistances. Here we present the combined experimental and first-principles calculations study on both doped and undoped VO{sub 2}(B) thin films enabling us to attain high TCR (−3.9%/k) and suitable square-resistance (32.7 kΩ) by controlled W doping employing the widely used magnetron sputtering technique. The TCR value is 50% larger than reported ones at the similar resistance. The underlying microscopic mechanism for the performance improvement was studied and results indicated that the introduction of extra electrons and the variation in the band structure resulting from the incorporation of W{sup 6+} ions in the VO{sub 2}(B) crystal lattice contribute to the enhancement of the electronic conductivity. Moreover, the special two-dimensional octahedral structure of monoclinic (C2/m) B-phase VO{sub 2} favors the strain control with W-doping for achieving a large TCR, which overcomes the analogous predicament between the high conductivity and large TCR
Energy Technology Data Exchange (ETDEWEB)
Ciftci, Yasemin Oe. [Gazi University Teknikokullar, Department of Physics, Faculty of Sciences, Ankara (Turkey); Evecen, Meryem; Aldirmaz, Emine [Amasya University, Department of Physics, Faculty of Arts and Sciences, Amasya (Turkey)
2017-01-15
First-principles calculations for the structural, elastic, electronic and vibrational properties of BeGeAs{sub 2} with chalcopyrite structure have been reported in the frame work of the density functional theory. The calculated ground state properties are in good agreement with the available data. By considering the electronic band structure and electronic density of states calculation, it is found that this compound is a semiconductor which confirmed the previous work. Single-crystal elastic constants and related properties such as Young's modulus, Poisson ratio, shear modulus and bulk modulus have been predicted using the stress-finite strain technique. It can be seen from the calculated elastic constants that this compound is mechanically stable in the chalcopyrite structure. Pressure dependences of elastic constants and band gap are also reported. Finally, the phonon dispersion curves and total and partial density of states were calculated and discussed. The calculated phonon frequencies BeGeAs{sub 2} are positive, indicating the dynamical stability of the studied compound. (orig.)
Stability of Cd_1_–_xZn_xO_yS_1_–_y Quaternary Alloys Assessed with First-Principles Calculations
International Nuclear Information System (INIS)
Varley, Joel B.; He, Xiaoqing; Rockett, Angus; Lordi, Vincenzo
2017-01-01
One route to decreasing the absorption in CdS buffer layers in Cu(In,Ga)Se_2 and Cu_2ZnSn(S,Se)_4 thin-film photovoltaics is by alloying. Here we use first-principles calculations based on hybrid functionals to assess the energetics and stability of quaternary Cd, Zn, O, and S (Cd_1_–_xZn_xO_yS_1_–_y) alloys within a regular solution model. Our results identify that full miscibility of most Cd_1_–_xZn_xO_yS_1_–_y compositions and even binaries like Zn(O,S) is outside typical photovoltaic processing conditions. Finally, the results suggest that the tendency for phase separation of the oxysulfides may drive the nucleation of other phases such as sulfates that have been increasingly observed in oxygenated CdS and ZnS.
Kobayashi, Hajime; Kobayashi, Norihito; Hosoi, Shizuka; Koshitani, Naoki; Murakami, Daisuke; Shirasawa, Raku; Kudo, Yoshihiro; Hobara, Daisuke; Tokita, Yuichi; Itabashi, Masao
2013-07-07
Hopping and band mobilities of holes in organic semiconductors at room temperature were estimated from first principle calculations. Relaxation times of charge carriers were evaluated using the acoustic deformation potential model. It is found that van der Waals interactions play an important role in determining accurate relaxation times. The hopping mobilities of pentacene, rubrene, and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) in bulk single crystalline structures were found to be smaller than 4 cm(2)∕Vs, whereas the band mobilities were estimated between 36 and 58 cm(2)∕Vs, which are close to the maximum reported experimental values. This strongly suggests that band conductivity is dominant in these materials even at room temperature.
International Nuclear Information System (INIS)
Muro, Maiko; Natsume, Yutaka; Kikuma, Jun; Setoyama, Hiroyuki
2014-01-01
X-ray photoelectron spectroscopy (XPS) valence band spectra reflect the chemical bonding states. To take this advantage, we tried to interpret experimental spectra by the occupied density of states (DOS) based on first principles calculation. In this work, we discussed XPS and X-ray Absorption Near Edge Structure (XANES) spectra of 6, 13-bis(triisopropylsilylethynyl) pentacene (TIPS-Pen), which is well known as an organic semiconductor. We studied chemical structure change of TIPS-Pen caused by heat-treatment at 300degC under nitrogen and under the air. It has been suggested that the structural change of pentacene skeleton by Diels-Alder type reaction occurs in both cases. In addition, the sample heat-treated under the air showed desorption of the isopropyl group and increase of oxygen concentration. (author)
Energy Technology Data Exchange (ETDEWEB)
Li, C., E-mail: canli1983@gmail.com; Zhao, Y. F.; Fu, C. X.; Gong, Y. Y. [Center for Coordination Bond Engineering, School of Materials Science and Engineering, China Jiliang University (China); Chi, B. Q. [College of Modem Science and Technology, Jiliang University, Hangzhou, 310018 (China); Sun, C. Q. [Center for Coordination Bond Engineering, School of Materials Science and Engineering, China Jiliang University (China); School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 (Singapore)
2014-10-15
The effects of vertical compressive stress on Sb{sub 2}Te{sub 3} nano-films have been investigated by the first principles calculation, including stability, electronic structure, crystal structure, and bond order. It is found that the band gap of nano-film is sensitive to the stress in Sb{sub 2}Te{sub 3} nano-film and the critical thickness increases under compressive stress. The band gap and band order of Sb{sub 2}Te{sub 3} film has been affected collectively by the surface and internal crystal structures, the contraction ratio between surface bond length of nano-film and the corresponding bond length of bulk decides the band order of Sb{sub 2}Te{sub 3} film.
Choi, Woo Seok; Jeen, Hyoungjeen; Lee, Jun Hee; Seo, S. S. Ambrose; Cooper, Valentino R.; Rabe, Karin M.; Lee, Ho Nyung
2013-08-01
Using real-time spectroscopic ellipsometry, we directly observed a reversible lattice and electronic structure evolution in SrCoOx (x=2.5-3) epitaxial thin films. Drastically different electronic ground states, which are extremely susceptible to the oxygen content x, are found in the two topotactic phases: i.e., the brownmillerite SrCoO2.5 and the perovskite SrCoO3. First-principles calculations confirmed substantial differences in the electronic structure, including a metal-insulator transition, which originate from the modification in the Co valence states and crystallographic structures. More interestingly, the two phases can be reversibly controlled by changing the ambient pressure at greatly reduced temperatures. Our finding provides an important pathway to understanding the novel oxygen-content-dependent phase transition uniquely found in multivalent transition metal oxides.
Choi, Woo Seok; Jeen, Hyoungjeen; Lee, Jun Hee; Seo, S S Ambrose; Cooper, Valentino R; Rabe, Karin M; Lee, Ho Nyung
2013-08-30
Using real-time spectroscopic ellipsometry, we directly observed a reversible lattice and electronic structure evolution in SrCoO(x) (x=2.5-3) epitaxial thin films. Drastically different electronic ground states, which are extremely susceptible to the oxygen content x, are found in the two topotactic phases: i.e., the brownmillerite SrCoO2.5 and the perovskite SrCoO3. First-principles calculations confirmed substantial differences in the electronic structure, including a metal-insulator transition, which originate from the modification in the Co valence states and crystallographic structures. More interestingly, the two phases can be reversibly controlled by changing the ambient pressure at greatly reduced temperatures. Our finding provides an important pathway to understanding the novel oxygen-content-dependent phase transition uniquely found in multivalent transition metal oxides.
International Nuclear Information System (INIS)
Nakamura, Hiroki; Okumura, Masahiko; Machida, Masahiko
2013-01-01
Zeolites have attracted attention in the reprocessing of radioactive nuclear waste because of their high selective affinity for radioisotopes of Cs. Very recently, their useful properties have been widely utilized in decontamination after the accident at the Fukushima Daiichi Nuclear Power Plants. In this study, we study the high selectivity in the Cs adsorption of zeolites using first-principles calculations and clarify the mechanism of the cation selectivity of zeolites. We obtain energy surfaces on all capture locations for Cs/Na ions inside the micropores of a zeolite, 'mordenite', and find three crucial conditions for the highly ion-selective exchange of Na for Cs: 1) micropores with a radius of ∼3 Å, 2) a moderate Al/Si ratio, and 3) a uniform distribution of Al atoms around each micropore. These insights suggest a guideline for developing zeolites with high Cs selectivity and for enhancing the cation selectivity in more general situations. (author)
International Nuclear Information System (INIS)
Min, Y.; Yao, K.L.; Liu, Z.L.; Cheng, H.G.; Zhu, S.C.; Gao, G.Y.
2009-01-01
We report on first-principles calculations of spin-dependent quantum transport in a CrAs(0 0 1)/AlAs(0 0 1) heterogeneous junction and predict a strong diode effect of charge and spin current. The minority spin current is absolutely inhibited when the bias voltage is applied to the terminals of both CrAs and AlAs. The majority spin current is inhibited when the bias voltage is applied to the terminal of CrAs and 'relaxed' when the bias voltage is applied to the terminal of AlAs. The charge and spin current diode are promising for reprogrammable logic applications in the field of spintronics
Energy Technology Data Exchange (ETDEWEB)
Benkabou, M. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, H. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Département de Physique, Faculté des Sciences, Université Hassiba Benbouali, Chlef 02000 (Algeria); Abdellaoui, A. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, D., E-mail: rachdj@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique de la Matière, (LPQ3M), Université de Mascara, Mascara 29000 (Algeria); and others
2015-10-25
First-principle calculations are performed to predict the electronic structure and elastic and magnetic properties of CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys. The calculations employ the full-potential linearized augmented plane wave. The exchange-correlations are treated within the generalized gradient approximation of Perdew–Burke and Ernzerhof (GGA-PBE). The electronic structure calculations show that these compounds exhibit a gap in the minority states band and are clearly half-metallic ferromagnets, with the exception of the CoRhMnAl and CoRhMnGa, which are simple ferromagnets that are nearly half metallic in nature. The CoRhMnGe and CoRhMnSi compounds and their magnetic moments are in reasonable agreement with the Slater-Pauling rule, which indicates the half metallicity and high spin polarization for these compounds. At the pressure transitions, these compounds undergo a structural phase transition from the Y-type I → Y-type II phase. We have determined the elastic constants C{sub 11}, C{sub 12} and C{sub 44} and their pressure dependence, which have not previously been established experimentally or theoretically. - Highlights: • Based on DFT calculations, CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys were investigated. • The magnetic phase stability was determined from the total energy calculations. • The mechanical properties were investigated.
Xu-Dong, Zhang; Wei, Jiang
2016-02-01
The effects of high pressure on lattice stability, mechanical and thermodynamic properties of L12 structure Al3Tm and Al3Lu are studied by first-principles calculations within the VASP code. The phonon dispersion curves and density of phonon states are calculated by using the PHONONPY code. Our results agree well with the available experimental and theoretical values. The vibrational properties indicate that Al3Tm and Al3Lu keep their dynamical stabilities in L12 structure up to 100 GPa. The elastic properties and Debye temperatures for Al3Tm and Al3Lu increase with the increase of pressure. The mechanical anisotropic properties are discussed by using anisotropic indices AG, AU, AZ, and the three-dimensional (3D) curved surface of Young’s modulus. The calculated results show that Al3Tm and Al3Lu are both isotropic at 0 GPa and anisotropic under high pressure. In the present work, the sound velocities in different directions for Al3Tm and Al3Lu are also predicted under high pressure. We also calculate the thermodynamic properties and provide the relationships between thermal parameters and temperature/pressure. These results can provide theoretical support for further experimental work and industrial applications. Project supported by the Scientific Technology Plan of the Educational Department of Liaoning Province and Liaoning Innovative Research Team in University, China (Grant No. LT2014004) and the Program for the Young Teacher Cultivation Fund of Shenyang University of Technology, China (Grant No. 005612).
Energy Technology Data Exchange (ETDEWEB)
Li, Li; Wang, Y.-J. [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, 2 Chongwen Road, Nan' an District, Chongqing 400065 (China); Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Liu, D.-X.; Ma, C.-G. [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, 2 Chongwen Road, Nan' an District, Chongqing 400065 (China); Brik, M.G., E-mail: mikhail.brik@ut.ee [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, 2 Chongwen Road, Nan' an District, Chongqing 400065 (China); Institute of Physics, University of Tartu, W. Ostwald Str. 1, Tartu 50411 (Estonia); Institute of Physics, Jan Długosz University, Armii Krajowej 13/15, PL-42200 Częstochowa (Poland); Suchocki, A. [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, 2 Chongwen Road, Nan' an District, Chongqing 400065 (China); Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Institute of Physics, Kazimierz Wielki University, Weyssenhoffa 11, 85-072 Bydgoszcz (Poland); Piasecki, M. [Institute of Physics, Jan Długosz University, Armii Krajowej 13/15, PL-42200 Częstochowa (Poland); Reshak, A.H. [New Technologies – Research Centre, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia)
2017-02-15
Three fluoroperovskites with the general formula XCaF{sub 3} (X = K, Rb, Cs) have been systematically studied using the first-principles methods. The structural, electronic, optical, elastic and thermodynamic properties of these three compounds were calculated at the ambient and elevated hydrostatic pressure. Variation of all these properties with pressure was analyzed; it was shown that the structural and elastic constants change linearly with increased pressure, whereas the calculated band gaps follow the quadratic dependence on pressure. Influence of the first cation variation (K – Rb – Cs) on these properties was discussed. Elastic anisotropy (directional dependence of the Young moduli) of these compounds was modeled and analyzed for the first time. - Highlights: • Three cubic perovskites XCaF{sub 3} (X = K, Rb, Cs) were studied by ab initio methods. • Systematic variation of physical properties with the first cation change was traced. • Pressure effects on physical properties were calculated and modeled. • Debye temperature and Grüneisen constant for all materials were calculated for the first time. • Elastic anisotropy was visualized by plotting Young moduli directional dependences.
Energy Technology Data Exchange (ETDEWEB)
Feng, Xuan-Kai [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Shi, Siqi, E-mail: sqshi@shu.edu.cn [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Shen, Jian-Yun [General Research Institute for Nonferrous Metals, Beijing 100088 (China); Shang, Shun-Li [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 (United States); Yao, Mei-Yi, E-mail: yaomeiyi@shu.edu.cn [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Liu, Zi-Kui [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 (United States)
2016-10-15
Since Zr-Fe-Sn is one of the key ternary systems for cladding and structural materials in nuclear industry, it is of significant importance to understand physicochemical properties related to Zr-Fe-Sn system. In order to design the new Zr alloys with advanced performance by CALPHAD method, the thermodynamic model for the lower order systems is required. In the present work, first-principles calculations are employed to obtain phonon, thermodynamic and elastic properties of Zr{sub 6}FeSn{sub 2} with C22 structure and the end-members (C22-Zr{sub 6}FeFe{sub 2}, C22-Zr{sub 6}SnSn{sub 2} and C22-Zr{sub 6}SnFe{sub 2}) in the model of (Zr){sub 6}(Fe, Sn){sub 2}(Fe, Sn){sub 1}. It is found that the imaginary phonon modes are absent for C22-Zr{sub 6}FeSn{sub 2} and C22-Zr{sub 6}SnSn{sub 2}, indicating they are dynamically stable, while the other two end-members are unstable. Gibbs energies of C22-Zr{sub 6}FeSn{sub 2} and C22-Zr{sub 6}SnSn{sub 2} are obtained from the quasiharmonic phonon approach and can be added in the thermodynamic database: Nuclearbase. The C22-Zr{sub 6}FeSn{sub 2}’s single-crystal elasticity tensor components along with polycrystalline bulk, shear and Young’s moduli are computed with a least-squares approach based upon the stress tensor computed from first-principles method. The results indicate that distortion is more difficult in the directions normal the c-axis than along to it.
First-principles calculations of a half-metallic ferromagnet zinc blende Zn{sub 1−x}V{sub x}Te
Energy Technology Data Exchange (ETDEWEB)
El Amine Monir, M.; Baltache, H. [Laboratoire de Physique Quantique de la Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 (Algeria); Murtaza, G. [Materials Modeling Laboratory, Department of Physics, Islamia College University, Peshawar (Pakistan); Azam, Sikander [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Bouhemadou, A. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University Setif 1, 19000 Setif (Algeria); Al-Douri, Y. [Institute of Nano Electronic Engineering, University Malaysia Perlis, 01000 Kangar, Perlis (Malaysia); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Ali, Roshan [Materials Modeling Lab, Department of Physics, Post Graduate Jahanzeb College, Swat (Pakistan)
2015-03-15
First-principles calculations have been used to study the structural, elastic, electronic, magnetic and thermal properties of zinc blende Zn{sub 1−x}V{sub x}Te for x=0, 0.25, 0.50, 0.75 and 1 using the full-potential linearized augmented plane wave method (FP-LAPW) based on spin-polarized density functional theory (DFT). The electronic exchange-correlation potential is approached using the spin generalized gradient approximation (spin-GGA). The structural properties of the Zn{sub 1−x}V{sub x}Te alloys (x=0, 0.25, 0.50, 0.75 and 1) are given for the lattice constants and the bulk moduli and their pressure derivatives. The elastic constants C{sub 11}, C{sub 12} and C{sub 44} are calculated using numerical first-principles calculations implemented in the WIEN2k package. An analysis of the band structures and the densities of states reveals that Zn{sub 0.50}V{sub 0.50}Te and Zn{sub 0.75}V{sub 0.25}Te exhibit a half-metallic character, while Zn{sub 0.25}V{sub 0.75}Te is nearly half-metallic. The band structure calculations are used to estimate the spin-polarized splitting energies Δ{sub x}(d) and Δ{sub x}(pd) produced by the V(3d)-doped and s(p)–d exchange constants N{sub 0α} (conduction band) and N{sub 0β} (valence band). The p–d hybridization reduces the magnetic moment of V from its atomic charge value of 3µ{sub B} and creates small local magnetic moments on the nonmagnetic Zn and Te sites. Finally, we present the thermal effect on the macroscopic properties of these alloys, such as the thermal expansion coefficient, heat capacity and Debye temperature, based on the quasi-harmonic Debye model. - Highlights: • Some physical properties of Vanadium doped ZnTe have been investigated. • Structural parameters for the parent compounds compare well with the available data. • The elastic and thermal properties are studied for the first time.
Energy Technology Data Exchange (ETDEWEB)
Liu, Qi-Jun, E-mail: qijunliu@home.swjtu.edu.cn [Bond and Band Engineering Group, Institute of High Temperature and High Pressure Physics, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Zhang, Ning-Chao; Liu, Fu-Sheng [Bond and Band Engineering Group, Institute of High Temperature and High Pressure Physics, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Liu, Zheng-Tang [State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an, Shaanxi 710072 (China)
2014-03-15
Highlights: • OsTM and TMOs{sub 2} compounds have no superhard character. • These compounds are mechanically stable and behave in ductile manner. • OsTM has a mixture of covalent-ionic and metallic character. -- Abstract: The first-principles calculations have been performed to study the structural, elastic, mechanical and electronic properties of cubic OsTM (TM = Ti, Zr, and Hf) and hexagonal TMOs{sub 2} compounds. The calculated structural parameters are in good agreement with the available experimental data. To the best of our knowledge, the elastic constants of OsTM and TMOs{sub 2} compounds have been obtained for the first time. The calculated elastic and mechanical properties show that these compounds have no superhard character. These compounds are mechanically stable and behave in ductile manner. The electronic band structures and densities of states of OsTM and TMOs{sub 2} compounds have been analysed. OsTM has a mixture of covalent-ionic and metallic character, and TMOs{sub 2} has strong metallic nature.
International Nuclear Information System (INIS)
Huang Chang-Bao; Wu Hai-Xin; Ni You-Bao; Wang Zhen-You; Qi Ming; Zhang Chun-Li
2016-01-01
The structural, electronic, mechanical properties, and frequency-dependent refractive indexes of GaSe 1–x S x (x = 0, 0.25, and 1) are studied by using the first-principles pseudopotential method within density functional theory. The calculated results demonstrate the relationships between intralayer structure and elastic modulus in GaSe 1–x S x (x = 0, 0.25, and 1). Doping of ε -GaSe with S strengthens the Ga– X bonds and increases its elastic moduli of C 11 and C 66 . Born effective charge analysis provides an explanation for the modification of cleavage properties about the doping of ε -GaSe with S. The calculated results of band gaps suggest that the distance between intralayer atom and substitution of S Se , rather than interlayer force, is a key factor influencing the electronic exciton energy of the layer semiconductor. The calculated refractive indexes indicate that the doping of ε -GaSe with S reduces its refractive index and increases its birefringence. (paper)
Energy Technology Data Exchange (ETDEWEB)
Yi, Guohui [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Zhang, Xinyu, E-mail: xyzhang@ysu.edu.cn [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Qin, Jiaqian, E-mail: jiaqianqin@gmail.com [Metallurgy and Materials Science Research Institute, Chulalongkorn University, Bangkok 10330 (Thailand); Ning, Jinliang; Zhang, Suhong; Ma, Mingzhen; Liu, Riping [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China)
2015-08-15
Highlights: • The mechanical and fundamental thermal data of Cu{sub 5}Zr and Cu{sub 5}Hf are determined. • The technologically important elastic anisotropy is obtained and discussed according to its industrial applications. • The brittle/ductile and bonding nature of Cu{sub 5}Zr and Cu{sub 5}Hf are analyzed in details. - Abstract: The structural, elastic, electronic and thermodynamic properties of Cu{sub 5}Zr and Cu{sub 5}Hf compounds are investigated by first-principles calculations combined with the quasi-harmonic Debye model. The calculated lattice parameters of cubic AuBe{sub 5}-type Cu{sub 5}Zr and Cu{sub 5}Hf agree well with available experimental and other theoretical results and the formation enthalpy calculations show that AuBe{sub 5}-type Cu{sub 5}Hf is more energetically stable than the competing hexagonal CaCu{sub 5}-type phase. The mechanical properties such as mechanical stabilities, anisotropy character, ductility (estimated from the value of B/G, Poisson’s ratio υ and Cauchy pressures C{sub 12}–C{sub 44}) and thermodynamic properties such as volume change under temperature and pressure (V/V{sub 0}), heat capacity (C{sub v}), Debye temperature (Θ), thermal expansion coefficient (α) of AuBe{sub 5}-type Cu{sub 5}Zr and Cu{sub 5}Hf are calculated together. Cu{sub 5}Hf has better performances than Cu{sub 5}Zr with higher hardness and better resistance to fracture which are rationalized from the calculated electronic structure (including density of states, charge density distributions, Mulliken’s population analysis) and we find that all ionic, covalent and metallic components exist in bonding of Cu{sub 5}Zr and Cu{sub 5}Hf but the covalent bonding in Cu{sub 5}Hf is stronger.
