Ab initio methods for electron-molecule collisions
International Nuclear Information System (INIS)
This review concentrates on the recent advances in treating the electronic aspect of the electron-molecule interaction and leaves to other articles the description of the rotational and vibrational motions. Those methods which give the most complete treatment of the direct, exchange, and correlation effects are focused on. Such full treatments are generally necessary at energies below a few Rydbergs (≅ 60 eV). This choice unfortunately necessitates omission of those active and vital areas devoted to the development of model potentials and approximate scattering formulations. The ab initio and model approaches complement each other and are both extremely important to the full explication of the electron-scattering process. Due to the rapid developments of recent years, the approaches that provide the fullest treatment are concentrated on. 81 refs
Ab initio electronic stopping power of protons in bulk materials
Shukri, Abdullah Atef; Bruneval, Fabien; Reining, Lucia
2016-01-01
The electronic stopping power is a crucial quantity for ion irradiation: it governs the deposited heat, the damage profile, and the implantation depth. Whereas experimental data are readily available for elemental solids, the data are much more scarce for compounds. Here we develop a fully ab initio computational scheme based on linear response time-dependent density-functional theory to predict the random electronic stopping power (RESP) of materials without any empirical fitting. We show that the calculated RESP compares well with experimental data, when at full convergence, with the inclusion of the core states and of the exchange correlation. We evaluate the unexpectedly limited magnitude of the nonlinear terms in the RESP by comparing with other approaches based on the time propagation of time-dependent density-functional theory. Finally, we check the validity of a few empirical rules of thumbs that are commonly used to estimate the electronic stopping power.
Ab initio electronic structure and optical conductivity of bismuth tellurohalides
Schwalbe, Sebastian; Starke, Ronald; Schober, Giulio A H; Kortus, Jens
2016-01-01
We investigate the electronic structure, dielectric and optical properties of bismuth tellurohalides BiTeX (X = I, Cl, Br) by means of all-electron density functional theory. In particular, we present the ab initio conductivities and dielectric tensors calculated over a wide frequency range, and compare our results with the recent measurements by Akrap et al. , Makhnev et al. , and Rusinov et al. . We show how the low-frequency branch of the optical conductivity can be used to identify characteristic intra- and interband transitions between the Rashba spin-split bands in all three bismuth tellurohalides. We further calculate the refractive indices and dielectric constants, which in turn are systematically compared to previous predictions and measurements. We expect that our quantitative analysis will contribute to the general assessment of bulk Rashba materials for their potential use in spintronics devices.
All-electron ab initio investigations of the electronic states of the NiC molecule
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, Karl. A.
1999-01-01
The low-lying electronic states of NiC are investigated by all-electron ab initio multi-configuration self-consistent-field (CASSCF) calculations including relativistic corrections. The electronic structure of NiC is interpreted as perturbed antiferromagnetic couplings of the localized angular...
Ab initio studies of phoshorene island single electron transistor.
Ray, S J; Venkata Kamalakar, M; Chowdhury, R
2016-05-18
Phosphorene is a newly unveiled two-dimensional crystal with immense potential for nanoelectronic and optoelectronic applications. Its unique electronic structure and two dimensionality also present opportunities for single electron devices. Here we report the behaviour of a single electron transistor (SET) made of a phosphorene island, explored for the first time using ab initio calculations. We find that the band gap and the charging energy decrease monotonically with increasing layer numbers due to weak quantum confinement. When compared to two other novel 2D crystals such as graphene and MoS2, our investigation reveals larger adsorption energies of gas molecules on phosphorene, which indicates better a sensing ability. The calculated charge stability diagrams show distinct changes in the presence of an individual molecule which can be applied to detect the presence of different molecules with sensitivity at a single molecular level. The higher charging energies of the molecules within the SET display operational viability at room temperature, which is promising for possible ultra sensitive detection applications. PMID:27093536
Ab initio studies of phosphorene island single electron transistor
Ray, S. J.; Venkata Kamalakar, M.; Chowdhury, R.
2016-05-01
Phosphorene is a newly unveiled two-dimensional crystal with immense potential for nanoelectronic and optoelectronic applications. Its unique electronic structure and two dimensionality also present opportunities for single electron devices. Here we report the behaviour of a single electron transistor (SET) made of a phosphorene island, explored for the first time using ab initio calculations. We find that the band gap and the charging energy decrease monotonically with increasing layer numbers due to weak quantum confinement. When compared to two other novel 2D crystals such as graphene and MoS2, our investigation reveals larger adsorption energies of gas molecules on phosphorene, which indicates better a sensing ability. The calculated charge stability diagrams show distinct changes in the presence of an individual molecule which can be applied to detect the presence of different molecules with sensitivity at a single molecular level. The higher charging energies of the molecules within the SET display operational viability at room temperature, which is promising for possible ultra sensitive detection applications.
All electron ab initio investigations of the electronic states of the FeC molecule
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, Karl A.
1999-01-01
The low lying electronic states of the molecule FeC have been investigated by performing all electron ab initio multi-configuration self-consistent-field (CASSCF) and multi reference configuration interaction (MRCI) calculations. The relativistic corrections for the one electron Darwin contact term...... and the relativistic mass-velocity correction have been determined in perturbation calculations. The electronic structure of the FeC molecule is interpreted as antiferromagnetic couplings of the localized angular momenta of the ions Fe+ and C resulting in a triple bond in the valence bond sense. The electronic ground...
All Electron ab initio Investigations of the Electronic States of the MoN Molecule
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, Karl A.
1999-01-01
The low lying electronic states of the molecule MoN have been investigated by performing all electron ab initio multi-configuration self-consistent-field (CASSCF) calculations. The relativistic corrections for the one electron Darwin contact term and the relativistic mass-velocity correction have...... been determined in perturbation calculations. The electronic ground state is confirmed as being 4 . The chemical bond of MoN has triple bond character due to the approximately fully occupied delocalized bonding and orbitals. The spectroscopic constants for the ground state and ten excited states have...... been derived. The excited doublet states, 2 , 2 , 2 , and 2 + are found to be lower lying than the 4 state that has been investigated experimentally. Elaborate multi configuration configuration interaction (MRCI) calculations have been carried out for the states 4 and 4 using various basis sets...
Palummo, Maurizia; Hogan, Conor; Sottile, Francesco; Bagalá, Paolo; Rubio, Angel
2009-08-28
We present a theoretical investigation of electronic and optical properties of free-base porphyrins based on density functional theory and many-body perturbation theory. The electronic levels of free-base porphine (H(2)P) and its phenyl derivative, free-base tetraphenylporphyrin (H(2)TPP) are calculated using the ab initio GW approximation for the self-energy. The approach is found to yield results that compare favorably with the available photoemission spectra. The excitonic nature of the optical peaks is revealed by solving the Bethe-Salpeter equation, which provides an accurate description of the experimental absorption spectra. The lowest triplet transition energies are in good agreement with the measured values. PMID:19725603
Ab initio calculations on twisted graphene/hBN: Electronic structure and STM image simulation
Correa, J. D.; Cisternas, E.
2016-09-01
By performing ab initio calculations we obtained theoretical scanning tunneling microscopy (STM) images and studied the electronic properties of graphene on a hexagonal boron-nitrite (hBN) layer. Three different stack configurations and four twisted angles were considered. All calculations were performed using density functional theory, including van der Waals interactions as implemented in the SIESTA ab initio package. Our results show that the electronic structure of graphene is preserved, although some small changes are induced by the interaction with the hBN layer, particularly in the total density of states at 1.5 eV under the Fermi level. When layers present a twisted angle, the density of states shows several van Hove singularities under the Fermi level, which are associated to moiré patterns observed in theoretical STM images.
Ab initio phonon coupling and optical response of hot electrons in plasmonic metals
Brown, Ana M; Narang, Prineha; Goddard, William A; Atwater, Harry A
2016-01-01
Ultrafast laser measurements probe the non-equilibrium dynamics of excited electrons in metals with increasing temporal resolution. Electronic structure calculations can provide a detailed microscopic understanding of hot electron dynamics, but a parameter-free description of pump-probe measurements has not yet been possible, despite intensive research, because of the phenomenological treatment of electron-phonon interactions. We present ab initio predictions of the electron-temperature dependent heat capacities and electron-phonon coupling coefficients of plasmonic metals. We find substantial differences from free-electron and semi-empirical estimates, especially in noble metals above transient electron temperatures of 2000 K, because of the previously-neglected strong dependence of electron-phonon matrix elements on electron energy. We also present first-principles calculations of the electron-temperature dependent dielectric response of hot electrons in plasmonic metals, including direct interband and phon...
Electronic properties of liquid Hg-In alloys : Ab-initio molecular dynamics study
Sharma, Nalini; Thakur, Anil; Ahluwalia, P. K.
2016-05-01
Ab-initio molecular dynamics simulations are performed to study the structural properties of liquid Hg-In alloys. The interatomic interactions are described by ab-initio pseudopotentials given by Troullier and Martins. Three liquid Hg-In alloys (Hg10In90, Hg30In70,. Hg50In50, Hg70In30, and Hg90Pb10) at 299 K are considered. The calculated results for liquid Hg (l-Hg) and lead (l-In) are also drawn. Along with the calculated results of considered five liquid alloys of Hg-In alloy. The results obtained from electronic properties namely total density of state and partial density of states help to find the local arrangement of Hg and In atoms and the presence of liquid state in the considered five alloys.
Ab Initio Study of Electronic States of Astrophysically Important Molecules
Valiev, R. R.; Berezhnoy, A. A.; Minaev, B. F.; Chernov, V. E.; Cherepanov, V. N.
2016-08-01
A study of electronic states of LiO, NaO, KO, MgO, and CaO molecules has been performed. Potential energy curves of the investigated molecules have been constructed within the framework of the XMC-QDPT2 method. Lifetimes and efficiencies of photolysis mechanisms of these monoxides have been estimated within the framework of an analytical model of photolysis. The results obtained show that oxides of the considered elements in the exospheres of the Moon and Mercury are destroyed by solar photons during the first ballistic flight.
Surface electron density models for accurate ab initio molecular dynamics with electronic friction
Novko, D.; Blanco-Rey, M.; Alducin, M.; Juaristi, J. I.
2016-06-01
Ab initio molecular dynamics with electronic friction (AIMDEF) is a valuable methodology to study the interaction of atomic particles with metal surfaces. This method, in which the effect of low-energy electron-hole (e-h) pair excitations is treated within the local density friction approximation (LDFA) [Juaristi et al., Phys. Rev. Lett. 100, 116102 (2008), 10.1103/PhysRevLett.100.116102], can provide an accurate description of both e-h pair and phonon excitations. In practice, its applicability becomes a complicated task in those situations of substantial surface atoms displacements because the LDFA requires the knowledge at each integration step of the bare surface electron density. In this work, we propose three different methods of calculating on-the-fly the electron density of the distorted surface and we discuss their suitability under typical surface distortions. The investigated methods are used in AIMDEF simulations for three illustrative adsorption cases, namely, dissociated H2 on Pd(100), N on Ag(111), and N2 on Fe(110). Our AIMDEF calculations performed with the three approaches highlight the importance of going beyond the frozen surface density to accurately describe the energy released into e-h pair excitations in case of large surface atom displacements.
Quantum chemistry the development of ab initio methods in molecular electronic structure theory
Schaefer III, Henry F
2004-01-01
This guide is guaranteed to prove of keen interest to the broad spectrum of experimental chemists who use electronic structure theory to assist in the interpretation of their laboratory findings. A list of 150 landmark papers in ab initio molecular electronic structure methods, it features the first page of each paper (which usually encompasses the abstract and introduction). Its primary focus is methodology, rather than the examination of particular chemical problems, and the selected papers either present new and important methods or illustrate the effectiveness of existing methods in predi
Ab initio determination of effective electron-phonon coupling factor in copper
Ji, Pengfei
2016-01-01
The electron temperature T_e dependent electron density of states g({\\epsilon}), Fermi-Dirac distribution f({\\epsilon}), and electron-phonon spectral function {\\alpha}^2 F({\\Omega}) are computed as prerequisites before achieving effective electron-phonon coupling factor. The obtained is implemented into a molecular dynamics (MD) and two-temperature model (TTM) coupled simulation of femtosecond laser heating. By monitoring temperature evolutions of electron and lattice subsystems, the result utilizing G_(e-ph) from ab initio calculation, shows a faster decrease of T_e and increase of T_l than those using G_(e-ph) from phenomenological treatment. The approach of calculating G_(e-ph) and its implementation into MD-TTM simulation is applicable to other metals.
Ji, Pengfei
2016-01-01
By combining ab initio quantum mechanics calculation and Drude model, electron temperature and lattice temperature dependent electron thermal conductivity is calculated and implemented into a multiscale model of laser material interaction, which couples the classical molecular dynamics and two-temperature model. The results indicated that the electron thermal conductivity obtained from ab initio calculation leads to faster thermal diffusion than that using the electron thermal conductivity from empirical determination, which further induces deeper melting region, larger number of density waves travelling inside the copper film and more various speeds of atomic clusters ablated from the irradiated film surface.
Ab initio study of the low-lying electronic states of the CaO molecule
International Nuclear Information System (INIS)
Graphical abstract: Highly correlated ab initio calculations have been performed for an accurate determination of the electronic structure of the low-lying electronic states of the CaO molecule. The computations are done using the aug-cc-pV5Z basis set for O and the cc-pCV5Z for Ca. The potential energy curves for the molecular states correlating to the lowest three asymptotes are calculated at the CASSCF level. The potential curves of the lowest five molecular states, X1Σ+, a3Π, A'1Π, b3Σ+ and A1Σ+, and the corresponding dipole moment functions have been determined using internally contracted multi-reference configuration interaction approaches. The spectroscopic constants associated with these electronic states are compared to experimental values. The corresponding electronic wavefunctions have also been analyzed using the dipole moment functions. Display Omitted Highlights: → The five lowest electronic states of Cao have been determined ab initio at a high level of accuracy. → Large active space, core-valence correlation and configuration interaction are required. → The multi-configurational nature of the electronic ground state is confirmed as well as its monovalent and divalent ionic nature using dipole moment analysis. → These interacting potentials will serve for future obtention of spin-rovibronic levels. - Abstract: Highly correlated ab initio calculations have been performed for an accurate determination of the electronic structure of the low-lying electronic states of the CaO molecule. The computations are done using the aug-cc-pV5Z basis set for O and the cc-pCV5Z for Ca. The potential energy curves for the molecular states correlating to the lowest three asymptotes are calculated at the CASSCF level. The potential curves of the lowest five molecular states, X1Σ+, a3Π, A'1Π, b3Σ+ and A1Σ+, and the corresponding dipole moment functions have been determined using internally contracted multi-reference configuration interaction approaches
Ab initio study of the low-lying electronic states of the CaO molecule
Energy Technology Data Exchange (ETDEWEB)
Khalil, Hossain; Brites, Vincent; Quere, Frederic Le [Universite Paris-Est, Laboratoire de Modelisation et Simulation Multi Echelle, UMR 8208 CNRS, Batiment Lavoisier, 5 boulevard Descartes, Champs sur Marne, 77454 Marne-la-Vallee, Cedex 2 (France); Leonard, Celine, E-mail: celine.leonard@univ-paris-est.fr [Universite Paris-Est, Laboratoire de Modelisation et Simulation Multi Echelle, UMR 8208 CNRS, Batiment Lavoisier, 5 boulevard Descartes, Champs sur Marne, 77454 Marne-la-Vallee, Cedex 2 (France)
2011-07-28
Graphical abstract: Highly correlated ab initio calculations have been performed for an accurate determination of the electronic structure of the low-lying electronic states of the CaO molecule. The computations are done using the aug-cc-pV5Z basis set for O and the cc-pCV5Z for Ca. The potential energy curves for the molecular states correlating to the lowest three asymptotes are calculated at the CASSCF level. The potential curves of the lowest five molecular states, X{sup 1}{Sigma}{sup +}, a{sup 3}{Pi}, A'{sup 1{Pi}}, b{sup 3}{Sigma}{sup +} and A{sup 1}{Sigma}{sup +}, and the corresponding dipole moment functions have been determined using internally contracted multi-reference configuration interaction approaches. The spectroscopic constants associated with these electronic states are compared to experimental values. The corresponding electronic wavefunctions have also been analyzed using the dipole moment functions. Display Omitted Highlights: {yields} The five lowest electronic states of Cao have been determined ab initio at a high level of accuracy. {yields} Large active space, core-valence correlation and configuration interaction are required. {yields} The multi-configurational nature of the electronic ground state is confirmed as well as its monovalent and divalent ionic nature using dipole moment analysis. {yields} These interacting potentials will serve for future obtention of spin-rovibronic levels. - Abstract: Highly correlated ab initio calculations have been performed for an accurate determination of the electronic structure of the low-lying electronic states of the CaO molecule. The computations are done using the aug-cc-pV5Z basis set for O and the cc-pCV5Z for Ca. The potential energy curves for the molecular states correlating to the lowest three asymptotes are calculated at the CASSCF level. The potential curves of the lowest five molecular states, X{sup 1}{Sigma}{sup +}, a{sup 3}{Pi}, A'{sup 1}{Pi}, b{sup 3}{Sigma}{sup +} and A{sup 1
Energy Technology Data Exchange (ETDEWEB)
Kimberg, Victor, E-mail: victor.kimberg@pks.mpi.de [Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden (Germany); Miron, Catalin, E-mail: miron@synchrotron-soleil.fr [Synchrotron SOLEIL, l’Orme des Merisiers, Saint-Aubin, BP 48, FR-91192 Gif-sur-Yvette Cedex (France)
2014-08-15
Highlights: • Some studies related to the vibrational wave functions mapping phenomenon are reviewed. • The core-excited vibrational wave functions were mapped using dissociative and bound final states. • High-resolution experimental data is accompanied by ab initio calculations. • The mapping phenomenon allows one to extract constants of the molecular potentials. • The mapping techniques are general and can be applied for the study of many systems. - Abstract: The recent development of high brightness 3{sup rd} generation soft X-ray sources and high energy resolution electron spectrometers made it possible to accurately trace quantum phenomena associated to the vibrational dynamics in core-excited molecules. The present paper reviews the recent results on mapping of vibrational wave functions and molecular potentials based on electron spectroscopy. We discuss and compare the mapping phenomena in various systems, stressing the advantages of the resonant X-ray scattering for studying of the nuclear dynamics and spectroscopic constants of small molecules. The experimental results discussed in the paper are most often accompanied by state-of-the-art ab initio calculations allowing for a deeper understanding of the quantum effects. Besides its fundamental interest, the vibrational wave function mapping is shown to be useful for the analysis of core- and valence-excited molecular states based on the reflection principle.
Atomic and Electronic Structures of C_60+BN Nanopeapods from ab initio Pseudopotential Calculations
Trave, Andrea; Ribeiro, Filipe; Louie, Steven G.; Cohen, Marvin L.
2004-03-01
Nanopeapods are structures of nanometric size consisting of an external carbon nanotube encapsulating a chain or complex array of fullerenes. Recent calculations and experiments have proven that nanopeapods can be obtained assembling fullerenes within boron nitride nanotubes, creating novel materials of possible interest for electronic transport applications. To improve the understanding of the properties of these composite systems, as compared to empty nanotubes and carbon nanopeapods, ab-initio total energy calculations have been performed within the pseudopotential Density Functional Theory in local density approximation. Results of these calculations on the energetics and geometrical deformations involved in the encapsulation will be presented, followed by a discussion of the consequences on the electronic structures of these systems, with particular focus on aspects relevant to electronic transport phenomena. This work is supported by NFS (Grant DMR00-87088) and DOE (Contract DE-AC03-76SF00098), using computational resources at NERSC and NPACI.
Ab-initio calculations on two-electron ions in strongly coupled plasma environment
Bhattacharyya, S; Mukherjee, T K
2015-01-01
In this work, the controversy between the interpretations of recent measurements on dense aluminum plasma created with Linac coherent light sources (LCLS) X-ray free electron laser (FEL) and Orion laser has been addressed. In both kind of experiments, helium-like and hydrogen-like spectral lines are used for plasma diagnostics . However, there exist no precise theoretical calculations for He-like ions within dense plasma environment. The strong need for an accurate theoretical estimates for spectral properties of He-like ions in strongly coupled plasma environment leads us to perform ab initio calculations in the framework of Rayleigh-Ritz variation principle in Hylleraas coordinates where ion-sphere potential is used. An approach to resolve the long-drawn problem of numerical instability for evaluating two-electron integrals with extended basis inside a finite domain is presented here. The present values of electron densities corresponding to disappearance of different spectral lines obtained within the fram...
Gao, Haiyuan; Li, Meijiao; Guo, Zhendong; Chen, Hongshen; Jin, Zhonghe; Yu, Bin
2011-01-01
Electronic transport properties of monolayer graphene with extreme physical bending up to 90o angle are studied using ab Initio first-principle calculations. The importance of key structural parameters including step height, curvature radius and bending angle are discussed how they modify the transport properties of the deformed graphene sheet comparing to the corresponding flat ones. The local density of state reveals that energy state modification caused by the physical bending is highly localized. It is observed that the transport properties of bent graphene with a wide range of geometrical configurations are insensitive to the structural deformation in the low-energy transmission spectra, even in the extreme case of bending. The results support that graphene, with its superb electromechanical robustness, could serve as a viable material platform in a spectrum of applications such as photovoltaics, flexible electronics, OLED, and 3D electronic chips.
Tunneling of electrons via rotor-stator molecular interfaces: combined ab initio and model study
Petreska, Irina; Pejov, Ljupco; Kocarev, Ljupco
2015-01-01
Tunneling of electrons through rotor-stator anthracene aldehyde molecular interfaces is studied with a combined ab initio and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons' formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that confirmation dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previ...
Ab initio study of the electronic properties of the planar Ga5N5 cluster
Institute of Scientific and Technical Information of China (English)
Zheng Hao-Ping; Hao Jing-An
2005-01-01
The first-principles, all electron, ab initio calculations have been performed for an the amazing stable planar structure of Ga5N5 cluster based on the density functional theory. Electronic structure, Electron affinity, ionization potential, and binding energy are obtained. No spin magnetic moment is found. The results show that the planar structure of the Ga5N5 cluster is stable. It is found that for the planar structure of Ga5N5 cluster, three nitrogen atoms in the N3 subunit bind together with large electon transfer although no free N3 can exist. This may be important to the stability of the planar structure of the Ga5N5 cluster which has the lowest ground-state energy.
Ab Initio Quantum Monte Carlo Simulation of the Warm Dense Electron Gas in the Thermodynamic Limit
Dornheim, Tobias; Groth, Simon; Sjostrom, Travis; Malone, Fionn D.; Foulkes, W. M. C.; Bonitz, Michael
2016-10-01
We perform ab initio quantum Monte Carlo (QMC) simulations of the warm dense uniform electron gas in the thermodynamic limit. By combining QMC data with the linear response theory, we are able to remove finite-size errors from the potential energy over the substantial parts of the warm dense regime, overcoming the deficiencies of the existing finite-size corrections by Brown et al. [Phys. Rev. Lett. 110, 146405 (2013)]. Extensive new QMC results for up to N =1000 electrons enable us to compute the potential energy V and the exchange-correlation free energy Fxc of the macroscopic electron gas with an unprecedented accuracy of |Δ V |/|V |,|Δ Fxc|/|F |xc˜10-3 . A comparison of our new data to the recent parametrization of Fxc by Karasiev et al. [Phys. Rev. Lett. 112, 076403 (2014)] reveals significant deviations to the latter.
Ab initio phonon coupling and optical response of hot electrons in plasmonic metals
Brown, Ana M.; Sundararaman, Ravishankar; Narang, Prineha; Goddard, William A.; Atwater, Harry A.
2016-08-01
Ultrafast laser measurements probe the nonequilibrium dynamics of excited electrons in metals with increasing temporal resolution. Electronic structure calculations can provide a detailed microscopic understanding of hot electron dynamics, but a parameter-free description of pump-probe measurements has not yet been possible, despite intensive research, because of the phenomenological treatment of electron-phonon interactions. We present ab initio predictions of the electron-temperature dependent heat capacities and electron-phonon coupling coefficients of plasmonic metals. We find substantial differences from free-electron and semiempirical estimates, especially in noble metals above transient electron temperatures of 2000 K, because of the previously neglected strong dependence of electron-phonon matrix elements on electron energy. We also present first-principles calculations of the electron-temperature dependent dielectric response of hot electrons in plasmonic metals, including direct interband and phonon-assisted intraband transitions, facilitating complete theoretical predictions of the time-resolved optical probe signatures in ultrafast laser experiments.
Galler, Anna; Gunacker, Patrik; Tomczak, Jan; Thunström, Patrik; Held, Karsten
Recently, approaches such as the dynamical vertex approximation (D ΓA) or the dual-fermion method have been developed. These diagrammatic approaches are going beyond dynamical mean field theory (DMFT) by including nonlocal electronic correlations on all length scales as well as the local DMFT correlations. Here we present our efforts to extend the D ΓA methodology to ab-initio materials calculations (ab-initio D ΓA). Our approach is a unifying framework which includes both GW and DMFT-type of diagrams, but also important nonlocal correlations beyond, e.g. nonlocal spin fluctuations. In our multi-band implementation we are using a worm sampling technique within continuous-time quantum Monte Carlo in the hybridization expansion to obtain the DMFT vertex, from which we construct the reducible vertex function using the two particle-hole ladders. As a first application we show results for transition metal oxides. Support by the ERC project AbinitioDGA (306447) is acknowledged.
Ab Initio Calculations on Halogen Bond Between N-Br and Electron-donating Groups
Institute of Scientific and Technical Information of China (English)
WANG Yan-hua; CHEN Xue-song; ZOU Jian-wei; YU Qing-sen
2007-01-01
Ab initio calculations of complexes formed between N-bromosuccinimide and a series of electron-donating groups were performed at the level of MP2/Lanl2DZ* to gain a deeper insight into the nature of the N-Br halogen stronger halogen-bonding complex than the C-Br. A comparison of neutral hydrogen bond complex series reveals that the electron-donating capacities of the atoms decrease in the order, N＞O＞S; O(sp3)＞O(sp2), which is adequate for the C-Br halogen bonding. Interaction energies, in conjunction with the geometrical parameters show that the affinitive capacity of trihalide anions X-3 with N-bromosuccinimide are markedly lower than that of the corresponding X- with N-bromosuccinimide, even lower than those of neutral molecules with N-bromosuccinimide. AIM analyses further confirmed the above results.
Ab initio electron scattering cross-sections and transport in liquid xenon
Boyle, G. J.; McEachran, R. P.; Cocks, D. G.; Brunger, M. J.; Buckman, S. J.; Dujko, S.; White, R. D.
2016-09-01
Ab initio fully differential cross-sections for electron scattering in liquid xenon are developed from a solution of the Dirac-Fock scattering equations, using a recently developed framework (Boyle et al 2015 J. Chem. Phys. 142 154507) which considers multipole polarizabilities, a non-local treatment of exchange, and screening and coherent scattering effects. A multi-term solution of Boltzmann’s equation accounting for the full anisotropic nature of the differential cross-section is used to calculate transport properties of excess electrons in liquid xenon. The results were found to agree to within 25% of the measured mobilities and characteristic energies over the reduced field range of 10-4-1 Td. The accuracies are comparable to those achieved in the gas phase. A simple model, informed by highly accurate gas-phase cross-sections, is presented to improve the liquid cross-sections, which was found to enhance the accuracy of the transport coefficient calculations.
Minimal parameter implicit solvent model for ab initio electronic structure calculations
Dziedzic, Jacek; Skylaris, Chris-Kriton; Mostofi, Arash A; Payne, Mike C
2011-01-01
We present an implicit solvent model for ab initio electronic structure calculations which is fully self-consistent and is based on direct solution of the nonhomogeneous Poisson equation. The solute cavity is naturally defined in terms of an isosurface of the electronic density according to the formula of Fattebert and Gygi (J. Comp. Chem. 23, 6 (2002)). While this model depends on only two parameters, we demonstrate that by using appropriate boundary conditions and dispersion-repulsion contributions, solvation energies obtained for an extensive test set including neutral and charged molecules show dramatic improvement compared to existing models. Our approach is implemented in, but not restricted to, a linear-scaling density functional theory (DFT) framework, opening the path for self-consistent implicit solvent DFT calculations on systems of unprecedented size, which we demonstrate with calculations on a 2615-atom protein-ligand complex.
Ab initio spectroscopic characterization of borane, BH, in its X1Σ+ electronic state.
Koput, Jacek
2015-11-15
The accurate potential energy and electric dipole moment functions of borane, BH, in its X1Σ+ electronic state have been determined from ab initio calculations using the multireference averaged coupled-pair functional method in conjunction with the correlation-consistent core-valence basis sets up to septuple-zeta quality. The higher-order electron correlation, scalar relativistic, adiabatic, and nonadiabatic effects were discussed. Vibration-rotation energy levels of the (11)BH, (11)BD, (10)BH, and (10)BD isotopologues were predicted to near "spectroscopic" accuracy. For the main isotopologue (11)BH, the adiabatic dissociation energy D0 and the effective equilibrium internuclear distance r(e) were predicted to be 28,469 ± 10 cm(-1) and 1.23214 ± 0.0001 Å, respectively. PMID:26444679
Structural and electronic properties of lead nanowires: Ab-initio study
International Nuclear Information System (INIS)
Highlights: → In the present revised manuscript entitled 'Structural and Electronic Properties of Lead Nanowires: Ab-initio study', we have analyzed the stability, electronic properties as well as ground state properties of various atomic configurations of Lead nanowires. → The two-atom zigzag shaped lead nanowire with highest binding energy and lowest total energy has been confirmed as the most stable structure out of the six atomic configurations taken into consideration. → The electronic band structure and density of states have been described in detail with a remarkable observation in case of three-atom triangular lead nanowire having a very small band gap while other atomic configurations are found to be metallic. → The bulk modulus and pressure derivatives for all the stable geometries have also been computed and discussed in the manuscript. The mechanical strength of nanowires has also been discussed in terms of its bulk modulus. → The two-atom ladder shaped nanowire with highest bulk modulus, defends this structure as mechanically stronger than the other tested structure. - Abstract: Ab-initio self-consistent study has been performed to analyze the stability of lead nanowires in its six stable configurations like linear, zigzag, triangular, ladder, square and dumbbell. In the present study, the lowest energy structures have been analyzed under the revised Perdew-Burke-Ernzerhof (revPBE) parameterization of generalized gradient approximation (GGA) potential. The two-atom zigzag shaped atomic configuration with highest binding energy and lowest total energy has been confirmed as the most stable structure out of the six atomic configurations. The electronic band structure and density of states have been discussed in detail with a remarkable observation in case of three-atom triangular lead nanowire having a very small band gap while other configurations are found to be metallic. Bulk modulus, pressure derivatives and lattice parameters for different
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, K. A.
2000-01-01
The three lowest-lying electronic states of RuC, (1)Sigma(+), (3)Delta, and (1)Delta, have been investigated by performing all-electron ab initio multi-configuration self-consistent-field (CASSCF) and multi-reference configuration interaction (MRCI) calculations including relativistic corrections....... The electronic ground state is derived as (1)Sigma(+) with the spectroscopic constants r(e) = 1.616 Angstrom and omega(e) = 1085 cm(-1). The lowest-lying excited state, (3)Delta, has r(e) = 1.632 Angstrom, omega(e) = 1063 cm(-1), and T-e = 912 cm(-1). These results are consistent with recent spectroscopic values...
Directory of Open Access Journals (Sweden)
A. V. Gulay
2014-01-01
Full Text Available Ab-Initio simulation of electronic features of sensoring nanomaterials based on rare earth oxides has been made by the example of yttrium oxide. The simulation method for thin films of nanometer scale consisted in the simulation of the material layer of the thickness equal to unit crystal cell size has been proposed within the VASP simulation package. The atomic bond breakdown in the crystal along one of the coordinate axes is simulated by the increase of a distance between the atomic layers along this axis up to values at which the value of free energy is stabilized. It has been found that the valence and conductivity bands are not revealed explicitly and the band gap is not formed in the hyperfine rare earth oxide film (at the film thickness close to 1 nm. In fact the hyperfine rare earth oxide film loses dielectric properties which were exhibited clear enough in continuum.
Electronic and optical properties of K-doped ZnO: Ab initio study
Aimouch, D. E.; Meskine, S.; Hayn, R.; Zaoui, A.; Boukortt, A.
2016-08-01
We present the results of ab initio calculations of K-doped ZnO in the wurtzite structure using a supercell of 32 atoms and density functional theory. A complete analysis of its electronic, optical and magnetic properties is provided. The local spin density approximation (LSDA) has been used to analyze the density of states and to understand the K influence at different concentration values. The material is revealed to become a p-type doped semiconductor. The optical constant or refractive index, the dielectric function, and the absorption coefficient were determined and show a good agreement with available experimental data. Potassium doping leads to an absorption peak at about 380 nm. That peak might improve the absorption characteristics of ZnO for solar cell or optical applications.
Ab initio study of pressure induced structural and electronic properties in TmPo
Energy Technology Data Exchange (ETDEWEB)
Makode, Chandrabhan, E-mail: cbmakode@gmail.com; Pataiya, Jagdish; Sanyal, Sankar P. [Department of Physics, Barkatullah University, Bhopal-462026 (India); Panwar, Y. S.; Aynyas, Mahendra [Department of Physics, C.S.A. Govt. P.G. College, Sehore-466001 (India)
2015-06-24
We report an ab initio calculation of pressure induced structural phase transition and electronic properties of Thulium Polonide (TmPo).The total energy as a function of volume is obtained by means of self-consistent tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA). It is found that TmPo is stable in NaCl-type (B{sub 1}-phase) structure to CsCl-type (B{sub 2}-phase) structure of this compound in the pressure range of 7.0 GPa. We also calculate the lattice parameter (a{sub 0}), bulk modulus (B{sub 0}), band structure and density of states. From energy diagram it is observed that TmPo exhibit metallic behavior. The calculated values of equilibrium lattice parameter and bulk modulus are in general good agreement.
Ji, Pengfei; Zhang, Yuwen
2016-01-01
On the basis of ab initio quantum mechanics (QM) calculation, the obtained electron heat capacity is implemented into energy equation of electron subsystem in two temperature model (TTM). Upon laser irradiation on the copper film, energy transfer from the electron subsystem to the lattice subsystem is modeled by including the electron-phonon coupling factor in molecular dynamics (MD) and TTM coupled simulation. The results show temperature and thermal melting difference between the QM-MD-TTM ...
Silvestrelli, P.-L.; Alavi, A.; Parrinello, M.; Frenkel, D.
1997-01-01
The method of ab initio molecular dynamics, based on finite-temperature density-functional theory, is used to simulate laser heating of crystalline silicon. We found that a high concentration of excited electrons dramatically weakens the covalent bonding. As a result the system undergoes a melting t
Giovannetti, Gianluca; Brocks, Geert; Brink, van den Jeroen
2008-01-01
We investigate the effect that potassium intercalation has on the electronic structure of copper phthalocyanine (CuPc) molecular crystals by means of ab initio density functional calculations. Pristine CuPc (in its alpha and beta structures) is found to be an insulator containing local magnetic mome
An ab initio study on single electron transfer between ClO2 and phenol
Institute of Scientific and Technical Information of China (English)
崔崇威; 黄君礼
2004-01-01
The SET mechanism between chlorine dioxide (ClO2 ) and phenol was studied by using ab initio method at 4-31G* level. Geometries of the reactants, intermediate and products of the reaction were optimized and the single point energy calculations of the species were performed. The relative structure data of the reactants, intermediate and products are given. The SET mechanism between ClO2 and phenol was confirmed by ab initio calculations. The reaction is exothermic about 200. 88 k J/mol.
Singh, Ram Sevak; Solanki, Ankit
2016-03-01
Silicon carbide nanotubes (SiCNTs) have received a great deal of scientific and commercial interest due to their intriguing properties that include high temperature stability and electronic properties. For their efficient and widespread applications, tuning of electronic properties of SiCNTs is an attractive study. In this article, electronic properties of sulphur doped (S-doped) zigzag (9 , 0) SiCNT is investigated by ab initio calculations based on density functional theory (DFT). Energy band structures and density of states of fully optimized undoped and doped structures with varying dopant concentration are calculated. S-doped on C-site of the nanotube exhibits a monotonic reduction of energy gap with increase in dopant concentration, and the nanotube transforms from semiconductor to metal at high dopant concentration. In case of S-doped on Si-site doping has less influence on modulating electronic structures, which results in reduction of energy gap up to a moderate doping concentration. Importantly, S preferential substitutes of Si-sites and the nanotube with S-doped on Si-site are energetically more stable as compared to the nanotube with S-doped on C-site. The study of tunable electronic properties in S-doped SiCNT may have potential in fabricating nanoelectronic devices, hydrogen storage and gas sensing applications.
Ab initio calculation of the electronic absorption spectrum of liquid water
International Nuclear Information System (INIS)
The electronic absorption spectrum of liquid water was investigated by coupling a one-body energy decomposition scheme to configurations generated by classical and Born-Oppenheimer Molecular Dynamics (BOMD). A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies in the liquid phase were calculated with the equation of motion coupled cluster with single and double excitations method. Molecular dynamics configurations were generated by different approaches. Classical MD were carried out with the TIP4P-Ew and AMOEBA force fields. The BLYP and BLYP-D3 exchange-correlation functionals were used in BOMD. Theoretical and experimental results for the electronic absorption spectrum of liquid water are in good agreement. Emphasis is placed on the relationship between the structure of liquid water predicted by the different models and the electronic absorption spectrum. The theoretical gas to liquid phase blue-shift of the peak positions of the electronic absorption spectrum is in good agreement with experiment. The overall shift is determined by a competition between the O–H stretching of the water monomer in liquid water that leads to a red-shift and polarization effects that induce a blue-shift. The results illustrate the importance of coupling many-body energy decomposition schemes to molecular dynamics configurations to carry out ab initio calculations of the electronic properties in liquid phase
Hoy, Erik P; Mazziotti, David A
2015-08-14
Tensor factorization of the 2-electron integral matrix is a well-known technique for reducing the computational scaling of ab initio electronic structure methods toward that of Hartree-Fock and density functional theories. The simplest factorization that maintains the positive semidefinite character of the 2-electron integral matrix is the Cholesky factorization. In this paper, we introduce a family of positive semidefinite factorizations that generalize the Cholesky factorization. Using an implementation of the factorization within the parametric 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)], we study several inorganic molecules, alkane chains, and potential energy curves and find that this generalized factorization retains the accuracy and size extensivity of the Cholesky factorization, even in the presence of multi-reference correlation. The generalized family of positive semidefinite factorizations has potential applications to low-scaling ab initio electronic structure methods that treat electron correlation with a computational cost approaching that of the Hartree-Fock method or density functional theory. PMID:26277123
Hoy, Erik P; Mazziotti, David A
2015-08-14
Tensor factorization of the 2-electron integral matrix is a well-known technique for reducing the computational scaling of ab initio electronic structure methods toward that of Hartree-Fock and density functional theories. The simplest factorization that maintains the positive semidefinite character of the 2-electron integral matrix is the Cholesky factorization. In this paper, we introduce a family of positive semidefinite factorizations that generalize the Cholesky factorization. Using an implementation of the factorization within the parametric 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)], we study several inorganic molecules, alkane chains, and potential energy curves and find that this generalized factorization retains the accuracy and size extensivity of the Cholesky factorization, even in the presence of multi-reference correlation. The generalized family of positive semidefinite factorizations has potential applications to low-scaling ab initio electronic structure methods that treat electron correlation with a computational cost approaching that of the Hartree-Fock method or density functional theory.
Electronic states and nature of bonding in the molecule MoC by all electron ab initio calculations
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, Karl A.
1997-01-01
In the present work all electron ab initio multiconfiguration self-consistent-held (CASSCF) and multireference configuration interaction (MRCI) calculations have been carried out to determine the low-lying electronic states of the molecule MoC. The relativistic corrections for the one electron...... Darwin contact term and the relativistic mass-velocity correction have been determined in perturbation calculations. The electronic ground state is predicted as (3) Sigma(-). The spectroscopic constants for the (3) Sigma(-) electronic ground state and eight low-lying excited states have been derived......, and the vibrational frequency as 997 cm(-1). The chemical bond in the (3) Sigma(-) electronic ground state has triple bond character due to the formation of delocalized bonding rr and a orbitals. The chemical bond in the MoC molecule is polar with charge transfer from Mo to C, giving rise to a dipole moment of 6.15 D...
Ab initio studies of transition metal complexes and related electron transfer properties
International Nuclear Information System (INIS)
Ab initio electronic structure calculations have been carried out for various aquo and ammine complexes of Fe, Co, and Ru in their 2+ and 3+ oxidation states. The results of these calculations are used as assessing a variety of factors controlling electron transfer kinetics including the charge-state dependence of various inner shell geometrical parameters and associated vibrational frequencies (metal-ligand and intra-ligand and intra-ligand stretching modes, and librational modes), and the dependence of electron transfer matrix elements on the nature of the ligand and the metal orbital type (/sup t/2/sub g/ vs. e/sub g/). The charge-state dependence of the OH bond lengths in hexa-aquo ions is predicted to yield H/D isotope effects (i.e., fractionation between bulk and first shell water), which should be detectable by neutron scattering experiments on appropriate aqueous solutions. The relationship between these thermodynamic isotope effects, which depend critically on strong OH triple bond O hydrogen bonding between first and second-shell water molecules, and kinetic H/D isotope effects in electron exchange involving hexa-aquo ions will be discussed
Role of ab-initio calculations in elucidating properties of hydrated and ammoniated electrons
International Nuclear Information System (INIS)
The properties of solvated electrons are analyzed in terms of a self-consistent modified continuum model based on the techniques of ab initio molecular quantum mechanics. The model is semiclassical in spirit, employing the quantum mechanical density for the excess charge and the first solvation shell in conjunction with classical electrostatics, and is developed in a general form which can be straightforwardly applied to special cases of interest, such as the solvated mono- and dielectron complexes. The advantages and disadvantages of the technique are discussed in relation to other more empirical approaches. Computational results are presented for excess electrons (mono- and dielectrons) in water and ammonia, and the role of long-range polarization of the medium in localizing the excess charge is analyzed. The variationally determined ground states are characterized in terms of equilibrium solvation shell geometry (appreciable cavities are implied for both water and ammonia), solvation energy, photoionization energy, and charge distribution. The finding of negative spin densities at the first solvent shell protons underscores the importance of a many electron theoretical treatment. Preliminary results for excited states are also reported. The calculated results are compared with experimental and other theoretical data, and the sensitivity of the results to various features of the model is discussed. Particular attention is paid to the number of solvent molecules required to trap the excess electron
Ab initio electronic properties of dual phosphorus monolayers in silicon
DEFF Research Database (Denmark)
Drumm, Daniel W.; Per, Manolo C.; Budi, Akin;
2014-01-01
In the midst of the epitaxial circuitry revolution in silicon technology, we look ahead to the next paradigm shift: effective use of the third dimension - in particular, its combination with epitaxial technology. We perform ab initio calculations of atomically thin epitaxial bilayers in silicon, ...
Energy Technology Data Exchange (ETDEWEB)
Hegde, Ganesh, E-mail: ganesh.h@ssi.samsung.com; Bowen, R. Chris [Advanced Logic Lab, Samsung Semiconductor Inc., Austin, TX 78754 (United States)
2015-10-15
The accuracy of a single s-orbital representation of Cu towards enabling multi-thousand atom ab initio calculations of electronic structure is evaluated in this work. If an electrostatic compensation charge of 0.3 electron per atom is used in this basis representation, the electronic transmission in bulk and nanocrystalline Cu can be made to compare accurately to that obtained with a Double Zeta Polarized basis set. The use of this representation is analogous to the use of single band effective mass representation for semiconductor electronic structure. With a basis of just one s-orbital per Cu atom, the representation is extremely computationally efficient and can be used to provide much needed ab initio insight into electronic transport in nanocrystalline Cu interconnects at realistic dimensions of several thousand atoms.
Tunneling of electrons via rotor-stator molecular interfaces: Combined ab initio and model study
Petreska, Irina; Ohanesjan, Vladimir; Pejov, Ljupčo; Kocarev, Ljupčo
2016-07-01
Tunneling of electrons through rotor-stator anthracene aldehyde molecular interfaces is studied with a combined ab initio and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons' formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that conformation-dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previous work where we investigated the coherent transport via strongly coupled delocalized orbital by application of Non-equilibrium Green's Function Formalism.
Ab initio calculations of the electronic structure and bonding characteristics of LaB6
Hossain, Faruque M.; Riley, Daniel P.; Murch, Graeme E.
2005-12-01
Lanthanum hexaboride ( LaB6 , NIST SRM-660a) is widely used as a standard reference material for calibrating the line position and line shape parameters of powder diffraction instruments. The accuracy of this calibration technique is highly dependent on how completely the reference material is characterized. Critical to x-ray diffraction, this understanding must include the valence of the La atomic position, which in turn will influence the x-ray form factor (f) and hence the diffracted intensities. The electronic structure and bonding properties of LaB6 have been investigated using ab initio plane-wave pseudopotential total energy calculations. The electronic properties and atomic bonding characteristics were analyzed by estimating the energy band structure and the density of states around the Fermi energy level. The calculated energy band structure is consistent with previously reported experimental findings; de Haas-van Alphen and two-dimensional angular correlation of electron-positron annihilation radiation. In addition, the bond strengths and types of atomic bonds in the LaB6 compound were estimated by analyzing the Mulliken charge density population. The calculated result revealed the coexistence of covalent, ionic, and metallic bonding in the LaB6 system and partially explains its high efficiency as a thermionic emitter.
Ab-initio electron scattering cross-sections and transport in liquid xenon
Boyle, Greg; Cocks, Daniel; Brunger, Michael; Buckman, Steve; Dujko, Sasa; White, Ron
2016-01-01
Ab-initio electron - liquid phase xenon fully differential cross-sections for electrons scattering in liquid xenon are developed from a solution of the Dirac-Fock scattering equations, using a recently developed framework [1] which considers multipole polarizabilities, a non-local treatment of exchange, and screening and coherent scattering effects. A multi-term solution of Boltzmann's equation accounting for the full anisotropic nature of the differential cross-section is used to calculate transport properties of excess electrons in liquid xenon. The results were found to agree to within 25% of the measured mobilities and characteristic energies over the reduced field range of 10^{-4} to 1 Td. The accuracies are comparable to those achieved in the gas phase. A simple model, informed by highly accurate gas-phase cross-sections, is presented to transform highly accurate gas-phase cross-sections to improve the liquid cross-sections, which was found to enhance the accuracy of the transport coefficient calculatio...
A Simple ab Initio Model for the Hydrated Electron That Matches Experiment.
Kumar, Anil; Walker, Jonathan A; Bartels, David M; Sevilla, Michael D
2015-08-27
Since its discovery over 50 years ago, the "structure" and properties of the hydrated electron have been a subject for wonderment and also fierce debate. In the present work we seriously explore a minimal model for the aqueous electron, consisting of a small water anion cluster embedded in a polarized continuum, using several levels of ab initio calculation and basis set. The minimum energy "zero Kelvin" structure found for any 4-water (or larger) anion cluster, at any post-Hartree–Fock theory level, is very similar to a recently reported embedded-DFT-in-classical-water-MD simulation (Uhlig, Marsalek, and Jungwirth, J. Phys. Chem. Lett. 2012, 3, 3071−3075), with four OH bonds oriented toward the maximum charge density in a small central "void". The minimum calculation with just four water molecules does a remarkably good job of reproducing the resonance Raman properties, the radius of gyration derived from the optical spectrum, the vertical detachment energy, and the hydration free energy. For the first time we also successfully calculate the EPR g-factor and (low temperature ice) hyperfine couplings. The simple tetrahedral anion cluster model conforms very well to experiment, suggesting it does in fact represent the dominant structural motif of the hydrated electron. PMID:26275103
A nonlocal, ab initio model of dissociative electron attachment and vibrational excitation of NO
Energy Technology Data Exchange (ETDEWEB)
Trevisan, Cynthia S.; Houfek, Karel; Zhang, Zhiyong; Orel, Ann E.; McCurdy, C. William; Rescigno, Thomas N.
2005-02-01
We present the results of an ab initio study of elastic scattering and vibrational excitation of NO by electron impact in the low-energy (0-2 eV) region where the cross sections are dominated by resonance contributions. The 3Sigma-, 1Delta and 1Sigma+ NO- resonance lifetimes are taken from our earlier study [Phys. Rev. A 69, 062711 (2004)], but the resonance energies used here are obtained from new configuration-interaction studies. Here we employ a more elaborate nonlocal treatment of the nuclear dynamics, which is found to remedy the principal deficiencies of the local complex potential model we employed in our earlier study, and gives cross sections in better agreement with the most recent experiments. We also present cross sections for dissociative electron attachment to NO leading to groundstate products. The calculations show that, while the peak cross sections starting from NO in its ground vibrational state are very small, the cross sections are extremely sensitive to vibrational excitation of the target and should be readily observable for target NO molecules excited to v = 10 and above.
PSI3: an open-source Ab Initio electronic structure package.
Crawford, T Daniel; Sherrill, C David; Valeev, Edward F; Fermann, Justin T; King, Rollin A; Leininger, Matthew L; Brown, Shawn T; Janssen, Curtis L; Seidl, Edward T; Kenny, Joseph P; Allen, Wesley D
2007-07-15
PSI3 is a program system and development platform for ab initio molecular electronic structure computations. The package includes mature programming interfaces for parsing user input, accessing commonly used data such as basis-set information or molecular orbital coefficients, and retrieving and storing binary data (with no software limitations on file sizes or file-system-sizes), especially multi-index quantities such as electron repulsion integrals. This platform is useful for the rapid implementation of both standard quantum chemical methods, as well as the development of new models. Features that have already been implemented include Hartree-Fock, multiconfigurational self-consistent-field, second-order Møller-Plesset perturbation theory, coupled cluster, and configuration interaction wave functions. Distinctive capabilities include the ability to employ Gaussian basis functions with arbitrary angular momentum levels; linear R12 second-order perturbation theory; coupled cluster frequency-dependent response properties, including dipole polarizabilities and optical rotation; and diagonal Born-Oppenheimer corrections with correlated wave functions. This article describes the programming infrastructure and main features of the package. PSI3 is available free of charge through the open-source, GNU General Public License. PMID:17420978
DEFF Research Database (Denmark)
Shim, Irene; Kingcade, Joseph E. , Jr.; Gingerich, Karl A.
1986-01-01
In the present work we present all-electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of six electronic states of the PdGe molecule. The molecule is predicted to have a 3Pi ground state and two low-lying excited states 3Sigma− and 1Sigma+. The electronic structure...
DEFF Research Database (Denmark)
Shim, Irene; Pelino, Mario; Gingerich, Karl A.
1992-01-01
In the present work we present results of all electron ab initio multiconfiguration self-consistent-field calculations of eight electronic states of the molecule YC. Also reported are the calculated spectroscopic constants. The predicted electronic ground state is 4PI, but this state is found to ...
Energy Technology Data Exchange (ETDEWEB)
Borges, P. D., E-mail: pdborges@gmail.com, E-mail: lscolfaro@txstate.edu; Scolfaro, L., E-mail: pdborges@gmail.com, E-mail: lscolfaro@txstate.edu [Department of Physics, Texas State University, San Marcos, Texas 78666 (United States)
2014-12-14
The thermoelectric properties of indium nitride in the most stable wurtzite phase (w-InN) as a function of electron and hole concentrations and temperature were studied by solving the semiclassical Boltzmann transport equations in conjunction with ab initio electronic structure calculations, within Density Functional Theory. Based on maximally localized Wannier function basis set and the ab initio band energies, results for the Seebeck coefficient are presented and compared with available experimental data for n-type as well as p-type systems. Also, theoretical results for electric conductivity and power factor are presented. Most cases showed good agreement between the calculated properties and experimental data for w-InN unintentionally and p-type doped with magnesium. Our predictions for temperature and concentration dependences of electrical conductivity and power factor revealed a promising use of InN for intermediate and high temperature thermoelectric applications. The rigid band approach and constant scattering time approximation were utilized in the calculations.
Directory of Open Access Journals (Sweden)
Hirokazu Takaki
2014-01-01
Full Text Available We present an efficient computation technique for ab-initio electron transport calculations based on density functional theory and the nonequilibrium Green’s function formalism for application to heterostructures with two-dimensional (2D interfaces. The computational load for constructing the Green’s functions, which depends not only on the energy but also on the 2D Bloch wave vector along the interfaces and is thus catastrophically heavy, is circumvented by parallel computational techniques with the message passing interface, which divides the calculations of the Green’s functions with respect to energy and wave vectors. To demonstrate the computational efficiency of the present code, we perform ab-initio electron transport calculations of Al(100-Si(100-Al(100 heterostructures, one of the most typical metal-semiconductor-metal systems, and show their transmission spectra, density of states (DOSs, and dependence on the thickness of the Si layers.
Ji, Pengfei
2016-01-01
On the basis of ab initio quantum mechanics (QM) calculation, the obtained electron heat capacity is implemented into energy equation of electron subsystem in two temperature model (TTM). Upon laser irradiation on the copper film, energy transfer from the electron subsystem to the lattice subsystem is modeled by including the electron-phonon coupling factor in molecular dynamics (MD) and TTM coupled simulation. The results show temperature and thermal melting difference between the QM-MD-TTM integrated simulation and pure MD-TTM coupled simulation. The successful construction of the QM-MD-TTM integrated simulation provide a general way that is accessible to other metals in laser heating.
Ji, Pengfei; Zhang, Yuwen
2016-03-01
On the basis of ab initio quantum mechanics (QM) calculation, the obtained electron heat capacity is implemented into energy equation of electron subsystem in two temperature model (TTM). Upon laser irradiation on the copper film, energy transfer from the electron subsystem to the lattice subsystem is modeled by including the electron-phonon coupling factor in molecular dynamics (MD) and TTM coupled simulation. The results show temperature and thermal melting difference between the QM-MD-TTM integrated simulation and pure MD-TTM coupled simulation. The successful construction of the QM-MD-TTM integrated simulation provides a general way that is accessible to other metals in laser heating.
Kühne, Thomas D
2012-01-01
Computer simulations and molecular dynamics in particular, is a very powerful method to provide detailed and essentially exact informations of classical many-body problems. With the advent of \\textit{ab-initio} molecular dynamics, where the forces are computed on-the-fly by accurate electronic structure calculations, the scope of either method has been greatly extended. This new approach, which unifies Newton's and Schr\\"odinger's equations, allows for complex simulations without relying on any adjustable parameter. This review is intended to outline the basic principles as well as a survey of the field. Beginning with the derivation of Born-Oppenheimer molecular dynamics, the Car-Parrinello method as well as novel hybrid scheme that unifies best of either approach are discussed. The predictive power is demonstrated by a series of applications ranging from insulators to semiconductors and even metals in condensed phases.
Directory of Open Access Journals (Sweden)
R.M. Balabai
2016-06-01
Full Text Available Within the methods of density functional theory and ab initio pseudopotential, we have obtained the spatial distributions of the density of valence electron and the electronic energy spectrum for the small clusters from the atoms of Cu, Ni, Co, O, Si with the aim to determine the mechanisms of their high catalytic activity. Electron’s levels of catalyst guide course of chemical reaction. We explored, that the organization of electronic states of nanocatalysts on the basis of transition metals possible control by changing the spatial organization of clusters and adding electronegative atoms.
Ab Initio Investigations of the Excited Electronic States of CaOCa
Fawzy, Wafaa M.; Heaven, Michael
2016-06-01
Chemical bonding in alkaline earth hypermetalic oxides is of fundamental interest. Previous Ab initio studies of CaOCa predicted a centrosymmetric linear geometry for both the 1Σg^+ ground state and the low lying triplet 3Σu^+ state. However, there have been no reports concerning the higher energy singlet and triplet states. The present work is focused on characterization of the potential energy surface (PES) of the excited 1Σu^+ state (assuming a centrosymmetric linear geometry) and obtaining predictions for the 1Σu^+←1Σg^+ vibronic transitions. We employed the multireference configuration interaction (MRCISD) method with state-averaged, full-valence complete active space self-consistent field (SA-FV-CASSCF) wavefunctions. In these calculations, the active space consisted of ten valence electrons in twelve orbitals, where all the valence electrons were correlated. Contributions of higher excitation and relativistic effects were taken into account using the Davidson correction and the Douglas-Kroll (DK) Hamiltonian, respectively. The correlation-consistent polarized weighed core-valence quadruple zeta basis set (cc-pwCVQZ-DK) was used for all three atoms. The full level of theory is abbreviated as SA-FV-CASSCF (10,12)-MRCISD-Q/cc-pwCVQZ-DK. The calculations were carried out using the MOLPRO2012 suite of programs. For the centrosymmetric linear geometry in all states, initial investigations of one-dimensional radial cuts provided equilibrium bond distances of 2.034 {Å}, 2.034 {Å}, and 1.999 {Å} for the 1Σg^+ , 3Σu^+ , and 1Σu^+ states, respectively. The vertical excitation frequency of the 1Σu^+←1Σg^+ optical transition was calculated to occur at 14801 wn. These predictions were followed by spectroscopic searches by Heaven et al. Indeed, rotationally resolved vibronic progressions were recorded in the vicinity of the predicted electronic band origin. Calculation of the three-dimensional PES showed that the potential minimum in the 1Σu^+ corresponds
Ab initio valence calculations in chemistry
Cook, D B
1974-01-01
Ab Initio Valence Calculations in Chemistry describes the theory and practice of ab initio valence calculations in chemistry and applies the ideas to a specific example, linear BeH2. Topics covered include the Schrödinger equation and the orbital approximation to atomic orbitals; molecular orbital and valence bond methods; practical molecular wave functions; and molecular integrals. Open shell systems, molecular symmetry, and localized descriptions of electronic structure are also discussed. This book is comprised of 13 chapters and begins by introducing the reader to the use of the Schrödinge
Ab initio study of vibronic transitions between x2π and 12Σ+ electronic states of HCP+ ion
Directory of Open Access Journals (Sweden)
Stojanović Ljiljana
2013-01-01
Full Text Available The ground and low-lying excited doublet electronic states of the HCP+ ion were studied by means of multireference configuration interaction method. Vibronic energy levels of the X2Π state of Σ, Π, Δ, and Φ symmetry, up to the 2500 cm-1, have been calculated variationally, employing previously developed ab initio methods which take into account vibronic and spin-orbit interactions. Obtained vibronic wave functions were used to estimate transition moments between vibronic energy levels of the X2Π and 12Σ+ electronic states. Results were compared to available experimental and theoretical data. [Projekat Ministarstva nauke Republike Srbije, br. 172040
Many-body effects on the electronic and optical properties of Si nanowires from ab initio approaches
Energy Technology Data Exchange (ETDEWEB)
Palummo, M.; Del Sole, R. [European Theoretical Spectroscopy Facility (ETSF), CNR-INFM-SMC, Roma (Italy); Dipartimento di Fisica - Universita di Roma, ' Tor Vergata' , Roma (Italy); Ossicini, S. [European Theoretical Spectroscopy Facility (ETSF), Reggio Emilia (Italy); Dipartimento di Scienze e Metodi dell' Ingegneria, Universita di Modena e Reggio Emilia (Italy)
2010-08-15
The study of semiconducting nanowires is one of the most rapidly growing research areas in materials science and nanotechnology, not only from the point of view of the possible applications, but also regarding the use of the latest developments in the theory. In this paper, we review the general ab initio many-body theory and methods and resume some of our very recent results regarding the structural, electronic, and optical properties of Silicon nanowires (Si-NWs), outlining both the reached achievements and some of the technical aspects necessary to obtain them. (Abstract Copyright [2010], Wiley Periodicals, Inc.)
Xavier, F. George D.; Kumar, Sanjay
2010-10-01
Ab initio global adiabatic and quasidiabatic potential energy surfaces of lowest four electronic (1-4 A3″) states of the H++O2 system have been computed in the Jacobi coordinates (R,r,γ) using Dunning's cc-pVTZ basis set at the internally contracted multireference (single and double) configuration interaction level of accuracy, which are relevant to the dynamics studies of inelastic vibrational and charge transfer processes observed in the scattering experiments. The computed equilibrium geometry parameters of the bound [HO2]+ ion in the ground electronic state and other parameters for the transition state for the isomerization process, HOO+⇌OOH+ are in good quantitative agreement with those available from the high level ab initio calculations, thus lending credence to the accuracy of the potential energy surfaces. The nonadiabatic couplings between the electronic states have been analyzed in both the adiabatic and quasidiabatic frameworks by computing the nonadiabatic coupling matrix elements and the coupling potentials, respectively. It is inferred that the dynamics of energy transfer processes in the scattering experiments carried out in the range of 9.5-23 eV would involve all the four electronic states.
Institute of Scientific and Technical Information of China (English)
ZHANG Zhi-jie; LIU Yu-hua; L(U) Zhong-yuan; LI Ze-sheng
2009-01-01
The rotational isomeric state(RIS) model was constructed for poly(vinylidene chloride)(PVDC) based on quantum chemistry calculations. The statistical weighted parameters were obtained from RIS representations and ab initio energies of conformers for model molecules 2,2,4,4-tetrachloropentane(TCP) and 2,2,4,4,6, 6-hexachlorohep-tane(HCH). By employing the RIS method, the characteristic ratio C∞ was calculated for PVDC. The calculated cha-racteristic ratio for PVDC is in good agreement with experiment result. Additionally, we studied the influence of the statistical weighted parameters on C∞ by calculating δC∞/δlnw. According to the values of δC∞/δlnw, the effects of second-order Cl-CH2 pentane type interaction and Cl-Cl long range interaction on C∞ were found to be important. In contrast, first-order interaction is unimportant.
