A first-principles approach to finite temperature elastic constants

International Nuclear Information System (INIS)

Wang, Y; Wang, J J; Zhang, H; Manga, V R; Shang, S L; Chen, L-Q; Liu, Z-K

2010-01-01

A first-principles approach to calculating the elastic stiffness coefficients at finite temperatures was proposed. It is based on the assumption that the temperature dependence of elastic stiffness coefficients mainly results from volume change as a function of temperature; it combines the first-principles calculations of elastic constants at 0 K and the first-principles phonon theory of thermal expansion. Its applications to elastic constants of Al, Cu, Ni, Mo, Ta, NiAl, and Ni 3 Al from 0 K up to their respective melting points show excellent agreement between the predicted values and existing experimental measurements.

First-principles study of complex material systems

Science.gov (United States)

He, Lixin

This thesis covers several topics concerning the study of complex materials systems by first-principles methods. It contains four chapters. A brief, introductory motivation of this work will be given in Chapter 1. In Chapter 2, I will give a short overview of the first-principles methods, including density-functional theory (DFT), planewave pseudopotential methods, and the Berry-phase theory of polarization in crystallines insulators. I then discuss in detail the locality and exponential decay properties of Wannier functions and of related quantities such as the density matrix, and their application in linear-scaling algorithms. In Chapter 3, I investigate the interaction of oxygen vacancies and 180° domain walls in tetragonal PbTiO3 using first-principles methods. Our calculations indicate that the oxygen vacancies have a lower formation energy in the domain wall than in the bulk, thereby confirming the tendency of these defects to migrate to, and pin, the domain walls. The pinning energies are reported for each of the three possible orientations of the original Ti--O--Ti bonds, and attempts to model the results with simple continuum models are discussed. CaCu3Ti4O12 (CCTO) has attracted a lot of attention recently because it was found to have an enormous dielectric response over a very wide temperature range. In Chapter 4, I study the electronic and lattice structure, and the lattice dynamical properties, of this system. Our first-principles calculations together with experimental results point towards an extrinsic mechanism as the origin of the unusual dielectric response.

First-Principles Study of Enhanced Magnetoelectric Effects at the Fe/MgO(001) Interface

Science.gov (United States)

Niranjan, M. K.; Jaswal, S. S.; Tsymbal, E. Y.; Duan, C.-G.

2010-03-01

The magnetoelectric effect allows affecting magnetic properties of materials by electric fields with potential for technological applications such as electrically controlled magnetic data storage. In this study we explore, using first-principles methods, the magnetoelectric effect at the Fe/MgO(001) interface^,1. By explicitly introducing an electric field in our density-functional calculations we demonstrate that the magnetic moment of Fe atoms at the interface changes linearly as a function of the applied electric field with the surface magnetoelectric coefficient being strongly enhanced as compared to that for the clean Fe(001) surface.^1 The effect originates from the increased screening charge associated with a large dielectric constant of MgO. The influence of electric field on relative occupancy of the Fe-3d orbitals leads to significant change in the surface magnetocrystalline anisotropy. These results are compared with the available experimental work.^2 Our results indicate that using high-k dielectrics at the interface with ferromagnetic metals may be very effective in controlling the magnetic properties by electric fields thereby leading to interesting device applications. ^1 C.-G. Duan et al., Phys. Rev. Lett. 101, 137201 (2008). ^2 T. Maruyama et al., Nat. Nanotech., 4, 158 (2009).

Quantum correlations are tightly bound by the exclusivity principle.

Science.gov (United States)

Yan, Bin

2013-06-28

It is a fundamental problem in physics of what principle limits the correlations as predicted by our current description of nature, based on quantum mechanics. One possible explanation is the "global exclusivity" principle recently discussed in Phys. Rev. Lett. 110, 060402 (2013). In this work we show that this principle actually has a much stronger restriction on the probability distribution. We provide a tight constraint inequality imposed by this principle and prove that this principle singles out quantum correlations in scenarios represented by any graph. Our result implies that the exclusivity principle might be one of the fundamental principles of nature.

Structural, electronic, and vibrational properties of high-density amorphous silicon: a first-principles molecular-dynamics study.

Science.gov (United States)

Morishita, Tetsuya

2009-05-21

We report a first-principles study of the structural, electronic, and dynamical properties of high-density amorphous (HDA) silicon, which was found to be formed by pressurizing low-density amorphous (LDA) silicon (a normal amorphous Si) [T. Morishita, Phys. Rev. Lett. 93, 055503 (2004); P. F. McMillan, M. Wilson, D. Daisenberger, and D. Machon, Nature Mater. 4, 680 (2005)]. Striking structural differences between HDA and LDA are revealed. The LDA structure holds a tetrahedral network, while the HDA structure contains a highly distorted tetrahedral network. The fifth neighboring atom in HDA tends to be located at an interstitial position of a distorted tetrahedron composed of the first four neighboring atoms. Consequently, the coordination number of HDA is calculated to be approximately 5 unlike that of LDA. The electronic density of state (EDOS) shows that HDA is metallic, which is consistent with a recent experimental measurement of the electronic resistance of HDA Si. We find from local EDOS that highly distorted tetrahedral configurations enhance the metallic nature of HDA. The vibrational density of state (VDOS) also reflects the structural differences between HDA and LDA. Some of the characteristic vibrational modes of LDA are dematerialized in HDA, indicating the degradation of covalent bonds. The overall profile of the VDOS for HDA is found to be an intermediate between that for LDA and liquid Si under pressure (high-density liquid Si).

Reliability evaluation of thermophysical properties from first-principles calculations.

Science.gov (United States)

Palumbo, Mauro; Fries, Suzana G; Dal Corso, Andrea; Kürmann, Fritz; Hickel, Tilmann; Neugebauer, Jürg

2014-08-20

Thermophysical properties, such as heat capacity, bulk modulus and thermal expansion, are of great importance for many technological applications and are traditionally determined experimentally. With the rapid development of computational methods, however, first-principles computed temperature-dependent data are nowadays accessible. We evaluate various computational realizations of such data in comparison to the experimental scatter. The work is focussed on the impact of different first-principles codes (QUANTUM ESPRESSO and VASP), pseudopotentials (ultrasoft and projector augmented wave) as well as phonon determination methods (linear response and direct force constant method) on these properties. Based on the analysis of data for two pure elements, Cr and Ni, consequences for the reliability of temperature-dependent first-principles data in computational thermodynamics are discussed.

First Principle simulations of electrochemical interfaces - a DFT study

DEFF Research Database (Denmark)

Ahmed, Rizwan

for the whole system to qualify as a proper electrochemical interface. I have also contributed to the model, which accounts for pH in the first principle electrode-electrolyte interface simulations. This is an important step forward, since electrochemical reaction rate and barrier for charge transfer can......In this thesis, I have looked beyond the computational hydrogen electrode (CHE) model, and focused on the first principle simulations which treats the electrode-electrolyte interfaces explicitly. Since obtaining a realistic electrode-electrolyte interface was difficult, I aimed to address various...... challenges regarding first principle electrochemical interface modeling in order to bridge the gap between the model interface used in simulations and real catalyst at operating conditions. Atomic scale insight for the processes and reactions that occur at the electrochemical interface presents a challenge...

First principles total energy calculations of the structural and electronic properties of ScxGa1-xN

International Nuclear Information System (INIS)

Moreno-Armenta, Maria Guadalupe; Mancera, Luis; Takeuchi, Noboru

2003-01-01

Using first principles total energy calculations within the the full-potential linearized augmented plane wave (FP-LAPW) method, we have investigated the structural and electronic properties of Sc x Ga 1-x N, with Sc concentrations varying from 0% up to 100%. In particular we have studied the relative stability of several configurations of Sc x Ga 1-x N in wurtzite-like structures (the ground state configuration of GaN), or in rocksalt-like structures (the ground state configuration of ScN). It is found that for Sc concentrations less than ∼65%, the favored structure is a wurtzite-like one, while for Sc concentrations greater than ∼65%, the favored structure is a NaCl-like structure. It is also found that for the wurtzite-like crystals, the fundamental gap is large and direct. For the rocksalt crystals the fundamental gap is small and indirect, but with an additional larger direct gap. In agreement with the experiments of Little and Kordesch [Appl. Phys. Lett. 78, 2891 (2001)] we found a decrease of the band gap with the increase of the Sc concentration. (Abstract Copyright [2003], Wiley Periodicals, Inc.)

Insights into the ammonia synthesis from first-principles

DEFF Research Database (Denmark)

Hellmann, A.; Honkala, Johanna Karoliina; Remediakis, Ioannis

2006-01-01

-properties, such as apparent activation energies and reaction orders, are calculated from the first-principles model. Our analysis shows that the reaction order of N-2 is unity under all considered conditions, whereas the reaction orders of H-2 and NH3 depend on reaction conditions. (c) 2006 Elsevier B.V. All rights reserved.......A new set of measurements is used to further test a recently published first-principles model for the ammonia (NH3) synthesis on an unpromoted Ru-based catalyst. A direct comparison shows an overall good agreement in NH3 productivity between the model and the experiment. In addition, macro...

Analytic representation for first-principles pseudopotentials

International Nuclear Information System (INIS)

Lam, P.K.; Cohen, M.L.; Zunger, A.

1980-01-01

The first-principles pseudopotentials developed by Zunger and Cohen are fit with a simple analytic form chosen to model the main physical properties of the potentials. The fitting parameters for the first three rows of the Periodic Table are presented, and the quality of the fit is discussed. The parameters reflect chemical trends of the elements. We find that a minimum of three parameters is required to reproduce the regularities of the Periodic Table. Application of these analytic potentials is also discussed

A first-principle for the nervous system

OpenAIRE

Vadakkan, Kunjumon

2016-01-01

Higher brain functions such as perception and memory are first-person internal sensations whose mechanisms can have options to concurrently activate motor neurons for behavioral action. By setting up all the required constraints using available information from different levels, a theoretical examination from a first-person frame of reference led to the derivation of a first-principle of the structure-function units. These units operate in synchrony with the synaptically-connected neural circ...

Diffusion in thorium carbide: A first-principles study

Energy Technology Data Exchange (ETDEWEB)

Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1025, Buenos Aires (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1025, Buenos Aires (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM–CNEA, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina)

2015-12-15

The prediction of the behavior of Th compounds under irradiation is an important issue for the upcoming Generation-IV nuclear reactors. The study of self-diffusion and hetero-diffusion is a central key to fulfill this goal. As a first approach, we obtained, by means of first-principles methods, migration and activation energies of Th and C atoms self-diffusion and diffusion of He atoms in ThC. We also calculate diffusion coefficients as a function of temperature. - Highlights: • Diffusion in thorium carbide by means of first-principles calculations is studied. • The most favorable migration event is a C atom moving through a C-vacancy aided path. • Calculated C atoms diffusion coefficients agree very well with the experimental data. • For He, the energetically most favorable migration path is through Th-vacancies.

Comment on "Current fluctuations in non-equilibrium diffusive systems: an additivity principle"

OpenAIRE

Sukhorukov, Eugene V.; Jordan, Andrew N.

2004-01-01

We point out that the "additivity principle" and "scaling hypothesis" postulated by Bodineau and Derrida in Phys. Rev. Lett 92, 180601 (2004), follow naturally from the saddle point evaluation of a diffusive field theory.

First-principles elasticity of monocarboaluminate hydrates

KAUST Repository

Moon, J.; Yoon, S.; Wentzcovitch, R. M.; Monteiro, P. J. M.

2014-01-01

The elasticity of monocarboaluminate hydrates, 3CaO·Al2O3·CaCO3·xH2O (x = 11 or 8), has been investigated by first-principles calculations. Previous experimental study revealed that the fully hydrated monocarboaluminate (x = 11) exhibits exceptionally low compressibility compared to other reported calcium aluminate hydrates. This stiff hydration product can contribute to the strength of concrete made with Portland cements containing calcium carbonates. In this study, full elastic tensors and mechanical properties of the crystal structures with different water contents (x = 11 or 8) are computed by first-principles methods based on density functional theory. The results indicate that the compressibility of monocarboaluminate is highly dependent on the water content in the interlayer region. The structure also becomes more isotropic with the addition of water molecules in this region. Since the monocarboaluminate is a key hydration product of limestone added cement, elasticity of the crystal is important to understand its mechanical impact on concrete. Besides, it is put forth that this theoretical calculation will be useful in predicting the elastic properties of other complex cementitous materials and the influence of ion exchange on compressibility.

First-principles elasticity of monocarboaluminate hydrates

KAUST Repository

Moon, J.

2014-07-01

The elasticity of monocarboaluminate hydrates, 3CaO·Al2O3·CaCO3·xH2O (x = 11 or 8), has been investigated by first-principles calculations. Previous experimental study revealed that the fully hydrated monocarboaluminate (x = 11) exhibits exceptionally low compressibility compared to other reported calcium aluminate hydrates. This stiff hydration product can contribute to the strength of concrete made with Portland cements containing calcium carbonates. In this study, full elastic tensors and mechanical properties of the crystal structures with different water contents (x = 11 or 8) are computed by first-principles methods based on density functional theory. The results indicate that the compressibility of monocarboaluminate is highly dependent on the water content in the interlayer region. The structure also becomes more isotropic with the addition of water molecules in this region. Since the monocarboaluminate is a key hydration product of limestone added cement, elasticity of the crystal is important to understand its mechanical impact on concrete. Besides, it is put forth that this theoretical calculation will be useful in predicting the elastic properties of other complex cementitous materials and the influence of ion exchange on compressibility.

First-principles investigation of quantum transport in GeP3 nanoribbon-based tunneling junctions

Science.gov (United States)

Wang, Qiang; Li, Jian-Wei; Wang, Bin; Nie, Yi-Hang

2018-06-01

Two-dimensional (2D) GeP3 has recently been theoretically proposed as a new low-dimensional material [ Nano Lett. 17(3), 1833 (2017)]. In this manuscript, we propose a first-principles calculation to investigate the quantum transport properties of several GeP3 nanoribbon-based atomic tunneling junctions. Numerical results indicate that monolayer GeP3 nanoribbons show semiconducting behavior, whereas trilayer GeP3 nanoribbons express metallic behavior owing to the strong interaction between each of the layers. This behavior is in accordance with that proposed in two-dimensional GeP3 layers. The transmission coefficient T( E) of tunneling junctions is sensitive to the connecting formation between the central monolayer GeP3 nanoribbon and the trilayer GeP3 nanoribbon at both ends. The T( E) value of the bottom-connecting tunneling junction is considerably larger than those of the middle-connecting and top-connecting ones. With increases in gate voltage, the conductances increase for the bottom-connecting and middle-connecting tunneling junctions, but decrease for the top-connecting tunneling junctions. In addition, the conductance decreases exponentially with respect to the length of the central monolayer GeP3 nanoribbon for all the tunneling junctions. I-V curves show approximately linear behavior for the bottom-connecting and middle-connecting structures, but exhibit negative differential resistance for the top-connecting structures. The physics of each phenomenon is analyzed in detail.

First-principle calculations of the structural, electronic ...

Indian Academy of Sciences (India)

First-principle calculations were performed to study the structural, electronic, thermodynamic and thermal properties of ... functional theory (DFT) combined with the quasi-harmonic .... is consistent with Vegard's law which assumes that the lat- tice constant varies .... reflects a charge-transfer effect which is due to the different.

First International Conference on Organic Nonlinear Optics. Section B: Nonlinear Optics, Principles, Materials, Phenomena, and Devices.

Science.gov (United States)

1994-01-01

HOSOTTE: Alignement and Orientation of Chromophores by Optical Pumping 327 CELINE FIORINI, FABRICE CHARRA, JEAN-MICHEL NUNZI and PAUL RAIMOND...Normandin, R. L. Williams and M. Dion , Electron. Lett., 28, 1540 (1992). 6. D. Vakhshoori and S. Wang, Appl. Phys. Lett., 53, 347 (1988). 7. D. Vakhshoori, J

First-principle calculations of structural, electronic, optical, elastic ...

Indian Academy of Sciences (India)

S CHEDDADI

2017-11-28

Nov 28, 2017 ... First-principle calculations on the structural, electronic, optical, elastic and thermal properties of the chalcopyrite ... The Kohn–Sham equations were solved using the ... RMTKmax = 7 was used for all the investigated systems,.

Thermodynamic assessment of the Sn–Sr system supported by first-principles calculations

International Nuclear Information System (INIS)

Zhao, Jingrui; Du, Yong; Zhang, Lijun; Wang, Aijun; Zhou, Liangcai; Zhao, Dongdong; Liang, Jianlie

2012-01-01

Highlights: ► All the literature data of Sn–Sr system is critically reviewed. ► First-principles calculation of enthalpy of formation is carried out for each compound. ► Thermodynamic parameters for Sn–Sr system are obtained by CALPHAD method. ► A hybrid approach of CALPHAD and first-principles calculations is recommended. - Abstract: A hybrid approach of CALPHAD and first-principles calculations was employed to perform a thermodynamic modeling of the Sn–Sr system. The experimental phase diagram and thermodynamic data available in the literature were critically reviewed. The enthalpies of formation for the 6 stoichiometric compounds (i.e. Sr 2 Sn, Sr 5 Sn 3 , SrSn, Sr 3 Sn 5 , SrSn 3 and SrSn 4 ) at 0 K were computed by means of first-principles calculations. These data were used as the experimental values in the optimization module PARROT in the subsequent CALPHAD assessment to provide thermodynamic parameters with sound physical meaning. A set of self-consistent thermodynamic parameters was finally obtained by considering reliable literature data and the first-principles computed results. Comprehensive comparisons between the calculated and measured quantities indicate that all the reliable experimental information can be satisfactorily accounted for by the present thermodynamic description.

First-principles study of point-defect production in Si and SiC

International Nuclear Information System (INIS)

Windl, W.; Lenosky, T.J.; Kress, J.D.; Voter, A.F.

1998-03-01

The authors have calculated the displacement-threshold energy E(d) for point-defect production in Si and SiC using empirical potentials, tight-binding, and first-principles methods. They show that -- depending on the knock-on direction -- 64-atom simulation cells can be sufficient to allow a nearly finite-size-effect-free calculation, thus making the use of first-principles methods possible. They use molecular dynamics (MD) techniques and propose the use of a sudden approximation which agrees reasonably well with the MD results for selected directions and which allows estimates of Ed without employing an MD simulation and the use of computationally demanding first-principles methods. Comparing the results with experiment, the authors find the full self-consistent first-principles method in conjunction with the sudden approximation to be a reliable and easy method to predict E d . Furthermore, they have examined the temperature dependence of E d for C in SiC and found it to be negligible

Thermopower switching by magnetic field: first-principles calculations

DEFF Research Database (Denmark)

Maslyuk, Volodymyr V.; Achilles, Steven; Sandratskii, Leonid

2013-01-01

We present first-principles studies of the thermopower of the organometallic V4Bz5 molecule attached between Co electrodes with noncollinear magnetization directions. Different regimes in the formation of the noncollinear magnetic state of the molecule lead to a remarkable nonmonotonous dependence...

Electrical properties of improper ferroelectrics from first principles

Science.gov (United States)

Stengel, Massimiliano; Fennie, Craig J.; Ghosez, Philippe

2012-09-01

We study the interplay of structural and polar distortions in hexagonal YMnO3 and short-period PbTiO3/SrTiO3 (PTO/STO) superlattices by means of first-principles calculations at constrained electric displacement field D. We find that in YMnO3 the tilts of the oxygen polyhedra produce a robustly polar ground state, which persists at any choice of the electrical boundary conditions. Conversely, in PTO/STO the antiferrodistortive instabilities alone do not break inversion symmetry, and open-circuit boundary conditions restore a nonpolar state. We suggest that this qualitative difference naturally provides a route to rationalizing the concept of “improper ferroelectricity” from the point of view of first-principles theory. We discuss the implications of our arguments for the design of novel multiferroic materials with enhanced functionalities and for the symmetry analysis of the phase transitions.

First-principle study of nanostructures of functionalized graphene

Indian Academy of Sciences (India)

We present first-principle calculations of 2D nanostructures of graphene functionalized with hydrogen and fluorine, respectively, in chair conformation. The partial density of states, band structure, binding energy and transverse displacement of C atoms due to functionalization (buckling) have been calculated within the ...

First-principles prediction of liquid/liquid interfacial tension

DEFF Research Database (Denmark)

Andersson, Martin Peter; Bennetzen, M.V.; Klamt, A.

2014-01-01

of groundwater aquifers contaminated by chlorinated solvents to drug delivery and a host of industrial processes. Here, we present a model for predicting interfacial tension from first principles using density functional theory calculations. Our model requires no experimental input and is applicable to liquid...

Molecular Electronics: Insight from First-Principles Transport Simulations

DEFF Research Database (Denmark)

Paulsson, Magnus; Frederiksen, Thomas; Brandbyge, Mads

2010-01-01

Conduction properties of nanoscale contacts can be studied using first-principles simulations. Such calculations give insight into details behind the conductance that is not readily available in experiments. For example, we may learn how the bonding conditions of a molecule to the electrodes affect...

Implementing first-year assessment principles: An analysis of selected scholarly literature

OpenAIRE

Theda Thomas

2018-01-01

Assessment plays an important role in students’ learning as students often frame their learning around their assessment tasks. Well-designed assessment can be used to facilitate first-year students making their social and academic transition to university. In 2009, Professor David Nicol prepared a framework for first-year assessment practices that included 12 principles. In this study, these principles were revisited and used to analyse papers from 2013 to 2016 in the journals: ‘Assessment & ...

Can the Tafel equation be derived from first principles?

International Nuclear Information System (INIS)

Gutman, E.M.

2005-01-01

A century ago, Tafel disapproved the attempts to derive the empirical equation named after him by thermodynamic methods. He noted that his observations referred to irreversible electrochemical reactions, where thermodynamics is inapplicable. This statement seems to remain valid until today. Indeed, it is impossible as yet to predict the kinetic parameters for chemical processes by determining rate constants and reaction orders from 'first principles', unless strictly specialized and, to a great extent, artificial models are developed. Nevertheless, in this paper an attempt to derive the kinetic law of mass action from 'first principles' is made in macroscopic formulation. It has turned out to be possible owing to the methods of thermodynamics of irreversible processes that were unknown in Tafel's time

Disordered crystals from first principles I: Quantifying the configuration space

Science.gov (United States)

Kühne, Thomas D.; Prodan, Emil

2018-04-01

This work represents the first chapter of a project on the foundations of first-principle calculations of the electron transport in crystals at finite temperatures. We are interested in the range of temperatures, where most electronic components operate, that is, room temperature and above. The aim is a predictive first-principle formalism that combines ab-initio molecular dynamics and a finite-temperature Kubo-formula for homogeneous thermodynamic phases. The input for this formula is the ergodic dynamical system (Ω , G , dP) defining the thermodynamic crystalline phase, where Ω is the configuration space for the atomic degrees of freedom, G is the space group acting on Ω and dP is the ergodic Gibbs measure relative to the G-action. The present work develops an algorithmic method for quantifying (Ω , G , dP) from first principles. Using the silicon crystal as a working example, we find the Gibbs measure to be extremely well characterized by a multivariate normal distribution, which can be quantified using a small number of parameters. The latter are computed at various temperatures and communicated in the form of a table. Using this table, one can generate large and accurate thermally-disordered atomic configurations to serve, for example, as input for subsequent simulations of the electronic degrees of freedom.

First-principles molecular dynamics for metals

International Nuclear Information System (INIS)

Fernando, G.W.; Qian, G.; Weinert, M.; Davenport, J.W.

1989-01-01

A Car-Parrinello-type first-principles molecular-dynamics approach capable of treating the partial occupancy of electronic states that occurs at the Fermi level in a metal is presented. The algorithms used to study metals are both simple and computationally efficient. We also discuss the connection between ordinary electronic-structure calculations and molecular-dynamics simulations as well as the role of Brillouin-zone sampling. This extension should be useful not only for metallic solids but also for solids that become metals in their liquid and/or amorphous phases

Prediction of solid oxide fuel cell cathode activity with first-principles descriptors

DEFF Research Database (Denmark)

Lee, Yueh-Lin; Kleis, Jesper; Rossmeisl, Jan

2011-01-01

In this work we demonstrate that the experimentally measured area specific resistance and oxygen surface exchange of solid oxide fuel cell cathode perovskites are strongly correlated with the first-principles calculated oxygen p-band center and vacancy formation energy. These quantities...... are therefore descriptors of catalytic activity that can be used in the first-principles design of new SOFC cathodes....

Roy's safety-first portfolio principle in financial risk management of disastrous events.

Science.gov (United States)

Chiu, Mei Choi; Wong, Hoi Ying; Li, Duan

2012-11-01

Roy pioneers the concept and practice of risk management of disastrous events via his safety-first principle for portfolio selection. More specifically, his safety-first principle advocates an optimal portfolio strategy generated from minimizing the disaster probability, while subject to the budget constraint and the mean constraint that the expected final wealth is not less than a preselected disaster level. This article studies the dynamic safety-first principle in continuous time and its application in asset and liability management. We reveal that the distortion resulting from dropping the mean constraint, as a common practice to approximate the original Roy's setting, either leads to a trivial case or changes the problem nature completely to a target-reaching problem, which produces a highly leveraged trading strategy. Recognizing the ill-posed nature of the corresponding Lagrangian method when retaining the mean constraint, we invoke a wisdom observed from a limited funding-level regulation of pension funds and modify the original safety-first formulation accordingly by imposing an upper bound on the funding level. This model revision enables us to solve completely the safety-first asset-liability problem by a martingale approach and to derive an optimal policy that follows faithfully the spirit of the safety-first principle and demonstrates a prominent nature of fighting for the best and preventing disaster from happening. © 2012 Society for Risk Analysis.

First-principles investigations of solid solution strengthening in Al alloys

OpenAIRE

Ma, Duancheng

2012-01-01

Any material properties, in principle, can be reproduced or predicted by performing firstprinciples calculations. Nowadays, however, we are dealing with complex alloy compositions and processes. The complexities cannot be fully described by first-principles, because of the limited computational power. The primary objective of this study is to investigate an important engineering problem, solid solution strengthening, in a simplified manner. The simplified scheme should allow fast and reliable...

First principles calculations of structural, electronic and thermal ...

Indian Academy of Sciences (India)

Home; Journals; Bulletin of Materials Science; Volume 37; Issue 5. First principles calculations of structural, electronic and thermal properties of lead chalcogenides PbS, PbSe and PbTe compounds. N Boukhris H Meradji S Amara Korba S Drablia S Ghemid F El Haj Hassan. Volume 37 Issue 5 August 2014 pp 1159-1166 ...

General principles of radiotherapy

International Nuclear Information System (INIS)

Easson, E.C.

1985-01-01

The daily practice of any established branch of medicine should be based on some acceptable principles. This chapter is concerned with the general principles on which the radiotherapy of the Manchester school is based. Though many radiotherapists in other centres would doubtless accept these principles, there are sufficiently wide differences in practice throughout the world to suggest that some therapists adhere to a fundamentally different philosophy. The authors believe it is important, especially for those beginning their formal training in radiotherapy, to subscribe to an internally consistent school of thought, employing methods of treatment for each type of lesion in each anatomical site that are based on accepted principles and subjected to continuous rigorous scrutiny to test their effectiveness. Not only must each therapeutic technique be evaluated, but the underlying principles too must be questioned if and when this seems indicated. It is a feature of this hospital that similar lesions are all treated by the same technique, so long as statistical evidence justifies such a policy. All members of the staff adhere to the accepted policy until or unless reliable reasons are adduced to change this policy

Boron Fullerenes: A First-Principles Study

Directory of Open Access Journals (Sweden)

Gonzalez Szwacki Nevill

2007-01-01

Full Text Available AbstractA family of unusually stable boron cages was identified and examined using first-principles local-density functional method. The structure of the fullerenes is similar to that of the B12icosahedron and consists of six crossing double-rings. The energetically most stable fullerene is made up of 180 boron atoms. A connection between the fullerene family and its precursors, boron sheets, is made. We show that the most stable boron sheets are not necessarily precursors of very stable boron cages. Our finding is a step forward in the understanding of the structure of the recently produced boron nanotubes.

First principles study of AlBi

International Nuclear Information System (INIS)

Amrani, B.; Achour, H.; Louhibi, S.; Tebboune, A.; Sekkal, N.

2008-05-01

Using the first principles method of the full potential linear augmented plane waves (FPLAPW), the structural and the electronic properties of AlBi are investigated. It is found that this compound has a small and direct semiconducting gap at Γ. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of the volume, the bulk modulus, the variation of the thermal expansion α, as well as the Debye temperature θ D and the heat capacity C v are successfully obtained in the whole range from 0 to 30 GPa and temperature range from 0 to 1200 K. (author)

Defects in boron carbide: First-principles calculations and CALPHAD modeling

International Nuclear Information System (INIS)

Saengdeejing, Arkapol; Saal, James E.; Manga, Venkateswara Rao; Liu Zikui

2012-01-01

The energetics of defects in B 4+x C boron carbide and β-boron are studied through first-principles calculations, the supercell phonon approach and the Debye–Grüneisen model. It is found that suitable sublattice models for β-boron and B 4+x C are B 101 (B,C) 4 and B 11 (B,C) (B,C,Va) (B,Va) (B,C,Va), respectively. The thermodynamic properties of B 4+x C, β-boron, liquid and graphite are modeled using the CALPHAD approach based on the thermochemical data from first-principles calculations and experimental phase equilibrium data in the literature. The concentrations of various defects are then predicted as a function of carbon composition and temperature.

First-Principles View on Photoelectrochemistry: Water-Splitting as Case Study

Directory of Open Access Journals (Sweden)

Anders Hellman

2017-06-01

Full Text Available Photoelectrochemistry is truly an interdisciplinary field; a natural nexus between chemistry and physics. In short, photoelectrochemistry can be divided into three sub-processes, namely (i the creation of electron-hole pairs by light absorption; (ii separation/transport on the charge carriers and finally (iii the water splitting reaction. The challenge is to understand all three processes on a microscopic scale and, perhaps even more importantly, how to combine the processes in an optimal way. This review will highlight some first-principles insights to the above sub-processes, in~particular as they occur using metal oxides. Based on these insights, challenges and future directions of first-principles methods in the field of photoelectrochemistry will be discussed.

First-principles and classical molecular dynamics study of threshold displacement energy in beryllium

Energy Technology Data Exchange (ETDEWEB)

Vladimirov, P.V. [Institute for Applied Materials – Applied Materials Physics, Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe (Germany); Borodin, V.A., E-mail: Borodin_VA@nrcki.ru [National Research Center “Kurchatov Institute”, 123182 Moscow (Russian Federation); NRNU MEPhI, 115409 Moscow (Russian Federation)

2017-02-15

Highlights: • Beryllium is a functional material of future fusion reactors. • The threshold displacement energy by fast particles is studied. • Classical and first principles simulations are used. - Abstract: Beryllium selected as a neutron multiplier material for the tritium breeding blanket of fusion reactor should withstand high doses of fast neutron irradiation. The damage produced by irradiation is usually evaluated assuming that the number of atomic displacements to the threshold displacement energy, E{sub d}, which is considered as an intrinsic material parameter. In this work the value of E{sub d} for hcp beryllium is estimated simultaneously from classical and first-principles molecular dynamics simulations. Quite similar quantitative pictures of defect production are observed in both simulation types, though the predicted displacement threshold values seem to be approximately two times higher in the first-principles approach. We expect that, after more detailed first-principles investigations, this approach can be used for scaling the damage prediction predictions by classical molecular dynamics, opening a way for more consistent calculations of displacement damage in materials.

Towards first principles modeling of electrochemical electrode-electrolyte interfaces

DEFF Research Database (Denmark)

Nielsen, Malte; Björketun, Mårten; Hansen, Martin Hangaard

2015-01-01

We present a mini-perspective on the development of first principles modeling of electrochemical interfaces. We show that none of the existing methods deal with all the thermodynamic constraints that the electrochemical environment imposes on the structure of the interface. We present two...