Energy Technology Data Exchange (ETDEWEB)
Zhou, Zhaobo [Key Laboratory of Advanced Materials of Yunnan Province & Key Laboratory of Advanced Materials of Non-Ferrous and Precious Rare Metals Ministry of Education, Kunming University of Science and Technology, Kunming 650093 (China); Zhou, Xiaolong, E-mail: kmzxlong@163.com [Key Laboratory of Advanced Materials of Yunnan Province & Key Laboratory of Advanced Materials of Non-Ferrous and Precious Rare Metals Ministry of Education, Kunming University of Science and Technology, Kunming 650093 (China); Zhang, Kunhua [State Key Laboratory of Rare Precious Metals Comprehensive Utilization of New Technologies, Kunming Institute of Precious Metals, Kunming 650106 (China)
2016-12-15
First-principle calculations were performed to investigate the structural, phase stability, electronic, elastic properties and hardness of monoclinic structure IrN{sub 2} (m-IrN{sub 2}), orthorhombic structure IrN{sub 2} (o-IrN{sub 2}) and zinc blende structure IrN (ZB IrN). The results show us that only m-IrN{sub 2} is both thermodynamic and dynamic stability. The calculated band structure and density of states (DOS) curves indicate that o-IrN{sub 2} and ZB Ir-N compounds we calculated have metallic behavior while m-IrN{sub 2} has a small band gap of ~0.3 eV, and exist a common hybridization between Ir-5d and N-2p states, which forming covalent bonding between Ir and N atoms. The difference charge density reveals the electron transfer from Ir atom to N atom for three Ir-N compounds, which forming strong directional covalent bonds. Notable, a strong N-N bond appeared in m-IrN{sub 2} and o-IrN{sub 2}. The ratio of bulk to shear modulus (B/G) indicate that three Ir-N compounds we calculated are ductile, and ZB IrN possesses a better ductility than two types IrN{sub 2}. m-IrN{sub 2} has highest Debye temperature (736 K), illustrating it possesses strongest covalent bonding. The hardness of three Ir-N compounds were also calculated, and the results reveal that m-IrN{sub 2} (18.23 GPa) and o-IrN{sub 2} (18.02 GPa) are ultraincompressible while ZB IrN has a negative value, which may be attributed to phase transition at ca. 1.98 GPa.
Energy Technology Data Exchange (ETDEWEB)
Wu Yurong [College of Electromechanical Engineering, Hunan University of Science and Technology, Xiantang 411201 (China); Hu Wangyu [Department of Applied Physics, Hunan University, Changsha 410082 (China)], E-mail: wangyuhu2001cn@yahoo.com.cn; Han Shaochang [Department of Applied Physics, Hunan University, Changsha 410082 (China)
2008-10-01
First-principles calculations have been used to study the elastic and electronic properties of ductility rare-earth alloy YM (M=Ag, Cu, Rh) systems. The ductility mechanism for these alloys is studied from microscopic aspect, via electronic density of states (DOS). The Fermi energy lies near a local minimum, and the hybridization is stronger than that of the common NiAl alloy, demonstrating that the ductility of these alloys is much better than that of NiAl alloy. Elastic modulus, namely, shear modulus C'=(C{sub 11}-C{sub 12})/2, bulk modulus B and C{sub 44} are calculated by volume-conserving orthorhombic, hydrostatic pressure and tri-axial shear strain, respectively. Moreover, lattice parameters, antiphase boundary (APB) energies and unstable stacking fault energies of these alloys are also studied. The APB energies are greater than the unstable stacking fault energies for these alloy systems, and this is a characteristic of the ductility rare-earth alloy. The APB energies of YRh are the highest ones in these three YM alloys, which make dislocation dissociation difficult. The DOS and APB energy results show that the ductility of YRh may be worst in these three YM systems.
International Nuclear Information System (INIS)
Mizutani, U; Asahi, R; Noritake, T; Sato, H; Takeuchi, T
2008-01-01
The first-principles FLAPW (full potential linearized augmented plane wave) electronic structure calculations were performed for the Ag 5 Li 8 gamma-brass, which contains 52 atoms in a unit cell and has been known for many years as one of the most structurally complex alloy phases. The calculations were also made for its neighboring phase AgLi B2 compound. The main objective in the present work is to examine if the Ag 5 Li 8 gamma-brass is stabilized at the particular electrons per atom ratio e/a = 21/13 in the same way as some other gamma-brasses like Cu 5 Zn 8 and Cu 9 Al 4 , obeying the Hume-Rothery electron concentration rule. For this purpose, the e/a value for the Ag 5 Li 8 gamma-brass as well as the AgLi B2 compound was first determined by means of the FLAPW-Fourier method we have developed. It proved that both the gamma-brass and the B2 compound possess an e/a value equal to unity instead of 21/13. Moreover, we could demonstrate why the Hume-Rothery stabilization mechanism fails for the Ag 5 Li 8 gamma-brass and proposed a new stability mechanism, in which the unique gamma-brass structure can effectively lower the band-structure energy by forming heavily populated bonding states near the bottom of the Ag-4d band
Musari, A. A.; Joubert, D. P.; Adebayo, G. A.
2018-04-01
Cuprite (Cu2O) is a solid mineral and a compound whose simplicity of preparation, non toxic nature, low band gap and its abundance has made it a prospective candidate for the realisation of low cost photovoltaic applications. The present work successfully dopes Cuprite with Ag ({{{Cu}}}2(1-{{x})}{{{Ag}}}2{{x}}{{O}}) at different concentrations x = 0, 0.25, 0.5, 0.75 and 1, their first-principle calculations of their electronic, dynamical and thermodynamic properties have been investigated extensively within the generalised gradient approximation. Direct band gap energies at {{Γ }} are predicted for all the studied systems. A small bowing parameter for lattice constants ba and bulk modulus bB of 0.4245 \\mathring{{A}} and 0.8747 GPa were obtained when compared to Vegard’s law. The results of phonon dispersion when x = 0 and 1 indicate stability, these agree with available theoretical and experimental results while negative frequencies observed along the Brillouin zone for the doped systems when x = 0.25, 0.5 and 0.75 imply that they are dynamically unstable. The thermodynamic properties between 0 to 800 K were determined using the calculated phonon density of states within the harmonic approximation and the values of the specific heat capacity at constant volume at ambient temperature and the temperature at which lattice vibrations and thermal motion of electrons contribute to the constant volume specific heat capacity are presented for all the systems.
Energy Technology Data Exchange (ETDEWEB)
Madjet, Mohamed E., E-mail: mmadjet@qf.org.qa; El-Mellouhi, Fedwa; Carignano, Marcelo A.; Berdiyorov, Golibjon R. [Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation, P. O. Box 5825, Doha (Qatar)
2016-04-28
We calculated the partial charges in methylammonium (MA) lead-iodide perovskite CH{sub 3}NH{sub 3}PbI{sub 3} in its different crystalline phases using different first-principles electronic charge partitioning approaches, including the Bader, ChelpG, and density-derived electrostatic and chemical (DDEC) schemes. Among the three charge partitioning methods, the DDEC approach provides chemically intuitive and reliable atomic charges for this material, which consists of a mixture of transition metals, halide ions, and organic molecules. The DDEC charges are also found to be robust against the use of hybrid functionals and/or upon inclusion of spin–orbit coupling or dispersive interactions. We calculated explicitly the atomic charges with a special focus on the dipole moment of the MA molecules within the perovskite structure. The value of the dipole moment of the MA is reduced with respect to the isolated molecule due to charge redistribution involving the inorganic cage. DDEC charges and dipole moment of the organic part remain nearly unchanged upon its rotation within the octahedral cavities. Our findings will be of both fundamental and practical importance, as the accurate and consistent determination of the atomic charges is important in order to understand the average equilibrium distribution of the electrons and to help in the development of force fields for larger scale atomistic simulations to describe static, dynamic, and thermodynamic properties of the material.
Study of Cs adsorption on Ga(Mg)0.75Al0.25N (0 0 0 1) surface: A first principle calculation
International Nuclear Information System (INIS)
Yang, Mingzhu; Chang, Benkang; Hao, Guanghui; Guo, Jing; Wang, Honggang; Wang, Meishan
2013-01-01
In order to study the activation process of Ga 1−x Al x N photocathodes theoretically, models of Cs adsorption on Ga(Mg) 0.75 Al 0.25 N (0 0 0 1) surface are built, then the atomic structure, electronic structure, adsorption energy, work function, dipole moment and optical properties of the models are calculated. All calculations are carried out using Cambridge Serial Total Energy Package (CASTEP) based on first principle. Results show that Cs adsorption on Mg doping Ga 1−x Al x N (0 0 0 1) surface can reduce work function of the surface, and the favorite adsorption site is on the top of p-type impurity. Cs adsorption on p-type Ga 1−x Al x N (0 0 0 1) surface can produce the structure of p-type bulk with n-type surface, which is helpful to surface band bend downward and decrease electron affinity seriously. The absorption coefficient of Cs adsorption system is less than that of the clean surface. Theoretical study of Cs adsorption on Ga 1−x Al x N (0 0 0 1) surface can help to improve activation technology of Ga 1−x Al x N photocathodes.
Huo, Lei; Wang, Shunhua; Pu, Jibin; Sun, Junhui; Lu, Zhibin; Ju, Pengfei; Wang, Liping
2018-04-01
The friction behavior and the mechanism of DLC films in CO2 atmosphere are rarely explored, which is a significant obstacle for the potential practical application of DLC films in primarily CO2 environment. Here, the experiments and first-principles calculations are performed to simultaneously investigate this theme. We find that DLC films in CO2 atmosphere exhibit astoundingly low friction coefficient compared with in ambient air and vacuum atmospheres. The XPS and Raman spectrums demonstrate the possibly activation of CO2 molecule in the shearing interfaces, which may be critical for the low friction of DLC films in CO2 atmosphere. The calculated results reveal that the lactone groups can easily form during the horizontally chemisorption of CO2 molecule on the DLC surface, which is energetic and is a favorable process under the interfacial stress. Because of the presence of the lone-pairs of the lactone group, the lactone-terminated surfaces appear to be responsible for the low friction of DLC films in CO2 atmosphere. The studies may open up the possibility for DLC films usage in Mars applications.
Directory of Open Access Journals (Sweden)
Kuankuan Chen
2017-03-01
Full Text Available Deformation modes were studied for Ti3AN (A = Al, In and Tl by applying strain to the materials using first-principle calculations. The states of the bonds changed during the deformation process, and the Ti-N bonds remained structurally stable under deformation. The elastic anisotropy, electronic structures, hardness, and minimum thermal conductivity of anti-perovskite Ti3AN were investigated using the pseudo potential plane-wave method based on density functional theory. We found that the anisotropy of Ti3InN was significantly larger than that of Ti3AlN and Ti3TlN. All three compounds were mechanically stable. The band structures of the three compounds revealed that they were conductors. The minimum thermal conductivities at high temperature in the propagation directions of [100], [110], and [111] were calculated by the acoustic wave velocity, which indicated that the thermal conductivity was also anisotropic. It is indicated that Ti3InN is a good thermal barrier material.
International Nuclear Information System (INIS)
Zhang, J.; Huang, Y.N.; Mao, C.; Peng, P.
2012-01-01
Highlights: ► The co-incorporation of Ti and F into MgH 2 lattice is energetically favorable. ► The incorporated Ti and F in MgH 2 preferably generate TiH 2 and MgF 2 , respectively. ► The synergistic effect of Ti and F is superior to that of pure Ti. ► The weakened interactions of Mg–H explain enhanced dehydrogenation properties. - Abstract: The energetic and electronic properties of MgH 2 co-doped with Ti and F are investigated using first-principles calculations based on density functional theory. The calculation results show that incorporation of Ti combined with F atoms into MgH 2 lattice is energetically favorable relative to single incorporation of Ti atom. After dehydrogenation, the co-doped Ti and F in MgH 2 preferably generate TiH 2 and MgF 2 , respectively. Comparatively, the combined effect of Ti and F in improving the dehydrogenation properties of MgH 2 is superior to that of pure Ti. These results provide a reasonable explanation for experimental observations. Analysis of electronic structures suggests the enhanced dehydrogenation properties of doped MgH 2 can be attributed to the weakened bonding interactions between Mg and H due to foreign species doping.
International Nuclear Information System (INIS)
Wu Yurong; Hu Wangyu; Han Shaochang
2008-01-01
First-principles calculations have been used to study the elastic and electronic properties of ductility rare-earth alloy YM (M=Ag, Cu, Rh) systems. The ductility mechanism for these alloys is studied from microscopic aspect, via electronic density of states (DOS). The Fermi energy lies near a local minimum, and the hybridization is stronger than that of the common NiAl alloy, demonstrating that the ductility of these alloys is much better than that of NiAl alloy. Elastic modulus, namely, shear modulus C'=(C 11 -C 12 )/2, bulk modulus B and C 44 are calculated by volume-conserving orthorhombic, hydrostatic pressure and tri-axial shear strain, respectively. Moreover, lattice parameters, antiphase boundary (APB) energies and unstable stacking fault energies of these alloys are also studied. The APB energies are greater than the unstable stacking fault energies for these alloy systems, and this is a characteristic of the ductility rare-earth alloy. The APB energies of YRh are the highest ones in these three YM alloys, which make dislocation dissociation difficult. The DOS and APB energy results show that the ductility of YRh may be worst in these three YM systems
International Nuclear Information System (INIS)
Kniznik, L; Alonso, P.R; Gargano, P.H; Rubiolo, G.H.
2012-01-01
We investigated the point defect structure of oI20 UAl 4 in order to study aluminum diffusion. We performed ab initio calculations within a pseudopotentials method implemented in the Vienna Ab initio Simulation Package (VASP) to obtain point defect formation energies: vacancies (V U and V A l ) and antisites (Al U and U A l). Using a statistical-thermodynamic model we calculated defects concentrations as function of temperature and deviation from stoichiometry. For stoichiometric UAl 4 antisites are the dominant thermal defects. In off-stoichiometric UAl 4 , antisites are the constitutional defects. For U-rich UAl 4 , the thermal defect is called Entre Ramas, where one antisite U atom is replaced by five Al vacancies. For Al-rich UAl 4 , the thermal defect is also an Entre Ramas, where four antisite Al atoms are replaced by five U vacancies. Our first principles results were used to model UAl 4 intermediate phase with a two sublattices Wagner-Schottky model. The Thermocalc data bases previously used were modified, including antisites and vacancies in both sublattices of the UAl 4 intermediate phase: (U,Al,VA) 0.2 : (Al,U,VA) 0.8 . We obtained a consistent thermodynamic database able to reproduce the entire U-Al equilibrium phase diagram (author)
Rouchdi, M.; Salmani, E.; Dehmani, M.; Ez-Zahraouy, H.; Hassanain, N.; Benyoussef, A.; Mzerd, A.
2018-02-01
Using the first-principles calculations within the Korringa-Kohn-Rostoker (KKR) method combined with the coherent potential approximation (CPA), the structural, optical and magnetic properties of rare-earth nitride Ho0.95TM0.05N doped with transition metal (TM) atoms (Ti, V, Cr, Mn, Co and Ni) are investigated as a function the generalized gradient approximation and self-interaction correction (GGA-SIC) approximation. The optical properties are studied in detail by using ab-initio calculations. Using GGA-SIC we have showed that the bandgap value is in good agreement with the experimental value. Using GGA-SIC approximation for HoN, we have obtained a bandgap of 0.9 eV. Some of the dilute magnetic semiconductors (DMS) like Ho0.95TM0.05N under study exhibit a half-metallic behavior, which makes them suitable for spintronic applications. Moreover, the optical absorption spectra confirm the ferromagnetic stability based on the charge state of magnetic impurities.
International Nuclear Information System (INIS)
Jiang, Bo; Hou, Na; Huang, Shanyan; Zhou, Gege; Hou, Jungang; Cao, Zhanmin; Zhu, Hongmin
2013-01-01
The lattice parameters, structural stability and electronic structure of titanium oxycarbides (TiC 1−x O x , 0≤x≤1) solid solution were investigated by Rietveld refinement and first-principles calculations. Series of TiC 1−x O x were precisely synthesized by sintering process under the vacuum. Rietveld refinement results of XRD patterns show the properties of continuous solid solution in TiC 1−x O x over the whole composition range. The lattice parameters vary from 0.4324 nm to 0.4194 nm decreasing with increasing oxygen concentration. Results of first-principles calculations reveal that the disorder C/O structure is stable than the order C/O structure. Further investigations of the vacancy in Ti 1−Va (C 1−x O x ) 1−Va solid solution present that the structure of vacancy segregated in TiO-part is more stable than the disorder C/O structure, which can be ascribed to the Ti–Ti bond across O-vacancy and the charge redistributed around Ti-vacancy via the analysis of the electron density difference plots and PDOS. - Graphical abstract: XRD of series of titanium oxycarbides (TiC 1−x O x , 0≤x≤1) solid solution prepared by adjusting the proportion of TiO in the starting material. Highlights: • Titanium oxycarbides were obtained by sintering TiO and TiC under carefully controlled conditions. • Rietveld refinement results show continuous solid solution with FCC structure in TiC 1−x O x . • The disorder C/O structure is stable than the order C/O structure. • Introduction of vacancy segregated in TiO-part is more stable than disorder C/O structure. • Ti–Ti bond across O-vacancy and the charge redistributed around Ti-vacancy enhance structural stability
International Nuclear Information System (INIS)
Zhao Wenjie; Wang Yuanxu
2009-01-01
First-principle calculations were performed to investigate the structural, elastic, and electronic properties of TaB 2 , TaB, IrB 2 , and IrB. The calculated equilibrium structural parameters, shear modulus, and Young's modulus of TaB 2 are well consistent with the available experimental data, and TaB 2 with P6/mmm space group has stronger directional bonding between ions than WB 2 , OsB 2 , IrN 2 , and PtN 2 . For TaB 2 , the hexagonal P6/mmm structure is more stable than the orthorhombic Pmmn one, while for IrB 2 the orthorhombic Pmmn structure is the most stable one. The high shear modulus of P6/mmm phase TaB 2 is mainly due to the strong covalent π-bonding of B-hexagon in the (0001) plane. Such a B-hexagon network can strongly resist against an applied [112-bar0] (0001) shear deformation. Correlation between the hardness and the elastic constants of TaB 2 was discussed. The band structure shows that P6/mmm phase TaB 2 and Pmmn phase IrB 2 are both metallic. The calculations show that both TaB and IrB are elastically stable with the hexagonal P6 3 /mmc structure. - Elastic constant c 44 of TaB 2 is calculated to be 235 GPa. This value is exceptionally high, exceeding those of WB 2 , OsB 2 , WB 4 , OsN 2 , IrN 2 , and PtN 2 .
Zhang, Pan; Shen, Yanqing; Wu, Wenjing; Li, Jun; Zhou, Zhongxiang
2018-03-01
Although a number of various reduced graphene oxide (RGO)-based nanomaterials with enhanced photocatalytic performance have recently been characterized, the effect of RGO reductivity on their performance is still not clear. Herein, KNbO3(100) surface modification with three RGO sheets of different reductivity is investigated using first-principles calculations, revealing that increasing RGO reductivity enhances the photocatalytic performance of KNbO3(100)/RGO nanocomposites. In contrast to CeO2/RGO nanocomposites, the O atoms of RGO inhibit the photoactivity of KNbO3/RGO nanocomposites by restraining the effect of inducing a red shift of the corresponding photocatalytic absorption spectra by C 2p states. Increased RGO reductivity extends its absorption edge to the visible light region of the optical absorption and also promotes charge transfer from the KNbO3(100) surface to RGO sheets, in contrast to the behavior observed for g-C3N4/RGO composites. Overall, this work provides a reasonable explanation of controversial experimental results obtained previously, paving the way to the development of highly efficient RGO-based photocatalysts and promoting further photocatalytic applications of KNbO3/RGO nanocomposites.
International Nuclear Information System (INIS)
Nakamura, Hiroki; Okumura, Masahiko; Machida, Masahiko
2015-01-01
The authors examined, based on first-principles calculation, the mechanism of mordenite as a species of zeolite to show high adsorption selectivity for Cs, with a focus on the pores as adsorption site. For increasing the adsorption selectivity for Cs, the following three conditions for mordenite were proposed: (1) to have many pores with a radius of about 3 Å, (2) relatively small ratio of Al and Si, and (3) uniform distribution of Al atoms around the pores to adsorb Cs. The superposition effect of the interaction obtained by embracing positive ions with all the pores was revealed to be important, which verified the importance of computational science. It was also successfully conducted to reproduce with Monte Carlo method the thermodynamic level data of ion exchange isotherms, which became engineering metrics after actual measurement. This method was able to reproduce the difference in properties shown by different zeolites, and also able to explain changes in the adsorption performance that depends on Al and Si ratio, which remained the findings from experience up to date, by utilizing the method to associate the result to microscopic factors. Based on these results, this paper discusses how far material development would be realized depending on the leadership of computational science, and what kinds of research and development would be required in the future. (A.O)
Energy Technology Data Exchange (ETDEWEB)
Xu, Canhui [Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang, 621900 (China); Zhang, Haibin, E-mail: hbzhang@caep.cn [Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang, 621900 (China); Hu, Shuanglin; Zhou, Xiaosong; Peng, Shuming [Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang, 621900 (China); Xiao, Haiyan [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu, 610054 (China); Zhang, Guojun [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Research Institute of Functional Materials, Donghua University, Shanghai, 201620 (China)
2017-05-15
In this paper, the effects of hydrogen interstitial defect on the structural stability of two kinds of MAX materials (Ti{sub 3}SiC{sub 2} and Ti{sub 3}AlC{sub 2}) were investigated by first-principles calculations. The results indicated that the hydrogen interstitial energetically prefers to reside at the 2Ti3Si site for Ti{sub 3}SiC{sub 2} and 3TiAl site for Ti{sub 3}AlC{sub 2}, respectively, and the latter has much lower formation energy. Both of these MAX phases are slightly hardened and the elastic anisotropy is reduced appreciably after the introduction of hydrogen interstitial. The hydrogen interstitial in Ti{sub 3}SiC{sub 2} and Ti{sub 3}AlC{sub 2} leads to an electronic localization effect on the Si/Al atom and the effect is more remarkable in Ti{sub 3}AlC{sub 2}. The interlayer bonding strength of Ti{sub 3}AlC{sub 2} is more weakened by hydrogen interstitials than that of Ti{sub 3}SiC{sub 2}. As a result, the interatomic bonding between Si/Al and Ti atom layers is deteriorated and their structural stabilities degrade subsequently.
Harb, Moussab
2013-05-02
Using first principles calculations, we investigate the structural, electronic, optical, and energetic properties of S-doped anatase TiO2 bulk systems. To ensure accurate band gap predictions, we use the HSE06 exchange correlation functional, and the absorption spectra are obtained with density functional perturbation (DFPT) theory by employing HSE06. Various oxidation states (anionic and cationic) of sulfur are considered depending on the location in bulk TiO2: in interstitial position or in substitution for either oxygen or titanium atoms. Among the explored structures, two anionic and one cationic configurations induce an improved optical absorption response in the visible region as observed experimentally. Moreover, we undertake a thermodynamic analysis as a function of the chemical potential of oxygen and considering three relevant sulfur chemical doping agents (S 2, H2S, and thiourea). It highlights that cationic configurations (S4+ and S6+) are strongly stabilized in a wide range of oxygen chemical potential (including standard conditions), whereas anionic species are stabilized only at very low chemical potential of oxygen. The metastable cationic Ti(1-2x)O2S2x system involving the presence of S4+ species in substitution for Ti 4+, with the formation of SO2 units, should offer the best compromise between the thermodynamic conditions and the expected optical properties. © 2013 American Chemical Society.
Energy Technology Data Exchange (ETDEWEB)
Shein, I.R. [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, Ekaterinburg 620990 (Russian Federation); Ivanovskii, A.L., E-mail: ivanovskii@ihim.uran.ru [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, Ekaterinburg 620990 (Russian Federation)
2013-02-01
Very recently (2012, Phys. Rev Lett., 109, 035502) a new hexagonal (s.g. P63/mmc, Music-Sharp-Sign 194) ternary phase Nb{sub 2}GeC, which belongs to so-called 211-like MAX phases, was discovered. In order to get a systematic insight into the structural, elastic, and electronic properties of Nb{sub 2}GeC, we used two complementary DFT-based first-principles approaches (as implemented in the VASP and Wien2k packages) to calculate the optimized structural parameters, band structure, densities of state, Fermi surface, and a set of elastic parameters: elastic constants (C{sub ij}), bulk modulus (B), compressibility ({beta}), shear modulus (G), Young's modulus (Y), and elastic anisotropy indexes, which were discussed in comparison with available data. Besides, the inter-atomic bonding picture for Nb{sub 2}GeC was discussed using electron density maps and Bader's charge analysis.