DEFF Research Database (Denmark)
Fürst, Joachim Alexander; Hashemi, J.; Markussen, Troels;
2009-01-01
Fullerene functionalized carbon nanotubes-NanoBuds-form a novel class of hybrid carbon materials, which possesses many advantageous properties as compared to the pristine components. Here, we report a theoretical study of the electronic transport properties of these compounds. We use both ab init...
All-electron ab initio investigation of the electronic states of the PdC molecule
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, Karl A.
2001-01-01
The electronic structure of transition metal containing molecules are extremely complicated and extensive calculations are required for reliable descriptions. In spite of this the results can often be interpreted in simple terms. The electronic structure of PdC is consistent with the molecular...... orbital diagram, as shown. Corrections for relativistic effects are shown to be extremely important for PdC....
Gharabaghi, Masumeh
2016-01-01
In this letter the conceptual and computational implications of the Hartree product type nuclear wavefunction introduced recently within context of the ab initio non-Born-Oppenheimer Nuclear-electronic orbital (NEO) methodology are considered. It is demonstrated that this wavefunction may imply a pseudo-adiabatic separation of the nuclei and electrons and each nucleus is conceived as a quantum oscillator while a non-Coulombic effective Hamiltonian is deduced for electrons. Using variational principle this Hamiltonian is used to derive a modified set of single-component Hartree-Fock equations which are equivalent to the multi-component version derived previously within context of the NEO and, easy to be implemented computationally.
Dornheim, Tobias; Sjostrom, Travis; Malone, Fionn D; Foulkes, W M C; Bonitz, Michael
2016-01-01
We perform \\emph{ab initio} quantum Monte Carlo (QMC) simulations of the warm dense uniform electron gas in the thermodynamic limit. By combining QMC data with linear response theory we are able to remove finite-size errors from the potential energy over the entire warm dense regime, overcoming the deficiencies of the existing finite-size corrections by Brown \\emph{et al.}~[PRL \\textbf{110}, 146405 (2013)]. Extensive new QMC results for up to $N=1000$ electrons enable us to compute the potential energy $V$ and the exchange-correlation free energy $F_{xc}$ of the macroscopic electron gas with an unprecedented accuracy of $|\\Delta V|/|V|, |\\Delta F_{xc}|/|F|_{xc} \\sim 10^{-3}$. A comparison of our new data to the recent parametrization of $F_{xc}$ by Karasiev {\\em et al.} [PRL {\\bf 112}, 076403 (2014)] reveals significant inaccuracies of the latter.
Reciprocity Theorems for Ab Initio Force Calculations
Wei, C; Mele, E J; Rappe, A M; Lewis, Steven P.; Rappe, Andrew M.
1996-01-01
We present a method for calculating ab initio interatomic forces which scales quadratically with the size of the system and provides a physically transparent representation of the force in terms of the spatial variation of the electronic charge density. The method is based on a reciprocity theorem for evaluating an effective potential acting on a charged ion in the core of each atom. We illustrate the method with calculations for diatomic molecules.
Roy, Soumendra K.; Jian, Tian; Lopez, Gary V.; Li, Wei-Li; Su, Jing; Bross, David H.; Peterson, Kirk A.; Wang, Lai-Sheng; Li, Jun
2016-02-01
The observation of the gaseous UFO- anion is reported, which is investigated using photoelectron spectroscopy and relativisitic ab initio calculations. Two strong photoelectron bands are observed at low binding energies due to electron detachment from the U-7sσ orbital. Numerous weak detachment bands are also observed due to the strongly correlated U-5f electrons. The electron affinity of UFO is measured to be 1.27(3) eV. High-level relativistic quantum chemical calculations have been carried out on the ground state and many low-lying excited states of UFO to help interpret the photoelectron spectra and understand the electronic structure of UFO. The ground state of UFO- is linear with an O-U-F structure and a 3H4 spectral term derived from a U 7sσ25fφ15fδ1 electron configuration, whereas the ground state of neutral UFO has a 4H7/2 spectral term with a U 7sσ15fφ15fδ1 electron configuration. Strong electron correlation effects are found in both the anionic and neutral electronic configurations. In the UFO neutral, a high density of electronic states with strong configuration mixing is observed in most of the scalar relativistic and spin-orbit coupled states. The strong electron correlation, state mixing, and spin-orbit coupling of the electronic states make the excited states of UFO very challenging for accurate quantum chemical calculations.
Devi, Assa Aravindh Sasikala
2014-05-01
Investigations on freestanding binary and ternary clusters of Fe (x) Co (y) Ir (z) (x + y + z = 5, 6) are carried out using ab initio density functional theory techniques. The geometry, chemical order, binding energy, magnetic moment and electronic structure of the clusters are analyzed for the entire range of composition. Composition dependent structural transition is observed in the five atom clusters, while octahedral geometry prevailed in clusters with six atoms. Both the clusters show increment in binding energy with the increase in number of heterogeneous bonds. Analysis based on the chemical order parameter indicates that clusters favor mixing rather than segregation. The clusters exhibit ferromagnetic ordering and the inter-dependence of optimal cluster geometry to the magnetic moments and electronic structure is observed.
Odell, Anders
2011-10-03
The influence of the electrode\\'s Fermi surface on the transport properties of a photoswitching molecule is investigated with state-of-the-art ab initio transport methods. We report results for the conducting properties of the two forms of dithienylethene attached either to Ag or to nonmagnetic Ni leads. The I-V curves of the Ag/dithienylethene/Ag device are found to be very similar to those reported previously for Au. In contrast, when Ni is used as the electrode material the zero-bias transmission coefficient is profoundly different as a result of the role played by the Ni d bands in the bonding between the molecule and the electrodes. Intriguingly, despite these differences the overall conducting properties depend little on the electrode material. We thus conclude that electron transport in dithienylethene is, for the cases studied, mainly governed by the intrinsic electronic structure of the molecule. © 2011 American Physical Society.
Mills, Jeffrey D; Ben-Nun, Michal; Rollin, Kyle; Bromley, Michael W J; Li, Jiabo; Hinde, Robert J; Winstead, Carl L; Sheehy, Jeffrey A; Boatz, Jerry A; Langhoff, Peter W
2016-08-25
Continuing attention has addressed incorportation of the electronically dynamical attributes of biomolecules in the largely static first-generation molecular-mechanical force fields commonly employed in molecular-dynamics simulations. We describe here a universal quantum-mechanical approach to calculations of the electronic energy surfaces of both small molecules and large aggregates on a common basis which can include such electronic attributes, and which also seems well-suited to adaptation in ab initio molecular-dynamics applications. In contrast to the more familiar orbital-product-based methodologies employed in traditional small-molecule computational quantum chemistry, the present approach is based on an "ex-post-facto" method in which Hamiltonian matrices are evaluated prior to wave function antisymmetrization, implemented here in the support of a Hilbert space of orthonormal products of many-electron atomic spectral eigenstates familiar from the van der Waals theory of long-range interactions. The general theory in its various forms incorporates the early semiempirical atoms- and diatomics-in-molecules approaches of Moffitt, Ellison, Tully, Kuntz, and others in a comprehensive mathematical setting, and generalizes the developments of Eisenschitz, London, Claverie, and others addressing electron permutation symmetry adaptation issues, completing these early attempts to treat van der Waals and chemical forces on a common basis. Exact expressions are obtained for molecular Hamiltonian matrices and for associated energy eigenvalues as sums of separate atomic and interaction-energy terms, similar in this respect to the forms of classical force fields. The latter representation is seen to also provide a long-missing general definition of the energies of individual atoms and of their interactions within molecules and matter free from subjective additional constraints. A computer code suite is described for calculations of the many-electron atomic eigenspectra and
An experimental and ab initio study of the electronic spectrum of the jet-cooled F2BO free radical
International Nuclear Information System (INIS)
We have studied the B~2A1–X~2B2 laser-induced fluorescence (LIF) spectrum of the jet-cooled F2BO radical for the first time. The transition consists of a strong 000 band at 446.5 nm and eight weak sequence bands to shorter wavelengths. Single vibronic level emission spectra obtained by laser excitation of individual levels of the B~ state exhibit two electronic transitions: a very weak, sparse B~–X~ band system in the 450–500 nm region and a stronger, more extensive set of B~2A1–A~2B1 bands in the 580–650 nm region. We have also performed a series of high level ab initio calculations to predict the electronic energies, molecular structures, vibrational frequencies, and rotational and spin-rotation constants in the X~2B2, A~2B1 and B~2A1 electronic states as an aid to the analysis of the experimental data. The theoretical results have been used as input for simulations of the rotationally resolved B~2A1–X~2B2 000 LIF band and Franck-Condon profiles of the LIF and single vibronic level emission spectra. The agreement between the simulations obtained with purely ab initio parameters and the experimental spectra validates the geometries calculated for the ground and excited states and the conclusion that the radical has C2v symmetry in the X~, A~, and B~ states. The spectra provide considerable new information about the vibrational energy levels of the X~ and A~ states, but very little for the B~ state, due to the very restrictive Franck-Condon factors in the LIF spectra
Calderín, L; González, L E; González, D J
2009-05-21
We report a study on several static, dynamic, and electronic properties of liquid Hg at room temperature. We have performed ab initio molecular dynamics simulations using Kohn-Sham density functional theory combined with a nonlocal ultrasoft pseudopotential. The calculated static structure shows good agreement with the available experimental data. We present results for the single-particle dynamics, and recent experimental data are analyzed. The calculated dynamic structure factors S(q,omega) fairly agree with their experimental counterparts as measured by inelastic x-ray (and neutron) scattering experiments. The dispersion relation exhibits a positive dispersion, which however is not so marked as suggested by the experiment; moreover, its slope at the long-wavelength limit provides a good estimate of the experimental sound velocity. We have also analyzed the dynamical processes behind the S(q,omega) in terms of a model including a relaxation mechanism with both fast and slow characteristic time scales. PMID:19466841
Mogulkoc, Y.; Ciftci, Y. O.; Kabak, M.; Colakoglu, K.
2014-07-01
The structural, elastic, thermodynamic, electronic and vibrational properties of CsCl-type TbMg have been studied by performing ab initio calculations based on density functional theory using the Vienna Ab initio Simulation Package (VASP). The exchange correlation potential within the generalized-gradient approximation (GGA) of projector augmented wave (PAW) method is used. The calculated structural parameters, such as the lattice constant, bulk modulus, its pressure derivative, formation energy and second-order elastic constants are presented in this paper. The obtained results are compared with related experimental and theoretical studies. The electronic band calculations, total density of states (DOS), partial DOS and charge density are also presented. Formation enthalpy and Cauchy pressure are determined. In order to obtain more information the elastic properties such as Zener anisotropy factor, Poisson’s ratio, Young modulus, isotropic shear modulus, Debye temperature and melting point have been carried out. The elastic constants are calculated in zero and different pressure ranges (0-50 GPa) with bulk modulus. We have performed the thermodynamic properties of TbMg by using quasi-harmonic Debye model. The temperature and pressure variation of the volume, bulk modulus, and thermal expansion coefficient have been predicted over a pressure range of 0-25 GPa for of TbMg. Pressure dependence of the anisotropy factors, Young’s modulus, Poisson’s ratios, bulk modulus and axis compressibility of TbMg are presented along different directions and planes. Finally, the phonon dispersion curves are presented for TbMg.
DEFF Research Database (Denmark)
Åstrand, Per-Olof; Ramanujam, P.S.; Hvilsted, Søren;
2000-01-01
Electronic excitation energies of 16 azobenzene dyes have been calculated by ab initio methods within the second-order polarization propagator approximation (SOPPA). Good agreement with expriment is found for the lowest singlet and triplet states for both the trans- and cis-azobenzene molecules...... candidates for azo components used in materials for data storage....
A theoretical-spectroscopy, ab-initio-based study of the electronic ground state of 121SbH3
Yurchenko, Sergei N.; Carvajal Zaera, Miguel; Yachmenev, Andrey; Thiel, Walter; Jensen, Per
2010-01-01
For the stibine isotopologue (SbH3)-Sb-121, we report improved theoretical calculations of the vibrational energies below 8000 cm- and simulations of the rovibrational spectrum in the 0-8000 cm(-1) region. The calculations are based on a refined ab initio potential energy surface and on a new dipole moment surface obtained at the coupled cluster CCSD(T) level. The theoretical results are compared with the available experimental data in order to validate the ab initio surfaces and the TROVE co...
Ab initio calculation of electron-phonon coupling in monoclinic β-Ga2O3 crystal
Ghosh, Krishnendu; Singisetti, Uttam
2016-08-01
The interaction between electrons and vibrational modes in monoclinic β-Ga2O3 is theoretically investigated using ab-initio calculations. The large primitive cell of β-Ga2O3 gives rise to 30 phonon modes all of which are taken into account in transport calculation. The electron-phonon interaction is calculated under density functional perturbation theory and then interpolated using Wannier-Fourier interpolation. The long-range interaction elements between electrons and polar optical phonon (POP) modes are calculated separately using the Born effective charge tensor. The direction dependence of the long-range POP coupling in a monoclinic crystal is explored and is included in the transport calculations. Scattering rate calculations are done using the Fermi golden rule followed by solving the Boltzmann transport equation using the Rode's method to estimate low field mobility. A room temperature mobility of 115 cm2/V s is observed. Comparison with recent experimentally reported mobility is done for a wide range of temperatures (30 K-650 K). It is also found that the POP interaction dominates the electron mobility under low electric field conditions. The relative contribution of the different POP modes is analyzed and the mode 21 meV POP is found to have the highest impact on low field electron mobility at room temperature.
Long, Run; Fang, Weihai; Akimov, Alexey V
2016-02-18
We report ab initio time-domain simulations of nonradiative electron-hole recombination and electronic dephasing in ideal and defect-containing monolayer black phosphorus (MBP). Our calculations predict that the presence of phosphorus divacancy in MBP (MBP-DV) substantially reduces the nonradiative recombination rate, with time scales on the order of 1.57 ns. The luminescence line width in ideal MBP of 150 meV is 2.5 times larger than MBP-DV at room temperature, and is in excellent agreement with experiment. We find that the electron-hole recombination in ideal MBP is driven by the 450 cm(-1) vibrational mode, whereas the recombination in the MBP-DV system is driven by a broad range of vibrational modes. The reduced electron-phonon coupling and increased bandgap in MBP-DV rationalize slower recombination in this material, suggesting that electron-phonon energy losses in MBP can be minimized by creating suitable defects in semiconductor device material.
Roy, Soumendra K; Jian, Tian; Lopez, Gary V; Li, Wei-Li; Su, Jing; Bross, David H; Peterson, Kirk A; Wang, Lai-Sheng; Li, Jun
2016-02-28
The observation of the gaseous UFO(-) anion is reported, which is investigated using photoelectron spectroscopy and relativisitic ab initio calculations. Two strong photoelectron bands are observed at low binding energies due to electron detachment from the U-7sσ orbital. Numerous weak detachment bands are also observed due to the strongly correlated U-5f electrons. The electron affinity of UFO is measured to be 1.27(3) eV. High-level relativistic quantum chemical calculations have been carried out on the ground state and many low-lying excited states of UFO to help interpret the photoelectron spectra and understand the electronic structure of UFO. The ground state of UFO(-) is linear with an O-U-F structure and a (3)H4 spectral term derived from a U 7sσ(2)5fφ(1)5fδ(1) electron configuration, whereas the ground state of neutral UFO has a (4)H(7/2) spectral term with a U 7sσ(1)5fφ(1)5fδ(1) electron configuration. Strong electron correlation effects are found in both the anionic and neutral electronic configurations. In the UFO neutral, a high density of electronic states with strong configuration mixing is observed in most of the scalar relativistic and spin-orbit coupled states. The strong electron correlation, state mixing, and spin-orbit coupling of the electronic states make the excited states of UFO very challenging for accurate quantum chemical calculations. PMID:26931704
Roy, Soumendra K; Jian, Tian; Lopez, Gary V; Li, Wei-Li; Su, Jing; Bross, David H; Peterson, Kirk A; Wang, Lai-Sheng; Li, Jun
2016-02-28
The observation of the gaseous UFO(-) anion is reported, which is investigated using photoelectron spectroscopy and relativisitic ab initio calculations. Two strong photoelectron bands are observed at low binding energies due to electron detachment from the U-7sσ orbital. Numerous weak detachment bands are also observed due to the strongly correlated U-5f electrons. The electron affinity of UFO is measured to be 1.27(3) eV. High-level relativistic quantum chemical calculations have been carried out on the ground state and many low-lying excited states of UFO to help interpret the photoelectron spectra and understand the electronic structure of UFO. The ground state of UFO(-) is linear with an O-U-F structure and a (3)H4 spectral term derived from a U 7sσ(2)5fφ(1)5fδ(1) electron configuration, whereas the ground state of neutral UFO has a (4)H(7/2) spectral term with a U 7sσ(1)5fφ(1)5fδ(1) electron configuration. Strong electron correlation effects are found in both the anionic and neutral electronic configurations. In the UFO neutral, a high density of electronic states with strong configuration mixing is observed in most of the scalar relativistic and spin-orbit coupled states. The strong electron correlation, state mixing, and spin-orbit coupling of the electronic states make the excited states of UFO very challenging for accurate quantum chemical calculations.
Energy Technology Data Exchange (ETDEWEB)
Tohme, Samir N.; Korek, Mahmoud, E-mail: mahmoud.korek@bau.edu.lb, E-mail: fkorek@yahoo.com; Awad, Ramadan [Faculty of Science, Beirut Arab University, P.O. Box 11-5020 Riad El Solh, Beirut 1107 2809 (Lebanon)
2015-03-21
Ab initio techniques have been applied to investigate the electronic structure of the LiYb molecule. The potential energy curves have been computed in the Born–Oppenheimer approximation for the ground and 29 low-lying doublet and quartet excited electronic states. Complete active space self-consistent field, multi-reference configuration interaction, and Rayleigh Schrödinger perturbation theory to second order calculations have been utilized to investigate these states. The spectroscopic constants, ω{sub e}, R{sub e}, B{sub e}, …, and the static dipole moment, μ, have been investigated by using the two different techniques of calculation with five different types of basis. The eigenvalues, E{sub v}, the rotational constant, B{sub v}, the centrifugal distortion constant, D{sub v}, and the abscissas of the turning points, R{sub min} and R{sub max}, have been calculated by using the canonical functions approach. The comparison between the values of the present work, calculated by different techniques, and those available in the literature for several electronic states shows a very good agreement. Twenty-one new electronic states have been studied here for the first time.
Tohme, Samir N.; Korek, Mahmoud; Awad, Ramadan
2015-03-01
Ab initio techniques have been applied to investigate the electronic structure of the LiYb molecule. The potential energy curves have been computed in the Born-Oppenheimer approximation for the ground and 29 low-lying doublet and quartet excited electronic states. Complete active space self-consistent field, multi-reference configuration interaction, and Rayleigh Schrödinger perturbation theory to second order calculations have been utilized to investigate these states. The spectroscopic constants, ωe, Re, Be, …, and the static dipole moment, μ, have been investigated by using the two different techniques of calculation with five different types of basis. The eigenvalues, Ev, the rotational constant, Bv, the centrifugal distortion constant, Dv, and the abscissas of the turning points, Rmin and Rmax, have been calculated by using the canonical functions approach. The comparison between the values of the present work, calculated by different techniques, and those available in the literature for several electronic states shows a very good agreement. Twenty-one new electronic states have been studied here for the first time.
Energy Technology Data Exchange (ETDEWEB)
Saalfrank, Peter [Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam (Germany); Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Juaristi, J. I. [Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, 20018 Donostia-San Sebastián (Spain); Departamento de Física de Materiales, Facultad de Químicas UPV/EHU, Apartado 1072, 20018 Donostia-San Sebastián (Spain); Alducin, M.; Muiño, R. Díez [Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, 20018 Donostia-San Sebastián (Spain); Blanco-Rey, M. [Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Departamento de Física de Materiales, Facultad de Químicas UPV/EHU, Apartado 1072, 20018 Donostia-San Sebastián (Spain)
2014-12-21
Using density functional theory and Ab Initio Molecular Dynamics with Electronic Friction (AIMDEF), we study the adsorption and dissipative vibrational dynamics of hydrogen atoms chemisorbed on free-standing lead films of increasing thickness. Lead films are known for their oscillatory behaviour of certain properties with increasing thickness, e.g., energy and electron spillout change in discontinuous manner, due to quantum size effects [G. Materzanini, P. Saalfrank, and P. J. D. Lindan, Phys. Rev. B 63, 235405 (2001)]. Here, we demonstrate that oscillatory features arise also for hydrogen when chemisorbed on lead films. Besides stationary properties of the adsorbate, we concentrate on finite vibrational lifetimes of H-surface vibrations. As shown by AIMDEF, the damping via vibration-electron hole pair coupling dominates clearly over the vibration-phonon channel, in particular for high-frequency modes. Vibrational relaxation times are a characteristic function of layer thickness due to the oscillating behaviour of the embedding surface electronic density. Implications derived from AIMDEF for frictional many-atom dynamics, and physisorbed species will also be given.
Li, Zi; Wang, Cong; Kang, Wei; Li, Chuanying; Zhang, Ping
2015-11-01
Ultrafast laser experiments on metals usually induce a high electron temperature and a low ion temperature and, thus, an energy relaxation process. The electron heat capacity and electron-phonon coupling factor are crucial thermal quantities to describe this process. We perform ab initio theoretical studies to determine these thermal quantities and their dependence on density and electron temperature for the metals aluminum and beryllium. The heat capacity shows an approximately linear dependence on the temperature, similar to free electron gas, and the compression only slightly affects the capacity. The electron-phonon coupling factor increases with both temperature and density, and the change observed for beryllium is more obvious than that for aluminum. The connections between thermal quantities and electronic/atomic structures are discussed in detail, and the different behaviors of aluminum and beryllium are well explained.
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, BP. 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)
2014-06-01
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 MnSe lattice. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Mn lattices. Magnetic moments 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. The zero-field high temperature static susceptibility series of the spin −4.28 nearest-neighbor Ising model on face centered cubic (fcc) and lattices is thoroughly analyzed by means of a power series coherent anomaly method (CAM). The exchange interaction between the magnetic atoms and the Néel temperature are deduced using the mean filed and HTSEs theories. - Highlights: • Ab initio calculations are used to investigate both electronic and magnetic properties of the MnSe alloys. • Obtained data from ab initio calculations are used as input for the HTSEs. • The Néel temperature is obtained for MnSe alloys.
International Nuclear Information System (INIS)
In this work, ab-initio, relativistic state dependent multi-configuration Dirac-Fock (MCDF) calculations have been done for determining the charge density at the nucleus of 7Be using MCDF program of Grant et al. and observed variations in electron density with the configurations considered which reflect different electronic environmental condition in a medium
Collective rotation from ab initio theory
Caprio, M A; Vary, J P; Smith, R
2015-01-01
Through ab initio approaches in nuclear theory, we may now seek to quantitatively understand the wealth of nuclear collective phenomena starting from the underlying internucleon interactions. No-core configuration interaction (NCCI) calculations for p-shell nuclei give rise to rotational bands, as evidenced by rotational patterns for excitation energies, electromagnetic moments, and electromagnetic transitions. In this review, NCCI calculations of 7-9Be are used to illustrate and explore ab initio rotational structure, and the resulting predictions for rotational band properties are compared with experiment. We highlight the robustness of ab initio rotational predictions across different choices for the internucleon interaction.
Sergey I. Bokarev; Dantz, Marcus; Suljoti, Edlira; Kühn, Oliver; Emad F. Aziz
2013-01-01
Non-radiative decay channels in the L-edge fluorescence spectra from transition metal-aqueous solutions give rise to spectral dips in X-ray transmission spectra. Their origin is unraveled here using partial and inverse partial fluorescence yields on the micro-jet combined with multi-reference ab initio electronic structure calculations. Comparing Fe2+, Fe3+, and Co2+ systems we demonstrate unequivocally that spectral dips are due to a state-dependent electron delocalization within the manifol...
Vázquez-Mayagoitia, Alvaro; Huertas, Oscar; Brancolini, Giorgia; Migliore, Agostino; Sumpter, Bobby G; Orozco, Modesto; Luque, F Javier; Di Felice, Rosa; Fuentes-Cabrera, Miguel
2009-10-29
The structural, tautomeric, hydrogen-bonding, stacking, and electronic properties of a seleno-derivative of thymine (T), denoted here as 4SeT and created by replacing O4 in T with Se, are investigated by means of ab initio computational techniques. The structural properties of T and 4SeT are very similar, and the geometrical differences are mainly limited to the adjacent environment of the C-Se bond. The canonical "keto" form is the most stable tautomer, in the gas phase and in aqueous solution, for both T and 4SeT. It is argued that the competition between two opposite trends, i.e., a decrease in the base-pairing ability and an increase of the stacking interaction upon incorporation of 4SeT into a duplex, likely explains the similar experimental melting points of a seleno-derivative duplex (Se-DNA) and its native counterpart. Interestingly, the underlying electronic structure shows that replacement of O4 with Se promotes a reduction in the HOMO-LUMO gap and an increase in interplane coupling, which suggests that Se-DNA could be potentially useful for nanodevice applications. This finding is further supported by the fact that transfer integrals between 4SeT...A stacked base pairs are larger than those determined for similarly stacked natural T...A pairs. PMID:19813710
Energy Technology Data Exchange (ETDEWEB)
Vazquez-Mayagoitia, Alvaro [ORNL; Fuentes-Cabrera, Miguel A [ORNL; Sumpter, Bobby G [ORNL; Luque, Javier [Universitat de Barcelona; Huertas, Oscar [Universitat de Barcelona; Orozco, Modesto [Institut de Recerca Biomedica, Parc Cientific de Barcelona, Barcelona, Spain; Felice, Rosa [INFM-CNR National Research Center S3; Brancolini, Giorgia [ORNL; Migliore, Agostino [University of Pennsylvania
2009-01-01
The structural, tautomeric, hydrogen-bonding, stacking and electronic properties of a seleno-derivative of thymine (T), denoted here as 4SeT and created by replacing O4 in T with Se, are investigated by means of ab initio computational techniques. The structural properties of T and 4SeT are very similar and the geometrical differences are mainly limited to the adjacent environment of the C-Se bond. The canonical keto form is the most stable tautomer, in gas phase and in aqueous solution, for both T and 4SeT. It is argued that the competition between two opposite trends, i.e. a decrease in the base-pairing ability and an increase of the stacking interaction upon incorporation of 4SeT into a duplex, likely explains the similar experimental melting points of a seleno-derivative duplex (Se-DNA) and its native counterpart. Interestingly, the underlying electronic structure shows that replacement of O4 with Se promotes a reduction in the HOMO-LUMO gap and an increase in inter-plane coupling, which suggests that Se-DNA could be potentially useful for nanodevice applications. This finding is further supported by the fact that transfer integrals between 4SeT---A stacked base pairs are larger than those determined for similarly stacked natural T---A pairs.
Chen, Hung-Cheng; Hsu, Chao-Ping
2005-12-29
To calculate electronic couplings for photoinduced electron transfer (ET) reactions, we propose and test the use of ab initio quantum chemistry calculation for excited states with the generalized Mulliken-Hush (GMH) method. Configuration-interaction singles (CIS) is proposed to model the locally excited (LE) and charge-transfer (CT) states. When the CT state couples with other high lying LE states, affecting coupling values, the image charge approximation (ICA), as a simple solvent model, can lower the energy of the CT state and decouple the undesired high-lying local excitations. We found that coupling strength is weakly dependent on many details of the solvent model, indicating the validity of the Condon approximation. Therefore, a trustworthy value can be obtained via this CIS-GMH scheme, with ICA used as a tool to improve and monitor the quality of the results. Systems we tested included a series of rigid, sigma-linked donor-bridge-acceptor compounds where "through-bond" coupling has been previously investigated, and a pair of molecules where "through-space" coupling was experimentally demonstrated. The calculated results agree well with experimentally inferred values in the coupling magnitudes (for both systems studied) and in the exponential distance dependence (for the through-bond series). Our results indicate that this new scheme can properly account for ET coupling arising from both through-bond and through-space mechanisms.
Energy Technology Data Exchange (ETDEWEB)
Scholes, G.D.; Fleming, G.R. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley National Lab., CA (United States). Physical Biosciences Div.; Gould, I.R. [Imperial Coll. of Science, Technology and Medicine, London (United Kingdom). Dept. of Chemistry; Cogdell, R.J. [Univ. of Glasgow (United Kingdom). Div. of Biochemistry and Molecular Biology
1999-04-01
The results of ab initio molecular orbital calculations of excited states and electronic couplings (for energy transfer) between the B800 and B850 bacteriochlorophyll a (Bchl) chromophores in the peripheral light-harvesting complex (LH2) of the purple photosynthetic bacterium Rhodopseudomonas acidophila are reported. Electronic couplings are estimated from supermolecule calculations of Bchl dimers using the Ci-singles methodology and 3-21G{sup *} or 6-31G{sup *} basis sets. A scheme for dissecting the coupling into contributions from the Coulombic coupling and the short-range coupling (i.e., dependent on interchromophore orbital overlap) is reported. B850 couplings are calculated to be [total (Coulombic + short)]: intrapolypeptide dimer 320 (265 + 55) cm{sup {minus}1} and interpolypeptide dimer 255 (195 + 60) cm{sup {minus}1} at the CIS/6-31G{sup *} level. These results differ significantly from those estimated using the point dipole approximation. The effect of including Mg ligands (His residues) and H-bonding residues (Trp and Tyr) is also investigated. The consequences for superradiance and energy transfer dynamics and mechanism are discussed.
Keith, J. Brandon; Fennick, Jacob R.; Junkermeier, Chad E.; Nelson, Daniel R.; Lewis, James P.
2009-03-01
FIREBALL is an ab initio technique for fast local orbital simulations of nanotechnological, solid state, and biological systems. We have implemented a convenient interface for new users and software architects in the platform-independent Java language to access FIREBALL's unique and powerful capabilities. The graphical user interface can be run directly from a web server or from within a larger framework such as the Computational Science and Engineering Online (CSE-Online) environment or the Distributed Analysis of Neutron Scattering Experiments (DANSE) framework. We demonstrate its use for high-throughput electronic structure calculations and a multi-100 atom quantum molecular dynamics (MD) simulation. Program summaryProgram title: FireballUI Catalogue identifier: AECF_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECF_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 279 784 No. of bytes in distributed program, including test data, etc.: 12 836 145 Distribution format: tar.gz Programming language: Java Computer: PC and workstation Operating system: The GUI will run under Windows, Mac and Linux. Executables for Mac and Linux are included in the package. RAM: 512 MB Word size: 32 or 64 bits Classification: 4.14 Nature of problem: The set up and running of many simulations (all of the same type), from the command line, is a slow process. But most research quality codes, including the ab initio tight-binding code FIREBALL, are designed to run from the command line. The desire is to have a method for quickly and efficiently setting up and running a host of simulations. Solution method: We have created a graphical user interface for use with the FIREBALL code. Once the user has created the files containing the atomic coordinates for each system that they are
Rajesh, C.; Majumder, C.; Rajan, M. G. R.; Kulshreshtha, S. K.
2005-12-01
The geometric and electronic structure of the Pbn clusters (n=2-15) has been calculated to elucidate its structural evolution and compared with other group-IV elemental clusters. The search for several low-lying isomers was carried out using the ab initio molecular dynamics simulations under the framework of the density functional theory formalism. The results suggest that unlike Si, Ge, and Sn clusters, which favor less compact prolate shape in the small size range, Pb clusters favor compact spherical structures consisting of fivefold or sixfold symmetries. The difference in the growth motif can be attributed to their bulk crystal structure, which is diamond-like for Si, Ge, and Sn but fcc for Pb. The relative stability of Pbn clusters is analyzed based on the calculated binding energies and second difference in energy. The results suggest that n=4 , 7, 10, and 13 clusters are more stable than their respective neighbors, reflecting good agreement with experimental observation. Based on the fragmentation pattern it is seen that small clusters up to n=12 favor monomer evaporation, larger ones fragment into two stable daughter products. The experimental observation of large abundance for n=7 and lowest abundance of n=14 have been demonstrated from their fragmentation pattern. Finally a good agreement of our theoretical results with that of the experimental findings reported earlier implies accurate predictions of the ground state geometries of these clusters.
Pask, J. E.; Sterne, P. A.
2004-03-01
The finite-element (FE) method is a general approach for the solution of partial differential equations. Like the planewave (PW) method, the FE method is a systematically improvable expansion approach. Unlike the PW method, however, its basis functions are strictly local in real space, which allows for variable resolution in real space and facilitates massively parallel implementation. We discuss the application of the FE method to ab initio electronic-structure calculations.(J.E. Pask, B.M. Klein, C.Y. Fong, and P.A. Sterne, Phys. Rev. B 59), 12352 (1999). In particular, we discuss the use of nonlocal pseudopotentials in bulk calculations, and the handling of long-range interactions in the construction of the Kohn-Sham effective potential and total energy. We show that the total energy converges variationally, and at the optimal theoretical rate consistent with the cubic completeness of the basis. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.
Energy Technology Data Exchange (ETDEWEB)
Olsson, Paer
2004-04-01
The efficiency of fast neutron reactors, such as for fusion, breeding and transmutation, depend strongly on the neutron radiation resistance of the materials used in the reactors. The binary Fe-Cr alloy, which has many attractive properties in this regard, is the base for the best steels of today which are, however, still not up to the required standards. Therefore, substantial effort has been devoted to finding new materials that can cope with the demands better. Experimental studies must be complemented with extensive theoretical modelling in order to understand the effects that different alloying elements has on the resistance properties of materials. To this end, the first steps of multi-scale modelling has been taken, starting out with ab initio calculations of the electronic structure of the complete concentration range range of the disordered binary Fe-C alloy. The mixing enthalpy of Fe-Cr has been quantitatively predicted and has, together with data from literature, been used in order to fit two sets of interatomic potentials for the purpose of simulating defect evolution with molecular dynamics and kinetic Monte-Carlo codes. These dedicated Fe-Cr alloy potentials are new and represent important additions to the pure element potentials that can be found in literature.
Ab initio molar volumes and Gaussian radii.
Parsons, Drew F; Ninham, Barry W
2009-02-12
Ab initio molar volumes are calculated and used to derive radii for ions and neutral molecules using a spatially diffuse model of the electron distribution with Gaussian spread. The Gaussian radii obtained can be used for computation of nonelectrostatic ion-ion dispersion forces that underlie Hofmeister specific ion effects. Equivalent hard-sphere radii are also derived, and these are in reasonable agreement with crystalline ionic radii. The Born electrostatic self-energy is derived for a Gaussian model of the electronic charge distribution. It is shown that the ionic volumes used in electrostatic calculations of strongly hydrated cosmotropic ions ought best to include the first hydration shell. Ionic volumes for weakly hydrated chaotropic metal cations should exclude electron overlap (in electrostatic calculations). Spherical radii are calculated as well as nonisotropic ellipsoidal radii for nonspherical ions, via their nonisotropic static polarizability tensors. PMID:19140766
Wang, Zi; Bevan, Kirk H.
2016-01-01
In the present work, we study the effects of the electronic relaxation of semicore levels on polaron activation energies and dynamics. Within the framework of adiabatic ab initio theory, we utilize both static transition state theory and molecular dynamics methods for an in-depth study of polaronic hopping in delithiated LiFePO4 (FePO4). Our results show that electronic relaxation of semicore states is significant in FePO4, resulting in a lower activation barrier and kinetics that is one to two orders faster compared to the result of calculations that do not incorporate semicore states. In general, the results suggest that the relaxation of states far below the Fermi energy could dramatically impact the ab initio polaronic barrier estimates for many transition metal oxides and phosphates.
Ferreira da Silva, F.; Lange, E.; Limão-Vieira, P.; Jones, N. C.; Hoffmann, S. V.; Hubin-Franskin, M.-J.; Delwiche, J.; Brunger, M. J.; Neves, R. F. C.; Lopes, M. C. A.; de Oliveira, E. M.; da Costa, R. F.; Varella, M. T. do N.; Bettega, M. H. F.; Blanco, F.; García, G.; Lima, M. A. P.; Jones, D. B.
2015-10-01
The electronic spectroscopy of isolated furfural (2-furaldehyde) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 3.5-10.8 eV energy-range, with absolute cross section measurements derived. Electron energy loss spectra are also measured over a range of kinematical conditions. Those energy loss spectra are used to derive differential cross sections and in turn generalised oscillator strengths. These experiments are supported by ab initio calculations in order to assign the excited states of the neutral molecule. The good agreement between the theoretical results and the measurements allows us to provide the first quantitative assignment of the electronic state spectroscopy of furfural over an extended energy range.
Energy Technology Data Exchange (ETDEWEB)
Ferreira da Silva, F.; Lange, E. [Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal); Limão-Vieira, P., E-mail: plimaovieira@fct.unl.pt, E-mail: michael.brunger@flinders.edu.au, E-mail: maplima@ifi.unicamp.br [Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal); School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001 (Australia); Jones, N. C.; Hoffmann, S. V. [ISA, Department of Physics and Astronomy, Aarhus University, Ny Munkegade, DK-8000 Århus C (Denmark); Hubin-Franskin, M.-J.; Delwiche, J. [Départment de Chimie, Institut de Chimie-Bât. B6C, Université de Liège, B-4000 Liège 1 (Belgium); Brunger, M. J., E-mail: plimaovieira@fct.unl.pt, E-mail: michael.brunger@flinders.edu.au, E-mail: maplima@ifi.unicamp.br [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001 (Australia); Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia); and others
2015-10-14
The electronic spectroscopy of isolated furfural (2-furaldehyde) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 3.5–10.8 eV energy-range, with absolute cross section measurements derived. Electron energy loss spectra are also measured over a range of kinematical conditions. Those energy loss spectra are used to derive differential cross sections and in turn generalised oscillator strengths. These experiments are supported by ab initio calculations in order to assign the excited states of the neutral molecule. The good agreement between the theoretical results and the measurements allows us to provide the first quantitative assignment of the electronic state spectroscopy of furfural over an extended energy range.
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, K. A.
1984-01-01
In the present study we present all-electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of the 2Sigma+ ground state as well as of 16 excited states of the RhC molecule. The calculated spectroscopic constants of the lowest lying states are in good agreement...... with the experimental data. The chemical bond in the electronic ground state is mainly due to interaction of the 4d orbitals of Rh with the 2s and 2p orbitals of C. The bond is a triple bond composed of two pi bonds and one sigma bond. The 5s electron of Rh hardly participates in the bond formation. It is located...
P-V Relation for Mercuric Calcogenides: Ab Initio Method
Directory of Open Access Journals (Sweden)
G. Misra
2011-01-01
Full Text Available Mercuric Calcogenides found many applications in electronic and optical devices as semiconducting materials. An equation of state provides useful information about the relationship between pressure (P, volume (V and temperature (T that helps to understand the behaviour of materials under the effect of high pressure and high temperature. The present paper sheds light on the electronic structure of Mercuric Calcogenides by simulating its electronic properties through ab initio method. This ab initio method is extended to derive the equation of state for Mercuric Calcogenides. The present equation of state has also been tested for the prediction of End Point. The computed results compare well with Quantum statistical data.
Maurer, Reinhard J; Batista, Victor S; Tully, John C
2016-01-01
Molecular adsorbates on metal surfaces exchange energy with substrate phonons and low-lying electron-hole pair excitations. In the limit of weak coupling, electron-hole pair excitations can be seen as exerting frictional forces on adsorbates that enhance energy transfer and facilitate vibrational relaxation or hot-electron mediated chemistry. We have recently reported on the relevance of tensorial properties of electronic friction [Phys. Rev. Lett. 116, 217601 (2016)] in dynamics at surfaces. Here we present the underlying implementation of tensorial electronic friction based on Kohn-Sham Density Functional Theory for condensed phase and cluster systems. Using local atomic-orbital basis sets, we calculate nonadiabatic coupling matrix elements and evaluate the full electronic friction tensor in the classical limit. Our approach is numerically stable and robust as shown by a detailed convergence analysis. We furthermore benchmark the accuracy of our approach by calculation of vibrational relaxation rates and li...
Long, Run; Prezhdo, Oleg V
2015-11-24
TiO2 sensitized with organohalide perovskites gives rise to solar-to-electricity conversion efficiencies reaching close to 20%. Nonradiative electron-hole recombination across the perovskite/TiO2 interface constitutes a major pathway of energy losses, limiting quantum yield of the photoinduced charge. In order to establish the fundamental mechanisms of the energy losses and to propose practical means for controlling the interfacial electron-hole recombination, we applied ab initio nonadiabatic (NA) molecular dynamics to pristine and doped CH3NH3PbI3(100)/TiO2 anatase(001) interfaces. We show that doping by substitution of iodide with chlorine or bromine reduces charge recombination, while replacing lead with tin enhances the recombination. Generally, lighter and faster atoms increase the NA coupling. Since the dopants are lighter than the atoms they replace, one expects a priori that all three dopants should accelerate the recombination. We rationalize the unexpected behavior of chlorine and bromine by three effects. First, the Pb-Cl and Pb-Br bonds are shorter than the Pb-I bond. As a result, Cl and Br atoms are farther away from the TiO2 surface, decreasing the donor-acceptor coupling. In contrast, some iodines form chemical bonds with Ti atoms, increasing the coupling. Second, chlorine and bromine reduce the NA electron-vibrational coupling, because they contribute little to the electron and hole wave functions. Tin increases the coupling, since it is lighter than lead and contributes to the hole wave function. Third, higher frequency modes introduced by chlorine and bromine shorten quantum coherence, thereby decreasing the transition rate. The recombination occurs due to coupling of the electronic subsystem to low-frequency perovskite and TiO2 modes. The simulation shows excellent agreement with the available experimental data and advances our understanding of electronic and vibrational dynamics in perovskite solar cells. The study provides design principles
Ab Initio Studies of Stratospheric Ozone Depletion Chemistry
Lee, Timothy J.; Head-Gordon, Martin; Langhoff, Stephen R. (Technical Monitor)
1995-01-01
An overview of the current understanding of ozone depletion chemistry, particularly with regards the formation of the so-called Antarctic ozone hole, will be presented together with an outline as to how ab initio quantum chemistry can be used to further our understanding of stratospheric chemistry. The ability of modern state-of-the art ab initio quantum chemical techniques to characterize reliably the gas-phase molecular structure, vibrational spectrum, electronic spectrum, and thermal stability of fluorine, chlorine, bromine and nitrogen oxide species will be demonstrated by presentation of some example studies. The ab initio results will be shown to be in excellent agreement with the available experimental data, and where the experimental data are either not known or are inconclusive, the theoretical results are shown to fill in the gaps and to resolve experimental controversies. In addition, ab initio studies in which the electronic spectra and the characterization of excited electronic states of halogen oxide species will also be presented. Again where available, the ab initio results are compared to experimental observations, and are used to aid in the interpretation of experimental studies.
High Throughput Ab initio Modeling of Charge Transport for Bio-Molecular-Electronics
Bruque, Nicolas A.
2009-01-01
Self-assembled nanostructures, composed of inorganic and organic materials, have multiple applications in the fields of engineering and nanotechnology. Experimental research using nanoscaled materials, such as semiconductor/metallic nanocrystals, nanowires (NW), and carbon nanotube (CNT)-molecular systems have potential applications in next generation nano electronic devices. Many of these molecular systems exhibit electronic device functionality. However, experimental analytical techniques t...
The new Resonating Valence Bond Method for ab-initio Electronic Simulations
Sorella, Sandro
2013-01-01
The Resonating Valence Bond theory of the chemical bond was introduced soon after the discovery of quantum mechanics and has contributed to explain the role of electron correlation within a particularly simple and intuitive approach where the chemical bond between two nearby atoms is described by one or more singlet electron pairs. In this chapter Pauling's resonating valence bond theory of the chemical bond is revisited within a new formulation, introduced by P.W. Anderson after the discovery of High-Tc superconductivity. It is shown that this intuitive picture of electron correlation becomes now practical and efficient, since it allows us to faithfully exploit the locality of the electron correlation, and to describe several new phases of matter, such as Mott insulators, High-Tc superconductors, and spin liquid phases.
Acceleration Schemes for Ab-Initio Molecular Dynamics and Electronic Structure Calculations
Tassone, Francesco; Mauri, Francesco; Car, Roberto
1994-01-01
We study the convergence and the stability of fictitious dynamical methods for electrons. First, we show that a particular damped second-order dynamics has a much faster rate of convergence to the ground-state than first-order steepest descent algorithms while retaining their numerical cost per time step. Our damped dynamics has efficiency comparable to that of conjugate gradient methods in typical electronic minimization problems. Then, we analyse the factors that limit the size of the integ...
Maurer, Reinhard J.; Askerka, Mikhail; Batista, Victor S.; Tully, John C.
2016-09-01
Molecular adsorbates on metal surfaces exchange energy with substrate phonons and low-lying electron-hole pair excitations. In the limit of weak coupling, electron-hole pair excitations can be seen as exerting frictional forces on adsorbates that enhance energy transfer and facilitate vibrational relaxation or hot-electron-mediated chemistry. We have recently reported on the relevance of tensorial properties of electronic friction [M. Askerka et al., Phys. Rev. Lett. 116, 217601 (2016), 10.1103/PhysRevLett.116.217601] in dynamics at surfaces. Here we present the underlying implementation of tensorial electronic friction based on Kohn-Sham density functional theory for condensed phase and cluster systems. Using local atomic-orbital basis sets, we calculate nonadiabatic coupling matrix elements and evaluate the full electronic friction tensor in the Markov limit. Our approach is numerically stable and robust, as shown by a detailed convergence analysis. We furthermore benchmark the accuracy of our approach by calculation of vibrational relaxation rates and lifetimes for a number of diatomic molecules at metal surfaces. We find friction-induced mode-coupling between neighboring CO adsorbates on Cu(100) in a c (2 ×2 ) overlayer to be important for understanding experimental findings.
Electronic, vibrational and related properties of group IV metal oxides by ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Leite Alves, H.W. [Departamento de Ciencias Naturais, Universidade Federal de Sao Joao del Rei, C.P. 110, Sao Joao del Rei, MG 36301-160 (Brazil)], E-mail: hwlalves@ufsj.edu.br; Silva, C.C. [Departamento de Ciencias Naturais, Universidade Federal de Sao Joao del Rei, C.P. 110, Sao Joao del Rei, MG 36301-160 (Brazil); Lino, A.T. [Departamento de Fisica, Universidade Federal de Uberlandia, C.P. 593, Uberlandia, MG 38400-902 (Brazil); Borges, P.D. [Departamento de Engenharia de Telecomunicacoes, Uniao Educacional de Minas Gerais, Uberlandia, MG 38411-113 (Brazil); Scolfaro, L.M.R. [Instituto de Fisica, Universidade de Sao Paulo, C.P. 66318, Sao Paulo, SP 05315-970 (Brazil); Silva, E.F. da [Departamento de Fisica, Universidade Federal de Pernambuco, Cidade Universitaria, Recife, PE 50670-901 (Brazil)
2008-11-30
We present our theoretical results for the structural, electronic, vibrational and optical properties of MO{sub 2} (M = Sn, Zr, Hf and Ti) obtained by first-principles calculations. Relativistic effects are demonstrated to be important for a realistic description of the detailed structure of the electronic frequency-dependent dielectric function, as well as of the carrier effective masses. Based on our results, we found that the main contribution of the high values calculated for the oxides dielectric constants arises from the vibrational properties of these oxides, and the vibrational static dielectric constant values diminish with increasing pressure.
Goumri-Said, Souraya
2010-08-01
In this Letter we investigate the electronic properties of the bulk and the nanofilm BeO in wurtzite structure. We performed a first-principles pseudo-potential method within the generalized gradient approximation. We will give more importance to the changes in band structure and density of states between the bulk structure and its derived nanofilms. The bonding characterization will be investigated via the analysis Mulliken population and charge density contours. It is found that the nanofilm retains the same properties as its bulk structure with slight changes in electronic properties and band structure which may offer some unusual transport properties. © 2010 Elsevier B.V. All rights reserved.
Ab initio calculations on collisions of low energy electrons with polyatomic molecules
Energy Technology Data Exchange (ETDEWEB)
Rescigno, T.N.
1991-08-01
The Kohn variational method is one of simplest, and oldest, techniques for performing scattering calculations. Nevertheless, a number of formal problems, as well as practical difficulties associated with the computation of certain required matrix elements, delayed its application to electron--molecule scattering problems for many years. This paper will describe the recent theoretical and computational developments that have made the complex'' Kohn variational method a practical tool for carrying out calculations of low energy electron--molecule scattering. Recent calculations on a number of target molecules will also be summarized. 41 refs., 7 figs.
Aryal, Sita Ram
The alumino-silicate solid solution series (Al 4+2xSi2-2 xO10-x) is an important class of ceramics. Except for the end member (x=0), Al2 SiO5 the crystal structures of the other phases, called mullite, have partially occupied sites. Stoichiometric supercell models for the four mullite phases 3Al2O 3 · 2SiO2 · 2Al 2O3 · SiO2, 4 Al2O3· SiO 2, 9Al2O3 · SiO2, and iota-Al2 O3 (iota-alumina) are constructed starting from experimentally reported crystal structures. A large number of models were built for each phase and relaxed using the Vienna ab initio simulation package (VASP) program. The model with the lowest total energy for a given x was chosen as the representative structure for that phase. Electronic structure and mechanical properties of mullite phases were studied via first-principles calculations. Of the various phases of transition alumina, iota-Al 2O3 is the least well known. In addition structural details have not, until now, been available. It is the end member of the aluminosilicate solid solution series with x=1. Based on a high alumina content mullite phase, a structural model for iota- Al2O3 is constructed. The simulated x-ray diffraction (XRD) pattern of this model agrees well with a measured XRD pattern. The iota-Al2 O3 is a highly disordered ultra-low-density phase of alumina with a theoretical density of 2854kg/m3. Using this theoretically constructed model, elastic, thermodynamic, electronic, and spectroscopic properties of iota-Al2 O3 have been calculated and compared it with those of alpha- Al2O3 and gamma- Al2O3. Boron carbide (B4C) undergoes an amorphization under high velocity impacts. The mechanism of amorphization is not clear. Ab initio methods are used to carry out large-scale uniaxial compression simulations on two polytypes of stoichiometric boron carbide (B4C), B 11C-CBC, and B12- CCC where B11C or B12 is the 12-atom icosahedron and CBC or CCC is the three-atom chain. The simulations were performed on large supercells of 180 atoms
Ab initio investigation of the electronic properties of HgmTen clusters
Nanavati, Sachin; Kumar, Vijay; Pandey, Ravindra; Dixit, Ambesh
2014-03-01
Nanostructured HgTe quantum dots have attracted attention due to their potential applications in novel mid-infrared (3 - 5 μm) wavelength photodetectors and other optoelectronic applications. HgTe bulk material is a semimetal with bandgap ~ -0.3 eV, however at nanoscale, we observe drastic changes in the optical and electronic properties such as band gap opening, that makes it possible for engineering optoelectronic properties. We investigated the structural, optical, and electronic properties of HgmTen (m = n = 12, 13, 33, and 34) nanoparticles using density functional theory and the pseudopotential method within the generalized gradient approximation. The structures are relaxed to achieve the stable configurations and corresponding electronic properties are calculated. We investigated the density of states, energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), binding energy, and the Hg-Te bond length variation as a function of the cluster size. We will discuss the changes in the electronic structure and optical properties for these clusters with respect to the cluster size variation. The authors would like to thank C-DAC, Pune, India for the computational resources and MHRD, Gov. of India for financial support.
Elastic, Electronic, Optical and Thermal Properties of Na2Po: An Ab Initio Study
Baki, N.; Eithiraj, R. D.; Khachai, H.; Khenata, R.; Murtaza, G.; Bouhemadou, A.; Seddik, T.; Bin-Omran, S.
2016-01-01
The structural, elastic, electronic, optical and thermodynamic properties of the sodium polonide Na2Po compound have been studied through the full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) and tight-binding linear muffin-tin orbital (TB-LMTO) methods. The exchange-correlation potential was treated within the local density approximation for the TB-LMTO calculations and within the generalized gradient approximation for the FP-LAPW + lo calculations. In addition, Tran and Blaha-modified Becke-Johnson (TB-mBJ) potential and Engel-Vosko generalized gradient approximation were used for the electronic and optical properties. Ground state properties such as the equilibrium lattice constant, bulk modulus and its pressure derivative were calculated and compared with available data. The single-crystal and polycrystalline elastic constants of the considered compound were calculated via the total energy versus strain in the framework of the FP-LAPW + lo approach. The calculated electronic structure reveals that Na2Po is a direct band gap semiconductor. The frequency-dependent dielectric function, refractive index, extinction coefficient, reflectivity coefficient and electron energy loss function spectra are calculated for a wide energy range. The variations of the lattice constant, bulk modulus, heat capacity, volume expansion coefficient and Debye temperature with temperature and pressure were calculated successfully using the FP-LAPW + lo method in combination with the quasi-harmonic Debye model.
Ab initio theory of the electronic structure of nf-ions in solids and liquids
International Nuclear Information System (INIS)
Full text: In the books and papers we developed the self-consistent field theory of nl- ions in Me+n:[L]k- clusters, where k is number of ligands - L, by ion-ligands distance - R. The results which were obtained for all RE and AC ions for Me+n:[L]k, where L- F-, O-2 and so on ligands, are closely corresponded to experimental data. The expression for energy of the cluster may be write as: E = E0 + kE1 + k'(Ez + Ec + Ee + Eex), (Eq.1), where E0 and E1 are the energies of the free nl-ion and surrounding one; Ez , Ec and Ee are the energy of electrons interaction with 'strange' nucleus, Coulomb electron-electron interaction and exchange one. Eex is the energy of the interaction of electrons and nucleus with external field. The equations for the radial one-electron wave functions of the ions in the cluster were obtained by minimizing the Eq. 1 for the radial orbitals of the central ion and ligand one. We have received the general system of equations of the self-consistent field for cluster in liquids and solid states. The results of calculations of the energy structure of clusters and values of the standard radial integrals (spectroscopy parameters) for Ac-ions in 1-2-3 superconductors and RE-ions in garnet crystals by different values of R are qualitatively and quantitatively correct. We've got the best results for pressure dependence of Nd ions spectra, change of optical and X-Ray spectra after irradiation of garnets. We explained the nature of anomalous in SrTiO3 and separate lasers crystals by used of results of the calculations. In the framework of our approach we obtained the best accuracy for the energy of X- Ray lines for all nf- ions in solids and liquids
Ab-initio computations of electronic and transport properties of wurtzite aluminum nitride (w-AlN)
Energy Technology Data Exchange (ETDEWEB)
Nwigboji, Ifeanyi H.; Ejembi, John I.; Malozovsky, Yuriy; Khamala, Bethuel; Franklin, Lashounda; Zhao, Guanglin [Department of Physics, Southern University and A& M College, Baton Rouge, LA 70813 (United States); Ekuma, Chinedu E. [Department of Physics & Astronomy and Center for Computation and Technology, Louisiana State University, Baton Rouge, LA 70803 (United States); Bagayoko, Diola, E-mail: bagayoko@aol.com [Department of Physics, Southern University and A& M College, Baton Rouge, LA 70813 (United States)
2015-05-01
We report findings from several ab-initio, self-consistent calculations of electronic and transport properties of wurtzite aluminum nitride (w-AlN). Our calculations utilized a local density approximation (LDA) potential and the linear combination of Gaussian orbitals (LCGO). Unlike some other density functional theory (DFT) calculations, we employed the Bagayoko, Zhao, and Williams' method, enhanced by Ekuma and Franklin (BZW-EF). The BZW-EF method verifiably leads to the minima of the occupied energies; these minima, the low laying unoccupied energies, and related wave functions provide the most variationally and physically valid density functional theory (DFT) description of the ground states of materials under study. With multiple oxidation states of Al (Al{sup 3+} to Al) and the availability of N{sup 3−} to N, the BZW-EF method required several sets of self-consistent calculations with different ionic species as input. The binding energy for (Al{sup 3+}& N{sup 3−)} as input was 1.5 eV larger in magnitude than those for other input choices; the results discussed here are those from the calculation that led to the absolute minima of the occupied energies with this input. Our calculated, direct band gap for w-AlN, at the Γ point, is 6.28 eV, in excellent agreement with the 6.28 eV experimental value at 5K. We discuss the bands, total and partial densities of states, and calculated, effective masses. - Highlights: • LDA BZW-EF calculated band gap of w-AlN agrees well with experiment. • Features (widths & others) of the valence bands of w-AlN agree with experiment. • BZW-EF strictly adheres to the intrinsic requirements of DFT (and of LDA). • This adherence is the reason it outperforms DFT calculations not using it.
Ab initio investigation of the structural and electronic properties of amorphous HgTe
International Nuclear Information System (INIS)
We present the structure and electronic properties of amorphous mercury telluride obtained from first-principle calculations. The initial configuration of amorphous mercury telluride is created by computation alchemy. According to different exchange–correlation functions in our calculations, we establish two 256-atom models. The topology of both models is analyzed in terms of radial and bond angle distributions. It is found that both the Te and the Hg atoms tend to be fourfold, but with a wrong bond rate of about 10%. The fraction of threefold and fivefold atoms also shows that there are a significant number of dangling and floating bonds in our models. The electronic properties are also obtained. It is indicated that there is a bandgap in amorphous HgTe, in contrast to the zero bandgap for crystalline HgTe. The structures of the band tail and defect states are also discussed. (paper)
Ab-initio study of electronic structure and elastic properties of ZrC
Mund, H. S.; Ahuja, B. L.
2016-05-01
The electronic and elastic properties of ZrC have been investigated using the linear combination of atomic orbitals method within the framework of density functional theory. Different exchange-correlation functionals are taken into account within generalized gradient approximation. We have computed energy bands, density of states, elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, lattice parameters and pressure derivative of the bulk modulus by calculating ground state energy of the rock salt structure type ZrC.
Konstantin P. Katin; Shostachenko, Stanislav A.; Avkhadieva, Alina I.; Mikhail M. Maslov
2015-01-01
We report geometry, energy, and some electronic properties of [n,4]- and [n,5]prismanes (polyprismanes): a special type of carbon nanotubes constructed from dehydrogenated cycloalkane C4- and C5-rings, respectively. Binding energies, interatomic bonds, and the energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) have been calculated using density functional approach and nonorthogonal tight-binding model for the systems up to thir...
Ab initio studies of electronic and structural transitions in low-Z liquids under extreme conditions
Bonev, Stanimir
2007-06-01
The liquids of group I elements (H, Li, Na, and K) are studied using first principles theory. It will be shown that they undergo electronic and structural transitions analogous to that observed in their solids, but commencing at much lower pressure in the presence of disorder. These changes result in exotic melting behavior and in molten phases with unusual properties. The theoretical predictions will be compared with experimental data and ways for further experimental verification of the theoretical results will be suggested.
Ab-initio calculations of electronic structure and optical properties of TiAl alloy
Energy Technology Data Exchange (ETDEWEB)
Hussain, Altaf [Department of Physics, The Islamia University of Bahawalpur, Bahawalpur 63120 (Pakistan); Sikandar Hayat, Sardar, E-mail: sikandariub@yahoo.co [Department of Physics, Hazara University, Mansehra 21300 (Pakistan); Choudhry, M.A. [Department of Physics, The Islamia University of Bahawalpur, Bahawalpur 63120 (Pakistan)
2011-05-01
The electronic structures and optical properties of TiAl intermetallic alloy system are studied by the first-principle orthogonalized linear combination of atomic orbitals method. Results on the band structure, total and partial density of states, localization index, effective atomic charges, and optical conductivity are presented and discussed in detail. Total density of states spectra reveal that (near the Fermi level) the majority of the contribution is from Ti-3d states. The effective charge calculations show an average charge transfer of 0.52 electrons from Ti to Al in primitive cell calculations of TiAl alloy. On the other hand, calculations using supercell approach reveal an average charge transfer of 0.48 electrons from Ti to Al. The localization index calculations, of primitive cell as well as of supercell, show the presence of relatively localized states even above the Fermi level for this alloy. The calculated optical conductivity spectra of TiAl alloy are rich in structures, showing the highest peak at 5.73 eV for supercell calculations. Calculations of the imaginary part of the linear dielectric function show a prominent peak at 5.71 eV and a plateau in the range 1.1-3.5 eV.
Ab-initio Calculations of Electronic Properties of Calcium Fluoride (CaF2)
Bohara, Bir; Franklin, Lashounda; Malozovsky, Yuriy; Bagayoko, Diola
We have performed first principle, local density approximation (LDA) calculations of electronic and related properties of cubic calcium fluorite (CaF2) . Our non-relativistic computations employed the Ceperley and Alder LDA potential and the linear combination of atomic orbitals (LCAO) formalism. The implementation of the LCAO formalism followed the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). We discuss the electronic energy bands, including the large band gap, total and partial density of states, electron and hole effective masses, and the bulk modulus. Our calculated, indirect (X- Γ) band gap is 12.98 eV; it is 1 eV above an experimental value of 11.8 eV. The calculated bulk modulus (82.89 GPA) is excellent agreement with the experimental result of 82.0 +/-0.7. Our predicted equilibrium lattice constant is 5.42Å. Acknowledgments: This work is funded in part by the National Science Foundation (NSF) and the Louisiana Board of Regents, through LASiGMA [Award Nos. EPS- 1003897, NSF (2010-15)-RII-SUBR], and NSF HRD-1002541, the US Department of Energy, National, Nuclear Security Administration (NNSA) (Award No. DE-NA-0002630), LaSPACE, and LONI-SUBR.