First principles study of lithium insertion in bulk silicon

KAUST Repository

Wan, Wenhui; Zhang, Qianfan; Cui, Yi; Wang, Enge

2010-01-01

Si is an important anode material for the next generation of Li ion batteries. Here the energetics and dynamics of Li atoms in bulk Si have been studied at different Li concentrations on the basis of first principles calculations. It is found

First principles studies of multiferroic materials

International Nuclear Information System (INIS)

Picozzi, Silvia; Ederer, Claude

2009-01-01

Multiferroics, materials where spontaneous long-range magnetic and dipolar orders coexist, represent an attractive class of compounds, which combine rich and fascinating fundamental physics with a technologically appealing potential for applications in the general area of spintronics. Ab initio calculations have significantly contributed to recent progress in this area, by elucidating different mechanisms for multiferroicity and providing essential information on various compounds where these effects are manifestly at play. In particular, here we present examples of density-functional theory investigations for two main classes of materials: (a) multiferroics where ferroelectricity is driven by hybridization or purely structural effects, with BiFeO 3 as the prototype material, and (b) multiferroics where ferroelectricity is driven by correlation effects and is strongly linked to electronic degrees of freedom such as spin-, charge-, or orbital-ordering, with rare-earth manganites as prototypes. As for the first class of multiferroics, first principles calculations are shown to provide an accurate qualitative and quantitative description of the physics in BiFeO 3 , ranging from the prediction of large ferroelectric polarization and weak ferromagnetism, over the effect of epitaxial strain, to the identification of possible scenarios for coupling between ferroelectric and magnetic order. For the second class of multiferroics, ab initio calculations have shown that, in those cases where spin-ordering breaks inversion symmetry (e.g. in antiferromagnetic E-type HoMnO 3 ), the magnetically induced ferroelectric polarization can be as large as a few μC cm -2 . The examples presented point the way to several possible avenues for future research: on the technological side, first principles simulations can contribute to a rational materials design, aimed at identifying spintronic materials that exhibit ferromagnetism and ferroelectricity at or above room temperature. On the

A first-principles study of short range order in Cu-Zn

International Nuclear Information System (INIS)

Slutter, M.; Turchi, P.E.A.; Johnson, D.D.; Nicholson, D.M.; Stocks, G.M.; Pinski, F.J.

1990-01-01

Recently, measurements of short-range order (SRO) diffuse neutron scattering intensity have been performed on quenched Cu-Zn alloys with 22.4 to 31.1 atomic percent (a/o) Zn, and pair interactions were obtained by inverse Monte Carlo simulation. These results are compared to SRO intensities and effective pair interactions obtained from first-principles electronic structure calculations. The theoretical SRO intensities were calculated with the cluster variation method (CVM) in the tetrahedron-octahedron approximation with first-principles pain interactions as input. More generally, phase stability in the Cu-Zn alloy system is discussed, using ab-initio energetic properties

Forecast of Piezoelectric Properties of Crystalline Materials from First Principles Calculation

International Nuclear Information System (INIS)

Zheng Yanqing; Shi Erwei; Chen Jianjun; Zhang Tao; Song Lixin

2006-01-01

In this paper, forecast of piezoelectric tensors are presented. Piezo crystals including quartz, quartz-like crystals, known and novel crystals of langasite-type structure are treated with density-functional perturb theory (DFPT) using plane-wave pseudopotentials method, within the local density approximation (LDA) to the exchange-correlation functional. Compared with experimental results, the ab initio calculation results have quantitative or semi-quantitative accuracy. It is shown that first principles calculation opens a door to the search and design of new piezoelectric material. Further application of first principles calculation to forecast the whole piezoelectric properties are also discussed

First Principles Calculations for X-ray Resonant Spectra and Elastic Properties

International Nuclear Information System (INIS)

Yongbin Lee

2006-01-01

In this thesis, we discuss applications of first principles methods to x-ray resonant spectra and elastic properties calculation. We start with brief reviews about theoretical background of first principles methods, such as density functional theory, local density approximation (LDA), LDA+U, and the linear augmented plane wave (LAPW) method to solve Kohn-Sham equations. After that we discuss x-ray resonant scattering (XRMS), x-ray magnetic circular dichroism (XMCD) and the branching problem in the heavy rare earths Ledges. In the last chapter we discuss the elastic properties of the second hardest material AlMgB 14

Hierarchical Coupling of First-Principles Molecular Dynamics with Advanced Sampling Methods.

Science.gov (United States)

Sevgen, Emre; Giberti, Federico; Sidky, Hythem; Whitmer, Jonathan K; Galli, Giulia; Gygi, Francois; de Pablo, Juan J

2018-05-14

We present a seamless coupling of a suite of codes designed to perform advanced sampling simulations, with a first-principles molecular dynamics (MD) engine. As an illustrative example, we discuss results for the free energy and potential surfaces of the alanine dipeptide obtained using both local and hybrid density functionals (DFT), and we compare them with those of a widely used classical force field, Amber99sb. In our calculations, the efficiency of first-principles MD using hybrid functionals is augmented by hierarchical sampling, where hybrid free energy calculations are initiated using estimates obtained with local functionals. We find that the free energy surfaces obtained from classical and first-principles calculations differ. Compared to DFT results, the classical force field overestimates the internal energy contribution of high free energy states, and it underestimates the entropic contribution along the entire free energy profile. Using the string method, we illustrate how these differences lead to different transition pathways connecting the metastable minima of the alanine dipeptide. In larger peptides, those differences would lead to qualitatively different results for the equilibrium structure and conformation of these molecules.

First-principles study of electron transport through monatomic Al and Na wires

DEFF Research Database (Denmark)

Kobayashi, Nobuhiko; Brandbyge, Mads; Tsukada, Masaru

2000-01-01

We present first-principles calculations of electron transport, in particular, the conduction channels of monatomic Al and Na atom wires bridged between metallic jellium electrodes. The electronic structures are calculated by the first-principles recursion-transfer matrix method, and the conduction...... channels are investigated using the eigenchannel decomposition (ECD) of the conductance, the local density of states (LDOS), and the current density. The ECD is different from the conventional decomposition of atomic orbitals, and the study of decomposed electronic structures is shown to be effective...

Adsorption of organic molecules on mineral surfaces studied by first-principle calculations: A review.

Science.gov (United States)

Zhao, Hongxia; Yang, Yong; Shu, Xin; Wang, Yanwei; Ran, Qianping

2018-04-09

First-principle calculations, especially by the density functional theory (DFT) methods, are becoming a power technique to study molecular structure and properties of organic/inorganic interfaces. This review introduces some recent examples on the study of adsorption models of organic molecules or oligomers on mineral surfaces and interfacial properties obtained from first-principles calculations. The aim of this contribution is to inspire scientists to benefit from first-principle calculations and to apply the similar strategies when studying and tailoring interfacial properties at the atomistic scale, especially for those interested in the design and development of new molecules and new products. Copyright © 2017. Published by Elsevier B.V.

First-principles calculations of novel materials

Science.gov (United States)

Sun, Jifeng

Computational material simulation is becoming more and more important as a branch of material science. Depending on the scale of the systems, there are many simulation methods, i.e. first-principles calculation (or ab-initio), molecular dynamics, mesoscale methods and continuum methods. Among them, first-principles calculation, which involves density functional theory (DFT) and based on quantum mechanics, has become to be a reliable tool in condensed matter physics. DFT is a single-electron approximation in solving the many-body problems. Intrinsically speaking, both DFT and ab-initio belong to the first-principles calculation since the theoretical background of ab-initio is Hartree-Fock (HF) approximation and both are aimed at solving the Schrodinger equation of the many-body system using the self-consistent field (SCF) method and calculating the ground state properties. The difference is that DFT introduces parameters either from experiments or from other molecular dynamic (MD) calculations to approximate the expressions of the exchange-correlation terms. The exchange term is accurately calculated but the correlation term is neglected in HF. In this dissertation, DFT based first-principles calculations were performed for all the novel materials and interesting materials introduced. Specifically, the DFT theory together with the rationale behind related properties (e.g. electronic, optical, defect, thermoelectric, magnetic) are introduced in Chapter 2. Starting from Chapter 3 to Chapter 5, several representative materials were studied. In particular, a new semiconducting oxytelluride, Ba2TeO is studied in Chapter 3. Our calculations indicate a direct semiconducting character with a band gap value of 2.43 eV, which agrees well with the optical experiment (˜ 2.93 eV). Moreover, the optical and defects properties of Ba2TeO are also systematically investigated with a view to understanding its potential as an optoelectronic or transparent conducting material. We find

First-principles Electronic Structure Calculations for Scintillation Phosphor Nuclear Detector Materials

Science.gov (United States)

Canning, Andrew

2013-03-01

Inorganic scintillation phosphors (scintillators) are extensively employed as radiation detector materials in many fields of applied and fundamental research such as medical imaging, high energy physics, astrophysics, oil exploration and nuclear materials detection for homeland security and other applications. The ideal scintillator for gamma ray detection must have exceptional performance in terms of stopping power, luminosity, proportionality, speed, and cost. Recently, trivalent lanthanide dopants such as Ce and Eu have received greater attention for fast and bright scintillators as the optical 5d to 4f transition is relatively fast. However, crystal growth and production costs remain challenging for these new materials so there is still a need for new higher performing scintillators that meet the needs of the different application areas. First principles calculations can provide a useful insight into the chemical and electronic properties of such materials and hence can aid in the search for better new scintillators. In the past there has been little first-principles work done on scintillator materials in part because it means modeling f electrons in lanthanides as well as complex excited state and scattering processes. In this talk I will give an overview of the scintillation process and show how first-principles calculations can be applied to such systems to gain a better understanding of the physics involved. I will also present work on a high-throughput first principles approach to select new scintillator materials for fabrication as well as present more detailed calculations to study trapping process etc. that can limit their brightness. This work in collaboration with experimental groups has lead to the discovery of some new bright scintillators. Work supported by the U.S. Department of Homeland Security and carried out under U.S. Department of Energy Contract no. DE-AC02-05CH11231 at Lawrence Berkeley National Laboratory.

A first principle study of band structure of III-nitride compounds

Energy Technology Data Exchange (ETDEWEB)

Ahmed, Rashid [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)]. E-mail: rasofi@hotmail.com; Akbarzadeh, H. [Department of Physics, Isfahan University of Technology, 841546 Isfahan (Iran, Islamic Republic of); Fazal-e-Aleem [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)

2005-12-15

The band structure of both phases, zinc-blende and wurtzite, of aluminum nitride, indium nitride and gallium nitride has been studied using computational methods. The study has been done using first principle full-potential linearized augmented plane wave (FP-LAPW) method, within the framework of density functional theory (DFT). For the exchange correlation potential, generalized gradient approximation (GGA) and an alternative form of GGA proposed by Engel and Vosko (GGA-EV) have been used. Results obtained for band structure of these compounds have been compared with experimental results as well as other first principle computations. Our results show a significant improvement over other theoretical work and are closer to the experimental data.

Quantum theory from first principles an informational approach

CERN Document Server

D'Ariano, Giacomo Mauro; Perinotti, Paolo

2017-01-01

Quantum theory is the soul of theoretical physics. It is not just a theory of specific physical systems, but rather a new framework with universal applicability. This book shows how we can reconstruct the theory from six information-theoretical principles, by rebuilding the quantum rules from the bottom up. Step by step, the reader will learn how to master the counterintuitive aspects of the quantum world, and how to efficiently reconstruct quantum information protocols from first principles. Using intuitive graphical notation to represent equations, and with shorter and more efficient derivations, the theory can be understood and assimilated with exceptional ease. Offering a radically new perspective on the field, the book contains an efficient course of quantum theory and quantum information for undergraduates. The book is aimed at researchers, professionals, and students in physics, computer science and philosophy, as well as the curious outsider seeking a deeper understanding of the theory.

THERMODYNAMIC MODELING AND FIRST-PRINCIPLES CALCULATIONS

Energy Technology Data Exchange (ETDEWEB)

Turchi, P; Abrikosov, I; Burton, B; Fries, S; Grimvall, G; Kaufman, L; Korzhavyi, P; Manga, R; Ohno, M; Pisch, A; Scott, A; Zhang, W

2005-12-15

The increased application of quantum mechanical-based methodologies to the study of alloy stability has required a re-assessment of the field. The focus is mainly on inorganic materials in the solid state. In a first part, after a brief overview of the so-called ab initio methods with their approximations, constraints, and limitations, recommendations are made for a good usage of first-principles codes with a set of qualifiers. Examples are given to illustrate the power and the limitations of ab initio codes. However, despite the ''success'' of these methodologies, thermodynamics of complex multi-component alloys, as used in engineering applications, requires a more versatile approach presently afforded within CALPHAD. Hence, in a second part, the links that presently exist between ab initio methodologies, experiments, and CALPHAD approach are examined with illustrations. Finally, the issues of dynamical instability and of the role of lattice vibrations that still constitute the subject of ample discussions within the CALPHAD community are revisited in the light of the current knowledge with a set of recommendations.

First principles, thermal stability and thermodynamic assessment of the binary Ni-W system

Energy Technology Data Exchange (ETDEWEB)

Isomaeki, Iikka; Haemaelaeinen, Marko; Gasik, Michael [Aalto Univ., Espoo (Finland). School of Chemical Engineering; Braga, Maria H. [Porto Univ. (Portugal). CEMUC, Physics Engineering Dept.

2017-12-15

The Ni-W binary system was assessed using critically evaluated experimental data with assistance from first principles analysis and the CALPHAD method. The solution phases (liquid, fcc-A1 and bcc-A2) were modeled using the substitutional regular solution model. The recently discovered Ni{sub 8}W metastable phase was evaluated as Fe{sub 16}C{sub 2}- like martensite with three sublattices, and shown to be possibly stable according to first principles calculations. Ni{sub 8}W was also modeled as an interstitial compound, but the model is not good because the solubility of tungsten in nickel is very low, especially at low temperatures. There is no experimental evidence for such low solubility. The other binary compounds Ni{sub 4}W and Ni{sub 3}W were assessed as stoichiometric ones. Compared independent experimental and first principles data agree well with the calculated phase diagram using updated thermodynamic parameters.

Thermodynamic modeling of the Sc-Zn system coupled with first-principles calculation

Directory of Open Access Journals (Sweden)

Tang C.

2012-01-01

Full Text Available The Sc-Zn system has been critically reviewed and assessed by means of CALPHAD (CALculation of PHAse Diagram approach. By means of first-principles calculation, the enthalpies of formation at 0 K for the ScZn, ScZn2, Sc17Zn58, Sc3Zn17 and ScZn12 have been computed with the desire to assist thermodynamic modeling. A set of self-consistent thermodynamic parameters for the Sc-Zn system is then obtained. The calculated phase diagram and thermodynamic properties agree well with the experimental data and first-principles calculations, respectively.

Quantum Well States in Fe/Nb(001) Multilayers: First Principles Study

National Research Council Canada - National Science Library

Sliukia, Nitya N; Sen, A; Prasad, R

2007-01-01

A first principle study to understand the phenomena of interlayer exchange coupling in Fe/Nb multilayers using the linearized-muffin-tin-orbitals method within the generalized gradient approximation was performed...

Sustainability in the Qatar national dietary guidelines, among the first to incorporate sustainability principles.

Science.gov (United States)

Seed, Barbara

2015-09-01

To present one of the first national dietary guidelines that incorporates food sustainability principles into its public health recommendations. The paper outlines recommendations and utilizes an ecological framework of policy analysis to examine context, drivers, consequences and future suggestions in establishing and maintaining sustainability principles within the Qatar Dietary Guidelines. Qatar. Population of Qatar. Qatar has produced one of the first national dietary guidelines to integrate principles of food sustainability. National interest in environmental sustainability and food security, population concern over food waste (reinforced by Islamic religious law), strong authority of the Supreme Council of Health (supported by an Emirate government), a small domestic food industry and a lack of food industry influence on the guidelines have contributed to the inclusion of sustainability principles within the document. Whether these principles will be embraced or rejected by the population in the long term will likely be determined by the Dietary Guidelines Task Force and the Supreme Council of Health's commitment to educating the population about the relevance and importance of these principles and establishing champions to advocate for them.

Thermodynamic modeling of the Ca-Sn system based on finite temperature quantities from first-principles and experiment

International Nuclear Information System (INIS)

Ohno, M.; Kozlov, A.; Arroyave, R.; Liu, Z.K.; Schmid-Fetzer, R.

2006-01-01

The thermodynamic model of the Ca-Sn system was obtained, utilizing the first-principles total energies and heat capacities calculated from 0 K to the melting points of the major phases. Since the first-principles result for the formation energy of the dominating Ca 2 Sn intermetallic phase is drastically different from the reported experimental data, we performed two types of thermodynamic modeling: one based on the first-principles output and the other based on the experimental data. In the former modeling, the Gibbs energies of the intermetallic compounds were fully quantified from the first-principles finite temperature properties and the superiority of the former thermodynamic description is demonstrated. It is shown that it is the combination of finite temperature first-principle calculations and the Calphad modeling tool that provides a sound basis for identifying and deciding on conflicting key thermodynamic data in the Ca-Sn system

First-principles approach to the dynamic magnetoelectric couplings for the non-reciprocal directional dichroism in BiFeO3

Science.gov (United States)

Lee, Jun Hee; Kézsmáki, István; Fishman, Randy S.

2016-04-01

Due to the complicated magnetic and crystallographic structures of BiFeO3, its magnetoelectric (ME) couplings and microscopic model Hamiltonian remain poorly understood. By employing a first-principles approach, we uncover all possible ME couplings associated with the spin-current (SC) and exchange-striction (ES) polarizations, and construct an appropriate Hamiltonian for the long-range spin-cycloid in BiFeO3. First-principles calculations are used to understand the microscopic origins of the ME couplings. We find that inversion symmetries broken by ferroelectric and antiferroelectric distortions induce the SC and the ES polarizations, which cooperatively produce the dynamic ME effects in BiFeO3. A model motivated by first principles reproduces the absorption difference of counter-propagating light beams called non-reciprocal directional dichroism. The current paper focuses on the spin-driven (SD) polarizations produced by a dynamic electric field, i.e. the dynamic ME couplings. Due to the inertial properties of Fe, the dynamic SD polarizations differ significantly from the static SD polarizations. Our systematic approach can be generally applied to any multiferroic material, laying the foundation for revealing hidden ME couplings on the atomic scale and for exploiting optical ME effects in the next generation of technological devices such as optical diodes. This manuscript has been written by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan.

Principles of a new type of great acceptance mass separator

International Nuclear Information System (INIS)

Chabert, A.; Ricaud, C.; Bru, B.

1993-01-01

Principles of a new method for performing selection of given charge/mass ratio ions among a stream of contaminating ions with very close charge/mass ratios, are presented. The mass spectrometer is basically composed of a series of three element sets carrying out the following functions: in a first section, a mass defect is transformed in a phase shift; a HF cavity (de-buncher) then transforms the phase shift in an energy variation; and an energy analysis magnetic system which transforms the energy difference in a radial separation. The transverse movement of the beam is thus controlled all along the course, and an excellent longitudinal capture of the ions is obtained thus ensuring a good global transmission

First-principles simulations of heat transport

Science.gov (United States)

Puligheddu, Marcello; Gygi, Francois; Galli, Giulia

2017-11-01

Advances in understanding heat transport in solids were recently reported by both experiment and theory. However an efficient and predictive quantum simulation framework to investigate thermal properties of solids, with the same complexity as classical simulations, has not yet been developed. Here we present a method to compute the thermal conductivity of solids by performing ab initio molecular dynamics at close to equilibrium conditions, which only requires calculations of first-principles trajectories and atomic forces, thus avoiding direct computation of heat currents and energy densities. In addition the method requires much shorter sequential simulation times than ordinary molecular dynamics techniques, making it applicable within density functional theory. We discuss results for a representative oxide, MgO, at different temperatures and for ordered and nanostructured morphologies, showing the performance of the method in different conditions.

Thermodynamics and elastic properties of Ir from first-principle calculations

International Nuclear Information System (INIS)

Li Qiang; Huang Duohui; Cao Qilong; Wang Fanhou

2013-01-01

Within the framework of the quasiharmonic approximation, the thermodynamics and elastic properties, including phonon dispersion curves, equation of state, linear thermal expansion coefficient and temperature-dependent entropy, enthalpy, heat capacity, elastic constants, bulk modulus, shear modulus, Young's modulus of Ir have been studied using first-principles projector-augmented wave method. The results revealed that the predicted phonon dispersion curves of Ir are in agreement with the experimental measurements by neutron diffractions. Considering the thermal electronic contribution to Helmholtz free energy, the calculated entropy, enthalpy, heat capacity and linear thermal expansion co- efficient from the first-principle are consistent well with the experimental data. At 2600 K, the electronic heat capacity accounts for 17% of the total heat capacity at constant pressure, thus the thermal electronic contribution to Helmholtz free energy is very important. The predicted elastic constants, bulk modulus, shear modulus and Young's modulus at room temperature are also in agreement with the available measurements and increase with the increasing temperature. (authors)

Hippocrates' First Aphorism: Reflections on Ageless Principles for the Practice of Medicine.

Science.gov (United States)

Loscalzo, Joseph

2016-01-01

Hippocrates' first aphorism presents a structurally simple but conceptually complex series of observations on the art and science of medicine. Its principles are timeless, relevant to physicians in antiquity as well as in the current era. This article analyzes Hippocrates' aphorism in light of Galen's and others' commentaries on it and interprets the principles espoused by Hippocrates in light of the perennial challenges of the practice of medicine.

Credibility is the first principle

International Nuclear Information System (INIS)

Beecher, William

2002-01-01

The first principle of an effective public affairs program on nuclear energy is credibility. If credibility is lacking, no matter how artful the message, it will not be persuasive. There has long been a problem in the United States. For years much of the industry followed the practice, when there was an event at a nuclear power plant that resulted in an unplanned release of radioactivity, to tell the public there was 'no release' if in fact the release was below the technical specifications of what the NRC mandates as being safe. The NRC is a safety regulator. It can tell nuclear power plant operators what to do, or not do, when it comes to safety, but doesn't have the right to tell them what to say to the public. The example of an emergency exercise and the NRC press release on that occasion showed the direction how companies could be influenced to behave in order to prevent such avoidably negative news coverage, i.e. attaining credibility when public anxiety is concerned

Integration of first-principles methods and crystallographic database searches for new ferroelectrics: Strategies and explorations

International Nuclear Information System (INIS)

Bennett, Joseph W.; Rabe, Karin M.

2012-01-01

In this concept paper, the development of strategies for the integration of first-principles methods with crystallographic database mining for the discovery and design of novel ferroelectric materials is discussed, drawing on the results and experience derived from exploratory investigations on three different systems: (1) the double perovskite Sr(Sb 1/2 Mn 1/2 )O 3 as a candidate semiconducting ferroelectric; (2) polar derivatives of schafarzikite MSb 2 O 4 ; and (3) ferroelectric semiconductors with formula M 2 P 2 (S,Se) 6 . A variety of avenues for further research and investigation are suggested, including automated structure type classification, low-symmetry improper ferroelectrics, and high-throughput first-principles searches for additional representatives of structural families with desirable functional properties. - Graphical abstract: Integration of first-principles methods with crystallographic database mining, for the discovery and design of novel ferroelectric materials, could potentially lead to new classes of multifunctional materials. Highlights: ► Integration of first-principles methods and database mining. ► Minor structural families with desirable functional properties. ► Survey of polar entries in the Inorganic Crystal Structural Database.

Parallelization for first principles electronic state calculation program

International Nuclear Information System (INIS)

Watanabe, Hiroshi; Oguchi, Tamio.

1997-03-01

In this report we study the parallelization for First principles electronic state calculation program. The target machines are NEC SX-4 for shared memory type parallelization and FUJITSU VPP300 for distributed memory type parallelization. The features of each parallel machine are surveyed, and the parallelization methods suitable for each are proposed. It is shown that 1.60 times acceleration is achieved with 2 CPU parallelization by SX-4 and 4.97 times acceleration is achieved with 12 PE parallelization by VPP 300. (author)

Ammonia synthesis and decomposition on a Ru-based catalyst modeled by first-principles

DEFF Research Database (Denmark)

Hellman, A.; Honkala, Johanna Karoliina; Remediakis, Ioannis

2009-01-01

A recently published first-principles model for the ammonia synthesis on an unpromoted Ru-based catalyst is extended to also describe ammonia decomposition. In addition, further analysis concerning trends in ammonia productivity, surface conditions during the reaction, and macro-properties, such ......A recently published first-principles model for the ammonia synthesis on an unpromoted Ru-based catalyst is extended to also describe ammonia decomposition. In addition, further analysis concerning trends in ammonia productivity, surface conditions during the reaction, and macro......-properties, such as apparent activation energies and reaction orders are provided. All observed trends in activity are captured by the model and the absolute value of ammonia synthesis/decomposition productivity is predicted to within a factor of 1-100 depending on the experimental conditions. Moreover it is shown: (i......) that small changes in the relative adsorption potential energies are sufficient to get a quantitative agreement between theory and experiment (Appendix A) and (ii) that it is possible to reproduce results from the first-principles model by a simple micro-kinetic model (Appendix B)....

First-principle optimal local pseudopotentials construction via optimized effective potential method

International Nuclear Information System (INIS)

Mi, Wenhui; Zhang, Shoutao; Wang, Yanchao; Ma, Yanming; Miao, Maosheng

2016-01-01

The local pseudopotential (LPP) is an important component of orbital-free density functional theory, a promising large-scale simulation method that can maintain information on a material’s electron state. The LPP is usually extracted from solid-state density functional theory calculations, thereby it is difficult to assess its transferability to cases involving very different chemical environments. Here, we reveal a fundamental relation between the first-principles norm-conserving pseudopotential (NCPP) and the LPP. On the basis of this relationship, we demonstrate that the LPP can be constructed optimally from the NCPP for a large number of elements using the optimized effective potential method. Specially, our method provides a unified scheme for constructing and assessing the LPP within the framework of first-principles pseudopotentials. Our practice reveals that the existence of a valid LPP with high transferability may strongly depend on the element.

First-Principles Definition and Measurement of Planetary Electromagnetic-Energy Budget

Science.gov (United States)

Mishchenko, Michael I.; Lock, James A.; Lacis, Andrew A.; Travis, Larry D.; Cairns, Brian

2016-01-01

The imperative to quantify the Earths electromagnetic-energy budget with an extremely high accuracy has been widely recognized but has never been formulated in the framework of fundamental physics. In this paper we give a first-principles definition of the planetary electromagnetic-energy budget using the Poynting- vector formalism and discuss how it can, in principle, be measured. Our derivation is based on an absolute minimum of theoretical assumptions, is free of outdated notions of phenomenological radiometry, and naturally leads to the conceptual formulation of an instrument called the double hemispherical cavity radiometer (DHCR). The practical measurement of the planetary energy budget would require flying a constellation of several dozen planet-orbiting satellites hosting identical well-calibrated DHCRs.

Electronic structure and ionicity of actinide oxides from first principles

DEFF Research Database (Denmark)

Petit, Leon; Svane, Axel; Szotek, Z.

2010-01-01

The ground-state electronic structures of the actinide oxides AO, A2O3, and AO2 (A=U, Np, Pu, Am, Cm, Bk, and Cf) are determined from first-principles calculations, using the self-interaction corrected local spin-density approximation. Emphasis is put on the degree of f-electron localization, whi...

Progress in basic principles of limitation in radiation protection

International Nuclear Information System (INIS)

Ramzaev, P.V.; Tarasov, S.I.; Troitskaya, M.N.; Ermolaeva, A.P.

1977-01-01

For purposes of limitation of harmful factors, e.g. radiation, it is proposed to divide all countless numbers of biological effects into three groups: 1) social important effects (ultimate and effects); 2) intermediate effects (different diseases etc.), which are connected with and controlled by the first group; 3) pure biological effects, importance of which is not known. To determine the first group effects there are identified four indices describing all significant sides of human life: time of life, life-time integral of mental and physical capacity for work, aesthetical satisfaction from organism itself, reproduction of descendants. They reflect the main social and individual interests related to functioning of organism. On the base of weighing these indices it is suggested the united general index of health in form of time of a full life. The united index can be used for different principles of limitation (based on threshold, acceptable risk, maximum benefit). To realize the principle of maximum public benefit as ideal principle in the future limitation all benefit and detriment from utilization of harmful sources must be expressed in the united index of health (instead of money), which is the greatest value of individual and society. Authors suggest to standartize ionizing radiation on the general methodological approaches that were acceptable to non-ionizing factors too

Engineering drawing from first principles using AutoCAD

CERN Document Server

Maguire, Dennis E

1998-01-01

Engineering Drawing From First Principles is a guide to good draughting for students of engineering who need to learn how to produce technically accurate and detailed designs to British and International Standards. Written by Dennis Maguire, an experienced author and City and Guilds chief examiner, this text is designed for use on Further Education and University courses where a basic understanding of draughtsmanship and CAD is necessary. Although not written as an AutoCAD tutor, the book will be a useful introduction to good CAD practice.Part of the Revision and Self-Assessmen

Obtaining the electrostatic screening from first principles

International Nuclear Information System (INIS)

Shaviv, N.J.; Shaviv, G.

2003-01-01

We derive the electrostatic screening effect from first principles and show the basic properties of the screening process. We in particular show that under the conditions prevailing in the Sun the number of particles in the Debye sphere is of the order of unity. Consequently; fluctuations play a dominant role in the screening process. The fluctuations lead to an effective time dependent potential. Particles with low kinetic energy lose on the average energy to the plasma and vice versa with high energy particles. We derive general conditions on the screening energy and show under what conditions the Salpeter approximation is obtained. The connection between the screening and relaxation processes in the plasma is exposed

First-principles modeling of magnetic misfit interfaces

KAUST Repository

Grytsiuk, Sergii

2013-08-16

We investigate the structural and magnetic properties of interfaces with large lattice mismatch, choosing Pt/Co and Au/Co as prototypes. For our first-principles calculations, we reduce the lattice mismatch to 0.2% by constructing Moiré supercells. Our results show that the roughness and atomic density, and thus the magnetic properties, depend strongly on the substrate and thickness of the Co slab. An increasing thickness leads to the formation of a Co transition layer at the interface, especially for Pt/Co due to strong Pt-Co interaction. A Moiré supercell with a transition layer is found to reproduce the main experimental findings and thus turns out to be the appropriate model for simulating magnetic misfit interfaces.

First-principles modeling of magnetic misfit interfaces

KAUST Repository

Grytsyuk, Sergiy; Schwingenschlö gl, Udo

2013-01-01

We investigate the structural and magnetic properties of interfaces with large lattice mismatch, choosing Pt/Co and Au/Co as prototypes. For our first-principles calculations, we reduce the lattice mismatch to 0.2% by constructing Moiré supercells. Our results show that the roughness and atomic density, and thus the magnetic properties, depend strongly on the substrate and thickness of the Co slab. An increasing thickness leads to the formation of a Co transition layer at the interface, especially for Pt/Co due to strong Pt-Co interaction. A Moiré supercell with a transition layer is found to reproduce the main experimental findings and thus turns out to be the appropriate model for simulating magnetic misfit interfaces.

First principles calculation of two dimensional antimony and antimony arsenide

Energy Technology Data Exchange (ETDEWEB)

Pillai, Sharad Babu, E-mail: sbpillai001@gmail.com; Narayan, Som; Jha, Prafulla K. [Department. of Physics, Faculty of Science, The M. S. University of Baroda, Vadodara-390002 (India); Dabhi, Shweta D. [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar-364001 (India)

2016-05-23

This work focuses on the strain dependence of the electronic properties of two dimensional antimony (Sb) material and its alloy with As (SbAs) using density functional theory based first principles calculations. Both systems show indirect bandgap semiconducting character which can be transformed into a direct bandgap material with the application of relatively small strain.

A maximum principle for the first-order Boltzmann equation, incorporating a potential treatment of voids

International Nuclear Information System (INIS)

Schofield, S.L.

1988-01-01

Ackroyd's generalized least-squares method for solving the first-order Boltzmann equation is adapted to incorporate a potential treatment of voids. The adaptation comprises a direct least-squares minimization allied with a suitably-defined bilinear functional. The resulting formulation gives rise to a maximum principle whose functional does not contain terms of the type that have previously led to difficulties in treating void regions. The maximum principle is derived without requiring continuity of the flux at interfaces. The functional of the maximum principle is concluded to have an Euler-Lagrange equation given directly by the first-order Boltzmann equation. (author)

First-principles lattice-gas Hamiltonian revisited: O-Pd(100)

OpenAIRE

Kappus, Wolfgang

2016-01-01

The methodology of deriving an adatom lattice-gas Hamiltonian (LGH) from first principles (FP) calculations is revisited. Such LGH cluster expansions compute a large set of lateral pair-, trio-, quarto interactions by solving a set of linear equations modelling regular adatom configurations and their FP energies. The basic assumption of truncating interaction terms beyond fifth nearest neighbors does not hold when adatoms show longer range interactions, e.g. substrate mediated elastic interac...