Directory of Open Access Journals (Sweden)
LIAO Fei
2016-12-01
Full Text Available Structural stabilities, mechanical properties and electronic structures of Al2Cu, Al2CuMg and MgZn2 intermetallics in Al-Zn-Mg-Cu aluminum alloys were determined from the first-principle calculations by VASP based on the density functional theory. The results show that the cohesive energy (Ecoh decreases in the order MgZn2 > Al2CuMg > Al2Cu, whereas the formation enthalpy (ΔH decreases in the order MgZn2 > Al2Cu > Al2CuMg. Al2Cu can act as a strengthening phase for its ductile and high Young's modulus. The Al2CuMg phase exhibits elastic anisotropy and may act as a crack initiation point. MgZn2 has good plasticity and low melting point, which is the main strengthening phase in the Al-Zn-Mg-Cu aluminum alloys. Metallic bonding mode coexists with a fractional ionic interaction in Al2Cu, Al2CuMg and MgZn2, and that improves the structural stability. In order to improve the alloys' performance further, the generation of MgZn2 phase should be promoted by increasing Zn content while Mg and Cu contents are decreased properly.
Wang, Cheng; Wang, Huiyuan; Huang, Tianlong; Xue, Xuena; Qiu, Feng; Jiang, Qichuan
2015-05-22
Although solid Au is usually most stable as a face-centered cubic (fcc) structure, pure hexagonal close-packed (hcp) Au has been successfully fabricated recently. However, the phase stability and mechanical property of this new material are unclear, which may restrict its further applications. Here we present the evidence that hcp → fcc phase transformation can proceed easily in Au by first-principles calculations. The extremely low generalized-stacking-fault (GSF) energy in the basal slip system implies a great tendency to form basal stacking faults, which opens the door to phase transformation from hcp to fcc. Moreover, the Au lattice extends slightly within the superficial layers due to the self-assembly of alkanethiolate species on hcp Au (0001) surface, which may also contribute to the hcp → fcc phase transformation. Compared with hcp Mg, the GSF energies for non-basal slip systems and the twin-boundary (TB) energies for and twins are larger in hcp Au, which indicates the more difficulty in generating non-basal stacking faults and twins. The findings provide new insights for understanding the nature of the hcp → fcc phase transformation and guide the experiments of fabricating and developing materials with new structures.
Study of interfacial strain at the α-Al2O3/monolayer MoS2 interface by first principle calculations
Yu, Sheng; Ran, Shunjie; Zhu, Hao; Eshun, Kwesi; Shi, Chen; Jiang, Kai; Gu, Kunming; Seo, Felix Jaetae; Li, Qiliang
2018-01-01
With the advances in two-dimensional (2D) transition metal dichalcogenides (TMDCs) based metal-oxide-semiconductor field-effect transistor (MOSFET), the interface between the semiconductor channel and gate dielectrics has received considerable attention due to its significant impacts on the morphology and charge transport of the devices. In this study, first principle calculations were utilized to investigate the strain effect induced by the interface between crystalline α-Al2O3 (0001)/h-MoS2 monolayer. The results indicate that the 1.3 nm Al2O3 can induce a 0.3% tensile strain on the MoS2 monolayer. The strain monotonically increases with thicker dielectric layers, inducing more significant impact on the properties of MoS2. In addition, the study on temperature effect indicates that the increasing temperature induces monotonic lattice expansion. This study clearly indicates that the dielectric engineering can effectively tune the properties of 2D TMDCs, which is very attractive for nanoelectronics.
Energy Technology Data Exchange (ETDEWEB)
Berdiyorov, G.R., E-mail: gberdiyorov@qf.org.qa; Madjet, M.E., E-mail: mmadjet@qf.org.qa
2016-12-30
Highlights: • Effect of surface termination on the optoelectronic properties of TiC{sub 2} is studied. • Fluorinated, oxidized and hydroxylated surfaces are considered. • Partial charges are calculated. • Absorption of the system increases by surface passivation. • Electronic transport reduces considerably due to the termination. - Abstract: Using the first-principles density functional theory, we study the effect of surface functionalization on the structural and optoelectronic properties of recently proposed quasi-two-dimensional material TiC{sub 2} [T. Zhao, S. Zhang, Y. Guo, Q. Wang, Nanoscale 8 (2016) 233]. Hydrogenated, fluorinated, oxidized and hydroxylated surfaces are considered. Significant changes in the lattice parameters and partial charge distributions are found due to the surface termination. Direct contribution of the adatoms to the system density of states near the Fermi level is obtained, which has a major impact on the optoelectronic properties of the material. For example, surface termination results in larger absorption in the visible range of the spectrum. The electronic transport is also affected by the surface functionalization: the current in the system can be reduced by an order of magnitude. These findings indicate the importance of the effects of surface passivation on optoelectronic properties of this quasi-2D material.
Tunable magnetism in the LaAlO3/SrTiO3 heterostructure: Insights from first-principles calculations
Xue, Yuanbin; Zhao, Jinzhu; Shan, Yueyue; Xu, Hu
2018-04-01
By performing first-principles calculations, we explored the origin and controlling methods of magnetism in ideal and oxygen deficient (001) LaAlO3/SrTiO3 (LAO/STO) heterostructures. It was found that the ferromagnetic ordering is the ground state and that the interfacial Ti 3d electrons introduced by the LaO-termination, polar catastrophe and oxygen vacancies can all contribute to the magnetism. With respect to the ways of tuning the magnetic properties, our results show that LaO-terminated films generally carry much stronger magnetic moments than their AlO2-terminated counterparts and that the magnitude of magnetic moments can also be effectively controlled by the LAO film thickness. In addition, oxygen vacancy leads to substantial electronic reconstruction of the interfacial Ti 3d orbitals, which enhances the magnetization and makes the magnetism emerge in thinner polar LAO films. This work offers useful information to facilitate one's understanding of the magnetism and to provide clues to engineer the magnetic behaviors in related oxide heterostructures.
Luo, Zhe; Zhu, Hong; Ying, Tao; Li, Dejiang; Zeng, Xiaoqin
2018-06-01
The influences of solute atoms (Li, Al, Mn, Zn, Fe, Ni, Cu, Y, Zr) and Cl adsorption on the anodic corrosion performance on Mg (0001) surface have been investigated based on first-principles calculations, which might be useful for the design of corrosion-resistant Mg alloys. Work function and local electrode potential shift are chosen as descriptors since they quantify the barrier for charge transfer and anodic stability. We found that at 25% surface doping rate, Y decreased the work function of Mg, while the impact of remaining doping elements on the work function of Mg was trivial due to the small surface dipole moment change. The adsorption of Cl destabilized the Mg atoms at surface by weakening the bonding between surface Mg atoms. We find that a stronger hybridization of d orbits of alloying elements (e.g. Zr) with the orbits of Mg can greatly increase the local electrode potential,which even overbalances the negative effect introduced by Cl adsorbates and hence improves the corrosion resistance of Mg alloys.
Fartab, Dorsa S.; Kordbacheh, Amirhossein Ahmadkhan
2018-06-01
The first-principles calculations based on spin-polarized density functional theory is carried out to investigate the structural, electronic and magnetic properties of a hexagonal boron nitride sheet (h-BNS) doped by one or two lithium atom(s). Moreover, a vacancy in the neighborhood of one Li-substituted atom is introduced into the system. All optimized structures indicate significant local deformations with Li atom(s) protruded to the exterior of the sheet. The defects considered at N site are energetically more favorable than their counterpart structures at B site. The spin-polarized impurity states appear within the bandgap region of the pristine h-BNS, which lead to a spontaneous magnetization with the largest magnetic moments of about 2 μB in where a single or two B atom(s) are replaced by Li atom(s). Furthermore, the Li substitution for a single B atom increases the density of holes compared to that of electrons forming a p-type semiconductor. More interestingly, the structure in which two Li are substituted two neighboring B atoms appears to show desired half-metallic behavior that may be applicable in spintronic. The results provide a way to enhance the conductivity and magnetism of the pristine h-BNS for potential applications in BN-based nanoscale devices.
Energy Technology Data Exchange (ETDEWEB)
Jiang, Haifeng, E-mail: jhf043@163.com [Department of Mechanics and Electronic Engineering, Chizhou College, Chizhou 247000 (China); Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Wang, Xiancai; Zang, Xueping; Wu, Weifeng [Department of Mechanics and Electronic Engineering, Chizhou College, Chizhou 247000 (China); Sun, Shunping [School of Materials Engineering, Jiangsu Teachers University of Technology, Changzhou 213001 (China); Xiong, Chao [School of Photoelectric Engineering, Changzhou Institute of Technology, Changzhou 213001 (China); Yin, Weiwei; Gui, Chuanyou [Department of Mechanics and Electronic Engineering, Chizhou College, Chizhou 247000 (China); Zhu, Xuebin [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China)
2013-03-15
Highlights: ► Electronic properties of CuAlO{sub 2} substituted with bivalent cations were studied. ► Denser band structures were observed in the substituted CuAlO{sub 2}. ► The defect (Be{sub Al}, −1) forms more easily compared to others. -- Abstract: Electronic properties of delafossite-type CuAlO{sub 2} doped with the bivalent cation (Be, Mg or Ca) were systematically calculated by using first-principles PAW method based on density functional theory. The calculated results show the Cu–O distance nearest to the substituted bivalent cation for Al (0.5 0.5 0.5) is decreased with the increase of atomic number from Be to Ca. Moreover, the denser energy band structures have been observed in the valence band in the substituted structures, which are related to the enhancement of covalent character of the Cu–O bond nearest to the substituted site. The contributions from the substituted bivalent cations (Be{sup 2+}, Mg{sup 2+} and Ca{sup 2+}) to the valence band begin at −6.5 eV, relative to −8 eV of Al{sup 3+}, which could be another cause to variations in band structures. From Be to Ca, their partial densities of states show the contributions to the valence band are gradually decreased, in great agreement with the variation trend for the pauling electronegativity. The calculated defect formation energies indicate the (Be{sub Al}, −1) forms more easily than the others.
Directory of Open Access Journals (Sweden)
Ala Aldin M. H. M. Darghouth
2015-12-01
Full Text Available Ionization potentials (IPs and electron affinities (EAs are important quantities input into most models for calculating the open-circuit voltage (Voc of organic solar cells. We assess the semi-empirical density-functional tight-binding (DFTB method with the third-order self-consistent charge (SCC correction and the 3ob parameter set (the third-order DFTB (DFTB3 organic and biochemistry parameter set against experiments (for smaller molecules and against first-principles GW (Green’s function, G, times the screened potential, W calculations (for larger molecules of interest in organic electronics for the calculation of IPs and EAs. Since GW calculations are relatively new for molecules of this size, we have also taken care to validate these calculations against experiments. As expected, DFTB is found to behave very much like density-functional theory (DFT, but with some loss of accuracy in predicting IPs and EAs. For small molecules, the best results were found with ΔSCF (Δ self-consistent field SCC-DFTB calculations for first IPs (good to ± 0.649 eV. When considering several IPs of the same molecule, it is convenient to use the negative of the orbital energies (which we refer to as Koopmans’ theorem (KT IPs as an indication of trends. Linear regression analysis shows that KT SCC-DFTB IPs are nearly as accurate as ΔSCF SCC-DFTB eigenvalues (± 0.852 eV for first IPs, but ± 0.706 eV for all of the IPs considered here for small molecules. For larger molecules, SCC-DFTB was also the ideal choice with IP/EA errors of ± 0.489/0.740 eV from ΔSCF calculations and of ± 0.326/0.458 eV from (KT orbital energies. Interestingly, the linear least squares fit for the KT IPs of the larger molecules also proves to have good predictive value for the lower energy KT IPs of smaller molecules, with significant deviations appearing only for IPs of 15–20 eV or larger. We believe that this quantitative analysis of errors in SCC-DFTB IPs and EAs may be of
International Nuclear Information System (INIS)
Lavrentyev, A.A.; Gabrelian, B.V.; Shkumat, P.N.; Nikiforov, I.Ya.; Zavaliy, I.Yu.; Sinelnichenko, A.K.; Izvekov, A.V.; Khyzhun, O.Yu.
2010-01-01
Electronic properties of Ti 4 Fe 2 O oxide, a very promising hydrogen-storage material, were studied both from theoretical and experimental points of view employing the first-principles band-structure augmented plane wave + local orbitals (APW + LO) method with the WIEN2k code as well as X-ray photoelectron spectroscopy (XPS) and soft X-ray emission spectroscopy (SXES). Total and partial densities of states of the constituent atoms of Ti 4 Fe 2 O have been derived from the APW + LO calculations. The XPS valence-band spectra as well as the SXES Ti Lα, Fe Lα and O Kα bands have been measured for a series of Ti 4 Fe 2 O x oxides (x = 1.0, 0.5, and 0.25). The present APW + LO calculations reveal that, the O 2p-like states are the dominant contributors into the bottom of the valence band, whilst the top of the valence band and the bottom of the conduction band of Ti 4 Fe 2 O are dominated by contributions of the Fe 3d- and Ti 3d-like states. The APW + LO results are confirmed experimentally by a comparison on a common energy scale of the XPS valence-band spectra and the SXES Ti Lα, Fe Lα and O Kα bands of the Ti 4 Fe 2 O x oxides. The XPS Ti 2p, Fe 2p and O 1s core-level binding energies have been measured for the compounds under consideration.
Energy Technology Data Exchange (ETDEWEB)
Jaeger, B.; Paluch, S.; Wolf, W.; Herzig, P.; Zogal, O.J.; Shitsevalova, N.; Paderno, Y
2004-11-30
Two compounds, tetragonal YB{sub 4} and cubic YB{sub 6}, have been investigated by electric-field gradient (EFG) and Knight shift measurements at the boron sites using the {sup 11}B nuclear magnetic resonance (NMR) technique and by performing first-principles calculations. In YB{sub 6} {sup 11}B (I=3/2) NMR spectra reveal patterns typical for an axially symmetric field gradient with a quadrupole coupling frequency of {nu}{sub Q}=600{+-}15 kHz. In the second boride (YB{sub 4}) three different EFGs were observed corresponding to the three inequivalent crystallographic sites for the boron atoms (4h, 4e, and 8j). They correspond to: {nu}{sub Q}(4h)=700{+-}30 kHz with an asymmetry parameter {eta}=0.02{+-}0.02, {nu}{sub Q}(4e)=515{+-}30 kHz, {eta}=0.00+0.02/-0.00, and {nu}{sub Q}(8j)=515{+-}40 kHz, {eta}=0.46{+-}0.08. The Knight shifts measured by magic-angle spinning (MAS) NMR at room temperature are very small being 0.6{+-}8 and -1{+-}8 ppm for YB{sub 4} and YB{sub 6}, respectively. For the theoretical calculations structure optimizations were performed as a first step. For the obtained structural parameters the EFGs were computed within the local-density approximation. Very satisfactory agreement between experimental and theoretical results is obtained both for the structural parameters and the B EFGs, thus confirming the underlying structural models. In addition to the EFGs, band structures, densities of states, and valence-electron densities are presented and the bonding situation in the two yttrium borides is discussed. The band-structure results are compatible with the very low values for the Knight shifts mentioned above.
N–Mg dual-acceptor co-doping in CuCrO{sub 2} studied by first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Xu, Ying, E-mail: 1080071@hnust.edu.cn [School of Physics, Hunan University of Science and Technology, Xiangtan 411201 (China); Nie, Guo-Zheng [School of Physics, Hunan University of Science and Technology, Xiangtan 411201 (China); Zou, Daifeng [School of Physics, Hunan University of Science and Technology, Xiangtan 411201 (China); Shenzhen Key Laboratory of Nanobiomechanics, Shenzhen Institutes of Advanced Technology, Chinese Academy of Science, Shenzhen 518055 (China); Tang, Jing-Wu [School of Physics, Hunan University of Science and Technology, Xiangtan 411201 (China); Ao, Zhimin, E-mail: Zhimin.Ao@gdut.edu.cn [Institute of Environmental Health and Pollution Control, School of Environmental Science and Engineering, Guangdong University of Technology, Guangzhou 510006 (China)
2016-11-25
In this paper, N–Mg dual-acceptor co-doping in CuCrO{sub 2} is investigated by first-principles calculations. The electronic structure and formation energies of Mg substituting Cr-site, N substituting O-site, and co-doping of both Mg on Cr-site and N on O-site in CuCrO{sub 2} are calculated. It is found that the structure with N and Mg codoped at the nearest sites has the lowest energy due to a modest attractive interaction between the two dopants. Compared with single N or Mg doped CuCrO{sub 2}, the N–Mg codoped CuCrO{sub 2} has a lower formation energy and shallower transition level. In addition, the total density of states (DOS) analysis shows that more hole states appear above the Fermi level and higher DOS for N–Mg co-doping is obtained in the N–Mg codoped CuCrO{sub 2}, which is good to enhance the p-type conductivity in CuCrO{sub 2}. - Highlights: • N–Mg dual-acceptor co-doping in CuCrO{sub 2} is investigated. • N–Mg complex has a lower formation energy and shallower transition level. • More hole states appear above the Fermi level for N–Mg co-doping. • N–Mg co-doping in CuCrO{sub 2} can be expected to have more stable p-type conductivity.
Energy Technology Data Exchange (ETDEWEB)
Dey, C.C., E-mail: chandicharan.dey@saha.ac.in [Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064 (India); Srivastava, S.K. [Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur 721302 (India)
2013-10-15
Electric quadrupole interactions at {sup 181}Ta impurity in the intermetallic compound Zr{sub 2}Ni{sub 7} have been studied by perturbed angular correlation technique. It has been found that there are two electric field gradients (EFG) at the {sup 181}Ta site due to two different crystalline configurations in Zr{sub 2}Ni{sub 7}, while contradictory results were reported from previous investigations. The values of EFG at room temperature have been found to be V{sub zz}=7.9×10{sup 17} V/cm{sup 2} and 7.1×10{sup 17} V/cm{sup 2} corresponding to present experimental values of quadrupole frequencies and asymmetry parameters for the two sites: ω{sub Q}{sup 1}=70.7(1) Mrad/s, η=0.28(1), δ=0.8(2)% (site fraction 84%) and ω{sub Q}{sup 2}=63(1) Mrad/s, η=0.35(5), δ∼0 (site fraction 9%). Electric field gradients and asymmetry parameters have been computed from the complementary first-principles density functional theory (DFT) to compare with present experimental results. Our calculated values of EFG are found to be in close agreement with the experimental results. No magnetic interactions in Zr{sub 2}Ni{sub 7} have been observed at 298 and 77 K which implies that there is no ferromagnetic ordering in this material down to 77 K. This observation is corroborated by theoretical calculations, wherein no magnetic moment or hyperfine field is found at any atomic site.
International Nuclear Information System (INIS)
Chen, Lanli; Wang, Xiaofang; Shi, Siqi; Cui, Yuanyuan; Luo, Hongjie; Gao, Yanfeng
2016-01-01
Graphical abstract: - Highlights: • After adsorption, there is a charge transfer from Ag to VO_2(1 0 0) surface, which thus increases the electron concentration in VO_2 thin film. • Ag adsorption on VO_2(1 0 0) surface process is an exothermic chemical process, and the adsorption system is stable. • The work function can be tuned by Ag adsorption on and incorporation into the VO_2(1 0 0) surface, which in turn regulates the phase transition temperature of VO_2. - Abstract: VO_2 is an attractive material for application to thermochromic optoelectronic devices such as smart windows, and Ag/VO_2 double-layered structure can effectively decrease the phase transition temperature (T_c) of VO_2 thin film, which is very important for practical application of VO_2. Previous works has shown that the decrease in phase transition temperature (T_c) seems to be relevant with the work function of VO_2 in Ag/VO_2 double-layered thin film, although the underlying mechanism of tuning its T_c by Ag incorporation and adsorption on the VO_2(1 0 0) surface has been rarely investigated. Our first-principles calculations reveal that the adsorption of Ag atoms on the VO_2(1 0 0) surface rather than incorporation of Ag exhibits a lower work function, which is ascribed to an integrated effect of charge transfer from Ag to VO_2(1 0 0) surface and enhanced surface dipole moment. The results suggest that the decrease in work function of VO_2 with Ag adsorption favors the reduction in T_c. The current findings are helpful to understand the fundamental mechanism for yielding high-efficiency VO_2-based optoelectronic devices.
Lan, Jianhui; Cao, Dapeng; Wang, Wenchuan; Smit, Berend
2010-07-27
We use the multiscale simulation approach, which combines the first-principles calculations and grand canonical Monte Carlo simulations, to comprehensively study the doping of a series of alkali (Li, Na, and K), alkaline-earth (Be, Mg, and Ca), and transition (Sc and Ti) metals in nanoporous covalent organic frameworks (COFs), and the effects of the doped metals on CO2 capture. The results indicate that, among all the metals studied, Li, Sc, and Ti can bind with COFs stably, while Be, Mg, and Ca cannot, because the binding of Be, Mg, and Ca with COFs is very weak. Furthermore, Li, Sc, and Ti can improve the uptakes of CO2 in COFs significantly. However, the binding energy of a CO2 molecule with Sc and Ti exceeds the lower limit of chemisorptions and, thus, suffers from the difficulty of desorption. By the comparative studies above, it is found that Li is the best surface modifier of COFs for CO2 capture among all the metals studied. Therefore, we further investigate the uptakes of CO2 in the Li-doped COFs. Our simulation results show that at 298 K and 1 bar, the excess CO2 uptakes of the Li-doped COF-102 and COF-105 reach 409 and 344 mg/g, which are about eight and four times those in the nondoped ones, respectively. As the pressure increases to 40 bar, the CO2 uptakes of the Li-doped COF-102 and COF-105 reach 1349 and 2266 mg/g at 298 K, respectively, which are among the reported highest scores to date. In summary, doping of metals in porous COFs provides an efficient approach for enhancing CO2 capture.
Energy Technology Data Exchange (ETDEWEB)
Chen, Lanli; Wang, Xiaofang [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Shi, Siqi, E-mail: sqshi@shu.edu.cn [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Cui, Yuanyuan [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Luo, Hongjie [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China); Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Gao, Yanfeng, E-mail: yfgao@shu.edu.cn [School of Materials Science and Engineering, Shanghai University, Shanghai 200444 (China)
2016-03-30
Graphical abstract: - Highlights: • After adsorption, there is a charge transfer from Ag to VO{sub 2}(1 0 0) surface, which thus increases the electron concentration in VO{sub 2} thin film. • Ag adsorption on VO{sub 2}(1 0 0) surface process is an exothermic chemical process, and the adsorption system is stable. • The work function can be tuned by Ag adsorption on and incorporation into the VO{sub 2}(1 0 0) surface, which in turn regulates the phase transition temperature of VO{sub 2}. - Abstract: VO{sub 2} is an attractive material for application to thermochromic optoelectronic devices such as smart windows, and Ag/VO{sub 2} double-layered structure can effectively decrease the phase transition temperature (T{sub c}) of VO{sub 2} thin film, which is very important for practical application of VO{sub 2}. Previous works has shown that the decrease in phase transition temperature (T{sub c}) seems to be relevant with the work function of VO{sub 2} in Ag/VO{sub 2} double-layered thin film, although the underlying mechanism of tuning its T{sub c} by Ag incorporation and adsorption on the VO{sub 2}(1 0 0) surface has been rarely investigated. Our first-principles calculations reveal that the adsorption of Ag atoms on the VO{sub 2}(1 0 0) surface rather than incorporation of Ag exhibits a lower work function, which is ascribed to an integrated effect of charge transfer from Ag to VO{sub 2}(1 0 0) surface and enhanced surface dipole moment. The results suggest that the decrease in work function of VO{sub 2} with Ag adsorption favors the reduction in T{sub c}. The current findings are helpful to understand the fundamental mechanism for yielding high-efficiency VO{sub 2}-based optoelectronic devices.
dos Santos, A. V.; Samudio Pérez, C. A.; Muenchen, D.; Anibele, T. P.