Extensive ab initio study of the electronic states of BSe radical including spin-orbit coupling
Liu, Siyuan; Zhai, Hongsheng; Liu, Yufang
2016-06-01
The internally contracted multi-reference configuration interaction method (MRCI) with Davidson modification and the Douglas-Kroll scalar relativistic correction has been used to calculate the BSe molecule at the level of aug-cc-pV5Z basis set. The calculated electronic states, including 9 doublet and 6 quartet Λ-S states, are correlated to the dissociation limit of B(2Pu) + Se(3Pg) and B(2Pu) + Se(1Dg). The Spin-orbit coupling (SOC) interaction is taken into account via the state interaction approach with the full Breit-Pauli Hamiltonian operator, which causes the entire 15 Λ-S states to split into 32 Ω states. This is the first time that the spin-orbit coupling calculation has been carried out on BSe. The potential energy curves of the Λ-S and Ω electronic states are depicted with the aid of the avoided crossing rule between electronic states of the same symmetry. The spectroscopic constants of the bound Λ-S and Ω states were determined, which are in good agreement with the experimental data. The transition dipole moments (TDMs) and the Franck-Condon factors (FCs) of the transitions from the low-lying bound Ω states A2Π(I)3/2, B2Π(I)1/2 and C2Δ(I)3/2 to the ground state X2Σ+1/2 have also been presented. Based on the previous calculations, the radiative lifetimes of the A2Π(I)3/2, B2Π(I)1/2 and C2Δ(I)3/2 were evaluated.
Ab initio study of the structural, electronic and optical properties of ZnTe compound
Energy Technology Data Exchange (ETDEWEB)
Bahloul, B. [Material Physics Laboratory, Faculty of Physical Sciences, USTHB, 16000 Algiers (Algeria); LCVRN laboratory, University of Bordj Bou-Arreridj, 34000 (Algeria); Deghfel, B., E-mail: b-deghfel@yahoo.fr [Physics Department, Faculty of Sciences, University of M’sila, 28000 M’Sila (Algeria); Amirouche, L.; Bounab, S. [Theoretical Physics Laboratory, Faculty of Physical Sciences, USTHB, 16000 Algiers (Algeria); Bentabet, A. [LCVRN laboratory, University of Bordj Bou-Arreridj, 34000 (Algeria); Bouhadda, Y. [Unit of Applied Research in Renewable Energy, 47000 Ghardaïa (Algeria); Fenineche, N. [LERMPS, UTBM University, Belfort (France)
2015-03-30
Structural, electronic and optical properties of ZnTe compound were calculated using Density Functional Theory (DFT) based on the pseudopotentials and planewaves (PP-PW) method as implemented in the ABINIT computer code, where the exchange–correlation functional is approximated using the local density approximation (LDA) and the generalized gradient approximation (GGA). The obtained results from either LDA or GGa calculation for lattice parameter, energy band gap and optical parameters, such as the fundamental absorption edge, the peaks observed in the imaginary part of the dielectric function, the macroscopic dielectric constants and the optical dielectric constant, are compared with the available theoretical results and experimental data.
Electronic structure calculations of rare-earth intermetallic compound YAg using ab initio methods
Institute of Scientific and Technical Information of China (English)
(S).U(g)ur; G.U(g)ur; F.Soyalp; R.Ellialtio(g)lu
2009-01-01
The structural,elastic and electronic properties of YAg-B2(CsC1) were investigated using the first-principles calculations.The energy band structure and the density of states were studied in detail,including partial density of states (PDOS),in order to identify the character of each band.The structural parameters (lattice constant,bulk modulus,pressure derivative of bulk modulus) and elastic constants were also obtained.The results were consistent with the experimental data available in the literature,as well as other theoretical results.
International Nuclear Information System (INIS)
The theoretical quantitative understanding of time-resolved processes of coherent excitation and decay in polyelectronic atoms, induced by hypershort electromagnetic pulses, is a prerequisite for their possible control. We review key elements of an approach to the ab initio determination of perturbative as well as of nonperturbative solutions of the time-dependent Schroedinger equation describing such processes. The essential element of this approach is the development of formalism and methods that utilize physically relevant state-specific wavefunctions of stationary states of the discrete and the continuous spectrum
Schiffmann, Florian; VandeVondele, Joost
2015-06-01
We present an improved preconditioning scheme for electronic structure calculations based on the orbital transformation method. First, a preconditioner is developed which includes information from the full Kohn-Sham matrix but avoids computationally demanding diagonalisation steps in its construction. This reduces the computational cost of its construction, eliminating a bottleneck in large scale simulations, while maintaining rapid convergence. In addition, a modified form of Hotelling's iterative inversion is introduced to replace the exact inversion of the preconditioner matrix. This method is highly effective during molecular dynamics (MD), as the solution obtained in earlier MD steps is a suitable initial guess. Filtering small elements during sparse matrix multiplication leads to linear scaling inversion, while retaining robustness, already for relatively small systems. For system sizes ranging from a few hundred to a few thousand atoms, which are typical for many practical applications, the improvements to the algorithm lead to a 2-5 fold speedup per MD step.
Ab initio investigation of the electronic structure and the magnetic trends within equiatomic FeN
Houari, A.; Matar, S. F.; Belkhir, M. A.
2007-05-01
The magnetic properties of equiatomic FeN nitride have been investigated within the density functional theory (DFT) using the augmented spherical wave method (ASW). Calculation of the energy versus volume in hypothetic rocksalt (RS), zinc-blende (ZB) and wurtzite (W) types structures show that the RS-type structure is preferred. At equilibrium, energy/volume spin polarized calculations indicate that the ground state of RS-FeN is ferromagnetic with a high moment, while ZB-FeN and W-FeN are non magnetic. The magnetovolume effects with respect to the Slater-Pauling-Friedel model are discussed. Analyses of the electronic structure (density of states and chemical bonding) are reported. A discussion of the structural and magnetic properties of FeN compound is given with respect to N local environment of Fe.
Ab initio calculations of electronic structure of anatase TiO2
Institute of Scientific and Technical Information of China (English)
Chen Qiang; Cao Hong-Hong
2004-01-01
This paper presents the results of the self-consistent calculations on the electronic structure of anatase phase of TiO2. The calculations were performed using the full potential-linearized augmented plane wave method (FP-LAPW)in the framework of the density functional theory (DFT) with the generalized gradient approximation (GGA). The fully optimized structure, obtained by minimizing the total energy and atomic forces, is in good agreement with experiment.We also calculated the band structure and the density of states. In particular, the calculated band structure prefers an indirect transition between wlence and conduction bands of anatase TiO2, which may be helpful for clarifying the ambiguity in other theoretical works.
Kafka, Graeme R; Masters, Sarah L; Rankin, David W H
2007-07-01
A new method of incorporating ab initio theoretical data dynamically into the gas-phase electron diffraction (GED) refinement process has been developed to aid the structure determination of large, sterically crowded molecules. This process involves calculating a set of differences between parameters that define the positions of peripheral atoms (usually hydrogen), as determined using molecular mechanics (MM), and those which use ab initio methods. The peripheral-atom positions are then updated continually during the GED refinement process, using MM, and the returned positions are modified using this set of differences to account for the differences between ab initio and MM methods, before being scaled back to the average parameters used to define them, as refined from experimental data. This allows the molecule to adopt a completely asymmetric structure if required, without being constrained by the MM parametrization, whereas the calculations can be performed on a practical time scale. The molecular structures of tri-tert-butylphosphine oxide and tri-tert-butylphosphine imide have been re-examined using this new technique, which we call SEMTEX (Structure Enhancement Methodology using Theory and EXperiment).
Ab initio approach to structural, electronic, and ferroelectric properties of antimony sulphoiodide
Amoroso, Danila; Picozzi, Silvia
2016-06-01
By means of first-principles calculations for the SbSI semiconductor, we show that bare density functional theory fails to reproduce the experimentally observed ferroelectric phase, whereas a more advanced approach, based on hybrid functionals, correctly works. When comparing the paraelectric and ferroelectric phases, our results show polar displacements along the c direction of the Sb and S sublattices with respect to the iodine framework, leading to a predicted spontaneous polarization of P ≃20 μ C/cm2 , in good agreement with experiments. In the ferroelectric phase, the semiconducting behavior of SbSI is confirmed by relatively large values for the indirect and direct gaps (≃2.15 eV and 2.3 eV , respectively). An analysis of the electronic structure, in terms of density of states, charge density distribution, and anomalies in the Born effective charges, reveals (i) the clear presence of a Sb(III) lone pair and (ii) a large covalency in the SbSI bonding, based on the hybridization between Sb and S ions, in turn more ionically bonded to iodine anions. Finally, the interplay between ferroelectricity and spin-orbit coupling reveals a coexistence of Dresselhaus and Rashba relativistic effects and a spin texture that can be reversed by switching the polarization, of potential appeal in electrically controlled spintronics.
An ab initio investigation of the low-lying electronic states of BeH
Institute of Scientific and Technical Information of China (English)
Dong Yan-Ran; Zhang Shu-Dong; Hou Sheng-Wei; Cheng Qi-Yuan
2012-01-01
Potential energy curves (PECs) for the ground state (X2Σ+) and the four excited electronic states (A2Π,B2Π,C2Σ+,41Π) of a BeH molecule are calculated using the multi-configuration reference single and double excited configuration interaction (MRCI) approach in combination with the aug-cc-pVTZ basis sets.The calculation covers the internuclear distance ranging from 0.07 nm to 0.70 nm,and the equilibrium bond length Re and the vertical excited energy Te are determined directly.It is evident that the X2Σ+,A2Π,B2Π,C2Σ+ states are bound and 4Π is a repulsive excited state.With the potentials,all of the vibrational levels and inertial rotation constants are predicted when the rotational quantum number J is set to be equal to zero (J =0) by numerically solving the radial Schr(o)dinger equation of nuclear motion.Then the spectroscopic data are obtained including the rotation coupling constant ωe,the anharmonic constant ωexe,the equilibrium rotation constant Be,and the vibration-rotation coupling constant α e.These values are compared with the theoretical and experimental results currently available,showing that they are in agreement with each other.
Ab initio study of long-range electron transfer between biphenyl anion radical and naphthalene
Institute of Scientific and Technical Information of China (English)
李象远; 肖顺清; 何福城
1999-01-01
After the separation of the donor, the aeceptor, and the σ-type bridge from the π-σ-π system, the geometries of biphenyl, biphenyl anion radical, naphthalene, and naphthalene anion radical are optimized, and then the reorganization energy for the intermolecular electron transfer （ET） at the levels of HF/4-31G and HF/DZP is calculated. The ET matrix elements of the self-exchange reactions of the π-σ-π systems have been calculated by means of both the direct calculation based on the variational principle, and the transition energy between the molecular orbitals at the linear coordinate R=0.5. For the cross reactions, the ET matrix element and the geometry of the transition state are determined by searching the minimum energy splitting △min along the reaction coordinate. In the evaluation of the solvent reorganization energy of the ET in solution, the Marcus’ two-sphere model has been invoked. A few of ET rate constants for the intramolecular ET reactions for the π-σ-π systems, which contain
Kinetic Formulation of the Kohn-Sham Equations for ab initio Electronic Structure Calculations
Mendoza, M; Herrmann, H J
2013-01-01
We introduce a new approach to density functional theory based on kinetic theory, showing that the Kohn-Sham equations can be derived as a macroscopic limit of a suitable Boltzmann kinetic equation in the limit of small mean free path versus the typical scale of density gradients (Chapman-Enskog expansion). To derive the approach, we first write the Schr\\"odinger equation as a special case of a Boltzmann equation for a gas of quasi-particles, with the potential playing the role of an external source that generates and destroys particles, so as to drive the system towards the ground state. The ions are treated as classical particles, using the Born-Oppenheimer dynamics, or by imposing concurrent evolution with the electronic orbitals. In order to provide quantitative support to our approach, we implement a discrete (lattice) model and compute, the exchange and correlation energies of simple atoms, and the geometrical configuration of the methane molecule. Excellent agreement with values in the literature is fo...
Kong, Bo; Zhang, Yachao
2016-07-01
The electronic structures of the cubic GdH3 are extensively investigated using the ab initio many-body GW calculations treating the Gd 4f electrons either in the core (4f-core) or in the valence states (4f-val). Different degrees of quasiparticle (QP) self-consistent calculations with the different starting points are used to correct the failures of the GGA/GGA + U/HSE03 calculations. In the 4f-core case, GGA + G0W0 calculations give a fundamental band gap of 1.72 eV, while GGA+ GW0 or GGA + GW calculations present a larger band gap. In the 4f-val case, the nonlocal exchange-correlation (xc) functional HSE03 can account much better for the strong localization of the 4f states than the semilocal or Hubbard U corrected xc functional in the Kohn-Sham equation. We show that the fundamental gap of the antiferromagnetic (AFM) or ferromagnetic (FM) GdH3 can be opened up by solving the QP equation with improved starting point of eigenvalues and wave functions given by HSE03. The HSE03 + G0W0 calculations present a fundamental band gap of 2.73 eV in the AFM configuration, and the results of the corresponding GW0 and GW calculations are 2.89 and 3.03 eV, respectively. In general, for the cubic structure, the fundamental gap from G0W0 calculations in the 4f-core case is the closest to the real result. By G0W0 calculations in the 4f-core case, we find that H or Gd defects can strongly affect the band structure, especially the H defects. We explain the mechanism in terms of the possible electron correlation on the hydrogen site. Under compression, the insulator-to-metal transition in the cubic GdH3 occurs around 40 GPa, which might be a satisfied prediction.
Ab Initio Study of the Electron Transfer in an Ionized Stacked Complex of Guanines
Cauët, Emilie; Liévin, Jacques
2009-08-01
The charge transfer process in an ionized stacking of two consecutive guanines (G5'G3')+ has been studied by means of state-averaged CASSCF/MRCI and RASSCF/RASPT2 calculations. The ground and two first excited states of the radical cation have been characterized, and the topology of the corresponding potential energy surfaces (PESs) has been studied as a function of all intermolecular geometrical parameters. The results demonstrate that the charge transfer process in (G5'G3')+ is governed by the avoiding crossing between the ground and first excited states of the complex. Relative translation motions of both guanines in their molecular planes are shown to lead to the charge migration between G5' and G3'. Five stationary points (three minima and two saddle points) have been characterized along the reaction path describing the passage of the positive charge from G5' to G3'. The global minimum on the PES is found to correspond to the charge configuration G5'+G3'. The existence of an intermediate minimum along the reaction path has been established, characterizing a structure where the positive charge is equally distributed between the two guanines. The calculated energy profile allowed us to determine the height of the potential energy barrier (7.33 kcal/mol) and to evaluate the electronic coupling at a geometry close to the avoiding crossing (3.6 kcal/mol). Test calculations showed that the topology of the ground state PES of the complex GG+ is qualitatively conserved upon optimization of the intramolecular geometrical parameters of the stationary points.
Electronic Transport Properties of a Naphthopyran-Based Optical Molecular Switch:an ab initio Study
Institute of Scientific and Technical Information of China (English)
XIA Cai-Juan; LIU De-Sheng; ZHANG Ying-Tang
2011-01-01
The electronic transport properties of a. Naphthopyran-based molecular optical switch are investigated by using the nonequilibrium Green's Function formalism combined with first-principles density functional theory. The molecule that comprises the switch can convert between its open and closed forms upon photoexcitation. Theoretical results show that the current through the open form is significantly larger than that through the closed form, which is different from other optical switches based on ring-opening reactions of the molecular bridge. The maximum on-off ratio (about 90) can be obtained at 1.4 V. The physical origin of the switching behavior is interpreted based on the spatial distributions of molecular orbitals and the HOMO-LUMO gap. Our result shows that the naphthopyran-based molecule is a good candidate for optical molecular switches and will be useful in the near future.%@@ ronic transport properties of a naphthopyran-based molecular optical switch are investigated by using the nonequilibrium Green's function formalism combined with first-principles density functional theory.The molecule that comprises the switch can convert between its open and closed forms upon photoexcitation.Theoretical results show that the current through the open form is significantly larger than that through the closed form,which is different from other optical switches based on ring-opening reactions of the molecular bridge.The maximum on-off ratio(about 90)can be obtained at 1.4 V.The physical origin of the switching behavior is interpreted based on the spatial distributions of molecular orbitals and the HOMO-LUMO gap.Our result shows that the naphthopyran-based molecule is a good candidate for optical molecular switches and will be useful in the near future.
de Melo, Pedro Miguel M. C.; Marini, Andrea
2016-04-01
We present a full ab initio description of the coupled out-of-equilibrium dynamics of photons, phonons, and electrons. In the present approach, the quantized nature of the electromagnetic field as well as of the nuclear oscillations is fully taken into account. The result is a set of integrodifferential equations, written on the Keldysh contour, for the Green's functions of electrons, phonons, and photons where the different kinds of interactions are merged together. We then concentrate on the electronic dynamics in order to reduce the problem to a computationally feasible approach. By using the generalized Baym-Kadanoff ansatz and the completed collision approximation, we introduce a series of efficient but controllable approximations. In this way, we reduce all equations to a set of decoupled equations for the density matrix that describe all kinds of static and dynamical correlations. The final result is a coherent, general, and inclusive scheme to calculate several physical quantities: carrier dynamics, transient photoabsorption, and light emission, all of which include, at the same time, electron-electron, electron-phonon, and electron-photon interactions. We further discuss how all these observables can be easily calculated within the present scheme using a fully atomistic ab initio approach.
Bokarev, Sergey I; Suljoti, Edlira; Kühn, Oliver; Aziz, Emad F
2013-01-01
Non-radiative decay channels in the L-edge fluorescence spectra from transition metal-aqueous solutions give rise to spectral dips in X-ray transmission spectra. Their origin is unraveled here using partial and inverse partial fluorescence yields on the micro-jet combined with multi-reference ab initio electronic structure calculations. Comparing Fe2+, Fe3+, and Co2+ systems we demonstrate unequivocally that spectral dips are due to a state-dependent electron delocalization within the manifold of d-orbitals.
International Nuclear Information System (INIS)
Spinel indium sulphide exists in three phases. The tetragonal β-phase transforms to the cubic α-phase at 420 °C which further transforms to the trigonal γ-phase at 754 °C. Due to wide energy bandgap, the phases of indium sulphide have possibilities of applications in photo-electrochemical solar cell devices as a replacement of toxic CdS. The electronic, optical and transport properties of the three phases have therefore been investigated using full potential linear augmented plane wave (FP-LAPW) + local orbitals (lo) scheme, in the framework of density functional theory (DFT) with generalized gradient approximation (GGA) for the purpose of exchange-correlation energy functional. We present the structure, energy bands and density of states (DOS) for α-, β- and γ-phases. The partial density of states (PDOS) of β-In2S3 is in good agreement with experiment and earlier ab initio calculations. To obtain the fundamental characteristics of these phases we have analysed their linear optical properties such as the dynamic dielectric function in the energy range of 0–15 eV. From the dynamic dielectric function it is seen that there is no directional anisotropy for α-phase since the longitudinal and transverse components are almost identical, however the β and γ-phases show birefringence. The optical absorption profiles clearly indicate that β-phase has possibility of greater multiple direct and indirect interband transitions in the visible regions compared to the other phases. To study the existence of interesting thermoelectric properties, transport properties like electrical and thermal conductivities, Seebeck and Hall coefficients etc. are also calculated. Good agreements are found with the available experimental results. -- Highlights: ► The electronic properties of phases of In2S3 have been investigated. ► The phases exhibit luminescence properties due to vacancies in crystal structure. ► The phases of In2S3 have low thermal conductivity and high
Extensive ab initio study of the electronic states of S2 molecule including spin-orbit coupling
Xing, Wei; Shi, Deheng; Sun, Jinfeng; Liu, Hui; Zhu, Zunlue
2013-03-01
The potential energy curves (PECs) of 15 Λ-S states and 24 Ω states generated from the 13 Λ-S bound states of the S2 molecule are investigated in detail using an ab initio quantum chemical method. The PECs are calculated for internuclear separations from 0.12 to 1.10 nm by the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson modification (MRCI + Q). The spin-orbit (SO) coupling effect is accounted for by the Breit-Pauli Hamiltonian. To discuss the effect on the energy splitting by the core-electron correlations, the all-electron basis set, cc-pCVTZ with and without 2s2p correlations, is used for the SO coupling calculations of the A3 ? and B‧3Πg Λ-S states since their measurements can be found in the literature. By comparison, the cc-pCVTZ basis set with 2s2p correlations is chosen for the SO coupling calculations of 13 Λ-S bound states. To improve the quality of PECs, core-valence correlation and scalar relativistic corrections are included. Scalar relativistic correction calculations are made using the third-order Douglas-Kroll Hamiltonian (DKH3) approximation at the level of a cc-pV5Z basis set. Core-valence correlation corrections are taken into account with a cc-pCVTZ basis set. The spectroscopic parameters of 13 Λ-S bound states and 24 Ω states are calculated. With the PECs obtained by the MRCI + Q/aug-cc-pV6Z + CV + DK + SO calculations, the SO coupling splitting energies are 379.25 cm-1 between the A‧3 and A‧2 Ω state, 83.40 cm-1 between the A1 and A0- Ω state and 210.91 cm-1 between the B‧2 and B‧1 Ω state, which agree well with the corresponding measurements of 383, 77.51 and 209 cm-1, respectively. Moreover, other spectroscopic parameters are also in excellent agreement with the measurements. It demonstrates that the spectroscopic parameters of 24 Ω states reported here for the first time can be expected to be
Energy Technology Data Exchange (ETDEWEB)
Sharma, Yamini, E-mail: sharma.yamini62@gmail.com [Department of Physics, Feroze Gandhi College, Rae Bareli 229001, U.P. (India); Srivastava, Pankaj [Department of Physics, Feroze Gandhi College, Rae Bareli 229001, U.P. (India)
2012-08-15
Spinel indium sulphide exists in three phases. The tetragonal {beta}-phase transforms to the cubic {alpha}-phase at 420 Degree-Sign C which further transforms to the trigonal {gamma}-phase at 754 Degree-Sign C. Due to wide energy bandgap, the phases of indium sulphide have possibilities of applications in photo-electrochemical solar cell devices as a replacement of toxic CdS. The electronic, optical and transport properties of the three phases have therefore been investigated using full potential linear augmented plane wave (FP-LAPW) + local orbitals (lo) scheme, in the framework of density functional theory (DFT) with generalized gradient approximation (GGA) for the purpose of exchange-correlation energy functional. We present the structure, energy bands and density of states (DOS) for {alpha}-, {beta}- and {gamma}-phases. The partial density of states (PDOS) of {beta}-In{sub 2}S{sub 3} is in good agreement with experiment and earlier ab initio calculations. To obtain the fundamental characteristics of these phases we have analysed their linear optical properties such as the dynamic dielectric function in the energy range of 0-15 eV. From the dynamic dielectric function it is seen that there is no directional anisotropy for {alpha}-phase since the longitudinal and transverse components are almost identical, however the {beta} and {gamma}-phases show birefringence. The optical absorption profiles clearly indicate that {beta}-phase has possibility of greater multiple direct and indirect interband transitions in the visible regions compared to the other phases. To study the existence of interesting thermoelectric properties, transport properties like electrical and thermal conductivities, Seebeck and Hall coefficients etc. are also calculated. Good agreements are found with the available experimental results. -- Highlights: Black-Right-Pointing-Pointer The electronic properties of phases of In{sub 2}S{sub 3} have been investigated. Black-Right-Pointing-Pointer The
Ab initio molecular dynamics simulation of laser melting of silicon
Silvestrelli, P.-L.; Alavi, A.; Parrinello, M.; Frenkel, D.
1996-01-01
The method of ab initio molecular dynamics, based on finite temperature density functional theory, is used to simulate laser heating of crystal silicon. We have found that a high concentration of excited electrons dramatically weakens the covalent bond. As a result, the system undergoes a melting tr
Energy Technology Data Exchange (ETDEWEB)
Benrekia, A.R., E-mail: benrekia.ahmed@yahoo.com [Faculty of Science and Technology, University of Medea (Algeria); Benkhettou, N. [Laboratoire des Materiaux Magnetiques, Faculte des Sciences, Universite Djillali Liabes de Sidi Bel Abbes (Algeria); Nassour, A. [Laboratoire de Cristallographie, Resonance Magnetique et Modelisations (CRM2, UMR CNRS 7036) Institut Jean Barriol, Nancy Universite BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-les-Nancy (France); Driz, M. [Applied Material Laboratory (AML), Electronics Department, University of Sidi bel Abbes (DZ 22000) (Algeria); Sahnoun, M. [Laboratoire de Physique Quantique de la Matiere et Modelisations Mathematique (LPQ3M), Faculty of Science and Technology,University of Mascara (Algeria); Lebegue, S. [Laboratoire de Cristallographie, Resonance Magnetique et Modelisations (CRM2, UMR CNRS 7036) Institut Jean Barriol, Nancy Universite BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-les-Nancy (France)
2012-07-01
We present first-principles VASP calculations of the structural, electronic, vibrational, and optical properties of paraelectric SrTiO{sub 3} and KTaO{sub 3}. The ab initio calculations are performed in the framework of density functional theory with different exchange-correlation potentials. Our calculated lattice parameters, elastic constants, and vibrational frequencies are found to be in good agreement with the available experimental values. Then, the bandstructures are calculated with the GW approximation, and the corresponding band gap is used to obtain the optical properties of SrTiO{sub 3} and KTaO{sub 3}.
P-V Relation for Mercuric Calcogenides: Ab Initio Method
G. Misra; S. Tenguria; Gautam, M.
2011-01-01
Mercuric Calcogenides found many applications in electronic and optical devices as semiconducting materials. An equation of state provides useful information about the relationship between pressure (P), volume (V) and temperature (T) that helps to understand the behaviour of materials under the effect of high pressure and high temperature. The present paper sheds light on the electronic structure of Mercuric Calcogenides by simulating its electronic properties through ab initio method. This a...
Long, Run; Fang, Weihai; Prezhdo, Oleg V
2016-08-18
Experiments show both positive and negative changes in performance of hybrid organic-inorganic perovskite solar cells upon exposure to moisture. Ab initio nonadiabatic molecular dynamics reveals the influence of humidity on nonradiative electron-hole recombination. In small amounts, water molecules perturb perovskite surface and localize photoexcited electron close to the surface. Importantly, deep electron traps are avoided. The electron-hole overlap decreases, and the excited state lifetime increases. In large amounts, water forms stable hydrogen-bonded networks, has a higher barrier to enter perovskite, and produces little impact on charge localization. At the same time, by contributing high frequency polar vibrations, water molecules increase nonadiabatic coupling and accelerate recombination. In general, short coherence between electron and hole benefits photovoltaic response of the perovskites. The calculated recombination time scales show excellent agreement with experiment. The time-domain atomistic simulations reveal the microscopic effects of humidity on perovskite excited-state lifetimes and rationalize the conflicting experimental observations. PMID:27485025
Kornobis, Karina; Wong, Bryan M; Lodowski, Piotr; Jaworska, Maria; Andruniów, Tadeusz; Rudd, Kenneth; Kozlowski, Pawel M; 10.1021/jp110914y
2011-01-01
Time-dependent density functional theory (TD-DFT) and correlated ab initio methods have been applied to the electronically excited states of vitamin B12 (cyanocobalamin or CNCbl). Different experimental techniques have been used to probe the excited states of CNCbl, revealing many issues that remain poorly understood from an electronic structure point of view. Due to its efficient scaling with size, TD-DFT emerges as one of the most practical tools that can be used to predict the electronic properties of these fairly complex molecules. However, the description of excited states is strongly dependent on the type of functional used in the calculations. In the present contribution, the choice of a proper functional for vitamin B12 was evaluated in terms of its agreement with both experimental results and correlated ab initio calculations. Three different functionals, i.e. B3LYP, BP86, and LC-BLYP, were tested. In addition, the effect of relative contributions of DFT and HF to the exchange-correlation functional ...
Energy Technology Data Exchange (ETDEWEB)
Zemen, J., E-mail: zemen@fzu.cz [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Institute of Physics ASCR, v. v. i., Cukrovarnická 10, 162 00 Praha 6 (Czech Republic); Mašek, J. [Institute of Physics ASCR, v. v. i., Na Slovance 2, 182 21 Praha 8 (Czech Republic); Kučera, J. [Institute of Physics ASCR, v. v. i., Cukrovarnická 10, 162 00 Praha 6 (Czech Republic); Mol, J.A. [Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft (Netherlands); Institute of Physics ASCR, v. v. i., Cukrovarnická 10, 162 00 Praha 6 (Czech Republic); Motloch, P. [Institute of Physics ASCR, v. v. i., Cukrovarnická 10, 162 00 Praha 6 (Czech Republic); Jungwirth, T. [Institute of Physics ASCR, v. v. i., Cukrovarnická 10, 162 00 Praha 6 (Czech Republic); School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom)
2014-04-01
An empirical multiorbital (spd) tight binding (TB) model including magnetism and spin–orbit coupling is applied to calculations of magnetic anisotropy energy (MAE) in CoPt L1{sub 0} structure. A realistic Slater–Koster parametrisation for single-element transition metals is adapted for the ordered binary alloy. Spin magnetic moment and density of states are calculated using a full-potential linearised augmented plane-wave (LAPW) ab initio method and our TB code with different variants of the interatomic parameters. Detailed mutual comparison of this data allows for determination of a subset of the compound TB parameters tuning of which improves the agreement of the TB and LAPW results. MAE calculated as a function of band filling using the refined parameters is in broad agreement with ab initio data for all valence states and in quantitative agreement with ab initio and experimental data for the natural band filling. Our work provides a practical basis for further studies of relativistic magnetotransport anisotropies by means of local Green's function formalism which is directly compatible with our TB approach. - Highlights: • Calculations of electronic structure properties of bulk ordered CoPt alloy using tight-binding (TB) and density functional theory (DFT) approach. • Refinement of existing single-element TB parameters for a binary alloy based on a comparison of band structure and spin magnetic moment per atom to DFT results. • Quantitative agreement of magnetic anisotropy energy (MAE) obtained by TB and DFT on a range of band fillings. • Successful description of ground state spin–orbit coupling phenomena using an extended TB model suitable for subsequent magnetotransport simulations.
Molexpl: a tool for ab initio data exploration and visualization
Wang, Xueying; Onofrio, Nicolas,; Strachan, Alejandro
2015-01-01
Density functional theory (DFT) based on ab initio theory, is a powerful method to resolve the electronic structure of atoms, molecules and solids. However, in practical, DFT is limited to few hundreds of atoms. To overcome this limitation, researchers have developed empirical interatomic potentials implemented in molecular dynamics (MD) simulations. MD ignores the movements of electrons and describes bonding and non-bonding interaction as a function of the distance between atoms called force...
Ab initio calculation of tight-binding parameters
Energy Technology Data Exchange (ETDEWEB)
McMahan, A.K.; Klepeis, J.E.
1997-12-01
We calculate ab initio values of tight-binding parameters for the f- electron metal Ce and various phases of Si, from local-density functional one-electron Hamiltonian and overlap matrix elements. Our approach allows us to unambiguously test the validity of the common minimal basis and two-center approximations as well as to determine the degree of transferability of both nonorthogonal and orthogonal hopping parameters in the cases considered.
Ab initio mass tensor molecular dynamics
Tsuchida, Eiji
2010-01-01
Mass tensor molecular dynamics was first introduced by Bennett [J. Comput. Phys. 19, 267 (1975)] for efficient sampling of phase space through the use of generalized atomic masses. Here, we show how to apply this method to ab initio molecular dynamics simulations with minimal computational overhead. Test calculations on liquid water show a threefold reduction in computational effort without making the fixed geometry approximation. We also present a simple recipe for estimating the optimal ato...
Highly scalable Ab initio genomic motif identification
Marchand, Benoît
2011-01-01
We present results of scaling an ab initio motif family identification system, Dragon Motif Finder (DMF), to 65,536 processor cores of IBM Blue Gene/P. DMF seeks groups of mutually similar polynucleotide patterns within a set of genomic sequences and builds various motif families from them. Such information is of relevance to many problems in life sciences. Prior attempts to scale such ab initio motif-finding algorithms achieved limited success. We solve the scalability issues using a combination of mixed-mode MPI-OpenMP parallel programming, master-slave work assignment, multi-level workload distribution, multi-level MPI collectives, and serial optimizations. While the scalability of our algorithm was excellent (94% parallel efficiency on 65,536 cores relative to 256 cores on a modest-size problem), the final speedup with respect to the original serial code exceeded 250,000 when serial optimizations are included. This enabled us to carry out many large-scale ab initio motiffinding simulations in a few hours while the original serial code would have needed decades of execution time. Copyright 2011 ACM.
International Nuclear Information System (INIS)
The evolution of the microstructure of dilute Fe alloys under irradiation has been modelled using a multiscale approach based on ab initio and atomistic kinetic Monte Carlo simulations. In these simulations, both self interstitials and vacancies, isolated or in clusters, are considered. Isochronal annealing after electron irradiation experiments have been simulated in pure Fe, Fe-Cu and Fe-Mn dilute alloys, focusing on recovery stages I and II. The parameters regarding the self interstitial - solute atom interactions are based on ab initio predictions and some of these interactions have been slightly adjusted, without modifying the interaction character, on isochronal annealing experimental data. The different recovery peaks are globally well reproduced. These simulations allow interpreting the different recovery peaks as well as the effect of varying solute concentration. For some peaks, these simulations have allowed to revisit and re-interpret the experimental data. In Fe-Cu, the trapping of self interstitials by Cu atoms allows experimental results to be reproduced, although no mixed dumbbells are formed, contrary to the former interpretations. Whereas, in Fe-Mn, the favorable formation of mixed dumbbell plays an important role in the Mn effect.
Ab Initio Calculations of Oxosulfatovanadates
DEFF Research Database (Denmark)
Frøberg, Torben; Johansen, Helge
1996-01-01
Restricted Hartree-Fock and multi-configurational self-consistent-field calculations together with secondorder perturbation theory have been used to study the geometry, the electron density, and the electronicspectrum of (VO2SO4)-. A bidentate sulphate attachment to vanadium was found to be stable...... with anO-V-O angle of 72.5 degrees . The calculated spectrum shows bands in reasonable agreement with anexperimental spectrum which has been attributed to (VO2SO4)-. The geometry and the electron density fortwo binuclear vanadium complexes proposed as intermediates in the vanadium catalyzed SO2...
Ab initio potential for solids
DEFF Research Database (Denmark)
Chetty, N.; Stokbro, Kurt; Jacobsen, Karsten Wedel;
1992-01-01
A total-energy theory for a solid is presented. It is based on density-functional theory and consists of a succession of approximations. At the most accurate level, the theory consists of a systematic derivation of an ansatz for the electron density which is best suited for the Harris functional....
Energy Technology Data Exchange (ETDEWEB)
Jaiganesh, G., E-mail: jaiganesh@igcar.gov.in; Jaya, S. Mathi [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam - 603102 (India)
2015-06-24
The magnetism, structure and spin polarized electronic structure of Ti substituted MO (M = Mg, Ca, Sr) are studied using the ab-initio techniques within the framework of the density functional theory. Appropriately constructed supercell along with the full structural optimization of these cells is used for studying the influence of Ti substitution on the magnetism and electronic structure of these compounds. We find from our calculations that the Ti substituted MO compounds energetically favor magnetically ordered state. The Ti concentration is found to be important in deciding the magnetic order and we have observed antiferromagnetic order for the Ti concentration of 0.25. The Ti substituted MO compounds are thus an interesting class of materials that deserve further studies.
Wang, J Y
2003-01-01
The pressure dependences of the lattice parameters, electronic structure, and bonding properties of the layered ternary compound Ti sub 3 SiC sub 2 were investigated by performing ab initio plane-wave pseudopotential total energy calculations. The material exhibited elastic anisotropy. The lattice constants and axial ratio were studied for different pressures, and the same trend was obtained as is measured in experiment. It was found that although the structure was stable at high pressure, the electronic structure and atomic bonding were definitely affected. The electrical conductivity was predicted to reduce with pressure, which was interpreted by analysing the band dispersion curve and density of states at the Fermi level. The strengths of the atomic bonds in Ti sub 3 SiC sub 2 were considered by analysing the Mulliken population and by examining the bond length contraction for various pressures. A redistribution of charge density that accompanied high pressures was also revealed.
Accurate ab initio spin densities
Boguslawski, Katharina; Legeza, Örs; Reiher, Markus
2012-01-01
We present an approach for the calculation of spin density distributions for molecules that require very large active spaces for a qualitatively correct description of their electronic structure. Our approach is based on the density-matrix renormalization group (DMRG) algorithm to calculate the spin density matrix elements as basic quantity for the spatially resolved spin density distribution. The spin density matrix elements are directly determined from the second-quantized elementary operators optimized by the DMRG algorithm. As an analytic convergence criterion for the spin density distribution, we employ our recently developed sampling-reconstruction scheme [J. Chem. Phys. 2011, 134, 224101] to build an accurate complete-active-space configuration-interaction (CASCI) wave function from the optimized matrix product states. The spin density matrix elements can then also be determined as an expectation value employing the reconstructed wave function expansion. Furthermore, the explicit reconstruction of a CA...
Ab-initio calculations for dilute magnetic semiconductors
Belhadji, Brahim
2008-01-01
This thesis focusses on ab-initio calculations for the electronic structure and the magnetic properties of dilute magnetic semiconductors (DMS). In particular we aim at the understanding of the complex exchange interactions in these systems. Our calculations are based on density functional theory, being ideally suited for a description of the material specific properties of the considered DMS. Moreover we use the KKR Green function method in connection with the coherent potential approximatio...
Thermochemical data for CVD modeling from ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Ho, P. [Sandia National Labs., Albuquerque, NM (United States); Melius, C.F. [Sandia National Labs., Livermore, CA (United States)
1993-12-31
Ab initio electronic-structure calculations are combined with empirical bond-additivity corrections to yield thermochemical properties of gas-phase molecules. A self-consistent set of heats of formation for molecules in the Si-H, Si-H-Cl, Si-H-F, Si-N-H and Si-N-H-F systems is presented, along with preliminary values for some Si-O-C-H species.
Energy Technology Data Exchange (ETDEWEB)
Ramos de Debiaggi, S., E-mail: sbramos@yahoo.com [Facultad de Ingenieria, Universidad Nacional del Comahue, Buenos Aires 1400, (8300) Neuquen (Argentina); CONICET (Argentina); Cabeza, G.F. [CONICET (Argentina); Dpto. de Fisica, Universidad Nacional del Sur, Bahia Blanca (Argentina); Toro, C. Deluque [Facultad de Ingenieria, Universidad Nacional del Comahue, Buenos Aires 1400, (8300) Neuquen (Argentina); Monti, A.M. [CNEA e Instituto Sabato (Univ. Nac. de San Martin/CNEA), Centro Atomico Constituyentes, Avda. General Paz 1499, B1650KNA, San Martin, Buenos Aires (Argentina); Sommadossi, S. [Facultad de Ingenieria, Universidad Nacional del Comahue, Buenos Aires 1400, (8300) Neuquen (Argentina); CONICET (Argentina); Guillermet, A. Fernandez [CONICET (Argentina); Centro Atomico Bariloche e Instituto Balseiro, Avda. Bustillo 9500, (8400) Bariloche (Argentina)
2011-02-17
Research highlights: > Cu{sub 10}In{sub 7} and Cu{sub 11}In{sub 9} are thermodynamically stable with respect to elements at 0 K. > Cu{sub 10}In{sub 7} phase is more stable than the modelled Cu{sub 11}In{sub 9} compound by only 0.92 kJ/mol. > The present ab initio results reproduce very well the available structural data. > Similar DOS for both phases, the most prominent bonding band comes from Cu-d states. > Enhanced relative thermodynamic stability is predicted for phases with 40-45 at.% In. - Abstract: The physico-chemical properties of the intermetallic phases in the Cu-In system have been a matter of considerable theoretical and experimental interest in connection with, i.a., the application of In-Sn alloys as lead-free micro-soldering alloys. Recently, a new binary compound with the chemical formula Cu{sub 10}In{sub 7} has been detected in a study of the {eta}-phase field. The structure of the Cu{sub 10}In{sub 7} phase has been determined as closely related to that of the Cu{sub 11}In{sub 9} compound occurring in the phase diagram, but no experimental or theoretical information on its electronic structure, thermodynamic and equation-of-state properties has yet been reported. In the present work we report the lattice parameters, bulk modulus, energy of formation from the constituent elements and the electronic structure of the new phase, calculated by applying an ab initio density-functional-theory method. Our calculation technique uses the projector augmented wave potentials and the exchange-correlation functions of Perdew and Wang in the generalized gradient approximation. The present results for the Cu{sub 10}In{sub 7} phase are compared with the experimental data available, and with the trends in structural and thermodynamic properties emerging from ab initio calculations also performed in the present study for various structurally related and neighboring compounds in the Cu-In phase diagram, viz., the ideal B8{sub 2}-Cu{sub 2}In, B8{sub 1}-CuIn, B8{sub 2
Saheer, V. C.; Kumar, Sanjay
2016-01-01
The global ground and first three excited electronic state adiabatic as well as the corresponding quasidiabatic potential energy surfaces is reported as a function of nuclear geometries in the Jacobi coordinates ( R → , r → , γ ) using Dunning's cc-pVTZ basis set at the internally contracted multi-reference (single and double) configuration interaction level of accuracy. Nonadiabatic couplings, arising out of relative motion of proton and the vibrational motion of CO, are also reported in terms of coupling potentials. The quasidiabatic potential energy surfaces and the coupling potentials have been obtained using the ab initio procedure [Simah et al., J. Chem. Phys. 111, 4523 (1999)] for the purpose of dynamics studies.
Chauhan, Mamta; Gupta, Dinesh C.
2015-12-01
The structural, electronic, mechanical, phase transition, and thermo-physical properties of refractory carbides, viz. VC, NbC, and TaC have been computed in stable B1 and high pressure B2 phases by means of two different ab initio calculations using pseudo- and full-potential schemes. These materials have mixed covalent-, metallic-, and ionic-type bonding. The calculations of elastic constants show the mechanical stability of these materials in B1 phase only. The brittle nature and anisotropy is observed in these materials in B1 phase. Non-central forces are present in both the phases. Elastic wave velocities and Debye temperature have also been calculated. The present results on structural, phase transition, elastic, and other properties are in reasonably good agreement with the available experimental and theoretical data. The calculations in high pressure phase need experimental verification.
Ab Initio Molecular Dynamics: A Virtual Laboratory
Hobbi Mobarhan, Milad
2014-01-01
In this thesis, we perform ab initio molecular dynamics (MD) simulations at the Hartree-Fock level, where the forces are computed on-the-fly using the Born-Oppenheimer approximation. The theory behind the Hartree-Fock method is discussed in detail and an implementation of this method based on Gaussian basis functions is explained. We also demonstrate how to calculate the analytic energy derivatives needed for obtaining the forces acting on the nuclei. Hartree-Fock calculations on the ground s...
Ab Initio Study on Hypothetical Silver Nitride
Institute of Scientific and Technical Information of China (English)
DELIGOZ Engin; COLAKOGLU Kemal; CIFTCI Yasemin Oztekin
2008-01-01
We perform the ab initio calculations based on norm-conserving pseudopotentials and density functional theory to investigate the structural, elastic, and thermodynamical properties for silver nitride (AgN) compound that is a member of the 4d transition metal group and has not been synthesized yet. The obtained results are compared with the other available theoretical data, and the agreement is, generally, quite good. We also present the pressure-dependent behaviour of some mechanical and thermodynamical properties for the same compounds.
Augmented wave ab initio EFG calculations: some methodological warnings
Energy Technology Data Exchange (ETDEWEB)
Errico, Leonardo A. [Departamento de Fisica-IFLP (CONICET), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC67 (1900) La Plata (Argentina); Renteria, Mario [Departamento de Fisica-IFLP (CONICET), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC67 (1900) La Plata (Argentina); Petrilli, Helena M. [Instituto de Fisica-DFMT, Universidade de Sao Paulo, C.P. 66318, 05315-970 Sao Paulo, SP (Brazil)]. E-mail: hmpetril@macbeth.if.usp.br
2007-02-01
We discuss some accuracy aspects inherent to ab initio electronic structure calculations in the understanding of nuclear quadrupole interactions. We use the projector augmented wave method to study the electric-field gradient (EFG) at both Sn and O sites in the prototype cases SnO and SnO{sub 2}. The term ab initio is used in the standard context of the also called first principles methods in the framework of the Density Functional Theory. As the main contributions of EFG calculations to problems in condensed matter physics are related to structural characterizations on the atomic scale, we discuss the 'state of the art' on theoretical EFG calculations and make a brief critical review on the subject, calling attention to some fundamental theoretical aspects.
Ab-initio calculations on melting of thorium
Mukherjee, D.; Sahoo, B. D.; Joshi, K. D.; Kaushik, T. C.; Gupta, Satish C.
2016-05-01
Ab-initio molecular dynamics study has been performed on face centered cubic structured thorium to determine its melting temperature at room pressure. The ion-electron interaction potential energy calculated as a function of temperature for three volumes (a0)3 and (1.02a0)3 and (1.04a0)3 increases gradually with temperature and undergoes a sharp jump at ~2200 K, ~2100 K and ~1800 K, respectively. Here, a0 = 5.043 Å is the equilibrium lattice parameter at 0 K obtained from ab-initio calculations. These jumps in interaction energy are treated as due to the onset of melting and corresponding temperatures as melting point. The melting point of 2100 K is close to the experimental value of 2023K. Further, the same has been verified by plotting the atomic arrangement evolved at various temperatures and corresponding pair correlation functions.
Pan, Yong; Guan, Weiming
2016-09-01
MoS3 has attracted considerable attention as potential hydrogen storage material due to the interaction between the hydrogen and unsaturated sulfur atoms. However, its structure and physical properties are unknown. By means of first-principles approach and Inorganic crystal structure Database (ISCD), we systematically investigated the structure, relevant physical and thermodynamic properties of MoS3. Phonon dispersion, electronic structure, band structure and heat capacity are calculated in detail. We predicted the orthorhombic B2ab (SrS3-type) and tetragonal P-421m (BaS3-type) structures of MoS3, which prefers to form the SrS3-type (Space group: B2ab, No.41) structure at the ground state. High pressure results in structural transition from SrS3-type structure to BaS3-type structure. This sulfide exhibits a degree of metallic behavior. The calculated heat capacity of MoS3 with SrS3-type structure is about of 39 J/(mol·K).
Hydrogen adsorption on boron doped graphene: an {\\it ab initio} study
Miwa, R. H.; Martins, T B; Fazzio, A.
2007-01-01
The electronic and structural properties of (i) boron doped graphene sheets, and (ii) the chemisorption processes of hydrogen adatoms on the boron doped graphene sheets have been examined by {\\it ab initio} total energy calculations.
Long, Run; English, Niall J; Prezhdo, Oleg V
2014-09-01
TiO2 sensitized with quantum dots (QDs) gives efficient photovoltaic and photocatalytic systems due to high stability and large absorption cross sections of QDs and rapid photoinduced charge separation at the interface. The yields of the light-induced processes are limited by electron-hole recombination that also occurs at the interface. We combine ab initio nonadiabatic molecular dynamics with analytic theory to investigate the experimentally studied charge recombination at the PbSe QD-TiO2 interface. The time-domain atomistic simulation directly mimics the laser experiment and generates important details of the recombination mechanism. The process occurs due to coupling of the electronic subsystem to polar optical modes of the TiO2 surface. The inelastic electron-phonon scattering happens on a picosecond time scale, while the elastic scattering takes 40 fs. Counter to expectations, the donor-acceptor bonding strengthens at an elevated temperature. An analytic theory extends the simulation results to larger QDs and longer QD-TiO2 bridges. It shows that the electron-hole recombination rate decreases significantly for longer bridges and larger dots and that the main effect arises due to reduced donor-acceptor coupling rather than changes in the donor-acceptor energy gap. The study indicates that by varying QD size or ligands one can reduce charge losses while still maintaining efficient charge separation, providing design principles for optimizing solar cell design and increasing photon-to-electron conversion efficiencies.
Ab Initio Nuclear Structure and Reaction Calculations for Rare Isotopes
Energy Technology Data Exchange (ETDEWEB)
Draayer, Jerry P. [Louisiana State Univ., Baton Rouge, LA (United States)
2014-09-28
We have developed a novel ab initio symmetry-adapted no-core shell model (SA-NCSM), which has opened the intermediate-mass region for ab initio investigations, thereby providing an opportunity for first-principle symmetry-guided applications to nuclear structure and reactions for nuclear isotopes from the lightest p-shell systems to intermediate-mass nuclei. This includes short-lived proton-rich nuclei on the path of X-ray burst nucleosynthesis and rare neutron-rich isotopes to be produced by the Facility for Rare Isotope Beams (FRIB). We have provided ab initio descriptions of high accuracy for low-lying (including collectivity-driven) states of isotopes of Li, He, Be, C, O, Ne, Mg, Al, and Si, and studied related strong- and weak-interaction driven reactions that are important, in astrophysics, for further understanding stellar evolution, X-ray bursts and triggering of s, p, and rp processes, and in applied physics, for electron and neutrino-nucleus scattering experiments as well as for fusion ignition at the National Ignition Facility (NIF).
A highly accurate ab initio potential energy surface for methane
Owens, Alec; Yurchenko, Sergei N.; Yachmenev, Andrey; Tennyson, Jonathan; Thiel, Walter
2016-09-01
A new nine-dimensional potential energy surface (PES) for methane has been generated using state-of-the-art ab initio theory. The PES is based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit and incorporates a range of higher-level additive energy corrections. These include core-valence electron correlation, higher-order coupled cluster terms beyond perturbative triples, scalar relativistic effects, and the diagonal Born-Oppenheimer correction. Sub-wavenumber accuracy is achieved for the majority of experimentally known vibrational energy levels with the four fundamentals of 12CH4 reproduced with a root-mean-square error of 0.70 cm-1. The computed ab initio equilibrium C-H bond length is in excellent agreement with previous values despite pure rotational energies displaying minor systematic errors as J (rotational excitation) increases. It is shown that these errors can be significantly reduced by adjusting the equilibrium geometry. The PES represents the most accurate ab initio surface to date and will serve as a good starting point for empirical refinement.
Ab initio multiple cloning algorithm for quantum nonadiabatic molecular dynamics
Makhov, Dmitry V.; Glover, William J.; Martinez, Todd J.; Shalashilin, Dmitrii V.
2014-08-01
We present a new algorithm for ab initio quantum nonadiabatic molecular dynamics that combines the best features of ab initio Multiple Spawning (AIMS) and Multiconfigurational Ehrenfest (MCE) methods. In this new method, ab initio multiple cloning (AIMC), the individual trajectory basis functions (TBFs) follow Ehrenfest equations of motion (as in MCE). However, the basis set is expanded (as in AIMS) when these TBFs become sufficiently mixed, preventing prolonged evolution on an averaged potential energy surface. We refer to the expansion of the basis set as "cloning," in analogy to the "spawning" procedure in AIMS. This synthesis of AIMS and MCE allows us to leverage the benefits of mean-field evolution during periods of strong nonadiabatic coupling while simultaneously avoiding mean-field artifacts in Ehrenfest dynamics. We explore the use of time-displaced basis sets, "trains," as a means of expanding the basis set for little cost. We also introduce a new bra-ket averaged Taylor expansion (BAT) to approximate the necessary potential energy and nonadiabatic coupling matrix elements. The BAT approximation avoids the necessity of computing electronic structure information at intermediate points between TBFs, as is usually done in saddle-point approximations used in AIMS. The efficiency of AIMC is demonstrated on the nonradiative decay of the first excited state of ethylene. The AIMC method has been implemented within the AIMS-MOLPRO package, which was extended to include Ehrenfest basis functions.
Ab initio multiple cloning algorithm for quantum nonadiabatic molecular dynamics
Energy Technology Data Exchange (ETDEWEB)
Makhov, Dmitry V.; Shalashilin, Dmitrii V. [Department of Chemistry, University of Leeds, Leeds LS2 9JT (United Kingdom); Glover, William J.; Martinez, Todd J. [Department of Chemistry and The PULSE Institute, Stanford University, Stanford, California 94305, USA and SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States)
2014-08-07
We present a new algorithm for ab initio quantum nonadiabatic molecular dynamics that combines the best features of ab initio Multiple Spawning (AIMS) and Multiconfigurational Ehrenfest (MCE) methods. In this new method, ab initio multiple cloning (AIMC), the individual trajectory basis functions (TBFs) follow Ehrenfest equations of motion (as in MCE). However, the basis set is expanded (as in AIMS) when these TBFs become sufficiently mixed, preventing prolonged evolution on an averaged potential energy surface. We refer to the expansion of the basis set as “cloning,” in analogy to the “spawning” procedure in AIMS. This synthesis of AIMS and MCE allows us to leverage the benefits of mean-field evolution during periods of strong nonadiabatic coupling while simultaneously avoiding mean-field artifacts in Ehrenfest dynamics. We explore the use of time-displaced basis sets, “trains,” as a means of expanding the basis set for little cost. We also introduce a new bra-ket averaged Taylor expansion (BAT) to approximate the necessary potential energy and nonadiabatic coupling matrix elements. The BAT approximation avoids the necessity of computing electronic structure information at intermediate points between TBFs, as is usually done in saddle-point approximations used in AIMS. The efficiency of AIMC is demonstrated on the nonradiative decay of the first excited state of ethylene. The AIMC method has been implemented within the AIMS-MOLPRO package, which was extended to include Ehrenfest basis functions.
Kopplung von Dichtefunktional- und ab-initio-Methoden
Goll, Erich
2008-01-01
Im Rahmen der Doktorarbeit wurde untersucht, inwieweit die Kopplung von Dichtefunktionalmethoden und ab-initio-Korrelationsmethoden der Quantenchemie eine Verbesserung bezüglich beider Grenzmethoden erbringt. Die Kopplung erfolgt durch eine Aufspaltung des interelektronischen Hamiltonoperators (abstoßende Coulombwechselwirkung). Die kurzreichweitige Wechselwirkung wird mit Dichtefunktionaltheorie behandelt, die langreichweitige mit Hilfe von ab-initio-Methoden. Diese Aufteilung soll dazu dien...
Energy Technology Data Exchange (ETDEWEB)
Ilyasov, V.V., E-mail: viily@mail.ru; Pham, Khang D., E-mail: dinhkhang307@gmail.com; Holodova, O.M.; Ershov, I.V., E-mail: thijd@mail.ru
2015-10-01
We have performed ab initio simulation of oxygen atom adsorption on TiC(0 0 1) laser-reconstructed surface. Relaxed atomic structures of the O/Ti{sub x}C{sub y}(0 0 1) surface observed upon thermal impact have been studied. DFT calculations of their thermodynamic, electronic, and elastic properties have been carried out. For the first time we have established the bond length and adsorption energy for various reconstructions of the O/Ti{sub x}C{sub y}(0 0 1) surface atomic structure. We have examined the effects of the oxygen adatom upon the band and electron spectra of the O/TiC(0 0 1) surface in its various reconstructions. For the first time we have established a correlation between the energy level of flat bands (−5.4 eV and −5.8 eV) responsible for the doublet of singular peaks of partial densities of oxygen 2p electrons, and the adsorption energy of oxygen atom in non-stoichiometric O/TiC{sub y}(0 0 1) systems. Effective charges of titanium and carbon atoms surrounding the oxygen adatom in various reconstructions have been identified. We have established charge transfer from titanium atom to oxygen and carbon atoms determined by the reconstruction of local atomic and electron structures which correlate with atomic electronegativity values and chemisorption processes. Potential mechanisms for laser nanostructuring of titanium carbide surface have been suggested.
Equations of state of heavy metals: ab initio approaches
International Nuclear Information System (INIS)
The determination of equations of states of heavy metals through ab initio calculation, i.e. without any adjustable parameter, allows to access to pressure and temperature thermodynamic conditions sometimes inaccessible to experiment. To perform such calculations, density functional theory (DFT) is a good starting point: when electronic densities are homogeneous enough, the local density approximation (LDA) remarkably accounts for thermodynamic properties of heavy metals, such as tantalum, or the light actinides, as well for static properties - equilibrium volume, elastic constants - as for dynamical quantities like phonon spectra. For heavier elements, like neptunium or plutonium, relativistic effects and strong electronic interactions must be taken into account, which requires more sophisticated theoretical approaches. (authors)
Ab initio calculations and modelling of atomic cluster structure
DEFF Research Database (Denmark)
Solov'yov, Ilia; Lyalin, Andrey G.; Solov'yov, Andrey V.;
2004-01-01
The optimized structure and electronic properties of small sodium and magnesium clusters have been investigated using it ab initio theoretical methods based on density-functional theory and post-Hartree-Fock many-body perturbation theory accounting for all electrons in the system. A new theoretical...... framework for modelling the fusion process of noble gas clusters is presented. We report the striking correspondence of the peaks in the experimentally measured abundance mass spectra with the peaks in the size-dependence of the second derivative of the binding energy per atom calculated for the chain...... of the noble gas clusters up to 150 atoms....
Ab initio alpha-alpha scattering
Elhatisari, Serdar; Rupak, Gautam; Epelbaum, Evgeny; Krebs, Hermann; Lähde, Timo A; Luu, Thomas; Meißner, Ulf-G
2015-01-01
Processes involving alpha particles and alpha-like nuclei comprise a major part of stellar nucleosynthesis and hypothesized mechanisms for thermonuclear supernovae. In an effort towards understanding alpha processes from first principles, we describe in this letter the first ab initio calculation of alpha-alpha scattering. We use lattice effective field theory to describe the low-energy interactions of nucleons and apply a technique called the adiabatic projection method to reduce the eight-body system to an effective two-cluster system. We find good agreement between lattice results and experimental phase shifts for S-wave and D-wave scattering. The computational scaling with particle number suggests that alpha processes involving heavier nuclei are also within reach in the near future.
Ab Initio Path to Heavy Nuclei
Binder, Sven; Calci, Angelo; Roth, Robert
2014-01-01
We present the first ab initio calculations of nuclear ground states up into the domain of heavy nuclei, spanning the range from 16-O to 132-Sn based on two- plus three-nucleon interactions derived within chiral effective field theory. We employ the similarity renormalization group for preparing the Hamiltonian and use coupled-cluster theory to solve the many-body problem for nuclei with closed sub-shells. Through an analysis of theoretical uncertainties resulting from various truncations in this framework, we identify and eliminate the technical hurdles that previously inhibited the step beyond medium-mass nuclei, allowing for reliable validations of nuclear Hamiltonians in the heavy regime. Following this path we show that chiral Hamiltonians qualitatively reproduce the systematics of nuclear ground-state energies up to the neutron-rich Sn isotopes.
Energy Technology Data Exchange (ETDEWEB)
Grimminger, Robert; Clouthier, Dennis J., E-mail: dclaser@uky.edu [Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055 (United States); Sheridan, Phillip M. [Department of Chemistry and Biochemistry, Canisius College, Buffalo, New York 14208 (United States)
2014-04-28
We have studied the B{sup ~} {sup 2}A{sub 1}–X{sup ~} {sup 2}B{sub 2} laser-induced fluorescence (LIF) spectrum of the jet-cooled F{sub 2}BO radical for the first time. The transition consists of a strong 0{sub 0}{sup 0} band at 446.5 nm and eight weak sequence bands to shorter wavelengths. Single vibronic level emission spectra obtained by laser excitation of individual levels of the B{sup ~} state exhibit two electronic transitions: a very weak, sparse B{sup ~}–X{sup ~} band system in the 450–500 nm region and a stronger, more extensive set of B{sup ~} {sup 2}A{sub 1}–A{sup ~} {sup 2}B{sub 1} bands in the 580–650 nm region. We have also performed a series of high level ab initio calculations to predict the electronic energies, molecular structures, vibrational frequencies, and rotational and spin-rotation constants in the X{sup ~} {sup 2}B{sub 2}, A{sup ~2}B{sub 1} and B{sup ~} {sup 2}A{sub 1} electronic states as an aid to the analysis of the experimental data. The theoretical results have been used as input for simulations of the rotationally resolved B{sup ~} {sup 2}A{sub 1}–X{sup ~} {sup 2}B{sub 2} 0{sub 0}{sup 0} LIF band and Franck-Condon profiles of the LIF and single vibronic level emission spectra. The agreement between the simulations obtained with purely ab initio parameters and the experimental spectra validates the geometries calculated for the ground and excited states and the conclusion that the radical has C{sub 2v} symmetry in the X{sup ~}, A{sup ~}, and B{sup ~} states. The spectra provide considerable new information about the vibrational energy levels of the X{sup ~} and A{sup ~} states, but very little for the B{sup ~} state, due to the very restrictive Franck-Condon factors in the LIF spectra.
Ab initio alpha-alpha scattering
Elhatisari, Serdar; Lee, Dean; Rupak, Gautam; Epelbaum, Evgeny; Krebs, Hermann; Lähde, Timo A.; Luu, Thomas; Meißner, Ulf-G.
2015-12-01
Processes such as the scattering of alpha particles (4He), the triple-alpha reaction, and alpha capture play a major role in stellar nucleosynthesis. In particular, alpha capture on carbon determines the ratio of carbon to oxygen during helium burning, and affects subsequent carbon, neon, oxygen, and silicon burning stages. It also substantially affects models of thermonuclear type Ia supernovae, owing to carbon detonation in accreting carbon-oxygen white-dwarf stars. In these reactions, the accurate calculation of the elastic scattering of alpha particles and alpha-like nuclei—nuclei with even and equal numbers of protons and neutrons—is important for understanding background and resonant scattering contributions. First-principles calculations of processes involving alpha particles and alpha-like nuclei have so far been impractical, owing to the exponential growth of the number of computational operations with the number of particles. Here we describe an ab initio calculation of alpha-alpha scattering that uses lattice Monte Carlo simulations. We use lattice effective field theory to describe the low-energy interactions of protons and neutrons, and apply a technique called the ‘adiabatic projection method’ to reduce the eight-body system to a two-cluster system. We take advantage of the computational efficiency and the more favourable scaling with system size of auxiliary-field Monte Carlo simulations to compute an ab initio effective Hamiltonian for the two clusters. We find promising agreement between lattice results and experimental phase shifts for s-wave and d-wave scattering. The approximately quadratic scaling of computational operations with particle number suggests that it should be possible to compute alpha scattering and capture on carbon and oxygen in the near future. The methods described here can be applied to ultracold atomic few-body systems as well as to hadronic systems using lattice quantum chromodynamics to describe the interactions of
Ab initio alpha-alpha scattering.