Absolute Hydration Free Energy of Proton from First Principles Electronic Structure Calculations

International Nuclear Information System (INIS)

Zhan, Chang-Guo; Dixon, David A.

2001-01-01

The absolute hydration free energy of the proton, DGhyd298(H+), is one of the fundamental quantities for the thermodynamics of aqueous systems. Its exact value remains unknown despite extensive experimental and computational efforts. We report a first-principles determination of DGhyd298(H+) by using the latest developments in electronic structure theory and massively parallel computers. DGhyd298(H+) is accurately predicted to be -262.4 kcal/mol based on high-level, first-principles solvation-included electronic structure calculations. The absolute hydration free energies of other cations can be obtained by using appropriate available thermodynamic data in combination with this value. The high accuracy of the predicted absolute hydration free energy of proton is confirmed by applying the same protocol to predict DGhyd298(Li+)

First-principles investigation of mechanical properties of silicene, germanene and stanene

Science.gov (United States)

Mortazavi, Bohayra; Rahaman, Obaidur; Makaremi, Meysam; Dianat, Arezoo; Cuniberti, Gianaurelio; Rabczuk, Timon

2017-03-01

Two-dimensional allotropes of group-IV substrates including silicene, germanene and stanene have recently attracted considerable attention in nanodevice fabrication industry. These materials involving the buckled structure have been experimentally fabricated lately. In this study, first-principles density functional theory calculations were utilized to investigate the mechanical properties of single-layer and free-standing silicene, germanene and stanene. Uniaxial tensile and compressive simulations were carried out to probe and compare stress-strain properties; such as the Young's modulus, Poisson's ratio and ultimate strength. We evaluated the chirality effect on the mechanical response and bond structure of the 2D substrates. Our first-principles simulations suggest that in all studied samples application of uniaxial loading can alter the electronic nature of the buckled structures into the metallic character. Our investigation provides a general but also useful viewpoint with respect to the mechanical properties of silicene, germanene and stanene.

Study on the high level radioactive wastes geological isolation seen from the social acceptance of science and technology. (1) The explanation based on the principle of risk and benefit for another field specialist

International Nuclear Information System (INIS)

Wada, Ryutaro; Tanaka, Satoru; Nagasaki, Shinya

2009-01-01

Generally speaking, a vast, advanced and unfamiliar science and technology is unacceptable by public for the fear of its unknown nature. The siting problem for the disposal of high level radioactive wastes is one of the typical examples. This study examined the desirable research scheme for geological disposal of the high level radioactive wastes seen from social acceptance of science and technology in the deductive approach by the technical essence described in the first report. As the safety is the most prioritized concern in the research of radioactive waste disposal, the correlation between safety and cost has not been argued. Therefore, the argument has only turned in seeking for limitless safety without paying attention to an economic principle. In this report, as the examination evolving from a social acceptability, the author tries to explain the safety together with cost information in accordance with the principle of the risk benefit. As a result, it turned out that the relation between the existing Japanese default proposal (H12 report) and overseas examples can be figured out to explain their relative position by the safety and cost correlation diagram made in accordance with the risk benefit principle. The nuclear field specialist can discuss a relative location of the Japanese disposal concept by this correlation diagram with another field specialist. (author)

First-principle approach based bandgap engineering for cubic boron nitride doped with group IIA elements

Science.gov (United States)

Li, Yubo; Wang, Pengtao; Hua, Fei; Zhan, Shijie; Wang, Xiaozhi; Luo, Jikui; Yang, Hangsheng

2018-03-01

Electronic properties of cubic boron nitride (c-BN) doped with group IIA elements were systematically investigated using the first principle calculation based on density functional theory. The electronic bandgap of c-BN was found to be narrowed when the impurity atom substituted either the B (IIA→B) or the N (IIA→N) atom. For IIA→B, a shallow accept level degenerated into valence band (VB); while for IIA→N, a shallow donor level degenerated conduction band (CB). In the cases of IIBe→N and IIMg→N, deep donor levels were also induced. Moreover, a zigzag bandgap narrowing pattern was found, which is in consistent with the variation pattern of dopants' radius of electron occupied outer s-orbital. From the view of formation energy, the substitution of B atom under N-rich conditions and the substitution of N atom under B-rich conditions were energetically favored. Our simulation results suggested that Mg and Ca are good candidates for p-type dopants, and Ca is the best candidate for n-type dopant.

Exploring the nucleon structure from first principles of QCD

Energy Technology Data Exchange (ETDEWEB)

Bietenholz, W. [Universidad Nacional Autonoma de Mexico (Mexico). Inst. de Ciencias Nucleares; Cundy, N.; Goeckeler, M. [Regensburg Univ. (DE). Inst. fuer Theoretische Physik] (and others)

2010-04-15

Quantum Chromodynamics (QCD) is generally assumed to be the fundamental theory underlying nuclear physics. In recent years there is progress towards investigating the nucleon structure from first principles of QCD. Although this structure is best revealed in Deep Inelastic Scattering, a consistent analysis has to be performed in a fully non-perturbative scheme. The only known method for this purpose are lattice simulations. We first sketch the ideas of Monte Carlo simulations in lattice gauge theory. Then we comment in particular on the issues of chiral symmetry and operator mixing. Finally we present our results for the Bjorken variable of a single quark, and for the second Nachtmann moment of the nucleon structure functions. (orig.)

Exploring the nucleon structure from first principles of QCD

International Nuclear Information System (INIS)

Bietenholz, W.; Cundy, N.; Goeckeler, M.

2010-04-01

Quantum Chromodynamics (QCD) is generally assumed to be the fundamental theory underlying nuclear physics. In recent years there is progress towards investigating the nucleon structure from first principles of QCD. Although this structure is best revealed in Deep Inelastic Scattering, a consistent analysis has to be performed in a fully non-perturbative scheme. The only known method for this purpose are lattice simulations. We first sketch the ideas of Monte Carlo simulations in lattice gauge theory. Then we comment in particular on the issues of chiral symmetry and operator mixing. Finally we present our results for the Bjorken variable of a single quark, and for the second Nachtmann moment of the nucleon structure functions. (orig.)

First-Principles Petascale Simulations for Predicting Deflagration to Detonation Transition in Hydrogen-Oxygen Mixtures

Energy Technology Data Exchange (ETDEWEB)

Khokhlov, Alexei [Univ. of Chicago, IL (United States). Dept. of Astronomy and Astrophysics. Enrico Fermi Inst.; Austin, Joanna [Argonne National Lab. (ANL), Argonne, IL (United States). Argonne Leadership Computing Facility; Bacon, C. [Univ. of Illinois, Urbana, IL (United States). Dept. of Aerospace Engineering

2015-03-02

Hydrogen has emerged as an important fuel across a range of industries as a means of achieving energy independence and to reduce emissions. DDT and the resulting detonation waves in hydrogen-oxygen can have especially catastrophic consequences in a variety of industrial and energy producing settings related to hydrogen. First-principles numerical simulations of flame acceleration and DDT are required for an in-depth understanding of the phenomena and facilitating design of safe hydrogen systems. The goals of this project were (1) to develop first-principles petascale reactive flow Navier-Stokes simulation code for predicting gaseous high-speed combustion and detonation (HSCD) phenomena and (2) demonstrate feasibility of first-principles simulations of rapid flame acceleration and deflagration-to-detonation transition (DDT) in stoichiometric hydrogen-oxygen mixture (2H₂ + O₂). The goals of the project have been accomplished. We have developed a novel numerical simulation code, named HSCD, for performing first-principles direct numerical simulations of high-speed hydrogen combustion. We carried out a series of validating numerical simulations of inert and reactive shock reflection experiments in shock tubes. We then performed a pilot numerical simulation of flame acceleration in a long pipe. The simulation showed the transition of the rapidly accelerating flame into a detonation. The DDT simulations were performed using BG/Q Mira at the Argonne National Laboratory, currently the fourth fastest super-computer in the world.

First principles molecular dynamics of metal/water interfaces under bias potential

Science.gov (United States)

Pedroza, Luana; Brandimarte, Pedro; Rocha, Alexandre; Fernandez-Serra, Marivi

2014-03-01

Understanding the interaction of the water-metal system at an atomic level is extremely important in electrocatalysts for fuel cells, photocatalysis among other systems. The question of the interface energetics involves a detailed study of the nature of the interactions between water-water and water-substrate. A first principles description of all components of the system is the most appropriate methodology in order to advance understanding of electrochemically processes. In this work we describe, using first principles molecular dynamics simulations, the dynamics of a combined surface(Au and Pd)/water system both in the presence and absence of an external bias potential applied to the electrodes, as one would come across in electrochemistry. This is accomplished using a combination of density functional theory (DFT) and non-equilibrium Green's functions methods (NEGF), thus accounting for the fact that one is dealing with an out-of-equilibrium open system, with and without van der Waals interactions. DOE Early Career Award No. DE-SC0003871.

First-principles studies of electronic, transport and bulk properties of pyrite FeS2

Directory of Open Access Journals (Sweden)

Dipendra Banjara

2018-02-01

Full Text Available We present results from first principle, local density approximation (LDA calculations of electronic, transport, and bulk properties of iron pyrite (FeS2. 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, total and partial densities of states, electron effective masses, and the bulk modulus. Our calculated indirect band gap of 0.959 eV (0.96, using an experimental lattice constant of 5.4166 Å, at room temperature, is in agreement with the measured indirect values, for bulk samples, ranging from 0.84 eV to 1.03 ± 0.05 eV. Our calculated bulk modulus of 147 GPa is practically in agreement with the experimental value of 145 GPa. The calculated, partial densities of states reproduced the splitting of the Fe d bands to constitute the dominant upper most valence and lower most conduction bands, separated by the generally accepted, indirect, experimental band gap of 0.95 eV.

Variational principles of fluid mechanics and electromagnetism: imposition and neglect of the Lin constraint

International Nuclear Information System (INIS)

Allen, R.R. Jr.

1987-01-01

The Lin constraint has been utilized by a number of authors who have sought to develop Eulerian variational principles in both fluid mechanics and electromagnetics (or plasmadynamics). This dissertation first reviews the work of earlier authors concerning the development of variational principles in both the Eulerian and Lagrangian nomenclatures. In the process, it is shown whether or not the Euler-Lagrange equations that result from the variational principles are equivalent to the generally accepted equations of motion. In particular, it is shown in the case of several Eulerian variational principles that imposition of the Lin constraint results in Euler-Lagrange equations equivalent to the generally accepted equations of motion, whereas neglect of the Lin constraint results in restrictive Euler-Lagrange equations. In an effort to improve the physical motivation behind introduction of the Lin constraint, a new variational constraint is developed based on teh concept of surface forces within a fluid. Additionally, it is shown that a quantity often referred to as the canonical momentum of a charged fluid is not always a constant of the motion of the fluid; and it is demonstrated that there does not exist an unconstrained Eulerian variational principle giving rise to the generally accepted equations of motion for both a perfect fluid and a cold, electromagnetic fluid

First-principles structures for the close-packed and the 7/2 motif of collagen

DEFF Research Database (Denmark)

Jalkanen, Karl J.; Olsen, Kasper; Knapp-Mohammady, Michaela

2012-01-01

The newly proposed close-packed motif for collagen and the more established 7/2 structure are investigated and compared. First-principles semi-empirical wave function theory and Kohn-Sham density functional theory are applied in the study of these relatively large and complex structures. The stru......The newly proposed close-packed motif for collagen and the more established 7/2 structure are investigated and compared. First-principles semi-empirical wave function theory and Kohn-Sham density functional theory are applied in the study of these relatively large and complex structures...

First principles study of electronic, elastic and thermal properties of lutetium intermetallics

International Nuclear Information System (INIS)

Pagare, Gitanjali; Chouhan, Sunil Singh; Soni, Pooja; Sanyal, S.P.; Rajagopalan, M.

2011-01-01

In the present work, the electronic, elastic and thermal properties of lutetium intermetallics LuX have been studied theoretically by using first principles calculations based on density functional theory (DFT) with the generalized gradient approximation (GCA)

TOPICAL REVIEW: First principles studies of multiferroic materials

Science.gov (United States)

Picozzi, Silvia; Ederer, Claude

2009-07-01

Multiferroics, materials where spontaneous long-range magnetic and dipolar orders coexist, represent an attractive class of compounds, which combine rich and fascinating fundamental physics with a technologically appealing potential for applications in the general area of spintronics. Ab initio calculations have significantly contributed to recent progress in this area, by elucidating different mechanisms for multiferroicity and providing essential information on various compounds where these effects are manifestly at play. In particular, here we present examples of density-functional theory investigations for two main classes of materials: (a) multiferroics where ferroelectricity is driven by hybridization or purely structural effects, with BiFeO3 as the prototype material, and (b) multiferroics where ferroelectricity is driven by correlation effects and is strongly linked to electronic degrees of freedom such as spin-, charge-, or orbital-ordering, with rare-earth manganites as prototypes. As for the first class of multiferroics, first principles calculations are shown to provide an accurate qualitative and quantitative description of the physics in BiFeO3, ranging from the prediction of large ferroelectric polarization and weak ferromagnetism, over the effect of epitaxial strain, to the identification of possible scenarios for coupling between ferroelectric and magnetic order. For the second class of multiferroics, ab initio calculations have shown that, in those cases where spin-ordering breaks inversion symmetry (e.g. in antiferromagnetic E-type HoMnO3), the magnetically induced ferroelectric polarization can be as large as a few µC cm-2. The examples presented point the way to several possible avenues for future research: on the technological side, first principles simulations can contribute to a rational materials design, aimed at identifying spintronic materials that exhibit ferromagnetism and ferroelectricity at or above room temperature. On the

Calibration of Recoil-In-Vacuum attenuations from first principles: comparison with recent experimental data on Fe isotopes

International Nuclear Information System (INIS)

Stone, Nicholas James; Stone, Jirina Rikovska; Stuchbery, Andrew E.; Jonsson, Per

2015-01-01

Precession of aligned nuclear spin systems in ions recoiling from the target into vacuum (RIV) with consequent attenuation of angular distributions of emitted radiation is, in principle, a versatile method for measurement of g-factors of nuclear excited states of lifetimes in the pico-second range (Stone et al., Phys. Rev. Lett., 94, 192501, 2005 and Stuchbery and Stone, Phys. Rev. C, 76, 034307, 2007). Calibration of the observed attenuations has been achieved in favourable cases through comparison with measurements on states having previously known g-factors and lifetimes. The general lack of suitable states with known g-factors has limited application of the RIV method. This paper concerns the present status of efforts to describe the states of excited ions recoiling into vacuum in detail so that the average interaction can be estimated with useful precision from a-priori theory. The calculations use the GRASP2K package (Froese-Fischer et al. 1997 and Jonsson, Comp. Phys. Comm., 177, 597, 2007 & 184, 2197, 2013) to obtain, for each recoiling ion change state, the individual possible electronic states, their configurations, lifetimes and hyperfine interactions. It is assumed that all possible ionic states are produced, up to a chosen excitation energy. This energy is selected to approximate the energy at which all states have lifetimes far shorter than the nuclear state of interest. It is further assumed that the ionic state total electron angular momenta are randomly oriented in space. The first estimates of the average attenuation of emission distributions, as a function of the product g τ of the nuclear state g-factor and mean lifetime, used an averaged precession frequency obtained neglecting transitions between electronic states. Improved calculations, which include such transitions, are described

Point defects in thorium nitride: A first-principles study

Energy Technology Data Exchange (ETDEWEB)

Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA (Argentina)

2016-11-15

Thorium and its compounds (carbides and nitrides) are being investigated as possible materials to be used as nuclear fuels for Generation-IV reactors. As a first step in the research of these materials under irradiation, we study the formation energies and stability of point defects in thorium nitride by means of first-principles calculations within the framework of density functional theory. We focus on vacancies, interstitials, Frenkel pairs and Schottky defects. We found that N and Th vacancies have almost the same formation energy and that the most energetically favorable defects of all studied in this work are N interstitials. These kind of results for ThN, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically.

Point defects in thorium nitride: A first-principles study

International Nuclear Information System (INIS)

Pérez Daroca, D.; Llois, A.M.; Mosca, H.O.

2016-01-01

Thorium and its compounds (carbides and nitrides) are being investigated as possible materials to be used as nuclear fuels for Generation-IV reactors. As a first step in the research of these materials under irradiation, we study the formation energies and stability of point defects in thorium nitride by means of first-principles calculations within the framework of density functional theory. We focus on vacancies, interstitials, Frenkel pairs and Schottky defects. We found that N and Th vacancies have almost the same formation energy and that the most energetically favorable defects of all studied in this work are N interstitials. These kind of results for ThN, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically.

First principles study of α and δ-Pu

International Nuclear Information System (INIS)

Chattaraj, Debabrata; Dash, Smruti

2017-01-01

The structural and electronic properties of α-and δ-Pu has been investigated using state of the art first principles method. All the calculations have been performed using a plane wave based pseudopotential method under the framework of spin polarized density functional theory. The effect of relativistic spin-orbit interactions on these properties has been investigated. The calculated lattice parameters are found to be within ±1% of the experimental data. The cohesive energy of α-and δ-Pu are calculated to be -3.125 and -3.126 eV/atom. The nature of chemical bonding present in those phases of Pu is depicted by calculated density of states spectra. (author)

Thermodynamics of the hexagonal close-packed iron-nitrogen system from first-principles

DEFF Research Database (Denmark)

Bakkedal, Morten Bjørn

to hexagonal systems and a numerically tractable extended equation of state is developed to describe thermody-namic equilibrium properties at finite temperature.The model is applied to ε-Fe3N specifically. Through the versatility of the model, equi-librium lattice parameters, the bulk modulus, and the thermal......First-principles thermodynamic models are developed for the hexagonal close-packed ε-Fe-N system. The system can be considered as a hexagonal close-packed host lattice of iron atoms and with the nitrogen atoms residing on a sublattice formed by the octahedral interstices. The iron host lattice...... is assumed fixed.The models are developed entirely from first-principles calculations based on fundamen-tal quantum mechanical calculation through the density functional theory approach with the atomic numbers and crystal structures as the only input parameters. A complete thermody-namic description should...

Development of a Knowledge Base of Ti-Alloys From First-Principles and Thermodynamic Modeling

Science.gov (United States)

Marker, Cassie

An aging population with an active lifestyle requires the development of better load-bearing implants, which have high levels of biocompatibility and a low elastic modulus. Titanium alloys, in the body centered cubic phase, are great implant candidates, due to their mechanical properties and biocompatibility. The present work aims at investigating the thermodynamic and elastic properties of bcc Tialloys, using the integrated first-principles based on Density Functional Theory (DFT) and the CALculation of PHAse Diagrams (CALPHAD) method. The use of integrated first-principles calculations based on DFT and CALPHAD modeling has greatly reduced the need for trial and error metallurgy, which is ineffective and costly. The phase stability of Ti-alloys has been shown to greatly affect their elastic properties. Traditionally, CALPHAD modeling has been used to predict the equilibrium phase formation, but in the case of Ti-alloys, predicting the formation of two metastable phases o and alpha" is of great importance as these phases also drastically effect the elastic properties. To build a knowledge base of Ti-alloys, for biomedical load-bearing implants, the Ti-Mo-Nb-Sn-Ta-Zr system was studied because of the biocompatibility and the bcc stabilizing effects of some of the elements. With the focus on bcc Ti-rich alloys, a database of thermodynamic descriptions of each phase for the pure elements, binary and Ti-rich ternary alloys was developed in the present work. Previous thermodynamic descriptions for the pure elements were adopted from the widely used SGTE database for global compatibility. The previous binary and ternary models from the literature were evaluated for accuracy and new thermodynamic descriptions were developed when necessary. The models were evaluated using available experimental data, as well as the enthalpy of formation of the bcc phase obtained from first-principles calculations based on DFT. The thermodynamic descriptions were combined into a database

First principles pharmacokinetic modeling: A quantitative study on Cyclosporin

DEFF Research Database (Denmark)

Mošat', Andrej; Lueshen, Eric; Heitzig, Martina

2013-01-01

renal and hepatic clearances, elimination half-life, and mass transfer coefficients, to establish drug biodistribution dynamics in all organs and tissues. This multi-scale model satisfies first principles and conservation of mass, species and momentum.Prediction of organ drug bioaccumulation...... as a function of cardiac output, physiology, pathology or administration route may be possible with the proposed PBPK framework. Successful application of our model-based drug development method may lead to more efficient preclinical trials, accelerated knowledge gain from animal experiments, and shortened time-to-market...

First-principles study of thermoelectric properties of CuI

International Nuclear Information System (INIS)

Yadav, Manoj K; Sanyal, Biplab

2014-01-01

Theoretical investigations of the thermoelectric properties of CuI have been carried out employing first-principles calculations followed by the calculations of transport coefficients based on Boltzmann transport theory. Among the three different phases of CuI, viz. zinc-blende, wurtzite and rock salt, the thermoelectric power factor is found to be the maximum for the rock salt phase. We have analysed the variations of Seebeck coefficients and thermoelectric power factors on the basis of calculated electronic structures near the valence band maxima of these phases. (papers)

Research on regularized mean-variance portfolio selection strategy with modified Roy safety-first principle.

Science.gov (United States)

Atta Mills, Ebenezer Fiifi Emire; Yan, Dawen; Yu, Bo; Wei, Xinyuan

2016-01-01

We propose a consolidated risk measure based on variance and the safety-first principle in a mean-risk portfolio optimization framework. The safety-first principle to financial portfolio selection strategy is modified and improved. Our proposed models are subjected to norm regularization to seek near-optimal stable and sparse portfolios. We compare the cumulative wealth of our preferred proposed model to a benchmark, S&P 500 index for the same period. Our proposed portfolio strategies have better out-of-sample performance than the selected alternative portfolio rules in literature and control the downside risk of the portfolio returns.

First principles design of a core bioenergetic transmembrane electron-transfer protein

Energy Technology Data Exchange (ETDEWEB)

Goparaju, Geetha; Fry, Bryan A.; Chobot, Sarah E.; Wiedman, Gregory; Moser, Christopher C.; Leslie Dutton, P.; Discher, Bohdana M.

2016-05-01

Here we describe the design, Escherichia coli expression and characterization of a simplified, adaptable and functionally transparent single chain 4-α-helix transmembrane protein frame that binds multiple heme and light activatable porphyrins. Such man-made cofactor-binding oxidoreductases, designed from first principles with minimal reference to natural protein sequences, are known as maquettes. This design is an adaptable frame aiming to uncover core engineering principles governing bioenergetic transmembrane electron-transfer function and recapitulate protein archetypes proposed to represent the origins of photosynthesis. This article is part of a Special Issue entitled Biodesign for Bioenergetics — the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson.

First-principles study of high-conductance DNA sequencing with carbon nanotube electrodes

KAUST Repository

Chen, X.; Rungger, I.; Pemmaraju, C. D.; Schwingenschlö gl, Udo; Sanvito, S.

2012-01-01

such electrodes by using first-principles quantum transport theory. In particular, we consider the extreme case where the separation between the electrodes is the smallest possible that still allows the DNA translocation. The benzene-like ring at the end cap

First-Principles Calculation of Lithium Adsorption and Diffusion on Silicene

International Nuclear Information System (INIS)

Huang Juan; Chen Hong-Jin; Wu Mu-Sheng; Liu Gang; Ouyang Chu-Ying; Xu Bo

2013-01-01

The adsorption and diffusion of lithium on silicene are studied by using the first-principles method. It is found that the adsorption energy of Li adsorbing on silicene is significantly larger than that of Li adsorbing on graphene. With the increasing concentration of adsorbed Li atoms, the adsorption energy also increases. The diffusion barrier of Li on silicene is relatively low, which is insensitive to the concentration of adsorbed atoms

Anomalous doping effect in black phosphorene from first-principles calculations

OpenAIRE

Yu, Weiyang; Zhu, Zhili; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu

2014-01-01

Using first-principles density functional theory calculations, we investigate the geometries, electronic structures, and thermodynamic stabilities of substitutionally doped phosphorene sheets with group III, IV, V, and VI elements. We find that the electronic properties of phosphorene are drastically modified by the number of valence electrons in dopant atoms. The dopants with even number of valence electrons enable the doped phosphorenes to have a metallic feature, while the dopants with odd...

Maximum Principles and Boundary Value Problems for First-Order Neutral Functional Differential Equations

Directory of Open Access Journals (Sweden)

Domoshnitsky Alexander

2009-01-01

Full Text Available We obtain the maximum principles for the first-order neutral functional differential equation where , and are linear continuous operators, and are positive operators, is the space of continuous functions, and is the space of essentially bounded functions defined on . New tests on positivity of the Cauchy function and its derivative are proposed. Results on existence and uniqueness of solutions for various boundary value problems are obtained on the basis of the maximum principles.

Introduction to First-Principles Electronic Structure Methods: Application to Actinide Materials

International Nuclear Information System (INIS)

Klepeis, J E

2005-01-01

The purpose of this paper is to provide an introduction for non-experts to first-principles electronic structure methods that are widely used in the field of condensed-matter physics, including applications to actinide materials. The methods I describe are based on density functional theory (DFT) within the local density approximation (LDA) and the generalized gradient approximation (GGA). In addition to explaining the meaning of this terminology I also describe the underlying theory itself in some detail in order to enable a better understanding of the relative strengths and weaknesses of the methods. I briefly mention some particular numerical implementations of DFT, including the linear muffin-tin orbital (LMTO), linear augmented plane wave (LAPW), and pseudopotential methods, as well as general methodologies that go beyond DFT and specifically address some of the weaknesses of the theory. The last third of the paper is devoted to a few selected applications that illustrate the ideas discussed in the first two-thirds. In particular, I conclude by addressing the current controversy regarding magnetic DFT calculations for actinide materials. Throughout this paper particular emphasis is placed on providing the appropriate background to enable the non-expert to gain a better appreciation of the application of first-principles electronic structure methods to the study of actinide and other materials

Foundations of Quantum Mechanics: Derivation of a dissipative Schrödinger equation from first principles

Energy Technology Data Exchange (ETDEWEB)

Gonçalves, L.A.; Olavo, L.S.F., E-mail: olavolsf@gmail.com

2017-05-15

Dissipation in Quantum Mechanics took some time to become a robust field of investigation after the birth of the field. The main issue hindering developments in the field is that the Quantization process was always tightly connected to the Hamiltonian formulation of Classical Mechanics. In this paper we present a quantization process that does not depend upon the Hamiltonian formulation of Classical Mechanics (although still departs from Classical Mechanics) and thus overcome the problem of finding, from first principles, a completely general Schrödinger equation encompassing dissipation. This generalized process of quantization is shown to be nothing but an extension of a more restricted version that is shown to produce the Schrödinger equation for Hamiltonian systems from first principles (even for Hamiltonian velocity dependent potential). - Highlights: • A Quantization process independent of the Hamiltonian formulation of quantum Mechanics is proposed. • This quantization method is applied to dissipative or absorptive systems. • A Dissipative Schrödinger equation is derived from first principles.

Negative thermal expansion in TiF{sub 3} from the first-principles prediction

Energy Technology Data Exchange (ETDEWEB)

Wang, Lei [International Laboratory for Quantum Functional Materials of Henan, Zhengzhou University, Zhengzhou 450001 (China); Yuan, Peng-Fei; Wang, Fei; Sun, Qiang; Liang, Er-Jun [International Laboratory for Quantum Functional Materials of Henan, Zhengzhou University, Zhengzhou 450001 (China); Center for Clean Energy and Quantum Structures, and School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052 (China); Jia, Yu, E-mail: jiayu@zzu.edu.cn [International Laboratory for Quantum Functional Materials of Henan, Zhengzhou University, Zhengzhou 450001 (China); Center for Clean Energy and Quantum Structures, and School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052 (China); Guo, Zheng-Xiao, E-mail: z.x.guo@ucl.ac.uk [Deparment of Chemistry, University College London, London WC1H 0AJ (United Kingdom)

2014-08-01

Highlights: • Rhombohedral TiF{sub 3} as a new NTE material is predicted from first-principles calculation. • The NTE mechanism is proposed based on the analysis of vibrational properties. • The rotation coupling of TiF{sub 6} octahedra at low frequencies is most responsible for NTE. - Abstract: In negative thermal expansion (NTE) materials, rhombohedral TiF{sub 3} as a new member is predicted from first-principles calculation. The NTE behavior of rhombohedral TiF{sub 3} occurs at low temperatures. In our work, the NTE mechanism is elaborated in accordance with vibrational modes. It is confirmed that the rigid unit mode (RUM) of internal TiF{sub 6} octahedra in low-frequency optical range is most responsible for the NTE properties.

First principle study of cubic ScGaN ternaries

International Nuclear Information System (INIS)

Adli, W.; Mecheref, R.; Sekkal, N.; Tair, F.; Amrani, B.

2008-08-01

The electronic properties of the Sc x Ga1- x N ternary alloy are investigated. The transition from rocksalt (B1) to zinc blende (B3) structure is found to occur rapidly after incorporating just a small fraction (less than 1%) of Ga. In the present paper, the first principles method the full potential linear muffin-tin orbitals method (FPLMTO) in its atomic sphere approximation (ASA) coupled to the technique of the empty spheres is employed. Our results concerning the electronic properties are different from those reported in literature. (author)

Whether FeTe is superconductor: Insights from first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Li, Jian; Huang, GuiQin, E-mail: huangguiqin@njnu.edu.cn; Zhu, XingFeng

2013-09-15

Highlights: • The ground state of FeTe is in the double stripe antiferromagnetic phase. • The nesting of electron and hole at the Fermi surface is not present in FeTe. • The spin–lattice interaction can lead to the phonon softening. • The electron–phonon coupling constant λ is enhanced due to spin–phonon coupling. • Whether FeTe can be superconductor? Some discussions are made. -- Abstract: We present a first-principles pseudopotential study on the electronic structure, phonon structure and the electron–phonon interaction of stoichiometric FeTe in both the nonmagnetic and double stripe antiferromagnetic phases. Our electronic structure calculations show that the nesting effect of Fermi surface is not present in stoichiometric FeTe after considering the magnetic interaction. Comparing the phonon behavior in the double stripe antiferromagnetic phase with that in the nonmagnetic phase, we find that the spin–lattice interaction can lead to the phonon softening and increase electron–phonon coupling constant λ by about 33%, which is similar to other iron-based superconductors in the single stripe antiferromagnetic phase. We suggest that the phonon softening may have no clear contact with the specific magnetic order in the ground state. Finally, we make some discussion about whether FeTe can be superconductor combining our first-principles calculations.

First-principles study of point defects in thorium carbide

International Nuclear Information System (INIS)

Pérez Daroca, D.; Jaroszewicz, S.; Llois, A.M.; Mosca, H.O.

2014-01-01

Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. One of the most important issues to be studied is their behavior under irradiation. A first approach to this goal is the study of point defects. By means of first-principles calculations within the framework of density functional theory, we study the stability and formation energies of vacancies, interstitials and Frenkel pairs in thorium carbide. We find that C isolated vacancies are the most likely defects, while C interstitials are energetically favored as compared to Th ones. These kind of results for ThC, to the best authors’ knowledge, have not been obtained previously, neither experimentally, nor theoretically. For this reason, we compare with results on other compounds with the same NaCl-type structure

First-principles study of point defects in thorium carbide

Energy Technology Data Exchange (ETDEWEB)

Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, (1033) Buenos Aires (Argentina); Jaroszewicz, S. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, (1033) Buenos Aires (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina)

2014-11-15

Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. One of the most important issues to be studied is their behavior under irradiation. A first approach to this goal is the study of point defects. By means of first-principles calculations within the framework of density functional theory, we study the stability and formation energies of vacancies, interstitials and Frenkel pairs in thorium carbide. We find that C isolated vacancies are the most likely defects, while C interstitials are energetically favored as compared to Th ones. These kind of results for ThC, to the best authors’ knowledge, have not been obtained previously, neither experimentally, nor theoretically. For this reason, we compare with results on other compounds with the same NaCl-type structure.

Constructing first-principles phase diagrams of amorphous LixSi using machine-learning-assisted sampling with an evolutionary algorithm

Science.gov (United States)

Artrith, Nongnuch; Urban, Alexander; Ceder, Gerbrand

2018-06-01

The atomistic modeling of amorphous materials requires structure sizes and sampling statistics that are challenging to achieve with first-principles methods. Here, we propose a methodology to speed up the sampling of amorphous and disordered materials using a combination of a genetic algorithm and a specialized machine-learning potential based on artificial neural networks (ANNs). We show for the example of the amorphous LiSi alloy that around 1000 first-principles calculations are sufficient for the ANN-potential assisted sampling of low-energy atomic configurations in the entire amorphous LixSi phase space. The obtained phase diagram is validated by comparison with the results from an extensive sampling of LixSi configurations using molecular dynamics simulations and a general ANN potential trained to ˜45 000 first-principles calculations. This demonstrates the utility of the approach for the first-principles modeling of amorphous materials.