2015-01-01
The ground state properties of Fe/N/Fe and Fe/O/Fe multilayers were investigated using the first principles calculations. The calculations were performed using the Linearized Augmented Plane Wave (LAPW) method implemented in the Wien2k code. A supercell consisting of one layer of nitride (or oxide) between two layers of Fe in the bcc structure was used to model the structure of the multilayer. The research in new materials also stimulated theoretical and experimental studies of iron-based nitrides due to their variety of structural and magnetic properties for the potential applications as in high strength steels and for high corrosion resistance. It is obvious from many reports that magnetic iron nitrides such as γ-Fe4N and α-Fe16N2 have interesting magnetic properties, among these a high magnetisation saturation and a high density crimp. However, although Fe-N films and multilayers have many potential applications, they can be produced in many ways and are being extensively studied from the theoretical point of view there is no detailed knowledge of their electronic structure. Clearly, efforts to understand the influence of the nitrogen atoms on the entire electronic structure are needed as to correctly interpret the observed changes in the magnetic properties when going from Fe-N bulk compounds to multilayer structures. Nevertheless, the N atoms are not solely responsible for electronics alterations in solid compounds. Theoretical results showed that Fe4X bulk compounds, where X is a variable atom with increasing atomic number (Z), the nature of bonding between X and adjacent Fe atoms changes from more covalent to more ionic and the magnetic moments of Fe also increase for Z=7, i.e. N. This is an indicative that atoms with a Z number higher than 7, i.e., O, can produce several new alterations in the entire magnetic properties of Fe multilayers. This paper presents the first results of an ab-initio electronic structure calculations, performed for Fe-N and Fe
Evolution of Si-2N2Nb island configuration on NbN (0 0 1) surface: A first-principles calculation
International Nuclear Information System (INIS)
Ren, Yuan; Xia, Qing; Zhang, Chao; Liu, Xuejie; Li, Zhi; Zhang, Fucheng
2015-01-01
Graphical abstract: - Highlights: • We investigate the separation and gathering of Nb, Si and N atom around come to NbN grain. • The adsorption and diffusion of single atom around 2N2Nb island were calculated by DFT. • The adsorption behavior of Si-2N2Nb island on NbN (0 0 1) surface were investigated. • The evolution of Si-2N2Nb island on NbN (0 0 1) were calculated by nudged elastic band. - Abstract: The separation and aggregation of Nb, Si, and N atoms around the NbN grain during the deposition of the Nb–Si–N nanocomposite film were discussed. The evolution behavior of the 2N2Nb island and the adsorption and diffusion energy of Nb, Si, and N atoms around the island on the NbN (0 0 1) surface were investigated using the first-principles method based on density functional theory. Results indicated that the most stable configuration of the Nb–Si–N island was the combination of Nb and N atoms to form the island and the possible aggregation of the Si atom to diagonal Nb atom outside the island. Substitution solid solution was eventually formed, in which the Nb atom of the 2N2Nb island was replaced by the Si atom during deposition. However, the Si atom was easily replaced by the Nb atom at the site with abundant Nb atoms. The diffusion energy of the evolution from Nb-2N1Nb1Si to Si-2N2Nb was 1.58 eV, and the total energy of the configuration decreased. Moreover, the interface of Si and NbN grains tended to separate. The highest energy adsorption sites for Nb, Si, N atoms adsorbed on the NbN (0 0 1) surface around the 2N2Nb island were P3, P1, and P2, respectively. The adsorption energies of Nb, Si, and N atoms on the NbN (0 0 1) surface around the 2N2Nb island were 7.3067, 5.3521, and 6.7113 eV, respectively, and their diffusion energies around the 2N2Nb island were 2.62, 1.35, and 5.094 eV, respectively. The low adsorption and diffusion energies of active Si atoms promoted the distribution of Nb and N atoms during deposition. Furthermore, the Nb
Semi-classical calculation of the spin-isospin response functions
International Nuclear Information System (INIS)
Chanfray, G.
1987-03-01
We present a semi-classical calculation of the nuclear response functions beyond the Thomas-Fermi approximation. We apply our formalism to the spin-isospin responses and show that the surface peaked h/2π corrections considerably decrease the ratio longitudinal/transverse as obtained through hadronic probes
Yang, Chen; Zhao, Zong-Yan
2017-11-08
In the field of photocatalysis, constructing hetero-structures is an efficient strategy to improve quantum efficiency. However, a lattice mismatch often induces unfavorable interfacial states that can act as recombination centers for photo-generated electron-hole pairs. If the hetero-structure's components have the same crystal structure, this disadvantage can be easily avoided. Conversely, in the process of loading a noble metal co-catalyst onto the TiO 2 surface, a transition layer of noble metal oxides is often formed between the TiO 2 layer and the noble metal layer. In this article, interfacial properties of hetero-structures composed of a noble metal dioxide and TiO 2 with a rutile crystal structure have been systematically investigated using first-principles calculations. In particular, the Schottky barrier height, band bending, and energy band alignments are studied to provide evidence for practical applications. In all cases, no interfacial states exist in the forbidden band of TiO 2 , and the interfacial formation energy is very small. A strong internal electric field generated by interfacial electron transfer leads to an efficient separation of photo-generated carriers and band bending. Because of the differences in the atomic properties of the components, RuO 2 /TiO 2 and OsO 2 /TiO 2 hetero-structures demonstrate band dividing, while RhO 2 /TiO 2 and IrO 2 /TiO 2 hetero-structures have a pseudo-gap near the Fermi energy level. Furthermore, NMO 2 /TiO 2 hetero-structures show upward band bending. Conversely, RuO 2 /TiO 2 and OsO 2 /TiO 2 hetero-structures present a relatively strong infrared light absorption, while RhO 2 /TiO 2 and IrO 2 /TiO 2 hetero-structures show an obvious absorption edge in the visible light region. Overall, considering all aspects of their properties, RuO 2 /TiO 2 and OsO 2 /TiO 2 hetero-structures are more suitable than others for improving the photocatalytic performance of TiO 2 . These findings will provide useful information
Energy Technology Data Exchange (ETDEWEB)
Zhang, Huijun [College of Information Science and Engineering, Yanshan University, Qinhuangdao 066004 (China); Ren, Jiadong, E-mail: jdren@ysu.edu.cn [College of Information Science and Engineering, Yanshan University, Qinhuangdao 066004 (China); Wu, Lailei [Key Laboratory of Metastable Materials Science and Technology, College of Material Science and Engineering, Yanshan University, Qinhuangdao 066004 (China); Zhang, Jingwu, E-mail: zjw@ysu.edu.cn [Key Laboratory of Metastable Materials Science and Technology, College of Material Science and Engineering, Yanshan University, Qinhuangdao 066004 (China)
2017-01-15
The structural, elastic and electronic properties of LiSi{sub 2}N{sub 3} and its substitutions by Na, K and Rb were investigated through first-principles computations. The expansion of lattice parameters of ASi{sub 2}N{sub 3} from Li, Na, K to Rb is found to be determined by the bond angle of Si–N1–Si, which suggests a possible way to improve the lithium ionic conductivity by substitutions. ASi{sub 2}N{sub 3} (A=Li, Na, K and Rb) shows the similar elastic behaviors, while the electronic band gap gradually decreases from 5.1 to 3.4 eV from LiSi{sub 2}N{sub 3} to RbSi{sub 2}N{sub 3}. Interestingly, the analysis of electronic structure, crystal orbital Hamiltonian populations and Bader charges shows that the covalence of Si–N bonding is critical for the stability of ASi{sub 2}N{sub 3} phase. Among ASi{sub 2}N{sub 3} phases, there is a relatively high ionicity in NaSi{sub 2}N{sub 3}; the Si–N bond strength in [Si{sub 2}N{sub 3}]{sup −} net for KSi{sub 2}N{sub 3} and RbSi{sub 2}N{sub 3} is comparable to LiSi{sub 2}N{sub 3}, but stronger than NaSi{sub 2}N{sub 3}. - Graphic abstract: Universal trend of structural and electronic properties in alkaline metal silicon nitrides, ASi{sub 2}N{sub 3}, A=Li, Na, K and Rb. - Highlights: • Trend in structure, electronic and mechanical properties of ASi{sub 2}N{sub 3} (A=Li-Rb) were predicted. • Lattice expansion of ASi{sub 2}N{sub 3} induced by the bond angle of Si–N1–Si was found. • Calculated band gap decreases from 5.1 to 3.4 eV from LiSi{sub 2}N{sub 3} to RbSi{sub 2}N{sub 3}. • Covalent Si–N bonding is critical for the stability of ASi{sub 2}N{sub 3}.
Energy Technology Data Exchange (ETDEWEB)
Rocquefelte, X.
2001-10-01
The functioning of a positive electrode in a lithium battery is based on the reversible intercalation of lithium. In some cases, such a reaction can lead to important structural modifications and therefore to an amorphization of the material. A theoretical approach is presented here that leads to structural predictions and simulations of electrochemical behaviour of positive electrode materials. In the first part, DFT (Density Functional Theory) formalisms and the respective advantages of FLAPW (Full potential Linearized Augmented Plane Waves) and PP/PW (Pseudopotential / Plane Waves) methods are discussed. In the second part are given some fundamental electrochemistry considerations related to the intercalation process, thermodynamics aspects and relationships with electronic structure. Then, an approach combining experimental data and geometry optimisation of structural hypotheses is given. This approach was first applied to a model compound LiMoS{sub 2}, and has been then generalised to systems of industrial interest such as Li{sub x}V{sub 2}O{sub 5} (0 {<=} x {<=} 3). The simulated X-ray diagrams of the optimised structures for LiMoS{sub 2} and {omega} - Li{sub 3}V{sub 2}O{sub 5} are in good agreement with experimental data. In the case of Li{sub x}V{sub 2}O{sub 5}, the first discharge curves starting from {alpha} - V{sub 2}O{sub 5} and {gamma}' - V{sub 2}O{sub 5} were then successfully simulated. A chemical bond analysis was carried out to help understand the origin of the distortion in LiMoS{sub 2} and the voltage variations in the electrochemical curves of Li{sub x}V{sub 2}O{sub 5}. This study clearly demonstrates that an approach combining first-principle calculations and available experimental data is invaluable in the structure determination of poorly crystallized compounds. Such a procedure contributes to the understanding of the phase transitions induced by the lithium intercalation in vanadium oxide compounds and can really be used in the research
Energy Technology Data Exchange (ETDEWEB)
Rocquefelte, X
2001-10-01
The functioning of a positive electrode in a lithium battery is based on the reversible intercalation of lithium. In some cases, such a reaction can lead to important structural modifications and therefore to an amorphization of the material. A theoretical approach is presented here that leads to structural predictions and simulations of electrochemical behaviour of positive electrode materials. In the first part, DFT (Density Functional Theory) formalisms and the respective advantages of FLAPW (Full potential Linearized Augmented Plane Waves) and PP/PW (Pseudopotential / Plane Waves) methods are discussed. In the second part are given some fundamental electrochemistry considerations related to the intercalation process, thermodynamics aspects and relationships with electronic structure. Then, an approach combining experimental data and geometry optimisation of structural hypotheses is given. This approach was first applied to a model compound LiMoS{sub 2}, and has been then generalised to systems of industrial interest such as Li{sub x}V{sub 2}O{sub 5} (0 {<=} x {<=} 3). The simulated X-ray diagrams of the optimised structures for LiMoS{sub 2} and {omega} - Li{sub 3}V{sub 2}O{sub 5} are in good agreement with experimental data. In the case of Li{sub x}V{sub 2}O{sub 5}, the first discharge curves starting from {alpha} - V{sub 2}O{sub 5} and {gamma}' - V{sub 2}O{sub 5} were then successfully simulated. A chemical bond analysis was carried out to help understand the origin of the distortion in LiMoS{sub 2} and the voltage variations in the electrochemical curves of Li{sub x}V{sub 2}O{sub 5}. This study clearly demonstrates that an approach combining first-principle calculations and available experimental data is invaluable in the structure determination of poorly crystallized compounds. Such a procedure contributes to the understanding of the phase transitions induced by the lithium intercalation in vanadium oxide compounds and can really be used in the research of
International Nuclear Information System (INIS)
Touzani, Rachid St.; Fokwa, Boniface P.T.
2014-01-01
The Nb 2 FeB 2 phase (U 3 Si 2 -type, space group P4/mbm, no. 127) is known for almost 50 years, but until now its magnetic properties have not been investigated. While the synthesis of Nb 2 OsB 2 (space group P4/mnc, no. 128, a twofold superstructure of U 3 Si 2 -type) with distorted Nb-layers and Os 2 -dumbbells was recently achieved, “Nb 2 RuB 2 ” is still not synthesized and its crystal structure is yet to be revealed. Our first principles density functional theory (DFT) calculations have confirmed not only the experimental structures of Nb 2 FeB 2 and Nb 2 OsB 2 , but also predict “Nb 2 RuB 2 ” to crystalize with the Nb 2 OsB 2 structure type. According to chemical bonding analysis, the homoatomic B–B interactions are optimized and very strong, but relatively strong heteroatomic M–B, B–Nb and M–Nb bonds (M=Fe, Ru, Os) are also found. These interactions, which together build a three-dimensional network, are mainly responsible for the structural stability of these ternary borides. The density-of-states at the Fermi level predicts metallic behavior, as expected, from metal-rich borides. Analysis of possible magnetic structures concluded preferred antiferromagnetic ordering for Nb 2 FeB 2 , originating from ferromagnetic interactions within iron chains and antiferromagnetic exchange interactions between them. -- Graphical abstract: Nb 2 FeB 2 (U 3 Si 2 structure type, space group P4/mbm, no. 127) is predicted to order antiferromagnetically, due to the presence of iron chains which show ferromagnetic interactions in the chains and antiferromagnetic interactions between them. “Nb 2 RuB 2 ” is predicted to crystallize with the recently discovered Nb 2 OsB 2 twofold superstructure (space group P4/mnc, no. 128) of U 3 Si 2 structure type. The building of ruthenium dumbbells instead of chains along [001] is found to be responsible for the stabilization of this superstructure. Highlights: • Nb 2 FeB 2 is predicted to order antiferromagnetically.
Calculation of the spin-isospin response functions in an extended semi-classical theory
International Nuclear Information System (INIS)
Chanfray, G.
1987-01-01
We present a semi-classical calculation of the spin isospin response-functions beyond Thomas-Fermi theory. We show that surface-peaked ℎ 2 corrections reduce the collective effects predicted by Thomas-Fermi calculations. These effects, small for a volume response, become important for surface responses probed by hadrons. This yields a considerable improvement of the agreement with the (p, p') Los Alamos data
Calculation of Multisphere Neutron Spectrometer Response Functions in Energy Range up to 20 MeV
Martinkovic, J
2005-01-01
Multisphere neutron spectrometer is a basic instrument of neutron measurements in the scattered radiation field at charged-particles accelerators for radiation protection and dosimetry purposes. The precise calculation of the spectrometer response functions is a necessary condition of the propriety of neutron spectra unfolding. The results of the response functions calculation for the JINR spectrometer with LiI(Eu) detector (a set of 6 homogeneous and 1 heterogeneous moderators, "bare" detector within cadmium cover and without it) at two geometries of the spectrometer irradiation - in uniform monodirectional and uniform isotropic neutron fields - are given. The calculation was carried out by the code MCNP in the neutron energy range 10$^{-8}$-20 MeV.
Hassan, Irtaza; Donati, Luca; Stensitzki, Till; Keller, Bettina G.; Heyne, Karsten; Imhof, Petra
2018-04-01
We have combined infrared (IR) experiments with molecular dynamics (MD) simulations in solution at finite temperature to analyse the vibrational signature of the small floppy peptide Alanine-Leucine. IR spectra computed from first-principles MD simulations exhibit no distinct differences between conformational clusters of α -helix or β -sheet-like folds with different orientations of the bulky leucine side chain. All computed spectra show two prominent bands, in good agreement with the experiment, that are assigned to the stretch vibrations of the carbonyl and carboxyl group, respectively. Variations in band widths and exact maxima are likely due to small fluctuations in the backbone torsion angles.
Wagle, Fabian; Steinle-Neumann, Gerd; de Koker, Nico
2018-03-01
We report results on electronic transport properties of liquid Fe-S alloys at conditions of planetary cores, computed using first-principle techniques in the Kubo-Greenwood formalism. We describe a combined effect of resistivity saturation due to temperature, compression, and chemistry by comparing the electron mean free path from the Drude response of optical conductivity to the mean interatomic distance. At high compression and high sulfur concentration the Ioffe-Regel condition is satisfied, and the temperature coefficient of resistivity changes sign from positive to negative. We show that this happens due to a decrease in the d density of states at the Fermi level in response to thermal broadening.
Schweda, K
2002-01-01
The analysis of (e,e'n) experiments at the Darmstadt superconducting electron linear accelerator S-DALINAC required the calculation of neutron response functions for the NE213 liquid scintillation detectors used. In an open geometry, these response functions can be obtained using the Monte Carlo codes NRESP7 and NEFF7. However, for more complex geometries, an extended version of the Monte Carlo code MCNP exists. This extended version of the MCNP code was improved upon by adding individual light-output functions for charged particles. In addition, more than one volume can be defined as a scintillator, thus allowing the simultaneous calculation of the response for multiple detector setups. With the implementation of sup 1 sup 2 C(n,n'3 alpha) reactions, all relevant reactions for neutron energies E sub n <20 MeV are now taken into consideration. The results of these calculations were compared to experimental data using monoenergetic neutrons in an open geometry and a sup 2 sup 5 sup 2 Cf neutron source in th...
International Nuclear Information System (INIS)
Zheng, Yuanliao; Huang, Yan; Shu, Haibo; Zhou, Xiaohao; Ding, Jiayi; Chen, Xiaoshuang; Lu, Wei
2016-01-01
The effect of lithium adsorption on the phase transition from 1H-MoS 2 to 1T-MoS 2 is studied by first-principles computations. The results indicate the possibilities of the phase transition for the lithium adsorption. Based on the results of charge density difference and charge-transfer of molybdenum disulfide with lithium adsorption, we elucidated that the mechanism of the changes of electronic property accompanying the phase transition is attributed to the electron transfer of different atoms. According to the result of transition state, it can be found that the phase-transition barrier is related to the coverage of lithium atoms on MoS 2 surface. It may be helpful to obtaining experimentally the stable 1T-MoS 2 structure. - Highlights: • The transformation of MoS 2 from semiconducting to metallic phases is elucidated on the essence of the electron transfer. • The relationship between Li coverage and phase transition barrier is obtained. • The decomposing of Lithiated 1T-MoS 2 at a high concentration of Li adsorption is explained. • The results can be helpful to obtaining experimentally the stable 1T-MoS 2 structure.
Karthikeyan, S; Singh, Jiten N; Park, Mina; Kumar, Rajesh; Kim, Kwang S
2008-06-28
Important structural isomers of NH(4) (+)(H(2)O)(n=4,6) have been studied by using density functional theory, Moller-Plesset second order perturbation theory, and coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. The zero-point energy (ZPE) correction to the complete basis set limit of the CCSD(T) binding energies and free energies is necessary to identify the low energy structures for NH(4) (+)(H(2)O)(n=4,6) because otherwise wrong structures could be assigned for the most probable structures. For NH(4) (+)(H(2)O)(6), the cage-type structure, which is more stable than the previously reported open structure before the ZPE correction, turns out to be less stable after the ZPE correction. In first principles Car-Parrinello molecular dynamics simulations around 100 K, the combined power spectrum of three lowest energy isomers of NH(4) (+)(H(2)O)(4) and two lowest energy isomers of NH(4) (+)(H(2)O)(6) explains each experimental IR spectrum.
International Nuclear Information System (INIS)
Zhang, Z.L.; Xiao, H.Y.; Zu, Xiaotao T.; Gao, Fei; Weber, William J.
2009-01-01
A first-principles method has been employed to investigate the structural and energetic properties for A2Ti2O7 (A = Lu, Er, Y, Gd, Sm, Nd, La), including the formation energies of the cation antisite-pair, the anion Frenkel pair that defines anion-disorder, and the coupled cation antisite-pair/anion-Frenkel. It is proposed that the interaction may have more significant influence on the radiation resistance behavior of titanate pyrochlores, although the interactions are relatively much stronger than the interactions. It is found that the defect formation energies are not simple functions of the A-site cation radii. The formation energy of the cation antisite-pair increases continuously as the A-site cation varies from Lu to Gd, and then decreases continuously with the variation of the A-site cation from Gd to La, in excellent agreement with the radiation-resistance trend of the titanate pyrochlores. The band gaps in these pyrochlores were also measured, and the band gap widths changed continuously with cation radius.
Lei, Xiang; Yu, Ke
2018-04-01
A purposeful modulation of physical properties of material via change external conditions has long captured people's interest and can provide many opportunities to improve the specific performance of electronic devices. In this work, a comprehensive first-principles survey was performed to elucidate that the bandgap and electronic properties of WSe2sbnd MoS2 heterostructure exhibited unusual response to exterior strain and electric field in comparison with pristine structures. It demonstrates that the WSe2sbnd MoS2 is a typical type-II heterostructure, and thus the electron-hole pairs can be effectively spatially separated. The external effects can trigger the electronic phase transition from semiconducting to metallic state, which originates from the internal electric evolution induced energy-level shift. Interestingly, the applied strain shows no direction-depended character for the modulation of bandgap of WSe2sbnd MoS2 heterostructure, while it exists in the electric field tuning processes and strongly depends on the direction of the electric field. Our findings elucidate the tunable electronic property of bilayer WSe2sbnd MoS2 heterostructure, and would provide a valuable reference to design the electronic nanodevices.
International Nuclear Information System (INIS)
Xiao, H. B.; Yang, C. P.; Wang, R. L.; Luo, X.; Marchenkov, V. V.
2014-01-01
The effect of the alloying element Indium (In) on the martensitic transition, magnetic properties, and phase stabilities of Ni 8 Mn 6 Sn 2−x In x shape memory alloys has been investigated using the first-principles pseudopotential plane-wave method based on density functional theory. The energy difference between the austenitic and martensitic phases was found to increase with increasing In content, which implies an enhancement of the martensitic phase transition temperature (T M ). Moreover, the formation energy results indicate that In-doping increases the relative stability of Ni 8 Mn 6 Sn 2−x In x both in austenite and martensite. This results from a reduction in density of states near the Fermi level regions caused by Ni-3d–In-5p hybridization when Sn is replaced by In. The equilibrium equation of state results show that the alloys Ni 8 Mn 6 Sn 2−x In x exhibit an energetically degenerated effect for an In content of x = ∼1.5. This implies the coexistence of antiparallel and parallel configurations in the austenite.
Energy Technology Data Exchange (ETDEWEB)
Jaeger, B [Institut fuer Physikalische Chemie, Universitaet Wien, Waehringer Strasse 42, 1090 Vienna (Austria); Paluch, S [Institute for Low Temperature and Structure Research, Polish Academy of Sciences, PO Box 1410, 50-950 Wroclaw (Poland); Zogal, O J [Institute for Low Temperature and Structure Research, Polish Academy of Sciences, PO Box 1410, 50-950 Wroclaw (Poland); Wolf, W [Materials Design s. a. r. l., 44, avenue F.-A. Bartholdi, 72000 Le Mans (France); Herzig, P [Institut fuer Physikalische Chemie, Universitaet Wien, Waehringer Strasse 42, 1090 Vienna (Austria); Filippov, V B [Institute for Problems of Materials Science, Academy of Sciences of Ukraine, 3 Krzhyzhanovsky street, 03680 Kiev, Ukraine (Ukraine); Shitsevalova, N [Institute for Problems of Materials Science, Academy of Sciences of Ukraine, 3 Krzhyzhanovsky street, 03680 Kiev, Ukraine (Ukraine); Paderno, Y [Institute for Problems of Materials Science, Academy of Sciences of Ukraine, 3 Krzhyzhanovsky street, 03680 Kiev, Ukraine (Ukraine)
2006-03-01
Three metallic dodecaborides, YB{sub 12}, ZrB{sub 12} and LuB{sub 12}, have been investigated by electric-field gradient (EFG) measurements at the boron sites using the {sup 11}B nuclear magnetic resonance (NMR) technique and by performing first-principles calculations. The NMR powder spectra reveal patterns typical for a completely asymmetric EFG tensor, i.e., an {eta} parameter close to unity. The absolute values of V{sub zz} (the largest component of the EFG) are determined from the spectra and they range between 11 x 10{sup 20} V m{sup -2} and 11.6 x 10{sup 20} V m{sup -2} with an uncertainty of 0.8 x 10{sup 20} V m{sup -2}, being in very good agreement with the first-principles results. In addition the electronic structure and chemical bonding are analysed from partial densities of states and electron densities.