Elhatisari, Serdar; Lee, Dean; Rupak, Gautam; Epelbaum, Evgeny; Krebs, Hermann; Lähde, Timo A; Luu, Thomas; Meißner, Ulf-G
2015-12-01
Processes such as the scattering of alpha particles ((4)He), the triple-alpha reaction, and alpha capture play a major role in stellar nucleosynthesis. In particular, alpha capture on carbon determines the ratio of carbon to oxygen during helium burning, and affects subsequent carbon, neon, oxygen, and silicon burning stages. It also substantially affects models of thermonuclear type Ia supernovae, owing to carbon detonation in accreting carbon-oxygen white-dwarf stars. In these reactions, the accurate calculation of the elastic scattering of alpha particles and alpha-like nuclei--nuclei with even and equal numbers of protons and neutrons--is important for understanding background and resonant scattering contributions. First-principles calculations of processes involving alpha particles and alpha-like nuclei have so far been impractical, owing to the exponential growth of the number of computational operations with the number of particles. Here we describe an ab initio calculation of alpha-alpha scattering that uses lattice Monte Carlo simulations. We use lattice effective field theory to describe the low-energy interactions of protons and neutrons, and apply a technique called the 'adiabatic projection method' to reduce the eight-body system to a two-cluster system. We take advantage of the computational efficiency and the more favourable scaling with system size of auxiliary-field Monte Carlo simulations to compute an ab initio effective Hamiltonian for the two clusters. We find promising agreement between lattice results and experimental phase shifts for s-wave and d-wave scattering. The approximately quadratic scaling of computational operations with particle number suggests that it should be possible to compute alpha scattering and capture on carbon and oxygen in the near future. The methods described here can be applied to ultracold atomic few-body systems as well as to hadronic systems using lattice quantum chromodynamics to describe the interactions of
International Nuclear Information System (INIS)
Highlights: • The lattice parameters changes by K doping is explained by ionic charge and the metal–metal bonding scenario. • Creation of a larger peak near the Fermi level and increase the DOS at the Fermi level by K doping. • The effects of K on DOS has been related to the magnetic transition, change of the lattice parameters and FeAs4 tetrahedron. • Investigation of the number of Fermi level crossed bands by K doping and the band changes near the Fermi level. - Abstract: The crystal and electronic structures of normal phase of Ba1−xKxFe2As2 for x = 0.0, 0.5 and 1.0 have been studied by using pseudopotential Quantum Espresso code based on ab-initio density functional theory. Effects of K doping on the crystal structure and lattice parameters have been calculated and compared with the experimental and computational reported data for similar compounds. The metal–metal bonding scenario was used to explain the changes of lattice parameters by K doping. The electronic structure of this system including of density of states and band structure have been calculated and investigated by K doping. One of the interesting results is that a larger peak is appeared near the Fermi level by increasing of the K doping. These changes could produce a potential for creation of the superconducting state in this system
Haddadi, K.; Bouhemadou, A.; Bin-Omran, S.; Maabed, S.; Khenata, R.
2015-01-01
The structural parameters, elastic constants, electronic structure and optical properties of the recently reported monoclinic quaternary nitridoaluminate LiCaAlN2 are investigated in detail using the ab initio plane-wave pseudopotential method within the generalized gradient approximation. The calculated equilibrium structural parameters are in excellent agreement with the experimental data, which validate the reliability of the applied theoretical method. The chemical and structural stabilities of LiCaAlN2 are confirmed by calculating the cohesion energy and enthalpy of formation. Chemical band stiffness is calculated to explain the pressure dependence of the lattice parameters. Through the band structure calculation, LiCaAlN2 is predicted to be an indirect band gap of 2.725 eV. The charge-carrier effective masses are estimated from the band structure dispersions. The frequency-dependent dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity coefficient and electron energy loss function spectra are calculated for polarized incident light in a wide energy range. Optical spectra exhibit a noticeable anisotropy. Single-crystal and polycrystalline elastic constants and related properties, including isotropic sound velocities and Debye temperatures, are numerically estimated. The calculated elastic constants and elastic compliances are used to analyse and visualize the elastic anisotropy of LiCaAlN2. The calculated elastic constants demonstrate the mechanical stability and brittle behaviour of the considered material.
Chen, K X; Wu, J A; Ji, R Y
1987-09-01
We investigated the cis- and trans-isomers of Pt(NH3)2Cl2 and [Pt(NH3)2]2+ using a quantum chemical non-empirical calculation method, the pseudopotential valence electron-only ab initio method. The electronic structure and electrostatic potential counter maps were in turn determined through the wave functions so obtained. There was a sharp difference between the dipole moments of the cis- and trans-isomers. The electrostatic counter maps of the isomers also had remarkably different features. Based on the interaction between the platinum (II) coordination compound and the base pairs of nucleic acid, the difference in antitumour activity of the isomeric compounds was discussed. It is pointed out that the key factor for antitumour activity is that the platinum (II) coordination compound must be mutually complementary with the target acceptor in both configuration and bonding activity. This mutual-complementary requirement includes a bonding ability of the platinum complex with two negative centers in DNA, so as to form an intrastrand crosslink with two neighbouring guanines.
Salami, N.; Shokri, A. A.; Elahi, S. M.
2016-03-01
Electronic and magnetic properties of a molybdenum disulfide (MoS2) monolayer with some intrinsic and extrinsic vacancies are investigated using ab initio method in the presence of planar strain distributions. The calculations are carried out within the density functional theory (DFT) as implemented in SIESTA package. By using fully relaxed structures and applying a full spin-polarized description to the system, we concentrate on created magnetic moment due to the vacancies under different planar strains. The results show that the extrinsic MoS6 vacancy induces a net magnetic moment of 6.00 μB per supercell. Also, it is found that the pure MoS2 monolayer for the most cases does not show any magnetic properties under the planar strain. While the net magnetic moment of MoS2 monolayer with the vacancies enhances as the planar tensile strain is applied. The tunable magnetic moment of MoS2 monolayer may be utilized for the development of spintronic and flexible electronic nano-devices.
Yamamoto, Takeshi; Kato, Shigeki
2007-06-14
In quantum-mechanical/molecular-mechanical (QM/MM) treatment of chemical reactions in condensed phases, one solves the electronic Schrodinger equation for the solute (or an active site) under the electrostatic field from the environment. This Schrodinger equation depends parametrically on the solute nuclear coordinates R and the external electrostatic potential V. This fact suggests that one may use R and V as natural collective coordinates for describing the entire system, where V plays the role of collective solvent variables. In this paper such an (R,V) representation of the QM/MM canonical ensemble is described, with particular focus on how to treat charge transfer processes in this representation. As an example, the above method is applied to the proton-coupled electron transfer of a ubiquinol analog with phenoxyl radical in acetonitrile solvent. Ab initio free-energy surfaces are calculated as functions of R and V using the reference interaction site model self-consistent field method, the equilibrium points and the minimum free-energy crossing point are located in the (R,V) space, and then the kinetic isotope effects (KIEs) are evaluated approximately. The results suggest that a stiffer proton potential at the transition state may be responsible for unusual KIEs observed experimentally for related systems. PMID:17581070
Accelerating ab initio molecular dynamics simulations by linear prediction methods
Herr, Jonathan D.; Steele, Ryan P.
2016-09-01
Acceleration of ab initio molecular dynamics (AIMD) simulations can be reliably achieved by extrapolation of electronic data from previous timesteps. Existing techniques utilize polynomial least-squares regression to fit previous steps' Fock or density matrix elements. In this work, the recursive Burg 'linear prediction' technique is shown to be a viable alternative to polynomial regression, and the extrapolation-predicted Fock matrix elements were three orders of magnitude closer to converged elements. Accelerations of 1.8-3.4× were observed in test systems, and in all cases, linear prediction outperformed polynomial extrapolation. Importantly, these accelerations were achieved without reducing the MD integration timestep.
Polymeric nitrogen in a graphene matrix: An ab initio study
Timoshevskii, V.; Ji, Wei; Abou-Rachid, Hakima; Lussier, Louis-Simon; Guo, H.
2009-09-01
A hybrid material where polymeric nitrogen chains are sandwiched between graphene sheets in the form of a three-dimensional crystal, is predicted by means of ab initio simulations. It is demonstrated that chainlike polymeric nitrogen phase becomes stable at ambient pressure when intercalated in a multilayer graphene matrix. The physical origin of this stabilization is identified by studying the electronic properties of the system. This approach of stabilizing polymeric nitrogen by means of external three-dimensional matrix constitutes a path toward synthesizing different types of nitrogen-based high-energy materials.
On the hierarchical parallelization of ab initio simulations
Ruiz-Barragan, Sergi; Shiga, Motoyuki
2016-01-01
A hierarchical parallelization has been implemented in a new unified code PIMD-SMASH for ab initio simulation where the replicas and the Born-Oppenheimer forces are parallelized. It is demonstrated that ab initio path integral molecular dynamics simulations can be carried out very efficiently for systems up to a few tens of water molecules. The code was then used to study a Diels-Alder reaction of cyclopentadiene and butenone by ab initio string method. A reduction in the reaction energy barrier is found in the presence of hydrogen-bonded water, in accordance with experiment.
Ab initio derivation of model energy density functionals
Dobaczewski, Jacek
2016-08-01
I propose a simple and manageable method that allows for deriving coupling constants of model energy density functionals (EDFs) directly from ab initio calculations performed for finite fermion systems. A proof-of-principle application allows for linking properties of finite nuclei, determined by using the nuclear nonlocal Gogny functional, to the coupling constants of the quasilocal Skyrme functional. The method does not rely on properties of infinite fermion systems but on the ab initio calculations in finite systems. It also allows for quantifying merits of different model EDFs in describing the ab initio results.
Energy Technology Data Exchange (ETDEWEB)
Ciftci, Yasemin Oe. [Gazi Univ., Ankara (Turkey). Dept. of Physics; Coban, Cansu [Balikesir Univ. (Turkey). Dept. of Physics
2016-05-01
The structural, mechanical, electronic, dynamic, and optical properties of the ZrPdSn compound crystallising into the MgAgAs structure are investigated by the ab initio calculations based on the density functional theory. The lattice constant, bulk modulus, and first derivative of bulk modulus were obtained by fitting the calculated total energy-atomic volume results to the Murnaghan equation of state. These results were compared to the previous data. The band structure and corresponding density of states (DOS) were also calculated and discussed. The elastic properties were calculated by using the stress-strain method, which shows that the MgAgAs phase of this compound is mechanically stable. The presented phonon dispersion curves and one-phonon DOS confirms that this compound is dynamically stable. In addition, the heat capacity, entropy, and free energy of ZrPdSn were calculated by using the phonon frequencies. Finally, the optical properties, such as dielectric function, reflectivity function, extinction coefficient, refractive index, and energy loss spectrum, were obtained under different pressures.
Energy Technology Data Exchange (ETDEWEB)
Raybaud, P.; Hafner, J.; Kresse, G.; Kasztelan, S.; Toulhoat, H.
2000-02-15
The determination of the local structure of cobalt- or nickel-promoted MoS{sub 2}-based hydrodesulfurization catalysts is of interest for understanding the mechanism leading to an increased activity brought by cobalt or nickel, the so-called synergetic effect. For that reason, the authors carried out ab initio calculations using density functional theory under the generalized gradient approximation for periodic systems. The edge substitution model emerges as the most stable structure and provides an excellent agreement with local structures experimentally determined on real catalysts by in situ extended X-ray absorption fine structure. The authors studied the absorption of sulfur on the active edge surface of the promoted MoS{sub 2} catalyst and determined the equilibrium coverage under sulfiding conditions. It is demonstrated that the incorporation of promoter atoms has a strong influence on the sulfur-metal bond energy at the surface and in particular leads to a reduction of the equilibrium S coverage of the active metal sites. A comparative study on the effects of Co, Ni, and Cu atoms as promoters was performed. Detailed results on the surface electronic structure of promoted MoS{sub 2} are presented.
Tuna, Deniz; Udvarhelyi, Anikó; Sobolewski, Andrzej L; Domcke, Wolfgang; Domratcheva, Tatiana
2016-04-14
Eumelanin is a naturally occurring skin pigment which is responsible for developing a suntan. The complex structure of eumelanin consists of π-stacked oligomers of various indole derivatives, such as the monomeric building block 5,6-dihydroxyindole (DHI). In this work, we present an ab initio wave-function study of the absorption behavior of DHI oligomers and of doubly and triply π-stacked species of these oligomers. We have simulated the onset of the electronic absorption spectra by employing the MP2 and the linear-response CC2 methods. Our results demonstrate the effect of an increasing degree of oligomerization of DHI and of an increasing degree of π-stacking of DHI oligomers on the onset of the absorption spectra and on the degree of red-shift toward the visible region of the spectrum. We find that π-stacking of DHI and its oligomers substantially red-shifts the onset of the absorption spectra. Our results also suggest that the optical properties of biological eumelanin cannot be simulated by considering the DHI building blocks alone, but instead the building blocks indole-semiquinone and indole-quinone have to be considered as well. This study contributes to advancing the understanding of the complex photophysics of the eumelanin biopolymer.
Saito, Minoru; Kashiwagi, Hiroshi
1985-04-01
For bis(pyridine)(porphinato) iron [FeP(py)2], a correlation between the iron electronic state and the equilibrium Fe-Npy distance was investigated. Potential energy curves as a function of the Fe-Npy distance were calculated for low-spin, intermediate-spin, and high-spin states of the ferric and ferrous ions by the ab initio SCF MO method. The equilibrium Fe-Npy distances were obtained from the potential curves. The values obtained for the ferric low-spin and high-spin states were in good agreement with the experimental values for Fe(III)(OEP)(3-Clpy)2 within the differences, ±0.05 Å. The following significant features were found. The equilibrium distance is elongated by the occupation of the 3dz2 orbital and is shortened by the oxidation of the iron atom. The distance and the force constant for the symmetrical py-Fe-py stretching are strongly correlated with the overlap population between the 3dz2 orbital and pyridine-nitrogen orbitals.
Demkov, Alexander A.; Navrotsky, Alexandra
2001-03-01
The International Technology Roadmap for Semiconductors (ITRS) predicts that the strategy of scaling complementary metal-oxide-semiconductor (CMOS) devices will come to an abrupt end around the year 2012. The main reason for this will be the unacceptably high leakage current through the silicon dioxide gate with a thickness below 20 ÅFinding a gate insulator alternative to SiO2 has proven to be far from trivial. Hafnium and zirconium dioxides and silicates have been recently considered as gate dielectrics with intermediate dielectric constants. Hafnia and ziconia are important ceramic materials as well, and their phase relations are rather well studied. There is also interest in hafnia as a constituent of ceramic waste forms for plutonium, based on its refractory nature and high neutron absorption cross section. We use a combination of the ab-initio calculations and calorimetry to investigate thermodynamic and electronic properties of hafnia and zirconia. We describe the cubic to tetragonal phase transition in the fluorite structure by computing the total energy surface for zone-edge distortions correct to fourth order in the soft-mode displacement with the strain coupling renormalization included. We compare the two materials using some simple chemical concepts.
Zemen, J.; Mašek, J.; Kučera, J.; Mol, J. A.; Motloch, P.; Jungwirth, T.
2014-04-01
An empirical multiorbital (spd) tight binding (TB) model including magnetism and spin-orbit coupling is applied to calculations of magnetic anisotropy energy (MAE) in CoPt L10 structure. A realistic Slater-Koster parametrisation for single-element transition metals is adapted for the ordered binary alloy. Spin magnetic moment and density of states are calculated using a full-potential linearised augmented plane-wave (LAPW) ab initio method and our TB code with different variants of the interatomic parameters. Detailed mutual comparison of this data allows for determination of a subset of the compound TB parameters tuning of which improves the agreement of the TB and LAPW results. MAE calculated as a function of band filling using the refined parameters is in broad agreement with ab initio data for all valence states and in quantitative agreement with ab initio and experimental data for the natural band filling. Our work provides a practical basis for further studies of relativistic magnetotransport anisotropies by means of local Green's function formalism which is directly compatible with our TB approach.
Molecular ion LiHe+: ab initio study
International Nuclear Information System (INIS)
Highlights: ► Excited electronic states of LiHe+ are studied. ► Potential energy curves of thirteen states are calculated. ► Dipole moment and transition dipole moment functions are determined. ► Basic spectroscopic properties of the electronic states are derived. - Abstract: High level ab initio calculations are performed on the molecular ion LiHe+. Potential energy curves for the low-lying singlet and triplet electronic states are calculated using the multi-reference configuration interaction and single-reference coupled cluster methods with large basis sets. The corresponding dipole moments and transition dipole moments functions are also determined. The basic spectroscopic properties and excitation energies of the electronic states are derived from rovibrational bound state calculations.
Ab initio calculation of the Hoyle state
Epelbaum, Evgeny; Lee, Dean; Meißner, Ulf-G
2011-01-01
The Hoyle state plays a crucial role in the hydrogen burning of stars heavier than our sun and in the production of carbon and other elements necessary for life. This excited state of the carbon-12 nucleus was postulated by Hoyle^{1} as a necessary ingredient for the fusion of three alpha particles to produce carbon at stellar temperatures. Although the Hoyle state was seen experimentally more than a half century ago^{2,3}, nuclear theorists have not yet uncovered the nature of this state from first principles. In this letter we report the first ab initio calculation of the low-lying states of carbon-12 using supercomputer lattice simulations and a theoretical framework known as effective field theory. In addition to the ground state and excited spin-2 state, we find a resonance at -85(3) MeV with all of properties of the Hoyle state and in agreement with the experimentally observed energy. These lattice simulations provide insight into the structure of this unique state and new clues as to the amount of fine...
Young Modulus of Crystalline Polyethylene from ab Initio Molecular Dynamics
Hageman, J.C.L.; Meier, Robert J.; M. Heinemann; de Groot, R. A.
1997-01-01
The Young modulus for crystalline polyethylene is calculated using ab initio molecular dynamics based on density functional theory in the local density approximation (DFT-LDA). This modulus, which can be seen as the ultimate value for the Young modulus of polyethylene fibers, is found to be 334 GPa. For the first time the modulus is evaluated ab initio (no bias from experimental data) with demonstrated basis set convergence.
Calzolari, Arrigo; Ferretti, Andrea; Nardelli, Marco Buongiorno
2007-01-01
Using first principles calculations in the framework of Density Functional Theory, we investigated the electronic and transport properties of metal(II)-phthalocyanine (M(II)Pc) systems, both in a single molecule configuration and in a model-device geometry. In particular, using the Copper(II)- and Manganese(II)-Pc as prototypical examples, we studied how electronic correlations on the central metal-ion influence the analysis of the electronic structure of the system and we demonstrated that t...
Abadias, G.; Kanoun, M. B.; Goumri-Said, S.; Koutsokeras, L.; Dub, S. N.; Djemia, Ph.
2014-10-01
The structure, phase stability, and mechanical properties of ternary alloys of the Zr-Ta-N system are investigated by combining thin-film growth and ab initio calculations. Zr1-xTaxN films with 0≤x≤1 were deposited by reactive magnetron cosputtering in Ar +N2 plasma discharge and their structural properties characterized by x-ray diffraction. We considered both ordered and disordered alloys, using supercells and special quasirandom structure approaches, to account for different possible metal atom distributions on the cation sublattice. Density functional theory within the generalized gradient approximation was employed to calculate the electronic structure as well as predict the evolution of the lattice parameter and key mechanical properties, including single-crystal elastic constants and polycrystalline elastic moduli, of ternary Zr1-xTaxN compounds with cubic rocksalt structure. These calculated values are compared with experimental data from thin-film measurements using Brillouin light scattering and nanoindentation tests. We also study the validity of Vegard's empirical rule and the effect of growth-dependent stresses on the lattice parameter. The thermal stability of these Zr1-xTaxN films is also studied, based on their structural and mechanical response upon vacuum annealing at 850 °C for 3 h. Our findings demonstrate that Zr1-xTaxN alloys with Ta fraction 0.51⩽x⩽0.78 exhibit enhanced toughness, while retaining high hardness ˜30 GPa, as a result of increased valence electron concentration and phase stability tuning. Calculations performed for disordered or ordered structures both lead to the same conclusion regarding the mechanical behavior of these nitride alloys, in agreement with recent literature findings [H. Kindlund, D. G. Sangiovanni, L. Martinez-de-Olcoz, J. Lu, J. Jensen, J. Birch, I. Petrov, J. E. Greene, V. Chirita, and L. Hultman, APL Materials 1, 042104 (2013), 10.1063/1.4822440].
International Nuclear Information System (INIS)
Influence of impurity Ni2+ ions on optical absorption spectra of layered CdI2 single crystals has been considered for localized level of doping. Optical properties of CdI2:Ni2+ crystals were modeled using two independent approaches: (i) DFT-based ab initio calculations and (ii) semi-empirical crystal field theory. The former method allowed for locating the Ni2+ 3d states with respect to the host's band structure, providing a link between the properties of impurity and host itself. The latter method allowed for calculations of crystal field splitting of the Ni2+ LS terms, giving an opportunity to assign the main bands in the absorption spectrum of the doped crystal. To increase accuracy in calculating the point charge contribution to the crystal field parameters (CFP), contributions of all crystal lattice ions located at a distance of up to 72.999 A from the Ni ion were included into the crystal lattice sums. The crystal field Hamiltonian was diagonalized in the space of 25 wave functions of the spin-triplet terms 3F, 3P and the spin-singlet terms 1S, 1D, 1G of the 3d8 electron configuration of Ni2+ ion. Additional calculations of the band structure and optical functions were performed to reveal the structure of the energy bands, their role in the formation of optical properties of this system in the overlapping impurity-ligand effects. Electron density distribution in the space between atoms before and after doping was compared; hybridization of the Ni 3d states with iodine 5p states was demonstrated. The role of the crystal anisotropy in the observed effects is discussed.
Interatomic Coulombic decay widths of helium trimer: Ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Kolorenč, Přemysl, E-mail: kolorenc@mbox.troja.mff.cuni.cz [Charles University in Prague, Faculty of Mathematics and Physics, Institute of Theoretical Physics, V Holešovičkách 2, 180 00 Prague (Czech Republic); Sisourat, Nicolas [Sorbonne Universités, UPMC Univ Paris 06, UMR 7614, Laboratoire de Chimie Physique Matière et Rayonnement, F-75005 Paris (France); CNRS, UMR 7614, Laboratoire de Chimie Physique Matière et Rayonnement, F-75005 Paris (France)
2015-12-14
We report on an extensive study of interatomic Coulombic decay (ICD) widths in helium trimer computed using a fully ab initio method based on the Fano theory of resonances. Algebraic diagrammatic construction for one-particle Green’s function is utilized for the solution of the many-electron problem. An advanced and universal approach to partitioning of the configuration space into discrete states and continuum subspaces is described and employed. Total decay widths are presented for all ICD-active states of the trimer characterized by one-site ionization and additional excitation of an electron into the second shell. Selected partial decay widths are analyzed in detail, showing how three-body effects can qualitatively change the character of certain relaxation transitions. Previously unreported type of three-electron decay processes is identified in one class of the metastable states.
A Review on Ab Initio Approaches for Multielectron Dynamics
Ishikawa, Kenichi L
2015-01-01
In parallel with the evolution of femtosecond and attosecond laser as well as free-electron laser technology, a variety of theoretical methods have been developed to describe the behavior of atoms, molecules, clusters, and solids under the action of those laser pulses. Here we review major ab initio wave-function-based numerical approaches to simulate multielectron dynamics in atoms and molecules driven by intense long-wavelength and/or ultrashort short-wavelength laser pulses. Direct solution of the time-dependent Schr\\"odinger equation (TDSE), though its applicability is limited to He, ${\\rm H}_2$, and Li, can provide an exact description and has been greatly contributing to the understanding of dynamical electron-electron correlation. Multiconfiguration self-consistent-field (MCSCF) approach offers a flexible framework from which a variety of methods can be derived to treat both atoms and molecules, with possibility to systematically control the accuracy. The equations of motion of configuration interactio...
Low-energy electron scattering from CO. 2: Ab-initio study using the frame-transformation theory
Chandra, N.
1976-01-01
The Wigner-Eisenbud R matrix method has been combined with the frame transformation theory to study electron scattering from molecular systems. The R matrix, calculated at the boundary point of the molecular core radius, has been transformed to the space frame in order to continue the solution of the scattering equations in the outer region where rotational motion of the nuclei is taken into account. This procedure has been applied to a model calculation of thermal energy electron scattering from CO.
Energy Technology Data Exchange (ETDEWEB)
Neef, Matthias
2007-03-19
Aim of this thesis was to reach by a systematic study of different ab initio procedures an improved description of the electronic properties of FeSi and FeGe. Central result is the itinerant description of FeSi as a semiconductor in the neighbourhood of a ferromagnetic instability. The regardment of the nonlocal exchange in the effective one-particle approximation leads to a metastable magnetic state scarcely above the magnetic ground state. The application of the hybrid functional leads to a 1st order metal-isolator transition for large lattice parameters: FeSi transforms at increasement of the lattice parameter from an unmagnetic isolator to a magnetic metal. A similar behavior is found in the isostructural compound FeGe. The two systems FeSi and FeGe were systematically and detailedly analyzed by means of ab initio procedures. Thereby the structural, electronic, and magnetic properties were studied with DFT and HF calculations. Both calculations with spin polarization and without spin polarization were performed.
AB INITIO SIMULATIONS FOR MATERIAL PROPERTIES ALONG THE JUPITER ADIABAT
International Nuclear Information System (INIS)
We determine basic thermodynamic and transport properties of hydrogen-helium-water mixtures for the extreme conditions along Jupiter's adiabat via ab initio simulations, which are compiled in an accurate and consistent data set. In particular, we calculate the electrical and thermal conductivity, the shear and longitudinal viscosity, and diffusion coefficients of the nuclei. We present results for associated quantities like the magnetic and thermal diffusivity and the kinematic shear viscosity along an adiabat that is taken from a state-of-the-art interior structure model. Furthermore, the heat capacities, the thermal expansion coefficient, the isothermal compressibility, the Grüneisen parameter, and the speed of sound are calculated. We find that the onset of dissociation and ionization of hydrogen at about 0.9 Jupiter radii marks a region where the material properties change drastically. In the deep interior, where the electrons are degenerate, many of the material properties remain relatively constant. Our ab initio data will serve as a robust foundation for applications that require accurate knowledge of the material properties in Jupiter's interior, e.g., models for the dynamo generation.
DEFF Research Database (Denmark)
Chaban, Vitaly V.; Prezhdo, Victor; Prezhdo, Oleg
2013-01-01
Nonadiabatic molecular dynamics combined with time-domain density functional theory are used to study electron transfer (ET) from a CdSe quantum dot (QD) to the C-60 fullerene, occurring in several types of hybrid organic/inorganic nanocomposites. By unveiling the time dependence of the ET process...
Institute of Scientific and Technical Information of China (English)
H. Koc; A. Yildirim; E. Deligoz
2012-01-01
The structural,elastic,electronic,optical,and vibrational properties of cubic PdGa compound are investigated using the norm-conserving pseudopotentials within the local density approximation (LDA) in the framework of the density functional theory.The calculated lattice constant has been compared with the experimental value and has been found to be in good agreement with experimental data.The obtained electronic band structures show that PdGa compound has no band gap.The second-order elastic constants have been calculated,and the other related quantities such as the Young's modulus,shear modulus,Poisson's ratio,anisotropy factor,sound velocities,and Debye temperature have also been estimated.Our calculated results of elastic constants show that this compound is mechanically stable.Furthermore,the real and imaginary parts of the dielectric function and the optical constants such as the electron energy-loss function,the optical dielectric constant and the effective number of electrons per unit cell are calculated and presented in the study.The phonon dispersion curves are also derived using the direct method.
High accuracy ab initio studies of electron-densities for the ground state of Be-like atomic systems
Komasa, J.; Słupski, R.; Jankowski, K.; Wasilewski, J.; Teale, A. M.
2013-04-01
Benchmark results for electron densities in the ground states of Li-, Be, C2+, Ne6+, and Ar14+ have been generated from very accurate variational wave functions represented in terms of extensive basis sets of exponentially correlated Gaussian functions. For Ne6+, and Ar14+, the upper bounds to the energies improve over previous results known from the literature. For the remaining systems our bounds are from 0.1 to 1.1 μhartree higher than the most accurate ones. We present in graphical and, partially, numerical form results both for the radial electron densities and for the difference radial density distributions (DRD) (defined with respect to the Hartree-Fock radial density) that highlight the impact of correlation effects on electron densities. Next, we have employed these DRD distributions in studies of the performance of several broadly used orbital-based quantum-chemical methods in accounting for correlation effects on the density. Our computed benchmark densities for Be have been also applied for testing the possibility of using the mathematically strict result concerning exact atomic electron densities, obtained by Ahlrichs et al. [Phys. Rev. A 23, 2106 (1981), 10.1103/PhysRevA.23.2106], for the determination of the reliability range of computed densities in the long-range asymptotic region. The results obtained for Be are encouraging.
Energy Technology Data Exchange (ETDEWEB)
Boyé-Péronne, Séverine; Gauyacq, Dolores [Institut des Sciences Moléculaires d’Orsay, UMR 8214, CNRS and Université Paris-Sud, Bât. 210, F-91405 Orsay Cedex (France); Liévin, Jacques, E-mail: jlievin@ulb.ac.be [Service de Chimie Quantique et Photophysique, Université Libre de Bruxelles, Cpi 160/09, 50 Av. F.D. Roosevelt, B-1050 Bruxelles (Belgium)
2014-11-07
The first quantitative description of the Rydberg and valence singlet electronic states of vinylidene lying in the 0–10 eV region is performed by using large scale ab initio calculations. A deep analysis of Rydberg-valence interactions has been achieved thanks to the comprehensive information contained in the accurate Multi-Reference Configuration Interaction wavefunctions and an original population analysis highlighting the respective role played by orbital and state mixing in such interactions. The present theoretical approach is thus adequate for dealing with larger than diatomic Rydberg systems. The nine lowest singlet valence states have been optimized. Among them, some are involved in strong Rydberg-valence interactions in the region of the Rydberg state equilibrium geometry. The Rydberg states of vinylidene present a great similarity with the acetylene isomer, concerning their quantum defects and Rydberg molecular orbital character. As in acetylene, strong s-d mixing is revealed in the n = 3 s-d supercomplex. Nevertheless, unlike in acetylene, the close-energy of the two vinylidene ionic cores {sup 2}A{sub 1} and {sup 2}B{sub 1} results into two overlapped Rydberg series. These Rydberg series exhibit local perturbations when an accidental degeneracy occurs between them and results in avoided crossings. In addition, some Δl = 1 (s-p and p-d) mixings arise for some Rydberg states and are rationalized in term of electrostatic interaction from the electric dipole moment of the ionic core. The strongest dipole moment of the {sup 2}B{sub 1} cationic state also stabilizes the lowest members of the n = 3 Rydberg series converging to this excited state, as compared to the adjacent series converging toward the {sup 2}A{sub 1} ionic ground state. The overall energies of vinylidene Rydberg states lie above their acetylene counterpart. Finally, predictions for optical transitions in singlet vinylidene are suggested for further experimental spectroscopic
Sambathkumar, K; Jeyavijayan, S; Arivazhagan, M
2015-08-01
Combined experimental and theoretical studies were conducted on the molecular structure and vibrational spectra of 4-AminoPhthalhydrazide (APH). The FT-IR and FT-Raman spectra of APH were recorded in the solid phase. The molecular geometry and vibrational frequencies of APH in the ground state have been calculated by using the ab initio HF (Hartree-Fock) and density functional methods (B3LYP) invoking 6-311+G(d,p) basis set. The optimized geometric bond lengths and bond angles obtained by HF and B3LYP method show best agreement with the experimental values. Comparison of the observed fundamental vibrational frequencies of APH with calculated results by HF and density functional methods indicates that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems. The difference between the observed and scaled wave number values of most of the fundamentals is very small. A detailed interpretation of the NMR spectra of APH was also reported. The theoretical spectrograms for infrared and Raman spectra of the title molecule have been constructed. UV-vis spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were performed by time dependent density functional theory (TD-DFT) approach. Finally the calculations results were applied to simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra. And the temperature dependence of the thermodynamic properties of constant pressure (Cp), entropy (S) and enthalpy change (ΔH0→T) for APH were also determined. PMID:25829160
Energy Technology Data Exchange (ETDEWEB)
Strak, Pawel; Sakowski, Konrad; Kempisty, Pawel [Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw (Poland); Krukowski, Stanislaw, E-mail: stach@unipress.waw.pl [Interdisciplinary Centre for Mathematical and Computational Modelling, University of Warsaw, Pawinskiego 5a, 02-106 Warsaw (Poland)
2015-09-07
Properties of bare and nitrogen-covered Al-terminated AlN(0001) surface were determined using density functional theory (DFT) calculations. At a low nitrogen coverage, the Fermi level is pinned by Al broken bond states located below conduction band minimum. Adsorption of nitrogen is dissociative with an energy gain of 6.05 eV/molecule at a H3 site creating an overlap with states of three neighboring Al surface atoms. During this adsorption, electrons are transferred from Al broken bond to topmost N adatom states. Accompanying charge transfer depends on the Fermi level. In accordance with electron counting rule (ECR), the DFT results confirm the Fermi level is not pinned at the critical value of nitrogen coverage θ{sub N}(1) = 1/4 monolayer (ML), but it is shifted from an Al-broken bond state to Np{sub z} state. The equilibrium thermodynamic potential of nitrogen in vapor depends drastically on the Fermi level pinning being shifted by about 4 eV for an ECR state at 1/4 ML coverage. For coverage above 1/4 ML, adsorption is molecular with an energy gain of 1.5 eV at a skewed on-top position above an Al surface atom. Electronic states of the admolecule are occupied as in the free molecule, no electron transfer occurs and adsorption of a N{sub 2} molecule does not depend on the Fermi level. The equilibrium pressure of molecular nitrogen above an AlN(0001) surface depends critically on the Fermi level position, being very low and very high for low and high coverage, respectively. From this fact, one can conclude that at typical growth conditions, the Fermi level is not pinned, and the adsorption and incorporation of impurities depend on the position of Fermi level in the bulk.
Ab initio engineering of materials with stacked hexagonal tin frameworks
Shao, Junping; Beaufils, Clément; Kolmogorov, Aleksey N.
2016-01-01
The group-IV tin has been hypothesized to possess intriguing electronic properties in an atom-thick hexagonal form. An attractive pathway of producing sizable 2D crystallites of tin is based on deintercalation of bulk compounds with suitable tin frameworks. Here, we have identified a new synthesizable metal distannide, NaSn2, with a 3D stacking of flat hexagonal layers and examined a known compound, BaSn2, with buckled hexagonal layers. Our ab initio results illustrate that despite being an exception to the 8-electron rule, NaSn2 should form under pressures easily achievable in multi-anvil cells and remain (meta)stable under ambient conditions. Based on calculated Z2 invariants, the predicted NaSn2 may display topologically non-trivial behavior and the known BaSn2 could be a strong topological insulator. PMID:27387140
Liu, Jin; Prezhdo, Oleg V
2015-11-19
Rapid development in lead halide perovskites has led to solution-processable thin film solar cells with power conversion efficiencies close to 20%. Nonradiative electron-hole recombination within perovskites has been identified as the main pathway of energy losses, competing with charge transport and limiting the efficiency. Using nonadiabatic (NA) molecular dynamics, combined with time-domain density functional theory, we show that nonradiative recombination happens faster than radiative recombination and long-range charge transfer to an acceptor material. Doping of lead iodide perovskites with chlorine atoms reduces charge recombination. On the one hand, chlorines decrease the NA coupling because they contribute little to the wave functions of the valence and conduction band edges. On the other hand, chlorines shorten coherence time because they are lighter than iodines and introduce high-frequency modes. Both factors favor longer excited-state lifetimes. The simulation shows good agreement with the available experimental data and contributes to the comprehensive understanding of electronic and vibrational dynamics in perovskites. The generated insights into design of higher-efficiency solar cells range from fundamental scientific principles, such as the role of electron-vibrational coupling and quantum coherence, to practical guidelines, such as specific suggestions for chemical doping. PMID:26505613
Energy Technology Data Exchange (ETDEWEB)
Winiarski, M.J., E-mail: M.Winiarski@int.pan.wroc.pl
2014-12-15
Highlights: • Fully relativistic calculations of electronic structures of Re{sub 24}Nb{sub 5} and Re{sub 24}Ti{sub 5}. • Strong effects of antisymmetric spin–orbit coupling on band structures. • Different, multi-band Fermi surfaces obtained for both systems. • Possible intermediate coupled superconductivity in Re{sub 24}Ti{sub 5}. - Abstract: Electronic structures of superconducting Re{sub 24}Nb{sub 5} and Re{sub 24}Ti{sub 5} have been calculated employing the full-potential local-orbital method within the density functional theory. The investigations were focused on the influence of the antisymmetric spin–orbit coupling on band structures and Fermi surfaces of these non-centrosymmetric systems. The predicted here density of states at the Fermi level for Re{sub 24}Ti{sub 5} is abnormally low with respect to that deduced from previous heat capacity measurements. This discrepancy suggests an intermediate coupled superconducting state in Re{sub 24}Ti{sub 5}. The differences between electronic properties of both compounds could explain more robust superconductivity in the Nb-based material.
Valiev, R R; Minaev, B F
2016-09-01
The electric dipole transitions between pure spin and mixed spin electronic states are calculated at the XMC-QDPT2 and MCSCF levels of theory, respectively, for different intermolecular distances of the C6H6 and O2 collisional complex. The magnetic dipole transition moment between the mixed-spin ground ("triplet") and the first excited ("singlet") states is calculated by quadratic response at MCSCF level of theory. The obtained results confirm the theory of intensity borrowing and increasing the intensity of electronic transitions in the C6H6 + O2 collision. The calculation of magnetically induced current density is performed for benzene molecule being in contact with O2 at the distances from 3.5 to 4.5 Å. The calculation shows that the aromaticity of benzene is rising due to the conjugation of π-MOs of both molecules. The C6H6 + O2 complex becomes nonaromatic at the short distances (r < 3.5 Å). The computation of static polarizability in the excited electronic states of the C6H6 + O2 collisional complex at various distances supports the theory of red solvatochromic shift of the a → X band. Graphical abstract The C6H6+ O2 collisional complex. PMID:27544142
Hydrogen effect on electronic and magnetic properties of Cd1-xMnxTe: Ab initio study
Larabi, A.; Merad, G.; Abdelaoui, I.; Sari, A.
2016-07-01
Hydrogen effect on electronic and magnetic properties of diluted magnetic semiconductor (DMS) Cd1-xMnxTe for x composition of 0.125 has been investigated using the projected augmented wave (PAW) based on density functional theory (DFT) formalism within the generalized gradient approximation (GGA). The results show that the Mn dopant is spin-polarized with magnetic moment of 4.189 μB per Mn atom at x≈0.125. The calculated formation energies indicate that the hydrogen is not stable in CdTe and the lowest energy position for H is at the Cd-Mn bond center in Cd0.875Mn0.125Te. We find also that the existence of interstitial hydrogen decreases the magnetic moment of Cd0.875Mn0.125Te diluted magnetic semiconductor. From the calculated density of state, we observed that the presence of hydrogen does not cause a change in electronic properties of Cd0.875Mn0.125Te.
Bensadiq, A.; Zaari, H.; Benyoussef, A.; El Kenz, A.
2016-09-01
Using the density functional theory, the electronic structure; density of states, band structure and exchange couplings of Tb Ni4 Si compound have been investigated. Magnetic and magnetocaloric properties of this material have been studied using Monte Carlo Simulation (MCS) and Mean Field Approximation (MFA) within a three dimensional Ising model. We calculated the isothermal magnetic entropy change, adiabatic temperature change and relative cooling power (RCP) for different external magnetic field and temperature. The highest obtained isothermal magnetic entropy change is of -14.52 J kg-1 K-1 for a magnetic field of H=4 T. The adiabatic temperature reaches a maximum value equal to 3.7 K and the RCP maximum value is found to be 125.12 J kg-1 for a field magnetic of 14 T.
Ab initio MRSDCI study on the low-lying electronic states of the lithium chloride molecule (LiCl).
Kurosaki, Yuzuru; Yokoyama, Keiichi
2012-08-14
Potential energy curves (PECs) for the low-lying states of the lithium chloride molecule (LiCl) have been calculated using the internally contracted multireference single- and double-excitation configuration interaction (MRSDCI) method with the aug-cc-PVnZ (AVnZ) and aug-cc-PCVnZ (ACVnZ) basis sets, where n = T, Q, and 5. First, we calculate PECs for 7 spin-orbit (SO)-free Λ-S states, X(1)Σ(+), A(1)Σ(+), (3)Σ(+), (1)Π, and (3)Π, and then obtain PECs for 13 SO Ω states, X0(+), A0(+), B0(+), 0(-)(I), 0(-)(II), 1(I), 1(II), 1(III), and 2, by diagonalizing the matrix of the electronic Hamiltonian plus the Breit-Pauli SO Hamiltonian. The MRSDCI calculations not including core orbital correlation through the single and double excitations are also performed with the AV5Z and ACV5Z basis sets. The Davidson corrections (Q0) are added to both the Λ-S and Ω state energies. Vibrational eigenstates for the obtained X(1)Σ(+) and X0(+) PECs are calculated by solving the time-independent Schrödinger equation with the grid method. Thus, the effects of basis set, core orbital correlation, and the Davidson correction on the X(1)Σ(+) and X0(+) PECs of LiCl are investigated by comparing the spectroscopic constants calculated from the PECs with one another and with experiment. It is confirmed that to accurately predict the spectroscopic constants we need to include core-electron correlation in the CI expansion and use the basis sets designed to describe core-valence correlation, i.e., ACVnZ. The SO PECs presented in this paper will be of help in the future study of diatomic alkali halide dynamics. PMID:22897271
Directory of Open Access Journals (Sweden)
H A Badehian
2015-07-01
Full Text Available In recent work the structural, electronic and optical properties of BSb compound in bulk and surface (110 states have been studied. Calculations have been performed using Full-Potential Augmented Plane Wave (FP-LAPW method by WIEN2k code in Density Functional Theory (DFT framework. The structural properties of the bulk such as lattice constant, bulk module and elastic constants have been investigated using four different approximations. The band gap energy of the bulk and the (110 surface of BSb were obtained about 1.082 and 0.38 eV respectively. Moreover the surface energy, the work function, the surface relaxation, surface state and the band structure of BSb (110 were investigated using symmetric and stoichiometric 15 layers slabs with the vacuum of 20 Bohr. In addition, the real and imaginary parts of the dielectric function of the bulk and the BSb (110 slab were calculated and compared to each other. Our obtained results have a good agreement with the available results.
Energy Technology Data Exchange (ETDEWEB)
Bentouaf, Ali, E-mail: lilo.btf@gmail.com [Département de Physique, Faculté des Sciences, Université de Hassiba Ben Bouali, Chlef 02000 (Algeria); Hassan, Fouad El Haj [Université Libanaise, Faculté des Sciences (I), Laboratoire de Physique et d' Electronique (LPE), Elhadath, Beirut (Lebanon); Condensed Matter Section, The Abdus Salam International Centre for Theoretical Physics (ICTP), Strada Costiera 11, 34014 Trieste (Italy)
2015-05-01
Density functional theory based on full-potential linearized augmented plane wave (FP LAPW) method is used to investigate the structural, electronic and magnetic properties of Co{sub 2}VSi Heusler alloys, with L2{sub 1} structure. It is shown that calculated lattice constants and spin magnetic moments using the general gradient approximation method are in good agreement with experimental values. We also presented the thermal effects using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. Temperature and pressure effects on the structural parameters, heat capacities, thermal expansion coefficient, and Debye temperatures are determined from the non-equilibrium Gibbs functions. - Highlights: • Our calculated total magnetic moment is 2.96 μB. • The quasi-harmonic Debye model has been used to predict the thermal properties. • The GGA method is a good tool to calculate the magnetic moment. • The total DOS is calculated for the majority and minority spin densities. • The d–d hybridization is essential for the formation of the gap at E{sub F}.
Institute of Scientific and Technical Information of China (English)
Feng Hong-Jian; Liu Fa-Min
2008-01-01
First-principles calculations have been performed to investigate the ground state electronic properties of BaFeO3 (BFO).Local spin density approximation (LSDA) plus U (LSDA+U) treatment modified the metallic behaviour to insulated one with a band gap of 4.12 eV.The spontaneous polarization was found to be 89.3#C/cm2 with Berry phase scheme in terms of the modern theory of polarization.Fe-3d eg were split into two singlet states (dz2 and dx2-y2 ),and Fe-3d t2g were split into one doublet states(dxz and duz) and one singlet states(dxy) after Fe and O displaced along thec axis.Meanwhile the occupation numbers of dz2,dxz,dyz and OT Pz (on the top of Fe) were increased at the expense of those in xy plane.Our results showed that it was the sensitivity of hybridization to ferroelectric distortions,not just the total change of hybridization,that produced the possibility of ferroelectricity.Moreover,the increasing occupation numbers of OT pz and Fe dz2 favoured the 180~ coupling between Fe-3d eg and Fe-3d t2g,leading to ferromagneticordering,which has been confirmed by the increase of magnetic moment by 0.13μB per formula unit in the polarized direction.Hence,the magnetization can be altered by the reversal of external electric field.
Energy Technology Data Exchange (ETDEWEB)
Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Laboratory, Department of Physics, Islamia College Peshawar (Pakistan); Gupta, S.K. [Department of Physics, Michigan Technological University, Houghton, MI 49931 (United States); Seddik, T. [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 Mascara (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 Mascara (Algeria); Alahmed, Z.A. [Department of Physics and Astronomy, College of Science, King Saud University, Riyadh 11451 (Saudi Arabia); Ahmed, R. [Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, UTM Skudai, 81310 Johor (Malaysia); Khachai, H. [Physics Department, Djillali Liabes University of Sidi Bel-Abbes (Algeria); Jha, P.K. [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar 364001 (India); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, Riyadh 11451 (Saudi Arabia)
2014-06-01
Highlights: • REGa{sub 3} (RE = Sc or Lu) compounds are mechanical stabile. • Both ScGa{sub 3} and LuGa{sub 3} exhibit metallic behavior just like other REGa{sub 3} compounds. • Melting temperature T{sub m} (K) for ScGa{sub 3} and LuGa{sub 3} are 1244.2 and 1143.8. • High absorption observed in the visible energy region. • The present study would be helpful for future experimental/theoretical explorations. - Abstract: Structural, elastic, optoelectronic and thermodynamic properties of REGa{sub 3} (RE = Sc and Lu) compounds have been studied self consistently by employing state of the art full potential (FP) linearized (L) approach of augmented plane wave (APW) plus local orbitals method. Calculations were executed at the level of Perdew–Burke and Ernzerhof (PBE) parameterized generalized gradient approximation (GGA) for exchange correlation functional in addition to modified Becke–Johnson (mBJ) potential. Our obtained results of lattice parameters show reasonable agreement to the previously reported experimental and other theoretical studies. Analysis of the calculated band structure of ScGa{sub 3} and LuGa{sub 3} compounds demonstrates their metallic character. Moreover, a positive value of calculated Cauchy pressure, in addition to reflecting their ductile nature, endorses their metallic character as well. To understand optical behavior calculations related to the important optical parameters; real and imaginary parts of the dielectric function, reflectivity R(ω), refractive index n(ω) and electron energy-loss function L(ω) have also been performed. In the present work, thermodynamically properties are also investigated by employing lattice vibrations integrated in quasi harmonic Debye model. Obtained results of volume, heat capacity and Debye temperature as a function of temperature for both compounds, at different values of pressure, are found to be consistent. The calculated value of melting temperature for both compounds (ScGa{sub 3} and Lu
Energy Technology Data Exchange (ETDEWEB)
Barrett, B R; Navratil, P; Vary, J P
2011-04-11
A long-standing goal of nuclear theory is to determine the properties of atomic nuclei based on the fundamental interactions among the protons and neutrons (i.e., nucleons). By adopting nucleon-nucleon (NN), three-nucleon (NNN) and higher-nucleon interactions determined from either meson-exchange theory or QCD, with couplings fixed by few-body systems, we preserve the predictive power of nuclear theory. This foundation enables tests of nature's fundamental symmetries and offers new vistas for the full range of complex nuclear phenomena. Basic questions that drive our quest for a microscopic predictive theory of nuclear phenomena include: (1) What controls nuclear saturation; (2) How the nuclear shell model emerges from the underlying theory; (3) What are the properties of nuclei with extreme neutron/proton ratios; (4) Can we predict useful cross sections that cannot be measured; (5) Can nuclei provide precision tests of the fundamental laws of nature; and (6) Under what conditions do we need QCD to describe nuclear structure, among others. Along with other ab initio nuclear theory groups, we have pursued these questions with meson-theoretical NN interactions, such as CD-Bonn and Argonne V18, that were tuned to provide high-quality descriptions of the NN scattering phase shifts and deuteron properties. We then add meson-theoretic NNN interactions such as the Tucson-Melbourne or Urbana IX interactions. More recently, we have adopted realistic NN and NNN interactions with ties to QCD. Chiral perturbation theory within effective field theory ({chi}EFT) provides us with a promising bridge between QCD and hadronic systems. In this approach one works consistently with systems of increasing nucleon number and makes use of the explicit and spontaneous breaking of chiral symmetry to expand the strong interaction in terms of a dimensionless constant, the ratio of a generic small momentum divided by the chiral symmetry breaking scale taken to be about 1 GeV/c. The
International Nuclear Information System (INIS)
A long-standing goal of nuclear theory is to determine the properties of atomic nuclei based on the fundamental interactions among the protons and neutrons (i.e., nucleons). By adopting nucleon-nucleon (NN), three-nucleon (NNN) and higher-nucleon interactions determined from either meson-exchange theory or QCD, with couplings fixed by few-body systems, we preserve the predictive power of nuclear theory. This foundation enables tests of nature's fundamental symmetries and offers new vistas for the full range of complex nuclear phenomena. Basic questions that drive our quest for a microscopic predictive theory of nuclear phenomena include: (1) What controls nuclear saturation; (2) How the nuclear shell model emerges from the underlying theory; (3) What are the properties of nuclei with extreme neutron/proton ratios; (4) Can we predict useful cross sections that cannot be measured; (5) Can nuclei provide precision tests of the fundamental laws of nature; and (6) Under what conditions do we need QCD to describe nuclear structure, among others. Along with other ab initio nuclear theory groups, we have pursued these questions with meson-theoretical NN interactions, such as CD-Bonn and Argonne V18, that were tuned to provide high-quality descriptions of the NN scattering phase shifts and deuteron properties. We then add meson-theoretic NNN interactions such as the Tucson-Melbourne or Urbana IX interactions. More recently, we have adopted realistic NN and NNN interactions with ties to QCD. Chiral perturbation theory within effective field theory (χEFT) provides us with a promising bridge between QCD and hadronic systems. In this approach one works consistently with systems of increasing nucleon number and makes use of the explicit and spontaneous breaking of chiral symmetry to expand the strong interaction in terms of a dimensionless constant, the ratio of a generic small momentum divided by the chiral symmetry breaking scale taken to be about 1 GeV/c. The resulting NN
Energy Technology Data Exchange (ETDEWEB)
Uvdal, P. (MAX-Chemistry, Department of Chemistry, Box 124, Lund University, S-22100 Lund (Sweden)); MacKerell, A.D. Jr. (Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland at Baltimore, Baltimore, Maryland 21201 (United States)); Wiegand, B.C.; Friend, C.M. (Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138 (United States))
1995-03-15
Interactions with the molybdenum surface have a strong influence on the vibrational spectrum of 2-propoxide on Mo(110). Using [ital ab] [ital initio] electronic-structure calculations the vibrational spectrum of the adsorbed 2-propoxide is determined. All major effects, experimentally observed by electron-energy-loss spectroscopy, are well reproduced by the calculation. Kinematic effects do not explain the observed changes. Calculations indicate that the changes in vibrational spectra are due to alterations of the intramolecular potential function and charge redistribution upon binding to the Mo.
The ab-initio density matrix renormalization group in practice
Energy Technology Data Exchange (ETDEWEB)
Olivares-Amaya, Roberto; Hu, Weifeng; Sharma, Sandeep; Yang, Jun; Chan, Garnet Kin-Lic [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States); Nakatani, Naoki [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States); Catalysis Research Center, Hokkaido University, Kita 21 Nishi 10, Sapporo, Hokkaido 001-0021 (Japan)
2015-01-21
The ab-initio density matrix renormalization group (DMRG) is a tool that can be applied to a wide variety of interesting problems in quantum chemistry. Here, we examine the density matrix renormalization group from the vantage point of the quantum chemistry user. What kinds of problems is the DMRG well-suited to? What are the largest systems that can be treated at practical cost? What sort of accuracies can be obtained, and how do we reason about the computational difficulty in different molecules? By examining a diverse benchmark set of molecules: π-electron systems, benchmark main-group and transition metal dimers, and the Mn-oxo-salen and Fe-porphine organometallic compounds, we provide some answers to these questions, and show how the density matrix renormalization group is used in practice.
Transport coefficients in diamond from ab-initio calculations
Löfâs, Henrik; Grigoriev, Anton; Isberg, Jan; Ahuja, Rajeev
2013-03-01
By combining the Boltzmann transport equation with ab-initio electronic structure calculations, we obtain transport coefficients for boron-doped diamond. We find the temperature dependence of the resistivity and the hall coefficients in good agreement with experimental measurements. Doping in the samples is treated via the rigid band approximation and scattering is treated in the relaxation time approximation. In contrast to previous results, the acoustic phonon scattering is the dominating scattering mechanism for the considered doping range. At room temperature, we find the thermopower, S, in the range 1-1.6 mV/K and the power factor, S2σ, in the range 0.004-0.16 μW /cm K2.
Highly anisotropic thermal conductivity of arsenene: An ab initio study
Zeraati, Majid; Vaez Allaei, S. Mehdi; Abdolhosseini Sarsari, I.; Pourfath, Mahdi; Donadio, Davide
2016-02-01
Elemental two-dimensional (2D) materials exhibit intriguing heat transport and phononic properties. Here we have investigated the lattice thermal conductivity of newly proposed arsenene, the 2D honeycomb structure of arsenic, using ab initio calculations. Solving the Boltzmann transport equation for phonons, we predict a highly anisotropic thermal conductivity of 30.4 and 7.8 W/mK along the zigzag and armchair directions, respectively, at room temperature. Our calculations reveal that phonons with mean free paths between 20 nm and 1 μ m provide the main contribution to the large thermal conductivity in the zigzag direction; mean free paths of phonons contributing to heat transport in the armchair directions range between 20 and 100 nm. The obtained anisotropic thermal conductivity and feasibility of synthesis, in addition to high electron mobility reported elsewhere, make arsenene a promising material for nanoelectronic applications and thermal management.
Ab-initio melting curve and principal Hugoniot of tantalum
International Nuclear Information System (INIS)
We report first principles calculations of the melting curve and principal Hugoniot (P - V curve) of body centered cubic (bcc) tantalum in the pressure range 0-300 GPa. A description of lattice dynamics and thermal properties of bcc Ta using finite temperature density functional theory (DFT) is presented. The approach works within the projector augmented wave (PAW) implementation of DFT and explicitly treats in valence the 5p, 6s and 5d electrons. The principal Hugoniot (P - V curve), obtained using the Rankine-Hugoniot equation, is investigated using the generalized gradient approximations (GGA). Very good agreement with the shock experiments is obtained with GGA in all the range of pressure. We also report the temperature-pressure relation on the shock Hugoniot and the full ab-initio melting curve of Ta
Ab Initio Study of KCl and NaCl Clusters
Brownrigg, Clifton; Hira, Ajit; Pacheco, Jose; Salazar, Justin
2013-03-01
We continue our interest in the theoretical study of molecular clusters to examine the chemical properties of small KnCln and NanCln clusters (n = 2 - 15). The potentially important role of these molecular species in biochemical and medicinal processes is well known. This work applies the hybrid ab initio methods of quantum chemistry to derive the different alkali-halide (MnHn) geometries. Of particular interest is the competition between hexagonal ring geometries and rock salt structures. Electronic energies, rotational constants, dipole moments, and vibrational frequencies for these geometries are calculated. Magic numbers for cluster stability are identified and are related to the property of cluster compactness. Mapping of the singlet, triplet, and quintet, potential energy surfaces is performed. Calculations have been performed to examine the interactions of these clusters with some atoms and molecules of biological interest, including O, O2, and Fe. The potential for design of new medicinal drugs is explored.
Ab initio study of II-(VI){sub 2} dichalcogenides
Energy Technology Data Exchange (ETDEWEB)
Olsson, P; Vidal, J; Lincot, D, E-mail: polsson@kth.se [Institut de R and D sur l' energie photovoltaique (IRDEP), UMR 7174-EDF-CNRS-ENSCP, 6 quai Watier, 78401 Chatou Cedex (France)
2011-10-12
The structural stabilities of the (Zn,Cd)(S,Se,Te){sub 2} dichalcogenides have been determined ab initio. These compounds are shown to be stable in the pyrite phase, in agreement with available experiments. Structural parameters for the ZnTe{sub 2} pyrite semiconductor compound proposed here are presented. The opto-electronic properties of these dichalcogenide compounds have been calculated using quasiparticle GW theory. Bandgaps, band structures and effective masses are proposed as well as absorption coefficients and refraction indices. The compounds are all indirect semiconductors with very flat conduction band dispersion and high absorption coefficients. The work functions and surface properties are predicted. The Te and Se based compounds could be of interest as absorber materials in photovoltaic applications. (paper)
Energy Technology Data Exchange (ETDEWEB)
Zhu, Xiaolei, E-mail: virtualzx@gmail.com; Yarkony, David R., E-mail: yarkony@jhu.edu [Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218 (United States)
2016-01-14
In this work, we demonstrate that for moderate sized systems, here a system with 13 atoms, global coupled potential energy surfaces defined for several electronic states over a wide energy range and for distinct regions of nuclear coordinate space characterized by distinct electron configurations, can be constructed with precise energetics and an excellent description of non-adiabatic interactions in all regions. This is accomplished using a recently reported algorithm for constructing quasi-diabatic representations, H{sup d}, of adiabatic electronic states coupled by conical intersections. In this work, the algorithm is used to construct an H{sup d} to describe the photodissociation of phenol from its first and second excited electronic states. The representation treats all 33 internal degrees of freedom in an even handed manner. The ab initio adiabatic electronic structure data used to construct the fit are obtained exclusively from multireference configuration interaction with single and double excitation wave functions comprised of 88 × 10{sup 6} configuration state functions, at geometries determined by quasi-classical trajectories. Since the algorithm uses energy gradients and derivative couplings in addition to electronic energies to construct H{sup d}, data at only 7379 nuclear configurations are required to construct a representation, which describes all nuclear configurations involved in H atom photodissociation to produce the phenoxyl radical in its ground or first excited electronic state, with a mean unsigned energy error of 202.9 cm{sup −1} for electronic energies <60 000 cm{sup −1}.
Ab initio calculation of double ionization of atoms
Energy Technology Data Exchange (ETDEWEB)
Serov, V. V., E-mail: vladislav.serov@mail.ru [Saratov State University, Department of Theoretical Physics (Russian Federation)
2013-02-15
The Solov'ev-Vinitsky method was used to perform an ab initio calculation of the triple-differential cross section for the double single-photon photoionization of helium for the case of equal emitted-electron energies. A Gaussian width {gamma} describing angular electron-electron correlations at the total electron energy E taking values in range between 0.1 and 100 eV was obtained for this cross section. The results agree with available experimental data, but they raise a doubt as to whether the well-known Wannier law {gamma} {proportional_to} E{sup 1/4} is applicable at experimentally accessible energies. The Gaussian width {gamma} was investigated as a function of the total emitted-electron energy for targets that have a strongly asymmetric configuration of the initial state-specifically, a negative atomic-hydrogen ion H{sup -} and heliumin the 1s2s{sup 1}S and 1s3s{sup 1}S excited states. It was found that this function, {gamma}(E), had a maximum at low energies. It was also shown that, at low energies, the dependence of the double-differential cross section on the angle between the emitted-electron momenta for the targets indicated above differed substantially from the Gaussian dependence, featuring maxima whose number was equal to the number of radial nodes in the initial state. This opens new possibilities for a qualitative analysis of the electron structure of targets.
Ab initio simulation of transport phenomena in rarefied gases.