Diffusion coefficients of alloying elements in dilute Mg alloys: A comprehensive first-principles study

International Nuclear Information System (INIS)

Zhou, Bi-Cheng; Shang, Shun-Li; Wang, Yi; Liu, Zi-Kui

2016-01-01

First-principles calculations based on density functional theory have been used to calculate the temperature-dependent dilute tracer diffusion coefficients for 47 substitutional alloying elements in hexagonal closed packed (hcp) Mg by combining transition state theory and an 8-frequency model. The minimum energy pathways and the saddle point configurations during solute migration are calculated with the climbing image nudged elastic band method. Vibrational properties are obtained using the quasi-harmonic Debye model with inputs from first-principles calculations. An improved generalized gradient approximation of PBEsol is used in the present first-principles calculations, which is able to well describe both vacancy formation energies and vibrational properties. It is found that the solute diffusion coefficients in hcp Mg are roughly inversely proportional to the bulk modulus of the dilute alloys, which reflects the solutes' bonding to Mg. Transition metal elements with d electrons show strong interactions with Mg and have large diffusion activation energies. Correlation effects are not negligible for solutes Ca, Na, Sr, Se, Te, and Y, in which the direct solute migration barriers are much smaller than the solvent (Mg) migration barriers. Calculated diffusion coefficients are in remarkable agreement with available experimental data in the literature.

Prospects for first-principle calculations of scintillator properties

International Nuclear Information System (INIS)

Derenzo, Stephen E.; Weber, Marvin J.

1999-01-01

Several scintillation processes can be modeled from first principles using quantum chemistry cluster calculations and recently available high-performance computers. These processes include the formation of excitons and trapping centers, the diffusion of ionization energy (electrons and holes) through a host crystal, and the efficient capture of these carriers by an activator atom to form a luminous, non-quenched excited state. As examples of such calculations, results are presented for (1) hole transport in the known scintillator host crystal CsI, (2) hole trapping in the non-scintillator PbF 2 , (3) hole transport in the experimentally unexplored PbF 4 , and (4) the electronic nature of excited states of CsI : Tl and CsI : Na

First-Principles Momentum-Dependent Local Ansatz Wavefunction and Momentum Distribution Function Bands of Iron

Science.gov (United States)

Kakehashi, Yoshiro; Chandra, Sumal

2016-04-01

We have developed a first-principles local ansatz wavefunction approach with momentum-dependent variational parameters on the basis of the tight-binding LDA+U Hamiltonian. The theory goes beyond the first-principles Gutzwiller approach and quantitatively describes correlated electron systems. Using the theory, we find that the momentum distribution function (MDF) bands of paramagnetic bcc Fe along high-symmetry lines show a large deviation from the Fermi-Dirac function for the d electrons with eg symmetry and yield the momentum-dependent mass enhancement factors. The calculated average mass enhancement m*/m = 1.65 is consistent with low-temperature specific heat data as well as recent angle-resolved photoemission spectroscopy (ARPES) data.

First principles studies of extrinsic and intrinsic defects in boron nitride nanotubes

CSIR Research Space (South Africa)

Mashapa, MG

2012-10-01

Full Text Available -1 Journal of Nanoscience and Nanotechnology 2012/ Vol. 12, 7807?7814 First Principles Studies of Extrinsic and Intrinsic Defects in Boron Nitride Nanotubes M. G. Mashapa 1, 2, ?, N. Chetty1, and S. Sinha Ray2, 3 1Physics Department, University...

A first-principles model for the freezing step in ice cream manufacture

NARCIS (Netherlands)

Dorneanu, B.; Bildea, C.S.; Girievink, J.; Bongers, P.M.M.; Jezowski, J.; Thullie, J.

2009-01-01

This contribution deals with the development of a first-principles model for ice cream formation in the freezing unit to support product design and plant operation. Conservation equations for the mass, energy and momentum, considering axial flow assumptions are taken into account. The distributed

In acceptance we trust? Conceptualising acceptance as a viable approach to NGO security management.

Science.gov (United States)

Fast, Larissa A; Freeman, C Faith; O'Neill, Michael; Rowley, Elizabeth

2013-04-01

This paper documents current understanding of acceptance as a security management approach and explores issues and challenges non-governmental organisations (NGOs) confront when implementing an acceptance approach to security management. It argues that the failure of organisations to systematise and clearly articulate acceptance as a distinct security management approach and a lack of organisational policies and procedures concerning acceptance hinder its efficacy as a security management approach. The paper identifies key and cross-cutting components of acceptance that are critical to its effective implementation in order to advance a comprehensive and systematic concept of acceptance. The key components of acceptance illustrate how organisational and staff functions affect positively or negatively an organisation's acceptance, and include: an organisation's principles and mission, communications, negotiation, programming, relationships and networks, stakeholder and context analysis, staffing, and image. The paper contends that acceptance is linked not only to good programming, but also to overall organisational management and structures. © 2013 The Author(s). Journal compilation © Overseas Development Institute, 2013.

New approaches for first-principles modelling of inelastic transport in nanoscale semiconductor devices with thousands of atoms

DEFF Research Database (Denmark)

Gunst, Tue; Brandbyge, Mads; Palsgaard, Mattias Lau Nøhr

2017-01-01

is in both methods calculated in a post-processing step to a self consistent DFT calculation. The first method is based on first order perturbation theory in the EPC self-energy within the Lowest Order Expansion (LOE) approximation. The method requires calculation of the first-principles EPC in the device......We present two different methods which both enable large-scale first-principles device simulations including electron-phonon coupling (EPC). The methods are based on Density Functional Theory and Nonequilibrium Greens Functions (DFT- NEGF) calculations of electron transport. The inelastic current...

Crystal structure of Earth's inner core: A first-principles study

Science.gov (United States)

Moustafa, S. G.; Schultz, A. J.; Zurek, E.; Kofke, D. A.

2017-12-01

Since the detection of the Earth's solid inner core (IC) by Lehmann in 1936, its composition and crystal structure (which are essential to understand Earth's evolution) have been controversial. While seismological measurements (e.g. PREM) can give a robust estimation of the density, pressure, and elasticity of the IC, they cannot be directly used to determine its composition and/or crystal structure. Experimentally, reaching the extreme IC conditions ( 330 GPa and 6000 K) and getting reliable measurements is very challenging. First-principles calculations provide a viable alternative that can work as a powerful investigative tool. Although several attempts have been made to assess phase stability at IC conditions computationally, they often use a low level of theory for electronic structure (e.g., classical force-field), adopt approximate methods (e.g., quasiharmonic approximation, fixed hcp-c/a), or do not consider finite-size effects. The study of phase stability using accurate first-principles methods is hampered in part by the difficulty of computing the free energy (FE), the central thermodynamic quantity that determines stability, while including anharmonic and finite-size effects. Additional difficulty related to the IC in particular is introduced by the dynamical instability of one of the IC candidate structures (bcc) at low temperature. Recently [1-3], we introduced a novel method (denoted as "harmonically mapped averaging", or HMA) to efficiently measure anharmonic properties (e.g. FE, pressure, elastic modulus) by molecular simulation, yielding orders of magnitude CPU speedup compared to conventional methods. We have applied this method to the hcp candidate phase of iron at the IC conditions, obtaining first-principles anharmonic FE values with unprecedented accuracy and precision [4]. We have now completed and report HMA calculations to assess the phase stability of all IC candidate phases (fcc/hcp/bcc). This knowledge is the prerequisite for

Photostriction and elasto-optic response in multiferroics and ferroelectrics from first principles

Science.gov (United States)

Yang, Yurong; Paillard, Charles; Xu, Bin; Bellaiche, L.

2018-02-01

The present work reviews a series of recent first-principles studies devoted to the description of the interaction of light and strain in ferroelectric and multiferroic materials. Specifically, the modelling schemes used in these works to describe the so-called photostriction and elasto-optic effects are presented, in addition to the results and analysis provided by these ab initio calculations. In particular, the large importance of the piezoelectric effect in the polar direction in the photostriction of ferroelectric materials is stressed. Similarly, the occurrence of low-symmetry phases in lead titanate thin films under tensile strain is demonstrated to result in large elasto-optic constants. In addition, first-principle calculations allow to gain microscopic knowledge of subtle effects, for instance in the case of photostriction, where the deformation potential effect in directions perpendicular to the polar axis is shown to be almost as significant as the piezoelectric effect. As a result, the numerical methods presented here could propel the design of efficient opto-mechanical devices.

Structural and electronic phase transitions of ThS2 from first-principles calculations

International Nuclear Information System (INIS)

Guo, Yongliang; Wang, Changying; Qiu, Wujie; Ke, Xuezhi

2016-01-01

Performed a systematic study using first-principles methods of the pressure-induced structural and electronic phase transitions in ThS_2, which may play an important role in the next generation nuclear energy fuel technology.

Graphene substrate-mediated catalytic performance enhancement of Ru nanoparticles: A first-principles study

KAUST Repository

Liu, Xin; Yao, Kexin; Meng, Changgong; Han, Yu

2012-01-01

The structural, energetic and magnetic properties of Ru nanoparticles deposited on pristine and defective graphene have been thoroughly studied by first-principles based calculations. The calculated binding energy of a Ru 13 nanoparticle on a single

First-principles study of Frenkel pair recombination in tungsten

International Nuclear Information System (INIS)

Qin, Shi-Yao; Jin, Shuo; Li, Yu-Hao; Zhou, Hong-Bo; Zhang, Ying; Lu, Guang-Hong

2017-01-01

The recombination of one Frenkel pair in tungsten has been investigated through first-principles simulation. Two different recombination types have been identified: instantaneous and thermally activated. The small recombination barriers for thermally activated recombination cases indicate that recombination can occur easily with a slightly increased temperature. For both of the two recombination types, recombination occurs through the self-interstitial atom moving towards the vacancy. The recombination process can be direct or through replacement sequences, depending on the vertical distance between the vacancy and the 〈1 1 1〉 line of self-interstitial atom pair.

First-principles momentum-dependent local ansatz wavefunction and momentum distribution function bands of iron

International Nuclear Information System (INIS)

Kakehashi, Yoshiro; Chandra, Sumal

2016-01-01

We have developed a first-principles local ansatz wavefunction approach with momentum-dependent variational parameters on the basis of the tight-binding LDA+U Hamiltonian. The theory goes beyond the first-principles Gutzwiller approach and quantitatively describes correlated electron systems. Using the theory, we find that the momentum distribution function (MDF) bands of paramagnetic bcc Fe along high-symmetry lines show a large deviation from the Fermi–Dirac function for the d electrons with e g symmetry and yield the momentum-dependent mass enhancement factors. The calculated average mass enhancement m*/m = 1.65 is consistent with low-temperature specific heat data as well as recent angle-resolved photoemission spectroscopy (ARPES) data. (author)

Thermodynamic modeling of the Co–Hf system supported by key experiments and first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Lu, Xingxu [School of Materials Science and Engineering, Central South University, Changsha, Hunan 410083 (China); State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Liu, Shuhong, E-mail: shhliu@csu.edu.cn [State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Sino-German Cooperation Group “Microstructure in Al alloys”, Central South University, Changsha, Hunan 410083 (China); Cheng, Kaiming; Tang, Ying [State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Ou, Pengfei [School of Materials Science and Engineering, Central South University, Changsha, Hunan 410083 (China); State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Nash, Philip [Thermal Processing Technology Center, Illinois Institute of Technology (IIT), 10 West 32nd Street, Chicago, IL 60616 (United States); Sundman, Bo [INSTN, CEA Saclay, 91191 Gif-Sur-Yvette Cedex (France); Du, Yong [State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Sino-German Cooperation Group “Microstructure in Al alloys”, Central South University, Changsha, Hunan 410083 (China); Zheng, Feng [School of Materials Science and Engineering, Central South University, Changsha, Hunan 410083 (China)

2015-05-20

Highlights: • Heat contents of Co{sub 2}Hf and CoHf{sub 2} were measured by drop calorimetry. • Enthalpy of formation for Co{sub 23}Hf{sub 6} was computed via first-principles calculations. • Co–Hf system was assessed by means of CALPHAD approach. • Order–disorder model is used to describe B2 (CoHf) and A2 (βHf). • Glass forming range of the Co–Hf amorphous alloys was predicted. - Abstract: Phase equilibria and thermodynamic properties of the Co–Hf system were investigated via calorimetric measurements, first-principles calculations and thermodynamic modeling. Heat contents of Co{sub 2}Hf and CoHf{sub 2} were measured by drop calorimetry from 300 to 1200 °C. The enthalpy of formation for Co{sub 23}Hf{sub 6} at 0 K was computed via first-principles calculations. Based on the experimental measurements and first-principles calculations from the present work and the literature, the Co–Hf system was assessed by means of CALPHAD (CALculation of PHAse Diagram) approach. The excess Gibbs energy of solution phases was modeled with Redlich–Kister polynomial. Sublattice models were employed to describe the homogeneity ranges of Co{sub 2}Hf, CoHf and CoHf{sub 2}. The order–disorder transition between B2 (CoHf) and A2 (βHf) phases was taken into account in the current optimization. Using the optimized parameters, glass forming range (GFR) of the Co–Hf amorphous alloys was predicted to be 15–75 at.% Hf, which is in satisfactory agreement with the experimental observation.

A review of human factors principles for the design and implementation of medication safety alerts in clinical information systems.

Science.gov (United States)

Phansalkar, Shobha; Edworthy, Judy; Hellier, Elizabeth; Seger, Diane L; Schedlbauer, Angela; Avery, Anthony J; Bates, David W

2010-01-01

The objective of this review is to describe the implementation of human factors principles for the design of alerts in clinical information systems. First, we conduct a review of alarm systems to identify human factors principles that are employed in the design and implementation of alerts. Second, we review the medical informatics literature to provide examples of the implementation of human factors principles in current clinical information systems using alerts to provide medication decision support. Last, we suggest actionable recommendations for delivering effective clinical decision support using alerts. A review of studies from the medical informatics literature suggests that many basic human factors principles are not followed, possibly contributing to the lack of acceptance of alerts in clinical information systems. We evaluate the limitations of current alerting philosophies and provide recommendations for improving acceptance of alerts by incorporating human factors principles in their design.

Phases of Ca from first principles

International Nuclear Information System (INIS)

Qiu, S L; Marcus, P M

2009-01-01

Structures and properties of many of the phases of Ca under pressure are calculated from first principles by a systematic procedure that minimizes total energy E with respect to structure under the constraint of constant volume V. The minima of E are followed on successive sweeps of lattice parameters for 11 of 14 Bravais symmetries for one-atom-per-cell structures. The structures include the four orthorhombic phases. Also included are the hexagonal close-packed and cubic diamond phases with two atoms per primitive cell. No uniquely orthorhombic phases are found; all one-atom orthorhombic phases over a mega-bar pressure range are identical to higher-symmetry phases. The simple cubic phase is shown to be stable where it is the ground state. The number of distinct one-atom phases reduces to five plus the two two-atom phases. For each of these phases the Gibbs free energy at pressure p, G(p), is calculated for a non-vibrating lattice; the functions G(p) give the ground state at each p, the relative stabilities of all phases and the thermodynamic phase transition pressures for all phase transitions over a several-megabar range.

Calculations of thermodynamic properties of PuO2 by the first-principles and lattice vibration

International Nuclear Information System (INIS)

Minamoto, Satoshi; Kato, Masato; Konashi, Kenji; Kawazoe, Yoshiyuki

2009-01-01

Plutonium dioxide (PuO 2 ) is a key compound of mixed oxide fuel (MOX fuel). To predict the thermal properties of PuO 2 at high temperature, it is important to understand the properties of MOX fuel. In this study, thermodynamic properties of PuO 2 were evaluated by coupling of first-principles and lattice dynamics calculation. Cohesive energy was estimated from first-principles calculations, and the contribution of lattice vibration to total energy was evaluated by phonon calculations. Thermodynamic properties such as volume thermal expansion, bulk modulus and specific heat of PuO 2 were investigated up to 1500 K

Hydrogen interactions with ZrCo nanoclusters: a first-principles study

International Nuclear Information System (INIS)

Chattaraj, D.; Parida, S.C.; Dash, Smruti; Bhattacharya, Saswata; Majumder, C.

2014-01-01

Tritium is one of the fuels going to be used in fusion reactor program. But, this radioactive isotope should be stored safely. ZrCo intermetallic has been chosen as a tritium storage material in ITER program. It is important to study how hydrogen interacts with ZrCo in its different dimensions. In this study we have investigated the hydrogen interaction with the Zr m Co n (m+n = 2, 4 and 6) nanoclusters using the state-of-the-art first principles method

Principles governing medical first aid to workers exposed to internal contamination

International Nuclear Information System (INIS)

Jammet, H.; Nenot, J.C.

1976-01-01

The growing use of radionuclides, whether at hospital, laboratory or nuclear facility level, increases the risk of internal contamination. Not only that, some particularly dangerous elements are being handled more and more frequently. Hence the importance of therapeutic concepts based on the general principles governing action to be taken in cases of internal contamination. These principles should be applicable without the nature of the contaminant having to be taken into account, and irrespective of whether it is transferable and of the route of entry, i.e. healthy skin, wound or bronchial tree. The basic principle is the concept of urgency: ''blind'' treatment should be applied merely on the supposition of internal contamination. It is desirable, moreover, that the first aid should be given at the site of the accident. Hence, the product used should be non-toxic under normal conditions of use and should be simple to apply, as, for example, the administration of an aerosol. It is not until later that the doctor should undertake treatment in the proper sense of the term, the emergency treatment having afforded him sufficient time to carry out the preliminary examination required to gain an exact idea of the internal contamination. (author)

Audio interfaces should be designed based on data visualisation first principles

OpenAIRE

Dewey, Christopher; Wakefield, Jonathan P.

2016-01-01

Audio mixing interfaces (AMIs) commonly conform to a small number of paradigms. These paradigms have\\ud significant shortcomings. Data visualisation first principles should be employed to consider alternatives. Existing AMI\\ud paradigms are discussed and concepts of image theory and elementary perceptual elements outlined. AMIs should be evaluated by usability experiments however performing these properly is time-consuming. There are many data visualisation options and combinations. Collabora...

First-principles calculations of mobility

Science.gov (United States)

Krishnaswamy, Karthik

First-principles calculations can be a powerful predictive tool for studying, modeling and understanding the fundamental scattering mechanisms impacting carrier transport in materials. In the past, calculations have provided important qualitative insights, but numerical accuracy has been limited due to computational challenges. In this talk, we will discuss some of the challenges involved in calculating electron-phonon scattering and carrier mobility, and outline approaches to overcome them. Topics will include the limitations of models for electron-phonon interaction, the importance of grid sampling, and the use of Gaussian smearing to replace energy-conserving delta functions. Using prototypical examples of oxides that are of technological importance-SrTiO3, BaSnO3, Ga2O3, and WO3-we will demonstrate computational approaches to overcome these challenges and improve the accuracy. One approach that leads to a distinct improvement in the accuracy is the use of analytic functions for the band dispersion, which allows for an exact solution of the energy-conserving delta function. For select cases, we also discuss direct quantitative comparisons with experimental results. The computational approaches and methodologies discussed in the talk are general and applicable to other materials, and greatly improve the numerical accuracy of the calculated transport properties, such as carrier mobility, conductivity and Seebeck coefficient. This work was performed in collaboration with B. Himmetoglu, Y. Kang, W. Wang, A. Janotti and C. G. Van de Walle, and supported by the LEAST Center, the ONR EXEDE MURI, and NSF.

First-Principle Characterization for Singlet Fission Couplings.

Science.gov (United States)

Yang, Chou-Hsun; Hsu, Chao-Ping

2015-05-21

The electronic coupling for singlet fission, an important parameter for determining the rate, has been found to be too small unless charge-transfer (CT) components were introduced in the diabatic states, mostly through perturbation or a model Hamiltonian. In the present work, the fragment spin difference (FSD) scheme was generalized to calculate the singlet fission coupling. The largest coupling strength obtained was 14.8 meV for two pentacenes in a crystal structure, or 33.7 meV for a transition-state structure, which yielded a singlet fission lifetime of 239 or 37 fs, generally consistent with experimental results (80 fs). Test results with other polyacene molecules are similar. We found that the charge on one fragment in the S1 diabatic state correlates well with FSD coupling, indicating the importance of the CT component. The FSD approach is a useful first-principle method for singlet fission coupling, without the need to include the CT component explicitly.

Safeguards First Principle Initiative (SFPI) Cost Model

International Nuclear Information System (INIS)

Price, Mary Alice

2010-01-01

The Nevada Test Site (NTS) began operating Material Control and Accountability (MC and A) under the Safeguards First Principle Initiative (SFPI), a risk-based and cost-effective program, in December 2006. The NTS SFPI Comprehensive Assessment of Safeguards Systems (COMPASS) Model is made up of specific elements (MC and A plan, graded safeguards, accounting systems, measurements, containment, surveillance, physical inventories, shipper/receiver differences, assessments/performance tests) and various sub-elements, which are each assigned effectiveness and contribution factors that when weighted and rated reflect the health of the MC and A program. The MC and A Cost Model, using an Excel workbook, calculates budget and/or actual costs using these same elements/sub-elements resulting in total costs and effectiveness costs per element/sub-element. These calculations allow management to identify how costs are distributed for each element/sub-element. The Cost Model, as part of the SFPI program review process, enables management to determine if spending is appropriate for each element/sub-element.

Primordial Black Holes from First Principles (Overview)

Science.gov (United States)

Lam, Casey; Bloomfield, Jolyon; Moss, Zander; Russell, Megan; Face, Stephen; Guth, Alan

2017-01-01

Given a power spectrum from inflation, our goal is to calculate, from first principles, the number density and mass spectrum of primordial black holes that form in the early universe. Previously, these have been calculated using the Press- Schechter formalism and some demonstrably dubious rules of thumb regarding predictions of black hole collapse. Instead, we use Monte Carlo integration methods to sample field configurations from a power spectrum combined with numerical relativity simulations to obtain a more accurate picture of primordial black hole formation. We demonstrate how this can be applied for both Gaussian perturbations and the more interesting (for primordial black holes) theory of hybrid inflation. One of the tools that we employ is a variant of the BBKS formalism for computing the statistics of density peaks in the early universe. We discuss the issue of overcounting due to subpeaks that can arise from this approach (the ``cloud-in-cloud'' problem). MIT UROP Office- Paul E. Gray (1954) Endowed Fund.

MICROSCOPE Mission: First Results of a Space Test of the Equivalence Principle.

Science.gov (United States)

Touboul, Pierre; Métris, Gilles; Rodrigues, Manuel; André, Yves; Baghi, Quentin; Bergé, Joël; Boulanger, Damien; Bremer, Stefanie; Carle, Patrice; Chhun, Ratana; Christophe, Bruno; Cipolla, Valerio; Damour, Thibault; Danto, Pascale; Dittus, Hansjoerg; Fayet, Pierre; Foulon, Bernard; Gageant, Claude; Guidotti, Pierre-Yves; Hagedorn, Daniel; Hardy, Emilie; Huynh, Phuong-Anh; Inchauspe, Henri; Kayser, Patrick; Lala, Stéphanie; Lämmerzahl, Claus; Lebat, Vincent; Leseur, Pierre; Liorzou, Françoise; List, Meike; Löffler, Frank; Panet, Isabelle; Pouilloux, Benjamin; Prieur, Pascal; Rebray, Alexandre; Reynaud, Serge; Rievers, Benny; Robert, Alain; Selig, Hanns; Serron, Laura; Sumner, Timothy; Tanguy, Nicolas; Visser, Pieter

2017-12-08

According to the weak equivalence principle, all bodies should fall at the same rate in a gravitational field. The MICROSCOPE satellite, launched in April 2016, aims to test its validity at the 10^{-15} precision level, by measuring the force required to maintain two test masses (of titanium and platinum alloys) exactly in the same orbit. A nonvanishing result would correspond to a violation of the equivalence principle, or to the discovery of a new long-range force. Analysis of the first data gives δ(Ti,Pt)=[-1±9(stat)±9(syst)]×10^{-15} (1σ statistical uncertainty) for the titanium-platinum Eötvös parameter characterizing the relative difference in their free-fall accelerations.

MICROSCOPE Mission: First Results of a Space Test of the Equivalence Principle

Science.gov (United States)

Touboul, Pierre; Métris, Gilles; Rodrigues, Manuel; André, Yves; Baghi, Quentin; Bergé, Joël; Boulanger, Damien; Bremer, Stefanie; Carle, Patrice; Chhun, Ratana; Christophe, Bruno; Cipolla, Valerio; Damour, Thibault; Danto, Pascale; Dittus, Hansjoerg; Fayet, Pierre; Foulon, Bernard; Gageant, Claude; Guidotti, Pierre-Yves; Hagedorn, Daniel; Hardy, Emilie; Huynh, Phuong-Anh; Inchauspe, Henri; Kayser, Patrick; Lala, Stéphanie; Lämmerzahl, Claus; Lebat, Vincent; Leseur, Pierre; Liorzou, Françoise; List, Meike; Löffler, Frank; Panet, Isabelle; Pouilloux, Benjamin; Prieur, Pascal; Rebray, Alexandre; Reynaud, Serge; Rievers, Benny; Robert, Alain; Selig, Hanns; Serron, Laura; Sumner, Timothy; Tanguy, Nicolas; Visser, Pieter

2017-12-01

According to the weak equivalence principle, all bodies should fall at the same rate in a gravitational field. The MICROSCOPE satellite, launched in April 2016, aims to test its validity at the 10-15 precision level, by measuring the force required to maintain two test masses (of titanium and platinum alloys) exactly in the same orbit. A nonvanishing result would correspond to a violation of the equivalence principle, or to the discovery of a new long-range force. Analysis of the first data gives δ (Ti ,Pt )=[-1 ±9 (stat)±9 (syst)]×10-15 (1 σ statistical uncertainty) for the titanium-platinum Eötvös parameter characterizing the relative difference in their free-fall accelerations.

Using continuous time stochastic modelling and nonparametric statistics to improve the quality of first principles models

DEFF Research Database (Denmark)

A methodology is presented that combines modelling based on first principles and data based modelling into a modelling cycle that facilitates fast decision-making based on statistical methods. A strong feature of this methodology is that given a first principles model along with process data......, the corresponding modelling cycle model of the given system for a given purpose. A computer-aided tool, which integrates the elements of the modelling cycle, is also presented, and an example is given of modelling a fed-batch bioreactor....

Electronic Stopping Power in LiF from First Principles

International Nuclear Information System (INIS)

Pruneda, J. M.; Sanchez-Portal, D.; Arnau, A.; Juaristi, J. I.; Artacho, Emilio

2007-01-01

Using time-dependent density-functional theory we calculate from first principles the rate of energy transfer from a moving proton or antiproton to the electrons of an insulating material, LiF. The behavior of the electronic stopping power versus projectile velocity displays an effective threshold velocity of ∼0.2 a.u. for the proton, consistent with recent experimental observations, and also for the antiproton. The calculated proton/antiproton stopping-power ratio is ∼2.4 at velocities slightly above the threshold (v∼0.4 a.u.), as compared to the experimental value of 2.1. The projectile energy loss mechanism is observed to be extremely local

The first principle calculation of two-dimensional Dirac materials

Science.gov (United States)

Lu, Jin

2017-12-01

As the size of integrated device becoming increasingly small, from the last century, semiconductor industry is facing the enormous challenge to break the Moore’s law. The development of calculation, communication and automatic control have emergent expectation of new materials at the aspect of semiconductor industrial technology and science. In spite of silicon device, searching the alternative material with outstanding electronic properties has always been a research point. As the discovery of graphene, the research of two-dimensional Dirac material starts to express new vitality. This essay studied the development calculation of 2D material’s mobility and introduce some detailed information of some approximation method of the first principle calculation.

First-principles calculation of the magnetic properties of paramagnetic fcc iron

International Nuclear Information System (INIS)

Johnson, D.D.; Gyorffy, B.L.; Pinski, F.J.; Staunton, J.; Stocks, G.M.

1985-01-01

Using the disordered local moment picture of itinerant magnetism, we present calculations of the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state. These calculations are based on the parameter-free, first principles approach of local spin density functional theory and the coherent potential approximation is used to treat the disorder associated with the random orientation of the local moments

The Interface between Gd and Monolayer MoS2: A First-Principles Study

KAUST Repository

Zhang, Xuejing; Mi, Wenbo; Wang, Xiaocha; Cheng, Yingchun; Schwingenschlö gl, Udo

2014-01-01

We analyze the electronic structure of interfaces between two-, four- and six-layer Gd(0001) and monolayer MoS2 by first-principles calculations. Strong chemical bonds shift the Fermi energy of MoS2 upwards into the conduction band. At the surface

Molecular electronics: insight from first-principles transport simulations.

Science.gov (United States)

Paulsson, Magnus; Frederiksen, Thomas; Brandbyge, Mads

2010-01-01

Conduction properties of nanoscale contacts can be studied using first-principles simulations. Such calculations give insight into details behind the conductance that is not readily available in experiments. For example, we may learn how the bonding conditions of a molecule to the electrodes affect the electronic transport. Here we describe key computational ingredients and discuss these in relation to simulations for scanning tunneling microscopy (STM) experiments with C60 molecules where the experimental geometry is well characterized. We then show how molecular dynamics simulations may be combined with transport calculations to study more irregular situations, such as the evolution of a nanoscale contact with the mechanically controllable break-junction technique. Finally we discuss calculations of inelastic electron tunnelling spectroscopy as a characterization technique that reveals information about the atomic arrangement and transport channels.

Anisotropic elastic and thermal properties of titanium borides by first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Sun, Liang; Gao, Yimin [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China); Xiao, Bing [Department of Physics and Quantum Theory Group, School of Science and Engineering, Tulane University, New Orleans, LA 70118 (United States); Li, Yefei, E-mail: yefeili@126.com [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China); Wang, Guoliang [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China)

2013-12-05

Highlights: •Elastic properties of titanium borides are calculated by first principles calculation. •Thermodynamical stability of titanium borides is analyzed. •Heat capacity and thermal expansion coefficient for titanium borides are calculated and compared. •Grüneisen parameters of titanium borides are calculated. -- Abstract: The anisotropic elastic and thermal expansions of the titanium borides (TiB{sub 2}, Ti{sub 3}B{sub 4}, TiB{sub P}nma and TiB{sub F}m3{sup ¯}m) are calculated from first-principles using density functional theory. All borides show different anisotropic elastic properties; the bulk, shear and Young’s moduli are consistent with those determined experimentally. The temperature dependence of thermal expansions is mainly caused by the restoration of thermal energy due to phonon excitations at low temperature. When the temperature is higher than 500 K, the volumetric coefficient is increased linearly by increasing temperature. Meanwhile, the heat capacities of titanium borides are obtained based on the knowledge of thermal expansion coefficient and the elasticity, the calculations are in good agreement with the experiments.

Pressure induced structural phase transition of OsB2: First-principles calculations

International Nuclear Information System (INIS)

Ren Fengzhu; Wang Yuanxu; Lo, V.C.

2010-01-01

Orthorhombic OsB 2 was synthesized at 1000 deg. C and its compressibility was measured by using the high-pressure X-ray diffraction in a Diacell diamond anvil cell from ambient pressure to 32 GPa [R.W. Cumberland, et al. (2005)]. First-principles calculations were performed to study the possibility of the phase transition of OsB 2 . An analysis of the calculated enthalpy shows that orthorhombic OsB 2 can transfer to the hexagonal phase at 10.8 GPa. The calculated results with the quasi-harmonic approximation indicate that this phase transition pressure is little affected by the thermal effect. The calculated phonon band structure shows that the hexagonal P 6 3 /mmc structure (high-pressure phase) is stable for OsB 2 . We expect the phase transition can be further confirmed by the experimental work. - Abstract: Graphical Abstract Legend (TOC Figure): Table of Contents Figure Pressure induced structural phase transition from the orthorhombic structure to the hexagonal one for OsB 2 takes place under 10.8 GPa (0 K), 10.35 GPa (300, 1000 K) by the first-principles predictions.