Particle-hole calculation of the longitudinal response function of 12C
International Nuclear Information System (INIS)
Dellafiore, A.; Lenz, F.; Brieva, F.A.
1985-01-01
The longitudinal response function of 12 C in the range of momentum transfers 200 MeV/c< or =q< or =550 MeV/c is calculated in the Tamm-Dancoff approximation. The particle-hole Green's function is evaluated by means of a doorway-state expansion. This method allows us to take into account finite-range residual interactions in the continuum, including exchange processes. At low momentum transfers, calculations agree qualitatively with the data. The data cannot be reproduced at momentum transfers around 450 MeV/c. This discrepancy can be accounted for neither by uncertainties in the residual interaction, nor by more complicated processes in the nuclear final states
Energy Technology Data Exchange (ETDEWEB)
Hashimoto, M.; Saito, K.; Ando, H. [Power Reactor and Nuclear Fuel Development Corp., Oarai, Ibaraki (Japan). Oarai Engineering Center
1998-05-01
The method to calculate the response function of spherical BF{sub 3} proportional counter, which is commonly used as neutron dose rate meter and neutron spectrometer with multi moderator system, is developed. As the calculation code for evaluating the response function, the existing code series NRESP, the Monte Carlo code for the calculation of response function of neutron detectors, is selected. However, the application scope of the existing NRESP is restricted, the NRESP98 is tuned as generally applicable code, with expansion of the geometrical condition, the applicable element, etc. The NRESP98 is tested with the response function of the spherical BF{sub 3} proportional counter. Including the effect of the distribution of amplification factor, the detailed evaluation of the charged particle transportation and the effect of the statistical distribution, the result of NRESP98 calculation fit the experience within {+-}10%. (author)
Energy Technology Data Exchange (ETDEWEB)
Guemou, M., E-mail: guemoumhamed7@gmail.com [Engineering Physics Laboratory, University Ibn Khaldoun of Tiaret, BP 78-Zaaroura, Tiaret 14000 (Algeria); Bouhafs, B. [Modelling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes (Algeria); Abdiche, A. [Applied Materials Laboratory, Research Center, University of Sidi Bel Abbes, 22000 Sidi Bel Abbes (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modelisation Mathematique (LPQ3M), Departement de Technologie, Universite de Mascara, 29000 Mascara (Algeria); Al Douri, Y. [Institute of Nano Electronic Engineering, Universiti Malaysia Perlis, Perlis (Malaysia); Bin Omran, S. [Department of Physics and Astronomy, Faculty of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia)
2012-04-15
Density functional calculations are performed to study the structural, electronic and optical properties of technologically important B{sub x}Ga{sub 1-x}As ternary alloys. The calculations are based on the total-energy calculations within the full-potential augmented plane-wave (FP-LAPW) method. For exchange-correlation potential, local density approximation (LDA) and the generalized gradient approximation (GGA) have been used. The structural properties, including lattice constants, bulk modulus and their pressure derivatives, are in very good agreement with the available experimental and theoretical data. The electronic band structure, density of states for the binary compounds and their ternary alloys are given. The dielectric function and the refractive index are also calculated using different models. The obtained results compare very well with previous calculations and experimental measurements.
Harb, Moussab; Masih, Dilshad; Ould-Chikh, Samy; Sautet, Philippe; Basset, Jean-Marie; Takanabe, Kazuhiro
2013-01-01
the optical transitions in these materials using the screened coulomb hybrid (HSE06) exchange-correlation formalism. The calculated density of states showed excellent agreement with UV-vis diffuse reflectance spectra predicting a significant red
International Nuclear Information System (INIS)
Downs, D.; Sharma, R.R.
1995-01-01
First numerical evaluations of T c for oxygenated and argon-reduced single-layered HgBa 2 CuO 4+δ superconductors have been presented. Our calculations are based on the dipolon theory and are found to provide an explanation for the occurrence of superconductivity in single-layered high-T c superconductors. Relevant expressions useful for the evaluation of T c have been given. Since the polarizabilities of the ions are not known exactly for the present systems we have performed calculations making use of Pauling's as well as Tessman, Kahn, and Shockley's polarizabilities in order to estimate the uncertainties in the calculated values of T c associated with uncertainties in the polarizabilities. The effective charges on the ions required for the evaluation of dipoles and dipolon frequencies have been obtained by means of the bond-valence sums. Without fitting with any parameters, our calculations yield T c values equal to 80±21 K for the oxygenated and 50±27 K for the argon-reduced HgBa 2 CuO 4+δ superconductors, in agreement with the corresponding experimental values 95 and 59 K. The uncertainties in the calculated values of T c arise because of the uncertainties in various physical parameters (including polarizabilities) used and due to errors involved in the calculations. The present results are consistent with the observed electronic Raman-scattering intensities which show anomalously broad peaks extended up to several electron volts in cuprate high-T c superconductors. Our calculated dipolon density of states predict four optical absorption peaks at about 77 cm -1 , 195 cm -1 , 1.6 eV, and 2.5 eV
Directory of Open Access Journals (Sweden)
H.Y. Wang
2012-03-01
Full Text Available The density-functional theory (DFT and density-functional perturbation theory (DFPT are employed to study the pressure dependence of elastic and dynamical properties of zinc-blende ZnS and ZnSe. The calculated elastic constants and phonon spectra from 0 GPa to 15 GPa are compared with the available experimental data. Generally, our calculated values are overestimated with experimental data, but agree well with recent other theoretical values. The discrepancies with experimental data are due to the use of local density approximation (LDA and effect of temperature. In this work, in order to compare with experimental data, we calculated and discussed the pressure derivatives of elastic constants, the pressure dependence of dynamical effect charge, and mode Grüneisen parameter at Γ.
Energy Technology Data Exchange (ETDEWEB)
Masrour, R., E-mail: rachidmasrour@hotmail.com [Laboratory of Materials, Processes, Environment and Quality, Cady Ayyed University, National School of Applied Sciences, 63 46000, Safi (Morocco); LMPHE (URAC 12), Faculty of Science, Mohammed V-Agdal University, Rabat (Morocco); Hlil, E.K. [Institut Néel, CNRS et Université Joseph Fourier, BP 166, F-38042 Grenoble cedex 9 (France); Hamedoun, M. [Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Benyoussef, A. [LMPHE (URAC 12), Faculty of Science, Mohammed V-Agdal University, Rabat (Morocco); Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Hassan II Academy of Science and Technology, Rabat (Morocco); Mounkachi, O.; El Moussaoui, H. [Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco)
2015-03-15
Self-consistent ab initio calculations, based on density functional theory (DFT) approach and using a full potential linear augmented plane wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the Fe{sub 3}O{sub 4}. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Fe plans. Magnetic moment considered to lie along (010) axes are computed. Obtained data from ab initio calculations are used as input for the high temperature series expansions (HTSEs) calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Fe–Fe in Fe{sub 3}O{sub 4} are given using the mean field theory. The high temperature series expansions (HTSEs) of the magnetic susceptibility of with the magnetic moments, m{sub Fe} in Fe{sub 3}O{sub 4} is given up to seventh order series in (1/k{sub B}T). The Néel temperature T{sub N} is obtained by HTSEs of the magnetic susceptibility series combined with the Padé approximant method. The critical exponent γ associated with the magnetic susceptibility is deduced as well. - Highlights: • Ab initio calculations, based on DFT approach and FLAPW are used to study the electronic properties of Fe{sub 3}O{sub 4}. • Magnetic moments of Fe{sub 1} and Fe{sub 2} are estimated to −/+3.44 µ{sub B}. • HTSE method is used to calculate the Néel temperature of Fe{sub 3}O{sub 4}.
Energy Technology Data Exchange (ETDEWEB)
Rached, H., E-mail: habib_rached@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences Exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès, 22000 (Algeria); Département de Physique, Faculté des Sciences Exactes et Informatique, Université Hassiba BenBouali de Chlef, Chlef, 02000 (Algeria); Bendaoudia, S. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences Exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès, 22000 (Algeria); Rached, D., E-mail: rachdj@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences Exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès, 22000 (Algeria)
2017-06-01
The main goal of the present work is to obtain report on the magnetic phase stability, mechanical, electronic and optical properties of double perovskite oxides Pb{sub 2}FeMO{sub 6} (M = Mo, Re and W) by employing the ab-initio plane-wave method, based on the density functional theory (DFT). The exchange-correlation (XC) energy of electrons was treated using the Perdew–Burke–Ernzerhof parametrization. The ground-state electronic properties for different magnetic configurations were calculated. The formation enthalpies has been evaluated in order to determinate the stability of our compounds. The independent elastic constants and the related mechanical properties are investigated. The electronic structure calculation reveal the half-metallic ferrimagnets (FiM-HM) for all investigated compounds. The optical constants as the dielectric function, refractive index, optical reflectivity and absorption coefficient were calculated and discussed in detail. Therefore, our compounds are identified as potential candidates for spintronic applications and high performance electronic devices. - Highlights: • Based on the DFT calculation, the Pb{sub 2}FeMO{sub 6} (M = Mo, Re and W) compounds have been investigated. • The ground-state properties are predicted. • The mechanical properties reveals that these compounds are stable against any elastic deformations. • The electronic structures reveals the half-metallic ferrimagnets (FiM-HM) for all investigated compounds.
Harb, Moussab
2013-08-29
Density functional theory (DFT) and density functional perturbation theory (DFPT) were applied to study the structural, electronic, and optical properties of a (Na2-xCux)Ta4O11 solid solution to accurately calculate the band gap and to predict the optical transitions in these materials using the screened coulomb hybrid (HSE06) exchange-correlation formalism. The calculated density of states showed excellent agreement with UV-vis diffuse reflectance spectra predicting a significant red-shift of the band gap from 4.58 eV (calculated 4.94 eV) to 2.76 eV (calculated 2.60 eV) as copper content increased from 0 to 83.3%. The band gap narrowing in these materials, compared to Na2Ta4O11, results from the incorporation of new occupied electronic states, which are strongly localized on the Cu 3d orbitals, and is located within 2.16-2.34 eV just above the valence band of Na2Ta4O11. These new occupied states, however, possess an electronic character localized on Cu, which makes hole mobility limited in the semiconductor. © 2013 American Chemical Society.
Kislov, V V; Islamova, N I; Kolker, A M; Lin, S H; Mebel, A M
2005-09-01
Extensive ab initio Gaussian-3-type calculations of potential energy surfaces (PES), which are expected to be accurate within 1-2 kcal/mol, combined with statistical theory calculations of reaction rate constants have been applied to study various possible pathways in the hydrogen abstraction acetylene addition (HACA) mechanism of naphthalene and acenaphthalene formation as well as Diels-Alder pathways to acenaphthalene, phenanthrene, and pyrene. The barrier heights; reaction energies; and molecular parameters of the reactants, products, intermediates, and transition states have been generated for all types of reactions involved in the HACA and Diels-Alder mechanisms, including H abstraction from various aromatic intermediates, acetylene addition to radical sites, ring closures leading to the formation of additional aromatic rings, elimination of hydrogen atoms, H disproportionation, C2H2 cycloaddition, and H2 loss. The reactions participating in various HACA sequences (e.g., Frenklach's, alternative Frenklach's, and Bittner and Howard's routes) are demonstrated to have relatively low barriers and high rate constants under combustion conditions. A comparison of the significance of different HACA mechanisms in PAH growth can be made in the future using PES and molecular parameters obtained in the present work. The results show that the Diels-Alder mechanism cannot compete with the HACA pathways even at high combustion temperatures, because of high barriers and consequently low reaction rate constants. The calculated energetic parameters and rate constants have been compared with experimental and theoretical data available in the literature.
Ishizaki, Akihito; Tanimura, Yoshitaka
2008-05-01
Based on the influence functional formalism, we have derived a nonperturbative equation of motion for a reduced system coupled to a harmonic bath with colored noise in which the system-bath coupling operator does not necessarily commute with the system Hamiltonian. The resultant expression coincides with the time-convolutionless quantum master equation derived from the second-order perturbative approximation, which is also equivalent to a generalized Redfield equation. This agreement occurs because, in the nonperturbative case, the relaxation operators arise from the higher-order system-bath interaction that can be incorporated into the reduced density matrix as the influence operator; while the second-order interaction remains as a relaxation operator in the equation of motion. While the equation describes the exact dynamics of the density matrix beyond weak system-bath interactions, it does not have the capability to calculate nonlinear response functions appropriately. This is because the equation cannot describe memory effects which straddle the external system interactions due to the reduced description of the bath. To illustrate this point, we have calculated the third-order two-dimensional (2D) spectra for a two-level system from the present approach and the hierarchically coupled equations approach that can handle quantal system-bath coherence thanks to its hierarchical formalism. The numerical demonstration clearly indicates the lack of the system-bath correlation in the present formalism as fast dephasing profiles of the 2D spectra.
Hydrogen storage of Mg1−xMxH2 (M = Ti, V, Fe) studied using first-principles calculations
International Nuclear Information System (INIS)
Bhihi, M.; Lakhal, M.; Benyoussef, A.; El Kenz, A.; Labrim, H.; Mounkachi, O.; Hlil, E.K.
2012-01-01
In this work, the hydrogen storage properties of the Mg-based hydrides, i.e., Mg 1−x M x H 2 (M = Ti, V, Fe, 0 ≤ x ≤ 0.1), are studied using the Korringa—Kohn—Rostoker (KKR) calculation with the coherent potential approximation (CPA). In particular, the nature and concentrations of the alloying elements and their effects are studied. Moreover, the material's stability and hydrogen storage thermodynamic properties are discussed. In particular, we find that the stability and the temperature of desorption decrease without significantly affecting the storage capacities
Phuc, Huynh V.; Hieu, Nguyen N.; Hoi, Bui D.; Hieu, Nguyen V.; Thu, Tran V.; Hung, Nguyen M.; Ilyasov, Victor V.; Poklonski, Nikolai A.; Nguyen, Chuong V.
2018-01-01
In this paper, we studied the electronic properties, effective masses, and carrier mobility of monolayer MoS_2 using density functional theory calculations. The carrier mobility was considered by means of ab initio calculations using the Boltzmann transport equation coupled with deformation potential theory. The effects of mechanical biaxial strain on the electronic properties, effective mass, and carrier mobility of monolayer MoS_2 were also investigated. It is demonstrated that the electronic properties, such as band structure and density of state, of monolayer MoS_2 are very sensitive to biaxial strain, leading to a direct-indirect transition in semiconductor monolayer MoS_2. Moreover, we found that the carrier mobility and effective mass can be enhanced significantly by biaxial strain and by lowering temperature. The electron mobility increases over 12 times with a biaxial strain of 10%, while the carrier mobility gradually decreases with increasing temperature. These results are very useful for the future nanotechnology, and they make monolayer MoS_2 a promising candidate for application in nanoelectronic and optoelectronic devices.
Wang, Yun-Jiang; Wang, Chong-Yu
2009-10-01
A model system consisting of Ni[001](100)/Ni3Al[001](100) multi-layers are studied using the density functional theory in order to explore the elastic properties of single crystal Ni-based superalloys. Simulation results are consistent with the experimental observation that rafted Ni-base superalloys virtually possess a cubic symmetry. The convergence of the elastic properties with respect to the thickness of the multilayers are tested by a series of multilayers from 2γ'+2γ to 10γ'+10γ atomic layers. The elastic properties are found to vary little with the increase of the multilayer's thickness. A Ni/Ni3Al multilayer with 10γ'+10γ atomic layers (3.54 nm) can be used to simulate the mechanical properties of Ni-base model superalloys. Our calculated elastic constants, bulk modulus, orientation-dependent shear modulus and Young's modulus, as well as the Zener anisotropy factor are all compatible with the measured results of Ni-base model superalloys R1 and the advanced commercial superalloys TMS-26, CMSX-4 at a low temperature. The mechanical properties as a function of the γ' phase volume fraction are calculated by varying the proportion of the γ and γ' phase in the multilayers. Besides, the mechanical properties of two-phase Ni/Ni3Al multilayer can be well predicted by the Voigt-Reuss-Hill rule of mixtures.
Zhao, Ting; Wang, Yu-An; Zhao, Zong-Yan; Liu, Qiang; Liu, Qing-Ju
2018-01-01
In order to explore the similarity, difference, and tendency of binary copper-based chalcogenides, the crystal structure, electronic structure, and optical properties of eight compounds of Cu2Q and CuQ (Q = O, S, Se, and Te) have been calculated by density functional theory with HSE06 method. According to the calculated results, the electronic structure and optical properties of Cu2Q and CuQ present certain similarities and tendencies, with the increase of atomic number of Q elements: the interactions between Cu-Q, Cu-Cu, and Q-Q are gradually enhancing; the value of band gap is gradually decreasing, due to the down-shifting of Cu-4p states; the covalent feature of Cu atoms is gradually strengthening, while their ionic feature is gradually weakening; the absorption coefficient in the visible-light region is also increasing. On the other hand, some differences can be found, owing to the different crystal structure and component, for example: CuO presents the characteristics of multi-band gap, which is very favorable to absorb infrared-light; the electron transfer in CuQ is stronger than that in Cu2Q; the absorption peaks and intensity are very strong in the ultraviolet-light region and infrared-light region. The findings in the present work will help to understand the underlying physical mechanism of binary copper-based chalcogenides, and available to design novel copper-based chalcogenides photo-electronics materials and devices.
Belfarh, T.; Batouche, M.; Seddik, T.; Uğur, G.; Omran, S. Bin; Bouhemadou, A.; Sandeep; Wang, Xiaotian; Sun, Xiao-Wei; Khenata, R.
2018-06-01
We have studied the structural, optical, electronic and thermoelectric properties of the CaCd2X2 (X = P, As) compounds by using the full-potential augmented plane wave plus local orbitals method (FP-APW + lo). The exchange-correlation potential was treated using both the gradient generalized approximation (WC-GGA) and local density approximation (LDA). The estimated structural parameters, including the lattice parameters and internal coordinates agree well with the available experimental data. Our computed band structure shows that both studied compounds are semiconductors, with direct band gaps (Γ-Γ) of approximately 1.78 eV and 1.2 eV for CaCd2P2 and CaCd2As2, respectively, using GGA-TB-mBJ approach. The calculated optical spectra reveal a strong response of these materials in the energy range between the visible light and extreme UV regions, making them a good candidate for optoelectronic devices. Thermoelectric parameters, such as thermal conductivity, electrical conductivity, Seebeck coefficient, power factor and figure of merit were calculated. We note that both the CaCd2P2 and CaCd2As2 compounds show promising thermoelectric properties.
International Nuclear Information System (INIS)
Nabok, Dmitrii; Puschnig, Peter; Ambrosch-Draxl, Claudia; Werzer, Oliver; Resel, Roland; Smilgies, Detlef-M.
2007-01-01
Combined experimental and theoretical investigations on thin films of pentacene are performed in order to determine the structure of the pentacene thin film phase. Grazing incidence x-ray diffraction is used for studying a pentacene thin film with a nominal thickness of 180 nm. The crystal structure is found to exhibit the lattice parameters a=0.592 nm, b=0.754 nm, c=1.563 nm, α=81.5 deg. , β=87.2 deg. , and γ=89.9 deg. . These crystallographic unit cell dimensions are used as the only input parameters for ab initio total-energy calculations within the framework of density functional theory revealing the molecular packing within the crystal structure. Moreover, we calculate the electronic band structure of the thin film phase and compare it to that of the bulk phase. We find the intermolecular bandwidths of the thin film phase to be significantly larger compared to the bulk structure, e.g., the valence bandwidth is twice as large. This remarkable effect is traced back to an enhanced intermolecular π-π overlap due to the upright standing molecules in the thin film phase
Energy Technology Data Exchange (ETDEWEB)
Ma, C.G.; Liu, D.X.; Feng, B.; Tian, Y.; Li, L. [College of Sciences, Chongqing University of Posts and Telecommunications, Chongqing 400065 (China); Brik, M.G., E-mail: mikhail.brik@ut.ee [College of Sciences, Chongqing University of Posts and Telecommunications, Chongqing 400065 (China); Institute of Physics, University of Tartu, Ravila 14C, Tartu 50411 (Estonia); Institute of Physics, Jan Dlugosz University, Armii Krajowej 13/15, PL-42200 Czestochowa (Poland)
2016-01-15
For the first time the structural, elastic and bonding properties of 15 elpasolite crystals Cs{sub 2}NaLnCl{sub 6} (Ln denotes all lanthanides from La to Lu) were calculated systematically using the CRYSTAL09 program. Several trends in the variation of these properties in relation to the atomic number Z of the Ln ions were found; in particular, the lattice parameter of these compounds decreases with Z (which can lead to the increased crystal field splittings of the 5d states for the heavier Ln ions), whereas the elastic constants and Debye temperature increase. The degree of covalency of the Ln–Cl chemical bonds is increased toward the end of the lanthanide series. - Highlights: • Structural, elastic and bonding properties of 15 cubic elpasolites Cs{sub 2}NaLnCl{sub 6} (Ln=La,…,Lu) are calculated. • Relations between these quantities and Ln atomic number were found. • Possible correlation between the elastic properties and Stokes shift is proposed.
Menezes, Marcos; Capaz, Rodrigo
Black Phosphorus (BP) is a promising material for applications in electronics, especially due to the tuning of its band gap by increasing the number of layers. In single-layer BP, also called Phosphorene, the P atoms form two staggered chains bonded by sp3 hybridization, while neighboring layers are bonded by Van-der-Waals interactions. In this work, we present a Tight-Binding (TB) parametrization of the electronic structure of single and few-layer BP, based on the Slater-Koster model within the two-center approximation. Our model includes all 3s and 3p orbitals, which makes this problem more complex than that of graphene, where only 2pz orbitals are needed for most purposes. The TB parameters are obtained from a least-squares fit of DFT calculations carried on the SIESTA code. We compare the results for different basis-sets used to expand the ab-initio wavefunctions and discuss their applicability. Our model can fit a larger number of bands than previously reported calculations based on Wannier functions. Moreover, our parameters have a clear physical interpretation based on chemical bonding. As such, we expect our results to be useful in a further understanding of multilayer BP and other 2D-materials characterized by strong sp3 hybridization. CNPq, FAPERJ, INCT-Nanomateriais de Carbono.
Feldbauer, Gregor; Wolloch, Michael; Bedolla, Pedro O.; Redinger, Josef; Vernes, András; Mohn, Peter
2018-03-01
The effect of monolayers of oxygen (O) and hydrogen (H) on the possibility of material transfer at aluminium/titanium nitride (Al/TiN) and copper/diamond (Cu/Cdia) interfaces, respectively, were investigated within the framework of density functional theory (DFT). To this end the approach, contact, and subsequent separation of two atomically flat surfaces consisting of the aforementioned pairs of materials were simulated. These calculations were performed for the clean as well as oxygenated and hydrogenated Al and Cdia surfaces, respectively. Various contact configurations were considered by studying several lateral arrangements of the involved surfaces at the interface. Material transfer is typically possible at interfaces between the investigated clean surfaces; however, the addition of O to the Al and H to the Cdia surfaces was found to hinder material transfer. This passivation occurs because of a significant reduction of the adhesion energy at the examined interfaces, which can be explained by the distinct bonding situations.
Directory of Open Access Journals (Sweden)
Niu Mang
2017-01-01
Full Text Available Using density functional theory (DFT, we have investigated the structural and electronic properties of dye-sensitized solar cells (DSSCs comprised of I-doped anatase TiO2(101 surface sensitized with NKX-2554 dye. The calculation results indicate that the cyanoacrylic acid anchoring group in NKX-2554 has a strong binding to the TiO2(101 surface. The dissociative and bidentate bridging type was found to be the most favorable adsorption configuration. On the other hand, the incorporations of I dopant can reduce the band gap of TiO2 photoanode and improve the of NKX-2554 dye, which can improve the visible-light absorption of anatase TiO2 and can also facilitate the electron injection from the dye molecule to the TiO2 substrate. As a result, the I doping can significantly enhance the incident photon-to-current conversion efficiency (IPCE of DSSCs.