Sharipov, Felix; Strapasson, José L
2012-09-01
Ab initio potentials are implemented into the direct simulation Monte Carlo (DSMC) method. Such an implementation allows us to model transport phenomena in rarefied gases without any fitting parameter of intermolecular collisions usually extracted from experimental data. Applying the method proposed by Sharipov and Strapasson [Phys. Fluids 24, 011703 (2012)], the use of ab initio potentials in the DSMC requires the same computational efforts as the widely used potentials such as hard spheres, variable hard sphere, variable soft spheres, etc. At the same time, the ab initio potentials provide more reliable results than any other one. As an example, the transport coefficients of a binary mixture He-Ar, viz., viscosity, thermal conductivity, and thermal diffusion factor, have been calculated for several values of the mole fraction. PMID:23030889
Towards new horizons in ab initio nuclear structure theory
International Nuclear Information System (INIS)
We review recent advances in ab initio nuclear structure theory, which have changed the horizons of this field. Starting from chiral effective field theory to construct the nuclear Hamiltonian and the similarity renormalization group to further soften it, we address several many-body approaches that have seen major developments over the past few years. We show that the domain of ab initio nuclear structure theory has been pushed well beyond the p-shell and that quantitative QCD-based predictions are becoming possible all the way from the proton to the neutron drip line up into the medium-mass regime. (authors)
Recent achievements in ab initio modelling of liquid water
Khaliullin, Rustam Z
2013-01-01
The application of newly developed first-principle modeling techniques to liquid water deepens our understanding of the microscopic origins of its unusual macroscopic properties and behaviour. Here, we review two novel ab initio computational methods: second-generation Car-Parrinello molecular dynamics and decomposition analysis based on absolutely localized molecular orbitals. We show that these two methods in combination not only enable ab initio molecular dynamics simulations on previously inaccessible time and length scales, but also provide unprecedented insights into the nature of hydrogen bonding between water molecules. We discuss recent applications of these methods to water clusters and bulk water.
Use of ab initio quantum chemical methods in battery technology
Energy Technology Data Exchange (ETDEWEB)
Deiss, E. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)
1997-06-01
Ab initio quantum chemistry can nowadays predict physical and chemical properties of molecules and solids. An attempt should be made to use this tool more widely for predicting technologically favourable materials. To demonstrate the use of ab initio quantum chemistry in battery technology, the theoretical energy density (energy per volume of active electrode material) and specific energy (energy per mass of active electrode material) of a rechargeable lithium-ion battery consisting of a graphite electrode and a nickel oxide electrode has been calculated with this method. (author) 1 fig., 1 tab., 7 refs.
Aguirrechu-Comerón, Amagoia; Hernández-Molina, Rita; Rodríguez-Hernández, Plácida; Muñoz, Alfonso; Rodríguez-Mendoza, Ulises R; Lavín, Vı́ctor; Angel, Ross J; Gonzalez-Platas, Javier
2016-08-01
Copper(I) iodine compounds can exhibit interesting mechanochromic and thermochromic luminescent properties with important technological applications. We report the synthesis and structure determination by X-ray diffraction of a new polymeric staircase copper(I) iodine compound catena(bis(μ2-iodo)-6-methylquinoline-copper(I), [C10H9CuIN]. The structure is composed of isolated polymeric staircase chains of copper-iodine coordinated to organic ligands through Cu-N bonds. High pressure X-ray diffraction to 6.45 GPa shows that the material is soft, with a bulk modulus K0 = 10.2(2)GPa and a first derivative K'0 = 8.1(3), typical for organometallic compounds. The unit-cell compression is very anisotropic with the stiffest direction [302] arising from a combination of the stiff CuI ladders and the shear of the planar quinolone ligands over one another. Full structure refinements at elevated pressures show that pressures reduce the Cu···Cu distances in the compound. This effect is detected in luminescence spectra with the appearance of four sub-bands at 515, 600, 647, and 712 nm above 3.5 GPa. Red-shifts are observed, and they are tentatively associated with interactions between copper(I) ions due to the shortening of the Cu···Cu distances induced by pressure, below twice the van der Waals limit (2.8 Å). Additionally, ab initio simulations were performed, and they confirmed the structure and the results obtained experimentally for the equation of state. The simulation allowed the band structure and the electronic density of states of this copper(I) iodine complex to be determined. In particular, the band gap decreases slowly with pressure in a quadratic way with dEg/dP = -0.011 eV/GPa and d(2)Eg/dP(2) = 0.001 eV/GPa(2). PMID:27429246
Ab Initio Calculation on Self-Assembled Base-Functionalized Single-Walled Carbon Nanotubes
Institute of Scientific and Technical Information of China (English)
SONG Chen; XIA Yue-Yuan; ZHAO Ming-Wen; LIU Xiang-Dong; LI Ji-Ling; LI Li-Juan; LI Feng; HUANG Bo-Da
2006-01-01
@@ We perform ab initio calculations on the self-assembled base-functionalized single-walled carbon nanotubes (SWNTs) which exhibit the quasi-1D ‘ladder’ structure. The optimized configuration in the ab initio calculation is very similar to that obtainedfrom molecular dynamics simulation. We also calculate the electronic structures of the self-assembled base-functionalized SWNTs that exhibit distinct difference from the single-branch base-functionalized SWNT with a localized state lying just below the Fermi level, which may result from the coupling interaction between the bases accompanied by the self-assembly behaviour.
Śmialek, Malgorzata A.; Łabuda, Marta; Guthmuller, Julien; Hubin-Franskin, Marie-Jeanne; Delwiche, Jacques; Hoffmann, Søren Vrønning; Jones, Nykola C.; Mason, Nigel J.; Limão-Vieira, Paulo
2016-06-01
The high-resolution vacuum ultraviolet photoabsorption spectrum of ethyl acetate, C4H8O2, is presented over the energy range 4.5-10.7 eV (275.5-116.0 nm). Valence and Rydberg transitions and their associated vibronic series observed in the photoabsorption spectrum, have been assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. Also, the photoabsorption cross sections have been used to calculate the photolysis lifetime of this ester in the upper stratosphere (20-50 km). Calculations have also been carried out to determine the ionisation energies and fine structure of the lowest ionic state of ethyl acetate and are compared with a newly recorded photoelectron spectrum (from 9.5 to 16.7 eV). Vibrational structure is observed in the first photoelectron band of this molecule for the first time.
Lucas, J. M.; de Andrés, J.; López, E.; Albertí, M.; Bofill, J. M.; Bassi, D.; Ascenzi, D.; Tosi, P.; Aguilar, A.
2009-08-01
The association reactions between Li+, K+, and Rb+ (M) and butanone and cyclohexanone molecules under single collision conditions have been studied using a radiofrequency-guided ion-beam apparatus, characterizing the adducts by mass spectrometry. The excitation function for the [M-(molecule)]+ adducts (in arbitrary units) has been obtained at low collision energies in the 0.10 eV up to a few eV range in the center of mass frame. The measured relative cross sections decrease when collision energy increases, showing the expected energy dependence for adduct formation. The energetics and structure of the different adducts have been calculated ab initio at the MP2(full) level, showing that the M+-molecule interaction takes place through the carbonyl oxygen atom, as an example of a nontypical covalent chemical bond. The cross-section energy dependence and the role of radiative cooling rates allowing the stabilization of the collision complexes are also discussed.
Ab initio and work function and surface energy anisotropy of LaB6
Uijttewaal, M. A.; de Wijs, G. A.; de Groot, R. A.
2006-01-01
Lanthanum hexaboride is one of the cathode materials most used in high-power electronics technology, but the many experimental results do not provide a consistent picture of the surface properties. Therefore, we report the first ab initio calculations of the work functions and surface energies of th
Relativistic ab initio spectroscopy study of forbidden lines of singly ionized zinc
Dixit, Gopal; Sahoo, Bijaya K.; Chaudhuri, Rajat K.; Majumder, Sonjoy
2009-01-01
The ab initio calculation has been carried out to study the astrophysically important forbidden electromagnetic transition rates of singly ionized zinc (Zn II). Electron correlations are considered to all orders using coupled-cluster theory in the relativistic framework. Calculated excitation energi
Cyanogen Azide. Ionization Potentials and Ab Initio SCF MO Calculation
DEFF Research Database (Denmark)
Bak, Börge; Jansen, Peter; Stafast, Herbert
1975-01-01
The Ne(I) and He(I) photoelectron(PE) spectra of cyanogen azide, NCN3, have been recorded at high resolution. Their interpretation is achieved by comparison with the PE spectrum of HN3 and an ab initio LCGO SCF MO calculation. Deviations from Koopmans' theorem of quite different magnitudes are fo...
Relaxation of Small Molecules: an ab initio Study
Institute of Scientific and Technical Information of China (English)
CAO Yi-Gang; JIAO Zheng-Kuan; A. Antons; K. Schroeder; S. Blügel2
2002-01-01
Using an ab initio total energy and force method, we have relaxed several group IV and group V elementalclusters, in detail the arsenic and antimony dimers, silicon, phosphorus, arsenic and antimony tetramers. The obtainedbond lengths and cohesive energies are more accurate than other calculating methods, and in excellent agreement withthe experimental results.
Young Modulus of Crystalline Polyethylene from ab Initio Molecular Dynamics
Hageman, J.C.L.; Meier, Robert J.; Heinemann, M.; Groot, R.A. de
1997-01-01
The Young modulus for crystalline polyethylene is calculated using ab initio molecular dynamics based on density functional theory in the local density approximation (DFT-LDA). This modulus, which can be seen as the ultimate value for the Young modulus of polyethylene fibers, is found to be 334 GPa.
DEFF Research Database (Denmark)
Shim, Irene; Kingcade, Joseph E.; Gingerich, Karl A.
1988-01-01
All electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations have been applied to investigate the low-lying electronic states of the NiGe molecule. The ground state of the NiGe molecule is predicted to be 1Sigma+. The chemical bond in the 1Sigma+ ground state is a double...... bond composed of one sigma and one pi bond. The sigma bond is due to a delocalized molecular orbital formed by combining the Ni 4s and the Ge 4psigma orbitals. The pi bond is a partly delocalized valence bond, originating from the coupling of the 3dpi hole on Ni with the 4ppi electron on Ge. The low......-lying electronic states of the NiGe molecule have all been characterized by the symmetry of the hole in the 3d shell of Ni. The dissociation energy of the NiGe molecule has been determined from our high temperature mass spectrometric equilibrium data in combination with the theoretical results as D [open circle] 0...
Marsalek, Ondrej
2015-01-01
Path integral molecular dynamics simulations, combined with an ab initio evaluation of interactions using electronic structure theory, incorporate the quantum mechanical nature of both the electrons and nuclei, which are essential to accurately describe systems containing light nuclei. However, path integral simulations have traditionally required a computational cost around two orders of magnitude greater than treating the nuclei classically, making them prohibitively costly for most applications. Here we show that the cost of path integral simulations can be dramatically reduced by extending our ring polymer contraction approach to ab initio molecular dynamics simulations. By using density functional tight binding as a reference system, we show that our ab initio ring polymer contraction (AI-RPC) scheme gives rapid and systematic convergence to the full path integral density functional theory result. We demonstrate the efficiency of this approach in ab initio simulations of liquid water and the reactive pro...
Energy Technology Data Exchange (ETDEWEB)
Dannenberg, Antje
2011-08-30
The mechanism which causes many of the unusual thermomechanical properties of martensitic alloys, as for example, superelasticity and the shape-memory effect, is the martensitic transformation. The prototype ferromagnetic shape memory alloy (FSMA) is Ni{sub 2}MnGa. But a technological breakthrough is missing due to its poor ductility and low operation temperatures. The goal of this thesis is the proposal of new FSMA appropriate for future technological applications. I focus on X{sub 2}YZ Heusler alloys which are mainly based on Mn, Fe, Co, and Ni for the X and Y sites and Z=Ga or Zn. The big challenge of this work is to find material classes which combine the unique magnetomechanical properties of FSMA which are large recoverable magnetostrictive strains, high magnetocrystalline anisotropy energy, and highly mobile twin boundaries with transformation temperatures clearly above room temperature and a reduced brittleness. Such a study, providing material classes which from a theoretical point of view are promising candidates for future FSMA, will help the experimental physicists to select interesting subgroups in the vast number of possible chemical compositions of X{sub 2}YZ Heusler alloys. I have systematically varied the composition in the new Heusler alloys in order to find trends indicating generic tendencies of the material properties, for instance, as a function of the valence electron concentration e/a. A main feature of this thesis is the attempt to find the origin of the competing structural ordering tendencies between conventional X{sub 2}YZ and inverse (XY)XZ Heusler structures which are observed for all systems investigated. In the first part of this work the accuracy and predictive power of ab initio and Monte Carlo simulations is demonstrated by reproducing the experimental phase diagram of Ni-Mn-(Ga,In,Sn,Sb). The linear increasing and decreasing slopes of T{sub M} and T{sub C} can be reproduced by total and free energy calculations and the analysis
Properties of metals during the heating by intense laser irradiation using ab initio simulations
Holst, Bastian; Recoules, Vanina; Torrent, Marc; Mazevet, Stephane
2011-10-01
Ultrashort laser pulses irradiating a target heat the electrons to very high temperatures. In contrast, the ionic lattice is unaffected on the time scale of the laser pulse since the heat capacity of electrons is much smaller than that of the lattice. This non-equilibrium system can be described as a composition of two subsystems: one consisting of hot electrons and the other of an ionic lattice at low temperature. We studied the effect of this intense electronic excitations on the optical properties of gold using ab initio simulations. We additionally use ab initio linear response to compute the phonon spectrum and the electron-phonon coupling constant within Density Functional Theory for several electronic temperatures of few eV. LULI, Ecole Polytechnique, CNRS, CEA, UPMC, 91128 Palaiseau, France.
Ab initio simulations of pseudomorphic silicene and germanene bidimensional heterostructures
Debernardi, Alberto; Marchetti, Luigi
2016-06-01
Among the novel two-dimensional (2D) materials, silicene and germanene, which are two honeycomb crystal structures composed of a monolayer of Si and Ge, respectively, have attracted the attention of material scientists because they combine the advantages of the new 2D ultimate-scaled electronics with their compatibility with industrial processes presently based on Si and Ge. We envisage pseudomorphic lateral heterostructures based on ribbons of silicene and germanene, which are the 2D analogs of conventional 3D Si/Ge superlattices and quantum wells. In spite of the considerable lattice mismatch (˜4 % ) between free-standing silicene and germanene, our ab initio simulations predict that, considering striped 2D lateral heterostructures made by alternating silicene and germanene ribbons of constant width, the silicene/germanene junction remains pseudomorphic—i.e., it maintains lattice-matched edges—up to critical ribbon widths that can reach some tens of nanometers. Such critical widths are one order of magnitude larger than the critical thickness measured in 3D pseudomorphic Si/Ge heterostructures and the resolution of state-of-the-art lithography, thus enabling the possibility of lithography patterned silicene/germanene junctions. We computed how the strain produced by the pseudomorphic growth modifies the crystal structure and electronic bands of the ribbons, providing a mechanism for band-structure engineering. Our results pave the way for lithography patterned lateral heterostructures that can serve as the building blocks of novel 2D electronics.
Ab-initio calculations for dilute magnetic semiconductors
Energy Technology Data Exchange (ETDEWEB)
Belhadji, Brahim
2008-03-03
This thesis focusses on ab-initio calculations for the electronic structure and the magnetic properties of dilute magnetic semiconductors (DMS). In particular we aim at the understanding of the complex exchange interactions in these systems. Our calculations are based on density functional theory, being ideally suited for a description of the material specific properties of the considered DMS. Moreover we use the KKR Green function method in connection with the coherent potential approximation (CPA), which allows to include the random substitutional disorder in a mean field-like approximation for the electronic structure. Finally we calculate the exchange coupling constants J{sub ij} between two impurities in a CPA medium by using the Lichtenstein formula and from this calculate the Curie temperature by a numerically exact Monte Carlo method. Based on this analysis we found and investigated four different exchange mechanisms being of importance in DMS systems: Double exchange, p-d exchange, antiferromagnetic superexchanges, and ferromagnetic superexchange. A second topic we have investigated in this thesis is the pressure dependence of the exchange interactions and the Curie temperatures in (Ga,Mn)As and (In,Mn)As, using the LDA and the LDA+U approximations. Exact calculations of T{sub C} by Monte Carlo simulations show a somehow different behavior. (orig.)
Bannikov, V. V.; Beketov, A. R.; Baranov, M. V.; Elagin, A. A.; Kudyakova, V. S.; Shishkin, R. A.
2016-05-01
The phase stability, electronic structure, and magnetic properties of Al1- x Ti x N compositions based on the metastable aluminum nitride modification with the rock-salt structure at low ( x = 0.03) and high ( x = 0.25) concentrations of titanium in the system have been investigated using the results of ab initio band calculations. It has been shown that, at low values of x, the partial substitution is characterized by a positive enthalpy, which, however, changes sign with an increase in the titanium concentration. According to the results of the band structure calculations, the doped compositions have electronic conductivity. For x = 0.03, titanium impurity atoms have local magnetic moments (˜0.6 μB), and the electronic spectrum is characterized by a 100% spin polarization of near-Fermi states. Some of the specific features of the chemical bonding in Al1- x Ti x N cubic phases have been considered.
Das, Uday; Naskar, Jishu; Mukherjee, Alok Kumar
2015-12-01
A terminally protected acyclic tetrapeptide has been synthesized, and the crystal structure of its hydrated form, Boc-Tyr-Aib-Tyr-Ile-OMe·2H2O (1), has been determined directly from powder X-ray diffraction data. The backbone conformation of tetrapeptide (1) exhibiting two consecutive β-turns is stabilized by two 4 → 1 intramolecular N-H · · · O hydrogen bonds. In the crystalline state, the tetrapeptide molecules are assembled through water-mediated O-H · · · O hydrogen bonds to form two-dimensional molecular sheets, which are further linked by intermolecular C-H · · · O hydrogen bonds into a three-dimensional supramolecular framework. The molecular electrostatic potential (MEP) surface of (1) has been used to supplement the crystallographic observations. The nature of intermolecular interactions in (1) has been analyzed quantitatively through the Hirshfeld surface and two-dimensional fingerprint plot. The DFT optimized molecular geometry of (1) agrees closely with that obtained from the X-ray structure analysis. The present structure analysis of Boc-Tyr-Aib-Tyr-Ile-OMe·2H2 O (1) represents a case where ab-initio crystal structure of an acyclic tetrapeptide with considerable molecular flexibility has been accomplished from laboratory X-ray powder diffraction data.
McKemmish, Laura K; Tennyson, Jonathan
2016-01-01
Accurate knowledge of the rovibronic near-infrared and visible spectra of vanadium monoxide (VO) is very important for studies of cool stellar and hot planetary atmospheres. Here, the required ab initio dipole moment and spin-orbit coupling curves for VO are produced. This data forms the basis of a new VO line list considering 13 different electronic states and containing over 277 million transitions. Open shell transition, metal diatomics are challenging species to model through ab initio quantum mechanics due to the large number of low-lying electronic states, significant spin-orbit coupling and strong static and dynamic electron correlation. Multi-reference configuration interaction methodologies using orbitals from a complete active space self-consistent-field (CASSCF) calculation are the standard technique for these systems. We use different state-specific or minimal-state CASSCF orbitals for each electronic state to maximise the calculation accuracy. The off-diagonal dipole moment controls the intensity...
Understanding phonon transport in thermoelectric materials using ab initio approaches
Broido, David
Good thermoelectric materials have low phonon thermal conductivity, kph. Accurate theories to describe kph are important components in developing predictive models of thermoelectric efficiency that can help guide synthesis and measurement efforts. We have developed ab initio approaches to calculate kph, in which phonon modes and phonon scattering rates are computed using interatomic force constants determined from density functional theory, and a full solution of the Boltzmann transport equation for phonons is implemented. A recent approach to calculate interatomic force constants using ab initio molecular dynamics has yielded a good description of the thermal properties of Bi2Te3. But, the complexity of new promising candidate thermoelectric materials introduces computational challenges in assessing their thermal properties. An example is germanane, a germanium based hydrogen-terminated layered semiconductor, which we will discuss in this talk.
The density matrix renormalization group for ab initio quantum chemistry
Wouters, Sebastian
2014-01-01
During the past 15 years, the density matrix renormalization group (DMRG) has become increasingly important for ab initio quantum chemistry. Its underlying wavefunction ansatz, the matrix product state (MPS), is a low-rank decomposition of the full configuration interaction tensor. The virtual dimension of the MPS, the rank of the decomposition, controls the size of the corner of the many-body Hilbert space that can be reached with the ansatz. This parameter can be systematically increased until numerical convergence is reached. The MPS ansatz naturally captures exponentially decaying correlation functions. Therefore DMRG works extremely well for noncritical one-dimensional systems. The active orbital spaces in quantum chemistry are however often far from one-dimensional, and relatively large virtual dimensions are required to use DMRG for ab initio quantum chemistry (QC-DMRG). The QC-DMRG algorithm, its computational cost, and its properties are discussed. Two important aspects to reduce the computational co...
Toward the Ab-initio Description of Medium Mass Nuclei
Barbieri, C; Soma, V; Duguet, T; Navratil, P
2012-01-01
As ab-initio calculations of atomic nuclei enter the A=40-100 mass range, a great challenge is how to approach the vast majority of open-shell (degenerate) isotopes. We add realistic three-nucleon interactions to the state of the art many-body Green's function theory of closed-shells, and find that physics of neutron driplines is reproduced with very good quality. Further, we introduce the Gorkov formalism to extend ab-initio theory to semi-magic, fully open-shell, isotopes. Proof-of-principle calculations for Ca-44 and Ni-74 confirm that this approach is indeed feasible. Combining these two advances (open-shells and three-nucleon interactions) requires longer, technical, work but it is otherwise within reach.
Serine Proteases an Ab Initio Molecular Dynamics Study
De Santis, L
1999-01-01
In serine proteases (SP's), the H-bond between His-57 and Asp-102, and that between Gly-193 and the transition state intermediate play a crucial role for enzymatic function. To shed light on the nature of these interactions, we have carried out ab initio molecular dynamics simulations on complexes representing adducts between the reaction intermediate and elastase (one protein belonging to the SP family). Our calculations indicate the presence of a low--barrier H-bond between His-57 and Asp-102, in complete agreement with NMR experiments on enzyme--transition state analog complexes. Comparison with an ab initio molecular dynamics simulation on a model of the substrate--enzyme adduct indicates that the Gly-193--induced strong stabilization of the intermediate is accomplished by charge/dipole interactions and not by H-bonding as previously suggested. Inclusion of the protein electric field in the calculations does not affect significantly the charge distribution.
The Pu–U–Am system: An ab initio informed CALPHAD thermodynamic study
Energy Technology Data Exchange (ETDEWEB)
Perron, A., E-mail: perron1@llnl.gov [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Turchi, P.E.A.; Landa, A.; Söderlind, P. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Ravat, B.; Oudot, B.; Delaunay, F. [CEA-Centre de Valduc, 21120 Is sur Tille (France)
2015-03-15
Highlights: • The ab initio informed CALPHAD assessment of the Am–U system has been realized. • A strong tendency toward phase separation across the whole composition range is predicted. • The ab initio informed Pu–U–Am thermodynamic database has been developed. • The solubility of Am and U in the liquid phase is improved by adding Pu. • The δ-Pu (fcc) phase is strongly stabilized by Am, on the contrary to the bcc phase. - Abstract: Phase diagram and thermodynamic properties of the Am–U system, that are experimentally unknown, are calculated using the CALPHAD method with input from ab initio electronic-structure calculations for the fcc and bcc phases. A strong tendency toward phase separation across the whole composition range is predicted. In addition, ab initio informed Pu–U and Am–Pu thermodynamic assessments are combined to build a Pu–U–Am thermodynamic database. Regarding the Pu-rich corner of the ternary system, predictions indicate that Am acts as a powerful δ-Pu (fcc) stabilizer. In the U-rich corner, similar predictions are made but to a lesser extent. In both cases, the bcc phase is destabilized and the fcc phase is enhanced. Finally, results and methodology are discussed and compared with previous assessments and guidelines are provided for further experimental studies.
Accurate ab initio vibrational energies of methyl chloride
Energy Technology Data Exchange (ETDEWEB)
Owens, Alec, E-mail: owens@mpi-muelheim.mpg.de [Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr (Germany); Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London (United Kingdom); Yurchenko, Sergei N.; Yachmenev, Andrey; Tennyson, Jonathan [Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London (United Kingdom); Thiel, Walter [Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr (Germany)
2015-06-28
Two new nine-dimensional potential energy surfaces (PESs) have been generated using high-level ab initio theory for the two main isotopologues of methyl chloride, CH{sub 3}{sup 35}Cl and CH{sub 3}{sup 37}Cl. The respective PESs, CBS-35{sup HL}, and CBS-37{sup HL}, are based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set (CBS) limit, and incorporate a range of higher-level (HL) additive energy corrections to account for core-valence electron correlation, higher-order coupled cluster terms, scalar relativistic effects, and diagonal Born-Oppenheimer corrections. Variational calculations of the vibrational energy levels were performed using the computer program TROVE, whose functionality has been extended to handle molecules of the form XY {sub 3}Z. Fully converged energies were obtained by means of a complete vibrational basis set extrapolation. The CBS-35{sup HL} and CBS-37{sup HL} PESs reproduce the fundamental term values with root-mean-square errors of 0.75 and 1.00 cm{sup −1}, respectively. An analysis of the combined effect of the HL corrections and CBS extrapolation on the vibrational wavenumbers indicates that both are needed to compute accurate theoretical results for methyl chloride. We believe that it would be extremely challenging to go beyond the accuracy currently achieved for CH{sub 3}Cl without empirical refinement of the respective PESs.
Rational design of electrolyte components by ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Johansson, Patrik; Jacobsson, Per [Department of Applied Physics, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)
2006-02-28
This paper is a small review of the use of computer simulations and especially the use of standard quantum-mechanical ab initio electronic structure calculations to rationally design and investigate different choices of chemicals/systems for lithium battery electrolytes. Covered systems and strategies to enhance the performance of electrolytes will range from assisting the interpretation of vibrational spectroscopy experiments over development of potentials for molecular dynamics simulations, to the design of new lithium salts and the lithium ion coordination in liquid, polymer, and gel polymer electrolytes. Examples of studied properties include the vibrational spectra of anions and ion pairs to characterize the nature and extent of the interactions present, the lithium ion affinities of anions, important for the salt solvation and the ability to provide a high concentration of charge carriers, the HOMO energies of the anions to estimate the stability versus oxidation, the anion volumes that correlate to the anion mobility, the lithium ion coordination and dynamics to reveal the limiting steps of lithium ion transport, etc. (author)
Volumic omit maps in ab initio dual-space phasing.
Oszlányi, Gábor; Sütő, András
2016-07-01
Alternating-projection-type dual-space algorithms have a clear construction, but are susceptible to stagnation and, thus, inefficient for solving the phase problem ab initio. To improve this behaviour new omit maps are introduced, which are real-space perturbations applied periodically during the iteration process. The omit maps are called volumic, because they delete some predetermined subvolume of the unit cell without searching for atomic regions or analysing the electron density in any other way. The basic algorithms of positivity, histogram matching and low-density elimination are tested by their solution statistics. It is concluded that, while all these algorithms based on weak constraints are practically useless in their pure forms, appropriate volumic omit maps can transform them to practically useful methods. In addition, the efficiency of the already useful reflector-type charge-flipping algorithm can be further improved. It is important that these results are obtained by using non-sharpened structure factors and without any weighting scheme or reciprocal-space perturbation. The mathematical background of volumic omit maps and their expected applications are also discussed. PMID:27357850
The density matrix renormalization group for ab initio quantum chemistry
Wouters, Sebastian
2015-01-01
During the past 15 years, the density matrix renormalization group (DMRG) has become increasingly important for ab initio quantum chemistry. It is used as a numerically exact solver for highly correlated regions in molecules. While the method works extremely well for one-dimensional systems, the correlated regions of interest are often far from one-dimensional. In this introductory talk, I will discuss the DMRG algorithm from a quantum information perspective, how quantum information theory h...
GAUSSIAN 76: an ab initio molecular orbital program
Energy Technology Data Exchange (ETDEWEB)
Binkley, J. S.; Whiteside, R.; Hariharan, P. C.; Seeger, R.; Hehre, W. J.; Lathan, W. A.; Newton, M. D.; Ditchfield, R.; Pople, J. A.
1978-06-01
Gaussian 76 is a general-purpose computer program for ab initio Hartree-Fock molecular orbital calculations. It can handle basis sets involving s, p and d-type gaussian functions. Certain standard sets (STO-3G, 4-31G, 6-31G*, etc.) are stored internally for easy use. Closed shell (RHF) or unrestricted open shell (UHF) wave functions can be obtained. Facilities are provided for geometry optimization to potential minima and for limited potential surface scans.
Acceleration of the Convergence in ab initio Atomic Relaxations
Zhao, Zhengji; Wang, Lin-Wang; Meza, Juan
2006-03-01
Atomic relaxations is often required to accurately describe the properties of nanosystems. In ab initio calculations, a common practice is to use a standard search algorithm, such as BFGS (Broyden-Fletcher-Goldfarb-Shanno) or CG (conjugate gradient) method, which starts the atomic relaxations without any knowledge of the Hessian matrix of the system. For example, the initial Hessian in BFGS method is often set to identity, and there is no preconditioning to CG method. One way to accelerate the convergence of the atomic relaxations is to estimate an approximate Hessian matrix of the system and then use it as the initial Hessian in BFGS method or a preconditioner in CG method. Previous attempts to obtain the approximated Hessian were focused on the use of classical force field models which rely on the existence of good parameters. Here, we present an alternative method to estimate the Hessian matrix of a nanosystem. First, we decompose the system into motifs which consist of a few atoms, then calculate the Hessian matrix elements on different motif types from ab initio calculations for small prototype systems. Then we generate the Hessian Matrix of the whole system by putting together these motif Hessians. We have applied our motif-based Hessian matrix in ab initio atomic relaxations in several bulk (with/without impurity) and quantum dot systems, and have found a speed up factor of 2 to 4 depending on the system size.
A Complete and Accurate Ab Initio Repeat Finding Algorithm.
Lian, Shuaibin; Chen, Xinwu; Wang, Peng; Zhang, Xiaoli; Dai, Xianhua
2016-03-01
It has become clear that repetitive sequences have played multiple roles in eukaryotic genome evolution including increasing genetic diversity through mutation, changes in gene expression and facilitating generation of novel genes. However, identification of repetitive elements can be difficult in the ab initio manner. Currently, some classical ab initio tools of finding repeats have already presented and compared. The completeness and accuracy of detecting repeats of them are little pool. To this end, we proposed a new ab initio repeat finding tool, named HashRepeatFinder, which is based on hash index and word counting. Furthermore, we assessed the performances of HashRepeatFinder with other two famous tools, such as RepeatScout and Repeatfinder, in human genome data hg19. The results indicated the following three conclusions: (1) The completeness of HashRepeatFinder is the best one among these three compared tools in almost all chromosomes, especially in chr9 (8 times of RepeatScout, 10 times of Repeatfinder); (2) in terms of detecting large repeats, HashRepeatFinder also performed best in all chromosomes, especially in chr3 (24 times of RepeatScout and 250 times of Repeatfinder) and chr19 (12 times of RepeatScout and 60 times of Repeatfinder); (3) in terms of accuracy, HashRepeatFinder can merge the abundant repeats with high accuracy. PMID:26272474
Ab initio nuclear structure - the large sparse matrix eigenvalue problem
International Nuclear Information System (INIS)
The structure and reactions of light nuclei represent fundamental and formidable challenges for microscopic theory based on realistic strong interaction potentials. Several ab initio methods have now emerged that provide nearly exact solutions for some nuclear properties. The ab initio no core shell model (NCSM) and the no core full configuration (NCFC) method, frame this quantum many-particle problem as a large sparse matrix eigenvalue problem where one evaluates the Hamiltonian matrix in a basis space consisting of many-fermion Slater determinants and then solves for a set of the lowest eigenvalues and their associated eigenvectors. The resulting eigenvectors are employed to evaluate a set of experimental quantities to test the underlying potential. For fundamental problems of interest, the matrix dimension often exceeds 1010 and the number of nonzero matrix elements may saturate available storage on present-day leadership class facilities. We survey recent results and advances in solving this large sparse matrix eigenvalue problem. We also outline the challenges that lie ahead for achieving further breakthroughs in fundamental nuclear theory using these ab initio approaches.
Ab initio vibrations in nonequilibrium nanowires
DEFF Research Database (Denmark)
Jauho, Antti-Pekka; Engelund, Mads; Markussen, T;
2010-01-01
We review recent results on electronic and thermal transport in two different quasi one-dimensional systems: Silicon nanowires (SiNW) and atomic gold chains. For SiNW's we compute the ballistic electronic and thermal transport properties on equal footing, allowing us to make quantitative...
Energy Technology Data Exchange (ETDEWEB)
Bernard, St
1998-12-31
The quest for metallic hydrogen is a major goal for both theoretical and experimental condensed matter physics. Hydrogen and deuterium have been compressed up to 200 GPa in diamond anvil cells, without any clear evidence for a metallic behaviour. Loubeyere has recently suggested that hydrogen could metallize, at pressures within experimental range, in a new Van der Waals compound: Ar(H{sub 2}){sub 2} which is characterized at ambient pressure by an open and anisotropic sublattice of hydrogen molecules, stabilized by an argon skeleton. This thesis deals with a detailed ab initio investigation, by Car-Parrinello molecular dynamics methods, of the evolution under pressure of this compound. In a last chapter, we go to much higher pressures and temperatures, in order to compare orbital and orbital free ab initio methods for the dense hydrogen plasma. (author) 109 refs.
Ab initio vibrations in nonequilibrium nanowires
International Nuclear Information System (INIS)
We review recent results on electronic and thermal transport in two different quasi one-dimensional systems: Silicon nanowires (SiNW) and atomic gold chains. For SiNW's we compute the ballistic electronic and thermal transport properties on equal footing, allowing us to make quantitative predictions for the thermoelectric properties, while for the atomic gold chains we evaluate microscopically the damping of the vibrations, due to the coupling of the chain atoms to the modes in the bulk contacts. Both approaches are based on the combination of density-functional theory, and nonequilibrium Green's functions.
DEFF Research Database (Denmark)
Palmer, Michael H.; Camp, Philip J.; Hoffmann, Søren Vrønning;
2012-01-01
The first vacuum ultraviolet absorption spectrum of a 1,2,4-triazole has been obtained and analyzed in detail, with assistance from both an enhanced UV photoelectron spectroscopic study and ab initio multi-reference multi-root configuration interaction procedures. For both 1H- and 1-methyl-1...... in terms of the near degeneracy of the first two ionization energies, leading to a pseudo Jahn-Teller effect. The “fingerprint” of the ionization spectrum yields band origins for several Rydberg states. The configuration interaction study shows that although the equilibrium structure for the first cation...... is effectively planar, the second cation shows significant twisting of the ring system. Some calculated singlet electronic states also show skeletal twisting in which the ring C–H is substantially out of plane....
Ab Initio Calculations for the BaTiO3 (001) Surface Structure
Institute of Scientific and Technical Information of China (English)
XUE Xu-Yan; WANG Chun-Lei; ZHONG Wei-Lie
2004-01-01
@@ The ab initio method within the local density approximation is applied to calculate cubic BaTiO3 (001) surface relaxation and rumpling for two different terminations (BaO and TiO2). Our calculations demonstrate that cubic perovskite BaTiO3 crystals possess surface polarization, accompanied by the presence of the relevant electric field.We analyse their electronic structures (band structure, density of states and the electronic density redistribution with emphasis on the covalency effects). The results are also compared with that of the previous ab initio calculations. Considerable increases of Ti-O chemical bond covalency nearby the surface have been observed.The band gap reduces especially for the TiO2 termination.
Ab initio modelling of the behaviour of point defects and fission products in nuclear fuel
International Nuclear Information System (INIS)
The aim of this work is to determine precisely the mechanisms of formation and migration of defects and fission products as well as the associated energies. Examples on uranium dioxide UO2 (standard nuclear fuel) and on uranium carbide UC (potential fuel for new generation reactors) are given. The obtained results are discussed and compared with the experimental results carried out. The ab initio method used is the Projector Augmented-Wave (PAW) method based on the density functional theory. The particular electronic properties of actinides are especially studied because, on account of their 5f orbitals more or less localized around the nucleus, it is difficult to model the actinide compounds by the DFT method. In particular, the modelling of the exchange-correlation interaction of the 5f electrons of UO2 requires approximations (as GGA+U) beyond those more currently used in ab initio calculations (LDA or GGA). (O.M.)
Ab initio potential energy surface for the highly nonlinear dynamics of the KCN molecule
Energy Technology Data Exchange (ETDEWEB)
Párraga, H.; Arranz, F. J., E-mail: fj.arranz@upm.es; Benito, R. M., E-mail: rosamaria.benito@upm.es [Grupo de Sistemas Complejos, ETSI Agrónomos, Universidad Politécnica de Madrid, 28040 Madrid (Spain); Borondo, F., E-mail: f.borondo@uam.es [Departamento de Química and Instituto de Ciencias Matemáticas (ICMAT), Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid (Spain)
2013-11-21
An accurate ab initio quantum chemistry study at level of quadratic configuration interaction method of the electronic ground state of the KCN molecule is presented. A fitting of the results to an analytical series expansion was performed to obtain a global potential energy surface suitable for the study of the associated vibrational dynamics. Additionally, classical Poincaré surfaces of section for different energies and quantum eigenstates were calculated, showing the highly nonlinear behavior of this system.
Ab initio calculation of positron distribution, ACAR and lifetime in TTF-TCNQ
International Nuclear Information System (INIS)
We have performed ab initio calculations of positron distribution, ACAR and lifetime in the quasi-one-dimensional organic conductor TTF-TCNQ. The electronic structure is obtained within the LDA, while the positron state is calculated either with the LDA or with the GGA. Except the positron lifetime, differences between the LDA and GGA results are rather small. The obtained results are compared with our previous experiments and calculations.
Ab initio calculation of positron distribution, ACAR and lifetime in TTF-TCNQ
Ishibashi, Shoji; Kohyama, Masanori
2000-06-01
We have performed ab initio calculations of positron distribution, ACAR and lifetime in the quasi-one-dimensional organic conductor TTF-TCNQ. The electronic structure is obtained within the LDA, while the positron state is calculated either with the LDA or with the GGA. Except the positron lifetime, differences between the LDA and GGA results are rather small. The obtained results are compared with our previous experiments and calculations.
Projector augmented wave method: ab initio molecular dynamics with full wave functions
Indian Academy of Sciences (India)
Peter E Blöchl; Clemens J Först; Johannes Schimpl
2003-01-01
A brief introduction to the projector augmented wave method is given and recent developments are reviewed. The projector augmented wave method is an all-electron method for efficient ab initio molecular dynamics simulations with full wave functions. It extends and combines the traditions of existing augmented wave methods and the pseudopotential approach. Without sacrificing efficiency, the PAW method avoids transferability problems of the pseudopotential approach and it has been valuable to predict properties that depend on the full wave functions.
Ab initio theory of galvanomagnetic phenomena in ferromagnetic metals and disordered alloys
Turek, Ilja; Kudrnovsky, Josef; Drchal, Vaclav
2011-01-01
We present an ab initio theory of transport quantities of metallic ferromagnets developed in the framework of the fully relativistic tight-binding linear muffin-tin orbital method. The approach is based on the Kubo-Streda formula for the conductivity tensor, on the coherent potential approximation for random alloys, and on the concept of interatomic electron transport. The developed formalism is applied to pure 3d transition metals (Fe, Co, Ni) and to random Ni-based ferromagnetic alloys (Ni-...
Ab initio molecular dynamics study of liquid sodium and cesium up to critical point
Energy Technology Data Exchange (ETDEWEB)
Yuryev, Anatoly A. [Institute of Metallurgy of Ural Branch of the Russian Academy of Sciences, Amundsen st. 101,620016, Yekaterinburg (Russian Federation); Ural Federal University, Vira st. 19, 620002, Yekaterinburg (Russian Federation); Gelchinski, Boris R. [Institute of Metallurgy of Ural Branch of the Russian Academy of Sciences, Amundsen st. 101,620016, Yekaterinburg (Russian Federation)
2015-08-17
Ab initio modeling of liquid metals Na and K is carried out using the program SIESTA. We have determined the parameters of the model (the optimal step, the number of particles, the initial state etc) and calculated a wide range of properties: the total energy, pair correlation function, coefficient of self-diffusion, heat capacity, statistics of Voronoi polyhedra, the density of electronic states up to the critical temperature.
Hyperfine tensors of nitrogen-vacancy center in diamond from \\emph{ab initio} calculations
Gali, Adam
2009-01-01
We determine and analyze the charge and spin density distributions of nitrogen-vacancy (N-V) center in diamond for both the ground and excited states by \\emph{ab initio} supercell calculations. We show that the hyperfine tensor of $^{15}$N nuclear spin is negative and strongly anisotropic in the excited state, in contrast to previous models used extensively to explain electron spin resonance measurements. In addition, we detect a significant redistribution of the spin density due to excitatio...
Tarighi Ahmadpour, Mahdi; Hashemifar, S. Javad; Rostamnejadi, Ali
2016-07-01
We use density functional computations to study the zero temperature structural, electronic, magnetic, and optical properties of (5,0) finite carbon nanotubes (FCNT), with length in the range of 4-44 Å. It is found that the structural and electronic properties of (5,0) FCNTs, in the ground state, converge at a length of about 30 Å, while the excited state properties exhibit long-range edge effects. We discuss that curvature effects enhance energy gap of FCNTs, in contrast to the known trend in the periodic limit. It is seen that compensation of curvature effects in two special small sizes may give rise to spontaneous magnetization. The obtained cohesive energies provide some insights into the effects of environment on the growth of FCNTs. The second-order difference of the total energies reveals an important magic size of about 15 Å. The optical and dynamical magnetic responses of the FCNTs to polarized electromagnetic pulses are studied by time dependent density functional theory. The results show that the static and dynamic magnetic properties mainly come from the edge carbon atoms. The optical absorption properties are described in terms of local field effects and characterized by Casida linear response method.
Ab initio structure determination via powder X-ray diffraction
Indian Academy of Sciences (India)
Digamber G Porob; T N Guru Row
2001-10-01
Structure determination by powder X-ray diffraction data has gone through a recent surge since it has become important to get to the structural information of materials which do not yield good quality single crystals. Although the method of structure completion when once the starting model is provided is facile through the Rietveld refinement technique, the structure solution ab initio os still not push-button technology. In this article a survey of the recent development in this area is provided with an illustration of the structure determination of -NaBi3V2O10.
Electrostriction coefficient of ferroelectric materials from ab initio computation
Directory of Open Access Journals (Sweden)
Z. Jiang
2016-06-01
Full Text Available Electrostriction is an important material property that characterizes how strain changes with the development of polarization inside a material. We show that ab initio techniques developed in recent years can be exploited to compute and understand electrostriction of ferroelectric materials. Here, electrostriction coefficients of ferroelectric BaTiO3, PbTiO3, as well as dielectric BaZrO3, are obtained and analyzed. Possible causes of the difference between experimental and numerical results are discussed. We also identified that relative displacements between certain ions at a given polarization could be a good indicator of a material’s electrostriction property.
Tailoring magnetoresistance at the atomic level: An ab initio study
Tao, Kun
2012-01-05
The possibility of manipulating the tunneling magnetoresistance (TMR) of antiferromagnetic nanostructures is predicted in the framework of ab initio calculations. By the example of a junction composed of an antiferromagnetic dimer and a spin-polarized scanning tunneling microscopy tip we show that the TMR can be tuned and even reversed in sign by lateral and vertical movements of the tip. Moreover, our finite-bias calculations demonstrate that the magnitude and the sign of the TMR can also be tuned by an external voltage. © 2012 American Physical Society.
Ab initio study of neutron drops with chiral Hamiltonians
Directory of Open Access Journals (Sweden)
H.D. Potter
2014-12-01
Full Text Available We report ab initio calculations for neutron drops in a 10 MeV external harmonic-oscillator trap using chiral nucleon–nucleon plus three-nucleon interactions. We present total binding energies, internal energies, radii and odd–even energy differences for neutron numbers N=2–18 using the no-core shell model with and without importance truncation. Furthermore, we present total binding energies for N=8,16,20,28,40,50 obtained in a coupled-cluster approach. Comparisons with quantum Monte Carlo results, where available, using Argonne v8′ with three-nucleon interactions reveal important dependences on the chosen Hamiltonian.
Ab initio Study of He Stability in hcp-Ti
Institute of Scientific and Technical Information of China (English)
DAI Yun-Ya; YANG Li; PENG Shu-Ming; LONG Xing-Gui; GAO Fei; ZU Xiao-Tao
2010-01-01
@@ The stability of He in hcp-Ti is studied using the ab initio method based on the density functional theory.The results indicate that a single He atom prefers to occupy the tetrahedral site rather than the octahedral site.The interaction of He defects with Ti atoms is employed to explain the relative stabilities of He point defects in hcp-Ti.The relative stability of He defects in hcp-Ti is useful for He clustering and bubble nucleation in metal tritides,which provides the basis for development of improved atomistic models.
Ab-initio study of transition metal hydrides
Energy Technology Data Exchange (ETDEWEB)
Sharma, Ramesh [Dept. of Physics, Feroze Gandhi Insititute of Engineering and Technology, Raebareli-229001 (India); Shukla, Seema, E-mail: sharma.yamini62@gmail.com; Dwivedi, Shalini, E-mail: sharma.yamini62@gmail.com; Sharma, Yamini, E-mail: sharma.yamini62@gmail.com [Theoretical Condensed Matter Physics Laboratory, Dept. of Physics Feroze Gandhi College, Raebareli-229001 (India)
2014-04-24
We have performed ab initio self consistent calculations based on Full potential linearized augmented plane wave (FP-LAPW) method to investigate the optical and thermal properties of yttrium hydrides. From the band structure and density of states, the optical absorption spectra and specific heats have been calculated. The band structure of Yttrium metal changes dramatically due to hybridization of Y sp orbitals with H s orbitals and there is a net charge transfer from metal to hydrogen site. The electrical resistivity and specific heats of yttrium hydrides are lowered but the thermal conductivity is slightly enhanced due to increase in scattering from hydrogen sites.
Ab initio study of phase equilibria in TiCx
DEFF Research Database (Denmark)
Korzhavyi, P.A.; Pourovskii, L.V.; Hugosson, H.W.;
2002-01-01
The phase diagram for the vacancy-ordered structures in the substoichiometric TiCx (x = 0.5-1.0) has been established from Monte Carlo simulations with the long-range pair and multisite effective interactions obtained from ab initio calculations. Three ordered superstructures of vacancies (Ti2C, Ti......3C2, and Ti6C5) are found to be ground state configurations. Their stability has been verified by full-potential total energy calculations of the fully relaxed structures....
Accelerating Ab Initio Nuclear Physics Calculations with GPUs
Potter, Hugh; Maris, Pieter; Sosonkina, Masha; Vary, James; Binder, Sven; Calci, Angelo; Langhammer, Joachim; Roth, Robert; Çatalyürek, Ümit; Saule, Erik
2014-01-01
This paper describes some applications of GPU acceleration in ab initio nuclear structure calculations. Specifically, we discuss GPU acceleration of the software package MFDn, a parallel nuclear structure eigensolver. We modify the matrix construction stage to run partly on the GPU. On the Titan supercomputer at the Oak Ridge Leadership Computing Facility, this produces a speedup of approximately 2.2x - 2.7x for the matrix construction stage and 1.2x - 1.4x for the entire run.
Kedziera, Dariusz; Mentel, Łukasz; Żuchowski, Piotr S.; Knoop, Steven
2015-06-01
We have obtained accurate ab initio +4Σ quartet potentials for the diatomic metastable triplet helium+alkali-metal (Li, Na, K, Rb) systems, using all-electron restricted open-shell coupled cluster singles and doubles with noniterative triples corrections CCSD(T) calculations and accurate calculations of the long-range C6 coefficients. These potentials provide accurate ab initio quartet scattering lengths, which for these many-electron systems is possible, because of the small reduced masses and shallow potentials that result in a small amount of bound states. Our results are relevant for ultracold metastable triplet helium+alkali-metal mixture experiments.
Ab initio calculations on the magnetic properties of transition metal complexes
International Nuclear Information System (INIS)
We present a protocol for the ab initio determination of the magnetic properties of mono- and polynuclear transition metal compounds. First, we obtain the low lying electronic states by multireference methods. Then, we include spin-orbit coupling and an external magnetic field for the determination of zero-field splitting and g-tensors. For the polynuclear complexes the magnetic exchange coupling constants are determined by a modified complete active space self consistent field method. Based on the results of the ab initio calculations, magnetic data such as magnetic susceptibility or magnetization are simulated and compared to experimental data. The results obtained for the polynuclear complexes are further analysed by calculations on model complexes where part of the magnetic centers are substituted by diamagnetic ions. The methods are applied to different Co and Ni containing transition metal complexes
B28: the smallest all-boron cage from an ab initio global search
Zhao, Jijun; Huang, Xiaoming; Shi, Ruili; Liu, Hongsheng; Su, Yan; King, R. Bruce
2015-09-01
Our ab initio global searches reveal the lowest-energy cage for B28, which is built from two B12 units and prevails over the competing structural isomers such as planar, bowl, and tube. This smallest boron cage extends the scope of all-boron fullerene and provides a new structural motif of boron clusters and nanostructures.Our ab initio global searches reveal the lowest-energy cage for B28, which is built from two B12 units and prevails over the competing structural isomers such as planar, bowl, and tube. This smallest boron cage extends the scope of all-boron fullerene and provides a new structural motif of boron clusters and nanostructures. Electronic supplementary information (ESI) available: Planar isomer structures of B28 and spatial distributions of front molecular orbitals. See DOI: 10.1039/c5nr04034e
A highly accurate {\\it ab initio} potential energy surface for methane
Owens, Alec; Yachmenev, Andrey; Tennyson, Jonathan; Thiel, Walter
2016-01-01
A new nine-dimensional potential energy surface (PES) for methane has been generated using state-of-the-art \\textit{ab initio} theory. The PES is based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit and incorporates a range of higher-level additive energy corrections. These include: core-valence electron correlation, higher-order coupled cluster terms beyond perturbative triples, scalar relativistic effects and the diagonal Born-Oppenheimer correction. Sub-wavenumber accuracy is achieved for the majority of experimentally known vibrational energy levels with the four fundamentals of $^{12}$CH$_4$ reproduced with a root-mean-square error of $0.70{\\,}$cm$^{-1}$. The computed \\textit{ab initio} equilibrium C{--}H bond length is in excellent agreement with previous values despite pure rotational energies displaying minor systematic errors as $J$ (rotational excitation) increases. It is shown that these errors can be significantly reduced by adjusting the e...
Knoop, S.; Żuchowski, P. S.; KÈ©dziera, D.; Mentel, Ł.; Puchalski, M.; Mishra, H. P.; Flores, A. S.; Vassen, W.
2014-08-01
We have investigated the ultracold interspecies scattering properties of metastable triplet He and Rb. We performed state-of-the-art ab initio calculations of the relevant interaction potential, and measured the interspecies elastic cross section for an ultracold mixture of metastable triplet He4 and Rb87 in a quadrupole magnetic trap at a temperature of 0.5 mK. Our combined theoretical and experimental study gives an interspecies scattering length a4+87=+17-4+1a0, which prior to this work was unknown. More general, our work shows the possibility of obtaining accurate scattering lengths using ab initio calculations for a system containing a heavy, many-electron atom, such as Rb.
Ab initio study of AlxMoNbTiV high-entropy alloys.
Cao, Peiyu; Ni, Xiaodong; Tian, Fuyang; Varga, Lajos K; Vitos, Levente
2015-02-25
The Al(x)MoNbTiV (x = 0-1.5) high-entropy alloys (HEAs) adopt a single solid-solution phase, having the body centered cubic (bcc) crystal structure. Here we employ the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation to investigate the equilibrium volume, elastic constants, and polycrystalline elastic moduli of Al(x)MoNbTiV HEAs. A comparison between the ab initio and experimental equilibrium volumes demonstrates the validity and accuracy of the present approach. Our results indicate that Al addition decreases the thermodynamic stability of the bcc structure with respect to face-centered cubic and hexagonal close packed lattices. For the elastically isotropic Al(0.4)MoNbTiV HEAs, the valence electron concentration (VEC) is about 4.82, which is slightly different from VEC ∼ 4.72 obtained for the isotropic Gum metals and refractory--HEAs. PMID:25640032
Liquid Be, Ca and Ba. An orbital-free ab-initio molecular dynamics study
Energy Technology Data Exchange (ETDEWEB)
Rio, B. G. del; González, L. E. [Departamento de Física Teórica, Atómica y Óptica, Universidad de Valladolid, 47011 Valladolid (Spain)
2015-08-17
Several static and dynamic properties of liquid beryllium (l-Be), liquid calcium (l-Ca) and liquid barium (l-Ba) near their triple point have been evaluated by the orbital-free ab initio molecular dynamics method (OF-AIMD), where the interaction between valence electrons and ions is described by means of local pseudopotentials. These local pseudopotentials used were constructed through a force-matching process with those obtained from a Kohn-Sham ab initio molecular dynamics study (KS-AIMD) of a reduced system with non-local pseudopotentials. The calculated static structures show good agreement with the available experimental data, including an asymmetric second peak in the structure factor which has been linked to the existence of a marked icosahedral short-range order in the liquid. As for the dynamic properties, we obtain collective density excitations whose associated dispersion relations exhibit a positive dispersion.
Melting of sodium under high pressure. An ab-initio study
Energy Technology Data Exchange (ETDEWEB)
González, D. J.; González, L. E. [Departamento de Física Teórica, Atómica y Optica, Universidad de Valladolid, 47011 Valladolid (Spain)
2015-08-17
We report ab-initio molecular dynamics simulations of dense liquid/solid sodium for a pressure range from 0 to 100 GPa. The simulations have been performed with the orbital free ab-initio molecular dynamics method which, by using the electron density as the basic variable, allows to perform simulations with large samples and for long runs. The calculated melting curve shows a maximum at a pressure ≈ 30 GPa and it is followed by a long, steep decrease. These features are in good agreement with the experimental data. For various pressures along the melting curve, we have calculated several liquid static properties (pair distribution functions, static structure factors and short-range order parameters) in order to analyze the structural effects of pressure.
An ab initio potential function for the ν13 vibrational mode of 1,3-butadiene
Senent, M. L.
1995-06-01
The restricted potential of the ν13 torsional mode of 1,3-butadiene has been determined from ab initio calculations. The relative energy and geometry of the second rotamer were calculated with the optimized couple cluster method with double substitutions. This ab initio level provides that the second stable structure attaches to a gauche form situated at 140.8°. The potential energy function was obtained by fitting to a symmetry-adapted Fourier series the total electronic energies of several selected conformations. These energies were calculated by the Möller-Plesset perturbation theory up to the second order (MP2) with full and partial optimization of the geometry. Torsional Raman band positions and fundamental frequencies were determined from the periodic potentials with a good agreement with experimental data. The convenience of performing fully optimized calculations to determine the restricted function is also refuted.
Ab initio calculation of valley splitting in monolayer δ-doped phosphorus in silicon.
Drumm, Daniel W; Budi, Akin; Per, Manolo C; Russo, Salvy P; L Hollenberg, Lloyd C
2013-02-27
: The differences in energy between electronic bands due to valley splitting are of paramount importance in interpreting transport spectroscopy experiments on state-of-the-art quantum devices defined by scanning tunnelling microscope lithography. Using vasp, we develop a plane-wave density functional theory description of systems which is size limited due to computational tractability. Nonetheless, we provide valuable data for the benchmarking of empirical modelling techniques more capable of extending this discussion to confined disordered systems or actual devices. We then develop a less resource-intensive alternative via localised basis functions in siesta, retaining the physics of the plane-wave description, and extend this model beyond the capability of plane-wave methods to determine the ab initio valley splitting of well-isolated δ-layers. In obtaining an agreement between plane-wave and localised methods, we show that valley splitting has been overestimated in previous ab initio calculations by more than 50%.
In pursuit of the ab initio limit for conformational energy prototypes
Császár, Attila G.; Allen, Wesley D.; Schaefer, Henry F.
1998-06-01
The convergence of ab initio predictions to the one- and n-particle limits has been systematically explored for several conformational energy prototypes: the inversion barriers of ammonia, water, and isocyanic acid, the torsional barrier of ethane, the E/Z rotamer separation of formic acid, and the barrier to linearity of silicon dicarbide. Explicit ab initio results were obtained with atomic-orbital basis sets as large as [7s6p5d4f3g2h1i/6s5p4d3f2g1h] and electron correlation treatments as extensive as fifth-order Møller-Plesset perturbation theory (MP5), the full coupled-cluster method through triple excitations (CCSDT), and Brueckner doubles theory including perturbational corrections for both triple and quadruple excitations [BD(TQ)]. Subsequently, basis set and electron correlation extrapolation schemes were invoked to gauge any further variations in arriving at the ab initio limit. Physical effects which are tacitly neglected in most theoretical work have also been quantified by computations of non-Born-Oppenheimer (BODC), relativistic, and core correlation shifts of relative energies. Instructive conclusions are drawn for the pursuit of spectroscopic accuracy in theoretical conformational analyses, and precise predictions for the key energetic quantities of the molecular prototypes are advanced.
An ab initio study of plutonium oxides surfaces; Etude ab initio des surfaces d'oxydes de Pu
Energy Technology Data Exchange (ETDEWEB)
Jomard, G.; Bottin, F.; Amadon, B
2007-07-01
By means of first-principles calculations, we have studied the atomic structure as well as the thermodynamic stability of various plutonium dioxide surfaces in function of their environment (in terms of oxygen partial pressure and temperature). All these simulations have been performed with the ABINIT code. It is well known that DFT fails to describe correctly plutonium-based materials since 5f electrons in such systems are strongly correlated. In order to go beyond DFT, we have treated PuO{sub 2} and {beta}-Pu{sub 2}O{sub 3} in a DFT+U framework. We show that the couple of parameters (U,J) that works well for pure Pu is also well designed for describing ground state (GS) properties of these two oxides. The major improvement with respect with DFT is that we are able to predict an insulating GS in agreement with experiments. The presence of a gap in the DOS (Density of States) of plutonium oxides should play a significant role in the predicted surface reactivity. However, performing DFT+U calculations on surfaces of plutonium oxide from scratch was too ambitious. That is why we decided, as a first step, to study the stability of the (100), (110) and (111) surfaces of PuO{sub 2} in a DFT-GGA framework. For each of these orientations, we considered various terminations. These ab initio results have been introduced in a thermodynamic model which allows us to predict the relative stability of the different terminations as a function of temperature and oxygen partial pressure (p{sub O{sub 2}}). We conclude that at room temperature and for p{sub O{sub 2}}{approx}10 atm., the polar O{sub 2}-(100) termination is favoured. The stabilization of such a polar stoichiometric surface is surprising and should be confirmed by DFT+U calculations before any final conclusion. (authors)
First fully ab initio potential energy surface of methane with a spectroscopic accuracy
Nikitin, A. V.; Rey, M.; Tyuterev, Vl. G.
2016-09-01
Full 9-dimensional ab initio potential energy surfaces for the methane molecule are constructed using extended electronic structure coupled-cluster calculations with various series of basis sets following increasing X cardinal numbers: cc-pVXZ (X = 3, 4, 5, 6), aug-cc-ACVXZ (X = 3, 4, 5), and cc-pCVXZ-F12 (X = 3, 4). High-order dynamic electron correlations including triple and quadrupole excitations as well as relativistic and diagonal Born-Oppenheimer breakdown corrections were accounted for. Analytical potential functions are parametrized as non-polynomial expansions in internal coordinates in irreducible tensor representation. Vibrational energy levels are reported using global variational nuclear motion calculations with exact kinetic energy operator and a full account of the tetrahedral symmetry of CH4. Our best ab initio surface including above-mentioned contributions provides the rms (obs.-calc.) errors of less than 0.11 cm-1 for vibrational band centers below 4700 cm-1, and ˜0.3 cm-1 for all 229 assigned experimentally determined vibrational levels up to the Icosad range <7900 cm-1 without empirically adjusted parameters. These results improve the accuracy of ab initio methane vibrational predictions by more than an order of magnitude with respect to previous works. This is an unprecedented accuracy of first-principles calculations of a five-atomic molecule for such a large data set. New ab initio potential results in significantly better band center predictions even in comparison with best available empirically corrected potential energy surfaces. The issues related to the basis set extrapolation and an additivity of various corrections at this level of accuracy are discussed.
Fink, Karin
2006-04-01
Oxygen vacancies at the polar O terminated (0001) surface of ZnO are of particular interest, because they are discussed as active sites in the methanol synthesis. In general, the polar ZnO surfaces are stabilized by OH groups, therefore O vacancies can be generated by removing either O atoms or OH or H2O groups from the surface. These defects differ in the number of electrons in the vacancy and the number of OH groups in the neighborhood. In the present study, the electronic structure and the adsorption properties of four different types of oxygen vacancies have been investigated by means of embedded cluster calculations. We performed ab initio calculations on F+ like surface excitations for the different defect types and found that the transition energies are above the optical band-gap, while F+ centers in bulk ZnO show a characteristic optical excitation at 3.19 eV. Furthermore, we studied the adsorption of CO2 and CO at the different defect sites by DFT calculations. We found that CO2 dissociates at electron rich vacancies into CO and an O atom which remains in the vacancy. At the OH vacancy which contains an unpaired electron CO2 adsorbed in the form of CO2-, while it adsorbed as a linear neutral molecule at the H2O defect. CO adsorbed preferentially at the H2O defect and the OH defect, both with a binding energy of 0.3 eV. PMID:16633631
Ab Initio Protein Structure Prediction Using Pathway Models
Directory of Open Access Journals (Sweden)
Christopher Bystroff
2006-04-01
Full Text Available Ab initio prediction is the challenging attempt to predict protein structures based only on sequence information and without using templates. It is often divided into two distinct sub-problems: (a the scoring function that can distinguish native, or native-like structures, from non-native ones; and (b the method of searching the conformational space. Currently, there is no reliable scoring function that can always drive a search to the native fold, and there is no general search method that can guarantee a significant sampling of near-natives. Pathway models combine the scoring function and the search. In this short review, we explore some of the ways pathway models are used in folding, in published works since 2001, and present a new pathway model, HMMSTR-CM, that uses a fragment library and a set of nucleation/propagation-based rules. The new method was used for ab initio predictions as part of CASP5. This work was presented at the Winter School in Bioinformatics, Bologna, Italy, 10Ã¢Â€Â“14 February 2003.