Accelerating the discovery of hidden two-dimensional magnets using machine learning and first principle calculations

Science.gov (United States)

Miyazato, Itsuki; Tanaka, Yuzuru; Takahashi, Keisuke

2018-02-01

Two-dimensional (2D) magnets are explored in terms of data science and first principle calculations. Machine learning determines four descriptors for predicting the magnetic moments of 2D materials within reported 216 2D materials data. With the trained machine, 254 2D materials are predicted to have high magnetic moments. First principle calculations are performed to evaluate the predicted 254 2D materials where eight undiscovered stable 2D materials with high magnetic moments are revealed. The approach taken in this work indicates that undiscovered materials can be surfaced by utilizing data science and materials data, leading to an innovative way of discovering hidden materials.

When Are Transport Pricing Policies Fair and Acceptable?

NARCIS (Netherlands)

Schuitema, Geertje; Steg, Linda; van Kruining, Monique

This study examines the relative importance of six policy outcomes related to different fairness principles for the perceived fairness and acceptability of pricing policies aimed at changing transport behaviour. The fairness and acceptability of six different types of transport pricing policies were

Automated first-principles mapping for phase-change materials.

Science.gov (United States)

Esser, Marc; Maintz, Stefan; Dronskowski, Richard

2017-04-05

Plotting materials on bi-coordinate maps according to physically meaningful descriptors has a successful tradition in computational solid-state science spanning more than four decades. Equipped with new ab initio techniques introduced in this work, we generate an improved version of the treasure map for phase-change materials (PCMs) as introduced previously by Lencer et al. which, other than before, charts all industrially used PCMs correctly. Furthermore, we suggest seven new PCM candidates, namely SiSb 4 Te 7 , Si 2 Sb 2 Te 5 , SiAs 2 Te 4 , PbAs 2 Te 4 , SiSb 2 Te 4 , Sn 2 As 2 Te 5 , and PbAs 4 Te 7 , to be used as synthetic targets. To realize aforementioned maps based on orbital mixing (or "hybridization") and ionicity coordinates, structural information was first included into an ab initio numerical descriptor for sp 3 orbital mixing and then generalized beyond high-symmetry structures. In addition, a simple, yet powerful quantum-mechanical ionization measure also including structural information was introduced. Taken together, these tools allow for (automatically) generating materials maps solely relying on first-principles calculations. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

First-principles study of the interaction and charge transfer between graphene and metals

NARCIS (Netherlands)

Khomyakov, Petr; Giovannetti, G.; Rusu, P.C.; Brocks, G.; van den Brink, J.; Kelly, Paul J.

2009-01-01

Measuring the transport of electrons through a graphene sheet necessarily involves contacting it with metal electrodes. We study the adsorption of graphene on metal substrates using first-principles calculations at the level of density-functional theory. The bonding of graphene to Al, Ag, Cu, Au,

Accounting Principles 30G. Interim Guide.

Science.gov (United States)

Manitoba Dept. of Education and Training, Winnipeg.

This curriculum guide was developed for a senior-level introductory accounting course for students in high schools in Manitoba. The course introduces Canadian accounting principles and practices; it applies Generally Accepted Accounting Principles (GAAP) to introductory financial accounting. The guide includes the following components: (1) an…

Electronic structure of B-doped diamond: A first-principles study

Directory of Open Access Journals (Sweden)

T. Oguchi

2006-01-01

Full Text Available Electronic structure of B-doped diamond is studied based on first-principles calculations with supercell models for substitutional and interstitial doping at 1.5–3.1 at.% B concentrations. Substitutional doping induces holes around the valence-band maximum in a rigid-band fashion. The nearest neighbor C site to B shows a large energy shift of 1s core state, which may explain reasonably experimental features in recent photoemission and X-ray absorption spectra. Doping at interstitial Td site is found to be unstable compared with that at the substitutional site

First-Principles Vibrational Electron Energy Loss Spectroscopy of β -Guanine

Science.gov (United States)

Radtke, G.; Taverna, D.; Lazzeri, M.; Balan, E.

2017-07-01

A general approach to model vibrational electron energy loss spectra obtained using an electron beam positioned away from the specimen is presented. The energy-loss probability of the fast electron is evaluated using first-principles quantum mechanical calculations (density functional theory) of the dielectric response of the specimen. The validity of the method is assessed using recently measured anhydrous β -guanine, an important molecular solid used by animals to produce structural colors. The good agreement between theory and experiments lays the basis for a quantitative interpretation of this spectroscopy in complex systems.

First-principle study of Mg adsorption on Si(111) surfaces

International Nuclear Information System (INIS)

Min-Ju, Ying; Ping, Zhang; Xiao-Long, Du

2009-01-01

We have carried out first-principle calculations of Mg adsorption on Si(111) surfaces. Different adsorption sites and coverage effects have been considered. We found that the threefold hollow adsorption is energy-favoured in each coverage considered, while for the clean Si(111) surface of metallic feature, we found that 0.25 and 0.5 ML Mg adsorption leads to a semiconducting surface. The results for the electronic behaviour suggest a polarized covalent bonding between the Mg adatom and Si(111) surface. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

AELAS: Automatic ELAStic property derivations via high-throughput first-principles computation

Science.gov (United States)

Zhang, S. H.; Zhang, R. F.

2017-11-01

The elastic properties are fundamental and important for crystalline materials as they relate to other mechanical properties, various thermodynamic qualities as well as some critical physical properties. However, a complete set of experimentally determined elastic properties is only available for a small subset of known materials, and an automatic scheme for the derivations of elastic properties that is adapted to high-throughput computation is much demanding. In this paper, we present the AELAS code, an automated program for calculating second-order elastic constants of both two-dimensional and three-dimensional single crystal materials with any symmetry, which is designed mainly for high-throughput first-principles computation. Other derivations of general elastic properties such as Young's, bulk and shear moduli as well as Poisson's ratio of polycrystal materials, Pugh ratio, Cauchy pressure, elastic anisotropy and elastic stability criterion, are also implemented in this code. The implementation of the code has been critically validated by a lot of evaluations and tests on a broad class of materials including two-dimensional and three-dimensional materials, providing its efficiency and capability for high-throughput screening of specific materials with targeted mechanical properties. Program Files doi:http://dx.doi.org/10.17632/f8fwg4j9tw.1 Licensing provisions: BSD 3-Clause Programming language: Fortran Nature of problem: To automate the calculations of second-order elastic constants and the derivations of other elastic properties for two-dimensional and three-dimensional materials with any symmetry via high-throughput first-principles computation. Solution method: The space-group number is firstly determined by the SPGLIB code [1] and the structure is then redefined to unit cell with IEEE-format [2]. Secondly, based on the determined space group number, a set of distortion modes is automatically specified and the distorted structure files are generated

A first-principles linear response description of the spin Nernst effect

OpenAIRE

Wimmer, S.; Ködderitzsch, D.; Chadova, K.; Ebert, H.

2013-01-01

A first-principles description of the spin Nernst effect, denoting the occurrence of a transverse spin current due to a temperature gradient, is presented. The approach, based on an extension to the Kubo-Streda equation for spin transport, supplies in particular the formal basis for investigations of diluted as well as concentrated alloys. Results for corresponding applications to the alloy system Au-Cu give the intrinsic and extrinsic contributions to the relevant transport coefficients. Usi...

The harm principle as a mid-level principle?: three problems from the context of infectious disease control.

Science.gov (United States)

Krom, André

2011-10-01

Effective infectious disease control may require states to restrict the liberty of individuals. Since preventing harm to others is almost universally accepted as a legitimate (prima facie) reason for restricting the liberty of individuals, it seems plausible to employ a mid-level harm principle in infectious disease control. Moral practices like infectious disease control support - or even require - a certain level of theory-modesty. However, employing a mid-level harm principle in infectious disease control faces at least three problems. First, it is unclear what we gain by attaining convergence on a specific formulation of the harm principle. Likely candidates for convergence, a harm principle aimed at preventing harmful conduct, supplemented by considerations of effectiveness and always choosing the least intrusive means still leave ample room for normative disagreement. Second, while mid-level principles are sometimes put forward in response to the problem of normative theories attaching different weight to moral principles, employing a mid-level harm principle completely leaves open how to determine what weight to attach to it in application. Third, there appears to be a trade-off between attaining convergence and finding a formulation of the harm principle that can justify liberty-restrictions in all situations of contagion, including interventions that are commonly allowed. These are not reasons to abandon mid-level theorizing altogether. But there is no reason to be too theory-modest in applied ethics. Morally justifying e.g. if a liberty-restriction in infectious disease control is proportional to the aim of harm-prevention, promptly requires moving beyond the mid-level harm principle. © 2011 Blackwell Publishing Ltd.

Dispersion correction derived from first principles for density functional theory and Hartree-Fock theory.

Science.gov (United States)

Guidez, Emilie B; Gordon, Mark S

2015-03-12

The modeling of dispersion interactions in density functional theory (DFT) is commonly performed using an energy correction that involves empirically fitted parameters for all atom pairs of the system investigated. In this study, the first-principles-derived dispersion energy from the effective fragment potential (EFP) method is implemented for the density functional theory (DFT-D(EFP)) and Hartree-Fock (HF-D(EFP)) energies. Overall, DFT-D(EFP) performs similarly to the semiempirical DFT-D corrections for the test cases investigated in this work. HF-D(EFP) tends to underestimate binding energies and overestimate intermolecular equilibrium distances, relative to coupled cluster theory, most likely due to incomplete accounting for electron correlation. Overall, this first-principles dispersion correction yields results that are in good agreement with coupled-cluster calculations at a low computational cost.

First principles calculation of material properties of group IV elements and III-V compounds

Science.gov (United States)

Malone, Brad Dean

This thesis presents first principles calculations on the properties of group IV elements and group III-V compounds. It includes investigations into what structure a material is likely to form in, and given that structure, what are its electronic, optical, and lattice dynamical properties as well as what are the properties of defects that might be introduced into the sample. The thesis is divided as follows: • Chapter 1 contains some of the conceptual foundations used in the present work. These involve the major approximations which allow us to approach the problem of systems with huge numbers of interacting electrons and atomic cores. • Then, in Chapter 2, we discuss one of the major limitations to the DFT formalism introduced in Chapter 1, namely its inability to predict the quasiparticle spectra of materials and in particular the band gap of a semiconductor. We introduce a Green's function approach to the electron self-energy Sigma known as the GW approximation and use it to compute the quasiparticle band structures of a number of group IV and III-V semiconductors. • In Chapter 3 we present a first-principles study of a number of high-pressure metastable phases of Si with tetrahedral bonding. The phases studied include all experimentally determined phases that result from decompression from the metallic beta-Sn phase, specifically the BC8 (Si-III), hexagonal diamond (Si-IV), and R8 (Si-XII). In addition to these, we also study the hypothetical ST12 structure found upon decompression from beta-Sn in germanium. • Our attention is then turned to the first principles calculations of optical properties in Chapter 4. The Bethe-Salpeter equation is then solved to obtain the optical spectrum of this material including electron-hole interactions. The calculated optical spectrum is compared with experimental data for other forms of silicon commonly used in photovoltaic devices, namely the cubic, polycrystalline, and amorphous forms. • In Chapter 5 we present

First principles calculations of interstitial and lamellar rhenium nitrides

Energy Technology Data Exchange (ETDEWEB)

Soto, G., E-mail: gerardo@cnyn.unam.mx [Universidad Nacional Autonoma de Mexico, Centro de Nanociencias y Nanotecnologia, Km 107 Carretera Tijuana-Ensenada, Ensenada Baja California (Mexico); Tiznado, H.; Reyes, A.; Cruz, W. de la [Universidad Nacional Autonoma de Mexico, Centro de Nanociencias y Nanotecnologia, Km 107 Carretera Tijuana-Ensenada, Ensenada Baja California (Mexico)

2012-02-15

Highlights: Black-Right-Pointing-Pointer The possible structures of rhenium nitride as a function of composition are analyzed. Black-Right-Pointing-Pointer The alloying energy is favorable for rhenium nitride in lamellar arrangements. Black-Right-Pointing-Pointer The structures produced by magnetron sputtering are metastable variations. Black-Right-Pointing-Pointer The structures produced by high-pressure high-temperature are stable configurations. Black-Right-Pointing-Pointer The lamellar structures are a new category of interstitial dissolutions. - Abstract: We report here a systematic first principles study of two classes of variable-composition rhenium nitride: i, interstitial rhenium nitride as a solid solution and ii, rhenium nitride in lamellar structures. The compounds in class i are cubic and hexagonal close-packed rhenium phases, with nitrogen in the octahedral and tetrahedral interstices of the metal, and they are formed without changes to the structure, except for slight distortions of the unit cells. In the compounds in class ii, by contrast, the nitrogen inclusion provokes stacking faults in the parent metal structure. These faults create trigonal-prismatic sites where the nitrogen residence is energetically favored. This second class of compounds produces lamellar structures, where the nitrogen lamellas are inserted among multiple rhenium layers. The Re{sub 3}N and Re{sub 2}N phases produced recently by high-temperature and high-pressure synthesis belong to this class. The ratio of the nitrogen layers to the rhenium layers is given by the composition. While the first principle calculations point to higher stability for the lamellar structures as opposed to the interstitial phases, the experimental evidence presented here demonstrates that the interstitial classes are synthesizable by plasma methods. We conclude that rhenium nitrides possess polymorphism and that the two-dimensional lamellar structures might represent an emerging class of materials

First principles calculations of interstitial and lamellar rhenium nitrides

International Nuclear Information System (INIS)

Soto, G.; Tiznado, H.; Reyes, A.; Cruz, W. de la

2012-01-01

Highlights: ► The possible structures of rhenium nitride as a function of composition are analyzed. ► The alloying energy is favorable for rhenium nitride in lamellar arrangements. ► The structures produced by magnetron sputtering are metastable variations. ► The structures produced by high-pressure high-temperature are stable configurations. ► The lamellar structures are a new category of interstitial dissolutions. - Abstract: We report here a systematic first principles study of two classes of variable-composition rhenium nitride: i, interstitial rhenium nitride as a solid solution and ii, rhenium nitride in lamellar structures. The compounds in class i are cubic and hexagonal close-packed rhenium phases, with nitrogen in the octahedral and tetrahedral interstices of the metal, and they are formed without changes to the structure, except for slight distortions of the unit cells. In the compounds in class ii, by contrast, the nitrogen inclusion provokes stacking faults in the parent metal structure. These faults create trigonal-prismatic sites where the nitrogen residence is energetically favored. This second class of compounds produces lamellar structures, where the nitrogen lamellas are inserted among multiple rhenium layers. The Re 3 N and Re 2 N phases produced recently by high-temperature and high-pressure synthesis belong to this class. The ratio of the nitrogen layers to the rhenium layers is given by the composition. While the first principle calculations point to higher stability for the lamellar structures as opposed to the interstitial phases, the experimental evidence presented here demonstrates that the interstitial classes are synthesizable by plasma methods. We conclude that rhenium nitrides possess polymorphism and that the two-dimensional lamellar structures might represent an emerging class of materials within binary nitride chemistry.

Comment on : "A novel approach for solving the Fisher equation using Exp-function method" [Phys. Lett. A 372 3836

NARCIS (Netherlands)

Kudryashov, Nikolai A.

2009-01-01

Using Exp-function method Ozis and Koroglu [T. Ozis, C. Koroglu, Phys. Lett. A 372 (2008) 3836] have found exact "solutions" of the Fisher equation. In this comment we demonstrate that all these solutions do not satisfy the Fisher equation. The efficiency of application of Exp-function method to

Multiphysics modeling using COMSOL a first principles approach

CERN Document Server

Pryor, Roger W

2011-01-01

Multiphysics Modeling Using COMSOL rapidly introduces the senior level undergraduate, graduate or professional scientist or engineer to the art and science of computerized modeling for physical systems and devices. It offers a step-by-step modeling methodology through examples that are linked to the Fundamental Laws of Physics through a First Principles Analysis approach. The text explores a breadth of multiphysics models in coordinate systems that range from 1D to 3D and introduces the readers to the numerical analysis modeling techniques employed in the COMSOL Multiphysics software. After readers have built and run the examples, they will have a much firmer understanding of the concepts, skills, and benefits acquired from the use of computerized modeling techniques to solve their current technological problems and to explore new areas of application for their particular technological areas of interest.

First-principles study of dielectric properties of cerium oxide

International Nuclear Information System (INIS)

Yamamoto, Takenori; Momida, Hiroyoshi; Hamada, Tomoyuki; Uda, Tsuyoshi; Ohno, Takahisa

2005-01-01

We have theoretically investigated the dielectric properties of fluorite CeO 2 as well as hexagonal and cubic Ce 2 O 3 by using first-principles pseudopotentials techniques within the local density approximation. Calculated electronic and lattice dielectric constants of CeO 2 are in good agreement with previous theoretical and experimental results. For Ce 2 O 3 , the hexagonal phase has a lattice dielectric constant comparable to that of CeO 2 , whereas the cubic phase has a much smaller one. We have concluded that the enhancement of the dielectric constant in CeO 2 epitaxially grown on Si is not due to its lattice expansion experimentally observed nor regular formation of oxygen vacancies in CeO 2

Magnetic materials at finite temperatures: thermodynamics and combined spin and molecular dynamics derived from first principles calculations

International Nuclear Information System (INIS)

Eisenbach, Markus; Perera, Meewanage Dilina N.; Landau, David P; Nicholson, Don M.; Yin, Junqi; Brown, Greg

2015-01-01

We present a unified approach to describe the combined behavior of the atomic and magnetic degrees of freedom in magnetic materials. Using Monte Carlo simulations directly combined with first principles the Curie temperature can be obtained ab initio in good agreement with experimental values. The large scale constrained first principles calculations have been used to construct effective potentials for both the atomic and magnetic degrees of freedom that allow the unified study of influence of phonon-magnon coupling on the thermodynamics and dynamics of magnetic systems. The MC calculations predict the specific heat of iron in near perfect agreement with experimental results from 300K to above Tc and allow the identification of the importance of the magnon-phonon interaction at the phase-transition. Further Molecular Dynamics and Spin Dynamics calculations elucidate the dynamics of this coupling and open the potential for quantitative and predictive descriptions of dynamic structure factors in magnetic materials using first principles-derived simulations.

Solid phase stability of molybdenum under compression: Sound velocity measurements and first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Zhang, Xiulu [Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, P.O. Box 919-102, 621900 Mianyang, Sichuan (China); Laboratory for Extreme Conditions Matter Properties, Southwest University of Science and Technology, 621010 Mianyang, Sichuan (China); Liu, Zhongli [Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, P.O. Box 919-102, 621900 Mianyang, Sichuan (China); College of Physics and Electric Information, Luoyang Normal University, 471022 Luoyang, Henan (China); Jin, Ke; Xi, Feng; Yu, Yuying; Tan, Ye; Dai, Chengda; Cai, Lingcang [Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, P.O. Box 919-102, 621900 Mianyang, Sichuan (China)

2015-02-07

The high-pressure solid phase stability of molybdenum (Mo) has been the center of a long-standing controversy on its high-pressure melting. In this work, experimental and theoretical researches have been conducted to check its solid phase stability under compression. First, we performed sound velocity measurements from 38 to 160 GPa using the two-stage light gas gun and explosive loading in backward- and forward-impact geometries, along with the high-precision velocity interferometry. From the sound velocities, we found no solid-solid phase transition in Mo before shock melting, which does not support the previous solid-solid phase transition conclusion inferred from the sharp drops of the longitudinal sound velocity [Hixson et al., Phys. Rev. Lett. 62, 637 (1989)]. Then, we searched its structures globally using the multi-algorithm collaborative crystal structure prediction technique combined with the density functional theory. By comparing the enthalpies of body centered cubic structure with those of the metastable structures, we found that bcc is the most stable structure in the range of 0–300 GPa. The present theoretical results together with previous ones greatly support our experimental conclusions.

[How to be prudent with synthetic biology. Synthetic Biology and the precautionary principle].

Science.gov (United States)

Rodríguez López, Blanca

2014-01-01

Synthetic biology is a new discipline that is twofold: firstly it offers the promise to pay benefits that can alleviate some of the ills that plague mankind; On the other hand, like all technologies, holds risks. Given these, the most critical and concerned about the risks, invoke the application of the precautionary principle, common in cases where an activity or new technology creates risks to the environment and/or human health, but far from universally accepted happens to be currently one of the most controversial principles. In this paper the question of the risks and benefits of synthetic biology and the relevance of applying the precautionary principle are analyzed. To do this we proceed as follows. The first part focuses on synthetic biology. At first, this discipline is characterized, with special attention to what is novel compared to the known as "genetic engineering". In the second stage both the benefits and the risks associated with it are discussed. The first part concludes with a review of the efforts currently being made to control or minimize the risks. The second part aims to analyze the precautionary principle and its possible relevance to the case of Synthetic Biology. At first, the different versions and interpretations of the principle and the various criticisms of which has been the subject are reviewed. Finally, after discarding the Precautionary Principle as an useful tool, it is seen as more appropriate some recent proposals to treat technologies that take into account not only risks but also their benefits.

Intrinsic and extrinsic spin-orbit torques from first principles

International Nuclear Information System (INIS)

Geranton, Guillaume

2017-01-01

This thesis attempts to shed light on the microscopic mechanisms underlying the current-induced magnetic torques in ferromagnetic heterostructures. We have developed first principles methods aiming at the accurate and effcient calculation of the so-called spin-orbit torques (SOTs) in magnetic thin films. The emphasis of this work is on the impurity-driven extrinsic SOTs. The main part of this thesis is dedicated to the development of a formalism for the calculation of the SOTs within the Korringa-Kohn-Rostoker (KKR) method. The impurity-induced transitions rates are obtained from first principles and their effect on transport properties is treated within the Boltzmann formalism. The developed formalism provides a mean to compute the SOTs beyond the conventional constant relaxation time approximation. We first apply our formalism to the investigation of FePt/Pt and Co/Cu bilayers in the presence of defects and impurities. Our results hint at a crucial dependence of the torque on the type of disorder present in the films, which we explain by a complex interplay of several competing Fermi surface contributions to the SOT. Astonishingly, specific defect distributions or doping elements lead respectively to an increase or a sign change of the torque, which can not be explained on the basis of simple models. We also compute the intrinsic SOT induced by electrical and thermal currents within the full potential linearized augmented plane-wave method. Motivated by recent experimental works, we then investigate the microscopic origin of the SOT in a Ag_2Bi-terminated Ag film grown on ferromagnetic Fe(110). We find that the torque in that system can not be explained solely by the spin-orbit coupling in the Ag_2Bi alloy, and instead results from the spin-orbit coupling in all regions of the film.Finally, we predict a large SOT in Fe/Ge bilayers and suggest that semiconductor substrates might be a promising alternative to heavy metals for the development of SOT-based magnetic

Intrinsic and extrinsic spin-orbit torques from first principles

Energy Technology Data Exchange (ETDEWEB)

Geranton, Guillaume

2017-09-01

This thesis attempts to shed light on the microscopic mechanisms underlying the current-induced magnetic torques in ferromagnetic heterostructures. We have developed first principles methods aiming at the accurate and effcient calculation of the so-called spin-orbit torques (SOTs) in magnetic thin films. The emphasis of this work is on the impurity-driven extrinsic SOTs. The main part of this thesis is dedicated to the development of a formalism for the calculation of the SOTs within the Korringa-Kohn-Rostoker (KKR) method. The impurity-induced transitions rates are obtained from first principles and their effect on transport properties is treated within the Boltzmann formalism. The developed formalism provides a mean to compute the SOTs beyond the conventional constant relaxation time approximation. We first apply our formalism to the investigation of FePt/Pt and Co/Cu bilayers in the presence of defects and impurities. Our results hint at a crucial dependence of the torque on the type of disorder present in the films, which we explain by a complex interplay of several competing Fermi surface contributions to the SOT. Astonishingly, specific defect distributions or doping elements lead respectively to an increase or a sign change of the torque, which can not be explained on the basis of simple models. We also compute the intrinsic SOT induced by electrical and thermal currents within the full potential linearized augmented plane-wave method. Motivated by recent experimental works, we then investigate the microscopic origin of the SOT in a Ag{sub 2}Bi-terminated Ag film grown on ferromagnetic Fe(110). We find that the torque in that system can not be explained solely by the spin-orbit coupling in the Ag{sub 2}Bi alloy, and instead results from the spin-orbit coupling in all regions of the film.Finally, we predict a large SOT in Fe/Ge bilayers and suggest that semiconductor substrates might be a promising alternative to heavy metals for the development of SOT

Quantitative analysis by X-ray fluorescence using first principles for matrix correction

International Nuclear Information System (INIS)

Hulett, L.D.; Dunn, H.W.; Tarter, J.G.

1978-01-01

The quantitative interpretation of X-ray fluorescence (XRF) data is often difficult because of matrix effects. The intensity of fluorescence measured for a given element is not only dependent on the element's concentration, but also on the mass absorption coefficients of the sample for the excitation and fluorescence radiation. Also, there are interelement effects in which high-energy fluorescence from heavier elements is absorbed by lighter elements with a resulting enhancement of their fluorescence. Recent theoretical treatments of this problem have shown that X-ray fluorescence data can be corrected for these matrix effects by calculations based on first principles. Fundamental constants, available in atomic physics data tables, are the only parameters needed. It is not necessary to make empirical calibrations. The application of this correctional procedure to alloys and alumina-supported catalysts is described. A description is given of a low-background spectrometer which uses monochromatic Ag Ksub(α) radiation for excitation. Matrix corrections by first principles can be easily applied to data from instruments of this type because fluorescence excitation cross-sections and mass absorption coefficients can be accurately defined for monochromatic radiation. (author)

Mechanical properties of layered oxysulfide CaZnOS from first principle calculations

Energy Technology Data Exchange (ETDEWEB)

Zhang, Zhi-Jun [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of); Feng, Ang [Key Laboratory of Transparent Opto-Functional Inorganic Materials of Chinese Academy of Sciences, Shanghai Institute of Ceramics, Shanghai, 200050 (China); Zhang, Shao-Lin; Zhang, Wei-Bin [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of); Yang, Woochul, E-mail: wyang@dongguk.edu [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of)

2016-06-15

Elastic and tensile properties of mixed-anion oxysulfide CaZnOS have been theoretically investigated by first principle method of density functional theory (DFT). Elastic constants were obtained by stress–strain relationships, and bulk structure parameters including bulk modulus, shear modulus, as well as Poisson's ratio were then calculated using Voigt-Reuses-Hill (VRH) approximation. The results of shear anisotropic factors, compressibility anisotropic factor and directional Young's modulus showed that CaZnOS is almost elastically isotropic in {001} planes and maintains elastic anisotropy in {100} or {010} planes. Chemical bond anisotropy shown by Mulliken atomic charges and bond overlap populations is responsible for the elastic anisotropy behavior aforementioned. Moreover, theoretical uniaxial and biaxial tensile results showed the crystal collapsed at strain more than 12%, except in the biaxial extension where CaZnOS collapsed at strain of 7%. - Highlights: • Elastic and theoretical tensile properties of CaZnOS have been investigated by first principle method. • CaZnOS is elastically isotropic in {001} planes and maintains elastic anisotropy in {100} or {010} planes. • Mulliken atomic charges and bond overlap populations are responsible for the elastic anisotropy behavior.

Improving accuracy of electrochemical capacitance and solvation energetics in first-principles calculations

Science.gov (United States)

Sundararaman, Ravishankar; Letchworth-Weaver, Kendra; Schwarz, Kathleen A.

2018-04-01

Reliable first-principles calculations of electrochemical processes require accurate prediction of the interfacial capacitance, a challenge for current computationally efficient continuum solvation methodologies. We develop a model for the double layer of a metallic electrode that reproduces the features of the experimental capacitance of Ag(100) in a non-adsorbing, aqueous electrolyte, including a broad hump in the capacitance near the potential of zero charge and a dip in the capacitance under conditions of low ionic strength. Using this model, we identify the necessary characteristics of a solvation model suitable for first-principles electrochemistry of metal surfaces in non-adsorbing, aqueous electrolytes: dielectric and ionic nonlinearity, and a dielectric-only region at the interface. The dielectric nonlinearity, caused by the saturation of dipole rotational response in water, creates the capacitance hump, while ionic nonlinearity, caused by the compactness of the diffuse layer, generates the capacitance dip seen at low ionic strength. We show that none of the previously developed solvation models simultaneously meet all these criteria. We design the nonlinear electrochemical soft-sphere solvation model which both captures the capacitance features observed experimentally and serves as a general-purpose continuum solvation model.

Using Principles of Programmed Instruction

Science.gov (United States)

Huffman, Harry

1971-01-01

Although programmed instruction in accounting is available, it is limited in scope and in acceptance. Teachers, however, may apply principles of programming to the individualizing of instruction. (Author)

First Principles Simulation of a Ceramic/ Metal Interface with Misfit

International Nuclear Information System (INIS)

Benedek, R.; Alavi, A.; Seidman, D. N.; Yang, L. H.; Muller, D. A.; Woodward, C.

2000-01-01

The relaxed atomic structure of a model ceramic/metal interface, {222}MgO/Cu , is simulated, including lattice constant mismatch, using first principles local-density functional theory plane wave pseudopotential methods. The 399-atom computational unit cell contains 36 O and 49 Cu atoms per layer in accordance with the 7/6 ratio of MgO to Cu lattice constants. The atomic layers on both sides of the interface warp to optimize the local bonding. The interface adhesive energy is calculated. The interface electronic structure is found to vary appreciably with the local environment. (c) 2000 The American Physical Society

Control-Oriented First Principles-Based Model of a Diesel Generator

DEFF Research Database (Denmark)

Knudsen, Jesper Viese; Bendtsen, Jan Dimon; Andersen, Palle

2016-01-01

This paper presents the development of a control-oriented tenth-order nonlinear model of a diesel driven generator set, using first principles modeling. The model provides physical system insight, while keeping the complexity at a level where it can be a tool for future design of improved automatic...... generation control (AGC), by including important nonlinearities of the machine. The nonlinearities are, as would be expected for a generator, primarily of bilinear nature. Validation of the model is done with measurements on a 60 kVA/48 kW diesel driven generator set in island operation during steps...

Thermal conductivities of phosphorene allotropes from first-principles calculations: a comparative study

OpenAIRE

Zhang, J.; Liu, H. J.; Cheng, L.; Wei, J.; Liang, J. H.; Fan, D. D.; Jiang, P. H.; Shi, J.

2017-01-01

Phosphorene has attracted tremendous interest recently due to its intriguing electronic properties. However, the thermal transport properties of phosphorene, especially for its allotropes, are still not well-understood. In this work, we calculate the thermal conductivities of five phosphorene allotropes ({\\alpha}-, \\b{eta}-, {\\gamma}-, {\\delta}- and {\\zeta}-phase) by using phonon Boltzmann transport theory combined with first-principles calculations. It is found that the {\\alpha}-phosphorene ...

Origin of current-induced forces in an atomic gold wire: A first-principles study

DEFF Research Database (Denmark)

Brandbyge, Mads; Stokbro, Kurt; Taylor, Jeremy Philip

2003-01-01

We address the microscopic origin of the current-induced forces by analyzing results of first principles density functional calculations of atomic gold wires connected to two gold electrodes with different electrochemical potentials. We find that current induced forces are closely related...

First principles studies of electron tunneling in proteins

Science.gov (United States)

Hayashi, Tomoyuki; Stuchebrukhov, Alexei A.

2014-01-01

A first principles study of electronic tunneling along the chain of seven Fe/S clusters in respiratory complex I, a key enzyme in the respiratory electron transport chain, is described. The broken-symmetry states of the Fe/S metal clusters calculated at both DFT and semi-empirical ZINDO levels were utilized to examine both the extremely weak electronic couplings between Fe/S clusters and the tunneling pathways, which provide a detailed atomistic-level description of the charge transfer process in the protein. One-electron tunneling approximation was found to hold within a reasonable accuracy, with only a moderate induced polarization of the core electrons. The method is demonstrated to be able to calculate accurately the coupling matrix elements as small as 10−4 cm−1. A distinct signature of the wave properties of electrons is observed as quantum interferences of multiple tunneling pathways. PMID:25383312

First-principles atomistic Wulff constructions for an equilibrium rutile TiO2 shape modeling

Science.gov (United States)

Jiang, Fengzhou; Yang, Lei; Zhou, Dali; He, Gang; Zhou, Jiabei; Wang, Fanhou; Chen, Zhi-Gang

2018-04-01

Identifying the exposed surfaces of rutile TiO2 crystal is crucial for its industry application and surface engineering. In this study, the shape of the rutile TiO2 was constructed by applying equilibrium thermodynamics of TiO2 crystals via first-principles density functional theory (DFT) and Wulff principles. From the DFT calculations, the surface energies of six low-index stoichiometric facets of TiO2 are determined after the calibrations of crystal structure. And then, combined surface energy calculations and Wulff principles, a geometric model of equilibrium rutile TiO2 is built up, which is coherent with the typical morphology of fully-developed equilibrium TiO2 crystal. This study provides fundamental theoretical guidance for the surface analysis and surface modification of the rutile TiO2-based materials from experimental research to industry manufacturing.