Directory of Open Access Journals (Sweden)
Martin Dahlqvist
2017-02-01
Full Text Available The data presented in this paper are related to the research article entitled “Theoretical stability and materials synthesis of a chemically ordered MAX phase, Mo2ScAlC2, and its two-dimensional derivate Mo2ScC” (Meshkian et al. 2017 [1]. This paper describes theoretical phase stability calculations of the MAX phase alloy MoxSc3-xAlC2 (x=0, 1, 2, 3, including chemical disorder and out-of-plane order of Mo and Sc along with related phonon dispersion and Bader charges, and Rietveld refinement of Mo2ScAlC2. The data is made publicly available to enable critical or extended analyzes.
Sun, Qiang; Selloni, Annabella; Myers, T. H.; Doolittle, W. Alan
2006-11-01
Density functional theory calculations of oxygen adsorption and incorporation at the polar GaN(0001) and GaN(0001¯) surfaces have been carried out to explain the experimentally observed reduced oxygen concentration in GaN samples grown by molecular beam epitaxy in the presence of high energy (˜10keV) electron beam irradiation [Myers , J. Vac. Sci. Technol. B 18, 2295 (2000)]. Using a model in which the effect of the irradiation is to excite electrons from the valence to the conduction band, we find that both the energy cost of incorporating oxygen impurities in deeper layers and the oxygen adatom diffusion barriers are significantly reduced in the presence of the excitation. The latter effect leads to a higher probability for two O adatoms to recombine and desorb, and thus to a reduced oxygen concentration in the irradiated samples, consistent with experimental observations.
Setiyanto, Henry; Muhida, Rifki; Kishi, Tomoya; Rempillo, Ofelia; Rahman, Mahmudur; Dipojono, Hermawan Kresno; Di\\ {n}o, Wilson Agerico; Matsumoto, Shigeno; Kasai, Hideaki
2006-10-01
We investigate the chemical reaction between a Cr transition-metal atom and sodium diethyldithiocarbamate (NaDDC), a complexing agent used to detect and extract Cr in human blood samples. Using density-functional-theory-based calculations, we determine their stable structures of Cr(DDC)2ODDC and Cr(DDC)3 complexes and obtain their dissociation energies. We found dissociation energies of -10.66 and -3.24 eV for Cr(DDC)2ODDC and Cr(DDC)3 complexes, respectively. Hence, on the basis of dissociation energies, we have verified that the reaction of NaDDC with Cr produces Cr(DDC)2ODDC as a major product.
Energy Technology Data Exchange (ETDEWEB)
Laukkanen, P., E-mail: pekka.laukkanen@utu.fi [Department of Physics and Astronomy, University of Turku, FI-20014 Turku (Finland); Punkkinen, M.P.J., E-mail: marko.punkkinen@utu.fi [Department of Physics and Astronomy, University of Turku, FI-20014 Turku (Finland); Lahti, A. [Department of Physics and Astronomy, University of Turku, FI-20014 Turku (Finland); Puustinen, J. [Optoelectronics Research Centre, Tampere University of Technology, FI-33101 Tampere (Finland); Tuominen, M. [Department of Physics and Astronomy, University of Turku, FI-20014 Turku (Finland); Hilska, J. [Optoelectronics Research Centre, Tampere University of Technology, FI-33101 Tampere (Finland); Mäkelä, J.; Dahl, J.; Yasir, M. [Department of Physics and Astronomy, University of Turku, FI-20014 Turku (Finland); Kuzmin, M. [Department of Physics and Astronomy, University of Turku, FI-20014 Turku (Finland); Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg 194021, Russian Federation (Russian Federation); Osiecki, J.R.; Schulte, K. [The MAX IV laboratory, P. O. Box 118, Lund University, SE-221 00 Lund (Sweden); Guina, M. [Optoelectronics Research Centre, Tampere University of Technology, FI-33101 Tampere (Finland); Kokko, K. [Department of Physics and Astronomy, University of Turku, FI-20014 Turku (Finland)
2017-02-28
Highlights: • XPS is used to study bulk-like properties of GaAsBi crystals. • Surface effects are removed from XPS signal by an epitaxial AlAs cap film. • Local variation of Bi composition is found. • The result is consistent with photoluminescence and theoretical results. • Ga vacancies and Bi crystallites are suggested to be dominating defects. - Abstract: Epitaxial Bi-containing III–V crystals (III-V{sub 1-x}Bi{sub x}) have attracted increasing interest due to their potential in infrared applications. Atomic-scale characterization and engineering of bulk-like III-V{sub 1-x}Bi{sub x} properties (e.g., Bi incorporation and defect formation) are challenging but relevant to develop applications. Toward that target, we report here that the traditional surface-science measurement of photoelectron spectroscopy (PES) is a potential, non-destructive method to be combined in the studies of bulk-like properties, when surface effects are properly removed. We have investigated epitaxial GaAs{sub 1-x}Bi{sub x} films, capped by epitaxial AlAs layers, with high-resolution photoelectron spectroscopy. The Bi5d core-level spectra of GaAs{sub 1-x}Bi{sub x} together with ab-initio calculations give direct evidence of variation of Bi bonding environment in the lattice sites. The result agrees with photoluminescence (PL) measurement which shows that the studied GaAs{sub 1-x}Bi{sub x} films include local areas with higher Bi content, which contribute to PL but do not readily appear in x-ray diffraction (XRD). The measured and calculated Bi core-level shifts show also that Ga vacancies and Bi clusters are dominant defects.
International Nuclear Information System (INIS)
Chui, S.T.; Kasowski, R.V.; Hsu, W.Y.
1989-01-01
We argue that because of the anisotropic nature of YBa 2 Cu 3 O/sub 7-//sub x/, one-dimensional-type charge- and spin-density fluctuations produce an effective attraction that overcomes the electron-electron Coulomb repulsion, but only at large distances. This effective attraction is further enhanced by band-structure effects such that a substantial superconducting transition temperature can be obtained. Without making any assumption of the symmetry of the gap function, we solve the Bardeen-Cooper-Schrieffer (BCS) superconducting gap equation for the six bands closest to the Fermi level. A highly anisotropic gap function with a maximum of about 0.11 eV is found. From the linearized gap equation, a transition temperature of about 0.035 eV is obtained. This is about one-quarter the maximum of the gap function, consistent with the experimental ratio of the transition temperature to the gap determined from tunneling, infrared, and nuclear quadrupole resonance measurements. The important participants to the superconducting pair come from electrons close to planar copper [Cu(2)] and chain oxygen [O(1) and O(4)] sites, consistent with recent quadrupole resonance measurements. Our calculation produces a coherence length of the order of 30 A in the xy direction, the same order of magnitude as the experimental result and considerably smaller than the conventional magnitude of ordinary BCS materials. Similar calculations for YBa 2 Cu 3 O/sub 6.5/ where periodic O vacancies are introduced along the one-dimensional Cu-O chains shows that the transition temperature is reduced by half
Angot, E.; Huang, B.; Levelut, C.; Le Parc, R.; Hermet, P.; Pereira, A. S.; Aquilanti, G.; Frapper, G.; Cambon, O.; Haines, J.
2017-08-01
α -Quartz-type gallium phosphate and representative compositions in the AlP O4-GaP O4 solid solution were studied by x-ray powder diffraction and absorption spectroscopy, Raman scattering, and by first-principles calculations up to pressures of close to 30 GPa. A phase transition to a metastable orthorhombic high-pressure phase along with some of the stable orthorhombic C m c m CrV O4 -type material is found to occur beginning at 9 GPa at 320 ∘C in GaP O4 . In the case of the AlP O4-GaP O4 solid solution at room temperature, only the metastable orthorhombic phase was obtained above 10 GPa. The possible crystal structures of the high-pressure forms of GaP O4 were predicted from first-principles calculations and the evolutionary algorithm USPEX. A predicted orthorhombic structure with a P m n 21 space group with the gallium in sixfold and phosphorus in fourfold coordination was found to be in the best agreement with the combined experimental data from x-ray diffraction and absorption and Raman spectroscopy. This method is found to very powerful to better understand competition between different phase transition pathways at high pressure.
International Nuclear Information System (INIS)
Zhao, Na; Wang, Yue-Hua; Wang, Qing-Xi; Hu, Wen-Jing
2012-01-01
The first-principles calculations are performed to investigate the cubic phase composite K 1−x Na x TaO 3 (x=0, 0.25, 0.5, 0.75, 1), by using density functional theory (DFT) with the full potential linearized augmented plane wave (FP-LAPW) method. The energy band structures, density of states (DOS), electron density and optical properties are obtained. The results show that Na ion plays an important role in K 1−x Na x TaO 3 . With the content of Na ion increasing, the changes of lattice parameters, energy gaps, bond lengths and optical properties of K 1−x Na x TaO 3 are regular. Moreover, the dependence of ferroelectric photocatalysis on both optical properties and internal electronic structure are analyzed in detail. It is proposed that the doped materials are promising photocatalytic materials. - Graphical abstract: The density of states (DOS) of K 1−x Na x TaO 3 (x=0.5). Highlights: ► The first-principles calculations are performed, by using DFT with FP-LAPW method. ► The changes of internal electronic structure and optical property of doped materials are regular. ► The dependence of ferroelectric photocatalysis on optical properties is analyzed. ► The dependence of ferroelectric photocatalysis on internal electronic structure is analyzed. ► The doped materials are promising photocatalytic materials.
Energy Technology Data Exchange (ETDEWEB)
Liebscher, C.H.; Freysoldt, C. [Max-Planck-Institut für Eisenforschung GmbH, 40237 Düsseldorf (Germany); Dennenwaldt, T. [Institute of Condensed Matter Physics and Interdisciplinary Center for Electron Microscopy, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne (Switzerland); Harzer, T.P.; Dehm, G. [Max-Planck-Institut für Eisenforschung GmbH, 40237 Düsseldorf (Germany)
2017-07-15
Metastable Cu–Cr alloy thin films with nominal thickness of 300 nm and composition of Cu{sub 67}Cr{sub 33} (at%) are obtained by co-evaporation using molecular beam epitaxy. The microstructure, chemical phase separation and electronic structure are investigated by transmission electron microscopy (TEM). The thin film adopts the body-centered cubic crystal structure and consists of columnar grains with ~50 nm diameter. Aberration-corrected scanning TEM in combination with energy dispersive X-ray spectroscopy confirms compositional fluctuations within the grains. Cu- and Cr-rich domains with composition of Cu{sub 85}Cr{sub 15} (at%) and Cu{sub 42}Cr{sub 58} (at%) and domain size of 1–5 nm are observed. The alignment of the interface between the Cu- and Cr-rich domains shows a preference for {110}-type habit plane. The electronic structure of the Cu–Cr thin films is investigated by electron energy loss spectroscopy (EELS) and is contrasted to an fcc-Cu reference sample. The experimental EEL spectra are compared to spectra computed by density functional theory. The main differences between bcc-and fcc-Cu are related to differences in van Hove singularities in the electron density of states. In Cu–Cr solid solutions with bcc crystal structure a single peak after the L{sub 3}-edge, corresponding to a van Hove singularity at the N-point of the first Brillouin zone is observed. Spectra computed for pure bcc-Cu and random Cu–Cr solid solutions with 10 at% Cr confirm the experimental observations. The calculated spectrum for a perfect Cu{sub 50}Cr{sub 50} (at%) random structure shows a shift in the van Hove singularity towards higher energy by developing a Cu–Cr d-band that lies between the delocalized d-bands of Cu and Cr. - Highlights: • Compositional fluctuations on the order of 1–5 nm in Cu- and Cr-rich domains are observed. • EELS determines a single van Hove singularity for bcc Cu–Cr solid solutions. • The electronic structure is dominated by d
Energy Technology Data Exchange (ETDEWEB)
Escaño, Mary Clare Sison, E-mail: mcescano@u-fukui.ac.jp [Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507 (Japan); Arevalo, Ryan Lacdao [Department of Precision Science and Technology and Applied Physics, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Gyenge, Elod [Department of Chemical and Biological Engineering, The University of British Columbia, Vancouver, BC, Canada V6T 1Z3 (Canada); Kasai, Hideaki [Department of Precision Science and Technology and Applied Physics, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)
2013-12-15
Highlights: ► Difference in Pt, Os electronic structures lead to different borohydride structures. ► Promotion of B–H bond breaking on Os due to water effects. ► Control of borohydride structure on Os catalyst using electric field. -- Abstract: Periodic density functional theory calculations are performed to investigate the nature of the BH{sub 4ad} and its interaction with H{sub 2}O{sub ad} in the presence of homogenous electric field. We observed a significant charge polarity of BH{sub 4ad} on Os(1 1 1) and such property could explain the electrostatic interaction with water monomer (H{sub ad}) with its HOH plane parallel to the surface. This interaction changes the BH{sub ad} molecular structure to BH{sub 3ad} + H{sub ad}. In the presence of homogenous electric field, the water co-adsorption effect is reduced due to the stabilization of H{sub 2}O{sub ad} on the surface and the deviation of the O–H bond from the plane, decreasing the electrostatic interaction between BH{sub 4ad} and H{sub 2}O{sub ad}. These fundamental findings imply accessible control of borohydride structures on an electrode surface, which could be relevant for direct borohydride fuel cell (DBFC) and reversible hydrogen storage/release applications.
International Nuclear Information System (INIS)
Escaño, Mary Clare Sison; Arevalo, Ryan Lacdao; Gyenge, Elod; Kasai, Hideaki
2013-01-01
Highlights: ► Difference in Pt, Os electronic structures lead to different borohydride structures. ► Promotion of B–H bond breaking on Os due to water effects. ► Control of borohydride structure on Os catalyst using electric field. -- Abstract: Periodic density functional theory calculations are performed to investigate the nature of the BH 4ad and its interaction with H 2 O ad in the presence of homogenous electric field. We observed a significant charge polarity of BH 4ad on Os(1 1 1) and such property could explain the electrostatic interaction with water monomer (H ad ) with its HOH plane parallel to the surface. This interaction changes the BH ad molecular structure to BH 3ad + H ad . In the presence of homogenous electric field, the water co-adsorption effect is reduced due to the stabilization of H 2 O ad on the surface and the deviation of the O–H bond from the plane, decreasing the electrostatic interaction between BH 4ad and H 2 O ad . These fundamental findings imply accessible control of borohydride structures on an electrode surface, which could be relevant for direct borohydride fuel cell (DBFC) and reversible hydrogen storage/release applications
Jörg, Tanja; Music, Denis; Hauser, Filipe; Cordill, Megan J; Franz, Robert; Köstenbauer, Harald; Winkler, Jörg; Schneider, Jochen M; Mitterer, Christian
2017-08-07
A major obstacle in the utilization of Mo thin films in flexible electronics is their brittle fracture behavior. Within this study, alloying with Re is explored as a potential strategy to improve the resistance to fracture. The sputter-deposited Mo 1-x Re x films (with 0 ≤ x ≤ 0.31) were characterized in terms of structural and mechanical properties, residual stresses as well as electrical resistivity. Their deformation behavior was assessed by straining 50 nm thin films on polyimide substrates in uniaxial tension, while monitoring crack initiation and propagation in situ by optical microscopy and electrical resistance measurements. A significant toughness enhancement occurs with increasing Re content for all body-centered cubic solid solution films (x ≤ 0.23). However, at higher Re concentrations (x > 0.23) the positive effect of Re is inhibited due to the formation of dual-phase films with the additional close packed A15 Mo 3 Re phase. The mechanisms responsible for the observed toughness behavior are discussed based on experimental observations and electronic structure calculations. Re gives rise to both increased plasticity and bond strengthening in these Mo-Re solid solutions.
Ahmed, Nisar; Nisar, Jawad; Kouser, R.; Nabi, Azeem G.; Mukhtar, S.; Saeed, Yasir; Nasim, M. H.
2017-06-01
Wide band gap magnetic semiconductors made of lanthanide compounds have a wide range of applications in opto-magneto-electronic industry and electro (photo) luminescence devices. We have carried out a systematic study of electronic, magnetic and optical properties of rare earth potassium sulfides KMS2 (M = Nd, Ho, Er, and Lu) using density functional theory (DFT) with full potential linearized augmented plane wave method (FP-LAPW). Different exchange and correlation approximations are employed such as generalized gradient approximation (GGA), GGA + U and TB-mBJ. It is inferred that the GGA + U approach correctly predicts the localized behavior of 4f electrons in lanthanide atoms for the calculation of band gaps, electronic, magnetic and optical properties. All compounds are stable in ferromagnetic phase except KLuS2, while KLuS2 is a non-magnetic semiconductor because there is no unpaired f-electron. Band gaps of KMS2 are estimated and these materials are found to be wide band gap semiconductors. These materials absorb mainly ultraviolet (UV) radiations, which make them good photoluminescent materials with a strong dependence on the direction of the polarization of incident photons.
Energy Technology Data Exchange (ETDEWEB)
Dimitrievska, Mirjana; White, James L.; Zhou, Wei; Stavila, Vitalie; Klebanoff, Leonard E.; Udovic, Terrence J.
2016-01-01
The structure-dependent vibrational properties of different Mg(BH4)2 polymorphs (..alpha.., ..beta.., ..gamma.., and ..delta.. phases) were investigated with a combination of neutron vibrational spectroscopy (NVS) measurements and density functional theory (DFT) calculations, with emphasis placed on the effects of the local structure and orientation of the BH4- anions. DFT simulations closely match the neutron vibrational spectra. The main bands in the low-energy region (20-80 meV) are associated with the BH4- librational modes. The features in the intermediate energy region (80-120 meV) are attributed to overtones and combination bands arising from the lower-energy modes. The features in the high-energy region (120-200 meV) correspond to the BH4- symmetric and asymmetric bending vibrations, of which four peaks located at 140, 142, 160, and 172 meV are especially intense. There are noticeable intensity distribution variations in the vibrational bands for different polymorphs. This is explained by the differences in the spatial distribution of BH4- anions within various structures. An example of the possible identification of products after the hydrogenation of MgB2, using NVS measurements, is presented. These results provide fundamental insights of benefit to researchers currently studying these promising hydrogen-storage materials.
Energy Technology Data Exchange (ETDEWEB)
Liu, Baoshun, E-mail: liubaoshun@126.com; Zhao, Xiujian
2017-03-31
Highlights: • The effect of Fe and V doping on TiO{sub 2} structure was studied with DFT + U calculation. • V and Fe co-doping affects the formation energies and electronic structure. • V and Fe co-doping causes the synergetic effect on the optical properties. - Abstract: Based on the density functional theory (DFT + U), a detailed study on the energetic, electronic, and optical properties of Fe-, V-, and Fe & V-co-doping anatase and rutile TiO{sub 2} was performed The synergetic effect of Fe & V bimetal co-doping on the optical absorption was discussed on electronic level. Two kinds of co-dopants were considered, which included edge-shared and corner-shared co-doping. It was shown that Fe and V atoms prefer to replace Ti atom in the O-rich contions than in the Ti-rich conditions. Co-doping in anatase reduces the formation energies in both cases, while the formation energies for rutile cannot be decreased. The Bader charge analysis indicates the +3 of Fe atom and +4 of V atom, and the obvious electron exchange between Fe and V atom in co-doping cases can be identified, which indicates the presence of synergetic effect induced by co-doping. The cooperation of Fe & V co-dopants was also supported by the result of projected density of states and spin charge density differences, as the hybridization of Fe3d with V3d orbitals was seen within the TiO{sub 2} forbidden band. Different from single-dopant systems, the V3d-Fe3d co-interaction leads to the formation of some spin mid-gap states, which have an obvious effect on the optical absorptions.
Energy Technology Data Exchange (ETDEWEB)
Boeck, Sixten
2009-09-03
which we developed in this work. In order to demonstrate the power of the this approach the full-featured plane-wave framework S/PHI/nX has been developed based on the new meta-language. The S/PHI/nX source code is remarkably short and transparent which simplifies code maintenance and the introduction of new sophisticated algorithms. Various benchmarks which have been conducted in this study compare S/PHI/nX with other state-of-the-art plane-wave packages with respect to runtime performance and accuracy. Based on these calculations we verified the general trends of phonon spectra, the location and amplitudes of the thermal anomalies of these systems. (orig.)
Electric dipole polarizability from first principles calculations
International Nuclear Information System (INIS)
Miorelli, M.; University of British Columbia, Vancouver, BC; Bacca, S.; University of Manitoba; Barnea, N.
2016-01-01
The electric dipole polarizability quantifies the low-energy behavior of the dipole strength and is related to critical observables such as the radii of the proton and neutron distributions. Its computation is challenging because most of the dipole strength lies in the scattering continuum. In our paper we combine integral transforms with the coupled-cluster method and compute the dipole polarizability using bound-state techniques. Furthermore, employing different interactions from chiral effective field theory, we confirm the strong correlation between the dipole polarizability and the charge radius, and study its dependence on three-nucleon forces. Finally, we find good agreement with data for the 4 He, 40 Ca, and 16 O nuclei, and predict the dipole polarizability for the rare nucleus 22 O.
International Nuclear Information System (INIS)
Ghosh, G.; Walle, A. van de; Asta, M.
2008-01-01
The thermodynamic properties of solid solutions with body-centered cubic (bcc), face-centered cubic (fcc) and hexagonal close-packed (hcp) structures in the Al-TM (TM = Ti, Zr and Hf) systems are calculated from first-principles using cluster expansion (CE), Monte-Carlo simulation and supercell methods. The 32-atom special quasirandom structure (SQS) supercells are employed to compute properties at 25, 50 and 75 at.% TM compositions, and 64-atom supercells have been employed to compute properties of alloys in the dilute concentration limit (one solute and 63 solvent atoms). In general, the energy of mixing (Δ m E) calculated by CE and dilute supercells agree very well. In the concentrated region, the Δ m E values calculated by CE and SQS methods also agree well in many cases; however, noteworthy discrepancies are found in some cases, which we argue originate from inherent elastic and dynamic instabilities of the relevant parent lattice structures. The importance of short-range order on the calculated values of Δ m E for hcp Al-Ti alloys is demonstrated. We also present calculated results for the composition dependence of the atomic volumes in random solid solutions with bcc, fcc and hcp structures. The properties of solid solutions reported here may be integrated within the CALPHAD formalism to develop reliable thermodynamic databases in order to facilitate: (i) calculations of stable and metastable phase diagrams of binary and multicomponent systems, (ii) alloy design, and (iii) processing of Al-TM-based alloys
International Nuclear Information System (INIS)
Xing, Wen-qing; Yu, Xin-ye; Li, Heng; Ma, Le; Zuo, Wei; Dong, Peng; Wang, Wen-xian; Ding, Min
2016-01-01
This paper studies microstructure and mechanical properties of Sn-9Zn-x Al 2 O 3 nanoparticles (x=0–1) lead-free solder alloy. The interface structure, interface energy and electronic properties of Al 2 O 3 /Sn9Zn interface are investigated by first-principle calculation. On the experimental part, in comparison with the plain Sn-9Zn solder, the Al 2 O 3 nanoparticles incorporated into the solder matrix can inhibit the growth of coarse dendrite Sn-Zn eutectic structure and refine grains of the composite solders during the solidification process of the alloys. Moreover, the microhardness and average tensile strength of the solders with addition of Al 2 O 3 nanoparticles increased with the increasing weight percentages of Al 2 O 3 nanoparticles. These improved mechanical properties can be attributed to the microstructure developments and the dispersed Al 2 O 3 nanoparticles.
First-principles molecular dynamics for metals
International Nuclear Information System (INIS)
Fernando, G.W.; Qian, G.; Weinert, M.; Davenport, J.W.
1989-01-01
A Car-Parrinello-type first-principles molecular-dynamics approach capable of treating the partial occupancy of electronic states that occurs at the Fermi level in a metal is presented. The algorithms used to study metals are both simple and computationally efficient. We also discuss the connection between ordinary electronic-structure calculations and molecular-dynamics simulations as well as the role of Brillouin-zone sampling. This extension should be useful not only for metallic solids but also for solids that become metals in their liquid and/or amorphous phases
Bouamama, Kh.; Djemia, P.; Benhamida, M.