Ab initio dynamics of the cytochrome P450 hydroxylation reaction
Energy Technology Data Exchange (ETDEWEB)
Elenewski, Justin E.; Hackett, John C, E-mail: jchackett@vcu.edu [Department of Physiology and Biophysics and The Massey Cancer Center, School of Medicine, Virginia Commonwealth University, 401 College Street, Richmond, Virginia 23219-1540 (United States)
2015-02-14
The iron(IV)-oxo porphyrin π-cation radical known as Compound I is the primary oxidant within the cytochromes P450, allowing these enzymes to affect the substrate hydroxylation. In the course of this reaction, a hydrogen atom is abstracted from the substrate to generate hydroxyiron(IV) porphyrin and a substrate-centered radical. The hydroxy radical then rebounds from the iron to the substrate, yielding the hydroxylated product. While Compound I has succumbed to theoretical and spectroscopic characterization, the associated hydroxyiron species is elusive as a consequence of its very short lifetime, for which there are no quantitative estimates. To ascertain the physical mechanism underlying substrate hydroxylation and probe this timescale, ab initio molecular dynamics simulations and free energy calculations are performed for a model of Compound I catalysis. Semiclassical estimates based on these calculations reveal the hydrogen atom abstraction step to be extremely fast, kinetically comparable to enzymes such as carbonic anhydrase. Using an ensemble of ab initio simulations, the resultant hydroxyiron species is found to have a similarly short lifetime, ranging between 300 fs and 3600 fs, putatively depending on the enzyme active site architecture. The addition of tunneling corrections to these rates suggests a strong contribution from nuclear quantum effects, which should accelerate every step of substrate hydroxylation by an order of magnitude. These observations have strong implications for the detection of individual hydroxylation intermediates during P450 catalysis.
Unified ab initio approaches to nuclear structure and reactions
Navrátil, Petr; Quaglioni, Sofia; Hupin, Guillaume; Romero-Redondo, Carolina; Calci, Angelo
2016-05-01
The description of nuclei starting from the constituent nucleons and the realistic interactions among them has been a long-standing goal in nuclear physics. In addition to the complex nature of the nuclear forces, with two-, three- and possibly higher many-nucleon components, one faces the quantum-mechanical many-nucleon problem governed by an interplay between bound and continuum states. In recent years, significant progress has been made in ab initio nuclear structure and reaction calculations based on input from QCD-employing Hamiltonians constructed within chiral effective field theory. After a brief overview of the field, we focus on ab initio many-body approaches—built upon the no-core shell model—that are capable of simultaneously describing both bound and scattering nuclear states, and present results for resonances in light nuclei, reactions important for astrophysics and fusion research. In particular, we review recent calculations of resonances in the 6He halo nucleus, of five- and six-nucleon scattering, and an investigation of the role of chiral three-nucleon interactions in the structure of 9Be. Further, we discuss applications to the 7Be {({{p}},γ )}8{{B}} radiative capture. Finally, we highlight our efforts to describe transfer reactions including the 3H{({{d}},{{n}})}4He fusion.
Three-cluster dynamics within an ab initio framework
Quaglioni, S; Navrátil, P
2013-01-01
We introduce a fully antisymmetrized treatment of three-cluster dynamics within the ab initio framework of the no-core shell model/resonating-group method (NCSM/RGM). Energy-independent non-local interactions among the three nuclear fragments are obtained from realistic nucleon-nucleon interactions and consistent ab initio many-body wave functions of the clusters. The three-cluster Schr\\"odinger equation is solved with bound-state boundary conditions by means of the hyperspherical-harmonic method on a Lagrange mesh. We discuss the formalism in detail and give algebraic expressions for systems of two single nucleons plus a nucleus. Using a soft similarity-renormalization-group evolved chiral nucleon-nucleon potential, we apply the method to an $^4$He+$n+n$ description of $^6$He and compare the results to experiment and to a six-body diagonalization of the Hamiltonian performed within the harmonic-oscillator expansions of the NCSM. Differences between the two calculations provide a measure of core ($^4$He) pola...
Ab initio and kinetic modeling studies of formic acid oxidation
DEFF Research Database (Denmark)
Marshall, Paul; Glarborg, Peter
2015-01-01
A detailed chemical kinetic model for oxidation of formic acid (HOCHO) in flames has been developed, based on theoretical work and data from literature. Ab initio calculations were used to obtain rate coefficients for reactions of HOCHO with H, O, and HO2. Modeling predictions with the mechanism ...... as the fate of HOCO, determines the oxidation rate of formic acid. At lower temperatures HO2, formed from HOCO + O2, is an important chain carrier and modeling predictions become sensitive to the HOCHO + HO2 reaction. © 2014 The Combustion Institute.......A detailed chemical kinetic model for oxidation of formic acid (HOCHO) in flames has been developed, based on theoretical work and data from literature. Ab initio calculations were used to obtain rate coefficients for reactions of HOCHO with H, O, and HO2. Modeling predictions with the mechanism...... on calculations with the kinetic model. Formic acid is consumed mainly by reaction with OH, yielding OCHO, which dissociates rapidly to CO2 + H, and HOCO, which may dissociate to CO + OH or CO2 + H, or react with H, OH, or O2 to form more stable products. The branching fraction of the HOCHO + OH reaction, as well...
Unified ab initio approaches to nuclear structure and reactions
Navratil, Petr; Hupin, Guillaume; Romero-Redondo, Carolina; Calci, Angelo
2016-01-01
The description of nuclei starting from the constituent nucleons and the realistic interactions among them has been a long-standing goal in nuclear physics. In addition to the complex nature of the nuclear forces, with two-, three- and possibly higher many-nucleon components, one faces the quantum-mechanical many-nucleon problem governed by an interplay between bound and continuum states. In recent years, significant progress has been made in {\\em ab initio} nuclear structure and reaction calculations based on input from QCD-employing Hamiltonians constructed within chiral effective field theory. After a brief overview of the field, we focus on ab initio many-body approaches - built upon the No-Core Shell Model - that are capable of simultaneously describing both bound and scattering nuclear states, and present results for resonances in light nuclei, reactions important for astrophysics and fusion research. In particular, we review recent calculations of resonances in the $^6$He halo nucleus, of five- and six...
George, D. X. F.; Kumar, Sanjay
2010-08-01
Ab initio global adiabatic as well as quasidiabatic potential energy surfaces for the ground and the first excited electronic states of the H + + CO system have been computed as a function of the Jacobi coordinates ( R, r, γ) using Dunning's cc-pVTZ basis set at the internally contracted multi-reference (single and double) configuration interaction level of accuracy. In addition, nonadiabatic coupling matrix elements arising from radial motion, mixing angle and coupling potential have been computed using the ab initio procedure [Simah et al. (1999) [66
Improved Ab Initio Molecular Dynamics by Minimal Biasing with Experimental Data
White, Andrew D; Hocky, Glen M; Voth, Gregory A
2016-01-01
Accounting for electrons and nuclei simultaneously is a key goal of computer simulation via ab initio molecular dynamics (AIMD). However, AIMD is often unable to accurately reproduce the properties of systems such as water due to inaccuracies in the underlying electronic density functionals, shortcomings that are often addressed by added empirical corrections and/or increasing the simulation temperature. We present here a maximum-entropy-based approach to directly incorporate limited experimental data via a minimal bias. The biased AIMD simulations of both water and of an excess proton in water are shown to give significantly improved properties for both the biased and unbiased observables.
Ab initio studies of ionization potentials of hydrated hydroxide and hydronium
Swartz, Charles W
2013-01-01
The ionization potential distributions of hydrated hydroxide and hydronium are computed with many-body approach for electron excitations with configurations generated by {\\it ab initio} molecular dynamics. The experimental features are well reproduced and found to be closely related to the molecular excitations. In the stable configurations, the ionization potential is mainly perturbed by water molecules within the first solvation shell. On the other hand, electron excitation is delocalized on both proton receiving and donating complex during proton transfer, which shifts the excitation energies and broadens the spectra for both hydrated ions.
Energy Technology Data Exchange (ETDEWEB)
Sandoghchi, M. [Advanced Materials Laboratory (AML), Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran, Islamic Republic of); Khosroabadi, H., E-mail: khosroabadi@sharif.edu [Advanced Materials Laboratory (AML), Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran, Islamic Republic of); Magnet Research Laboratory (MRL), Department of Physics, Sharif University of Technology, P.O. Box 11365-916, Tehran (Iran, Islamic Republic of); Akhavan, M. [Magnet Research Laboratory (MRL), Department of Physics, Sharif University of Technology, P.O. Box 11365-916, Tehran (Iran, Islamic Republic of)
2014-12-15
Highlights: • The lattice parameters changes by K doping is explained by ionic charge and the metal–metal bonding scenario. • Creation of a larger peak near the Fermi level and increase the DOS at the Fermi level by K doping. • The effects of K on DOS has been related to the magnetic transition, change of the lattice parameters and FeAs{sub 4} tetrahedron. • Investigation of the number of Fermi level crossed bands by K doping and the band changes near the Fermi level. - Abstract: The crystal and electronic structures of normal phase of Ba{sub 1−x}K{sub x}Fe{sub 2}As{sub 2} for x = 0.0, 0.5 and 1.0 have been studied by using pseudopotential Quantum Espresso code based on ab-initio density functional theory. Effects of K doping on the crystal structure and lattice parameters have been calculated and compared with the experimental and computational reported data for similar compounds. The metal–metal bonding scenario was used to explain the changes of lattice parameters by K doping. The electronic structure of this system including of density of states and band structure have been calculated and investigated by K doping. One of the interesting results is that a larger peak is appeared near the Fermi level by increasing of the K doping. These changes could produce a potential for creation of the superconducting state in this system.
A Photoelectron Spectroscopy and ab initio Study of B3- and B4- Anions and Their Neutrals
Energy Technology Data Exchange (ETDEWEB)
Zhai, Hua-Jin; Wang, Lai S.; Alexandrova, A N.; Boldyrev, Alexander I.; Zakrzewski, V G.
2003-11-06
The two smallest boron clusters (B3 and B4) in their neutral and anionic forms were studied by photoelectron spectroscopy and ab initio calculations. Vibrationally resolved photoelectron spectra were observed for B3- at three photon energies (355, 266, and 193 nm) and the electron affinity of B3 was measured to be+0.02 eV.
Ab initio study of the transition-metal carbene cations
Institute of Scientific and Technical Information of China (English)
李吉海; 冯大诚; 冯圣玉
1999-01-01
The geometries and bonding characteristics of the first-row transition-metal carbene cations MCH2+ were investigated by ab initio molecular orbital theory （HF/LANL2DZ）. All of MCH2+ are coplanar. In the closed shell structures the C bonds to M with double bonds; while in the open shell structures the partial double bonds are formed, because one of the σ and π orbitals is singly occupied. It is mainly the π-type overlap between the 2px orbital of C and 4px, 3dxz, orbitals of M+ that forms the π orbitals. The dissociation energies of C—M bond appear in periodic trend from Sc to Cu. Most of the calculated bond dissociation energies are close to the experimental ones.
High-throughput ab-initio dilute solute diffusion database.
Wu, Henry; Mayeshiba, Tam; Morgan, Dane
2016-01-01
We demonstrate automated generation of diffusion databases from high-throughput density functional theory (DFT) calculations. A total of more than 230 dilute solute diffusion systems in Mg, Al, Cu, Ni, Pd, and Pt host lattices have been determined using multi-frequency diffusion models. We apply a correction method for solute diffusion in alloys using experimental and simulated values of host self-diffusivity. We find good agreement with experimental solute diffusion data, obtaining a weighted activation barrier RMS error of 0.176 eV when excluding magnetic solutes in non-magnetic alloys. The compiled database is the largest collection of consistently calculated ab-initio solute diffusion data in the world. PMID:27434308
Efficient Ab initio Modeling of Random Multicomponent Alloys.
Jiang, Chao; Uberuaga, Blas P
2016-03-11
We present in this Letter a novel small set of ordered structures (SSOS) method that allows extremely efficient ab initio modeling of random multicomponent alloys. Using inverse II-III spinel oxides and equiatomic quinary bcc (so-called high entropy) alloys as examples, we demonstrate that a SSOS can achieve the same accuracy as a large supercell or a well-converged cluster expansion, but with significantly reduced computational cost. In particular, because of this efficiency, a large number of quinary alloy compositions can be quickly screened, leading to the identification of several new possible high-entropy alloy chemistries. The SSOS method developed here can be broadly useful for the rapid computational design of multicomponent materials, especially those with a large number of alloying elements, a challenging problem for other approaches. PMID:27015491
Efficient Ab initio Modeling of Random Multicomponent Alloys
Jiang, Chao; Uberuaga, Blas P.
2016-03-01
We present in this Letter a novel small set of ordered structures (SSOS) method that allows extremely efficient ab initio modeling of random multicomponent alloys. Using inverse II-III spinel oxides and equiatomic quinary bcc (so-called high entropy) alloys as examples, we demonstrate that a SSOS can achieve the same accuracy as a large supercell or a well-converged cluster expansion, but with significantly reduced computational cost. In particular, because of this efficiency, a large number of quinary alloy compositions can be quickly screened, leading to the identification of several new possible high-entropy alloy chemistries. The SSOS method developed here can be broadly useful for the rapid computational design of multicomponent materials, especially those with a large number of alloying elements, a challenging problem for other approaches.
Ab initio H2O in realistic hydrophilic confinement.
Allolio, Christoph; Klameth, Felix; Vogel, Michael; Sebastiani, Daniel
2014-12-15
A protocol for the ab initio construction of a realistic cylindrical pore in amorphous silica, serving as a geometric nanoscale confinement for liquids and solutions, is presented. Upon filling the pore with liquid water at different densities, the structure and dynamics of the liquid inside the confinement can be characterized. At high density, the pore introduces long-range oscillations into the water density profile, which makes the water structure unlike that of the bulk across the entire pore. The tetrahedral structure of water is also affected up to the second solvation shell of the pore wall. Furthermore, the effects of the confinement on hydrogen bonding and diffusion, resulting in a weakening and distortion of the water structure at the pore walls and a slowdown in diffusion, are characterized. PMID:25208765
Quantum plasmonics: from jellium models to ab initio calculations
Directory of Open Access Journals (Sweden)
Varas Alejandro
2016-08-01
Full Text Available Light-matter interaction in plasmonic nanostructures is often treated within the realm of classical optics. However, recent experimental findings show the need to go beyond the classical models to explain and predict the plasmonic response at the nanoscale. A prototypical system is a nanoparticle dimer, extensively studied using both classical and quantum prescriptions. However, only very recently, fully ab initio time-dependent density functional theory (TDDFT calculations of the optical response of these dimers have been carried out. Here, we review the recent work on the impact of the atomic structure on the optical properties of such systems. We show that TDDFT can be an invaluable tool to simulate the time evolution of plasmonic modes, providing fundamental understanding into the underlying microscopical mechanisms.
An Efficient Approach to Ab Initio Monte Carlo Simulation
Leiding, Jeff
2013-01-01
We present a Nested Markov Chain Monte Carlo (NMC) scheme for building equilibrium averages based on accurate potentials such as density functional theory. Metropolis sampling of a reference system, defined by an inexpensive but approximate potential, is used to substantially decorrelate configurations at which the potential of interest is evaluated, thereby dramatically reducing the number needed to build ensemble averages at a given level of precision. The efficiency of this procedure is maximized on-the-fly through variation of the reference system thermodynamic state (characterized here by its inverse temperature \\beta^0), which is otherwise unconstrained. Local density approximation (LDA) results are presented for shocked states in argon at pressures from 4 to 60 GPa. Depending on the quality of the reference potential, the acceptance probability is enhanced by factors of 1.2-28 relative to unoptimized NMC sampling, and the procedure's efficiency is found to be competitive with that of standard ab initio...
Ab initio Potential Energy Surface for H-H2
Partridge, Harry; Bauschlicher, Charles W., Jr.; Stallcop, James R.; Levin, Eugene
1993-01-01
Ab initio calculations employing large basis sets are performed to determine an accurate potential energy surface for H-H2 interactions for a broad range of separation distances. At large distances, the spherically averaged potential determined from the calculated energies agrees well with the corresponding results determined from dispersion coefficients; the van der Waals well depth is predicted to be 75 +/- (mu)E(sub h). Large basis sets have also been applied to reexamine the accuracy of theoretical repulsive potential energy surfaces. Multipolar expansions of the computed H-H2 potential energy surface are reported for four internuclear separation distances (1.2, 1.401, 1.449, and 1.7a(sub 0) of the hydrogen molecule. The differential elastic scattering cross section calculated from the present results is compared with the measurements from a crossed beam experiment.
Ab initio investigation of the mechanical properties of copper
Institute of Scientific and Technical Information of China (English)
Liu Yue-Lin; Gui Li-Jiang; Jin Shuo
2012-01-01
Employing the ab initio total energy method based on the density functional theory with the generalized gradient approximation,we have systematically investigated the theoretical mechanical properties of copper (Cu).The theoretical tensile strengths are calculated to be 25.3 GPa,5.9 GPa,and 37.6 GPa for the fcc Cu single crystal in the [001],[110],and [111] directions,respectively.Among the three directions,the [110] direction is the weakest one due to the occurrence of structure transition at the lower strain and the weakest interaction of atoms between the (110) planes,while the [111] direction is the strongest direction because of the strongest interaction of atoms between the (111) planes.In terms of the elastic constants of Cu single crystal,we also estimate some mechanical quantities of polycrystalline Cu,including bulk modulus B,shear modulus G,Young's modulus Ep,and Poisson's ratio v.
Ab Initio Prediction of 29Si-NMR Chemical Shifts
Institute of Scientific and Technical Information of China (English)
CHU Shidong; LI Yingxia; SONG Ni; GUAN Huashi
2002-01-01
The ability of several ab initio models to predict experimental 29Si-NMR chemical shift is examined. The shielding values of trimethylsilyl chloride (A), t-butyldimethylsilyl chloride (B) and allyltrimethylsilane (C) are calculated by GIAO, CSGT and IGAIM methods, using HF/6-31G*, B3LYP/6-31G*, HF/6-311+G**, B3LYP/6-311+G** and MPWlPW91/6-311+G** models respectively. The 29Si chemical shifts calculated by GIAO method using HF/6-311+G**model are highly in agreement with those obtained experimentally. All of the models above reproduce the trends of chemical shifts in all cases studied, suggesting that the models are of practical value.
Ab initio quantum dynamics using coupled-cluster.
Kvaal, Simen
2012-05-21
The curse of dimensionality (COD) limits the current state-of-the-art ab initio propagation methods for non-relativistic quantum mechanics to relatively few particles. For stationary structure calculations, the coupled-cluster (CC) method overcomes the COD in the sense that the method scales polynomially with the number of particles while still being size-consistent and extensive. We generalize the CC method to the time domain while allowing the single-particle functions to vary in an adaptive fashion as well, thereby creating a highly flexible, polynomially scaling approximation to the time-dependent Schrödinger equation. The method inherits size-consistency and extensivity from the CC method. The method is dubbed orbital-adaptive time-dependent coupled-cluster, and is a hierarchy of approximations to the now standard multi-configurational time-dependent Hartree method for fermions. A numerical experiment is also given. PMID:22612082
Ab initio Molecular Dynamics Study on Small Carbon Nanotubes
Institute of Scientific and Technical Information of China (English)
叶林晖; 刘邦贵; 王鼎盛
2001-01-01
Ab initio molecular dynamics simulations are performed on small single wall nanotubes. By structural relaxation,the equilibrium C-C bond lengths and bond angles are determined. Our result shows that for both zigzag and armchair nanotubes there are two nonequivalent bond lengths. One bond stretches from that of the graphene sheet, while the other shrinks. Small variations on bond angles are also shown. Energy bands are calculated for the optimized structures. It is found that the intrinsic curvature of the very small nanotube greatly modifies the energy band which can no longer be well described in the tight-binding zone-folding picture. In our calculation very small nanotubes are metallic. The energy per atom fits quite well with the relation of E(R) = E0 + f/R2 even for the extreme small radius. The implications of the results on the properties of small nanotubes are discussed.
Energy Technology Data Exchange (ETDEWEB)
Yao, Yongxin [Iowa State Univ., Ames, IA (United States)
2009-01-01
also plays an important role, as it may directly track the movement of every atom. Simulation time is a major limit for molecular dynamics, not only because of “slow” computer speed, but also because of the accumulation error in the numerical treatment of the motion equations. There is also a great concern about the reliability of the emperical potentials if using classical molecular dynamics. Ab initio methods based on density functional theory(DFT) do not have this problem, however, it suffers from small simulation cells and is more demanding computationally. When crystal phase is involved, size effect of the simulation cell is more pronounced since long-range elastic energy would be established. Simulation methods which are more efficient in computation but yet have similar reliability as the ab initio methods, like tight-binding method, are highly desirable. While the complexity of metallic glasses comes from the atomistic level, there is also a large field which deals with the complexity from electronic level. The only “ab initio” method applicable to solid state systems is density functional theory with local density approximation( LDA) or generalized gradient approximation(GGA) for the exchange-correlation energy. It is very successful for simple sp element, where it reaches an high accuracy for determining the surface reconstruction. However, there is a large class of materials with strong electron correlation, where DFT based on LDA or GGA fails in a fundamental way. An “ab initio” method which can generally apply to correlated materials, as LDA for simple sp element, is still to be developed. The thesis is prepared to address some of the above problems.
Ziat, Younes; Zarhri, Zakaryaa; Hammi, Maryama; Slassi, Amine; Echihi, Siham; El Kenz, Abdallah; Benyoussef, Abdelilah
2016-07-01
The ab-initio calculations, based on the Korringa-Kohn-Rostoker approximation combined with Coherent Potential Approximation (KKR-CPA) and the local density approximation (LDA) have been used to study the electronic and magnetic properties of 3% of N-doped Fe0.98TM0.02S2 (TM=V or Cr) pyrite. The N is occurred as a non-metallic impurity to evaluate its effect on conductivity type and the stability of the studied systems. Our investigation confirms the p-type conductivity. The stabilization of the ferromagnetic state in N-doped Fe0.98V0.02S2 is observed due to the incorporation of N impurity. The majority-spin related to t2g+ is located around the Fermi level. And the ferromagnetic state connected to the half metal is potentially utilized in spintronic field. In Fe0.98Cr0.02S1.97N0.03, the 3% of N induced a hybridization between (Cr[3d] and N[2p]). We predicted an enlargement of the peak of the Cr[3d]. In addition, the total moment of the studied systems is augmented as well as the Curie temperature (TC).
DEFF Research Database (Denmark)
Bork, Nicolai Christian; Du, Lin; Reiman, Heidi;
2014-01-01
Gibbs free binding energies in molecular complexes and clusters based on gas phase FTIR spectroscopy. The acetonitrile-HCl molecular complex is identified via its redshifted H-Cl stretching vibrational mode. We determine the Gibbs free binding energy, ΔG°295 K, to between 4.8 and 7.9 kJ mol(-1) and......Models of formation and growth of atmospheric aerosols are highly dependent on accurate cluster binding energies. These are most often calculated by ab initio electronic structure methods but remain associated with significant uncertainties. We present a computational benchmarking study of the...
Monte Carlo methods in AB initio quantum chemistry quantum Monte Carlo for molecules
Lester, William A; Reynolds, PJ
1994-01-01
This book presents the basic theory and application of the Monte Carlo method to the electronic structure of atoms and molecules. It assumes no previous knowledge of the subject, only a knowledge of molecular quantum mechanics at the first-year graduate level. A working knowledge of traditional ab initio quantum chemistry is helpful, but not essential.Some distinguishing features of this book are: Clear exposition of the basic theory at a level to facilitate independent study. Discussion of the various versions of the theory: diffusion Monte Carlo, Green's function Monte Carlo, and release n
Structure and lattice dynamics of PrFe3(BO3)4: Ab initio calculation
Chernyshev, V. A.; Nikiforov, A. E.; Petrov, V. P.
2016-06-01
The crystal structure and phonon spectrum of PrFe3(BO3)4 are ab initio calculated in the context of the density functional theory. The ion coordinates in the unit cell of a crystal and the lattice parameters are evaluated from the calculations. The types and frequencies of the fundamental vibrations, as well as the line intensities of the IR spectrum, are determined. The elastic constants of the crystal are calculated. A "seed" frequency of the vibration strongly interacting with the electron excitation on the praseodymium ion is obtained for low-frequency A 2 mode. The calculated results are in agreement with the known experimental data.
Ab initio adiabatic and quasidiabatic potential energy surfaces of H++ CN system
Indian Academy of Sciences (India)
Bhargava Anusuri; Sanjay Kumar
2016-02-01
We present restricted geometry (collinear and perpendicular approaches of proton) ab initio three dimensional potential energy surfaces for H++ CN system. The calculations were performed at the internally contracted multi-reference configuration interaction level of theory using Dunning’s correlation consistent polarized valence triple zeta basis set. Adiabatic and quasidiabatic surfaces have been computed for the ground and the first excited electronic states. Nonadiabatic effects arising from radial coupling have been analyzed in terms of nonadiabatic coupling matrix elements and coupling potentials.
Ab initio molecular simulations on specific interactions between amyloid beta and monosaccharides
Nomura, Kazuya; Okamoto, Akisumi; Yano, Atsushi; Higai, Shin'ichi; Kondo, Takashi; Kamba, Seiji; Kurita, Noriyuki
2012-09-01
Aggregation of amyloid β (Aβ) peptides, which is a key pathogenetic event in Alzheimer's disease, can be caused by cell-surface saccharides. We here investigated stable structures of the solvated complexes of Aβ with some types of monosaccharides using molecular simulations based on protein-ligand docking and classical molecular mechanics methods. Moreover, the specific interactions between Aβ and the monosaccharides were elucidated at an electronic level by ab initio fragment molecular orbital calculations. Based on the results, we proposed which type of monosaccharide prefers to have large binding affinity to Aβ and inhibit the Aβ aggregation.
Ab initio studies on the mechanic and magnetic properties of PdHx
Institute of Scientific and Technical Information of China (English)
Cui Xin; Liang Xi-Xia; Wang Jian-Tao; Zhao Guo-Zhong
2011-01-01
Based on ab initio total energy calculations, the structural, electronic, mechanic, and magnetic properties of PdHx are investigated. It is found that bulk modulus of PdHx is larger than the metal Pd with the hydrogen storage except Pd4H2. The calculated results for the magnetic moments show that the hydrogen addition weakens the magnetic properties of the PdHx systems. A strong magneto-volume effect is found in PdHx structures as well as Pd. The transition from paramagnetism to ferromagnetism is discussed. The corresponding densities of states for both structures are also shown to understand the magnetic behaviour.
Curchod, Basile F. E.; Rauer, Clemens; Marquetand, Philipp; González, Leticia; Martínez, Todd J.
2016-03-01
Full multiple spawning is a formally exact method to describe the excited-state dynamics of molecular systems beyond the Born-Oppenheimer approximation. However, it has been limited until now to the description of radiationless transitions taking place between electronic states with the same spin multiplicity. This Communication presents a generalization of the full and ab initio multiple spawning methods to both internal conversion (mediated by nonadiabatic coupling terms) and intersystem crossing events (triggered by spin-orbit coupling matrix elements) based on a spin-diabatic representation. The results of two numerical applications, a model system and the deactivation of thioformaldehyde, validate the presented formalism and its implementation.
Ab initio study of spin-dependent transport in carbon nanotubes with iron and vanadium adatoms
DEFF Research Database (Denmark)
Fürst, Joachim Alexander; Brandbyge, Mads; Jauho, Antti-Pekka;
2008-01-01
We present an ab initio study of spin-dependent transport in armchair carbon nanotubes with transition metal adsorbates: iron or vanadium. The method based on density functional theory and nonequilibrium Green's functions is used to compute the electronic structure and zero-bias conductance...... (majority or minority) being scattered depends on the adsorbate and is explained in terms of d-state filling. We contrast the single-walled carbon nanotube results to the simpler case of the adsorbate on a flat graphene sheet with periodic boundary conditions and corresponding width in the zigzag direction...
Ab-initio density functional theory study of a WO3 NH3-sensing mechanism
Institute of Scientific and Technical Information of China (English)
Hu Ming; Zhang Jie; Wang Wei-Dan; Qin Yu-Xiang
2011-01-01
WO3 bulk and various surfaces are studied by an ab-initio density functional theory technique.The band structures and electronic density states of WO3 bulk are investigated.The surface energies of different WO3 surfaces are compared and then the(002)surface with minimum energy is computed for its NH3 sensing mechanism which explains the results in the experiments.Three adsorption sites are considered.According to the comparisons of the energy and the charge change between before and after adsorption in the optimal adsorption site O1c,the NH3 sensing mechanism is obtained.
An Ab initio Theoretical Study on the Nonadiabatic Coupling for Na＋I2 Collision System
Institute of Scientific and Technical Information of China (English)
孙孝敏; 蔡政亭; 冯大诚
2003-01-01
The ionic and neutral state potential energy surfaces (PESs) of Na+I2 collision system have been calculated on QCISD(T) level by using ab initio method.The location and depth of the potential well,the collision radius and their fine structures have been analyzed at the equilibrium geometry of I2 molecule.The electronic transfer probabilities are also calculated in terms of Landau-Zener model.The lifetime of scattering resonance state is evaluated by the uncertainty principle.All the results have been compared with those obtained according to the Aten-Lanting-Los PES and Feng's PES.
Accelerating Ab Initio Path Integral Simulations via Imaginary Multiple-Timestepping.
Cheng, Xiaolu; Herr, Jonathan D; Steele, Ryan P
2016-04-12
This work investigates the use of multiple-timestep schemes in imaginary time for computationally efficient ab initio equilibrium path integral simulations of quantum molecular motion. In the simplest formulation, only every n(th) path integral replica is computed at the target level of electronic structure theory, whereas the remaining low-level replicas still account for nuclear motion quantum effects with a more computationally economical theory. Motivated by recent developments for multiple-timestep techniques in real-time classical molecular dynamics, both 1-electron (atomic-orbital basis set) and 2-electron (electron correlation) truncations are shown to be effective. Structural distributions and thermodynamic averages are tested for representative analytic potentials and ab initio molecular examples. Target quantum chemistry methods include density functional theory and second-order Møller-Plesset perturbation theory, although any level of theory is formally amenable to this framework. For a standard two-level splitting, computational speedups of 1.6-4.0x are observed when using a 4-fold reduction in time slices; an 8-fold reduction is feasible in some cases. Multitiered options further reduce computational requirements and suggest that quantum mechanical motion could potentially be obtained at a cost not significantly different from the cost of classical simulations. PMID:26966920
Emergence of rotational bands in ab initio no-core configuration interaction calculations
Caprio, M A; Vary, J P; Smith, R
2015-01-01
Rotational bands have been observed to emerge in ab initio no-core configuration interaction (NCCI) calculations for p-shell nuclei, as evidenced by rotational patterns for excitation energies, electromagnetic moments, and electromagnetic transitions. We investigate the ab initio emergence of nuclear rotation in the Be isotopes, focusing on 9Be for illustration, and make use of basis extrapolation methods to obtain ab initio predictions of rotational band parameters for comparison with experiment. We find robust signatures for rotational motion, which reproduce both qualitative and quantitative features of the experimentally observed bands.
International Nuclear Information System (INIS)
The effects of the 4f shell of electrons and the relativity of valence electrons are compared. The effect of 4f shell (lanthanide contraction) is estimated from the numerical Hartree-Fock (HF) calculations of pseudo-atoms corresponding to Hf, Re, Au, Hg, Tl, Pb and Bi without 4f electrons and with atomic numbers reduced by 14. The relativistic effect estimated from the numerical Dirac-Hartree-Fock (DHF) calculations of those atoms is comparable in the magnitude with that of the 4f shell of electrons. Both are larger for 6s than for 5d or 6p electrons. The various relativistic effects on valence electrons are discussed in detail to determine the proper level of the approximation for the valence electron calculations of systems with heavy elements. An effective core potential system has been developed for heavy atoms in which relativistic effects are included in the effective potentials
Energy Technology Data Exchange (ETDEWEB)
Lee, Y.S.
1977-11-01
The effects of the 4f shell of electrons and the relativity of valence electrons are compared. The effect of 4f shell (lanthanide contraction) is estimated from the numerical Hartree-Fock (HF) calculations of pseudo-atoms corresponding to Hf, Re, Au, Hg, Tl, Pb and Bi without 4f electrons and with atomic numbers reduced by 14. The relativistic effect estimated from the numerical Dirac-Hartree-Fock (DHF) calculations of those atoms is comparable in the magnitude with that of the 4f shell of electrons. Both are larger for 6s than for 5d or 6p electrons. The various relativistic effects on valence electrons are discussed in detail to determine the proper level of the approximation for the valence electron calculations of systems with heavy elements. An effective core potential system has been developed for heavy atoms in which relativistic effects are included in the effective potentials.
Energy Technology Data Exchange (ETDEWEB)
Lavrentyev, A.A.; Gabrelian, B.V.; Vorzhev, V.B.; Nikiforov, I.Ya. [Department of Physics, Don State Technical University, Gagarin Sq. 1, Rostov-on-Don (Russian Federation); Khyzhun, O.Yu. [Frantsevych Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, UA-03142 Kyiv (Ukraine)], E-mail: khyzhun@ipms.kiev.ua
2009-03-20
To investigate the influence of substitution of carbon atoms for nitrogen atoms in the cubic TaC{sub x}N{sub 1-x} carbonitrides, total and partial densities of states were calculated for TaC, TaC{sub 0.5}N{sub 0.5} and TaN compounds (NaCl structure) using the self-consistent cluster (with the FEFF8 code) and ab initio band-structure augmented plane wave + local orbitals (APW + LO) methods. In the present work a rather good agreement of the theoretical FEFF8 and APW + LO data for electronic properties of the TaC{sub x}N{sub 1-x} system under consideration was obtained. The results indicate that a strong hybridization of the Ta 5d- and C(N) 2p-like states is characteristic for the valence band of the TaC{sub x}N{sub 1-x} carbonitrides. When going from TaC to TaN through the TaC{sub 0.5}N{sub 0.5} carbonitride, the main maxima of curves representing total and partial Ta 5d densities of states shift in the direction opposite to the position of the Fermi level. In the above sequence of compounds, an increase of occupation of the near-Fermi sub-band formed by contributions of Ta 5d(t{sub 2g}) states has been detected. The theoretical FEFF8 and APW + LO results for the electronic structure of the TaC{sub x}N{sub 1-x} carbonitrides were found to be in excellent agreement with the experimental data derived in the present work employing X-ray photoelectron, emission and absorption spectroscopy methods for cubic TaC{sub 0.98}, TaC{sub 0.52}N{sub 0.49} and TaN{sub 0.97} compounds.
Ab initio intermolecular potential energy surface of He-LiH
Institute of Scientific and Technical Information of China (English)
鄢国森; 杨明晖; 谢代前
1997-01-01
The intermolecular potential energy surface of He-LiH complex was studied using the full-electronic complete forth-order Miller-Plesset perturbation (MPPT) method.In ab initio calculations,the bond length of LiH was fixed at 0 159 5 nm.The potential has two local minima of Vm=-179.93 cm for the linear He LiH geormetrv at Rm=0.227 nm and Vm=-10.44 cm-1 for the linear He-HL1 geometry at Rm=0.516 nm The potemal exhibits strong anisotropy The analytic potential function with 31 parameters was determined by fitting to the calculated ab,mtio potentials The influence of variation of LiH bond length on the potential energy surface was also studied
The {\\it ab initio} calculation of spectra of open shell diatomic molecules
Tennyson, Jonathan; McKemmish, Laura K; Yurchenko, Sergei N
2016-01-01
The spectra (rotational, rotation-vibrational or electronic) of diatomic molecules due to transitions involving only closed-shell ($^1\\Sigma$) electronic states follow very regular, simple patterns and their theoretical analysis is usually straightforward. On the other hand, open-shell electronic states lead to more complicated spectral patterns and, moreover, often appear as a manifold of closely lying electronic states, leading to perturbations with even larger complexity. This is especially true when at least one of the atoms is a transition metal. Traditionally these complex cases have been analysed using approaches based on perturbation theory, with semi-empirical parameters determined by fitting to spectral data. Recently the needs of two rather diverse scientific areas have driven the demand for improved theoretical models of open-shell diatomic systems based on an \\emph{ab initio} approach, these areas are ultracold chemistry and the astrophysics of "cool" stars, brown dwarfs and most recently extraso...
Morrison, Carole; Bil, Andrzej; Hutter, Jurg
2014-01-01
Light metal atoms such as Li, K (electronic state 2S 1/2) or Ca (1S0) encapsulated in a C 70 cage considerably modifies the chemical properties of the fullerene surface due to metal-to-cage electron transfer. H-doped and anion ozonide systems were also considered to validate the electron transfer hypothesis. The relative stabilities of the eight isomers of the C 70O3 molozonide series at room temperature depend on the identity of the endohedral guest, as was the preferred channel for thermal ...
Institute of Scientific and Technical Information of China (English)
郑浩平; 吴丽华; 李根
2013-01-01
用第一性原理、全电子、从头计算方法构造了水溶液对缬氨酸(Val)电子结构的等效势.首先用自由团簇计算法得到能量最低时水分子与缬氨酸的相对空间位形,然后用团簇埋入自洽计算(SCCE)方法计算缬氨酸在水分子势下的电子结构,最后用偶极子势代替水分子势.结果表明:由于水溶液的存在,缬氨酸费米面下八个能级每个能级平均上升了约0.775 5 eV；水溶液对缬氨酸电子结构的影响可以很好地被偶极子势模拟.因此,所得的偶极子势可以直接运用到水溶液中蛋白质电子结构的计算中.%The equivalent potential of water for the electronic structure of valine (Val) was constructed on the basis of the first-principles, all-electron, ab initio calculations. The process involved three steps. First, a search for the minimum-energy configuration of the system Val + 7H2O was carried out by free cluster calculation. Then, the electronic structure of valine with the potential of water molecules was calculated with the self-consistent cluster-embedding (SCCE) method. Finally, the effect of water was simulated on valine by dipoles. Results show that the major effect of water on the electronic structure of valine is to raise the eigenvalues of eight orbitals under Fermi surface by about 0. 775 5 eV on average. The effect of water on the electronic structure of valine can be well simulated by dipoles. The equivalent potential obtained can be applied directly to the calculation of the electronic structures of proteins in solution.
Ab-initio study of magnetic properties and phase transitions in Ga (Mn) N with Monte Carlo approach
Energy Technology Data Exchange (ETDEWEB)
Sbai, Y.; Ait Raiss, A.; Salmani, E. [LMPHE (URAC 12), Faculty of Science, Mohammed V University, Av. Ibn Batouta, Rabat (Morocco); Bahmad, L., E-mail: Bahmad@fsr.ac.ma [LMPHE (URAC 12), Faculty of Science, Mohammed V University, Av. Ibn Batouta, Rabat (Morocco); Benyoussef, A. [LMPHE (URAC 12), Faculty of Science, Mohammed V University, Av. Ibn Batouta, Rabat (Morocco); Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Hassan II Academy of Science and Technology, Rabat (Morocco)
2015-12-15
On the basis of ab-initio calculations and Monte Carlo simulations the magnetic and electronic properties of Gallium nitride (GaN) doped with the transition metal Manganese (Mn) were studied. The ab initio calculations were done using the AKAI–KKR–CPA method within the Local Density Approximation (LDA) approximation. We doped our Diluted Magnetic Semiconductor (DMS), with different concentrations of magnetic impurities Mn and plotted the density of state (DOS) for each one. Showing a half-metallic behavior and ferromagnetic state especially for Ga{sub 0.95}Mn{sub 0.05}N making this DMS a strong candidate for spintronic applications. Moreover, the magnetization and susceptibility of our system as a function of the temperature has been calculated and give for various system size L to study the size effect. In addition, the transition temperature was deduced from the peak of the susceptibility. The Ab initio results are in good agreement with literature especially for (x=0.05) of Mn which gives the most interesting results. - Highlights: • The AKAI–KKR–CPA method has been applied to study the doped compound GaN:Mn. • The local density approximation (LDA) has been applied. • The ab-initio calculations have been performed. • The density of states (DOS) have been plotted for differents doping concentrations, using Monte Carlo simulations.
Marsalek, Ondrej; Markland, Thomas E
2016-02-01
Path integral molecular dynamics simulations, combined with an ab initio evaluation of interactions using electronic structure theory, incorporate the quantum mechanical nature of both the electrons and nuclei, which are essential to accurately describe systems containing light nuclei. However, path integral simulations have traditionally required a computational cost around two orders of magnitude greater than treating the nuclei classically, making them prohibitively costly for most applications. Here we show that the cost of path integral simulations can be dramatically reduced by extending our ring polymer contraction approach to ab initio molecular dynamics simulations. By using density functional tight binding as a reference system, we show that our ring polymer contraction scheme gives rapid and systematic convergence to the full path integral density functional theory result. We demonstrate the efficiency of this approach in ab initio simulations of liquid water and the reactive protonated and deprotonated water dimer systems. We find that the vast majority of the nuclear quantum effects are accurately captured using contraction to just the ring polymer centroid, which requires the same number of density functional theory calculations as a classical simulation. Combined with a multiple time step scheme using the same reference system, which allows the time step to be increased, this approach is as fast as a typical classical ab initio molecular dynamics simulation and 35× faster than a full path integral calculation, while still exactly including the quantum sampling of nuclei. This development thus offers a route to routinely include nuclear quantum effects in ab initio molecular dynamics simulations at negligible computational cost. PMID:26851913
International Nuclear Information System (INIS)
Path integral molecular dynamics simulations, combined with an ab initio evaluation of interactions using electronic structure theory, incorporate the quantum mechanical nature of both the electrons and nuclei, which are essential to accurately describe systems containing light nuclei. However, path integral simulations have traditionally required a computational cost around two orders of magnitude greater than treating the nuclei classically, making them prohibitively costly for most applications. Here we show that the cost of path integral simulations can be dramatically reduced by extending our ring polymer contraction approach to ab initio molecular dynamics simulations. By using density functional tight binding as a reference system, we show that our ring polymer contraction scheme gives rapid and systematic convergence to the full path integral density functional theory result. We demonstrate the efficiency of this approach in ab initio simulations of liquid water and the reactive protonated and deprotonated water dimer systems. We find that the vast majority of the nuclear quantum effects are accurately captured using contraction to just the ring polymer centroid, which requires the same number of density functional theory calculations as a classical simulation. Combined with a multiple time step scheme using the same reference system, which allows the time step to be increased, this approach is as fast as a typical classical ab initio molecular dynamics simulation and 35× faster than a full path integral calculation, while still exactly including the quantum sampling of nuclei. This development thus offers a route to routinely include nuclear quantum effects in ab initio molecular dynamics simulations at negligible computational cost
Energy Technology Data Exchange (ETDEWEB)
Marsalek, Ondrej; Markland, Thomas E., E-mail: tmarkland@stanford.edu [Department of Chemistry, Stanford University, Stanford, California 94305 (United States)
2016-02-07
Path integral molecular dynamics simulations, combined with an ab initio evaluation of interactions using electronic structure theory, incorporate the quantum mechanical nature of both the electrons and nuclei, which are essential to accurately describe systems containing light nuclei. However, path integral simulations have traditionally required a computational cost around two orders of magnitude greater than treating the nuclei classically, making them prohibitively costly for most applications. Here we show that the cost of path integral simulations can be dramatically reduced by extending our ring polymer contraction approach to ab initio molecular dynamics simulations. By using density functional tight binding as a reference system, we show that our ring polymer contraction scheme gives rapid and systematic convergence to the full path integral density functional theory result. We demonstrate the efficiency of this approach in ab initio simulations of liquid water and the reactive protonated and deprotonated water dimer systems. We find that the vast majority of the nuclear quantum effects are accurately captured using contraction to just the ring polymer centroid, which requires the same number of density functional theory calculations as a classical simulation. Combined with a multiple time step scheme using the same reference system, which allows the time step to be increased, this approach is as fast as a typical classical ab initio molecular dynamics simulation and 35× faster than a full path integral calculation, while still exactly including the quantum sampling of nuclei. This development thus offers a route to routinely include nuclear quantum effects in ab initio molecular dynamics simulations at negligible computational cost.
Bil, Andrzej; Hutter, Jürg; Morrison, Carole A.
2014-06-01
Light metal atoms such as Li, K (electronic state 2S1/2) or Ca (1S0) encapsulated in a C70 cage considerably modifies the chemical properties of the fullerene surface due to metal-to-cage electron transfer. H-doped and anion ozonide systems were also considered to validate the electron transfer hypothesis. The relative stabilities of the eight isomers of the C70O3 molozonide series at room temperature depend on the identity of the endohedral guest, as was the preferred channel for thermal decomposition. No electron transfer was observed for the complex N@C70 where the fullerene acts as an inert container for the 4S3/2 radical.
DEFF Research Database (Denmark)
Wolf, T. J. A.; Kuhlman, Thomas Scheby; Schalk, O.;
2014-01-01
Time-resolved photoelectron spectroscopy and ab initio multiple spawning were applied to the ultrafast non-adiabatic dynamics of hexamethylcyclopentadiene. The high level of agreement between experiment and theory associates wavepacket motion with a distinct degree of freedom....
Exploring the free energy surface using ab initio molecular dynamics.
Samanta, Amit; Morales, Miguel A; Schwegler, Eric
2016-04-28
Efficient exploration of configuration space and identification of metastable structures in condensed phase systems are challenging from both computational and algorithmic perspectives. In this regard, schemes that utilize a set of pre-defined order parameters to sample the relevant parts of the configuration space [L. Maragliano and E. Vanden-Eijnden, Chem. Phys. Lett. 426, 168 (2006); J. B. Abrams and M. E. Tuckerman, J. Phys. Chem. B 112, 15742 (2008)] have proved useful. Here, we demonstrate how these order-parameter aided temperature accelerated sampling schemes can be used within the Born-Oppenheimer and the Car-Parrinello frameworks of ab initio molecular dynamics to efficiently and systematically explore free energy surfaces, and search for metastable states and reaction pathways. We have used these methods to identify the metastable structures and reaction pathways in SiO2 and Ti. In addition, we have used the string method [W. E, W. Ren, and E. Vanden-Eijnden, Phys. Rev. B 66, 052301 (2002); L. Maragliano et al., J. Chem. Phys. 125, 024106 (2006)] within the density functional theory to study the melting pathways in the high pressure cotunnite phase of SiO2 and the hexagonal closed packed to face centered cubic phase transition in Ti. PMID:27131525
Ab initio no-core solutions for $^6$Li
Shin, Ik Jae; Maris, Pieter; Vary, James P; Forssén, Christian; Rotureau, Jimmy; Michel, Nicolas
2016-01-01
We solve for properties of $^6$Li in the ab initio No-Core Full Configuration approach and we separately solve for its ground state and $J^{\\pi}=2_{2}^{+}$ resonance with the Gamow Shell Model in the Berggren basis. We employ both the JISP16 and chiral NNLO$_{opt}$ realistic nucleon-nucleon interactions and investigate the ground state energy, excitation energies, point proton root-mean-square radius and a suite of electroweak observables. We also extend and test methods to extrapolate the ground state energy, point proton root-mean-square radius, and electric quadrupole moment. We attain improved estimates of these observables in the No-Core Full Configuration approach by using basis spaces up through N$_{max}$=18 that enable more definitive comparisons with experiment. Using the Density Matrix Renormalization Group approach with the JISP16 interaction, we find that we can significantly improve the convergence of the Gamow Shell Model treatment of the $^6$Li ground state and $J^{\\pi}=2_{2}^{+}$ resonance by ...
Ab initio evaluations of the He solubility in liquid Li
Energy Technology Data Exchange (ETDEWEB)
Sedano, Luis A. [EURATOM-CIEMAT Assoc., Materials for Fusion Program, Bd. 43 P0.04, Avda. Complutense 22, 28040 Madrid (Spain)]. E-mail: luis.sedano@ciemat.es; Hassanein, Ahmed [Argonne Nat. Lab, 9700 South Class Av., Argonne, IL (United States)]. E-mail: hassanein@anl.gov; Sanz, Javier [ETSII-UNED, c/Juan del Rosal, 12, 28040 Madrid (E) (Spain)]. E-mail: jsanz@ind.UNED.es
2005-11-15
Modified embedding atom methods (MEAM) are developed to have predictions of the partial molar heat of solution (-H{sub s}) by direct simulation of metal cohesion, He-metal and He-He interaction. Transitions from crystalline Li to configurations, having the liquid Li structure's factors (h-bar (q)), are simulated ab initio. Once h-bar (q) reproduced, He atoms are added, one by one, to the Li system. Parallel lines for each case, with slopes clearly independent on the number of He atoms in the system, are obtained for energy versus pressure at given temperatures. Average differences between two adjacent parallels at zero pressure, once kinetic energy of the system discounted, represents the energy gained by an He atom when added to the Li system, related to the solution energy -H{sub s}. The molar excess entropy of gas in solution (S-bar {sub l}{sup ex}) is previously evaluated following diverse fundamental approaches: a 'thermodynamic liquid-hole' (TL-H) model for alkali liquids and a statistical-mechanics (Neff and McQuarrie's) model (SMM). Between 600 and 900 deg. C, a typical range of interest for the use of Li in fusion technology, the computed values for the (He) Henry's constant in Li range from 8x10{sup -14} to 10{sup -13} at. fr. Pa{sup -1}.
Ab initio transport across bismuth selenide surface barriers
Narayan, Awadhesh
2014-11-24
© 2014 American Physical Society. We investigate the effect of potential barriers in the form of step edges on the scattering properties of Bi2Se3(111) topological surface states by means of large-scale ab initio transport simulations. Our results demonstrate the suppression of perfect backscattering, while all other scattering processes, which do not entail a complete spin and momentum reversal, are allowed. Furthermore, we find that the spin of the surface state develops an out-of-plane component as it traverses the barrier. Our calculations reveal the existence of quasibound states in the vicinity of the surface barriers, which appear in the form of an enhanced density of states in the energy window corresponding to the topological state. For double barriers we demonstrate the formation of quantum well states. To complement our first-principles results we construct a two-dimensional low-energy effective model and illustrate its shortcomings. Our findings are discussed in the context of a number of recent experimental works.
Engineering Room-temperature Superconductors Via ab-initio Calculations
Gulian, Mamikon; Melkonyan, Gurgen; Gulian, Armen
The BCS, or bosonic model of superconductivity, as Little and Ginzburg have first argued, can bring in superconductivity at room temperatures in the case of high-enough frequency of bosonic mode. It was further elucidated by Kirzhnitset al., that the condition for existence of high-temperature superconductivity is closely related to negative values of the real part of the dielectric function at finite values of the reciprocal lattice vectors. In view of these findings, the task is to calculate the dielectric function for real materials. Then the poles of this function will indicate the existence of bosonic excitations which can serve as a "glue" for Cooper pairing, and if the frequency is high enough, and the dielectric matrix is simultaneously negative, this material is a good candidate for very high-Tc superconductivity. Thus, our approach is to elaborate a methodology of ab-initio calculation of the dielectric function of various materials, and then point out appropriate candidates. We used the powerful codes (TDDF with the DP package in conjunction with ABINIT) for computing dielectric responses at finite values of the wave vectors in the reciprocal lattice space. Though our report is concerned with the particular problem of superconductivity, the application range of the data processing methodology is much wider. The ability to compute the dielectric function of existing and still non-existing (though being predicted!) materials will have many more repercussions not only in fundamental sciences but also in technology and industry.
The Hydration Structure of Carbon Monoxide by Ab Initio Methods
Awoonor-Williams, Ernest
2016-01-01
The solvation of carbon monoxide (CO) in liquid water is important for understanding its toxicological effects and biochemical roles. In this paper, we use ab initio molecular dynamics (AIMD) and CCSD(T)-F12 calculations to assess the accuracy of the Straub and Karplus molecular mechanical (MM) model for CO(aq). The CCSD(T)-F12 CO--H2O potential energy surfaces show that the most stable structure corresponds to water donating a hydrogen bond to the C center. The MM-calculated surface it incorrectly predicts that the O atom is a stronger hydrogen bond acceptor than the C atom. The AIMD simulations indicate that CO is solvated like a hydrophobic solute, with very limited hydrogen bonding with water. The MM model tends to overestimate the degree of hydrogen bonding and overestimates the atomic radius of the C atom. The calculated Gibbs energy of hydration is in good agreement with experiment (9.3 kJ/mol calc. vs 10.7 kJ/mol exptl.). The calculated diffusivity of CO(aq) in TIP3P-model water was 5.19 x 10-5 cm2/s ...
Renison, C Alicia; Fernandes, Kyle D; Naidoo, Kevin J
2015-07-01
This article describes an extension of the quantum supercharger library (QSL) to perform quantum mechanical (QM) gradient and optimization calculations as well as hybrid QM and molecular mechanical (QM/MM) molecular dynamics simulations. The integral derivatives are, after the two-electron integrals, the most computationally expensive part of the aforementioned calculations/simulations. Algorithms are presented for accelerating the one- and two-electron integral derivatives on a graphical processing unit (GPU). It is shown that a Hartree-Fock ab initio gradient calculation is up to 9.3X faster on a single GPU compared with a single central processing unit running an optimized serial version of GAMESS-UK, which uses the efficient Schlegel method for s- and l-orbitals. Benchmark QM and QM/MM molecular dynamics simulations are performed on cellobiose in vacuo and in a 39 Å water sphere (45 QM atoms and 24843 point charges, respectively) using the 6-31G basis set. The QSL can perform 9.7 ps/day of ab initio QM dynamics and 6.4 ps/day of QM/MM dynamics on a single GPU in full double precision. © 2015 Wiley Periodicals, Inc. PMID:25975864
Atomic carbon chains as spin-transmitters: An ab initio transport study
DEFF Research Database (Denmark)
Fürst, Joachim Alexander; Brandbyge, Mads; Jauho, Antti-Pekka
2010-01-01
An atomic carbon chain joining two graphene flakes was recently realized in a ground-breaking experiment by Jin et al. (Phys. Rev. Lett., 102 (2009) 205501). We present ab initio results for the electron transport properties of such chains and demonstrate complete spin-polarization of the transmi......An atomic carbon chain joining two graphene flakes was recently realized in a ground-breaking experiment by Jin et al. (Phys. Rev. Lett., 102 (2009) 205501). We present ab initio results for the electron transport properties of such chains and demonstrate complete spin......-polarization of the transmission in large energy ranges. The effect is due to the spin-polarized zig-zag edge terminating each graphene flake causing a spin-splitting of the graphene pi(z) bands, and the chain states. Transmission occurs when the graphene p-states resonate with similar states in the strongly hybridized edges...... and chain. This effect should in general hold for any p-conjugated molecules bridging the zig-zag edges of graphene electrodes. The polarization of the transmission can be controlled by chemically or mechanically modifying the molecule, or by applying an electrical gate....
Directory of Open Access Journals (Sweden)
S. J Hashemifar
2015-01-01
Full Text Available In this paper, the structural, magnetic, and electronic properties of two- to nine-atom copper and silver clusters and their alloys with one palladium atom are investigated by using full-potential all-electron density functional computations. After calculating minimized energy of several structural isomers of every nanocluster, it is argued that the small size nanoclusters (up to size of 6, prefer planar structures, while by increasing size a 2D-3D structural transformation is observed. The structural transformation of pure and copper-palladium clusters occurs in the size of seven and that of silver-palladium cluster in happens at the size of six. The calculated second difference and dissociation energies confirm that the two- and eight- atom pure clusters and three- and seven- atom alloyed clusters are magic clusters. The electronic and magnetic properties of stable isomers are calculated and considered after applying many body based GW correction.
Demiray, Ferhat; Sıdır, İsa; Gülseven Sıdır, Yadigar
2016-08-01
Density functional theory calculations at the LDA level have been performed to investigate the geometrical structure, stabilities and electronic properties of cyanide-coated fullerene C20@(CN) n, with n=0-20 in the ground state. From the binding energy, dissociation energy and second-order energy, even-number-coated fullerenes are more stable than odd-number ones. C20 has been successfully coated with electron-withdrawing group CN, achieving fullerene electron acceptors which have low-LUMO levels. The lowest LUMO value obtained for C20@(CN)12 is -5.89 eV, which is comparable with or lower than that of C60 and C60@(CN)2 fullerenes. Each of the cyanide coatings makes the fullerenes more stable with a larger HOMO-LUMO gap. Designed cyanide-coated fullerene compounds are promising and progressive to achieve a wider range of donor materials and high efficiencies in organic photovoltaic devices.
An ab initio Non-Equilibrium Green Function Approach to Charge Transport: Dithiolethine
Institute of Scientific and Technical Information of China (English)
Alexander Schnurpfeil; SONG Bo; Martin Albrecht
2006-01-01
@@ We present a novel ab initio non-equilibrium approach to calculate the current across a molecular junction. The method rests on a wavefunction-based full ab initio description of the central region of the junction combined with a tight binding approximation for the electrodes in the frame of the Keldysh Green function formalism. Our procedure is demonstrated for a dithiolethine molecule located between silver electrodes. The main conducting channel is identified and the full current-voltage characteristic is calculated.
Energy Technology Data Exchange (ETDEWEB)
Allali, D. [Laboratory for Developing New Materials and their Characterization, University of Setif 1, 19000 Setif (Algeria); Bouhemadou, A., E-mail: a_bouhemadou@yahoo.fr [Laboratory for Developing New Materials and their Characterization, University of Setif 1, 19000 Setif (Algeria); Safi, E. Muhammad Abud Al [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Bin-Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Department of Physics, Faculty of Science and Humanitarian Studies, Salman Bin Abdalaziz University, Alkharj 11942 (Saudi Arabia); Chegaar, M. [Department of Physics, Faculty of Science, University of Setif 1, 19000 Setif (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, 29000 Mascara (Algeria); Reshak, A.H. [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilson (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia)
2014-06-15
We report ab initio density functional theory calculations of the structural, electronic and optical properties of the spinel oxides SiMg{sub 2}O{sub 4}, SiZng{sub 2}O{sub 4}, and SiCd{sub 2}O{sub 4} using the full-potential linearized augmented plane-wave method. The structural parameters calculated using both the local density and generalized gradient approximations to the exchange-correlation potential are consistent with the literature data. To calculate the electronic properties, the exchange-correlation potential is treated with various functionals, and we find that the newly developed Tran–Blaha-modified Becke–Johnson functional significantly improves the band gap. We predict a direct band gap in all of the considered SiB{sub 2}O{sub 4} compounds, and the band gaps continuously decrease as the atomic size of the B element increases. The decrease in the fundamental direct band gap (Γ–Γ) from SiMg{sub 2}O{sub 4} to SiZn{sub 2}O{sub 4} to SiCd{sub 2}O{sub 4} can be attributed to p–d mixing in the upper valence bands of SiZn{sub 2}O{sub 4} and SiCd{sub 2}O{sub 4}. The lowest conduction band is well dispersive, similar to that found for transparent conducting oxides such as ZnO. This band is mainly defined by the s and p electrons of the Si and B (B=Mg, Zn, Cd) atoms. The topmost valence band is considerably less dispersive and is defined by O-2p and B–d electrons. The charge-carrier effective masses are evaluated at the topmost valence band and at the bottommost conduction band that were calculated. The frequency-dependent complex dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity and electron energy loss function were estimated. We find that the value of the zero-frequency limit of the dielectric function ε(0) increases as the band gap decreases. The origins of the peaks and structures in the optical spectra are determined in terms of the calculated energy band structures.
Energy Technology Data Exchange (ETDEWEB)
Guemou, M., E-mail: guemoumhamed7@gmail.com [Engineering Physics Laboratory, Ibn Khaldoun University of Tiaret, Postbox 78-Zaaroura, 14000 Tiaret (Algeria); Abdiche, A.; Riane, R. [Applied Materials Laboratory, Research Center, University of Sidi Bel Abbes, 22000 Sidi Bel Abbes (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, 29000 Mascara (Algeria)
2014-03-01
In this work, we present a density-functional theory study of structural, electronic and optical properties of BAs, BN binary compounds and their ternary BN{sub x}As{sub 1−x} solid solutions. The calculations are done by using the all-electron full potential linear augmented plane-wave method (FP-LAPW) as employed in WIEN2k code. For the exchange-correlation potential, local-density approximation (LDA) and generalized gradient approximation (GGA) have been used to calculate theoretical lattice parameters, bulk modulus, and its pressure derivative. The electronic band structure of these compounds have been calculated by using the above two approximations. We have also investigated in this article the density of state and the optical properties such as the dielectric function and the refractive index of BAs, BN and BN{sub 0.25}As{sub 0.75} compounds by using the above method. The results obtained for structural and electronic properties are compared with experimental data and other computational work. It has been found that the energy bands with all these approximations are similar except the band gap values. It has also been found that our results with LDA and GGA are in good agreement with other computational work wherever these are available.
Teeninga, Hermannus
1983-01-01
This thesis describes an investigation of the electronic structure of sulfonamidyl radicals (R1SO2NR2) and some structurally related carboxamidyl radicals (R1C(0)NR2). Both types of radicals have been invoked as intermediates in several chemical reactions. The present work originates from our intere
Arghavani Nia, Borhan; Sedighi, Matin; Shahrokhi, Masoud; Moradian, Rostam
2013-11-01
A density functional theory study of structural, electronical and optical properties of Ca3Sb2 compound in hexagonal and cubic phases is presented. In the exchange-correlation potential, generalized gradient approximation (PBE-GGA) has been used to calculate lattice parameters, bulk modulus, cohesive energy, dielectric function and energy loss spectra. The electronic band structure of this compound has been calculated using the above two approximations as well as another form of PBE-GGA, proposed by Engle and Vosko (EV-GGA). It is found that the hexagonal phase of Ca3Sb2 has an indirect gap in the Γ→N direction; while in the cubic phase there is a direct-gap at the Γ point in the PBE-GGA and EV-GGA. Effects of applying pressure on the band structure of the system studied and optical properties of these systems were calculated.