First-Principles Lattice Dynamics Method for Strongly Anharmonic Crystals

Science.gov (United States)

Tadano, Terumasa; Tsuneyuki, Shinji

2018-04-01

We review our recent development of a first-principles lattice dynamics method that can treat anharmonic effects nonperturbatively. The method is based on the self-consistent phonon theory, and temperature-dependent phonon frequencies can be calculated efficiently by incorporating recent numerical techniques to estimate anharmonic force constants. The validity of our approach is demonstrated through applications to cubic strontium titanate, where overall good agreement with experimental data is obtained for phonon frequencies and lattice thermal conductivity. We also show the feasibility of highly accurate calculations based on a hybrid exchange-correlation functional within the present framework. Our method provides a new way of studying lattice dynamics in severely anharmonic materials where the standard harmonic approximation and the perturbative approach break down.

Calculations of thermodynamic properties of PuO{sub 2} by the first-principles and lattice vibration

Energy Technology Data Exchange (ETDEWEB)

Minamoto, Satoshi [Energy and Industrial Systems Department, ITOCHU Techno-Solutions Corporation, Kasumigaseki 3-chome, Chiyoda-ku, Tokyo 100-6080 (Japan)], E-mail: satoshi.minamoto@ctc-g.co.jp; Kato, Masato [Japan Atomic Energy Agency, 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki 319-1194 (Japan); Konashi, Kenji [Institute for Materials Research, Tohoku University, 2145-2 Narita-chou, Oarai-chou, Ibaraki 311-1313 (Japan); Kawazoe, Yoshiyuki [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)

2009-03-15

Plutonium dioxide (PuO{sub 2}) is a key compound of mixed oxide fuel (MOX fuel). To predict the thermal properties of PuO{sub 2} at high temperature, it is important to understand the properties of MOX fuel. In this study, thermodynamic properties of PuO{sub 2} were evaluated by coupling of first-principles and lattice dynamics calculation. Cohesive energy was estimated from first-principles calculations, and the contribution of lattice vibration to total energy was evaluated by phonon calculations. Thermodynamic properties such as volume thermal expansion, bulk modulus and specific heat of PuO{sub 2} were investigated up to 1500 K.

Addendum to: ''The SNO solar neutrino data, neutrinoless double beta-decay and neutrino mass spectrum'' [Phys. Lett. B 544 (2002) 239

International Nuclear Information System (INIS)

Pascoli, S.; Petcov, S.T.

2004-01-01

We update our earlier study [Phys. Lett. B 544 (2002) 239], which was inspired by the 2002 SNO data, on the implications of the results of the solar neutrino experiments for the predictions of the effective Majorana mass in neutrinoless double beta-decay, vertical bar vertical bar. We obtain predictions for vertical bar vertical bar using the values of the neutrino oscillation parameters, obtained in the analyzes of the presently available solar neutrino data, including the just published data from the salt phase of the SNO experiment, the atmospheric neutrino and CHOOZ data and the first data from the KamLAND experiment. The main conclusion reached in the previous study [Phys. Lett. B 544 (2002) 239] of the existence of significant lower bounds on vertical bar vertical bar in the cases of neutrino mass spectrum of inverted hierarchical (IH) and quasi-degenerate (QD) type is strongly reinforced by fact that combined solar neutrino data (i) exclude the possibility of cos2θ o =0 at more than 5 s.d., (ii) determine as a best fit value cos2θ o =0.40, and (iii) imply at 95% C.L. that cos2θ o ∼>0.22, θ o being the solar neutrino mixing angle. For the IH and QD spectra we get using, e.g., the 90% C.L. allowed ranges of values of the oscillation parameters, vertical bar vertical bar ∼>0.010 eV and vertical bar vertical bar ∼>0.043 eV, respectively. We also comment on the possibility to get information on the neutrino mass spectrum and on the CP-violation in the lepton sector due to Majorana CP-violating phases

Probabilistic relationships in acceptable risk studies

International Nuclear Information System (INIS)

Benjamin, J.R.

1977-01-01

Acceptable risk studies involve uncertainties in future events; consequences and associated values, the acceptability levels, and the future decision environment. Probabilistic procedures afford the basic analytical tool to study the influence of each of these parameters on the acceptable risk decision, including their interrelationships, and combinations. A series of examples are presented in the paper in increasing complexity to illustrate the principles involved and to quantify the relationships to the acceptable risk decision. The basic objective of such studies is to broaden the scientific basis of acceptable risk decision making. It is shown that rationality and consistency in decision making is facilitated by such studies and that rather simple relationships exist in many situations of interest. The variation in criteria associated with an increase in the state of knowledge or change in the level of acceptability is also discussed. (Auth.)

Probabilistic relationships in acceptable risk studies

International Nuclear Information System (INIS)

Benjamin, J.R.

1977-01-01

Acceptable risk studies involve uncertainties in future events: consequences and associated values, the acceptability levels, and the future decision environment. Probabilistic procedures afford the basic analytical tool to study the influence of each of these parameters on the acceptable risk decision, including their interrelationships, and combinations. A series of examples are presented in the paper in increasing complexity to illustrate the principles involved and to quantify the relationships to the acceptable risk decision. The basic objective of such studies is to broaden the scientific basis of acceptable risk decision making. It is shown that rationality and consistency in decision making is facilitated by such studies and that rather simple relationships exist in many situations of interest. The variation in criteria associated with an increase in the state of knowledge or change in the level of acceptability is also discussed

When four principles are too many: a commentary.

Science.gov (United States)

Gillon, Raanan

2012-04-01

This commentary briefly argues that the four prima facie principles of beneficence, non-maleficence, respect for autonomy and justice enable a clinician (and anybody else) to make ethical sense of the author's proposed reliance on professional guidance and rules, on law, on professional integrity and on best interests, and to subject them all to ethical analysis and criticism based on widely acceptable basic prima facie moral obligations; and also to confront new situations in the light of those acceptable principles.

Phase Transition and Thermodynamics of Ruthenium Diboride via First-Principles Calculations

International Nuclear Information System (INIS)

Fen, Luo; Yan, Cheng; Xiang-Rong, Chen; Guang-Fu, Ji

2009-01-01

The pressure induced phase transitions of RuB 2 from the OsB 2 -type structure to the ReB 2 -type structure are investigated by first-principles calculations based on the plane-wave basis set with the generalized gradient approximation for exchange and correlation. It is found that the phase transition occurs at 18.6 GPa. We predict the phase transition from the OsB 2 -type RuB 2 to the ReB 2 -type RuB 2 at high temperatures for the first time. The dependences of the heat capacity, thermal expansion coefficient, and the Grüneisen parameter on pressure and temperature for OsB 2 -type RuB 2 and ReB 2 -type RuB 2 are also investigated

Maquet principle

Energy Technology Data Exchange (ETDEWEB)

Levine, R.B.; Stassi, J.; Karasick, D.

1985-04-01

Anterior displacement of the tibial tubercle is a well-accepted orthopedic procedure in the treatment of certain patellofemoral disorders. The radiologic appearance of surgical procedures utilizing the Maquet principle has not been described in the radiologic literature. Familiarity with the physiologic and biochemical basis for the procedure and its postoperative appearance is necessary for appropriate roentgenographic evaluation and the radiographic recognition of complications.

Magnetism, microstructure and First Principles calculations of atomized and annealed Ni3Al

International Nuclear Information System (INIS)

García-Escorial, A.; Crespo, P.; Hernando, A.; Lieblich, M.; Marín, P.; Velasco, V.; Ynduráin, F.

2014-01-01

Highlights: • The microstructure and order of as-atomized Ni 3 Al powder change with annealing. • The change of the magnetic properties shows the influence of the chemical order. • First Principles calculations show the effect of the density of states to the order. - Abstract: In this work Ni 3 Al powder particles obtained by atomization were characterized magnetically and microstructurally in as-atomized state and after annealing. Upon annealing the X-ray diffraction patterns show a noticeable increase of the signal of the ordered phase γ′-Ni 3 Al, L1 2 , phase and the microstructure evolves from a lamellar and dendrite to a large grain microstructure. The Curie temperature of the as-atomized powder particles is 85 K and decreases after annealing down to 50 K. First Principles calculations were carried out to correlate the experimental observations with local order of Ni and Al atoms and illustrate the importance of the local order in the density of states at the Fermi level, showing how the magnetic moment depends on the Ni and Al atomic position

Study on atomic and electronic structures of ceramic materials using spectroscopy, microscopy, and first principles calculation

International Nuclear Information System (INIS)

Mizoguchi, Teruyasu

2011-01-01

In this review, following two topics are introduced: 1) experimental and theoretical electron energy loss (EEL) near edge structures (ELNES) and X-ray absorption near edge structures (XANES), and 2) atomic and electronic structure analysis of ceramic interface by combing spectroscopy, microscopy, and first principles calculation. In the ELNES/XANES calculation, it is concluded that inclusion of core-hole effect in the calculation is essential. By combining high energy resolution observation and theoretical calculation, detailed analysis of the electronic structure is achieved. In addition, overlap population (OP) diagram is used to interpret the spectrum. In the case of AlN, sharp and intense first peak of N-K edge is found to reflect narrow dispersion of the conduction band bottom. By applying ELNES and the OP diagram to Cu/Al 2 O 3 heterointerface, it is revealed that intensity of prepeak in O-K edge is inverse proportional to interface strength. The relationships between atomic structure and defect energetics at SrTiO 3 grain boundary are also investigated, and reveal that the formation behavior of Ti vacancy is sensitive to the structural distortion. In addition, by using state-of-the-art spectroscopy, microscopy, and first principles calculations, atomic scale visualization of fluorine dopant in LaFeOAs and first principles calculation of HfO 2 phase transformation are demonstrated. (author)

Non-metallic dopant modulation of conductivity in substoichiometric tantalum pentoxide: A first-principles study

Science.gov (United States)

Bondi, Robert J.; Fox, Brian P.; Marinella, Matthew J.

2017-06-01

We apply density-functional theory calculations to predict dopant modulation of electrical conductivity (σo) for seven dopants (C, Si, Ge, H, F, N, and B) sampled at 18 quantum molecular dynamics configurations of five independent insertion sites into two (high/low) baseline references of σo in amorphous Ta2O5, where each reference contains a single, neutral O vacancy center (VO0). From this statistical population (n = 1260), we analyze defect levels, physical structure, and valence charge distributions to characterize nanoscale modification of the atomistic structure in local dopant neighborhoods. C is the most effective dopant at lowering Ta2Ox σo, while also exhibiting an amphoteric doping behavior by either donating or accepting charge depending on the host oxide matrix. Both B and F robustly increase Ta2Ox σo, although F does so through elimination of Ta high charge outliers, while B insertion conversely creates high charge O outliers through favorable BO3 group formation, especially in the low σo reference. While N applications to dope and passivate oxides are prevalent, we found that N exacerbates the stochasticity of σo we sought to mitigate; sensitivity to the N insertion site and some propensity to form N-O bond chemistries appear responsible. We use direct first-principles predictions of σo to explore feasible Ta2O5 dopants to engineer improved oxides with lower variance and greater repeatability to advance the manufacturability of resistive memory technologies.

Band gap of β-PtO2 from first-principles

Directory of Open Access Journals (Sweden)

Yong Yang

2012-06-01

Full Text Available We studied the band gap of β-PtO2 using first-principles calculations based on density functional theory (DFT. The results are obtained within the framework of the generalized gradient approximation (GGA, GGA+U, GW, and the hybrid functional methods. For the different types of calculations, the calculated band gap increases from ∼0.46 eV to 1.80 eV. In particular, the band gap by GW (conventional and self-consistent calculation shows a tendency of converging to ∼1.25 ± 0.05 eV. The effect of on-site Coulomb interaction on the bonding characteristics is also analyzed.

Heating electrons with ion irradiation: A first-principles approach

International Nuclear Information System (INIS)

Pruneda, J.M.; Sanchez-Portal, D.; Arnau, A.; Juaristi, J.I.; Artacho, E.

2009-01-01

Using time-dependent density functional theory we calculate from first-principles the rate of energy transfer from a moving charged particle to the electrons in an insulating material. The behavior of the electronic stopping power in LiF (a wide band gap insulator) versus projectile velocity displays an effective threshold velocity of 8.2 Bohr/asec for the proton, consistent with recent experimental observations. The calculated proton/antiproton stopping power ratio is 2.4 at velocities slightly above the threshold (16.5 Bohr/asec) as compared to the experimental value of 2.1. The approximations introduced in this new non-perturbative methodology are discussed, and results on the velocity dependence of the stopping power, the locality of the energy transfer, and other characteristics of the host material are presented.

Towards Rational Design of Functional Fluoride and Oxyfluoride Materials from First Principles

Science.gov (United States)

Charles, Nenian

Complex transition metal compounds (TMCs) research has produced functional materials with a range of properties, including ferroelectricity, colossal magnetoresistance, nonlinear optical activity and high-temperature superconductivity. Conventional routes to tune properties in transition metal oxides, for example, have relied primarily on cation chemical substitution and interfacial effects in thin film heterostructures. In heteroanionic TMCs, exhibiting two chemically distinct anions coordinating the same or different cations, engineering of the anion sub-lattice for property control is a promising alternative approach. The presence of multiple anions provides additional design variables, such as anion order, that are absent in homoanionic counterparts. The more complex structural and chemical phase space of heteroanionic materials provides a unique opportunity to realize enhanced or unanticipated electronic, optical, and magnetic responses. Although there is growing interest in heteroanionic materials, and synthetic and characterization advances are occurring for these materials, the crystal-chemistry principles for realizing structural and property control are only slowing emerging. This dissertation employs anion engineering to investigate phenomena in transition metal fluorides and oxyfluorides compounds using first principles density functional theory calculations. Oxyfluorides are particularly intriguing owing their tendency to stabilize highly ordered anion sublattices as well as the potential to combine the advantageous properties of transition metal oxides and fluorides. This work 1) addresses the challenges of studying fluorides and oxyfluorides using first principles calculations; 2) evaluates the feasibility of using external stimuli, such as epitaxial strain and hydrostatic pressure, to control properties of fluorides and oxyfluorides; and 3) formulates a computational workflow based on multiple levels of theory and computation to elucidate structure

Physical properties of the tetragonal CuMnAs: A first-principles study

Czech Academy of Sciences Publication Activity Database

Máca, František; Kudrnovský, Josef; Drchal, Václav; Carva, K.; Baláž, P.; Turek, I.

2017-01-01

Roč. 96, č. 9 (2017), s. 1-8, č. článku 094406. ISSN 2469-9950 R&D Projects: GA ČR GB14-37427G Grant - others:GA MŠk(CZ) LM2015042 Institutional support: RVO:68378271 Keywords : first-principles calculations * defects * CuMnAs * transport properties Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 3.836, year: 2016

Toward a first-principles integrated simulation of tokamak edge plasmas

International Nuclear Information System (INIS)

Chang, C S; Klasky, Scott A; Cummings, Julian; Samtaney, Ravi; Shoshani, A.; Sugiyama, L.; Keyes, David E; Ku, Seung-Hoe; Park, G.; Parker, Scott; Podhorszki, Norbert; Strauss, H.; Abbasi, H.; Adams, Mark; Barreto, Roselyne D; Bateman, Glenn; Bennett, K.; Chen, Yang; D'Azevedo, Eduardo; Docan, Ciprian; Ethier, Stephane; Feibush, E.; Greengard, Leslie; Hahm, Taik Soo; Hinton, Fred; Jin, Chen; Khan, A.; Kritz, Arnold; Krstic, Predrag S; Lao, T.; Lee, Wei-Li; Lin, Zhihong; Lofstead, J.; Mouallem, P. A.; Nagappan, M.; Pankin, A.; Parashar, Manish; Pindzola, Michael S.; Reinhold, Carlos O; Schultz, David Robert; Schwan, Karsten; Silver, D.; Sim, A.; Stotler, D.

2008-01-01

Performance of the ITER is anticipated to be highly sensitive to the edge plasma condition. The edge pedestal in ITER needs to be predicted from an integrated simulation of the necessary first principles, multi-scale physics codes. The mission of the SciDAC Fusion Simulation Project (FSP) Prototype Center for Plasma Edge Simulation (CPES) is to deliver such a code integration framework by (1) building new kinetic codes XGC0 and XGC1, which can simulate the edge pedestal buildup; (2) using and improving the existing MHD codes ELITE, M3D-OMP, M3D-MPP and NIMROD, for study of large-scale edge instabilities called Edge Localized Modes (ELMs); and (3) integrating the codes into a framework using cutting-edge computer science technology. Collaborative effort among physics, computer science, and applied mathematics within CPES has created the first working version of the End-to-end Framework for Fusion Integrated Simulation (EFFIS), which can be used to study the pedestal-ELM cycles

Valley Hall effect in disordered monolayer MoS₂ from first principles

DEFF Research Database (Denmark)

Olsen, Thomas; Souza, Ivo

2015-01-01

("unfolding") the Berry curvature from the folded Brillouin zone of the disordered supercell onto the normal Brillouin zone of the pristine crystal, and then averaging over several realizations of disorder. We use this scheme to study from first principles the effect of sulfur vacancies on the valley Hall...

Erratum: Laser-Induced Graphite Plasma Kinetic Spectroscopy under Different Ambient Pressures [Chin. Phys. Lett. Vol. 32, No. 4, 043201(2015)

International Nuclear Information System (INIS)

Chaudhary, K.; Rosalan, S.; Aziz, M. S.; Bahadoran, M.; Ali, J; Bidin, N.; Saktioto; Yupapin, P. P.

2015-01-01

There is a typewriting mistake in our previous report [Chin. Phys. Lett. 32, 4 (2015) 043201], the name of the fourth author M. Bohadoran should be M. Bahadoran. We note that this mistake does not affect the conclusion of our report, and apologize for any inconvenience for readers caused by our oversight. (paper)

Generalization of first-principles thermodynamic model: Application to hexagonal close-packed ε-Fe3N

DEFF Research Database (Denmark)

Bakkedal, Morten B.; Shang, Shu- Li; Liu, Zi-Kui

2016-01-01

A complete first-principles thermodynamic model was developed and applied to hexagonal close-packed structure ε-Fe3N. The electronic structure was calculated using density functional theory and the quasiharmonic phonon approximation to determine macroscopic thermodynamic properties at finite...

Predicting catalysis: Understanding ammonia synthesis from first-principles calculations

DEFF Research Database (Denmark)

Hellmann, A.; Baerends, E.J.; Biczysko, M.

2006-01-01

. Furthermore, our studies provide new insight into several related fields, for instance, gas-phase and electrochemical ammonia synthesis. The success of predicting the outcome of a catalytic reaction from first-principles calculations supports our point of view that, in the future, theory will be a fully......Here, we give a full account of a large collaborative effort toward an atomic-scale understanding of modern industrial ammonia production over ruthenium catalysts. We show that overall rates of ammonia production can be determined by applying various levels of theory (including transition state...... for any given point along an industrial reactor, and the kinetic results can be integrated over the catalyst bed to determine the industrial reactor yield. We find that, given the present uncertainties, the rate of ammonia production is well-determined directly from our atomic-scale calculations...

First principle study of sodium decorated graphyne

Energy Technology Data Exchange (ETDEWEB)

Sarkar, Utpal, E-mail: utpalchemiitkgp@yahoo.com [Assam University, Silchar (India); Bhattacharya, Barnali [Assam University, Silchar (India); Seriani, Nicola [The Abdus Salam ICTP, Trieste (Italy)

2015-11-05

Highlights: • Presence of Na decreases the stability of the system. • Na-decorated graphyne compounds are metallic and might be used in electronics. • The sodium-adsorbed graphyne can be used as electrodes in Na-ion battery. - Abstract: We present first-principles calculations of the electronic properties of Na-decorated graphyne. This structure of the graphyne family is a direct band gap semiconductor with a band gap of 0.44 eV in absence of sodium, but Na-decorated graphyne compounds are metallic, and can then be employed as carbon-based conductors. Metallization is due to charge donation from sodium to carbon. Pristine graphyne is more stable than Na-decorated graphyne, therefore is seems probable that, if this material should be employed as electrode in Na-ion batteries, it would lead to the formation of metallic sodium rather than well dispersed sodium ions. On the other side, this property might be useful if graphyne is employed in water desalination. Finally, the abrupt change from a semiconducting to a metallic state in presence of a small amount of sodium might be exploited in electronics, e.g. for the production of smooth metal–semiconductor interfaces through spatially selective deposition of sodium.

Equilibration and analysis of first-principles molecular dynamics simulations of water

Science.gov (United States)

Dawson, William; Gygi, François

2018-03-01

First-principles molecular dynamics (FPMD) simulations based on density functional theory are becoming increasingly popular for the description of liquids. In view of the high computational cost of these simulations, the choice of an appropriate equilibration protocol is critical. We assess two methods of estimation of equilibration times using a large dataset of first-principles molecular dynamics simulations of water. The Gelman-Rubin potential scale reduction factor [A. Gelman and D. B. Rubin, Stat. Sci. 7, 457 (1992)] and the marginal standard error rule heuristic proposed by White [Simulation 69, 323 (1997)] are evaluated on a set of 32 independent 64-molecule simulations of 58 ps each, amounting to a combined cumulative time of 1.85 ns. The availability of multiple independent simulations also allows for an estimation of the variance of averaged quantities, both within MD runs and between runs. We analyze atomic trajectories, focusing on correlations of the Kohn-Sham energy, pair correlation functions, number of hydrogen bonds, and diffusion coefficient. The observed variability across samples provides a measure of the uncertainty associated with these quantities, thus facilitating meaningful comparisons of different approximations used in the simulations. We find that the computed diffusion coefficient and average number of hydrogen bonds are affected by a significant uncertainty in spite of the large size of the dataset used. A comparison with classical simulations using the TIP4P/2005 model confirms that the variability of the diffusivity is also observed after long equilibration times. Complete atomic trajectories and simulation output files are available online for further analysis.

First principle study of structural, electronic and fermi surface properties of aluminum praseodymium

Science.gov (United States)

Shugani, Mani; Aynyas, Mahendra; Sanyal, S. P.

2018-05-01

We present a structural, Electronic and Fermi surface properties of Aluminum Praseodymium (AlPr) using First-principles density functional calculation by using full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA). The ground state properties along with electronic and Fermi surface properties are studied. It is found that AlPr is metallic and the bonding between Al and Pr is covalent.

Ethics needs principles--four can encompass the rest--and respect for autonomy should be "first among equals".

Science.gov (United States)

Gillon, R

2003-10-01

It is hypothesised and argued that "the four principles of medical ethics" can explain and justify, alone or in combination, all the substantive and universalisable claims of medical ethics and probably of ethics more generally. A request is renewed for falsification of this hypothesis showing reason to reject any one of the principles or to require any additional principle(s) that can't be explained by one or some combination of the four principles. This approach is argued to be compatible with a wide variety of moral theories that are often themselves mutually incompatible. It affords a way forward in the context of intercultural ethics, that treads the delicate path between moral relativism and moral imperialism. Reasons are given for regarding the principle of respect for autonomy as "first among equals", not least because it is a necessary component of aspects of the other three. A plea is made for bioethicists to celebrate the approach as a basis for global moral ecumenism rather than mistakenly perceiving and denigrating it as an attempt at global moral imperialism.

A first-principle investigation into effect of B-and BN-doped C60 in ...

Indian Academy of Sciences (India)

Annual Meetings · Mid Year Meetings · Discussion Meetings · Public Lectures · Lecture Workshops · Refresher Courses · Symposia · Live Streaming. Home; Journals; Bulletin of Materials Science; Volume 40; Issue 7. A first-principle investigation into effect of B- and BN-doped C 60 in lowering dehydrogenation of MXH 4 ...

Investigating the Thermochemical Response of Avcoat TPS from First Principles for Comparison with EFT-1 Data

Data.gov (United States)

National Aeronautics and Space Administration — The objective of our work is to develop improved thermal response models of the AVCOAT thermal protection system (TPS) from first principles, and to validate the...

Corrigendum to ;Lotka-Volterra systems satisfying a strong Painlevé property; [Phys. Lett. A 380 (47) (2016) 3977-3982

Science.gov (United States)

Bountis, Tassos; Vanhaecke, Pol

2017-12-01

The comment made after the proof of Proposition 3.3, in our paper [T. Bountis, P. Vanhaecke, Lotka-Volterra systems satisfying a strong Pailevé property, Phys. Lett. A 380 (47) (2016) 3977-3982], saying that the proposition can be generalized when linear terms are added to the Lotka-Volterra systems considered in the paper, is wrong. In general such deformed systems are not even Hamiltonian.

Is principle based legislation smart choice for capital market’s regulation

Directory of Open Access Journals (Sweden)

Borut Stražišar

2012-09-01

Full Text Available Global financial crisis in 2008 posted numerous questions about the reasons and triggers. In past three years world’s economic literature has been full of academic articles analysing each reason or trigger and scientific explanations of possible connections. Majority outcome was, that key factor was excessive use of derivatives and synthetic financial products, which were under regulated or not regulated at all. The outcome was that countries with developed financial markets introduced new regulations and controls in the field of derivatives and synthetic financial products. Term “systemic risk” was introduced in global financial market. But will this approach really prevent such global crisis? Submission is divided in three parts. First part deals with the theory of principle based regulation. Principle based regulation was firstly introduced in UK and latter accepted by European Union in the field of capital markets. It was a way, together with the Lamfalussy process, to make EU regulation acceptable for all member states. Instead of detailed prescribed behaviour, legislation texts prescribe only desirable goals. Implementation is left to each state or, even worse, to each supervised subject. So the implementation should depend on the capital market’s development, capital product’s structure, tradition, investment companies’ size etc. From a distant view, principle based legislation could be seen as a great legislation writing’s technique. It could be seen as an effective solution to regulate a fast developing field without need to change the regulation. But is it true? Second part of the submission addresses the legal questions and problems, connected to the principle based regulation starting with the validity of regulations. Broad definitions in Market in financial instruments Directive (MiFID, introduced for fast adaptation to new financial products and instruments, are now turning into dinosaurs. Contrary to US’s fast

Exact results and open questions in first principle functional RG

International Nuclear Information System (INIS)

Le Doussal, Pierre

2010-01-01

Some aspects of the functional RG (FRG) approach to pinned elastic manifolds (of internal dimension d) at finite temperature T > 0 are reviewed and reexamined in this much expanded version of Le Doussal (2006) . The particle limit d = 0 provides a test for the theory: there the FRG is equivalent to the decaying Burgers equation, with viscosity ν ∼ T-both being formally irrelevant. An outstanding question in FRG, i.e. how temperature regularizes the otherwise singular flow of T = 0 FRG, maps to the viscous layer regularization of inertial range Burgers turbulence (i.e. to the construction of the inviscid limit). Analogy between Kolmogorov scaling and FRG cumulant scaling is discussed. First, multi-loop FRG corrections are examined and the direct loop expansion at T > 0 is shown to fail already in d = 0, a hierarchy of ERG equations being then required (introduced in Balents and Le Doussal (2005) ). Next we prove that the FRG function R(u) and higher cumulants defined from the field theory can be obtained for any d from moments of a renormalized potential defined in an sliding harmonic well. This allows to measure the fixed point function R(u) in numerics and experiments. In d = 0 the beta function (of the inviscid limit) is obtained from first principles to four loop. For Sinai model (uncorrelated Burgers initial velocities) the ERG hierarchy can be solved and the exact function R(u) is obtained. Connections to exact solutions for the statistics of shocks in Burgers and to ballistic aggregation are detailed. A relation is established between the size distribution of shocks and the one for droplets. A droplet solution to the ERG functional hierarchy is found for any d, and the form of R(u) in the thermal boundary layer is related to droplet probabilities. These being known for the d = 0 Sinai model the function R(u) is obtained there at any T. Consistency of the ε=4-d expansion in one and two loop FRG is studied from first principles, and connected to shock and

A first principles investigation of the electronic structure of actinide oxides

DEFF Research Database (Denmark)

Petit, Leon; Svane, Axel; Szotek, Zdzislawa

2010-01-01

The ground state electronic structures of the actinide oxides AO, A2O3 and AO2 (A=U, Np, Pu, Am, Cm, Bk, Cf) are determined from first-principles calculations using the selfinteraction corrected local spin-density approximation. Our study reveals a strong link between preferred oxidation number...... and degree of localization. The ionic nature of the actinide oxides emerges from the fact that those oxides where the ground state is calculated to be metallic do not exist in nature, as the corresponding delocalized f-states favour the accommodation of additional O atoms into the crystal lattice....

Effect of contact deformation on contact electrification: a first-principles calculation

International Nuclear Information System (INIS)

Zhang, Yuanyue; Shao, Tianmin

2013-01-01

The effect of contact deformation on contact electrification of metallic materials was studied by the first-principles method. The results of charge population and the densities of states of the deformed contact models demonstrated that the magnitude of the transferred charge increased with deformation. The mechanism of the effect of deformation was investigated by studying the electronic properties of the deformed surface slabs. The results showed that crystal deformation led to a change in the electrostatic potential of the metal, where the number of nearly free electrons and unoccupied orbitals for charge transfer increased, and their energy barrier decreased. (paper)

First-principles calculations of a high-pressure synthesized compound PtC

International Nuclear Information System (INIS)

Li Linyan; Yu Wen; Jin Changqing

2005-01-01

The first-principles density-functional method is used to study the recently high-pressure synthesized compound PtC. It is confirmed by our calculations that platinum carbide has a zinc-blende ground-state phase at zero pressure and that the rock-salt structure is a high-pressure phase. The theoretical transition pressure from zinc-blende to rock-salt structure is determined to be 52 GPa. Furthermore, our calculation shows the possibility that the PtC experimentally synthesized under high pressure conditions might undergo a transition from rock-salt to zinc-blende structure after a pressure quench to ambient conditions

Chemical analysis using coincidence Doppler broadening and supporting first-principles theory: Applications to vacancy defects in compound semiconductors

International Nuclear Information System (INIS)

Makkonen, I.; Rauch, C.; Mäki, J.-M.; Tuomisto, F.

2012-01-01

The Doppler broadening of the positron annihilation radiation contains information on the chemical environment of vacancy defects trapping positrons in solids. The measured signal can, for instance, reveal impurity atoms situated next to vacancies. As compared to integrated quantities such as the positron annihilation rate or the annihilation line shape parameters, the full Doppler spectrum measured in the coincidence mode contains much more useful information for defect identification. This information, however, is indirect and complementary understanding is needed to fully interpret the results. First-principles calculations are a valuable tool in the analysis of measured spectra. One can construct an atomic-scale model for a given candidate defect, calculate from first principles the corresponding Doppler spectrum, and directly compare results between experiment and theory. In this paper we discuss recent examples of successful combinations of coincidence Doppler broadening measurements and supporting first-principles calculations. These demonstrate the predictive power of state-of-the-art calculations and the usefulness of such an approach in the chemical analysis of vacancy defects.

Leptogenesis from first principles in the resonant regime

International Nuclear Information System (INIS)

Garny, Mathias; Kartavtsev, Alexander; Hohenegger, Andreas

2011-12-01

The lepton asymmetry generated by the out-of-equilibrium decays of heavy Majorana neutrinos with a quasi-degenerate mass spectrum is resonantly enhanced. In this work, we study this scenario within a first-principle approach. The quantum field theoretical treatment is applicable for mass splittings of the order of the width of the Majorana neutrinos, for which the enhancement is maximally large. The non-equilibrium evolution of the mixing Majorana neutrino fields is described by a formal analytical solution of the Kadanoff-Baym equations, that is obtained by neglecting the back-reaction. Based on this solution, we derive approximate analytical expressions for the generated asymmetry and compare them to the Boltzmann result. We find that the resonant enhancement obtained from the Kadanoff-Baym approach is smaller compared to the Boltzmann approach, due to additional contributions that describe coherent transitions between the Majorana neutrino species. We also discuss corrections to the masses and widths of the degenerate pair of Majorana neutrinos that are relevant for very small mass splitting, and compare the approximate analytical result for the lepton asymmetry with numerical results. (orig.)