2015-09-01
First-principles pseudo-potentials calculations of the mixing enthalpy, of the lattice constants a0 and of the single-crystal elastic constants cij for ternary metal nitrides TaxMe1-xN (Me=Mo or W) alloys considering the cubic B1-rocksalt structure is carried out. For disordered ternary alloys, we employ the virtual crystal approximation VCA in which the alloy pseudopotentials are constructed within a first-principles VCA scheme. The supercell method SC is also used for ordered structures in order to evaluate clustering effects. We find that the mixing enthalpy still remains negative for TaxMe1-xN alloys in the whole composition range which implies these cubic TaxMo1-xN and TaxW1-xN ordered solid solutions are stable. We investigate the effect of Mo and W alloying on the trend of the mechanical properties of TaN. The effective shear elastic constant c44, the Cauchy pressure (c12-c44), and the shear to bulk modulus G/B ratio are used to discuss, respectively, the mechanical stability of the ternary structure and the brittle/ductile behavior in reference to TaN, MeN alloys. We determine the onset transition from the unstable structure to the stable one B1-rocksalt from the elastic stability criteria when alloying MeN with Ta. In a second stage, in the frame of anisotropic elasticity, we estimate by one homogenization method the averaged constants of the polycrystalline TaxMe1-xN alloys considering the special case of an isotropic medium with no crystallographic texture.
A first-principles approach to finite temperature elastic constants
Energy Technology Data Exchange (ETDEWEB)
Wang, Y; Wang, J J; Zhang, H; Manga, V R; Shang, S L; Chen, L-Q; Liu, Z-K [Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802 (United States)
2010-06-09
A first-principles approach to calculating the elastic stiffness coefficients at finite temperatures was proposed. It is based on the assumption that the temperature dependence of elastic stiffness coefficients mainly results from volume change as a function of temperature; it combines the first-principles calculations of elastic constants at 0 K and the first-principles phonon theory of thermal expansion. Its applications to elastic constants of Al, Cu, Ni, Mo, Ta, NiAl, and Ni{sub 3}Al from 0 K up to their respective melting points show excellent agreement between the predicted values and existing experimental measurements.
A first-principles approach to finite temperature elastic constants
International Nuclear Information System (INIS)
Wang, Y; Wang, J J; Zhang, H; Manga, V R; Shang, S L; Chen, L-Q; Liu, Z-K
2010-01-01
A first-principles approach to calculating the elastic stiffness coefficients at finite temperatures was proposed. It is based on the assumption that the temperature dependence of elastic stiffness coefficients mainly results from volume change as a function of temperature; it combines the first-principles calculations of elastic constants at 0 K and the first-principles phonon theory of thermal expansion. Its applications to elastic constants of Al, Cu, Ni, Mo, Ta, NiAl, and Ni 3 Al from 0 K up to their respective melting points show excellent agreement between the predicted values and existing experimental measurements.
Yang, D; Wei, L L; Chao, X L; Yang, Z P; Zhou, X Y
2016-03-21
The crystal structures of the lead-free piezoelectric ceramics (K0.5Na0.5)NbO3 and (K0.5Na0.5)0.94Li0.06NbO3 prepared by a solid-state method were investigated using first-principles calculations. The calculated values of piezoelectricity were in good agreement with the experimental data. We found that the primary contribution to piezoelectricity in this material comes from the hybridization of the O 2p and Nb 4d orbitals, which causes a change in the Nb-O bond length and the distortion of the Nb-O octahedral structure. Analysis of the band structure and the total density of states revealed that Li-doped (K0.5Na0.5)NbO3 enhances hybridization of the O 2p and Nb 4d orbitals. This hybridization enhancement further reduces the Nb-O1 bond length and enhances the distortion of the Nb-O octahedron along the [001] direction, which may be the main reason for the improvement of the piezoelectric properties. In addition, the piezoelectric coefficients are calculated here, which show the same trend as the experimental results.
Credibility is the first principle
International Nuclear Information System (INIS)
Beecher, William
2002-01-01
The first principle of an effective public affairs program on nuclear energy is credibility. If credibility is lacking, no matter how artful the message, it will not be persuasive. There has long been a problem in the United States. For years much of the industry followed the practice, when there was an event at a nuclear power plant that resulted in an unplanned release of radioactivity, to tell the public there was 'no release' if in fact the release was below the technical specifications of what the NRC mandates as being safe. The NRC is a safety regulator. It can tell nuclear power plant operators what to do, or not do, when it comes to safety, but doesn't have the right to tell them what to say to the public. The example of an emergency exercise and the NRC press release on that occasion showed the direction how companies could be influenced to behave in order to prevent such avoidably negative news coverage, i.e. attaining credibility when public anxiety is concerned
First-principles elasticity of monocarboaluminate hydrates
Moon, J.
2014-07-01
The elasticity of monocarboaluminate hydrates, 3CaO·Al2O3·CaCO3·xH2O (x = 11 or 8), has been investigated by first-principles calculations. Previous experimental study revealed that the fully hydrated monocarboaluminate (x = 11) exhibits exceptionally low compressibility compared to other reported calcium aluminate hydrates. This stiff hydration product can contribute to the strength of concrete made with Portland cements containing calcium carbonates. In this study, full elastic tensors and mechanical properties of the crystal structures with different water contents (x = 11 or 8) are computed by first-principles methods based on density functional theory. The results indicate that the compressibility of monocarboaluminate is highly dependent on the water content in the interlayer region. The structure also becomes more isotropic with the addition of water molecules in this region. Since the monocarboaluminate is a key hydration product of limestone added cement, elasticity of the crystal is important to understand its mechanical impact on concrete. Besides, it is put forth that this theoretical calculation will be useful in predicting the elastic properties of other complex cementitous materials and the influence of ion exchange on compressibility.
First-principles elasticity of monocarboaluminate hydrates
Moon, J.; Yoon, S.; Wentzcovitch, R. M.; Monteiro, P. J. M.
2014-01-01
The elasticity of monocarboaluminate hydrates, 3CaO·Al2O3·CaCO3·xH2O (x = 11 or 8), has been investigated by first-principles calculations. Previous experimental study revealed that the fully hydrated monocarboaluminate (x = 11) exhibits exceptionally low compressibility compared to other reported calcium aluminate hydrates. This stiff hydration product can contribute to the strength of concrete made with Portland cements containing calcium carbonates. In this study, full elastic tensors and mechanical properties of the crystal structures with different water contents (x = 11 or 8) are computed by first-principles methods based on density functional theory. The results indicate that the compressibility of monocarboaluminate is highly dependent on the water content in the interlayer region. The structure also becomes more isotropic with the addition of water molecules in this region. Since the monocarboaluminate is a key hydration product of limestone added cement, elasticity of the crystal is important to understand its mechanical impact on concrete. Besides, it is put forth that this theoretical calculation will be useful in predicting the elastic properties of other complex cementitous materials and the influence of ion exchange on compressibility.
Energy Technology Data Exchange (ETDEWEB)
Shen, Lanxian [Education Ministry Key Laboratory of Renewable Energy Advanced Materials and Manufacturing Technology, Yunnan Provincial Renewable Energy Engineering Key Lab, Solar Energy Research Institution, Yunnan Normal University, Kunming 650500 (China); Li, Decong [College of Optoelectronic Engineering, Yunnan Open University, Kunming 650500 (China); Liu, Hongxia; Liu, Zuming [Education Ministry Key Laboratory of Renewable Energy Advanced Materials and Manufacturing Technology, Yunnan Provincial Renewable Energy Engineering Key Lab, Solar Energy Research Institution, Yunnan Normal University, Kunming 650500 (China); Deng, Shukang, E-mail: skdeng@126.com [Education Ministry Key Laboratory of Renewable Energy Advanced Materials and Manufacturing Technology, Yunnan Provincial Renewable Energy Engineering Key Lab, Solar Energy Research Institution, Yunnan Normal University, Kunming 650500 (China)
2016-12-01
In this study, the structural and electronic structural properties of Ba{sub 8}Ga{sub 16}Sn{sub 30−x}Ge{sub x} (0≤x≤30) are determined by the first-principle method on the basis of density functional theory. Consistent with experimental findings, calculated results reveal that Ge atoms preferentially occupy the 2a and 24g sites in these compounds. As the content of Ge in Ge-substituted clathrate is increased, the lattice parameter is decreased, and the structural stability is enhanced. The bandgaps of the compound at 1≤x≤10 are smaller than those of Ba{sub 8}Ga{sub 16}Sn{sub 30}. By contrast, the bandgaps of the compound at x>10 are larger than those of Ba{sub 8}Ga{sub 16}Sn{sub 30}. The substitution of Ge for Sn affects p-type conductivity but not n-type conductivity. As Ge content increases, the whole conduction band moves to the direction of high energy, and the density of states of valence-band top decreases. The calculated potential energy versus displacement of Ba indicates that the vibration energy of this atom increases as cage size decreases. Because Ge substitution also affects clathrate structural symmetry, the distance of Ba atom deviation from the center of the cage initially increases and subsequently decreases as the Ge content increases.
International Nuclear Information System (INIS)
Wu Kong-Ping; Zhou Meng-Ran; Huang You-Rui; Gu Shu-Lin; Ye Jian-Dong; Zhu Shun-Ming; Zhang Rong; Zheng You-Dou; Tang Kun
2013-01-01
The structural, energetic, and electronic properties of lattice highly mismatched ZnY 1−x O x (Y = S, Se, Te) ternary alloys with dilute O concentrations are calculated from first principles within the density functional theory. We demonstrate the formation of an isolated intermediate electronic band structure through diluted O-substitute in zinc-blende ZnY (Y = S, Se, Te) at octahedral sites in a semiconductor by the calculations of density of states (DOS), leading to a significant absorption below the band gap of the parent semiconductor and an enhancement of the optical absorption in the whole energy range of the solar spectrum. It is found that the intermediate band states should be described as a result of the coupling between impurity O 2p states with the conduction band states. Moreover, the intermediate bands (IBs) in ZnTeO show high stabilization with the change of O concentration resulting from the largest electronegativity difference between O and Te compared with in the other ZnSO and ZnSeO. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
A NRESPG Monte Carlo code for the calculation of neutron response functions for gas counters
Energy Technology Data Exchange (ETDEWEB)
Kudo, K; Takeda, N; Fukuda, A [Electrotechnical Lab., Tsukuba, Ibaraki (Japan); Torii, T; Hashimoto, M; Sugita, T; Yang, X; Dietze, G
1996-07-01
In this paper, we show the outline of the NRESPG and some typical results of the response functions and efficiencies of several kinds of gas counters. The cross section data for the several kinds of filled gases and the wall material of stainless steel or aluminum are taken mainly from ENDF/B-IV. The ENDF/B-V for stainless steel is also used to investigate the influence on pulse height spectra of gas counters due to the difference of nuclear data files. (J.P.N.)
International Nuclear Information System (INIS)
Ivashchenko, V.I.; Veprek, S.; Argon, A.S.; Turchi, P.E.A.; Gorb, L.; Hill, F.; Leszczynski, J.
2015-01-01
TiN/SiN x heterostructures with one monolayer of the interfacial SiN x have been investigated in the framework of first-principles molecular dynamics calculations in the temperature range of 0 to 1400 K with subsequent static relaxation. The atomic configurations, thermal stability and stress–strain relations have been calculated. Among the heterostructures studied, only the TiN(111)/SiN/TiN(111) and TiN(111)/Si 2 N 3 /TiN(111) ones are thermally stable. Upon tensile load, decohesion occurs between the Ti−N bonds adjacent to the SiN x interfacial layer for TiN(001)/SiN/TiN(001) and TiN(111)/Si 2 N 3 /TiN(111) heterostructures, and inside the TiN slab for TiN(001)/Si 3 N 4 /TiN(001) and TiN(110)/SiN/TiN(110) ones. Upon shear, failure occurs in TiN near the interfaces in all the heterostructures, except for the TiN(001)/Si 3 N 4 /TiN(001) one, for which the plastic flow occurs inside the TiN slab. Based on these results we estimate the maximum achievable hardness of nc-TiN/Si 3 N 4 nanocomposites free of impurities to be about 170 GPa. - Highlights: • Interface stability in TiN/SiN x heterostructures at T ≤ 1400 K is studied by quantum molecular dynamics. • Ideal decohesion and shear strengths of the heterostructures have been calculated. • Achievable hardness of nc-TiN/Si 3 N 4 -like nanocomposites of about 170 GPa is calculated. • Experimentally achieved lower hardness is limited by flaws, such as oxygen impurities
Energy Technology Data Exchange (ETDEWEB)
Ivashchenko, V.I., E-mail: ivash@ipms.kiev.ua [Institute of Problems of Material Science, National Academy of Science of Ukraine, Krzhyzhanosky Str. 3, 03142 Kyiv (Ukraine); Veprek, S., E-mail: stan.veprek@lrz.tum.de [Department of Chemistry, Technical University Munich, Lichtenbergstrasse 4, D-85747 Garching (Germany); Argon, A.S. [Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Turchi, P.E.A. [Lawrence Livermore National Laboratory (L-352), P.O. Box 808, Livermore, CA 94551 (United States); Gorb, L. [Badger Technical Services, LLC, Vicksburg, MS 39180 (United States); U.S. Army ERDC, Vicksburg, MS 39180 (United States); Hill, F. [U.S. Army ERDC, Vicksburg, MS 39180 (United States); Leszczynski, J. [Department of Chemistry and Biochemistry, Interdisciplinary Center for Nanotoxicity, Jackson State University, Jackson, MS 39217 (United States)
2015-03-02
TiN/SiN{sub x} heterostructures with one monolayer of the interfacial SiN{sub x} have been investigated in the framework of first-principles molecular dynamics calculations in the temperature range of 0 to 1400 K with subsequent static relaxation. The atomic configurations, thermal stability and stress–strain relations have been calculated. Among the heterostructures studied, only the TiN(111)/SiN/TiN(111) and TiN(111)/Si{sub 2}N{sub 3}/TiN(111) ones are thermally stable. Upon tensile load, decohesion occurs between the Ti−N bonds adjacent to the SiN{sub x} interfacial layer for TiN(001)/SiN/TiN(001) and TiN(111)/Si{sub 2}N{sub 3}/TiN(111) heterostructures, and inside the TiN slab for TiN(001)/Si{sub 3}N{sub 4}/TiN(001) and TiN(110)/SiN/TiN(110) ones. Upon shear, failure occurs in TiN near the interfaces in all the heterostructures, except for the TiN(001)/Si{sub 3}N{sub 4}/TiN(001) one, for which the plastic flow occurs inside the TiN slab. Based on these results we estimate the maximum achievable hardness of nc-TiN/Si{sub 3}N{sub 4} nanocomposites free of impurities to be about 170 GPa. - Highlights: • Interface stability in TiN/SiN{sub x} heterostructures at T ≤ 1400 K is studied by quantum molecular dynamics. • Ideal decohesion and shear strengths of the heterostructures have been calculated. • Achievable hardness of nc-TiN/Si{sub 3}N{sub 4}-like nanocomposites of about 170 GPa is calculated. • Experimentally achieved lower hardness is limited by flaws, such as oxygen impurities.
Primordial Black Holes from First Principles (Overview)
Lam, Casey; Bloomfield, Jolyon; Moss, Zander; Russell, Megan; Face, Stephen; Guth, Alan
2017-01-01
Given a power spectrum from inflation, our goal is to calculate, from first principles, the number density and mass spectrum of primordial black holes that form in the early universe. Previously, these have been calculated using the Press- Schechter formalism and some demonstrably dubious rules of thumb regarding predictions of black hole collapse. Instead, we use Monte Carlo integration methods to sample field configurations from a power spectrum combined with numerical relativity simulations to obtain a more accurate picture of primordial black hole formation. We demonstrate how this can be applied for both Gaussian perturbations and the more interesting (for primordial black holes) theory of hybrid inflation. One of the tools that we employ is a variant of the BBKS formalism for computing the statistics of density peaks in the early universe. We discuss the issue of overcounting due to subpeaks that can arise from this approach (the ``cloud-in-cloud'' problem). MIT UROP Office- Paul E. Gray (1954) Endowed Fund.
Energy Technology Data Exchange (ETDEWEB)
Lu, Haipeng; Deng, Longjiang [National Engineering Research Center of Electromagnetic Radiation Control Materials, University of Electronic Science and Technology of China, Chengdu, Sichuan, 610054 (China); State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, Sichuan, 610054 (China); Sun, Xun, E-mail: sunxunphy@hotmail.com; Hou, Zhihua; Yang, Wen; Wang, Siyuan; Xie, Jianliang [State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, Sichuan, 610054 (China)
2016-03-15
Employing first-principles calculations, structural, electronic properties of new multiferroic material Er{sub 2}NiMnO{sub 6}/La{sub 2}NiMnO{sub 6} perovskite superlattice are investigated. This structure is computed as monoclinic phase with obvious distortion. The average in-plane anti-phase rotation angle, average out-of-plane in-phase rotation angle and other microscopic features are reported in this paper. Ni and Mn are found in this superlattice that stay high spin states. These microscopic properties play important roles in multiferroic properties. Based on these microscopic features, the relationship between the direction of spontaneous polarization and the order of substitution in neighboring A-O layers is explained. Finally, we try to enhance the electrical polarization magnitude by 32% by altering the previous superlattice as LaEr{sub 2}NiMnO{sub 7} structure. Our results show that both repulsion force of A site rare earth ions and the arrangement of B site ions can exert influences on spontaneous polarization.
Directory of Open Access Journals (Sweden)
Haipeng Lu
2016-03-01
Full Text Available Employing first-principles calculations, structural, electronic properties of new multiferroic material Er2NiMnO6/La2NiMnO6 perovskite superlattice are investigated. This structure is computed as monoclinic phase with obvious distortion. The average in-plane anti-phase rotation angle, average out-of-plane in-phase rotation angle and other microscopic features are reported in this paper. Ni and Mn are found in this superlattice that stay high spin states. These microscopic properties play important roles in multiferroic properties. Based on these microscopic features, the relationship between the direction of spontaneous polarization and the order of substitution in neighboring A-O layers is explained. Finally, we try to enhance the electrical polarization magnitude by 32% by altering the previous superlattice as LaEr2NiMnO7 structure. Our results show that both repulsion force of A site rare earth ions and the arrangement of B site ions can exert influences on spontaneous polarization.
Kerber, Rachel Nathaniel; Kermagoret, Anthony; Callens, Emmanuel; Florian, Pierre A.; Massiot, Dominique; Lesage, Anne; Copé ret, Christophe; Delbecq, Franç oise; Rozanska, Xavier; Sautet, Philippe
2012-01-01
The determination of the nature and structure of surface sites after chemical modification of large surface area oxides such as silica is a key point for many applications and challenging from a spectroscopic point of view. This has been, for instance, a long-standing problem for silica reacted with alkylaluminum compounds, a system typically studied as a model for a supported methylaluminoxane and aluminum cocatalyst. While 27Al solid-state NMR spectroscopy would be a method of choice, it has been difficult to apply this technique because of large quadrupolar broadenings. Here, from a combined use of the highest stable field NMR instruments (17.6, 20.0, and 23.5 T) and ultrafast magic angle spinning (>60 kHz), high-quality spectra were obtained, allowing isotropic chemical shifts, quadrupolar couplings, and asymmetric parameters to be extracted. Combined with first-principles calculations, these NMR signatures were then assigned to actual structures of surface aluminum sites. For silica (here SBA-15) reacted with triethylaluminum, the surface sites are in fact mainly dinuclear Al species, grafted on the silica surface via either two terminal or two bridging siloxy ligands. Tetrahedral sites, resulting from the incorporation of Al inside the silica matrix, are also seen as minor species. No evidence for putative tri-coordinated Al atoms has been found. © 2012 American Chemical Society.
Energy Technology Data Exchange (ETDEWEB)
Xing, Wen-qing; Yu, Xin-ye; Li, Heng; Ma, Le; Zuo, Wei [Taiyuan University of Technology, College of Material Science and Technology, Taiyuan 030024 (China); Dong, Peng; Wang, Wen-xian [Taiyuan University of Technology, College of Material Science and Technology, Taiyuan 030024 (China); Shanxi Key Laboratory of Advanced Magnesium-based Materials, Taiyuan 030024 (China); Key Laboratory of Interface Science and Engineering in Advanced Materials, Ministry of Education, Taiyuan University of Technology, Taiyuan 030024 (China); Ding, Min, E-mail: dingmin@tyut.edu.cn [Taiyuan University of Technology, College of Material Science and Technology, Taiyuan 030024 (China); Shanxi Key Laboratory of Advanced Magnesium-based Materials, Taiyuan 030024 (China); Key Laboratory of Interface Science and Engineering in Advanced Materials, Ministry of Education, Taiyuan University of Technology, Taiyuan 030024 (China)
2016-12-15
This paper studies microstructure and mechanical properties of Sn-9Zn-x Al{sub 2}O{sub 3} nanoparticles (x=0–1) lead-free solder alloy. The interface structure, interface energy and electronic properties of Al{sub 2}O{sub 3}/Sn9Zn interface are investigated by first-principle calculation. On the experimental part, in comparison with the plain Sn-9Zn solder, the Al{sub 2}O{sub 3} nanoparticles incorporated into the solder matrix can inhibit the growth of coarse dendrite Sn-Zn eutectic structure and refine grains of the composite solders during the solidification process of the alloys. Moreover, the microhardness and average tensile strength of the solders with addition of Al{sub 2}O{sub 3} nanoparticles increased with the increasing weight percentages of Al{sub 2}O{sub 3} nanoparticles. These improved mechanical properties can be attributed to the microstructure developments and the dispersed Al{sub 2}O{sub 3} nanoparticles.
Kerber, Rachel Nathaniel
2012-04-18
The determination of the nature and structure of surface sites after chemical modification of large surface area oxides such as silica is a key point for many applications and challenging from a spectroscopic point of view. This has been, for instance, a long-standing problem for silica reacted with alkylaluminum compounds, a system typically studied as a model for a supported methylaluminoxane and aluminum cocatalyst. While 27Al solid-state NMR spectroscopy would be a method of choice, it has been difficult to apply this technique because of large quadrupolar broadenings. Here, from a combined use of the highest stable field NMR instruments (17.6, 20.0, and 23.5 T) and ultrafast magic angle spinning (>60 kHz), high-quality spectra were obtained, allowing isotropic chemical shifts, quadrupolar couplings, and asymmetric parameters to be extracted. Combined with first-principles calculations, these NMR signatures were then assigned to actual structures of surface aluminum sites. For silica (here SBA-15) reacted with triethylaluminum, the surface sites are in fact mainly dinuclear Al species, grafted on the silica surface via either two terminal or two bridging siloxy ligands. Tetrahedral sites, resulting from the incorporation of Al inside the silica matrix, are also seen as minor species. No evidence for putative tri-coordinated Al atoms has been found. © 2012 American Chemical Society.