Teeninga, Hermannus
1983-01-01
This thesis describes an investigation of the electronic structure of sulfonamidyl radicals (R1SO2NR2) and some structurally related carboxamidyl radicals (R1C(0)NR2). Both types of radicals have been invoked as intermediates in several chemical reactions. The present work originates from our interest in the influence of the sulfonyl group on a nitrogen-free radical center in comparison with that of the carbonyl group. ... Zie: Summary
Directory of Open Access Journals (Sweden)
H. Allmaier
2008-06-01
Full Text Available Using a combination of electronic-structure and many-body calculations, we investigate correlations effects in the halfmetallic ferromagnet NiMnSb. A realistic many-body Hamiltonian, containing only Mn-d orbitals shows the importance of non-quasiparticle states just above the Fermi level. Our results suggest that for a better description of low energy states around Fermi level, Ni-d orbitals should be explicitly included.
Ab initio study of the effects of Ag/Mn doping on the electronic structure of LiFePO4
Institute of Scientific and Technical Information of China (English)
HOU XianHua; HU SheJun; LI WeiShan; ZHAO LingZhi; RU Qiang; YU HongWen; HUANG ZhaoWen
2008-01-01
Based on density functional theory (DFT) of the first-principle for the cathode materials of lithium ion battery, the electronic structures of Li(Fe1-xMex)PO4 (Me = Ag/Mn, x =0-0.40) are calculated by plane wave pseudo-potential method using Cambridge serial total energy package (CASTEP) program. The calculated results show that the Fermi level of mixed atoms Fe1-xAgx moves into its conduction bands (CBs) due to the Ag doping. The Li(Fe1-xAgx)PO4 system displays the periodic direct semiconductor characteristic with the increase of Ag-doped concentration. However, for Fe1-xMnx mixed atoms, the Fermi level is pined at the bottom of conduction bands (CBs), which is ascribed to the interaction between Mn(3d) electrons and Fe(4s) electrons. The intensity of the partial density of states (PDOS) near the bottom of CBs becomes stronger with the increase of Mn-doped concentration. The Fermi energy of the Li(Fe1-xMnx)PO4 reaches maximum at x = 0.25, which is consistent with the experimental value of x =0,20, The whole conduction property of Mn-doped LiFePO4 is superior to that of Ag-doped LiFePO4 cathode material, but the structural stability is reverse.
Energy Technology Data Exchange (ETDEWEB)
Arghavani Nia, Borhan, E-mail: b.arghavani@gmail.com [Department of Physics, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Sedighi, Matin [Department of Physics, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Shahrokhi, Masoud [Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Moradian, Rostam [Nano-Science and Nano-Technology Research Center, Razi University, Kermanshah (Iran, Islamic Republic of); Computational Physics Science Research Laboratory, Department of Nano-Science, Institute for Studies in Theoretical Physics and Mathematics (IPM), P.O. Box 19395-1795, Tehran (Iran, Islamic Republic of)
2013-11-15
A density functional theory study of structural, electronical and optical properties of Ca{sub 3}Sb{sub 2} compound in hexagonal and cubic phases is presented. In the exchange–correlation potential, generalized gradient approximation (PBE-GGA) has been used to calculate lattice parameters, bulk modulus, cohesive energy, dielectric function and energy loss spectra. The electronic band structure of this compound has been calculated using the above two approximations as well as another form of PBE-GGA, proposed by Engle and Vosko (EV-GGA). It is found that the hexagonal phase of Ca{sub 3}Sb{sub 2} has an indirect gap in the Γ→N direction; while in the cubic phase there is a direct-gap at the Γ point in the PBE-GGA and EV-GGA. Effects of applying pressure on the band structure of the system studied and optical properties of these systems were calculated. - Graphical abstract: A density functional theory study of structural, electronic and optical properties of Ca{sub 3}Sb{sub 2} compound in hexagonal and cubic phases is presented. Display Omitted - Highlights: • Physical properties of Ca{sub 3}Sb{sub 2} in hexagonal and cubic phases are investigated. • It is found that the hexagonal phase is an indirect gap semiconductor. • Ca{sub 3}Sb{sub 2} is a direct-gap semiconductor at the Γ point in the cubic phase. • By increasing pressure the semiconducting band gap and anti-symmetry gap are decreased.
Ray, Rajyavardhan; Himanshu, A. K.; Bandyopadhyay, S K; Sen, Pintu; Kumar, Uday; Sinha, T. P.
2013-01-01
First principles study of the electronic structures and optical properties of recently synthesized double perovskite $A_2ScSbO_6$ $(A=Sr, Ca)$ have been performed within the framework of density functional theory using WIEN2k. With increasing temperature, the $Sr$ compound has three phase transitions at ${\\rm 400K}$, ${\\rm 550K}$ and ${\\rm 650K}$ approximately, leading to the following sequence of phases: $P21/n \\rightarrow I2/m \\rightarrow I4/m \\rightarrow Fm\\bar{3}m$. Starting from the mono...
Energy Technology Data Exchange (ETDEWEB)
Deretzis, I., E-mail: ioannis.deretzis@imm.cnr.it; La Magna, A.
2014-02-01
The graphitization of the SiC(0 0 0 1{sup ¯}) plane, commonly referred to as the C-face of SiC, takes place through the sublimation and reorganization of surface atoms upon high-temperature annealing. Often, such reorganization gives rise to ordered atomic reconstructions over the ideally flat (0 0 0 1{sup ¯}) plane. In this article, we use the density functional theory to model graphene/SiC(0 0 0 1{sup ¯}) interfaces with an (1 × 1), (2 × 2) and (3 × 3) SiC periodicity. Our results indicate that the interface geometry can be crucial for both the stability and the electronic characteristics of the first graphitic layer, revealing a complex scenario of binding, doping and electronic correlations. We argue that the presence of more than one interface geometry at different areas of the same sample could be a reason for structural inhomogeneity and n- to p-type transitions.
Stoeffler, Daniel
2012-02-01
Using the first-principles full potential linearized augmented plane wave method, the electronic structure of Sr(2-x)La(x)Fe(1+y/2)Mo(1-y/2)O6 (SLFMO) double-perovskite systems is investigated for x = 1/2 and 1 and for y = +1 and -1. Substituting Sr atoms by La atoms allows one to tune the electrons added into the minority spin band and enhances the half-metal feature--according to the rigid band shift model--even if the magnetization decreases with increasing La concentration. By taking into account the chemical disorder on the Fe and Mo sites, resulting from the introduction of La as shown experimentally, it is shown (i) that a supplemental magnetization reduction occurs because the magnetic moment on the Fe antisite is opposite to the one on the Fe regular sites and (ii) that the half-metal feature is preserved in SLFMO for x = 1/2 and 1 contrary to the case for SFMO. Finally, because surface or interface Fe deficiency should have a more limited impact on the spin polarization than for SFMO, SLFMO/SrTiO3 multilayers are investigated in order to confirm this prediction by determining the spin polarization at the interface, which is found to remain high. PMID:22223617
Seda, Josef; Burda, Jaroslav V; Leszczynski, Jerzy
2005-02-01
SAC (symmetry adapted cluster)/SAC-CI and CASPT2 (multiconfigurational second-order perturbation theory) electron excitation spectra of free-base porphin and magnesium-porphin were determined using basis set functions augmented by both the polarization and diffuse functions-6-31+G(d). Such basis is recommended for correct description of the spectra because diffuse functions play fundamental roles in the formation of Rydberg MOs. The obtained results indicated that already the lowest roots in A(u), B(1u), B(2g), and B(3g) irreducible representations display Rydberg character. The calculated spectra are in a good agreement with both experimental and recently calculated electronic transitions. It is concluded that the SAC/SAC-CI level spectral lines are significantly affected by configuration selection when energy thresholds 5.0 x 10(-6) and 5.0 x 10(-7) a.u. are used for the determination of ground and excited state properties.
Directory of Open Access Journals (Sweden)
Chelli S.
2015-12-01
Full Text Available The structural, elastic, electronic and thermodynamic properties of BaxSr1−xS ternary alloys have been investigated using the full-potential (linearized augmented plane wave method. The ground state properties, such as lattice constant, bulk modulus and elastic constants, are in good agreement with numerous experimental and theoretical data. The dependence of the lattice parameters, bulk modulus and band gap on the composition x was analyzed. Deviation of the lattice constant from Vegard’s law and the bulk modulus from linear concentration dependence (LCD was observed. The microscopic origins of the gap bowing were explained by using the approach of Zunger et al. The thermodynamic stability of BaxSr1−xS alloy was investigated by calculating the excess enthalpy of mixing, ΔHm and the calculated phase diagram showed a broad miscibility gap with a critical temperature.
Institute of Scientific and Technical Information of China (English)
ZHANG Hong; TANG Jin; CHENG Xin-Lu
2008-01-01
We calculate structural,electromc properties and chemical bonding of borate Li4CaB2O6 under high pressure by means of the local density-functional pseudopotential approach.The equilibrium lattice constants,density of states,Mulliken population,bond lengths,bond angles as well as the pressure dependence of the band gap are presented.Analysis of the simulated high pressure band structure suggests that borate Li4CaB2O6 can be used as the semi-conductor optical material.Based on the Mulliken population analysis,it is found that the electron transfer of the Li atom is very different from that of other atoms in the studied range of high pressures.The charge populations of the Li atom decrease with the pressure up to 60GPa,then increase with the pressure.
DEFF Research Database (Denmark)
Jónsson, E. Ö.; Thygesen, Kristian Sommer; Ulstrup, Jens;
2011-01-01
Os(II)/(III) and Co(II)/(III) polypyridine complexes in aqueous solution are robust molecular entities both in freely solute state and adsorbed on Au(111)- and Pt(111)-electrode surfaces. This class of robust coordination chemical compounds have recently been characterized by electrochemical...... of the complexes in both free and adsorbate state, in either state exposed to both stoichiometric counterions and a large assembly of solvent water molecules. The oxidation states of the complexes were controlled, first by introducing chlorine counter atoms followed by spontaneous attraction of electrons from...... the complexes, also at first in electrostatically neutral form. Second, the solvent is found to provide strong dielectric screening of this charge transfer process and to be crucial for achieving the full chemically meaningful charge separated ionic oxidation states. The molecular charge and structure...
Energy Technology Data Exchange (ETDEWEB)
Mahmoud, Nada T.; Khalifeh, Jamil M. [Physics Department, The University of Jordan, Amman 11942 (Jordan); Mousa, Ahmad A., E-mail: amousa@meu.edu.jo [Middle East University, P.O. Box 383, Amman 11831 (Jordan); Juwhari, Hassan K.; Hamad, Bothina A. [Physics Department, The University of Jordan, Amman 11942 (Jordan)
2013-12-01
Density Functional Theory (DFT) calculations of a series of the nonstoichiometric Fe{sub 2−x}Co{sub x}VSn full Heusler alloy were carried out utilizing the full potential linearized augmented plane wave (FP-LAPW) method to investigate the electronic, energetic, and magnetic structures of the above systems. Unlike many concentration curves, increasing the cobalt concentration had a crucial effect on the spin polarization as it flattened at 100% at x=1.50, 1.75, and 2.00 where the half- metallic behavior was located with negative formation energy. Moreover, the total magnetic moment of the host material is found to increase with increasing Co concentration. Finally, the half metallic compounds found in some structures of this series might be useful in spintronic devices.
Energy Technology Data Exchange (ETDEWEB)
Kuzmin, Stanislav L.; Duley, Walter W. [Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1 (Canada)
2013-04-15
The vibrational and electronic properties of a new class of organometallic sandwich molecules, (C{sub 6}){sub n}Me{sub n-1}, based on stacks of cyclic C{sub 6} intercalated with Fe and Ru have been studied using first principles density functional techniques (DFT). Spectral properties as well as the HOMO-LUMO gap energy in molecules containing up to eight C{sub 6} layers have been calculated. The HOMO-LUMO energy gap in these molecules is < 1 eV and decreases significantly in longer molecules. It is shown that infinite chains should have excellent metallic properties. These molecules are promising for nanoelectronic applications, due to their predicted high stability, conductivity, and magnetic properties. (copyright 2013 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Energy Technology Data Exchange (ETDEWEB)
Chen, Chung-De [National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30076, Taiwan (China); National Tsing Hua University, Hsinchu, Taiwan (China); Huang, Yen-Chieh [National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30076, Taiwan (China); Chiang, Hsin-Lin [National Tsing Hua University, Hsinchu, Taiwan (China); Hsieh, Yin-Cheng; Guan, Hong-Hsiang; Chuankhayan, Phimonphan [National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30076, Taiwan (China); Chen, Chun-Jung, E-mail: cjchen@nsrrc.org.tw [National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30076, Taiwan (China); National Tsing Hua University, Hsinchu, Taiwan (China); National Cheng Kung University, Tainan City 701, Taiwan (China); National Cheng Kung University, Tainan City 701, Taiwan (China)
2014-09-01
A novel direct phase-selection method to select optimized phases from the ambiguous phases of a subset of reflections to replace the corresponding initial SAD phases has been developed. With the improved phases, the completeness of built residues of protein molecules is enhanced for efficient structure determination. Optimization of the initial phasing has been a decisive factor in the success of the subsequent electron-density modification, model building and structure determination of biological macromolecules using the single-wavelength anomalous dispersion (SAD) method. Two possible phase solutions (ϕ{sub 1} and ϕ{sub 2}) generated from two symmetric phase triangles in the Harker construction for the SAD method cause the well known phase ambiguity. A novel direct phase-selection method utilizing the θ{sub DS} list as a criterion to select optimized phases ϕ{sub am} from ϕ{sub 1} or ϕ{sub 2} of a subset of reflections with a high percentage of correct phases to replace the corresponding initial SAD phases ϕ{sub SAD} has been developed. Based on this work, reflections with an angle θ{sub DS} in the range 35–145° are selected for an optimized improvement, where θ{sub DS} is the angle between the initial phase ϕ{sub SAD} and a preliminary density-modification (DM) phase ϕ{sub DM}{sup NHL}. The results show that utilizing the additional direct phase-selection step prior to simple solvent flattening without phase combination using existing DM programs, such as RESOLVE or DM from CCP4, significantly improves the final phases in terms of increased correlation coefficients of electron-density maps and diminished mean phase errors. With the improved phases and density maps from the direct phase-selection method, the completeness of residues of protein molecules built with main chains and side chains is enhanced for efficient structure determination.
International Nuclear Information System (INIS)
This thesis reports on theoretical, methodical and experimental studies concerning scattering and structural properties of InxGa1-xNyAs1-y using transmission electron microscopy (TEM). First, theoretical concepts to describe electron scattering at real crystals including the effects of bonding and static atomic displacements (SAD) are considered. The approach of modified atomic scattering amplitudes (MASA), which uses density functional theory (DFT) to model bonding in an atomistic manner, is exploited to calculate compositiondependent MASA for InGaNAs. Valence force field (VFF) calculations are applied to determine SAD caused by atom size effects. Huang scattering caused by SAD is shown to pile up in the vicinity of Bragg peaks, contrary to the smooth background caused by thermal diffuse scattering (TDS). Furthermore, results for composition-dependent structure factors calculated by full DFT and atomistic models are compared. Second, structure factors for GaAs and InAs are measured by parallel and convergent beam electron diffraction (PBED and CBED) to verify the MASA approach. The PBED method was implemented in Bloch wave routines embedded in a least-squares refinement that allows for a refinement of structure factors, Debye-Waller factors, specimen thickness and -orientation. Errors in PBED are estimated from the application to simulated diffraction patterns with TDS background, and rules for the recognition of reasonable initial refinement conditions are derived. Then, PBED is applied to the measurement of the 200 structure factors of GaAs and InAs. Conversion to X-ray structure factors yields XGaAs200=-6.366±0.015 and XInAs200=53.687±0.110, respectively. By CBED, XGaAs200=-6.350±0.015 is measured. Additionally, Debye-Waller factors for GaAs have been refined to BGa=0.275±0.003 Aa2 and BAs=0.242±0.003 Aa2 at 99 K using PBED. Third, above theoretical scattering data is used in composition measurements in InGaNAs solar cell and laser structures via TEM
Ab initio prediction on ferrotoroidic and electronic properties of olivine Li4MnFeCoNiP4O16
Institute of Scientific and Technical Information of China (English)
Feng Hong-Jian; Liu Fa-Min
2009-01-01
First-principles calculations predict that olivine Li4MnFeCoNiP4O16 has a large toroidal moment and ferrimagnetic configuration with a magnetic moment of 1.99μB per formula unit. Density functional theory pins U (DFT+U) shows an indirect band gap of 0.65 eV in this hypothetical material. The band gap is not simply related to the electronic conductivity when it is used as cathode material in rechargeable Li-ion batteries. Based on the orbital-resolved density of states for the transition-metal ions in the hypothetical material, Co, Ni and Mn are in the high-spin configuration while Fe is in the low-spin configuration, which leads to a large resulting toroidal moment deriving from the Co and Ni ions.The spin configuration of the transition-metal ions in the system breaks the space- and time-inversion symmetry and leads to the magnetoelectric property simultaneously. The ferrotoroidic domain, the fourth form of ferroic, is observed in this new material, as in the case of LiCoPO4 reported recently.
Thermodynamic assessment of the Ho–Te system supported by ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Ghamri, H.; Belgacem-Bouzida, A. [Laboratoire d’étude Physico-Chimique des Matériaux, Département de Physique, Faculté des Sciences, Université de Batna, Rue Chahid Boukhlouf, 05000 Batna (Algeria); Djaballah, Y., E-mail: ydjaballah@yahoo.fr [Laboratoire d’étude Physico-Chimique des Matériaux, Département de Physique, Faculté des Sciences, Université de Batna, Rue Chahid Boukhlouf, 05000 Batna (Algeria); Hidoussi, A. [Laboratoire d’étude Physico-Chimique des Matériaux, Département de Physique, Faculté des Sciences, Université de Batna, Rue Chahid Boukhlouf, 05000 Batna (Algeria)
2013-03-05
Highlights: ► We calculated enthalpies of formation of the HoTe and Ho{sub 2}Te{sub 5} compounds by using ab initio method. ► We modeled the Gibbs energy of the HoTe intermediate phase for the first time. ► The thermodynamic parameters of the all phases existing in the system were determined. ► The complete phase diagram of the system (Ho–Te) is calculated. -- Abstract: The phase diagram of the Ho–Te binary system has been assessed by using the CALPHAD (Calculation of Phase Diagrams) method on the basis of the experimental data of the phase equilibria and enthalpies of formation from ab initio electronic-structure calculations within the framework of density-functional theory. Reasonable models were constructed for all the phases of the system. The liquid phase was described as the substitutional solution model with excess energy expressed by Redlich–Kister polynomial. The compounds Ho{sub 2}Te{sub 5} and HoTe{sub 3} were expressed as stoichiometric phases. The (HoTe) phase was modeled by two-sublattices; (Ho,Va){sub 1}(Te){sub 1}. A consistent set of thermodynamic parameters has been derived, and calculated phase diagram was compared with the experimental data. A good agreement between the calculated results and experimental data was obtained.
Embedding parameters in ab initio theory to develop approximations based on molecular similarity
Tanha, Matteus; Kaul, Shiva; Cappiello, Alexander; Gordon, Geoffrey J; Yaron, David J
2015-01-01
A means to take advantage of molecular similarity to lower the computational cost of electronic structure theory is explored, in which parameters are embedded into a low-cost, low-level (LL) ab initio model and adjusted to obtain agreement with results from a higher-level (HL) ab initio model. A parametrized LL (pLL) model is created by multiplying selected matrix elements of the Hamiltonian operators by scaling factors that depend on element types. Various schemes for applying the scaling factors are compared, along with the impact of making the scaling factors linear functions of variables related to bond lengths, atomic charges, and bond orders. The models are trained on ethane and ethylene, substituted with -NH2, -OH and -F, and tested on substituted propane, propylene and t-butane. Training and test datasets are created by distorting the molecular geometries and applying uniform electric fields. The fitted properties include changes in total energy arising from geometric distortions or applied fields, an...
Ground state analytical ab initio intermolecular potential for the Cl{sub 2}-water system
Energy Technology Data Exchange (ETDEWEB)
Hormain, Laureline; Monnerville, Maurice, E-mail: maurice.monnerville@univ-lille1.fr; Toubin, Céline; Duflot, Denis; Pouilly, Brigitte; Briquez, Stéphane [Laboratoire de Physique des Lasers Atomes et Molécules, Unité Mixte de Recherche (UMR) 8523, Université Lille I, Bât. P5, 59655 Villeneuve d’Ascq Cedex (France); Bernal-Uruchurtu, Margarita I.; Hernández-Lamoneda, Ramón [Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Cuernavaca 62209, México (Mexico)
2015-04-14
The chlorine/water interface is of crucial importance in the context of atmospheric chemistry. Modeling the structure and dynamics at this interface requires an accurate description of the interaction potential energy surfaces. We propose here an analytical intermolecular potential that reproduces the interaction between the Cl{sub 2} molecule and a water molecule. Our functional form is fitted to a set of high level ab initio data using the coupled-cluster single double (triple)/aug-cc-p-VTZ level of electronic structure theory for the Cl{sub 2} − H{sub 2}O complex. The potential fitted to reproduce the three minima structures of 1:1 complex is validated by the comparison of ab initio results of Cl{sub 2} interacting with an increasing number of water molecules. Finally, the model potential is used to study the physisorption of Cl{sub 2} on a perfectly ordered hexagonal ice slab. The calculated adsorption energy, in the range 0.27 eV, shows a good agreement with previous experimental results.
Ab initio calculation of oxygen self-diffusion coefficient in uranium dioxide UO2
Dorado, Boris; Garcia, Philippe; Torrent, Marc
Uranium dioxide UO2 is the most widely used nuclear fuel worldwide and its atomic transport properties are relevant to practically all engineering aspects of the material. Although transport properties have already been studied in UO2 by means of first-principles calculations, the ab initio determination of self-diffusion coefficients has up to now remained unreachable because the relevant computational tools were neither available or adapted. The present work reports our results related to the ab initio calculation of the oxygen self-diffusion coefficient in UO2. We first determine the Gibbs free energies of formation of oxygen charged defects by calculating both the electronic and vibrational (hence entropic) contributions. Then, we use the transition state theory in order to compute the effective jump frequency of the defects, which in turn provides us with the value of the pre-exponential factor. The results are compared to self-diffusion data obtained experimentally with a careful monitoring of the relevant thermodynamic conditions (oxygen partial pressure, temperature, impurity content).
Experimental and ab initio investigations on textured Li–Mn–O spinel thin film cathodes
Energy Technology Data Exchange (ETDEWEB)
Fischer, J., E-mail: Julian.Fischer@kit.edu [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Music, D. [RWTH Aachen University, Materials Chemistry, Kopernikusstrasse 10, 52074 Aachen (Germany); Bergfeldt, T.; Ziebert, C.; Ulrich, S.; Seifert, H.J. [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)
2014-12-01
This paper describes the tailored preparation of nearly identical lithium–manganese–oxide thin film cathodes with different global grain orientations. The thin films were synthesized by rf magnetron sputtering from a LiMn{sub 2}O{sub 4}-target in a pure argon plasma. Under appropriate processing conditions, thin films with a cubic spinel structure and a nearly similar density and surface topography but different grain orientation, i.e. (111)- and (440)-textured films, were achieved. The chemical composition was determined by inductively coupled plasma optical emission spectroscopy and carrier gas hot extraction. The constitution- and microstructure were evaluated by X-ray diffraction and Raman spectroscopy. The surface morphology and roughness were investigated by scanning electron and atomic force microscopy. The differently textured films represent an ideal model system for studying potential effects of grain orientation on the lithium ion diffusion and electrochemical behavior in LiMn{sub 2}O{sub 4}-based thin films. They are nearly identical in their chemical composition, atomic bonding behavior, surface-roughness, morphology and thickness. Our initial ab initio molecular dynamics data indicate that Li ion transport is faster in (111)-textured structure than in (440)-textured one. - Highlights: • Thin film model system of differently textured cubic Li–Mn–O spinels. • Investigation of the Li–Mn–O thin film mass density by X-ray reflectivity. • Ab initio molecular dynamics simulation on Li ion diffusion in LiMn{sub 2}O{sub 4}.
Experimental and ab initio investigations on textured Li–Mn–O spinel thin film cathodes
International Nuclear Information System (INIS)
This paper describes the tailored preparation of nearly identical lithium–manganese–oxide thin film cathodes with different global grain orientations. The thin films were synthesized by rf magnetron sputtering from a LiMn2O4-target in a pure argon plasma. Under appropriate processing conditions, thin films with a cubic spinel structure and a nearly similar density and surface topography but different grain orientation, i.e. (111)- and (440)-textured films, were achieved. The chemical composition was determined by inductively coupled plasma optical emission spectroscopy and carrier gas hot extraction. The constitution- and microstructure were evaluated by X-ray diffraction and Raman spectroscopy. The surface morphology and roughness were investigated by scanning electron and atomic force microscopy. The differently textured films represent an ideal model system for studying potential effects of grain orientation on the lithium ion diffusion and electrochemical behavior in LiMn2O4-based thin films. They are nearly identical in their chemical composition, atomic bonding behavior, surface-roughness, morphology and thickness. Our initial ab initio molecular dynamics data indicate that Li ion transport is faster in (111)-textured structure than in (440)-textured one. - Highlights: • Thin film model system of differently textured cubic Li–Mn–O spinels. • Investigation of the Li–Mn–O thin film mass density by X-ray reflectivity. • Ab initio molecular dynamics simulation on Li ion diffusion in LiMn2O4
Energy Technology Data Exchange (ETDEWEB)
Miloud Abid, O.; Yakoubi, A. [Laboratoire d’Etudes des Matériaux et Instrumentations Expérimentales, Université Djilali Liabes de Sidi Bel-Abbes, 22000 (Algeria); Tadjer, A. [Modeling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, Sidi Bel-Abbes (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 (Algeria); Ahmed, R. [Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, UTM Skudai, 81310 Johor (Malaysia); Murtaza, G. [Materials Modeling Laboratory, Department of Physics, Islamia College University, Peshawar (Pakistan); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Azam, Sikander [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic)
2014-12-15
Highlights: • The calculated structural parameters of RMn{sub 2}Ge{sub 2} (R = Ca, Nd and Y) compounds are found in good agreement with the experimental data. • The structural and band structure calculation reveals that these compounds are ferromagnetic brittle metals. • The elastic and thermodynamic properties for the herein studied compounds are investigated for the first time. - Abstract: Intermetallic RMn{sub 2}Ge{sub 2} ternary compounds have attracted considerable attention from researchers in recent years because they show strong indications for novel magnetic characteristics and they have the potential to reveal the mechanism of superlattices. The study of the paramagnetic, ferromagnetic and antiferromagnetic phases affirms the strong dependence to the distance between atomic species in these compounds. In this study, we investigated the structural, elastic, electronic and thermodynamic properties of the intermetallic RMn{sub 2}Ge{sub 2} (R = Ca, Nd and Y) compounds. To carry out this study, we used the full potential (FP) linearized (L) augmented plane wave plus local orbitals (APW + lo), a scheme of calculations developed within the frame work of density functional theory (DFT). To incorporate the exchange correlation (XC) energy and corresponding potential into the total energy calculations, local density approximation (LDA) parameterized by Perdew and Wang is taken into account. Analysis of the density of states (DOS) profile illustrates the conducting nature of these intermetallic compounds; with a predominantly contribution from the R and Mn-d states. At ambient conditions, calculations for elastic constants (C{sub 11}, C{sub 12}, C{sub 13}, C{sub 44}, C{sub 33} and C{sub 66}) are also performed, which point to their brittle character. In addition, the quasi harmonic Debye model was used to predict the thermal properties, together with relative expansion coefficients and heat capacity.
Ab initio no-core shell model with continuum
Navratil, Petr
2008-04-01
The ab initio no-core shell model (NCSM) is a many-body approach to nuclear structure of light nuclei. The NCSM adopts an effective interaction theory to transform fundamental inter-nucleon interactions into effective interactions for a specified nucleus in a selected harmonic oscillator basis space [1]. The method is capable of predicting nuclear structure from inter-nucleon forces derived from quantum chromodynamics by means of chiral effective field theory [2]. NCSM extensions to the microscopic description of nuclear reactions are now under development. In my talk, I will first discuss our recent calculations of the ^4He total photo-absorption cross section using two- and three-nucleon interactions from chiral effective field theory [3]. I will then outline our effort to augment the NCSM by the resonating group method (RGM) technique to develop a new method capable of describing simultaneously both bound states and nuclear reactions on light nuclei [4]. This approach, which preserves translational symmetry and the Pauli principle, will allow us to calculate cross sections of reactions important for astrophysics and describe weakly-bound systems from first principles. I will present our first phase shift results for neutron scattering off ^3H, ^4He and ^7Li and proton scattering off ^3He, ^4He and ^7Be using realistic nucleon-nucleon potentials. 3mm [1] P. Navr'atil, J. P. Vary and B. R. Barrett, Phys. Rev. C 62, 054311 (2000). [2] P. Navr'atil and V. G. Gueorguiev and J. P. Vary, W. E. Ormand and A. Nogga, Phys. Rev. Lett. 99, 042501 (2007). [3] S. Quaglioni and P. Navr'atil, Phys. Lett. B 652, 370 (2007). [4] S. Quaglioni and P. Navr'atil, arXiv:0712.0855.
Lithium Insertion In Silicon Nanowires: An ab Initio Study
Zhang, Qianfan
2010-09-08
The ultrahigh specific lithium ion storage capacity of Si nanowires (SiNWs) has been demonstrated recently and has opened up exciting opportunities for energy storage. However, a systematic theoretical study on lithium insertion in SiNWs remains a challenge, and as a result, understanding of the fundamental interaction and microscopic dynamics during lithium insertion is still lacking. This paper focuses on the study of single Li atom insertion into SiNWs with different sizes and axis orientations by using full ab initio calculations. We show that the binding energy of interstitial Li increases as the SiNW diameter grows. The binding energies at different insertion sites, which can be classified as surface, intermediate, and core sites, are quite different. We find that surface sites are energetically the most favorable insertion positions and that intermediate sites are the most unfavorable insertion positions. Compared with the other growth directions, the [110] SiNWs with different diameters always present the highest binding energies on various insertion locations, which indicates that [110] SiNWs are more favorable by Li doping. Furthermore, we study Li diffusion inside SiNWs. The results show that the Li surface diffusion has a much higher chance to occur than the surface to core diffusion, which is consistent with the experimental observation that the Li insertion in SiNWs is layer by layer from surface to inner region. After overcoming a large barrier crossing surface-to-intermediate region, the diffusion toward center has a higher possibility to occur than the inverse process. © 2010 American Chemical Society.
i-PI: A Python interface for ab initio path integral molecular dynamics simulations
Ceriotti, Michele; More, Joshua; Manolopoulos, David E.
2014-03-01
Recent developments in path integral methodology have significantly reduced the computational expense of including quantum mechanical effects in the nuclear motion in ab initio molecular dynamics simulations. However, the implementation of these developments requires a considerable programming effort, which has hindered their adoption. Here we describe i-PI, an interface written in Python that has been designed to minimise the effort required to bring state-of-the-art path integral techniques to an electronic structure program. While it is best suited to first principles calculations and path integral molecular dynamics, i-PI can also be used to perform classical molecular dynamics simulations, and can just as easily be interfaced with an empirical forcefield code. To give just one example of the many potential applications of the interface, we use it in conjunction with the CP2K electronic structure package to showcase the importance of nuclear quantum effects in high-pressure water. Catalogue identifier: AERN_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AERN_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 138626 No. of bytes in distributed program, including test data, etc.: 3128618 Distribution format: tar.gz Programming language: Python. Computer: Multiple architectures. Operating system: Linux, Mac OSX, Windows. RAM: Less than 256 Mb Classification: 7.7. External routines: NumPy Nature of problem: Bringing the latest developments in the modelling of nuclear quantum effects with path integral molecular dynamics to ab initio electronic structure programs with minimal implementational effort. Solution method: State-of-the-art path integral molecular dynamics techniques are implemented in a Python interface. Any electronic structure code can be patched to receive the atomic
Ab initio interaction potentials for X and B excited states of He-I{sub 2} for studying dynamics
Energy Technology Data Exchange (ETDEWEB)
Prosmiti, Rita; Garcia-Gutierrez, Leonor; Delgado-Tellez, Laura; Valdes, Alvaro; Villarreal, Pablo; Delgado-Barrio, Gerardo, E-mail: rita@imaff.cfmac.csic.e [Instituto de Fisica Fundamental (CSIC), Serrano 123, 28006 Madrid (Spain)
2009-11-01
Ab initio CCSD(T) and MRCI approaches were employed to construct potential energy surfaces of the ground and the B electronic excited states of He-I{sub 2} complex, while full quantum mechanical methods were applied to study its spectroscopy and dynamics. A description of the approach adopted, together with the results obtained and their comparison with recent experimental data, as well as further improvements are presented.
Ab initio theory for ultrafast magnetization dynamics with a dynamic band structure
Mueller, B. Y.; Haag, M.; Fähnle, M.
2016-09-01
Laser-induced modifications of magnetic materials on very small spatial dimensions and ultrashort timescales are a promising field for novel storage and spintronic devices. Therefore, the contribution of electron-electron spin-flip scattering to the ultrafast demagnetization of ferromagnets after an ultrashort laser excitation is investigated. In this work, the dynamical change of the band structure resulting from the change of the magnetization in time is taken into account on an ab initio level. We find a large influence of the dynamical band structure on the magnetization dynamics and we illustrate the thermalization and relaxation process after laser irradiation. Treating the dynamical band structure yields a demagnetization comparable to the experimental one.
i-PI: A Python interface for ab initio path integral molecular dynamics simulations
Ceriotti, Michele; Manolopoulos, David E
2014-01-01
Recent developments in path integral methodology have significantly reduced the computational expense of including quantum mechanical effects in the nuclear motion in ab initio molecular dynamics simulations. However, the implementation of these developments requires a considerable programming effort, which has hindered their adoption. Here we describe i-PI, an interface written in Python that has been designed to minimise the effort required to bring state-of-the-art path integral techniques to an electronic structure program. While it is best suited to first principles calculations and path integral molecular dynamics, i-PI can also be used to perform classical molecular dynamics simulations, and can just as easily be interfaced with an empirical forcefield code. To give just one example of the many potential applications of the interface, we use it in conjunction with the CP2K electronic structure package to showcase the importance of nuclear quantum effects in high pressure water.
Pressure-induced semimetallic behavior of calcium from ab initio calculations
International Nuclear Information System (INIS)
A loss of metallic properties in fcc calcium under high pressure is studied ab initio using the density functional theory (DFT) and GW approximation. It is found that a more correct description of many-electron effects given by GW method does not provide significant changes in the behavior of electronic spectrum in comparison with DFT approach. We note that the obtained width of (pseudo)gap is highly sensitive to the k-point sampling used for density of states calculation. The analysis of fcc calcium's band structure at p ∼ 20 GPa shows that the crossing of bands at the Fermi level is removed if the spin-orbit coupling is taken into account.
An investigation of ab initio shell-model interactions derived by no-core shell model
Wang, XiaoBao; Dong, GuoXiang; Li, QingFeng; Shen, CaiWan; Yu, ShaoYing
2016-09-01
The microscopic shell-model effective interactions are mainly based on the many-body perturbation theory (MBPT), the first work of which can be traced to Brown and Kuo's first attempt in 1966, derived from the Hamada-Johnston nucleon-nucleon potential. However, the convergence of the MBPT is still unclear. On the other hand, ab initio theories, such as Green's function Monte Carlo (GFMC), no-core shell model (NCSM), and coupled-cluster theory with single and double excitations (CCSD), have made many progress in recent years. However, due to the increasing demanding of computing resources, these ab initio applications are usually limited to nuclei with mass up to A = 16. Recently, people have realized the ab initio construction of valence-space effective interactions, which is obtained through a second-time renormalization, or to be more exactly, projecting the full-manybody Hamiltonian into core, one-body, and two-body cluster parts. In this paper, we present the investigation of such ab initio shell-model interactions, by the recent derived sd-shell effective interactions based on effective J-matrix Inverse Scattering Potential (JISP) and chiral effective-field theory (EFT) through NCSM. In this work, we have seen the similarity between the ab initio shellmodel interactions and the interactions obtained by MBPT or by empirical fitting. Without the inclusion of three-body (3-bd) force, the ab initio shell-model interactions still share similar defects with the microscopic interactions by MBPT, i.e., T = 1 channel is more attractive while T = 0 channel is more repulsive than empirical interactions. The progress to include more many-body correlations and 3-bd force is still badly needed, to see whether such efforts of ab initio shell-model interactions can reach similar precision as the interactions fitted to experimental data.
D'Yachkov, P. N.; Makaev, D. V.
2007-11-01
Every carbon single-walled nanotube (SWNT) can be generated by first mapping only two nearest-neighbor C atoms onto a surface of a cylinder and then using the rotational and helical symmetry operators to determine the remainder of the tubule [C. T. White , Phys. Rev. B 47, 5485 (1993)]. With account of these symmetries, we developed a symmetry-adapted version of a linear augmented cylindrical wave method. In this case, the cells contain only two carbon atoms, and the ab initio theory becomes applicable to any SWNT independent of the number of atoms in a translational unit cell. The approximations are made in the sense of muffin-tin (MT) potentials and local-density-functional theory only. An electronic potential is suggested to be spherically symmetrical in the regions of atoms and constant in an interspherical region up to the two essentially impenetrable cylinder-shaped potential barriers. To construct the basis wave functions, the solutions of the Schrödinger equation for the interspherical and MT regions of the tubule were sewn together using a theorem of addition for cylindrical functions, the resulting basis functions being continuous and differentiable anywhere in the system. With account of analytical equations for these functions, the overlap and Hamiltonian integrals are calculated, which permits determination of electronic structure of nanotube. We have calculated the total band structures and densities of states of the chiral and achiral, semiconducting, semimetallic, and metallic carbon SWNTs (13, 0), (12, 2), (11, 3), (10, 5), (9, 6), (8, 7), (7, 7), (12, 4), and (100, 99) containing up to the 118 804 atoms per translational unit cell. Even for the (100, 99) system with huge unit cell, the band structure can be easily calculated and the results can be presented in the standard form of four curves for the valence band plus one curve for the low-energy states of conduction band. About 150 functions produce convergence of the band structures better then
Fawzy, Wafaa M.; Elsayed, Mahmoud; Zhang, Yuchen
2013-01-01
This work reports the first highly correlated ab initio study of the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the O_2^ - (X{}^2Π _g) - HF(X{}^1Σ^+) complex. Accurate electronic structure calculations were performed using the coupled cluster method including single and double excitations with addition of the perturbative triples correction [CCSD(T)] with the Dunning's correlation consistent basis sets aug-cc-pVnZ, n = 2-5. Also, the explicitly correlated CCSD(T)-F12a level of theory was employed with the AVnZ basis as well as the Peterson and co-workers VnZ-F12 basis sets with n = 2 and 3. Results of all levels of calculations predicted two equivalent minimum energy structures of planar geometry and Cs symmetry along the A″ surface of the complex, whereas the A' surface is repulsive. Values of the geometrical parameters and the counterpoise corrected dissociation energies (Cp-De) that were calculated using the CCSD(T)-F12a/VnZ-F12 level of theory are in excellent agreement with those obtained from the CCSD(T)/aug-cc-pV5Z calculations. The minimum energy structure is characterized by a very short hydrogen bond of length of 1.328 Å, with elongation of the HF bond distance in the complex by 0.133 Å, and De value of 32.313 Kcal/mol. Mulliken atomic charges showed that 65% of the negative charge is localized on the hydrogen bonded end of the superoxide radical and the HF unit becomes considerably polarized in the complex. These results suggest that the hydrogen bond is an incipient ionic bond. Exploration of the potential energy surface confirmed the identified minimum and provided support for vibrationally induced intramolecular proton transfer within the complex. The T-shaped geometry that possesses C2v symmetry presents a saddle point on the top of the barrier to the in-plane bending of the hydrogen above and below the axis that connects centers of masses of the monomers. The height of this barrier is 7
Knyazev, D. V.; Levashov, P. R.
2014-01-01
This work is devoted to the investigation of transport and optical properties of liquid aluminum in the two-temperature case. At first optical properties, static electrical and thermal conductivities were obtained in the \\textit{ab initio} calculation. The \\textit{ab initio} calculation is based on the quantum molecular dynamics, density functional theory and the Kubo-Greenwood formula. The semiempirical approximation was constructed based on the results of the \\textit{ab initio} caculation. ...
Comparative studies of the spectroscopy of CuCl2: DFT versus standard ab initio approaches.
Ramírez-Solís, A; Poteau, R; Vela, A; Daudey, J P
2005-04-22
The X2Pi g-2Sigma g+, X2Pi g-2Delta g, X2Pi g-2Sigma u+, X2Pi g-2Pi u transitions on CuCl2 have been studied using several exchange-correlation functionals from the various types of density functional theory (DFT) approaches like local density approximation (LDA), generalized gradient approximation (GGA), hybrid and meta-GGA. The results are compared with the experience and with those coming from the most sophisticated nondynamic and dynamic electronic correlation treatments using the same relativistic effective core potentials and especially developed basis sets to study the electronic structure of the five lowest states and the corresponding vertical and adiabatic transition energies. The calculated transition energies for three of the hybrid functionals (B3LYP, B97-2, and PBE0) are in very good agreement with the benchmark ab initio results and experimental figures. All of the other functionals largely overestimate the X2Pi g-2Sigma g+ and X2Pi g-2Delta g transition energies, many of them even placing the 2Delta g ligand field state above the charge transfer 2Pi u and 2Sigma u+ states. The relative weight of the Hartree-Fock exchange in the definition of the functional used appears to play a key role in the accurate description of the LambdaSSigma density defined by the orientation of the 3d hole (sigma, pi, or delta) on Cu in the field of both chlorine atoms, but no simple connection of this weight with the quality of the spectra has been found. Mulliken charges and spin densities are carefully analyzed; a possible link between the extent of spin density on the metal for the X2Pi g state and the performance of the various functionals was observed, suggesting that those that lead to the largest values (close to 0.65) are the ones that best reproduce these four transitions. Most functionals lead to a remarkably low ionicity for the three ligand field states even for the best performing functionals, compared to the complete active space (SCF) (21, 14) ab initio
Energy Technology Data Exchange (ETDEWEB)
Palacios, P. [Instituto de Energia Solar and Dpt. de Tecnologias Especiales, ETSI de Telecomunicacion, UPM. Ciudad Universitaria s/n, 28040 Madrid (Spain); Instituto de Catalisis y Petroleoquimica, CSIC. Marie Curie 2, Cantoblanco, 28049 Madrid (Spain)], E-mail: pablop@etsit.upm.es; Aguilera, I.; Wahnon, P. [Instituto de Energia Solar and Dpt. de Tecnologias Especiales, ETSI de Telecomunicacion, UPM. Ciudad Universitaria s/n, 28040 Madrid (Spain)
2008-08-30
In this work, we present frozen phonon and linear response ab-initio research into the vibrational properties of the CuGaS{sub 2} chalcopyrite and transition metal substituted (CuGaS{sub 2})M alloys. These systems are potential candidates for developing a novel solar-cell material with enhanced optoelectronic properties based in the implementation of the intermediate-band concept. We have previously carried out ab-initio calculations of the electronic properties of these kinds of chalcopyrite metal alloys showing a narrow transition metal band isolated in the semiconductor band gap. The substitutes used in the present work are the 3d metal elements, Titanium and Chromium. For the theoretical calculations we use standard density functional theory at local density and generalized gradient approximation levels. We found that the optical phonon branches of the transition metal chalcopyrite, are very sensitive to the specific bonding geometry and small changes in the transition metal environment.
Realization of prediction of materials properties by ab initio computer simulation
Indian Academy of Sciences (India)
Yoshiyuki Kawazoe
2003-01-01
Ab initio treatment is becoming realistic to predict physical, chemical, and even mechanical properties of academically and industrially interesting materials. There is, however, some limitation in size and time of the system up to the order of several hundred atoms and ∼ 1 pico second, even if we use the fastest supercomputer efficiently. Therefore, it is very difficult to simulate realistic materials with grain boundaries and important reactions like diffusion in materials. To improve this situation, two ways have been invented. One way is to upgrade approximations to match the necessary levels according to inhomogeneous electron gas theory beyond the present day standard, i.e. local density approximation (LDA). The reason is simply that the system we are interested in is composed of many particles interacting with Coulomb forces governed by quantum mechanics. (Complete knowledge is available, and only what we should do is to make better approximations to explain the phenomena!). Another is to extract the necessary parameters from the ab initio calculations on systems with limited number of atoms, and apply these results into cluster variation, direct, or any other sophisticated methods based on classical concepts such as statistical mechanics. In this paper, several typical examples recently worked out by our research group are introduced to indicate that these methodologies are actually possible to be successfully used to predict materials properties before experiments based on the present day state-of-art supercomputing systems. It includes scientific visualization of the results of ab initio molecular dynamics simulation on atom insertion process to C60 and to carbon nanotube, tight-binding calculation of single electron conductance properties in nanotube to create nano-scale diode virtually by computer, which will be a base of future nanoscale electric device in nanometer size, Li + H reaction without Born–Oppenheimer approximation, structural phase
Heuvel, Willem Van den; Soncini, Alessandro
2015-01-01
We present an ab initio methodology dedicated to the determination of the electronic structure and magnetic properties of ground and low-lying excited states, i.e., the crystal field levels, in lanthanide(III) complexes. Currently, the most popular and successful ab initio approach is the CASSCF/RASSI-SO method, consisting of the optimization of multiple complete active space self-consistent field (CASSCF) spin eigenfunctions, followed by full diagonalization of the spin--orbit coupling (SOC) Hamiltonian in the basis of the CASSCF spin states featuring spin-dependent orbitals. Based on two simple observations valid for Ln(III) complexes, namely: (i) CASSCF 4f atomic orbitals are expected to change very little when optimized for different multiconfigurational states belonging to the 4f-electronic configuration, (ii) due to strong SOC the total spin is not a good quantum number, we propose here an efficient ab initio strategy which completely avoids any multiconfigurational calculation, by optimizing a unique s...
Ab Initio Calculation of Vacancies and Interstitials in NiSi2
Institute of Scientific and Technical Information of China (English)
WANG Tao; DAI Yong-Bing; OUYANG Si-Ke; WU Jian-Sheng; SHEN He-Sheng
2004-01-01
@@ An ab initio plane-wave ultrasoft pseudopotential method based on the generalized gradient approximations has been utilized to investigate the electronic structure, atomic geometry, formation energy to provide a better understanding of properties of Ni disilicide. The vacancy and interstitial formation energies largely depend on the atomic chemical potentials. The formation energies of vacancies Vsi and VNi are in the range of 0.04-0.56 eV and 1.25-2.3 eV, respectively and the formation energies of Si and Ni interstitials are 3.89-4.42 eV and 0.67-1.71 eV,respectively. The smaller Ni interstitial formation energy is in agreement with the experimental result that Ni interstitial atom is dominant diffusion species in NiSi2.
High-pressure elastic properties of cubic Ir2P from ab initio calculations
Sun, Xiao-Wei; Bioud, Nadhira; Fu, Zhi-Jian; Wei, Xiao-Ping; Song, Ting; Li, Zheng-Wei
2016-10-01
A study of the high-pressure elastic properties of new synthetic Ir2P in the anti-fluorite structure is conducted using ab initio calculations based on density functional theory. The elastic constants C11, C12 and C44 for the cubic Ir2P are obtained by the stress-strain method and the elastic stability calculations under pressure indicate that it is stable at least 100 GPa. Additionally, the electronic density of states, the aggregate elastic moduli, that is bulk modulus, shear modulus, and Young's modulus along with the Debye temperature, Poisson's ratio, and elastic anisotropy factor are all successfully obtained. Moreover, the pressure dependence of the longitudinal and shear wave velocities in three different directions [100], [110], and [111] for Ir2P are also predicted for the first time.
Femtosecond Laser Processing of Germanium: An Ab Initio Molecular Dynamics Study
Ji, Pengfei
2016-01-01
An ab initio molecular dynamics study of femtosecond laser processing of germanium is presented in this paper. The method based on the finite temperature density functional theory is adopted to probe the structural change, thermal motion of the atoms, dynamic property of the velocity autocorrelation, and the vibrational density of states. Starting from a cubic system at room temperature (300 K) containing 64 germanium atoms with an ordered arrangement of 1.132 nm in each dimension, the femtosecond laser processing is simulated by imposing the Nose Hoover thermostat to the electronic subsystem lasting for ~100 fs and continuing with microcanonical ensemble simulation of ~200 fs. The simulation results show solid, liquid and gas phases of germanium under adjusted intensities of the femtosecond laser irradiation. We find the irradiated germanium distinguishes from the usual germanium crystal by analyzing their melting and dynamic properties.
Iftimie, R; Schofield, J P; Iftimie, Radu; Salahub, Dennis; Schofield, Jeremy
2003-01-01
In this article, we propose an efficient method for sampling the relevant state space in condensed phase reactions. In the present method, the reaction is described by solving the electronic Schr\\"{o}dinger equation for the solute atoms in the presence of explicit solvent molecules. The sampling algorithm uses a molecular mechanics guiding potential in combination with simulated tempering ideas and allows thorough exploration of the solvent state space in the context of an ab initio calculation even when the dielectric relaxation time of the solvent is long. The method is applied to the study of the double proton transfer reaction that takes place between a molecule of acetic acid and a molecule of methanol in tetrahydrofuran. It is demonstrated that calculations of rates of chemical transformations occurring in solvents of medium polarity can be performed with an increase in the cpu time of factors ranging from 4 to 15 with respect to gas-phase calculations.
Lattice thermal conductivity of UO2 using ab-initio and classical molecular dynamics
International Nuclear Information System (INIS)
We applied the non-equilibrium ab-initio molecular dynamics and predict the lattice thermal conductivity of the pristine uranium dioxide for up to 2000 K. We also use the equilibrium classical molecular dynamics and heat-current autocorrelation decay theory to decompose the lattice thermal conductivity into acoustic and optical components. The predicted optical phonon transport is temperature independent and small, while the acoustic component follows the Slack relation and is in good agreement with the limited single-crystal experimental results. Considering the phonon grain-boundary and pore scatterings, the effective lattice thermal conductivity is reduced, and we show it is in general agreement with the sintered-powder experimental results. The charge and photon thermal conductivities are also addressed, and we find small roles for electron, surface polaron, and photon in the defect-free structures and for temperatures below 1500 K
A set of molecular models based on quantum mechanical ab initio calculations and thermodynamic data
Eckl, Bernhard; Hasse, Hans
2009-01-01
A parameterization strategy for molecular models on the basis of force fields is proposed, which allows a rapid development of models for small molecules by using results from quantum mechanical (QM) ab initio calculations and thermodynamic data. The geometry of the molecular models is specified according to the atom positions determined by QM energy minimization. The electrostatic interactions are modeled by reducing the electron density distribution to point dipoles and point quadrupoles located in the center of mass of the molecules. Dispersive and repulsive interactions are described by Lennard-Jones sites, for which the parameters are iteratively optimized to experimental vapor-liquid equilibrium (VLE) data, i.e. vapor pressure, saturated liquid density, and enthalpy of vaporization of the considered substance. The proposed modeling strategy was applied to a sample set of ten molecules from different substance classes. New molecular models are presented for iso-butane, cyclohexane, formaldehyde, dimethyl...
Relaxation of the excited -(2-hydroxy benzylidene) aniline molecule: An ab initio and TD DFT study
Indian Academy of Sciences (India)
Biswajit Chowdhury; Rina De; Pinaky Sett; Joydeep Chowdhury
2010-11-01
The photophysical behaviour of N-(2-hydroxy benzylidene) aniline or most commonly known as salicylideneaniline (SA) has been investigated using the ab initio and DFT levels of theory. The quantum chemical calculations show that the optimized non planar enol (1) form of the SA molecule is the most stable conformer in the ground state and is marked by the twisting of the phenolic and anilino rings of the molecule. The geometry optimizations and the subsequent frequency calculations of the excited singlet electronic states of the various tautomeric forms of SA molecule were performed with the CIS level of theory. A detail theoretical investigation on the relaxation dynamics of the SA molecule has been presented. Possible explanation on the excitation wavelength dependence of the photochromic yield of the molecule is also reported.
Structure and lattice dynamics of rare-earth ferroborate crystals: Ab initio calculation
Chernyshev, V. A.; Nikiforov, A. E.; Petrov, V. P.; Serdtsev, A. V.; Kashchenko, M. A.; Klimin, S. A.
2016-08-01
The ab initio calculation of the crystal structure and the phonon spectrum of crystals RFe3(BO3)4 ( R = Pr, Nd, Sm) has been performed in the framework of the density functional theory. The ion coordinates in the unit cell, the lattice parameters, the frequencies and the types of fundamental vibrations, and also the intensities of lines in the Raman spectrum and infrared reflection spectra have been found. The elastic constants of the crystals have been calculated. For low-frequency A 2 mode in PrFe3(BO3)4, a "seed" vibration frequency that strongly interacts with the electronic excitation on a praseodymium ion was found. The calculation results satisfactory agree with the experimental data.
Directory of Open Access Journals (Sweden)
Karl-Heinz Böhm
2014-04-01
Full Text Available We present ab-initio calculations of secondary isotope effects on NMR chemical shieldings. The change of the NMR chemical shift of a certain nucleus that is observed if another nucleus is replaced by a different isotope can be calculated by computing vibrational corrections on the NMR parameters using electronic structure methods. We demonstrate that the accuracy of the computational results is sufficient to even distinguish different conformers. For this purpose, benchmark calculations for fluoro(2-2Hethane in gauche and antiperiplanar conformation are carried out at the HF, MP2 and CCSD(T level of theory using basis sets ranging from double- to quadruple-zeta quality. The methodology is applied to the secondary isotope shifts for 2-fluoronorbornane in order to resolve an ambiguity in the literature on the assignment of endo- and exo-2-fluoronorbornanes with deuterium substituents in endo-3 and exo-3 positions, also yielding insight into mechanistic details of the corresponding synthesis.
Ab Initio Investigation of the Structures of Fe-Doped Carbon Clusters
Lovato, Christella; Brownrigg, Clifton; Hira, Ajit
2012-02-01
We continue our interest in the theoretical study of carbon clusters to examine the effects of the doping of small carbon clusters (Cn, n = 2 - 15) with iron atoms. This work applies the hybrid ab initio methods of quantum chemistry to derive the different FemCn (m = 1-3) geometries. Of particular interest are linear, fan, and cyclic geometries. Electronic energies, rotational constants, dipole moments, and vibrational frequencies for these geometries are calculated. Exploration of the singlet, triplet, quintet, and septet potential energy surfaces is performed. The type of bonding in terms of competition between sp^2 and sp^3 hybridization is examined, with a view to addressing the possibility of the stabilization of the doped carbon nano-particles in a diamond type structure. The potential for the existence of new pathways to the fabrication of nanotubes is explored.
Wood, Brandon; Choi, Woon Ih; Schwegler, Eric; Ogitsu, Tadashi
2013-03-01
Photoelectrodes made of III-V semiconductors are known to exhibit very high solar-to-hydrogen conversion efficiency (from solar energy to chemical energy as H2 bond); however, photocorrosion of the electrode in electrolyte solution remains an issue. Based on ab-initio molecular dynamics simulations, we study the structure, stability, and chemical activity of GaP/InP(001) semiconductor electrodes in contact with water. We will show how surface oxygen and hydroxyl change the electronic and chemical properties of water at the interface, leading to the formation of a strong hydrogen-bond network where fast surface hydrogen transport seems to be realized. Implications from our findings will be discussed in detail at the presentation. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52- 07NA27344.
International Nuclear Information System (INIS)
C and N atoms are the most frequent foreign interstitial atoms (FIAs), and often incorporated into the surface layers of steels to enhance their properties by thermochemical treatments. Al, Si, Ti, V, Cr, Mn, Co, Ni, Cu, Nb and Mo are the most common alloying elements in steels, also can be called foreign substitutional atoms (FSAs). The FIA and FSA interactions play an important role in the diffusion of C and N atoms, and the microstructures and mechanical properties of surface modified layers. Ab initio calculations based on the density functional theory are carried out to investigate FIA interactions with FSA in ferromagnetic bcc iron. The FIA–FSA interactions are analyzed systematically from five aspects, including interaction energies, density of states (DOS), bond populations, electron density difference maps and local magnetic moments
Ab initio simulations for the ion-ion structure factor of warm dense aluminum.
Rüter, Hannes R; Redmer, Ronald
2014-04-11
We perform ab initio simulations based on finite-temperature density functional theory in order to determine the static and dynamic ion-ion structure factor in aluminum. We calculate the dynamic structure factor via the intermediate scattering function and extract the dispersion relation for the collective excitations. The results are compared with available experimental x-ray scattering data. Very good agreement is obtained for the liquid metal domain. In addition we perform simulations for warm dense aluminum in order to obtain the ion dynamics in this strongly correlated quantum regime. We determine the sound velocity for both liquid and warm dense aluminum which can be checked experimentally using narrow-bandwidth free electron laser radiation. PMID:24765982
Ab-initio study of magnetism behavior in TiO2 semiconductor with structural defects
Zarhri, Z.; Houmad, M.; Ziat, Y.; El Rhazouani, O.; Slassi, A.; Benyoussef, A.; El Kenz, A.
2016-05-01
Magnetic, electronic and structural properties of titanium dioxide material with different structural defects are studied using the first-principles ab-initio calculations and the Korringa-Kohn-Rostoker method (KKR) combined with the coherent potential approximation (CPA) method in connection with the local density approximation (LDA). We investigated all structural defects in rutile TiO2 such as Titanium interstitial (Tii), Titanium anti-sites (Tio), Titanium vacancies (VTi), Oxygen interstitial (Oi), Oxygen anti-sites (OTi) and oxygen vacancies (Vo). Mechanisms of hybridization and interaction between magnetic atoms are investigated. The transition temperature is computed using the Mean Field Approximation (MFA).Magnetic stability energy of ferromagnetic and disordered local moment states is calculated to determine the most stable state. Titanium anti-sites have a half-metallic aspect. We also studied the change type caused by structural defects in this material.
An ab initio potential energy surface and vibrational energy levels of HXeBr
Institute of Scientific and Technical Information of China (English)
Zheng Guo Huang; En Cui Yang; Dai Qian Xie
2008-01-01
A three-dimensional global potential energy surface for the electronic ground state of HXeBr molecule is constructed from morethan 4200 ab initio points. These points are generated using an internally contracted multi-reference configuration interactionmethod with the Davidson correction (icMRCI + Q) and large basis sets. The stabilities and dissociation barriers are identified fromthe potential energy surfaces. The three-body dissociation channel is found to be the dominate dissociation channel for HXeBr.Based on the obtained potentials, low-lying vibrational energy levels of HXeBr calculated using the Lanczos algorithm is found tobe in good agreement with the available experimental band origins.2008 Zheng Guo Huang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Mundy, Christopher J; Curioni, Alessandro; Goldman, Nir; Will Kuo, I-F; Reed, Evan J; Fried, Laurence E; Ianuzzi, Marcella
2008-05-14
We report herein ab initio molecular dynamics simulations of graphite under shock compression in conjunction with the multiscale shock technique. Our simulations reveal that a novel short-lived layered diamond intermediate is formed within a few hundred of femtoseconds upon shock loading at a shock velocity of 12 kms (longitudinal stress>130 GPa), followed by formation of cubic diamond. The layered diamond state differs from the experimentally observed hexagonal diamond intermediate found at lower pressures and previous hydrostatic calculations in that a rapid buckling of the graphitic planes produces a mixture of hexagonal and cubic diamond (layered diamond). Direct calculation of the x-ray absorption spectra in our simulations reveals that the electronic structure of the final state closely resembles that of compressed cubic diamond.
Ab initio study of transport properties in defected carbon nanotubes: an O(N) approach
Energy Technology Data Exchange (ETDEWEB)
Biel, Blanca; GarcIa-Vidal, F J; Flores, Fernando [Departamento de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Rubio, Angel [European Theoretical Spectroscopy Facility (ETSF), Departamento de Fisica de Materiales, Universidad PaIs Vasco, Edificio Korta, Avenida Tolosa 72, 20018 San Sebastian (Spain)], E-mail: blanca.biel@cea.fr
2008-07-23
A combination of ab initio simulations and linear-scaling Green's functions techniques is used to analyze the transport properties of long (up to 1 {mu}m) carbon nanotubes with realistic disorder. The energetics and the influence of single defects (monovacancies and divacancies) on the electronic and transport properties of single-walled armchair carbon nanotubes are analyzed as a function of the tube diameter by means of the local orbital first-principles Fireball code. Efficient O(N) Green's functions techniques framed within the Landauer-Buettiker formalism allow a statistical study of the nanotube conductance averaged over a large sample of defected tubes and thus extraction of the nanotube localization length. The cases of zero and room temperature are both addressed.
Ab initio theory for current-induced molecular switching: Melamine on Cu(001)
Ohto, Tatsuhiko
2013-05-28
Melamine on Cu(001) is mechanically unstable under the current of a scanning tunneling microscope tip and can switch among configurations. However, these are not equally accessible, and the switching critical current depends on the bias polarity. In order to explain such rich phenomenology, we have developed a scheme to evaluate the evolution of the reaction paths and activation barriers as a function of bias, which is rooted in the nonequilibrium Green\\'s function method implemented within density functional theory. This, combined with the calculation of the inelastic electron tunneling spectroscopy signal, allows us to identify the vibrational modes promoting the observed molecular conformational changes. Finally, once our ab initio results are used within a resonance model, we are able to explain the details of the switching behavior, such as its dependence on the bias polarity, and the noninteger power relation between the reaction rate constants and both the bias voltage and the electric current. © 2013 American Physical Society.