Leptogenesis from first principles in the resonant regime

Energy Technology Data Exchange (ETDEWEB)

Garny, Mathias [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Kartavtsev, Alexander [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Hohenegger, Andreas [Ecole Polytechnique Federale de Lausanne (Switzerland)

2011-12-15

The lepton asymmetry generated by the out-of-equilibrium decays of heavy Majorana neutrinos with a quasi-degenerate mass spectrum is resonantly enhanced. In this work, we study this scenario within a first-principle approach. The quantum field theoretical treatment is applicable for mass splittings of the order of the width of the Majorana neutrinos, for which the enhancement is maximally large. The non-equilibrium evolution of the mixing Majorana neutrino fields is described by a formal analytical solution of the Kadanoff-Baym equations, that is obtained by neglecting the back-reaction. Based on this solution, we derive approximate analytical expressions for the generated asymmetry and compare them to the Boltzmann result. We find that the resonant enhancement obtained from the Kadanoff-Baym approach is smaller compared to the Boltzmann approach, due to additional contributions that describe coherent transitions between the Majorana neutrino species. We also discuss corrections to the masses and widths of the degenerate pair of Majorana neutrinos that are relevant for very small mass splitting, and compare the approximate analytical result for the lepton asymmetry with numerical results. (orig.)

Design and exploration of semiconductors from first principles: A review of recent advances

Science.gov (United States)

Oba, Fumiyasu; Kumagai, Yu

2018-06-01

Recent first-principles approaches to semiconductors are reviewed, with an emphasis on theoretical insight into emerging materials and in silico exploration of as-yet-unreported materials. As relevant theory and methodologies have developed, along with computer performance, it is now feasible to predict a variety of material properties ab initio at the practical level of accuracy required for detailed understanding and elaborate design of semiconductors; these material properties include (i) fundamental bulk properties such as band gaps, effective masses, dielectric constants, and optical absorption coefficients; (ii) the properties of point defects, including native defects, residual impurities, and dopants, such as donor, acceptor, and deep-trap levels, and formation energies, which determine the carrier type and density; and (iii) absolute and relative band positions, including ionization potentials and electron affinities at semiconductor surfaces, band offsets at heterointerfaces between dissimilar semiconductors, and Schottky barrier heights at metal–semiconductor interfaces, which are often discussed systematically using band alignment or lineup diagrams. These predictions from first principles have made it possible to elucidate the characteristics of semiconductors used in industry, including group III–V compounds such as GaN, GaP, and GaAs and their alloys with related Al and In compounds; amorphous oxides, represented by In–Ga–Zn–O transparent conductive oxides (TCOs), represented by In2O3, SnO2, and ZnO; and photovoltaic absorber and buffer layer materials such as CdTe and CdS among group II–VI compounds and chalcopyrite CuInSe2, CuGaSe2, and CuIn1‑ x Ga x Se2 (CIGS) alloys, in addition to the prototypical elemental semiconductors Si and Ge. Semiconductors attracting renewed or emerging interest have also been investigated, for instance, divalent tin compounds, including SnO and SnS; wurtzite-derived ternary compounds such as ZnSnN2 and Cu

Quantum deletion: Beyond the no-deletion principle

International Nuclear Information System (INIS)

Adhikari, Satyabrata

2005-01-01

Suppose we are given two identical copies of an unknown quantum state and we wish to delete one copy from among the given two copies. The quantum no-deletion principle restricts us from perfectly deleting a copy but it does not prohibit us from deleting a copy approximately. Here we construct two types of a 'universal quantum deletion machine' which approximately deletes a copy such that the fidelity of deletion does not depend on the input state. The two types of universal quantum deletion machines are (1) a conventional deletion machine described by one unitary operator and (2) a modified deletion machine described by two unitary operators. Here it is shown that the modified deletion machine deletes a qubit with fidelity 3/4, which is the maximum limit for deleting an unknown quantum state. In addition to this we also show that the modified deletion machine retains the qubit in the first mode with average fidelity 0.77 (approx.) which is slightly greater than the fidelity of measurement for two given identical states, showing how precisely one can determine its state [S. Massar and S. Popescu, Phys. Rev. Lett. 74, 1259 (1995)]. We also show that the deletion machine itself is input state independent, i.e., the information is not hidden in the deleting machine, and hence we can delete the information completely from the deletion machine

Danish first aid books compliance with the new evidence-based non-resuscitative first aid guidelines

DEFF Research Database (Denmark)

Jensen, Theo Walther; Møller, Thea Palsgaard; Viereck, Søren

2018-01-01

BACKGROUND: The European Resuscitation Council (ERC) released new guidelines on resuscitation in 2015. For the first time, the guidelines included a separate chapter on first aid for laypersons. We analysed the current major Danish national first aid books to identify potential inconsistencies...... between the current books and the new evidence-based first aid guidelines. METHODS: We identified first aid books from all the first aid courses offered by major Danish suppliers. Based on the new ERC first aid guidelines, we developed a checklist of 26 items within 16 different categories to assess...... the content; this checklist was adapted following the principle of mutually exclusive and collectively exhaustive questioning. To assess the agreement between four raters, Fleiss' kappa test was used. Items that did not reach an acceptable kappa score were excluded. RESULTS: We evaluated 10 first aid books...

Magnetism, microstructure and First Principles calculations of atomized and annealed Ni{sub 3}Al

Energy Technology Data Exchange (ETDEWEB)

García-Escorial, A., E-mail: age@cenim.csic.es [CENIM-CSIC, Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); Crespo, P.; Hernando, A. [Instituto de Magnetismo Aplicado, IMA-UCM, P.O. Box 155, 28230 Madrid (Spain); Lieblich, M. [CENIM-CSIC, Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); Marín, P.; Velasco, V. [Instituto de Magnetismo Aplicado, IMA-UCM, P.O. Box 155, 28230 Madrid (Spain); Ynduráin, F. [Dpto. de Física de la Materia Condensada, UAM, Cantoblanco, 28049 Madrid (Spain)

2014-12-05

Highlights: • The microstructure and order of as-atomized Ni{sub 3}Al powder change with annealing. • The change of the magnetic properties shows the influence of the chemical order. • First Principles calculations show the effect of the density of states to the order. - Abstract: In this work Ni{sub 3}Al powder particles obtained by atomization were characterized magnetically and microstructurally in as-atomized state and after annealing. Upon annealing the X-ray diffraction patterns show a noticeable increase of the signal of the ordered phase γ′-Ni{sub 3}Al, L1{sub 2}, phase and the microstructure evolves from a lamellar and dendrite to a large grain microstructure. The Curie temperature of the as-atomized powder particles is 85 K and decreases after annealing down to 50 K. First Principles calculations were carried out to correlate the experimental observations with local order of Ni and Al atoms and illustrate the importance of the local order in the density of states at the Fermi level, showing how the magnetic moment depends on the Ni and Al atomic position.

Response to 'Comment on 'Pinch current limitation effect in plasma focus'' [Appl. Phys. Lett. 94, 076101 (2009)

International Nuclear Information System (INIS)

Lee, S.; Saw, S. H.

2009-01-01

The main point of the comment [Appl. Phys. Lett. 94, 076101 (2009)] is that Eq. (2) and consequentially Eq. (3) of the commented paper [Appl. Phys. Lett. 92, 021503 (2008)] require correction. The alternative equation suggested in the comment is derived using Kirchhoff's voltage rule. The comment consider only the energy distribution in the inductive components and the resultant equation confirms a progressive lowering of the I pinch /I peak ratio as the static inductance L 0 is reduced, lowering from 0.87 to 0.31 as L 0 is reduced from 100 to 5 nH according to the revised formula corresponding to Eq. (3), compared to 0.63-0.25 according to Eq. (3). This progressive lowering of the ratio I pinch /I peak due to the inductive energy distribution is one of two factors responsible for the pinch current limitation. The other factor is the progressive reduction in the L-C interaction time compared to the current dip duration denoted by δ cap in Eq. (2). The comment does not deal with δ cap at all; hence, its conclusion based on inductive energy distribution only is not useful, since in the low L 0 region when pinch current limitation begins to manifest, δ cap becomes more and more the dominant factor. In any case, the results of the paper do not depend on Eqs. (2) and (3), which are used in the paper only for illustrative purposes

Planning and acceptance testing of MV therapy installations

International Nuclear Information System (INIS)

Almond, Peter R.; Horton, John L.

1995-01-01

Purpose: This course is designed for practitioners and beginners in brachytherapy. The aim is to review biological principles equipment are aware of all aspects involved. The object is to cover in a broad overview the considerations that go into selecting, installing, testing and accepting megavoltage therapy equipment and to provide a resource for more detailed information. Planning and acceptance testing of a megavoltage therapy installation is a major undertaking for any size group, institution or department. It can take approximately two years from the time a decision is made to get a machine to where the first patient is treated. Because the equipment and site preparation are expensive, and most of the machines are complex and can be supplied by several different manufacturers, it is imperative that a great deal of thought and care go into the decision: the aim being that the specifications of the machine that is installed meet the immediate need of the department and the needs for the projected lifetime of the equipment. A general survey of the types of equipment available will be presented. This will concentrate on general purpose linear accelerators, although Cobalt 60 machines, microtrons and special purpose machines (intra-operative equipment) will also be covered. General descriptions of the machines along with typical specifications will be given. Selecting the best machine to meet specific needs can be quite complex and criteria for making the selection are presented in a series of twelve steps. site selection and room design, including the console area, are also critical. The general principles for shielding calculations will be provided. Critical to any installation is the acceptance testing of the equipment including material and radiation oncology performance tests. These tests will be outlined. A reading list of suitable references describing in detail many of the aspects of this course will be provided

First-principles studies of PETN molecular crystal vibrational frequencies under high pressure

Science.gov (United States)

Perger, Warren; Zhao, Jijun

2005-07-01

The vibrational frequencies of the PETN molecular crystal were calculated using the first-principles CRYSTAL03 program which employs an all-electron LCAO approach and calculates analytic first derivatives of the total energy with respect to atomic displacements. Numerical second derivatives were used to enable calculation of the vibrational frequencies at ambient pressure and under various states of compression. Three different density functionals, B3LYP, PW91, and X3LYP were used to examine the effect of the exchange-correlation functional on the vibrational frequencies. The pressure-induced shift of the vibrational frequencies will be presented and compared with experiment. The average deviation with experimental results is shown to be on the order of 2-3%, depending on the functional used.

First-principles study of hydrogen diffusion in transition metal Rhodium

International Nuclear Information System (INIS)

Bao, Wulijibilige; Cui, Xin; Wang, Zhi-Ping

2015-01-01

In this study, the diffuse pattern and path of hydrogen in transition metal rhodium are investigated by the first-principles calculations. Density functional theory is used to calculate the system energies of hydrogen atom occupying different positions in rhodium crystal lattice. The results indicate that the most stable position of hydrogen atom in rhodium crystal lattice locates at the octahedral interstice, and the tetrahedral interstice is the second stable site. The activation barrier energy for the diffusion of atomic hydrogen in transition metal rhodium is quantified by determining the most favorable path, i.e., the minimum-energy pathway for diffusion, that is the indirect octahedral-tetrahedral-octahedral (O-T-O) pathway, and the activation energy is 0.8345eV

Quantum Chemistry of Solids The LCAO First Principles Treatment of Crystals

CERN Document Server

Evarestov, Robert A

2007-01-01

Quantum Chemistry of Solids delivers a comprehensive account of the main features and possibilities of LCAO methods for the first principles calculations of electronic structure of periodic systems. The first part describes the basic theory underlying the LCAO methods applied to periodic systems and the use of wave-function-based (Hartree-Fock), density-based (DFT) and hybrid hamiltonians. The translation and site symmetry consideration is included to establish connection between k-space solid-state physics and real-space quantum chemistry methods in the framework of cyclic model of an infinite crystal. The inclusion of electron correlation effects for periodic systems is considered on the basis of localized crystalline orbitals. The possibilities of LCAO methods for chemical bonding analysis in periodic systems are discussed. The second part deals with the applications of LCAO methods for calculations of bulk crystal properties, including magnetic ordering and crystal structure optimization. The discussion o...

First-principles study on the creation of holes in high Tc cuprates

International Nuclear Information System (INIS)

Ambrosch-Draxl, C.; Sherman, E.Ya.; Auer, H.; Thonhauser, T.

2004-01-01

We investigate the charge redistribution in high T c cuprates as a function of pressure, composition, and doping. To this extent we have performed first-principles calculations based on density functional theory for several representatives of the Hg based cuprates. In particular, we focus on the creation of holes in the copper-oxygen planes. Conclusions are drawn about the similarities and differences between the three parameters influencing the superconducting transition temperature. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Thermodynamic properties of Mg2Si and Mg2Ge investigated by first principles method

International Nuclear Information System (INIS)

Wang, Hanfu; Jin, Hao; Chu, Weiguo; Guo, Yanjun

2010-01-01

The lattice dynamics and thermodynamic properties of Mg 2 Si and Mg 2 Ge are studied based on the first principles calculations. We obtain the phonon dispersion curves and phonon density of states spectra using the density functional perturbation theory with local density approximations. By employing the quasi-harmonic approximation, we calculate the temperature dependent Helmholtz free energy, bulk modulus, thermal expansion coefficient, specific heat, Debye temperature and overall Grueneisen coefficient. The results are in good agreement with available experimental data and previous theoretical studies. The thermal conductivities of both compounds are then estimated with the Slack's equation. By carefully choosing input parameters, especially the acoustic Debye temperature, we find that the calculated thermal conductivities agree fairly well with the experimental values above 80 K for both compounds. This demonstrates that the lattice thermal conductivity of simple cubic semiconductors may be estimated with satisfactory accuracy by combining the Slack's equation with the necessary thermodynamics parameters derived completely from the first principles calculations.

Surface Reactivity of Li2MnO3: First-Principles and Experimental Study.

Science.gov (United States)

Quesne-Turin, Ambroise; Flahaut, Delphine; Croguennec, Laurence; Vallverdu, Germain; Allouche, Joachim; Charles-Blin, Youn; Chotard, Jean-Noël; Ménétrier, Michel; Baraille, Isabelle

2017-12-20

This article deals with the surface reactivity of (001)-oriented Li 2 MnO 3 crystals investigated from a multitechnique approach combining material synthesis, X-ray photoemission spectroscopy (XPS), scanning electron microscopy, Auger electron spectroscopy, and first-principles calculations. Li 2 MnO 3 is considered as a model compound suitable to go further in the understanding of the role of tetravalent manganese atoms in the surface reactivity of layered lithium oxides. The knowledge of the surface properties of such materials is essential to understand the mechanisms involved in parasitic phenomena responsible for early aging or poor storage performances of lithium-ion batteries. The surface reactivity was probed through the adsorption of SO 2 gas molecules on large Li 2 MnO 3 crystals to be able to focus the XPS beam on the top of the (001) surface. A chemical mapping and XPS characterization of the material before and after SO 2 adsorption show in particular that the adsorption is homogeneous at the micro- and nanoscale and involves Mn reduction, whereas first-principles calculations on a slab model of the surface allow us to conclude that the most energetically favorable species formed is a sulfate with charge transfer implying reduction of Mn.

Safety culture and public acceptance

International Nuclear Information System (INIS)

Mikhalevich, Alexander A.

2002-01-01

After the Chernobyl NPP accident a public acceptance has become a key factor in nuclear power development all over the world. Therefore, nuclear safety culture should be based not only on technical principles, responsibilities, supervision, regulatory provisions, emergency preparedness, but the public awareness of minimum risk during the operation and decommissioning of NPPs, radioactive waste management, etc. (author)

Challenge and Opportunity: the ALI/III Global Principles Project ...

African Journals Online (AJOL)

This contribution explains the process whereby the American Law Institute and the International Insolvency Institute (1) developed principles of cooperation with regard to cross-border insolvency; (2) established acceptance of these principles in jurisdictions across the world, subject to any necessary local modifications; and ...

Geometric treatment of electromagnetic phenomena in conducting materials: variational principles

Energy Technology Data Exchange (ETDEWEB)

BadIa-Majos, A [Departamento de Fisica de la Materia Condensada-ICMA, Universidad de Zaragoza (Spain); Carinena, J F [Departamento de Fisica Teorica, Universidad de Zaragoza (Spain); Lopez, C [Departamento de Matematicas, Universidad de Alcala de Henares (Spain)

2006-11-24

The dynamical equations of an electromagnetic field coupled with a conducting material are studied. The properties of the interaction are described by a classical field theory with tensorial material laws in spacetime geometry. We show that the main features of superconducting response emerge in a natural way within the covariance, gauge invariance and variational formulation requirements. In particular, the Ginzburg-Landau theory follows straightforwardly from the London equations when fundamental symmetry properties are considered. Unconventional properties, such as the interaction of superconductors with electrostatic fields are naturally introduced in the geometric theory, at a phenomenological level. The BCS background is also suggested by macroscopic fingerprints of the internal symmetries. It is also shown that dissipative conducting behaviour may be approximately treated in a variational framework after breaking covariance for adiabatic processes. Thus, nonconservative laws of interaction are formulated by a purely spatial variational principle, in a quasi-stationary time discretized evolution. This theory justifies a class of nonfunctional phenomenological principles, introduced for dealing with exotic conduction properties of matter (BadIa and Lopez 2001 Phys. Rev. Lett. 87 127004)

First Principles Calculations of Oxygen Adsorption on the UN(001) Surface

International Nuclear Information System (INIS)

Zhukovskii, Yuri F.; Bocharov, Dmitry; Kotomin, Eugene Alexej; Evarestov, Robert; Bandura, A.V.

2009-01-01

Fabrication, handling and disposal of nuclear fuel materials require comprehensive knowledge of their surface morphology and reactivity. Due to unavoidable contact with air components (even at low partial pressures), UN samples contain considerable amount of oxygen impurities affecting fuel properties. In this study we focus on reactivity of the energetically most stable (001) substrate of uranium nitride towards the atomic oxygen as one of initial stages for further UN oxidation. The basic properties of O atoms adsorbed on the UN(001) surface are simulated here combining the two first principles calculation methods based on the plane wave basis set and that of the localized orbitals.

Stability, electronic and thermodynamic properties of aluminene from first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Yuan, Junhui [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Yu, Niannian [School of Science, Wuhan University of Technology, Wuhan, Hubei 430070 (China); Xue, Kanhao, E-mail: xkh@hust.edu.cn [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Miao, Xiangshui [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)

2017-07-01

Highlights: • We have predicted two NEW stable phases of atomic layer aluminum, buckled and 8-Pmmn aluminene. • We have revealed the electronic structures and bonding characteristics of aluminene. • Thermodynamic properties of aluminene were investigated based on phonon properties. - Abstract: Using first-principles calculations based on density functional theory (DFT), we have investigated the structure stability and electronic properties of both buckled and 8-Pmmn phase aluminene. Phonon dispersion analysis reveals that the buckled and 8-Pmmn aluminene are dynamically stable. The band structure shows that both the buckled and 8-Pmmn aluminene exhibit metallic behavior. Finally, the thermodynamic properties are investigated based on phonon properties.

Stability, electronic and thermodynamic properties of aluminene from first-principles calculations

International Nuclear Information System (INIS)

Yuan, Junhui; Yu, Niannian; Xue, Kanhao; Miao, Xiangshui

2017-01-01

Highlights: • We have predicted two NEW stable phases of atomic layer aluminum, buckled and 8-Pmmn aluminene. • We have revealed the electronic structures and bonding characteristics of aluminene. • Thermodynamic properties of aluminene were investigated based on phonon properties. - Abstract: Using first-principles calculations based on density functional theory (DFT), we have investigated the structure stability and electronic properties of both buckled and 8-Pmmn phase aluminene. Phonon dispersion analysis reveals that the buckled and 8-Pmmn aluminene are dynamically stable. The band structure shows that both the buckled and 8-Pmmn aluminene exhibit metallic behavior. Finally, the thermodynamic properties are investigated based on phonon properties.

First-principles theory of inelastic currents in a scanning tunneling microscope

DEFF Research Database (Denmark)

Stokbro, Kurt; Hu, Ben Yu-Kuang; Thirstrup, C.

1998-01-01

A first-principles theory of inelastic tunneling between a model probe tip and an atom adsorbed on a surface is presented, extending the elastic tunneling theory of Tersoff and Hamann. The inelastic current is proportional to the change in the local density of states at the center of the tip due...... to the addition of the adsorbate. We use the theory to investigate the vibrational heating of an adsorbate below a scanning tunneling microscopy tip. We calculate the desorption rate of PI from Si(100)-H(2 X 1) as a function of the sample bias and tunnel current, and find excellent a,agreement with recent...

A first-principles study of the electronic structure and stability of Be(BH4)2

NARCIS (Netherlands)

Setten, M.J. van; Wijs, G.A. de; Brocks, G.

2007-01-01

Alanates and boranates are studied intensively because of their potential use as hydrogen storage materials. In this paper we present a first-principles study of the electronic structure and the energetics of beryllium boranate, Be(BH4)2. From total energy calculations we show that - in contrast to

Electronic and optical properties of new multifunctional materials via half-substituted hematite: First principles calculations

KAUST Repository

Yang, Hua; Mi, Wenbo; Bai, Haili; Cheng, Yingchun

2012-01-01

Electronic structure and optical properties of α-FeMO 3 systems (M = Sc, Ti, V, Cr, Cu, Cd or In) have been investigated using first principles calculations. All of the FeMO 3 systems have a large net magnetic moment. The ground state of pure α-Fe 2

First-principles calculation of the structural stability of 6d transition metals

International Nuclear Information System (INIS)

Oestlin, A.; Vitos, L.

2011-01-01

The phase stability of the 6d transition metals (elements 103-111) is investigated using first-principles electronic-structure calculations. Comparison with the lighter transition metals reveals that the structural sequence trend is broken at the end of the 6d series. To account for this anomalous behavior, the effect of relativity on the lattice stability is scrutinized, taking different approximations into consideration. It is found that the mass-velocity and Darwin terms give important contributions to the electronic structure, leading to changes in the interstitial charge density and, thus, in the structural energy difference.

First-principle calculation of refractive indices of BAlN and BGaN

KAUST Repository

Alqatari, Feras; Li, Kuang-Hui; Liu, Kaikai; Li, Xiaohang

2018-01-01

The refractive indices of BAlN and BGaN ternary alloys are being investigated using first-principle calculation. The hybrid density functional theory is applied to determine the refractive indices of different alloys. A peculiar bowing effect in the static refractive indices and crossovers of different refractive index curves are found. We speculate that the explanation to these phenomena lies in the interband transitions of electrons where each band bows at a different rate from the other. An average of these bowing effects may result in the bowing of refractive indices.

First principles calculations for interaction of tyrosine with (ZnO)3 cluster

Science.gov (United States)

Singh, Satvinder; Singh, Gurinder; Kaura, Aman; Tripathi, S. K.

2018-04-01

First Principles Calculations have been performed to study interactions of Phenol ring of Tyrosine (C6H5OH) with (ZnO)3 atomic cluster. All the calculations have been performed under the Density Functional Theory (DFT) framework. Structural and electronic properties of (ZnO)3/C6H5OH have been studied. Gaussian basis set approach has been adopted for the calculations. A ring type most stable (ZnO)3 atomic cluster has been modeled, analyzed and used for the calculations. The compatibility of the results with previous studies has been presented here.

First-principle calculation of refractive indices of BAlN and BGaN

KAUST Repository

Alqatari, Feras

2018-03-27

The refractive indices of BAlN and BGaN ternary alloys are being investigated using first-principle calculation. The hybrid density functional theory is applied to determine the refractive indices of different alloys. A peculiar bowing effect in the static refractive indices and crossovers of different refractive index curves are found. We speculate that the explanation to these phenomena lies in the interband transitions of electrons where each band bows at a different rate from the other. An average of these bowing effects may result in the bowing of refractive indices.

First principles studies of complex oxide surfaces and interfaces

International Nuclear Information System (INIS)

Noguera, Claudine; Finocchi, Fabio; Goniakowski, Jacek

2004-01-01

Oxides enter our everyday life and exhibit an impressive variety of physical and chemical properties. The understanding of their behaviour, which is often determined by the electronic and atomic structures of their surfaces and interfaces, is a key question in many fields, such as geology, environmental chemistry, catalysis, thermal coatings, microelectronics, and bioengineering. In the last decade, first principles methods, mainly those based on the density functional theory, have been frequently applied to study complex oxide surfaces and interfaces, complementing the experimental observations. In this work, we discuss some of these contributions, with emphasis on several issues that are especially important when dealing with oxides: the local electronic structure at interfaces, and its connection with chemical reactivity; the charge redistribution and the bonding variations, in relation to screening properties; and the possibility of bridging the gap between model and real systems by taking into account the chemical environments and the effect of finite temperatures, and by performing simulations on systems of an adequate (large) size

First-principles prediction of Tl/SiC for valleytronics

KAUST Repository

Xu, Zhen; Zhang, Qingyun; Shen, Qian; Cheng, Yingchun; Schwingenschlö gl, Udo; Huang, Wei

2017-01-01

Recently, monolayer Tl on a Si or Ge substrate has been proposed for potential valleytronic systems. However, the band gaps of these systems are less than 0.1 eV, which is too small to be applied because an electric field or magnetic doping will reduce the band gaps further for the systems to become metallic. Here, we investigate SiC as an alternative substrate. By first-principles calculations we demonstrate that monolayer Tl can be grown on SiC. There are two valleys around the K/K′ points and the Berry curvature shows that the two valleys are inequivalent, indicating valley pseudospin. Moreover, due to the larger band gap of SiC (3.3 eV), the band gap of the Tl/SiC system is 0.6 eV, which is large enough for valley manipulation. Furthermore, we demonstrate that Cr doping can achieve valley polarization. Our study shows that the Tl/SiC system is promising for valleytronic applications.

First-principles prediction of Tl/SiC for valleytronics

KAUST Repository

Xu, Zhen

2017-09-22

Recently, monolayer Tl on a Si or Ge substrate has been proposed for potential valleytronic systems. However, the band gaps of these systems are less than 0.1 eV, which is too small to be applied because an electric field or magnetic doping will reduce the band gaps further for the systems to become metallic. Here, we investigate SiC as an alternative substrate. By first-principles calculations we demonstrate that monolayer Tl can be grown on SiC. There are two valleys around the K/K′ points and the Berry curvature shows that the two valleys are inequivalent, indicating valley pseudospin. Moreover, due to the larger band gap of SiC (3.3 eV), the band gap of the Tl/SiC system is 0.6 eV, which is large enough for valley manipulation. Furthermore, we demonstrate that Cr doping can achieve valley polarization. Our study shows that the Tl/SiC system is promising for valleytronic applications.

Comment on "Total Negative Refraction in Real Crystals for Ballistic Electrons and Light" (Phys. Rev. Lett. 91, 157404 (2003))

OpenAIRE

Yau, H. -F.; Liu, J. -P.; Ke, B.; Kuo, C. -H.; Ye, Z.

2003-01-01

Recently, Zhang et al. (Phys. Rev. Lett. 91, 157404 (2003)) have demonstrated that an amphoteric refraction, i. e. both positive and negative refraction, may prevail at the interface of two uniaxial anisotropic crystals when their optical axes are in different directions. The authors subsequently made a correspondence between such a refraction with the negative refraction expected for Left Handed Materials (LHMs). Here we comment that the amphoteric refraction can be observed even with one un...

The principle of territoriality and cross-border loss compensation

NARCIS (Netherlands)

Marres, O.

2011-01-01

Member States are free to define their income tax base. They may in principle disregard foreign-sourced income, resulting in the impossibility of cross-border loss compensation. The European Court of Justice (ECJ) has accepted the principle of territoriality as a criterion for the division of the

First principles calculation of thermodynamic properties of NaAlSi ternary

International Nuclear Information System (INIS)

Qin Jining; Lu Weijie; Zhang Di; Fan Tongxiang

2012-01-01

PbFCl-type NaAlSi ternary is a corrosion compound found in aluminum, which is used as a sealing material in sodium sulfur battery. To understand and control the corrosion process, it is important to predict its quantitative properties. In this study, a first-principles calculation has been carried out to calculate its equilibrium lattice parameters, bulk modulus and pressure derivative of bulk modulus by both all-electron full-potential linear augmented plane wave scheme and pseudopotential plane wave scheme within the generalized gradient approximation. The theoretical results show good agreement with the available experimental data. The thermodynamic properties, including the specific heat capacity and entropy with pressure up to 9 GPa, have been investigated for the first time by coupling of density functional perturbation theory and quasiharmonic approximation. The volume and linear thermal expansion coefficients were estimated and the results show that the linear thermal expansion on c-axis is nearly twice as large as that on a-axis within the calculated temperature.

Oxidation of InP nanowires: a first principles molecular dynamics study.

Science.gov (United States)

Berwanger, Mailing; Schoenhalz, Aline L; Dos Santos, Cláudia L; Piquini, Paulo

2016-11-16

InP nanowires are candidates for optoelectronic applications, and as protective capping layers of III-V core-shell nanowires. Their surfaces are oxidized under ambient conditions which affects the nanowire physical properties. The majority of theoretical studies of InP nanowires, however, do not take into account the oxide layer at their surfaces. In this work we use first principles molecular dynamics electronic structure calculations to study the first steps in the oxidation process of a non-saturated InP nanowire surface as well as the properties of an already oxidized surface of an InP nanowire. Our calculations show that the O 2 molecules dissociate through several mechanisms, resulting in incorporation of O atoms into the surface layers. The results confirm the experimental observation that the oxidized layers become amorphous but the non-oxidized core layers remain crystalline. Oxygen related bonds at the oxidized layers introduce defective levels at the band gap region, with greater contributions from defects involving In-O and P-O bonds.

A first-principles study of phase transitions in ultrathin films of BaTiO 3

Indian Academy of Sciences (India)

We determine the effects of film thickness, epitaxial strain and the nature of electrodes on ferroelectric phase transitions in ultrathin films of BaTiO3 using a first-principles effective Hamiltonian in classical molecular dynamics simulations. We present results for polarization and dielectric properties as a function of temperature ...

First-principles determination of the Raman fingerprint of rhombohedral graphite

Science.gov (United States)

Torche, Abderrezak; Mauri, Francesco; Charlier, Jean-Christophe; Calandra, Matteo

2017-09-01

Multilayer graphene with rhombohedral stacking is a promising carbon phase possibly displaying correlated states like magnetism or superconductivity due to the occurrence of a flat surface band at the Fermi level. Recently, flakes of thickness up to 17 layers were tentatively attributed to ABC sequences although the Raman fingerprint of rhombohedral multilayer graphene is currently unknown and the 2D resonant Raman spectrum of Bernal graphite is not understood. We provide a first principles description of the 2D Raman peak in three and four layers graphene (all stackings) as well as in Bernal, rhombohedral, and an alternation of Bernal and rhombohedral graphite. We give practical prescriptions to identify long range sequences of ABC multilayer graphene. Our work is a prerequisite to experimental nondestructive identification and synthesis of rhombohedral graphite.

Nanoparticle shapes by using Wulff constructions and first-principles calculations

Directory of Open Access Journals (Sweden)

Georgios D. Barmparis

2015-02-01

Full Text Available Background: The majority of complex and advanced materials contain nanoparticles. The properties of these materials depend crucially on the size and shape of these nanoparticles. Wulff construction offers a simple method of predicting the equilibrium shape of nanoparticles given the surface energies of the material.Results: We review the mathematical formulation and the main applications of Wulff construction during the last two decades. We then focus to three recent extensions: active sites of metal nanoparticles for heterogeneous catalysis, ligand-protected nanoparticles generated as colloidal suspensions and nanoparticles of complex metal hydrides for hydrogen storage.Conclusion: Wulff construction, in particular when linked to first-principles calculations, is a powerful tool for the analysis and prediction of the shapes of nanoparticles and tailor the properties of shape-inducing species.

First-Principles Study of the Polar TiC/Ti Interface

Institute of Scientific and Technical Information of China (English)

Limin LIU; Shaoqing WANG; Hengqiang YE

2003-01-01

The interface structure, work of adhesion, and bonding character of the polar TiC/Ti interface have been examined by the first-principles density functional plane-wave pseudopotential calculations. Both Ti- and C-terminated interfaces including six different interface structures were calculated, which present quite different features. For the Ti-terminated interface, the interfacial Ti-Ti bond has a strong metallic and weak covalent character; while for the C-terminated interface, the interfacial bond is a strong polar covalent interaction between the Ti-3d and C-2p orbital.The work of adhesion of C-terminated interface is nearly 9 J/m2 stronger than that of the Ti-terminated. It is found that each termination has relatively large work of adhesion, which is consistent with other polar interfaces.