International Nuclear Information System (INIS)
Zhang Zhao-Fu; Zhou Tie-Ge; Zhao Hai-Yang; Wei Xiang-Lei
2014-01-01
The geometry, electronic structure and magnetic property of the hexagonal AlN (h-AlN) sheet doped by 5d atoms (Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) are investigated by first-principles calculations based on the density functional theory. The influence of symmetry and symmetry-breaking is also studied. There are two types of local symmetries of the doped systems: C 3v and D 3h . The symmetry will deviate from exact C 3v and D 3h for some particular dopants after optimization. The total magnetic moments of the doped systems are 0μ B for Lu, Ta and Ir; 1μ B for Hf, W, Pt and Hg; 2μ B for Re and Au; and 3μ B for Os and Al-vacancy. The total densities of state are presented, where impurity energy levels exist. The impurity energy levels and total magnetic moments can be explained by the splitting of 5d orbitals or molecular orbitals under different symmetries. (condensed matter: structural, mechanical, and thermal properties)
Watanabe, Shinta; Sato, Toshikazu; Yoshida, Tomoko; Nakaya, Masato; Yoshino, Masahito; Nagasaki, Takanori; Inaba, Yusuke; Takeshita, Kenji; Onoe, Jun
2018-04-01
We have investigated the chemical forms of palladium (Pd) ion in nitric acid solution, using XAFS/UV-vis spectroscopic and first-principles methods in order to develop the disposal of high-level radioactive nuclear liquid wastes (HLLW: radioactive metal ions in 2 M nitric acid solution). The results of theoretical calculations and XAFS/UV-vis spectroscopy indicate that Pd is a divalent ion and forms a square-planar complex structure coordinated with four nitrate ions, [Pd(NO3)4]2-, in nitric acid solution. This complex structure is also thermodynamically predicted to be most stable among complexes [Pd(H2O)x(NO3)4-x]x-2 (x = 0-4). Since the overall feature of UV-vis spectra of the Pd complex was independent of nitric acid concentration in the range 1-6 M, the structure of the Pd complex remains unchanged in this range. Furthermore, we examined the influence of γ-ray radiation on the [Pd(NO3)4]2- complex, using UV-vis spectroscopy, and found that UV-vis spectra seemed not to be changed even after 1.0 MGy irradiation. This implies that the Pd complex structure will be still stable in actual HLLW. These findings obtained above are useful information to develop the vitrification processes for disposal of HLLW.
Tian, Guang; Zha, Liang; Yang, Wenyun; Qiao, Guanyi; Wang, Changsheng; Yang, Yingchang; Yang, Jinbo
2018-06-01
The preferential site substitution of the Fe by Si, Ga and Zr in the Y(Fe,M)9.2 and Y(Fe,M)9.2C compounds, and the doping effects on the magnetic properties have been studied by the first-principles calculations. It is found that the doping of the Si or Zr can improve the thermodynamic stability of the 1:9 phase, while the substitution of the Fe by Ga makes it unstable. Si atom tends to enter the 3g crystal site and Zr prefers to occupy the 2e site when Y(Fe,M)9.2 and their carbides are synthesized. Although the substitution of the Fe by Si and Zr will reduce the total magnetic moments of the YFe9.2 and their carbides, the volumetric and the d-band narrowing effects caused by the doping can still modify the electron density distributions of the Fe near the Fermi level, improving the magnetic ordering temperature of the non-carbonated compound YFe9.2. The calculated magnetic ordering temperatures of Y(Fe,M)9.2C decrease with the increasing content of the doping elements M due to the stronger hybridization of the d bands in the carbides. For the rare-earth(RE) iron based intermetallics REFe9.2 with the TbCu7-type structure, it is suggested that Zr is able to stabilize the phase and enhance the magnetic ordering temperature, indicating the possible further application in the field of permanent magnets, which has not been reported before.
International Nuclear Information System (INIS)
Guo Kai; Man Zhenyong; Cao Qigao; Chen Haohong; Guo Xiangxin; Zhao Jingtai
2011-01-01
Graphical abstract: The structure stability of REZnOSb decreases with varying rare-earth from La to Gd because of the increased binding energy. Research highlights: → As increasing the atomic number of the RE, the structural stability of REZnOSb decreases. → Varying the rare-earth elements from La to Gd, the covalent interactions between [ZnSb] and [LaO] layer are enhanced by 4f-electrons. → The electrical transport properties of REZnOSb could be improved using the large atomic number of the RE. - Abstract: The structural stability, chemical bonding, Mulliken populations, and charge-density distribution of REZnOSb (RE = La-Nd, Sm-Gd) were investigated by first-principles calculations. Unit cell parameters calculated by the generalized gradient approximation (GGA) are in better agreement with experimental results than those derived from the local density approximation (LDA). Binding energy comparisons indicate that the structural stability of REZnOSb decreases with the increment of the atomic number of the RE, as confirmed by X-ray diffraction (XRD) results. Semimetal or narrow band-gap semiconductor behaviors are found for selected REZnOSb. Moreover, chemical bonding analysis shows that there exist considerable polar covalent interactions between the participating atoms. It also reveals that the [ZnSb] layers receive some electrons from the [LaO] layers (donor) as an electrons acceptor and holes transport tunnel. The covalent interactions between the [ZnSb] and [LaO] layers, which are enhanced by 4f-electrons of the RE, are supposed to improve the electrical transport properties.
Energy Technology Data Exchange (ETDEWEB)
Endo, Akira; Kim, Eunjoo; Yamaguchi, Yasuhiro [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
2001-10-01
A Monte Carlo code SCINFUL has been utilized for calculating response functions of organic scintillators for high-energy neutron spectroscopy. However, the applicability of SCINFUL is limited to the calculations for cylindrical NE213 and NE110 scintillators. In the present study, SCINFUL-CG was developed by introducing a geometry specifying function and high-energy neutron cross section data into SCINFUL. The geometry package MARS-CG, the extended version of the CG (Combinatorial Geometry), was programmed into SCINFUL-CG to express various geometries of detectors. Neutron spectra in the regions specified by the CG can be evaluated by the track length estimator. The cross section data of silicon, oxygen and aluminum for neutron transport calculation were incorporated up to 100 MeV using the data of LA150 library. Validity of SCINFUL-CG was examined by comparing calculated results with those by SCINFUL and MCNP and experimental data measured using high-energy neutron fields. SCINFUL-CG can be used for the calculations of the response functions and neutron spectra in the organic scintillators in various shapes. The computer code will be applicable to the designs of high-energy neutron spectrometers and neutron monitors using the organic scintillators. The present report describes the new features of SCINFUL-CG and explains how to use the code. (author)
First-principles simulations of heat transport
Puligheddu, Marcello; Gygi, Francois; Galli, Giulia
2017-11-01
Advances in understanding heat transport in solids were recently reported by both experiment and theory. However an efficient and predictive quantum simulation framework to investigate thermal properties of solids, with the same complexity as classical simulations, has not yet been developed. Here we present a method to compute the thermal conductivity of solids by performing ab initio molecular dynamics at close to equilibrium conditions, which only requires calculations of first-principles trajectories and atomic forces, thus avoiding direct computation of heat currents and energy densities. In addition the method requires much shorter sequential simulation times than ordinary molecular dynamics techniques, making it applicable within density functional theory. We discuss results for a representative oxide, MgO, at different temperatures and for ordered and nanostructured morphologies, showing the performance of the method in different conditions.
Cyclic Voltammograms from First Principles
DEFF Research Database (Denmark)
Karlberg, Gustav; Jaramillo, Thomas; Skulason, Egill
2007-01-01
Cyclic voltammetry is a fundamental experimental tool for characterizing electrochemical surfaces. Whereas cyclic voltammetry is widely used within the field of electrochemistry, a way to quantitatively and directly relate the cyclic voltammogram to ab initio calculations has been lacking, even f...
International Nuclear Information System (INIS)
Pereira, Luciano Fabricio Dias
2006-01-01
In this work the magnetic hyperfine field acting on Ce atoms substituting the rare-earths in R Ag compounds (R = Gd e Nd) was studied by means of first-principles electronic structure calculations. The employed method was the Augmented Plane Waves plus local orbitals (APW+lo), embodied in the WIEN2k program, within the framework of the Density Functional Theory (DFT) and with the Generalized Gradient Approximation (GGA) for the exchange and correlation potential. The super-cell approach was utilized in order to simulate for the Ce atoms acting as impurities in the R Ag matrix. In order to improve for correlation effects within the 4f shells, a Hubbard term was added to the DFT Hamiltonian, within a procedure called GGA+U. It was found that the magnetic hyperfine field (MHF) generated by the Ce 4f electron is the main component of the total MHF and that the Ce 4f ground state level is probably a combination of the m l = -2 and m l = -1 sub-levels. In addition, the ground-state magnetic structure was determined for Ho Ag and Nd Ag by observing the behavior of the total energy as a function of the lattice volume for several possible magnetic ordering in these compounds, namely, ferromagnetic, and the (0,0,π), (π,π,0) and ((π,π,π) types of anti-ferromagnetic ordering of rare-earth atoms. It was found that the ground-state magnetic structure is anti-ferromagnetic of type (π,π,0) for both, the Ho Ag and Nd Ag compounds. The energy difference of the ferromagnetic and antiferromagnetic ordering is very small in the case of the Nd Ag compound. (author)
Calculation and applications of the frequency dependent neutron detector response functions
International Nuclear Information System (INIS)
Van Dam, H.; Van Hagen, T.H.J.J. der; Hoogenboom, J.E.; Keijzer, J.
1994-01-01
The theoretical basis is presented for the evaluation of the frequency dependent function that enables to calculate the response of a neutron detector to parametric fluctuations ('noise') or oscillations in reactor core. This function describes the 'field view' of a detector and can be calculated with a static transport code under certain conditions which are discussed. Two applications are presented: the response of an ex-core detector to void fraction fluctuations in a BWR and of both in and ex-core detectors to a rotating neutron absorber near or inside a research reactor core. (authors). 7 refs., 4 figs
First-principle study of nanostructures of functionalized graphene
Indian Academy of Sciences (India)
We present first-principle calculations of 2D nanostructures of graphene functionalized with hydrogen and fluorine, respectively, in chair conformation. The partial density of states, band structure, binding energy and transverse displacement of C atoms due to functionalization (buckling) have been calculated within the ...
First principles studies of multiferroic materials
International Nuclear Information System (INIS)
Picozzi, Silvia; Ederer, Claude
2009-01-01
Multiferroics, materials where spontaneous long-range magnetic and dipolar orders coexist, represent an attractive class of compounds, which combine rich and fascinating fundamental physics with a technologically appealing potential for applications in the general area of spintronics. Ab initio calculations have significantly contributed to recent progress in this area, by elucidating different mechanisms for multiferroicity and providing essential information on various compounds where these effects are manifestly at play. In particular, here we present examples of density-functional theory investigations for two main classes of materials: (a) multiferroics where ferroelectricity is driven by hybridization or purely structural effects, with BiFeO 3 as the prototype material, and (b) multiferroics where ferroelectricity is driven by correlation effects and is strongly linked to electronic degrees of freedom such as spin-, charge-, or orbital-ordering, with rare-earth manganites as prototypes. As for the first class of multiferroics, first principles calculations are shown to provide an accurate qualitative and quantitative description of the physics in BiFeO 3 , ranging from the prediction of large ferroelectric polarization and weak ferromagnetism, over the effect of epitaxial strain, to the identification of possible scenarios for coupling between ferroelectric and magnetic order. For the second class of multiferroics, ab initio calculations have shown that, in those cases where spin-ordering breaks inversion symmetry (e.g. in antiferromagnetic E-type HoMnO 3 ), the magnetically induced ferroelectric polarization can be as large as a few μC cm -2 . The examples presented point the way to several possible avenues for future research: on the technological side, first principles simulations can contribute to a rational materials design, aimed at identifying spintronic materials that exhibit ferromagnetism and ferroelectricity at or above room temperature. On the
Phases of Ca from first principles
International Nuclear Information System (INIS)
Qiu, S L; Marcus, P M
2009-01-01
Structures and properties of many of the phases of Ca under pressure are calculated from first principles by a systematic procedure that minimizes total energy E with respect to structure under the constraint of constant volume V. The minima of E are followed on successive sweeps of lattice parameters for 11 of 14 Bravais symmetries for one-atom-per-cell structures. The structures include the four orthorhombic phases. Also included are the hexagonal close-packed and cubic diamond phases with two atoms per primitive cell. No uniquely orthorhombic phases are found; all one-atom orthorhombic phases over a mega-bar pressure range are identical to higher-symmetry phases. The simple cubic phase is shown to be stable where it is the ground state. The number of distinct one-atom phases reduces to five plus the two two-atom phases. For each of these phases the Gibbs free energy at pressure p, G(p), is calculated for a non-vibrating lattice; the functions G(p) give the ground state at each p, the relative stabilities of all phases and the thermodynamic phase transition pressures for all phase transitions over a several-megabar range.
Safeguards First Principle Initiative (SFPI) Cost Model
International Nuclear Information System (INIS)
Price, Mary Alice
2010-01-01
The Nevada Test Site (NTS) began operating Material Control and Accountability (MC and A) under the Safeguards First Principle Initiative (SFPI), a risk-based and cost-effective program, in December 2006. The NTS SFPI Comprehensive Assessment of Safeguards Systems (COMPASS) Model is made up of specific elements (MC and A plan, graded safeguards, accounting systems, measurements, containment, surveillance, physical inventories, shipper/receiver differences, assessments/performance tests) and various sub-elements, which are each assigned effectiveness and contribution factors that when weighted and rated reflect the health of the MC and A program. The MC and A Cost Model, using an Excel workbook, calculates budget and/or actual costs using these same elements/sub-elements resulting in total costs and effectiveness costs per element/sub-element. These calculations allow management to identify how costs are distributed for each element/sub-element. The Cost Model, as part of the SFPI program review process, enables management to determine if spending is appropriate for each element/sub-element.
International Nuclear Information System (INIS)
Abdel Aal, S.
2007-01-01
The optical properties of the F A1 :Ag + color centers and CN interactions at the flat, edge and corner surfaces of LiI (0 0 1) were investigated by using quantum mechanical configuration interaction singles (CIS) and density functional theory (DFT) ab initio methods. Clusters of variable sizes were embedded in the simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces, and the nearest-neighbor ions to the defect site were allowed to relax to equilibrium in order to calculate the optical properties. The sensitivity of the calculated transition energies (Stokes shifts) of F A1 :Ag + centers as well as related optical properties such as optical-optical conversion efficiency, relaxed excited states of the defect-containing surface, orientational destruction of the point defect, recording sensitivity, and the Glasner-Tompkins empirical rule, to the coordination number of the surface ion and artificial polarization were examined. The dependance of the adsorption energies of CN at LiI (0 0 1) surface, the coadsorption of CN, and the charge transfer reactions between CN and the paramagnetic iodine vacancy on the coordination number and artificial polarization effects were also clarified
First principle study of sodium decorated graphyne
Energy Technology Data Exchange (ETDEWEB)
Sarkar, Utpal, E-mail: utpalchemiitkgp@yahoo.com [Assam University, Silchar (India); Bhattacharya, Barnali [Assam University, Silchar (India); Seriani, Nicola [The Abdus Salam ICTP, Trieste (Italy)
2015-11-05
Highlights: • Presence of Na decreases the stability of the system. • Na-decorated graphyne compounds are metallic and might be used in electronics. • The sodium-adsorbed graphyne can be used as electrodes in Na-ion battery. - Abstract: We present first-principles calculations of the electronic properties of Na-decorated graphyne. This structure of the graphyne family is a direct band gap semiconductor with a band gap of 0.44 eV in absence of sodium, but Na-decorated graphyne compounds are metallic, and can then be employed as carbon-based conductors. Metallization is due to charge donation from sodium to carbon. Pristine graphyne is more stable than Na-decorated graphyne, therefore is seems probable that, if this material should be employed as electrode in Na-ion batteries, it would lead to the formation of metallic sodium rather than well dispersed sodium ions. On the other side, this property might be useful if graphyne is employed in water desalination. Finally, the abrupt change from a semiconducting to a metallic state in presence of a small amount of sodium might be exploited in electronics, e.g. for the production of smooth metal–semiconductor interfaces through spatially selective deposition of sodium.
International Nuclear Information System (INIS)
Wiegel, B.; Alevra, A.V.; Siebert, B.R.L.
1994-11-01
A realistic geometry model of a Bonner sphere system with a spherical 3 He-filled proportional counter and 12 polyethylene moderating spheres with diameters ranging from 7,62 cm (3'') to 45,72 cm (18'') is introduced. The MCNP Monte Carlo computer code is used to calculate the responses of this Bonner sphere system to monoenergetic neutrons in the energy range between 1 meV to 20 MeV. The relative uncertainties of the responses due to the Monte Carlo calculations are less than 1% for spheres up to 30,48 cm (12'') in diameter and less than 2% for the 15'' and 18'' spheres. Resonances in the carbon cross section are seen as significant structures in the response functions. Additional calculations were made to study the influence of the 3 He number density and the polyethylene mass density on the response as well as the angular dependence of the Bonner sphere system. The calculated responses can be adjusted to a large set of calibration measurements with only a single fit factor common to all sphere diameters and energies. (orig.) [de
Insights into the ammonia synthesis from first-principles
DEFF Research Database (Denmark)
Hellmann, A.; Honkala, Johanna Karoliina; Remediakis, Ioannis
2006-01-01
-properties, such as apparent activation energies and reaction orders, are calculated from the first-principles model. Our analysis shows that the reaction order of N-2 is unity under all considered conditions, whereas the reaction orders of H-2 and NH3 depend on reaction conditions. (c) 2006 Elsevier B.V. All rights reserved.......A new set of measurements is used to further test a recently published first-principles model for the ammonia (NH3) synthesis on an unpromoted Ru-based catalyst. A direct comparison shows an overall good agreement in NH3 productivity between the model and the experiment. In addition, macro...
Electronic structure and ionicity of actinide oxides from first principles
DEFF Research Database (Denmark)
Petit, Leon; Svane, Axel; Szotek, Z.
2010-01-01
The ground-state electronic structures of the actinide oxides AO, A2O3, and AO2 (A=U, Np, Pu, Am, Cm, Bk, and Cf) are determined from first-principles calculations, using the self-interaction corrected local spin-density approximation. Emphasis is put on the degree of f-electron localization, whi...
First principles study of lithium insertion in bulk silicon
Wan, Wenhui; Zhang, Qianfan; Cui, Yi; Wang, Enge
2010-01-01
Si is an important anode material for the next generation of Li ion batteries. Here the energetics and dynamics of Li atoms in bulk Si have been studied at different Li concentrations on the basis of first principles calculations. It is found
First-principles prediction of liquid/liquid interfacial tension
DEFF Research Database (Denmark)
Andersson, Martin Peter; Bennetzen, M.V.; Klamt, A.
2014-01-01
of groundwater aquifers contaminated by chlorinated solvents to drug delivery and a host of industrial processes. Here, we present a model for predicting interfacial tension from first principles using density functional theory calculations. Our model requires no experimental input and is applicable to liquid...
Molecular Electronics: Insight from First-Principles Transport Simulations
DEFF Research Database (Denmark)
Paulsson, Magnus; Frederiksen, Thomas; Brandbyge, Mads
2010-01-01
Conduction properties of nanoscale contacts can be studied using first-principles simulations. Such calculations give insight into details behind the conductance that is not readily available in experiments. For example, we may learn how the bonding conditions of a molecule to the electrodes affect...
Energy Technology Data Exchange (ETDEWEB)
Touzani, Rachid St.; Fokwa, Boniface P.T., E-mail: Boniface.Fokwa@ac.rwth-aachen.de
2014-03-15
The Nb{sub 2}FeB{sub 2} phase (U{sub 3}Si{sub 2}-type, space group P4/mbm, no. 127) is known for almost 50 years, but until now its magnetic properties have not been investigated. While the synthesis of Nb{sub 2}OsB{sub 2} (space group P4/mnc, no. 128, a twofold superstructure of U{sub 3}Si{sub 2}-type) with distorted Nb-layers and Os{sub 2}-dumbbells was recently achieved, “Nb{sub 2}RuB{sub 2}” is still not synthesized and its crystal structure is yet to be revealed. Our first principles density functional theory (DFT) calculations have confirmed not only the experimental structures of Nb{sub 2}FeB{sub 2} and Nb{sub 2}OsB{sub 2}, but also predict “Nb{sub 2}RuB{sub 2}” to crystalize with the Nb{sub 2}OsB{sub 2} structure type. According to chemical bonding analysis, the homoatomic B–B interactions are optimized and very strong, but relatively strong heteroatomic M–B, B–Nb and M–Nb bonds (M=Fe, Ru, Os) are also found. These interactions, which together build a three-dimensional network, are mainly responsible for the structural stability of these ternary borides. The density-of-states at the Fermi level predicts metallic behavior, as expected, from metal-rich borides. Analysis of possible magnetic structures concluded preferred antiferromagnetic ordering for Nb{sub 2}FeB{sub 2}, originating from ferromagnetic interactions within iron chains and antiferromagnetic exchange interactions between them. -- Graphical abstract: Nb{sub 2}FeB{sub 2} (U{sub 3}Si{sub 2} structure type, space group P4/mbm, no. 127) is predicted to order antiferromagnetically, due to the presence of iron chains which show ferromagnetic interactions in the chains and antiferromagnetic interactions between them. “Nb{sub 2}RuB{sub 2}” is predicted to crystallize with the recently discovered Nb{sub 2}OsB{sub 2} twofold superstructure (space group P4/mnc, no. 128) of U{sub 3}Si{sub 2} structure type. The building of ruthenium dumbbells instead of chains along [001] is found to be
Diffusion in thorium carbide: A first-principles study
Energy Technology Data Exchange (ETDEWEB)
Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1025, Buenos Aires (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1025, Buenos Aires (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM–CNEA, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina)
2015-12-15
The prediction of the behavior of Th compounds under irradiation is an important issue for the upcoming Generation-IV nuclear reactors. The study of self-diffusion and hetero-diffusion is a central key to fulfill this goal. As a first approach, we obtained, by means of first-principles methods, migration and activation energies of Th and C atoms self-diffusion and diffusion of He atoms in ThC. We also calculate diffusion coefficients as a function of temperature. - Highlights: • Diffusion in thorium carbide by means of first-principles calculations is studied. • The most favorable migration event is a C atom moving through a C-vacancy aided path. • Calculated C atoms diffusion coefficients agree very well with the experimental data. • For He, the energetically most favorable migration path is through Th-vacancies.
Analytic representation for first-principles pseudopotentials
International Nuclear Information System (INIS)
Lam, P.K.; Cohen, M.L.; Zunger, A.
1980-01-01
The first-principles pseudopotentials developed by Zunger and Cohen are fit with a simple analytic form chosen to model the main physical properties of the potentials. The fitting parameters for the first three rows of the Periodic Table are presented, and the quality of the fit is discussed. The parameters reflect chemical trends of the elements. We find that a minimum of three parameters is required to reproduce the regularities of the Periodic Table. Application of these analytic potentials is also discussed
International Nuclear Information System (INIS)
Abdou, M.A.; Gohar, Y.; Wright, R.Q.
1978-07-01
MACK-IV calculates nuclear response functions important to the neutronics analysis of nuclear and fusion systems. A central part of the code deals with the calculation of the nuclear response function for nuclear heating more commonly known as the kerma factor. Pointwise and multigroup neutron kerma factors, individual reactions, helium, hydrogen, and tritium production response functions are calculated from any basic nuclear data library in ENDF/B format. The program processes all reactions in the energy range of 0 to 20 MeV for fissionable and nonfissionable materials. The program also calculates the gamma production cross sections and the gamma production energy matrix. A built-in computational capability permits the code to calculate the cross sections in the resolved and unresolved resonance regions from resonance parameters in ENDF/B with an option for Doppler broadening. All energy pointwise and multigroup data calculated by the code can be punched, printed and/or written on tape files. Multigroup response functions (e.g., kerma factors, reaction cross sections, gas production, atomic displacements, etc.) can be outputted in the format of MACK-ACTIVITY-Table suitable for direct use with current neutron (and photon) transport codes
Electrical properties of improper ferroelectrics from first principles
Stengel, Massimiliano; Fennie, Craig J.; Ghosez, Philippe
2012-09-01
We study the interplay of structural and polar distortions in hexagonal YMnO3 and short-period PbTiO3/SrTiO3 (PTO/STO) superlattices by means of first-principles calculations at constrained electric displacement field D. We find that in YMnO3 the tilts of the oxygen polyhedra produce a robustly polar ground state, which persists at any choice of the electrical boundary conditions. Conversely, in PTO/STO the antiferrodistortive instabilities alone do not break inversion symmetry, and open-circuit boundary conditions restore a nonpolar state. We suggest that this qualitative difference naturally provides a route to rationalizing the concept of “improper ferroelectricity” from the point of view of first-principles theory. We discuss the implications of our arguments for the design of novel multiferroic materials with enhanced functionalities and for the symmetry analysis of the phase transitions.