Rosenow, Phil
2016-01-01
The extent of hydrogen coverage of the Si(001)c(4x2) surface in the presence of hydrogen gas has been studied with dispersion corrected density functional theory. Electronic energy contributions are well described using a hybrid functional. The temperature dependence of the coverage in thermodynamic equilibrium was studied computing the phonon spectrum in a supercell approach. As an approximation to these demanding computations, an interpolated phonon approach was found to give comparable accuracy. The simpler ab initio thermodynamic approach is not accurate enough for the system studied, even if corrections by the Einstein model for surface vibrations are considered. The on-set of H2 desorption from the fully hydrogenated surface is predicted to occur at temperatures around 750 K. Strong changes in hydrogen coverage are found between 1000 and 1200 K in good agreement with previous reflectance anisotropy spectroscopy experiments. These findings allow a rational choice for the surface state in the computationa...
Energy Technology Data Exchange (ETDEWEB)
Śmiałek, M. A., E-mail: smialek@pg.gda.pl [Department of Control and Energy Engineering, Faculty of Ocean Engineering and Ship Technology, Gdańsk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdańsk (Poland); Łabuda, M.; Guthmuller, J. [Department of Theoretical Physic and Quantum Information, Faculty of Applied Physics and Mathematics, Gdańsk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdańsk (Poland); Hubin-Franskin, M.-J.; Delwiche, J. [Département de Chimie, Université de Liège, Institut de Chimie-Bât. B6C, B-4000 Liège (Belgium); Duflot, D. [Laboratoire de Physique des Lasers, Atomes et Molécules (PhLAM), UMR CNRS 8523, Université Lille1 Sciences et Technologies, F-59655 Villeneuve d' Ascq Cedex (France); Mason, N. J. [Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom); Hoffmann, S. V.; Jones, N. C. [ISA, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, Building 1520, DK-8000 Aarhus C (Denmark); Limão-Vieira, P., E-mail: plimaovieira@fct.unl.pt [Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal)
2014-09-14
The highest resolution vacuum ultraviolet photoabsorption spectrum of ethyl formate, C{sub 2}H{sub 5}OCHO, yet reported is presented over the wavelength range 115.0–275.5 nm (10.75–4.5 eV) revealing several new spectral features. Valence and Rydberg transitions and their associated vibronic series, observed in the photoabsorption spectrum, have been assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of ethyl formate and are compared with a newly recorded He(I) photoelectron spectrum (from 10.1 to 16.1 eV). New vibrational structure is observed in the first photoelectron band. The photoabsorption cross sections have been used to calculate the photolysis lifetime of ethyl formate in the upper stratosphere (20–50 km)
Electrical resistivity of NaPb compound-forming liquid alloy using ab initio pseudopotentials
Indian Academy of Sciences (India)
Anil Thakur; N S Negi; P K Ahluwalla
2005-08-01
The study of electrical resistivity of compound-forming liquid alloy, NaPb, is presented as a function of concentration. Hard sphere diameters of Na and Pb are obtained through the interionic pair potentials evaluated using Troullier and Martins ab initio pseudopotential, which have been used to calculate the partial structure factors (). Considering the liquid alloy to be a ternary mixture, Ziman formula, modified for complex formation has been used for calculating resistivity of binary liquid alloys. Form factors are calculated using ab initio pseudopotentials. The results suggest that Ziman formalism, when used with ab initio pseudopotentials, are quite successful in explaining the electrical resistivity data of compound-forming binary liquid alloys.
Energy Technology Data Exchange (ETDEWEB)
Sahli, Beat [Integrated Systems Laboratory, ETH Zurich, Gloriastrasse 35, 8092 Zurich (Switzerland)], E-mail: sahli@iis.ee.ethz.ch; Vollenweider, Kilian [Integrated Systems Laboratory, ETH Zurich, Gloriastrasse 35, 8092 Zurich (Switzerland); Zographos, Nikolas; Zechner, Christoph [Synopsys Switzerland LLC, Affolternstrasse 52, 8050 Zurich (Switzerland)
2008-12-05
We present the results of extensive ab initio simulations for phosphorus clusters, arsenic clusters and mixed phosphorus/arsenic clusters in silicon. The specific defects and the parameters that are investigated are selected according to the needs of state-of-the-art diffusion and activation models, taking into account the availability of experimental data, the capabilities of current ab initio methods and the requirements for advanced technology development. The calculated binding energies are used to determine a good starting point for the calibration of a new clustering model implemented in an atomistic process simulator. The defect species V, I, P, PV, PI, As, AsV, AsI and clusters containing up to four dopant atoms and up to one V or I are considered in all relevant charge states. The ab initio results are discussed as well as the challenges arising in the transfer of this information into the process simulation model.
An Efficient Time-Stepping Scheme for Ab Initio Molecular Dynamics Simulations
Tsuchida, Eiji
2016-08-01
In ab initio molecular dynamics simulations of real-world problems, the simple Verlet method is still widely used for integrating the equations of motion, while more efficient algorithms are routinely used in classical molecular dynamics. We show that if the Verlet method is used in conjunction with pre- and postprocessing, the accuracy of the time integration is significantly improved with only a small computational overhead. We also propose several extensions of the algorithm required for use in ab initio molecular dynamics. The validity of the processed Verlet method is demonstrated in several examples including ab initio molecular dynamics simulations of liquid water. The structural properties obtained from the processed Verlet method are found to be sufficiently accurate even for large time steps close to the stability limit. This approach results in a 2× performance gain over the standard Verlet method for a given accuracy. We also show how to generate a canonical ensemble within this approach.
Energy Technology Data Exchange (ETDEWEB)
Keegan, Ronan M. [STFC Rutherford Appleton Laboratory, Didcot OX11 0FA (United Kingdom); Bibby, Jaclyn; Thomas, Jens [University of Liverpool, Liverpool L69 7ZB (United Kingdom); Xu, Dong [Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037 (United States); Zhang, Yang [University of Michigan, Ann Arbor, MI 48109 (United States); Mayans, Olga [University of Liverpool, Liverpool L69 7ZB (United Kingdom); Winn, Martyn D. [Science and Technology Facilities Council Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Rigden, Daniel J., E-mail: drigden@liv.ac.uk [University of Liverpool, Liverpool L69 7ZB (United Kingdom); STFC Rutherford Appleton Laboratory, Didcot OX11 0FA (United Kingdom)
2015-02-01
Two ab initio modelling programs solve complementary sets of targets, enhancing the success of AMPLE with small proteins. AMPLE clusters and truncates ab initio protein structure predictions, producing search models for molecular replacement. Here, an interesting degree of complementarity is shown between targets solved using the different ab initio modelling programs QUARK and ROSETTA. Search models derived from either program collectively solve almost all of the all-helical targets in the test set. Initial solutions produced by Phaser after only 5 min perform surprisingly well, improving the prospects for in situ structure solution by AMPLE during synchrotron visits. Taken together, the results show the potential for AMPLE to run more quickly and successfully solve more targets than previously suspected.
Chan, Garnet Kin-Lic; Nakatani, Naoki; Li, Zhendong; White, Steven R
2016-01-01
Current descriptions of the ab initio DMRG algorithm use two superficially different languages: an older language of the renormalization group and renormalized operators, and a more recent language of matrix product states and matrix product operators. The same algorithm can appear dramatically different when written in the two different vocabularies. In this work, we carefully describe the translation between the two languages in several contexts. First, we describe how to efficiently implement the ab-initio DMRG sweep using a matrix product operator based code, and the equivalence to the original renormalized operator implementation. Next we describe how to implement the general matrix product operator/matrix product state algebra within a pure renormalized operator-based DMRG code. Finally, we discuss two improvements of the ab initio DMRG sweep algorithm motivated by matrix product operator language: Hamiltonian compression, and a sum over operators representation that allows for perfect computational par...
ab initio Studies on Molecular Conductor (BEDSe-TTF)2[Fe(CN)5NO
Institute of Scientific and Technical Information of China (English)
YAO Kai-Lun; TU Hai-Bo; WANG Wei-Zhong
2001-01-01
In this paper the ab initio study using pseudopotential plane wave method with the local spin density functional approximation is presented for the molecular conductor (BEDSe-TTF)2[Fe(CN)5NO]. The mean electronic density distributions are obtained, and we find that the extended π orbital of the selenium does not affect the properties of material as assumed in other papers and the "side-by-side" type S...S interaction is the primary interaction between donors. From band structure calculations we analyze the influence of the NO groups on the electronic structure and magnetic properties of molecule. It is shown that the itinerant electrons important to electronic properties in these types of hybrids are delocalized electrons contributed by NO groups, instead of by the 3d electrons of Fe. Additionally, we have found that the localized magnetic moment is also contributed by the NO groups in this molecular conductor. From total energy calculations the molecular structure with the lowest energy is found due to the interaction between split spins, and the particular positions of the NO groups are obtained.
Ab initio calculations versus polarized neutron diffraction for the spin density of free radicals
International Nuclear Information System (INIS)
The determination of the magnetization distribution using polarized neutron diffraction has played a key role during the last twenty years in the field of molecular magnetism. This distribution can also be obtained by first principle ab initio calculations. Such calculations always rely on approximations and the question that arises is to know whether the obtained results are reliable enough to represent accurately the properties of these molecules. The comparison between polarized neutron experimental results and ab initio calculations has turned to provide stringent tests for these methods. In the resent article a comparison between experimental and theoretical results is made and is illustrated by examples based on magnetic free radicals. (author)
Sakane, Shinichi; Yezdimer, Eric M.; Liu, Wenbin; Barriocanal, Jose A.; Doren, Douglas J.; Wood, Robert H.
2000-08-01
The ab initio/classical free energy perturbation (ABC-FEP) method proposed previously by Wood et al. [J. Chem. Phys. 110, 1329 (1999)] uses classical simulations to calculate solvation free energies within an empirical potential model, then applies free energy perturbation theory to determine the effect of changing the empirical solute-solvent interactions to corresponding interactions calculated from ab initio methods. This approach allows accurate calculation of solvation free energies using an atomistic description of the solvent and solute, with interactions calculated from first principles. Results can be obtained at a feasible computational cost without making use of approximations such as a continuum solvent or an empirical cavity formation energy. As such, the method can be used far from ambient conditions, where the empirical parameters needed for approximate theories of solvation may not be available. The sources of error in the ABC-FEP method are the approximations in the ab initio method, the finite sample of configurations, and the classical solvent model. This article explores the accuracy of various approximations used in the ABC-FEP method by comparing to the experimentally well-known free energy of hydration of water at two state points (ambient conditions, and 973.15 K and 600 kg/m3). The TIP4P-FQ model [J. Chem. Phys. 101, 6141 (1994)] is found to be a reliable solvent model for use with this method, even at supercritical conditions. Results depend strongly on the ab initio method used: a gradient-corrected density functional theory is not adequate, but a localized MP2 method yields excellent agreement with experiment. Computational costs are reduced by using a cluster approximation, in which ab initio pair interaction energies are calculated between the solute and up to 60 solvent molecules, while multi-body interactions are calculated with only a small cluster (5 to 12 solvent molecules). Sampling errors for the ab initio contribution to
Keegan, Ronan M; Bibby, Jaclyn; Thomas, Jens; Xu, Dong; Zhang, Yang; Mayans, Olga; Winn, Martyn D; Rigden, Daniel J
2015-02-01
AMPLE clusters and truncates ab initio protein structure predictions, producing search models for molecular replacement. Here, an interesting degree of complementarity is shown between targets solved using the different ab initio modelling programs QUARK and ROSETTA. Search models derived from either program collectively solve almost all of the all-helical targets in the test set. Initial solutions produced by Phaser after only 5 min perform surprisingly well, improving the prospects for in situ structure solution by AMPLE during synchrotron visits. Taken together, the results show the potential for AMPLE to run more quickly and successfully solve more targets than previously suspected.
Ab Initio Calculations of Deuterium Isotope Effects on Chemical Shifts of Salt-Bridged Lysines
DEFF Research Database (Denmark)
Ullah, Saif; Ishimoto, Takayoshi; Williamson, Mike P.;
2011-01-01
Deuterium isotope effects measure the change in chemical shift on substitution of a proton by deuterium. They have been calculated by direct treatment of the H/D nuclear quantum effect using a multicomponent ab initio molecular orbital method based on a non-Born−Oppenheimer approximation. This me......Deuterium isotope effects measure the change in chemical shift on substitution of a proton by deuterium. They have been calculated by direct treatment of the H/D nuclear quantum effect using a multicomponent ab initio molecular orbital method based on a non-Born−Oppenheimer approximation...
Energy Technology Data Exchange (ETDEWEB)
Willaime, F. [Division de l' energie nucleaire, CEA Centre de Saclay, 91191 Gif-sur-Yvette (France); Deutsch, T.; Pochet, P. [INAC, Direction des sciences de la matiere, CEA Centre de Grenoble, 38054 Grenoble Cedex 9 (France)
2010-07-01
Ab-initio calculation methods, for the purposes of computing electronic structures, have made it possible, since the early nineties, to simulate the properties of perfect crystalline materials (materials free of any defect). By improving such methods, and with the increasing power of supercomputers, it has now become feasible to simulate the properties of elementary defects, which may seldom be accessed directly through experiments. This has opened up a vast, fruitful field of multi-scale simulations, where such data yield the basis for realistic simulations of the kinetics of materials evolution. The kinetic Monte-Carlo method thus provides the means to model phenomena acting at the scale of a second, or even of a year. In the issue of self-diffusion in silicon, multi-scale simulation has been successful in predicting an asymmetrical behaviour: a speeding up of vacancy diffusion under compression and a tailing off under tension, and conversely, a speeding up of interstitial diffusion under tension and a falling off under compression. Multi-scale modeling has also been successful in simulating irradiation defects in iron. (A.C.)
Energy Technology Data Exchange (ETDEWEB)
Ganster, P
2004-10-15
A calcium aluminosilicate glass of molar composition 67 % SiO{sub 2} - 12 % Al{sub 2}O{sub 3} - 21 % CaO was modelled by classical and ab initio molecular dynamics. The size effect study in classical MD shows that the systems of 100 atoms are more ordered than the larger ones. These effects are mainly due to the 3-body terms in the empirical potentials. Nevertheless, these effects are small and the structures generated are in agreement with experimental data. In such kind of glass, we denote an aluminium avoidance and an excess of non bridging oxygens which can be compensated by tri coordinated oxygens. When the dynamics of systems of 100 and 200 atoms is followed by ab initio MD, some local arrangements occurs (bond length, angular distributions). Thus, more realistic vibrational properties are obtained in ab initio MD. The modelling of thin films shows that aluminium atoms extend to the most external part of the surface and they are all tri-coordinated. Calcium atoms are set in the sub layer part of the surface and they produce a depolymerization of the network. In classical MD, tri-coordinated aluminium atoms produce an important electric field above the surface. With non bridging oxygens, they constitute attractive sites for single water molecules. (author)
High pressure behaviour of uranium dicarbide (UC2): Ab-initio study
Sahoo, B. D.; Mukherjee, D.; Joshi, K. D.; Kaushik, T. C.
2016-08-01
The structural stability of uranium dicarbide has been examined under hydrostatic compression employing evolutionary structure search algorithm implemented in the universal structure predictor: evolutionary Xtallography (USPEX) code in conjunction with ab-initio electronic band structure calculation method. The ab-initio total energy calculations involved for this purpose have been carried out within both generalized gradient approximations (GGA) and GGA + U approximations. Our calculations under GGA approximation predict the high pressure structural sequence of tetragonal → monoclinic → orthorhombic for this material with transition pressures of ˜8 GPa and 42 GPa, respectively. The same transition sequence is predicted by calculations within GGA + U also with transition pressures placed at ˜24 GPa and ˜50 GPa, respectively. Further, on the basis of comparison of zero pressure equilibrium volume and equation of state with available experimental data, we find that GGA + U approximation with U = 2.5 eV describes this material better than the simple GGA approximation. The theoretically predicted high pressure structural phase transitions are in disagreement with the only high experimental study by Dancausse et al. [J. Alloys. Compd. 191, 309 (1993)] on this compound which reports a tetragonal to hexagonal phase transition at a pressure of ˜17.6 GPa. Interestingly, during lowest enthalpy structure search using USPEX, we do not see any hexagonal phase to be closer to the predicted monoclinic phase even within 0.2 eV/f. unit. More experiments with varying carbon contents in UC2 sample are required to resolve this discrepancy. The existence of these high pressure phases predicted by static lattice calculations has been further substantiated by analyzing the elastic and lattice dynamic stability of these structures in the pressure regimes of their structural stability. Additionally, various thermo-physical quantities such as equilibrium volume, bulk modulus, Debye
Ab initio simulations of doped single-walled carbon nanotube sensors
International Nuclear Information System (INIS)
Graphical abstract: Ab initio calculations used to study O-doped and N-doped SWNT within the framework of the DFT. We introduced new type of gas sensor that can detect the presence of H2, Cl2, NO, and CO molecules. Band-gap narrowing occurs when the nanotube is doped with oxygen or nitrogen atoms. We proposed a new methodology of designing reliable, sensitive, and selective nanotube sensors. Highlights: ►Ab initio calculations used to study O-doped and N-doped SWNT within the framework of the DFT. ► We introduced new type of gas sensor that can detect the presence of H2, Cl2, NO, and CO molecules. ►Band-gap narrowing occurs when the nanotube is doped with oxygen or nitrogen atoms. ► We proposed a new methodology of designing reliable, sensitive, and selective nanotube sensors. - Abstract: The interactions between oxygen and nitrogen atoms with single-walled carbon nanotubes were investigated for nanotubes with two different geometrical configurations using first-principle calculations within the framework of the density functional theory. We introduced a new type of toxic gas sensor that can detect the presence of H2, Cl2, CO, and NO molecules. We also demonstrated that the sensitivity of this device can be controlled by the concentration of the dopants on the surface of the nanotube. In addition, the transport properties of the doped nanotube were studied for different concentrations of oxygen or nitrogen atoms that were randomly distributed on the surface of the single-walled carbon nanotube. We observed that small amounts of dopants can modify the electronic and transport properties of the nanotube and can lend metallic properties to the nanotube. Band-gap narrowing occurs when the nanotube is doped with either oxygen or nitrogen atoms.
Study on the effects of fluorine and oxygen deficiency on YBa2Cu3O7 by ab initio method
Institute of Scientific and Technical Information of China (English)
刘洪霖; 曹晓卫; 瞿丽曼; 陈念贻
1997-01-01
The calculations of clusters modeling the fluorine-doping and oxygen deficiency of YBa2Cu3O2,have been performed by the method of all-electron ab initio Hartree-Fock with self-consistent crystal field Results show that in CuO planes electric charge significantly increases,the chemical valence of Cu decreases and the covalent bonding of Cu-O greatly weakens owing to oxygen deficiency,while the effect of F restores the local electronic structure of YBa2Cu3O7 The reported opinion that F occupied the oxygen vacancy in Cu-O chains seems disputable according to the calculated bonding characteristics.
Switchable magnetic moment in cobalt-doped graphene bilayer on Cu(111): An ab initio study
Souza, Everson S.; Scopel, Wanderlã L.; Miwa, R. H.
2016-06-01
In this work, we have performed an ab initio theoretical investigation of substitutional cobalt atoms in the graphene bilayer supported on the Cu(111) surface (Co/GBL/Cu). Initially, we examined the separated systems, namely, graphene bilayer adsorbed on Cu(111) (GBL/Cu) and a free standing Co-doped GBL (Co/GBL). In the former system, the GBL becomes n -type doped, where we map the net electronic charge density distribution along the GBL-Cu(111) interface. The substitutional Co atom in Co/GBL lies between the graphene layers, and present a net magnetic moment mostly due to the unpaired Co-3 dz2 electrons. In Co/GBL/Cu, we found that the Cu(111) substrate rules (i) the energetic stability, and (ii) the magnetic properties of substitutional Co atoms in the graphene bilayer. In (i), the substitutional Co atom becomes energetically more stable lying on the GBL surface, and in (ii), the magnetic moment of Co/GBL has been quenched due to the Cu(111) → Co/GBL electronic charge transfer. We verify that such a charge transfer can be tuned upon the application of an external electric field, and thus mediated by a suitable change on the electronic occupation of the Co-dz2 orbitals, we found a way to switch-on and -off the magnetization of the Co-doped GBL adsorbed on the Cu(111) surface.
Ab initio random structure search for 13-atom clusters of fcc elements.
Chou, J P; Hsing, C R; Wei, C M; Cheng, C; Chang, C M
2013-03-27
The 13-atom metal clusters of fcc elements (Al, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au) were studied by density functional theory calculations. The global minima were searched for by the ab initio random structure searching method. In addition to some new lowest-energy structures for Pd13 and Au13, we found that the effective coordination numbers of the lowest-energy clusters would increase with the ratio of the dimer-to-bulk bond length. This correlation, together with the electronic structures of the lowest-energy clusters, divides the 13-atom clusters of these fcc elements into two groups (except for Au13, which prefers a two-dimensional structure due to the relativistic effect). Compact-like clusters that are composed exclusively of triangular motifs are preferred for elements without d-electrons (Al) or with (nearly) filled d-band electrons (Ni, Pd, Cu, Ag). Non-compact clusters composed mainly of square motifs connected by some triangular motifs (Rh, Ir, Pt) are favored for elements with unfilled d-band electrons.
Energy Technology Data Exchange (ETDEWEB)
Alipour, Mojtaba, E-mail: malipour@shirazu.ac.ir [Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of); Mohajeri, Afshan, E-mail: amohajeri@shirazu.ac.ir [Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of)
2011-08-25
Graphical abstract: The electronic properties such as the static dipole polarizability, anisotropy of the polarizability, and dipole moment of yttrium bromide, YBr (X{sup 1}{Sigma}) have been theoretically studied. Highlights: {yields} Conventional ab initio and density functional theory methods were employed to study linear optical properties of YBr molecule. {yields} Properties derivatives and their level of theory dependence were studied. {yields} Electron correlation effects and rovibrational corrections have also been discussed. - Abstract: We have employed conventional ab initio and density functional theory methods to study the electronic properties such as the mean static dipole polarizability, {alpha}-bar, anisotropy of the polarizability, {Delta}{alpha}, and dipole moment, {mu}, of yttrium bromide. The bond length dependence of properties is determined at different levels of theory and appropriate expansions around experimental internuclear distance have been presented. Moreover, the first and second geometrical derivatives for each property are quantified and their level of theory dependence has been analyzed. To study the effect of molecular rotation and vibration on the electronic properties, the rovibrational corrections have also been carried out. It is found that these corrections are less pronounced for considered properties of YBr. In all calculations, the electron correlation effects have been considered and discussed. The obtained results show that the electron correlation is more significant in the calculation of the mean and the anisotropy of dipole polarizability.
Ab-initio modeling of an anion $C_{60}^-$ pseudopotential for fullerene-based compounds
Vrubel, I I; Ivanov, V K
2015-01-01
A pseudopotential of $C_{60}^-$ has been constructed from ab-initio quantum-mechanical calculations. Since the obtained pseudopotential can be easily fitted by rather simple analytical approximation it can be effectively used both in classical and quantum molecular dynamics of fullerene-based compounds.
Mechanical properties of carbynes investigated by ab initio total-energy calculations
DEFF Research Database (Denmark)
Castelli, Ivano E.; Salvestrini, Paolo; Manini, Nicola
2012-01-01
As sp carbon chains (carbynes) are relatively rigid molecular objects, can we exploit them as construction elements in nanomechanics? To answer this question, we investigate their remarkable mechanical properties by ab initio total-energy simulations. In particular, we evaluate their linear respo...
Chan, Garnet Kin-Lic; Keselman, Anna; Nakatani, Naoki; Li, Zhendong; White, Steven R
2016-07-01
Current descriptions of the ab initio density matrix renormalization group (DMRG) algorithm use two superficially different languages: an older language of the renormalization group and renormalized operators, and a more recent language of matrix product states and matrix product operators. The same algorithm can appear dramatically different when written in the two different vocabularies. In this work, we carefully describe the translation between the two languages in several contexts. First, we describe how to efficiently implement the ab initio DMRG sweep using a matrix product operator based code, and the equivalence to the original renormalized operator implementation. Next we describe how to implement the general matrix product operator/matrix product state algebra within a pure renormalized operator-based DMRG code. Finally, we discuss two improvements of the ab initio DMRG sweep algorithm motivated by matrix product operator language: Hamiltonian compression, and a sum over operators representation that allows for perfect computational parallelism. The connections and correspondences described here serve to link the future developments with the past and are important in the efficient implementation of continuing advances in ab initio DMRG and related algorithms. PMID:27394094
Ab Initio Investigations of the C2F4S Isomers and of Their Interconversions
DEFF Research Database (Denmark)
Shim, Irene; Vallano-Lorenzo, Sandra; Lisbona-Martin, Pilar;
2003-01-01
The transition states and the activation energies for the unobserved isomerization reactions between the three possible C2F4S isomers with divalent sulfur, trifluorothioacetyl fluoride 1, tetrafluorothiirane 2, and trifluoroethenesulfenyl fluoride 3, have been determined by ab initio Hartree-Fock...
Ab initio prediction of vacancy properties in concentrated alloys: The case of fcc Cu-Ni
Zhang, X.; Sluiter, M.H.F.
2015-01-01
Vacancy properties in concentrated alloys continue to be of great interest because nowadays ab initio supercell simulations reach a scale where even defect properties in disordered alloys appear to be within reach. We show that vacancy properties cannot generally be extracted from supercell total en
New approaches for molecular conformer force field analysis in combination with ab initio results
Kuramshina, G. M.; Pentin, Yu. A.; Yagola, A. G.
1999-10-01
Ab initio and DFT results on harmonic force constants for trans- and gauche-conformers of CH 3CH 2CH 2Cl, CF 3CH 2CH 2Cl and CCl 3CH 2CH 2Cl are used for formulating constraints in molecular force field models described compounds with hindered internal rotation around the C-C bond.
Ab initio I-V characteristics of short C-20 chains
DEFF Research Database (Denmark)
Roland, C.; Larade, B.; Taylor, Jeremy Philip;
2002-01-01
We have calculated the I-V characteristics of short chains of C-20 molecular cages between Al and Au leads with an ab initio formalism. The results indicate that a linear chain of such molecules acts primarily as metallic nanowires. The transmission, however, depends sensitively both on the...
Chan, Garnet Kin-Lic; Keselman, Anna; Nakatani, Naoki; Li, Zhendong; White, Steven R.
2016-07-01
Current descriptions of the ab initio density matrix renormalization group (DMRG) algorithm use two superficially different languages: an older language of the renormalization group and renormalized operators, and a more recent language of matrix product states and matrix product operators. The same algorithm can appear dramatically different when written in the two different vocabularies. In this work, we carefully describe the translation between the two languages in several contexts. First, we describe how to efficiently implement the ab initio DMRG sweep using a matrix product operator based code, and the equivalence to the original renormalized operator implementation. Next we describe how to implement the general matrix product operator/matrix product state algebra within a pure renormalized operator-based DMRG code. Finally, we discuss two improvements of the ab initio DMRG sweep algorithm motivated by matrix product operator language: Hamiltonian compression, and a sum over operators representation that allows for perfect computational parallelism. The connections and correspondences described here serve to link the future developments with the past and are important in the efficient implementation of continuing advances in ab initio DMRG and related algorithms.
Stabilization of Ab Initio Molecular Dynamics Simulations at Large Time Steps
Tsuchida, Eiji
2014-01-01
The Verlet method is still widely used to integrate the equations of motion in ab initio molecular dynamics simulations. We show that the stability limit of the Verlet method may be significantly increased by setting an upper limit on the kinetic energy of each atom with only a small loss in accuracy. The validity of this approach is demonstrated for molten lithium fluoride.
Computer simulation of acetonitrile and methanol with ab initio-based pair potentials
Hloucha, M.; Sum, A. K.; Sandler, S. I.
2000-10-01
This study address the adequacy of ab initio pair interaction energy potentials for the prediction of macroscopic properties. Recently, Bukowski et al. [J. Phys. Chem. A 103, 7322 (1999)] performed a comprehensive study of the potential energy surfaces for several pairs of molecules using symmetry-adapted perturbation theory. These ab initio energies were then fit to an appropriate site-site potential form. In an attempt to bridge the gap between ab initio interaction energy information and macroscopic properties prediction, we performed Gibbs ensemble Monte Carlo (GEMC) simulations using their developed pair potentials for acetonitrile and methanol. The simulations results show that the phase behavior of acetonitrile is well described by just the pair interaction potential. For methanol, on the other hand, pair interactions are insufficient to properly predict its vapor-liquid phase behavior, and its saturated liquid density. We also explored simplified forms for representing the ab initio interaction energies by refitting a selected range of the data to a site-site Lennard-Jones and to a modified Buckingham (exponential-6) potentials plus Coulombic interactions. These were also used in GEMC simulations in order to evaluate the quality and computational efficiency of these different potential forms. It was found that the phase behavior prediction for acetonitrile and methanol are highly dependent on the details of the interaction potentials developed.
New ab initio based pair potential for accurate simulation of phase transitions in ZnO
Wang, Shuaiwei; Fan, Zhaochuan; Koster, Rik S.; Fang, Changming; Van Huis, Marijn A.; Yalcin, Anil O.; Tichelaar, Frans D.; Zandbergen, Henny W.; Vlugt, Thijs J H
2014-01-01
A set of interatomic pair potentials is developed for ZnO based on the partially charged rigid ion model (PCRIM). The derivation of the potentials combines lattice inversion, empirical fitting, and ab initio energy surface fitting. We show that, despite the low number of parameters in this model (8)
Ab initio Defect Energetics in LaBO3 Perovskite Solid Oxide Fuel Cell Materials
DEFF Research Database (Denmark)
Lee, Yueh-Lin; Morgan, Dane; Kleis, Jesper;
2009-01-01
Perovskite materials of the form ABO3 are a promising family of compounds for use in solid oxide fuel cell (SOFC) cathodes. Study of the physics of these compounds under SOFC conditions with ab initio methods is particularly challenging due to high temperatures, exchange of oxygen with O2 gas, and...
Raman and ab initio studies of simple and binary 1-alkyl-3-methylimidazolium ionic liquids
DEFF Research Database (Denmark)
Berg, R.W.; Deetlefs, M.; Seddon, K.R.;
2005-01-01
Raman spectra of the ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([C(4)mim][PF6]), 1-hexyl-3-methylimidazolium chloride ([C(6)mim]Cl), and 1-hexyl-3-methylimidazolium hexafluorophosphate ([C(6)mim][PF6]), and binary mixtures thereof, have been assigned using ab initio MP2...
Ab initio charge-carrier mobility model for amorphous molecular semiconductors
Massé, Andrea; Friederich, Pascal; Symalla, Franz; Liu, Feilong; Nitsche, Robert; Coehoorn, Reinder; Wenzel, Wolfgang; Bobbert, Peter A.
2016-05-01
Accurate charge-carrier mobility models of amorphous organic molecular semiconductors are essential to describe the electrical properties of devices based on these materials. The disordered nature of these semiconductors leads to percolative charge transport with a large characteristic length scale, posing a challenge to the development of such models from ab initio simulations. Here, we develop an ab initio mobility model using a four-step procedure. First, the amorphous morphology together with its energy disorder and intermolecular charge-transfer integrals are obtained from ab initio simulations in a small box. Next, the ab initio information is used to set up a stochastic model for the morphology and transfer integrals. This stochastic model is then employed to generate a large simulation box with modeled morphology and transfer integrals, which can fully capture the percolative charge transport. Finally, the charge-carrier mobility in this simulation box is calculated by solving a master equation, yielding a mobility function depending on temperature, carrier concentration, and electric field. We demonstrate the procedure for hole transport in two important molecular semiconductors, α -NPD and TCTA. In contrast to a previous study, we conclude that spatial correlations in the energy disorder are unimportant for α -NPD. We apply our mobility model to two types of hole-only α -NPD devices and find that the experimental temperature-dependent current density-voltage characteristics of all devices can be well described by only slightly decreasing the simulated energy disorder strength.
DEFF Research Database (Denmark)
Wolf, T. J. A.; Kuhlman, Thomas Scheby; Schalk, O.;
2014-01-01
comparing time-resolved photoelectron spectroscopy (TRPES) with ab initio multiple spawning (AIMS) simulations on the MS-MR-CASPT2 level of theory. We disentangle the relationship between two phenomena that dominate the immediate molecular response upon light absorption: a spectrally dependent delay of the...
Ab initio study of energy-level alignments in polymer-dye blends
Pasveer, W.F.; Bobbert, P.A.; Michels, M.A.J.; Langeveld-Voss, B.M.W.; Schoo, H.F.M.; Bastiaansen, J.J.A.M.
2003-01-01
Polymers with a small amount of dye blended in offer an attractive possibility to change the color of the emitted light by changing the dye. We present ab initio calculations within density-functional theory of the HOMO/ LUMO energies for dipyrrolomethane dyes, polyphenylenevinylene and polyfluorene
Chan, Garnet Kin-Lic; Keselman, Anna; Nakatani, Naoki; Li, Zhendong; White, Steven R
2016-07-01
Current descriptions of the ab initio density matrix renormalization group (DMRG) algorithm use two superficially different languages: an older language of the renormalization group and renormalized operators, and a more recent language of matrix product states and matrix product operators. The same algorithm can appear dramatically different when written in the two different vocabularies. In this work, we carefully describe the translation between the two languages in several contexts. First, we describe how to efficiently implement the ab initio DMRG sweep using a matrix product operator based code, and the equivalence to the original renormalized operator implementation. Next we describe how to implement the general matrix product operator/matrix product state algebra within a pure renormalized operator-based DMRG code. Finally, we discuss two improvements of the ab initio DMRG sweep algorithm motivated by matrix product operator language: Hamiltonian compression, and a sum over operators representation that allows for perfect computational parallelism. The connections and correspondences described here serve to link the future developments with the past and are important in the efficient implementation of continuing advances in ab initio DMRG and related algorithms.
Study on the surface hydroxyl group on solid breeding materials by ab-initio calculations
Energy Technology Data Exchange (ETDEWEB)
Tanaka, Satoru; Taniguchi, Masaki [Tokyo Univ. (Japan). Faculty of Engineering
1996-10-01
The nature of -OH on the surface of Li{sub 2}O was analyzed with the ab-initio quantum chemical calculation technique. Calculation results showed that the stretching vibration of O-H is affected by the chemical species around the -OH. (author)
Periodic Trends in Lanthanide Compounds through the Eyes of Multireference ab Initio Theory.
Aravena, Daniel; Atanasov, Mihail; Neese, Frank
2016-05-01
Regularities among electronic configurations for common oxidation states in lanthanide complexes and the low involvement of f orbitals in bonding result in the appearance of several periodic trends along the lanthanide series. These trends can be observed on relatively different properties, such as bonding distances or ionization potentials. Well-known concepts like the lanthanide contraction, the double-double (tetrad) effect, and the similar chemistry along the lanthanide series stem from these regularities. Periodic trends on structural and spectroscopic properties are examined through complete active space self-consistent field (CASSCF) followed by second-order N-electron valence perturbation theory (NEVPT2) including both scalar relativistic and spin-orbit coupling effects. Energies and wave functions from electronic structure calculations are further analyzed in terms of ab initio ligand field theory (AILFT), which allows one to rigorously extract angular overlap model ligand field, Racah, and spin-orbit coupling parameters directly from high-level ab initio calculations. We investigated the elpasolite Cs2NaLn(III)Cl6 (Ln(III) = Ce-Nd, Sm-Eu, Tb-Yb) crystals because these compounds have been synthesized for most Ln(III) ions. Cs2NaLn(III)Cl6 elpasolites have been also thoroughly characterized with respect to their spectroscopic properties, providing an exceptionally vast and systematic experimental database allowing one to analyze the periodic trends across the lanthanide series. Particular attention was devoted to the apparent discrepancy in metal-ligand covalency trends between theory and spectroscopy described in the literature. Consistent with earlier studies, natural population analysis indicates an increase in covalency along the series, while a decrease in both the nephelauxetic (Racah) and relativistic nephelauxetic (spin-orbit coupling) reduction with increasing atomic number is calculated. These apparently conflicting results are discussed on the
Timko, Jeff; Kuyucak, Serdar
2012-11-01
Polarization is an important component of molecular interactions and is expected to play a particularly significant role in inhomogeneous environments such as pores and interfaces. Here we investigate the effects of polarization in the gramicidin A ion channel by performing quantum mechanics/molecular mechanics molecular dynamics (MD) simulations and comparing the results with those obtained from classical MD simulations with non-polarizable force fields. We consider the dipole moments of backbone carbonyl groups and channel water molecules as well as a number of structural quantities of interest. The ab initio results show that the dipole moments of the carbonyl groups and water molecules are highly sensitive to the hydrogen bonds (H-bonds) they participate in. In the absence of a K+ ion, water molecules in the channel are quite mobile, making the H-bond network highly dynamic. A central K+ ion acts as an anchor for the channel waters, stabilizing the H-bond network and thereby increasing their average dipole moments. In contrast, the K+ ion has little effect on the dipole moments of the neighboring carbonyl groups. The weakness of the ion-peptide interactions helps to explain the near diffusion-rate conductance of K+ ions through the channel. We also address the sampling issue in relatively short ab initio MD simulations. Results obtained from a continuous 20 ps ab initio MD simulation are compared with those generated by sampling ten windows from a much longer classical MD simulation and running each window for 2 ps with ab initio MD. Both methods yield similar results for a number of quantities of interest, indicating that fluctuations are fast enough to justify the short ab initio MD simulations.
Timko, Jeff; Kuyucak, Serdar
2012-11-28
Polarization is an important component of molecular interactions and is expected to play a particularly significant role in inhomogeneous environments such as pores and interfaces. Here we investigate the effects of polarization in the gramicidin A ion channel by performing quantum mechanics/molecular mechanics molecular dynamics (MD) simulations and comparing the results with those obtained from classical MD simulations with non-polarizable force fields. We consider the dipole moments of backbone carbonyl groups and channel water molecules as well as a number of structural quantities of interest. The ab initio results show that the dipole moments of the carbonyl groups and water molecules are highly sensitive to the hydrogen bonds (H-bonds) they participate in. In the absence of a K(+) ion, water molecules in the channel are quite mobile, making the H-bond network highly dynamic. A central K(+) ion acts as an anchor for the channel waters, stabilizing the H-bond network and thereby increasing their average dipole moments. In contrast, the K(+) ion has little effect on the dipole moments of the neighboring carbonyl groups. The weakness of the ion-peptide interactions helps to explain the near diffusion-rate conductance of K(+) ions through the channel. We also address the sampling issue in relatively short ab initio MD simulations. Results obtained from a continuous 20 ps ab initio MD simulation are compared with those generated by sampling ten windows from a much longer classical MD simulation and running each window for 2 ps with ab initio MD. Both methods yield similar results for a number of quantities of interest, indicating that fluctuations are fast enough to justify the short ab initio MD simulations.
Ab Initio Enhanced calphad Modeling of Actinide-Rich Nuclear Fuels
Energy Technology Data Exchange (ETDEWEB)
Morgan, Dane [Univ. of Wisconsin, Madison, WI (United States); Yang, Yong Austin [Univ. of Wisconsin, Madison, WI (United States)
2013-10-28
The process of fuel recycling is central to the Advanced Fuel Cycle Initiative (AFCI), where plutonium and the minor actinides (MA) Am, Np, and Cm are extracted from spent fuel and fabricated into new fuel for a fast reactor. Metallic alloys of U-Pu-Zr-MA are leading candidates for fast reactor fuels and are the current basis for fast spectrum metal fuels in a fully recycled closed fuel cycle. Safe and optimal use of these fuels will require knowledge of their multicomponent phase stability and thermodynamics (Gibbs free energies). In additional to their use as nuclear fuels, U-Pu-Zr-MA contain elements and alloy phases that pose fundamental questions about electronic structure and energetics at the forefront of modern many-body electron theory. This project will validate state-of-the-art electronic structure approaches for these alloys and use the resulting energetics to model U-Pu-Zr-MA phase stability. In order to keep the work scope practical, researchers will focus on only U-Pu-Zr-{Np,Am}, leaving Cm for later study. The overall objectives of this project are to: Provide a thermodynamic model for U-Pu-Zr-MA for improving and controlling reactor fuels; and, Develop and validate an ab initio approach for predicting actinide alloy energetics for thermodynamic modeling.
Jackels, C. F.; Phillips, D. H.
1986-01-01
Ab initio quantum chemical techniques have been used to investigate covalently-bonded and hydrogen-bonded species that may be important intermediates in the reaction of hydroxyl and hydroperoxyl radicals. Stable structures of both types were identified. Basic sets of polarized double-zeta quality and large scale configuration interaction wave functions have been utilized. Based upon electronic energies, the covalently-bonded HOOOH species is found to be 26.4 kcal/mol more stable than the OH and HO2 radicals. Similarly, the hydrogen-bonded HO-HO2 species is found to have an electronic energy 4.7 kcal/mol below that of the component radicals, after correction is made for the basis set superposition error. The hydrogen-bonded form is found to be planar, to possess one relatively 'normal' hydrogen bond, and to have lowest energy 3A-prime and 1A-prime states that are essentially degenerate. The 1A-double prime and 3A-double prime excited states produced by rotation of the unpaired OH electron into the molecular plane are found to be very slightly bound.
Acidity of HOCH, HSCN, HNCO, HNCS: a treatment from the viewpoint of ab initio approach
Directory of Open Access Journals (Sweden)
ALEXEI N. PANKRATOV
2005-10-01
Full Text Available The electronic structures of the molecules HOCN, HSCN, HNCO, HNCS and the anions [OCN]-, [SCN]- have been investigated ab initio at the RHF/6-31G(d, RHF/6-31G(d,p, MP2/6-31G(d//RHF/6-31G(d and MP2/6-31G(d,p//RHF/6-31G(d,p theory levels. The thermodynamic stability of the HNCO and HNCS molecules was shown to be higher than that of the HOCH and HSCN molecules, respectively.The following series of the alteration of the protolytes strength HSCN > HOCH, HNCS > HNCO, HOCN > HNCO, HSCN > HNCS was substantiated. The computations taking into account the electronic correlation (MP2/6-31G(d//RHF/6-31G(d and MP2/6-31G(d,p//RHF/6-31G(d,p reflect the general sequence of change in the proton-donor properties: HSCN > HOCN > HNCS > HNCO, coinciding with the order of descending hydrophobicity of the compounds. The comparative proton-donor ability of the above acids in aqueous solutions is determined basically from the electronic structure and size of their molecules and anions [OCN]-, [SCN]-, but not on medium effects.
Hafner, Jürgen
2010-09-29
During the last 20 years computer simulations based on a quantum-mechanical description of the interactions between electrons and atomic nuclei have developed an increasingly important impact on materials science, not only in promoting a deeper understanding of the fundamental physical phenomena, but also enabling the computer-assisted design of materials for future technologies. The backbone of atomic-scale computational materials science is density-functional theory (DFT) which allows us to cast the intractable complexity of electron-electron interactions into the form of an effective single-particle equation determined by the exchange-correlation functional. Progress in DFT-based calculations of the properties of materials and of simulations of processes in materials depends on: (1) the development of improved exchange-correlation functionals and advanced post-DFT methods and their implementation in highly efficient computer codes, (2) the development of methods allowing us to bridge the gaps in the temperature, pressure, time and length scales between the ab initio calculations and real-world experiments and (3) the extension of the functionality of these codes, permitting us to treat additional properties and new processes. In this paper we discuss the current status of techniques for performing quantum-based simulations on materials and present some illustrative examples of applications to complex quasiperiodic alloys, cluster-support interactions in microporous acid catalysts and magnetic nanostructures.
Institute of Scientific and Technical Information of China (English)
YAO Wen-Zhi; YAO Jian-Bin; LI Si-Dian
2012-01-01
A systematic density functional theory and wave function theory investigation on the geometrical and electronic properties of A1Aun0/" (n = 2-4) clusters has been performed in this work. A1Aun- anions prove to possess ground states of the V-shaped C2v A1Au2, umbrella-shaped C3v A1Au3, and perfect tetrahedral Td A1Au4", while their neutrals favor the V-shaped CEv A1Au2, perfect planar triangular D3h A1Au3, and severely distorted Cs A1Au4, respectively. Aluminum aurides appear to be analogous to the corresponding aluminum hydrides, expect C~ A1Au4. Molecular orbitals (MOs) analyses also support this conclusion. Detailed orbital analyses indicate that Au 6s makes 94-96% and Au 5d makes 6-4% contribution to the Au-based orbitals in A1-Au bonds, which is smaller than the BAun0/- series, partially reflecting the relativistic effect of gold. The one-electron detachment energies of the anions and characteristic stretching vibrational frequencies of A1-Au bonds between 100-400 cm-1 have been calculated to facilitate future experimental characterization of these clusters.
Relaxation of Small Molecules：an ab initio Study
Institute of Scientific and Technical Information of China (English)
CAOYi－Gang; A.Antons; 等
2002-01-01
Using an ab inito total energy and force method,we have relaxed several group IV and group V elemental clusters,in detail the arsenic and antimony dimers,silicon,phosphorus,arsenic and antimony tetraners,The obtained bond lengths and cohesive energies are more accurate than other calculating methods,and in excellent agreement with the experimental results.
Energy Technology Data Exchange (ETDEWEB)
Kim, B.
1990-10-01
This report discusses the following topics: molecular structure of NO{sub 3} radical studied by laser induced fluorescence; photodissociation and fluorescence spectroscopy of NO{sub 3} in molecular beam; vertical electronic spectrum of NO{sub 3}:{sup 2}A{prime}{sub 2}, {sup 2}E{double prime}({sup 2}A{sub 2}{sup 2}B{sub 1}), and {sup 2}E{prime} states; and Ab initio study of the vibrational spectra of NO{sub 3}.
DEFF Research Database (Denmark)
Tao, Kun; Stepanyuk, V.S.; Bruno, P.;
2008-01-01
The state of the art ab initio calculations reveal the effect of a scanning tunneling microscopy tip on magnetic properties and conductance of a benzene-adatom sandwich on Cu(001). We concentrate on a benzene-Co system interacting with a Cr tip. Our studies give a clear evidence that magnetism...... and conductance in molecule-adatom junctions can be tailored by the STM tip. Varying the tip-substrate distance the magnetic moment of the Co adatom can be switched on/off. The interplay between spin-polarized electron transport through the junction and its magnetic properties is demonstrated. A spin...
Vonci, Michele; Giansiracusa, Marcus J; Gable, Robert W; Van den Heuvel, Willem; Latham, Kay; Moubaraki, Boujemaa; Murray, Keith S; Yu, Dehong; Mole, Richard A; Soncini, Alessandro; Boskovic, Colette
2016-02-01
Ab initio calculations carried out on the Tb analogue of the single-molecule magnet family Na9[Ln(W5O18)2] (Ln = Nd, Gd, Ho and Er) have allowed interpretation of the inelastic neutron scattering spectra. The combined experimental and theoretical approach sheds new light on the sensitivity of the electronic structure of the Tb(III) ground and excited states to small structural distortions from axial symmetry, thus revealing the subtle relationship between molecular geometry and magnetic properties of the two isostructural species that comprise the sample. PMID:26690503
Ab-initio study of high temperature lattice dynamics of BCC zirconium (β-Zr) and uranium (γ-U)
Energy Technology Data Exchange (ETDEWEB)
Ghosh, Partha S., E-mail: parthasarathi13@gmail.com; Arya, A., E-mail: parthasarathi13@gmail.com; Dey, G. K., E-mail: parthasarathi13@gmail.com [Materials Science Division, Bhabha Atomic Research Centre, Mumbai-400085 (India)
2014-04-24
Using self consistent ab-initio lattice dynamics calculations, we show that bcc structures of Zr and U phases become stable at high temperature by phonon-phonon interactions. The calculated temperature dependent phonon dispersion curve (PDC) of β-Zr match excellently with experimental PDC. But the calculated PDC for γ-U shows negative phonon frequencies even at solid to liquid transition temperature. We show that this discrepancy is due to an overestimation of instability depth of bcc U phase which is removed by incorporation of spin-orbit coupling in the electronic structure calculations.
Sun, Hosung; Freed, Karl F.
1984-01-01
The exact ab initio effective valence shell Hamiltonian, which is mimicked by semiempirical theories of valence, is calculated for CH at 11 bond lengths using quasidegenerate many-body perturbation theory to incorporate extensive correlation contributions. Least squares fits of the bond length dependence of the calculated CH matrix elements provide simple formulas which are compared with the intuitive forms introduced into semiempirical theories. Some of the semiempirical formulas, e.g., one-center, one-electron integrals and two-center, two-electron integrals, are in good agreement with our correlated ab initio calculations, while others display substantial departures. For example, the bond length dependence of one-center, two-electron integrals, which are assumed to be independent of bond length in semiempirical theories, is substantial but physically understandable. Corrections are found to the assumed proportionality of resonance and overlap integrals. The bond length dependence of nonclassical three-electron integrals is presented along with the hybrid and exchange integrals that are ignored in zero differential overlap methods.
Brandt, Erik G.; Agosta, Lorenzo; Lyubartsev, Alexander P.
2016-07-01
Small-sized wet TiO2 nanoparticles have been investigated by ab initio molecular dynamics simulations. Chemical and physical adsorption of water on the TiO2-water interface was studied as a function of water content, ranging from dry nanoparticles to wet nanoparticles with monolayer coverage of water. The surface reactivity was shown to be a concave function of water content and driven by surface defects. The local coordination number at the defect was identified as the key factor to decide whether water adsorption proceeds through dissociation or physisorption on the surface. A consistent picture of TiO2 nanoparticle wetting at the microscopic level emerges, which corroborates existing experimental data and gives further insight into the molecular mechanisms behind nanoparticle wetting. These calculations will facilitate the engineering of metal oxide nanoparticles with a controlled catalytic water activity.Small-sized wet TiO2 nanoparticles have been investigated by ab initio molecular dynamics simulations. Chemical and physical adsorption of water on the TiO2-water interface was studied as a function of water content, ranging from dry nanoparticles to wet nanoparticles with monolayer coverage of water. The surface reactivity was shown to be a concave function of water content and driven by surface defects. The local coordination number at the defect was identified as the key factor to decide whether water adsorption proceeds through dissociation or physisorption on the surface. A consistent picture of TiO2 nanoparticle wetting at the microscopic level emerges, which corroborates existing experimental data and gives further insight into the molecular mechanisms behind nanoparticle wetting. These calculations will facilitate the engineering of metal oxide nanoparticles with a controlled catalytic water activity. Electronic supplementary information (ESI) available: Simulation data on equilibration of energies and structures (root-mean-square-deviations and
Directory of Open Access Journals (Sweden)
Lei Li
2015-01-01
Full Text Available The ab initio calculations about the properties of the interstitials doping in the rutile TiO2 and their impact on the transport coefficients are reported. As the doping of the Zr or Ti interstitials in the TiO2, the lattice Ti4+ ions acquire the excess electrons so reduced to the Ti3+ or Ti2+ ions. However, the Cu interstitials could not lose enough electrons to reduce the lattice Ti4+ ions. Furthermore, the Ti or Cu interstitials in the ZrO2 also are unable to promote the lattice Zr4+ ions to form the lattice Zr3+ or Zr2+ ions. The high transport coefficients are observed in the defected TiO2 with the Ti or Zr interstitials as the high concentration of the Ti3+ or Ti2+ ions. So, the Zr interstitials are the favorable choice for the extra-doping to improve the transport properties in the TiO2-based resistive random access memory.
Laser spectroscopy and ab initio studies of metal-containing free radicals
Greetham, G M
2000-01-01
strontium-containing free radical is reported, that of SrCCH. This new excited electronic state is accessed by the orbitally-forbidden B-tilde' sup 2 DELTA-X-tilde sup 2 SIGMA sup + transition. Spin-orbit and vibrational structure have been seen in spectra of SrCCH and SrCCD and confirmed the assignment. Finally, observation of a new transition in an unidentified gallium-containing molecule is reported. Two progressions corresponding to two different vibrational modes of the molecule are seen in the spectrum. Potential spectral carriers, including Ga sub x clusters and other gallium-containing molecules formed by reaction with impurities, are discussed in an attempt to explain the observed spectrum. This work describes the use of laser spectroscopy and ab initio calculations in the investigation of several new electronic transitions in metal-containing free radicals. These free radicals were prepared in a supersonic jet by laser ablation of solid metal samples in the presence of appropriate precursor molecule...
Neukirch, Amanda; Nei, Wanyi; Pedesseau, Laurent; Even, Jacky; Katan, Claudine; Mohite, Aditya; Tretiak, Segrei
2015-03-01
The need for an inexpensive, clean, and plentiful source of energy has generated large amounts of research in an assortment of solution processed organic and hybrid organic-inorganic solar cells. A relative newcomer to the field of solution processed photovoltaics is the lead halide perovskite solar cell. In the past 5 years, the efficiencies of devices made from this material have increased from 3.5% to nearly 20%. Despite the rapid development of organic-inorganic perovskite solar cells, a thorough understanding of the fundamental photophysical processes driving the high performance of these devices is not well understood. I am using state-of-the-art ab initio computational techniques in order to characterize the properties at the interface of perovskite devices in order to aide in materials design and device engineering. I will present an in-depth analysis of the electronic and optical properties of bulk and surface states of pure and mixed halide systems. The high-level static quantum mechanical calculations, including spin-orbit-coupling and the many body GW approach, identify the key electronic states involved in photoinduced dynamics. This knowledge provides important information on how the optical properties change with variations to the system. Supported by the DOE, the LANL LDRD program XW11, and CNLS.
An ab initio quantum chemical investigation of the structure and stability of ozone-water complexes
Energy Technology Data Exchange (ETDEWEB)
Kumar, Pradeep [Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016 (India); Sathyamurthy, N., E-mail: nsath@iitk.ac.in [Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016 (India); Indian Institute of Science Education and Research Mohali, Sector 81, SAS Nagar, Manauli 140306 (India)
2013-03-29
Highlights: ► Eclipse geometry most stable for the 1:1 ozone-water complex. ► Cyclic structure most stable for the 1:2 complex. ► Shift in the vertical electronic excitation energy of ozone due to hydration. - Abstract: Ab initio quantum chemical calculations have been carried out to investigate the structure and stability of 1:1 and 1:2 ozone-water complexes. All the geometries have been optimized at the CCSD level of theory using aug-cc-pVDZ and aug-cc-pVTZ basis sets. The importance of correlation-consistent basis sets in deciding the nature of critical points on these complexes is emphasized. An analysis based on the dipole moment of the complexes and the charge distribution on atoms follows. The effect of ozone molecule on the structure and properties of water dimer is also investigated. Values of the vertical electronic excitation energy and the corresponding transition dipole moment have been calculated for the ozone-water complexes using the multi-reference-configuration-interaction method and the aug-cc-pVTZ basis set. The calculated shift in vibrational frequencies due to complex formation is compared with the earlier reported experimental and theoretical values.
The ab initio calculation of spectra of open shell diatomic molecules
Tennyson, Jonathan; Lodi, Lorenzo; McKemmish, Laura K.; Yurchenko, Sergei N.
2016-05-01
The spectra (rotational, rotation-vibrational or electronic) of diatomic molecules due to transitions involving only closed-shell (1Σ ) electronic states follow very regular, simple patterns and their theoretical analysis is usually straightforward. On the other hand, open-shell electronic states lead to more complicated spectral patterns and, moreover, often appear as a manifold of closely lying electronic states, leading to perturbed spectra of even greater complexity. This is especially true when at least one of the atoms is a transition metal. Traditionally these complex cases have been analysed using approaches based on perturbation theory, with semi-empirical parameters determined by fitting to spectral data. Recently the needs of two rather diverse scientific areas have driven the demand for improved theoretical models of open-shell diatomic systems based on an ab initio approach; these areas are ultracold chemistry and the astrophysics of ‘cool’ stars, brown dwarfs and most recently extrasolar planets. However, the complex electronic structure of these molecules combined with the accuracy requirements of high-resolution spectroscopy render such an approach particularly challenging. This review describes recent progress in developing methods for directly solving the effective Schrödinger equation for open-shell diatomic molecules, with a focus on molecules containing a transtion metal. It considers four aspects of the problem: (i) the electronic structure problem; (ii) non-perturbative treatments of the curve couplings; (iii) the solution of the nuclear motion Schrödinger equation; (iv) the generation of accurate electric dipole transition intensities. Examples of applications are used to illustrate these issues.
Allen, B. Danette; Alexandrov, Natalia
2016-01-01
Incremental approaches to air transportation system development inherit current architectural constraints, which, in turn, place hard bounds on system capacity, efficiency of performance, and complexity. To enable airspace operations of the future, a clean-slate (ab initio) airspace design(s) must be considered. This ab initio National Airspace System (NAS) must be capable of accommodating increased traffic density, a broader diversity of aircraft, and on-demand mobility. System and subsystem designs should scale to accommodate the inevitable demand for airspace services that include large numbers of autonomous Unmanned Aerial Vehicles and a paradigm shift in general aviation (e.g., personal air vehicles) in addition to more traditional aerial vehicles such as commercial jetliners and weather balloons. The complex and adaptive nature of ab initio designs for the future NAS requires new approaches to validation, adding a significant physical experimentation component to analytical and simulation tools. In addition to software modeling and simulation, the ability to exercise system solutions in a flight environment will be an essential aspect of validation. The NASA Langley Research Center (LaRC) Autonomy Incubator seeks to develop a flight simulation infrastructure for ab initio modeling and simulation that assumes no specific NAS architecture and models vehicle-to-vehicle behavior to examine interactions and emergent behaviors among hundreds of intelligent aerial agents exhibiting collaborative, cooperative, coordinative, selfish, and malicious behaviors. The air transportation system of the future will be a complex adaptive system (CAS) characterized by complex and sometimes unpredictable (or unpredicted) behaviors that result from temporal and spatial interactions among large numbers of participants. A CAS not only evolves with a changing environment and adapts to it, it is closely coupled to all systems that constitute the environment. Thus, the ecosystem that
Ab initio STM and STS simulations on magnetic and nonmagnetic metallic surfaces
Energy Technology Data Exchange (ETDEWEB)
Dick, Alexey
2008-04-14
The aim of this work was to provide an in-depth understanding of a new generation of scan- ning tunneling microscopy experiments, performed employing different regimes of the STM: the spectroscopy-mode (the so-called Fourier Transformed STM, FT-STM), and the spin-sensitive mode (the so-called spin-polarized STM, SP-STM). In the present thesis ab initio tools are proposed that are based on DFT calculations to theoretically predict and analyze such types of the STM. The first part of this thesis focusses on the simulation of FT-STM, the mode that allows to probe local dispersion properties of the electrons at the surface. In order to provide the theoretical counterpart of the experimental FT-STM spectra we have introduced a new implicit approach that is derived from Tersoff-Hamann theory of the STM. The importance of an accurate description of surface wavefunctions at 5-15 A above the surface as well as the spurious quantum- size effects have been discussed in detail together with approaches to obtain converged FT-STM images. We applied our method to FT-STM experiments performed on Ag(110) surfaces. In the second part of the thesis we discuss the modeling of the spin-resolved STM, the mode that allows to characterize the magnetic structure of a surface. As a case system we studied here the magnetically-ordered transition-metal nitride surface Mn{sub 3}N{sub 2}(010). Because SP-STM experiments did not allow a conclusive understanding of the surface structure, we have first employed ab initio thermodynamics to figure out the most stable magnetic and atomic configuration of the surface that are consistent with experiments. To simulate SP-STM images on the most stable Mn{sub 3}N{sub 2}(010) surface we have employed the spin-generalized transfer-Hamiltonian formalism, assuming that the tip wavefunctions have dominant radial symmetry (s-like tip). (orig.)
Pierce, Levi C. T.; Markwick, Phineus R. L.; McCammon, J. Andrew; Doltsinis, Nikos L.
2011-01-01
A biased potential molecular dynamics simulation approach, accelerated molecular dynamics (AMD), has been implemented in the framework of ab initio molecular dynamics for the study of chemical reactions. Using two examples, the double proton transfer reaction in formic acid dimer and the hypothetical adiabatic ring opening and subsequent rearrangement reactions in methylenecyclopropane, it is demonstrated that ab initio AMD can be readily employed to efficiently explore the reactive potential energy surface, allowing the prediction of chemical reactions and the identification of metastable states. An adaptive variant of the AMD method is developed, which additionally affords an accurate representation of both the free-energy surface and the mechanism associated with the chemical reaction of interest and can also provide an estimate of the reaction rate. PMID:21548673
Study of atomic structure of liquid Hg-In alloys using ab-initio molecular dynamics
Energy Technology Data Exchange (ETDEWEB)
Sharma, Nalini; Ahluwalia, P. K. [Department of Physics, Himachal Pradesh University, Shimla(HP)-171005 (India); Thakur, Anil [Department of Physics, Govt. P. G. College Solan (HP)-173212 (India)
2015-05-15
Ab-initio molecular dynamics simulations are performed to study the structural properties of liquid Hg-In alloys. The interatomic interactions are described by ab-initio pseudopotentials given by Troullier and Martins. Five liquid Hg-In mixtures (Hg{sub 10}In{sub 90}, Hg{sub 30}In{sub 70}, Hg{sub 50}In{sub 50}, Hg{sub 70}In{sub 30} and Hg{sub 90}In{sub 10}) at 299K are considered. The radial distribution function g(r) and structure factor S(q) of considered alloys are compared with respective experimental results for liquid Hg (l-Hg) and (l-In). The radial distribution function g(r) shows the presence of short range order in the systems considered. Smooth curves of Bhatia-Thornton partial structure factors factor shows the presence of liquid state in the considered alloys.