First-principles method for electron-phonon coupling and electron mobility

DEFF Research Database (Denmark)

Gunst, Tue; Markussen, Troels; Stokbro, Kurt

2016-01-01

We present density functional theory calculations of the phonon-limited mobility in n-type monolayer graphene, silicene, and MoS2. The material properties, including the electron-phonon interaction, are calculated from first principles. We provide a detailed description of the normalized full......-band relaxation time approximation for the linearized Boltzmann transport equation (BTE) that includes inelastic scattering processes. The bulk electron-phonon coupling is evaluated by a supercell method. The method employed is fully numerical and does therefore not require a semianalytic treatment of part...... of the problem and, importantly, it keeps the anisotropy information stored in the coupling as well as the band structure. In addition, we perform calculations of the low-field mobility and its dependence on carrier density and temperature to obtain a better understanding of transport in graphene, silicene...

Core structure of screw dislocations in Fe from first-principles

International Nuclear Information System (INIS)

Ventelon, L.

2008-11-01

The various methods appropriate for the simulation of dislocations within first-principles calculations have been set up, improved and compared between them. They have been applied to study screw dislocations in body-centered cubic iron using the SIESTA code. A non-degenerate core structure is obtained; its detailed analysis reveals a dilatation effect. Taking it into account in an anisotropic elasticity model, allows explaining the cell-size dependence of the energetics, obtained within the dipole approach. The Peierls potential obtained in ab initio suggests that the metastable core configuration at halfway position in the Peierls barrier, predicted by empirical potential, does not exist. We show how to construct tri-periodic cells optimized to study kinked dislocations. Using empirical potential, we demonstrate the feasibility of ab initio calculations of Peierls stress and kink formation. (author)

The Maquet principle

International Nuclear Information System (INIS)

Levine, R.B.; Stassi, J.; Karasick, D.

1985-01-01

Anterior displacement of the tibial tubercle is a well-accepted orthopedic procedure in the treatment of certain patellofemoral disorders. The radiologic appearance of surgical procedures utilizing the Maquet principle has not been described in the radiologic literature. Familiarity with the physiologic and biochemical basis for the procedure and its postoperative appearance is necessary for appropriate roentgenographic evaluation and the radiographic recognition of complications. (orig.)

Principles of Need and the Aggregation Thesis.

Science.gov (United States)

Gustavsson, Erik; Juth, Niklas

2017-09-02

Principles of need are constantly referred to in health care priority setting. The common denominator for any principle of need is that it will ascribe some kind of special normative weight to people being worse off. However, this common ground does not answer the question how a plausible principle of need should relate to the aggregation of benefits across individuals. Principles of need are sometimes stated as being incompatible with aggregation and sometimes characterized as accepting aggregation in much the same way as utilitarians do. In this paper we argue that if one wants to take principles of need seriously both of these positions have unreasonable implications. We then characterize and defend a principle of need consisting of sufficientarian elements as well as prioritarian which avoids these unreasonable implications.

Universal uncertainty principle in the measurement operator formalism

International Nuclear Information System (INIS)

Ozawa, Masanao

2005-01-01

Heisenberg's uncertainty principle has been understood to set a limitation on measurements; however, the long-standing mathematical formulation established by Heisenberg, Kennard, and Robertson does not allow such an interpretation. Recently, a new relation was found to give a universally valid relation between noise and disturbance in general quantum measurements, and it has become clear that the new relation plays a role of the first principle to derive various quantum limits on measurement and information processing in a unified treatment. This paper examines the above development on the noise-disturbance uncertainty principle in the model-independent approach based on the measurement operator formalism, which is widely accepted to describe a class of generalized measurements in the field of quantum information. We obtain explicit formulae for the noise and disturbance of measurements given by measurement operators, and show that projective measurements do not satisfy the Heisenberg-type noise-disturbance relation that is typical in the gamma-ray microscope thought experiments. We also show that the disturbance on a Pauli operator of a projective measurement of another Pauli operator constantly equals √2, and examine how this measurement violates the Heisenberg-type relation but satisfies the new noise-disturbance relation

On the use of risk acceptance criteria in the offshore oil and gas industry

International Nuclear Information System (INIS)

Aven, Terje; Vinnem, Jan Erik

2005-01-01

Risk acceptance criteria, as upper limits of acceptable risks, have been used for offshore activities on the Norwegian Continental Shelf for more than 20 years. The common thinking has been that risk analyses and assessments cannot be conducted in a meaningful way without the use of such criteria. The ALARP principle also applies, but the risk acceptance criteria have played a more active role in the assessment processes than seen for example in the UK. Recently there has, however, been a discussion about the suitability of risk acceptance criteria to assess and control risks. The purpose of this paper is to contribute to this discussion by presenting and discussing a risk analysis regime that is not based on the use of risk acceptance criteria at all. We believe that we can do better if cost-effectiveness (in a wide sense) is the ruling thinking rather than adoption of pre-defined risk acceptance limits. This means a closer resemblance with the ALARP principle as adopted in the UK and other countries, but is not a direct application of this practice. Also the building blocks of the common way of applying the ALARP principle are reviewed. The Norwegian offshore oil and gas industry is the starting point, but the discussion is to large extent general

First-principles calculations, experimental study, and thermodynamic modeling of the Al-Co-Cr system.

Directory of Open Access Journals (Sweden)

Xuan L Liu

Full Text Available The phase relations and thermodynamic properties of the condensed Al-Co-Cr ternary alloy system are investigated using first-principles calculations based on density functional theory (DFT and phase-equilibria experiments that led to X-ray diffraction (XRD and electron probe micro-analysis (EPMA measurements. A thermodynamic description is developed by means of the calculations of phase diagrams (CALPHAD method using experimental and computational data from the present work and the literature. Emphasis is placed on modeling the bcc-A2, B2, fcc-γ, and tetragonal-σ phases in the temperature range of 1173 to 1623 K. Liquid, bcc-A2 and fcc-γ phases are modeled using substitutional solution descriptions. First-principles special quasirandom structures (SQS calculations predict a large bcc-A2 (disordered/B2 (ordered miscibility gap, in agreement with experiments. A partitioning model is then used for the A2/B2 phase to effectively describe the order-disorder transitions. The critically assessed thermodynamic description describes all phase equilibria data well. A2/B2 transitions are also shown to agree well with previous experimental findings.

Temperature-dependent stability of stacking faults in Al, Cu and Ni: first-principles analysis.

Science.gov (United States)

Bhogra, Meha; Ramamurty, U; Waghmare, Umesh V

2014-09-24

We present comparative analysis of microscopic mechanisms relevant to plastic deformation of the face-centered cubic (FCC) metals Al, Cu, and Ni, through determination of the temperature-dependent free energies of intrinsic and unstable stacking faults along [1 1̄ 0] and [1 2̄ 1] on the (1 1 1) plane using first-principles density-functional-theory-based calculations. We show that vibrational contribution results in significant decrease in the free energy of barriers and intrinsic stacking faults (ISFs) of Al, Cu, and Ni with temperature, confirming an important role of thermal fluctuations in the stability of stacking faults (SFs) and deformation at elevated temperatures. In contrast to Al and Ni, the vibrational spectrum of the unstable stacking fault (USF[1 2̄ 1]) in Cu reveals structural instabilities, indicating that the energy barrier (γusf) along the (1 1 1)[1 2̄ 1] slip system in Cu, determined by typical first-principles calculations, is an overestimate, and its commonly used interpretation as the energy release rate needed for dislocation nucleation, as proposed by Rice (1992 J. Mech. Phys. Solids 40 239), should be taken with caution.

Novel Designs for the Audio Mixing Interface Based on Data Visualisation First Principles

OpenAIRE

Dewey, Christopher; Wakefield, Jonathan P.

2016-01-01

Given the shortcomings of current audio mixing interfaces (AMIs) this study focuses on the development of alternative AMIs based on data visualisation first principles. The elementary perceptual tasks defined by Cleveland informed the design process. Two design ideas were considered for pan: using the elementary perceptual tasks ‘scale’ to display pan on either a single or multiple horizontal lines. Four design ideas were considered for level:\\ud using ‘length’, ‘area’, ‘saturation’ or ‘scala...

First-principles-based Landau-Devonshire potential for BiFeO.sub.3./sub.

Czech Academy of Sciences Publication Activity Database

Márton, Pavel; Klíč, Antonín; Pasciak, Marek; Hlinka, Jiří

2017-01-01

Roč. 96, č. 17 (2017), s. 1-5, č. článku 174110. ISSN 2469-9950 R&D Projects: GA ČR GA15-04121S Grant - others:GA MŠk(CZ) LM2015042 Institutional support: RVO:68378271 Keywords : Landau-Devonshire potential * first-principles calculations * BiFeO3 * Energy-sampling technique Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 3.836, year: 2016

Accurate line intensities of methane from first-principles calculations

Science.gov (United States)

Nikitin, Andrei V.; Rey, Michael; Tyuterev, Vladimir G.

2017-10-01

In this work, we report first-principle theoretical predictions of methane spectral line intensities that are competitive with (and complementary to) the best laboratory measurements. A detailed comparison with the most accurate data shows that discrepancies in integrated polyad intensities are in the range of 0.4%-2.3%. This corresponds to estimations of the best available accuracy in laboratory Fourier Transform spectra measurements for this quantity. For relatively isolated strong lines the individual intensity deviations are in the same range. A comparison with the most precise laser measurements of the multiplet intensities in the 2ν3 band gives an agreement within the experimental error margins (about 1%). This is achieved for the first time for five-atomic molecules. In the Supplementary Material we provide the lists of theoretical intensities at 269 K for over 5000 strongest transitions in the range below 6166 cm-1. The advantage of the described method is that this offers a possibility to generate fully assigned exhaustive line lists at various temperature conditions. Extensive calculations up to 12,000 cm-1 including high-T predictions will be made freely available through the TheoReTS information system (http://theorets.univ-reims.fr, http://theorets.tsu.ru) that contains ab initio born line lists and provides a user-friendly graphical interface for a fast simulation of the absorption cross-sections and radiance.

First-principles calculations of structural, electronic and optical properties of CdxZn1-xS alloys

KAUST Repository

Noor, Naveed Ahmed; Ikram, Nazma; Ali, Sana Zulfiqar; Nazir, Safdar; Alay-E-Abbas, Syed Muhammad; Shaukat, Ali

2010-01-01

Structural, electronic and optical properties of ternary alloy system CdxZn1-xS have been studied using first-principles approach based on density functional theory. Electronic structure, density of states and energy band gap values for CdxZn1-xS

First-principles-based study of transport properties of Fe thin films on Cu surfaces

Energy Technology Data Exchange (ETDEWEB)

Kishi, Tomoya [Department of Applied Physics, Osaka University, Suita, Osaka 565-0871 (Japan); Kasai, Hideaki [Department of Applied Physics, Osaka University, Suita, Osaka 565-0871 (Japan); Nakanishi, Hiroshi [Department of Applied Physics, Osaka University, Suita, Osaka 565-0871 (Japan); Dino, Wilson Agerico [Department of Applied Physics, Osaka University, Suita, Osaka 565-0871 (Japan); Komori, Fumio [Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8587 (Japan)

2004-12-08

We investigate the transport properties of Fe thin films on Cu(111) based on first principles calculation. We calculate the electron current through these Fe thin films, which can be observed by using a double-tipped scanning tunnelling microscope. We find that the conductance is majority spin polarized. On the basis of the band structures for this system, we discuss the origin of these interesting transport properties.

First-principles-based study of transport properties of Fe thin films on Cu surfaces

International Nuclear Information System (INIS)

Kishi, Tomoya; Kasai, Hideaki; Nakanishi, Hiroshi; Dino, Wilson Agerico; Komori, Fumio

2004-01-01

We investigate the transport properties of Fe thin films on Cu(111) based on first principles calculation. We calculate the electron current through these Fe thin films, which can be observed by using a double-tipped scanning tunnelling microscope. We find that the conductance is majority spin polarized. On the basis of the band structures for this system, we discuss the origin of these interesting transport properties

Arsenene as a promising candidate for NO and NO{sub 2} sensor: A first-principles study

Energy Technology Data Exchange (ETDEWEB)

Liu, Can [School of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China); Key Laboratory of Radio Frequency and Micro-Nano Electronics of Jiangsu Province, Nanjing 210023, Jiangsu (China); Liu, Chun-Sheng, E-mail: csliu@njupt.edu.cn [School of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China); Key Laboratory of Radio Frequency and Micro-Nano Electronics of Jiangsu Province, Nanjing 210023, Jiangsu (China); Yan, Xiaohong [School of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China); Key Laboratory of Radio Frequency and Micro-Nano Electronics of Jiangsu Province, Nanjing 210023, Jiangsu (China); College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 211106 (China)

2017-03-26

Based on first-principles calculations, we have studied the adsorption of CO, CO{sub 2}, N{sub 2}, NH{sub 3}, NO and NO{sub 2} molecules on the pristine arsenene monolayer. These gas molecules are held by an interaction that is intermediate between the physisorbed and chemisorbed states. Furthermore, the adsorption of NO and NO{sub 2} can produce a noticeable modifications of the density of states near the Fermi level. Interestingly, only the adsorption of NO and NO{sub 2} can lead to a magnetic moment of 1 μB. Therefore, our results can provide a theoretical basis for the potential applications of arsenene monolayer in gas sensing with electrical and magnetic methods. - Highlights: • A new type of two-dimensional single element semiconductor. • Investigated by first-principles calculations. • Easy desorption and good reversibility. • Gas sensing with electrical and magnetic methods.

Quantum theory and statistical thermodynamics principles and worked examples

CERN Document Server

Hertel, Peter

2017-01-01

This textbook presents a concise yet detailed introduction to quantum physics. Concise, because it condenses the essentials to a few principles. Detailed, because these few principles –  necessarily rather abstract – are illustrated by several telling examples. A fairly complete overview of the conventional quantum mechanics curriculum is the primary focus, but the huge field of statistical thermodynamics is covered as well. The text explains why a few key discoveries shattered the prevailing broadly accepted classical view of physics. First, matter appears to consist of particles which, when propagating, resemble waves. Consequently, some observable properties cannot be measured simultaneously with arbitrary precision. Second, events with single particles are not determined, but are more or less probable. The essence of this is that the observable properties of a physical system are to be represented by non-commuting mathematical objects instead of real numbers.  Chapters on exceptionally simple, but h...

Draft principles, policy, and acceptance criteria for decommissioning of U.S. Department of Energy contaminated surplus facilities and summary of international decommissioning programs

International Nuclear Information System (INIS)

Singh, B.K.

1994-12-01

Decommissioning activities enable the DOE to reuse all or part of a facility for future activities and reduce hazards to the general public and any future work force. The DOE Office of Environment, Health and Safety has prepared this document, which consists of decommissioning principles and acceptance criteria, in an attempt to establish a policy that is in agreement with the NRC policy. The purpose of this document is to assist individuals involved with decommissioning activities in determining their specific responsibilities as identified in Draft DOE Order 5820.DDD, ''Decommissioning of US Department of Energy Contaminated Surplus Facilities'' (Appendix A). This document is not intended to provide specific decommissioning methodology. The policies and principles of several international decommissioning programs are also summarized. These programs are from the IAEA, the NRC, and several foreign countries expecting to decommission nuclear facilities. They are included here to demonstrate the different policies that are to be followed throughout the world and to allow the reader to become familiar with the state of the art for environment, safety, and health (ES and H) aspects of nuclear decommissioning

Glass polymorphism in amorphous germanium probed by first-principles computer simulations

Science.gov (United States)

Mancini, G.; Celino, M.; Iesari, F.; Di Cicco, A.

2016-01-01

The low-density (LDA) to high-density (HDA) transformation in amorphous Ge at high pressure is studied by first-principles molecular dynamics simulations in the framework of density functional theory. Previous experiments are accurately reproduced, including the presence of a well-defined LDA-HDA transition above 8 GPa. The LDA-HDA density increase is found to be about 14%. Pair and bond-angle distributions are obtained in the 0-16 GPa pressure range and allowed us a detailed analysis of the transition. The local fourfold coordination is transformed in an average HDA sixfold coordination associated with different local geometries as confirmed by coordination number analysis and shape of the bond-angle distributions.

Isobaric-isothermal Monte Carlo simulations from first principles: Application to liquid water at ambient conditions

Energy Technology Data Exchange (ETDEWEB)

McGrath, M; Siepmann, J I; Kuo, I W; Mundy, C J; VandeVondele, J; Hutter, J; Mohamed, F; Krack, M

2004-12-02

A series of first principles Monte Carlo simulations in the isobaric-isothermal ensemble were carried out for liquid water at ambient conditions (T = 298 K and p = 1 atm). The Becke-Lee-Yang-Parr (BLYP) exchange and correlation energy functionals and norm-conserving Goedecker-Teter-Hutter (GTH) pseudopotentials were employed with the CP2K simulation package to examine systems consisting of 64 water molecules. The fluctuations in the system volume encountered in simulations in the isobaric-isothermal ensemble requires a reconsideration of the suitability of the typical charge density cutoff and the regular grid generation method previously used for the computation of the electrostatic energy in first principles simulations in the microcanonical or canonical ensembles. In particular, it is noted that a much higher cutoff is needed and that the most computationally efficient method of creating grids can result in poor simulations. Analysis of the simulation trajectories using a very large charge density cutoff at 1200 Ry and four different grid generation methods point to a substantially underestimated liquid density of about 0.85 g/cm{sup 3} resulting in a somewhat understructured liquid (with a value of about 2.7 for the height of the first peak in the oxygen/oxygen radial distribution function) for BLYP-GTH water at ambient conditions.

First-principles simulation of Raman spectra and structural properties of quartz up to 5 GPa

International Nuclear Information System (INIS)

Liu Lei; Lv Chao-Jia; Yi Li; Liu Hong; Du Jian-Guo; Zhuang Chun-Qiang

2015-01-01

The crystal structure and Raman spectra of quartz are calculated by using first-principles method in a pressure range from 0 to 5 GPa. The results show that the lattice constants (a, c, and V) decrease with increasing pressure and the a-axis is more compressible than the c axis. The Si–O bond distance decreases with increasing pressure, which is in contrast to experimental results reported by Hazen et al. [Hazen R M, Finger L W, Hemley R J and Mao H K 1989 Solid State Communications 725 507–511], and Glinnemann et al. [Glinnemann J, King H E Jr, Schulz H, Hahn T, La Placa S J and Dacol F 1992 Z. Kristallogr. 198 177–212]. The most striking changes are of inter-tetrahedral O–O distances and Si–O–Si angles. The volume of the tetrahedron decreased by 0.9% (from 0 to 5 GPa), which suggests that it is relatively rigid. Vibrational models of the quartz modes are identified by visualizing the associated atomic motions. Raman vibrations are mainly controlled by the deformation of the tetrahedron and the changes in the Si–O–Si bonds. Vibrational directions and intensities of atoms in all Raman modes just show little deviations when pressure increases from 0 to 5 GPa. The pressure derivatives (dν i /dP) of the 12 Raman frequencies are obtained at 0 GPa–5 GPa. The calculated results show that first-principles methods can well describe the high-pressure structural properties and Raman spectra of quartz. The combination of first-principles simulations of the Raman frequencies of minerals and Raman spectroscopy experiments is a useful tool for exploring the stress conditions within the Earth. (paper)

First-principles data-driven discovery of transition metal oxides for artificial photosynthesis

Science.gov (United States)

Yan, Qimin

We develop a first-principles data-driven approach for rapid identification of transition metal oxide (TMO) light absorbers and photocatalysts for artificial photosynthesis using the Materials Project. Initially focusing on Cr, V, and Mn-based ternary TMOs in the database, we design a broadly-applicable multiple-layer screening workflow automating density functional theory (DFT) and hybrid functional calculations of bulk and surface electronic and magnetic structures. We further assess the electrochemical stability of TMOs in aqueous environments from computed Pourbaix diagrams. Several promising earth-abundant low band-gap TMO compounds with desirable band edge energies and electrochemical stability are identified by our computational efforts and then synergistically evaluated using high-throughput synthesis and photoelectrochemical screening techniques by our experimental collaborators at Caltech. Our joint theory-experiment effort has successfully identified new earth-abundant copper and manganese vanadate complex oxides that meet highly demanding requirements for photoanodes, substantially expanding the known space of such materials. By integrating theory and experiment, we validate our approach and develop important new insights into structure-property relationships for TMOs for oxygen evolution photocatalysts, paving the way for use of first-principles data-driven techniques in future applications. This work is supported by the Materials Project Predictive Modeling Center and the Joint Center for Artificial Photosynthesis through the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05CH11231. Computational resources also provided by the Department of Energy through the National Energy Supercomputing Center.

Erratum to “Neutron–19C scattering: Emergence of universal properties in a finite range potential” [Phys. Lett. B 764 (2017 196

Directory of Open Access Journals (Sweden)

M.A. Shalchi

2017-08-01

Full Text Available Numerical results for the function (1−EK/E0kcot⁡δ0R, as given in Phys. Lett. B 764 (2017 196, are revised. Fig. 2 and Tables 2 and 3 should be replaced by the following corresponding figure and tables. The conclusions of the original paper remain unchanged.

Fraction of boroxol rings in vitreous boron oxide from a first-principles analysis of Raman and NMR spectra.

Science.gov (United States)

Umari, P; Pasquarello, Alfredo

2005-09-23

We determine the fraction f of B atoms belonging to boroxol rings in vitreous boron oxide through a first-principles analysis. After generating a model structure of vitreous B2O3 by first-principles molecular dynamics, we address a large set of properties, including the neutron structure factor, the neutron density of vibrational states, the infrared spectra, the Raman spectra, and the 11B NMR spectra, and find overall good agreement with corresponding experimental data. From the analysis of Raman and 11B NMR spectra, we yield consistently for both probes a fraction f of approximately 0.75. This result indicates that the structure of vitreous boron oxide is largely dominated by boroxol rings.

First-principles study of rare-earth (RE) cobaltites (RE=Nd,Sm,Gd,Dy,Er,Lu)

Science.gov (United States)

Topsakal, M.; Wentzcovitch, R. M.

2014-12-01

The lanthanide series of the periodic table comprises 15 members ranging from Lanthanum (La) to Lutetium (Lu). Although they are more abundant than silver, and some of them are more abundant than lead, they are known as rare-earth (RE) elements. The "rare" in their name refers to the difficulty of obtaining the pure elements, not to their abundances in nature. They are never found as free metals in the Earth's crust and do not exist as pure minerals. Using first-principles plane-wave calculations, we investigate the structural and electronic properties of rare-earth cobaltites (RECoO3). Structurally consistent Hubbard U treatment was shown to essential for proper description of strongly correlated cobalt-d electrons. We successfully capture the experimentally observed structural trends and give first-principles insights on interesting phenomena related with the cobalt spin state change. It was demonstrated that increase of crystal-field splitting energy between eg-t2g orbitals and shrinking of unoccupied σ*-bonding eg bands are responsible for the increase of onset spin-state transition temperature along the series.

First-principles study of the diffusion mechanisms of the self-interstitial in germanium

International Nuclear Information System (INIS)

Carvalho, A; Jones, R; Janke, C; Goss, J P; Briddon, P R; Oeberg, S

2008-01-01

The self-interstitial in germanium can assume multiple configurations depending on the temperature and charge state. Here, we employ a first-principles density functional method to investigate the diffusion mechanisms of this defect. The energy barriers associated with the transformation between different structures are determined by the climbing nudged elastic band method, as a function of the charge state. The relation between the thermodynamic properties of the self-interstitial and the temperature evolution of electron radiation damage in germanium are discussed

Site-specific electronic structure analysis by channeling EELS and first-principles calculations.

Science.gov (United States)

Tatsumi, Kazuyoshi; Muto, Shunsuke; Yamamoto, Yu; Ikeno, Hirokazu; Yoshioka, Satoru; Tanaka, Isao

2006-01-01

Site-specific electronic structures were investigated by electron energy loss spectroscopy (EELS) under electron channeling conditions. The Al-K and Mn-L(2,3) electron energy loss near-edge structure (ELNES) of, respectively, NiAl2O4 and Mn3O4 were measured. Deconvolution of the raw spectra with the instrumental resolution function restored the blunt and hidden fine features, which allowed us to interpret the experimental spectral features by comparing with theoretical spectra obtained by first-principles calculations. The present method successfully revealed the electronic structures specific to the differently coordinated cationic sites.

Aqueous Stability of Alkali Superionic Conductors from First-Principles Calculations

International Nuclear Information System (INIS)

Radhakrishnan, Balachandran; Ong, Shyue Ping

2016-01-01

Ceramic alkali superionic conductor solid electrolytes (SICEs) play a prominent role in the development of rechargeable alkali-ion batteries, ranging from replacement of organic electrolytes to being used as separators in aqueous batteries. The aqueous stability of SICEs is an important property in determining their applicability in various roles. In this work, we analyze the aqueous stability of twelve well-known Li-ion and Na-ion SICEs using Pourbaix diagrams constructed from first-principles calculations. We also introduce a quantitative free-energy measure to compare the aqueous stability of SICEs under different environments. Our results show that though oxides are, in general, more stable in aqueous environments than sulfides and halide-containing chemistries, the cations present play a crucial role in determining whether solid phases are formed within the voltage and pH ranges of interest.

First Principles Modelling of Shape Memory Alloys Molecular Dynamics Simulations

CERN Document Server

Kastner, Oliver

2012-01-01

Materials sciences relate the macroscopic properties of materials to their microscopic structure and postulate the need for holistic multiscale research. The investigation of shape memory alloys is a prime example in this regard. This particular class of materials exhibits strong coupling of temperature, strain and stress, determined by solid state phase transformations of their metallic lattices. The present book presents a collection of simulation studies of this behaviour. Employing conceptually simple but comprehensive models, the fundamental material properties of shape memory alloys are qualitatively explained from first principles. Using contemporary methods of molecular dynamics simulation experiments, it is shown how microscale dynamics may produce characteristic macroscopic material properties. The work is rooted in the materials sciences of shape memory alloys and  covers  thermodynamical, micro-mechanical  and crystallographical aspects. It addresses scientists in these research fields and thei...

Beyond the Virtues-Principles Debate.

Science.gov (United States)

Keat, Marilyn S.

1992-01-01

Indicates basic ontological assumptions in the virtues-principles debate in moral philosophy, noting Aristotle's and Kant's fundamental ideas about morality and considering a hermeneutic synthesis of theories. The article discusses what acceptance of the synthesis might mean in the theory and practice of moral pedagogy, offering examples of…

Dynamical coupling in Pb(Zr,Ti)O.sub.3./sub. solid solutions from first principles

Czech Academy of Sciences Publication Activity Database

Wang, D.; Weerasinghe, J.; Bellaiche, L.; Hlinka, Jiří

2011-01-01

Roč. 83, č. 2 (2011), "020301-1"-"020301-4" ISSN 1098-0121 R&D Projects: GA MŠk ME08109 Institutional research plan: CEZ:AV0Z10100520 Keywords : first-principles * ferroelectric * PZT Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.691, year: 2011 http://link.aps.org/doi/10.1103/PhysRevB.83.020301

From First Principles: The Application of Quantum Mechanics to Complex Molecules and Solvated Systems

Energy Technology Data Exchange (ETDEWEB)

Freitag, Mark A. [Iowa State Univ., Ames, IA (United States)

2001-12-31

The major title of this dissertation, 'From first principles,' is a phase often heard in the study of thermodynamics and quantum mechanics. These words embody a powerful idea in the physical sciences; namely, that it is possible to distill the complexities of nature into a set of simple, well defined mathematical laws from which specific relations can then be derived . In thermodynamics, these fundamental laws are immediately familiar to the physical scientist by their numerical order: the First, Second and Third Laws. However, the subject of the present volume is quantum mechanics-specifically, non-relativistic quantum mechanics, which is appropriate for most systems of chemical interest.

First-principles studies on the adsorption of molecular oxygen on Ba(110) surface

International Nuclear Information System (INIS)

Li, S.F.; Xue Xinlian; Li Pinglin; Li Xinjian; Jia Yu

2006-01-01

The adsorption of O 2 on Ba(110) surface is studied with first-principles calculations based on density functional theory. Our calculations predict that O 2 may prefer to dissociative adsorption on Ba(110) surface without obvious barrier. Also our results do not support the model of charge transfer from the surface to the molecule as a bond breaking mechanism. Instead, the increasing hybridization between O 2 orbitals and the d states of Ba(110) surface may play an important role in the dissociation adsorption

First-principles-based analysis of the influence of Cu on CdTe electronic properties

International Nuclear Information System (INIS)

Krasikov, D.; Knizhnik, A.; Potapkin, B.; Selezneva, S.; Sommerer, T.

2013-01-01

The maximum voltage of CdTe solar cells is limited by low majority carrier concentration and doping difficulty. Copper that enters from the back contact can form both donors and acceptors in CdTe. It is empirically known that the free carrier concentration is several orders lower than the total Cu concentration. Simplified thermodynamic models of defect compensation after Cu introduction can be found in literature. We present a first-principles-based analysis of kinetics of defect formation upon Cu introduction, and show that Cu i is mobile at room temperature. Calculations of properties of Cu i –V Cd and Cu i –Cu Cd complexes show that the neutral Cu i –Cu Cd complex is mobile at elevated temperatures, while formation of the V Cd –Cu i complex is unlikely because it transforms into the Cu Cd defect. - Highlights: ► First-principles calculations of copper defects in CdTe are performed. ► Formation of Cd vacancy + Cu interstitial(Cu i ) complex is unlikely. ► Cu i defect is mobile at room temperature. ► Cu i + Cu on Cd-site (Cu Cd ) complex is mobile at elevated temperature. ► Cu Cd defect forms by kicking-out of the regular lattice Cd by Cu i

Rectification of graphene self-switching diodes: First-principles study

Science.gov (United States)

Ghaziasadi, Hassan; Jamasb, Shahriar; Nayebi, Payman; Fouladian, Majid

2018-05-01

The first principles calculations based on self-consistent charge density functional tight-binding have performed to investigate the electrical properties and rectification behavior of the graphene self-switching diodes (GSSD). The devices contained two structures called CG-GSSD and DG-GSSD which have metallic or semiconductor gates depending on their side gates have a single or double hydrogen edge functionalized. We have relaxed the devices and calculated I-V curves, transmission spectrums and maximum rectification ratios. We found that the DG-MSM devices are more favorable and more stable. Also, the DG-MSM devices have better maximum rectification ratios and current. Moreover, by changing the side gates widths and behaviors from semiconductor to metal, the threshold voltages under forward bias changed from +1.2 V to +0.3 V. Also, the maximum currents are obtained from 1.12 μA to 10.50 μA. Finally, the MSM and SSS type of all devices have minimum and maximum values of voltage threshold and maximum rectification ratios, but the 769-DG devices don't obey this rule.

First-principles calculations on Mg/Al2CO interfaces

International Nuclear Information System (INIS)

Wang, F.; Li, K.; Zhou, N.G.

2013-01-01

The electronic structure, work of adhesion, and interfacial energy of the Mg(0 0 0 2)/Al 2 CO(0 0 0 1) interface were studied with the first-principles calculations to clarify the heterogeneous nucleation potential of Al 2 CO particles in Mg melt. AlO-terminated Al 2 CO(0 0 0 1) slabs with seven atomic layers were adopted for interfacial model geometries. Results show that the “Over O” stacking interface is more stable than the “Over Al” stacking interface due to the larger interfacial adhesion and stronger mixed ionic/metallic bond formed across the interface. The calculated interfacial energies of Mg/Al 2 CO depend on the value of Δμ Al + Δμ C , proving Al 2 CO particles can exist stably in Mg–Al alloys melt and become effective nucleation substrate for α-Mg grain under certain conditions. The above calculation and corresponding analysis provide strong theoretical support to the Al 2 CO nucleus hypothesis from interfacial atomic structure and atomic bonding energy considerations.

What is so important about completing lives? A critique of the modified youngest first principle of scarce resource allocation.

Science.gov (United States)

Gamlund, Espen

2016-04-01

Ruth Tallman has recently offered a defense of the modified youngest first principle of scarce resource allocation [1]. According to Tallman, this principle calls for prioritizing adolescents and young adults between 15-40 years of age. In this article, I argue that Tallman's defense of the modified youngest first principle is vulnerable to important objections, and that it is thus unsuitable as a basis for allocating resources. Moreover, Tallman makes claims about the badness of death for individuals at different ages, but she lacks an account of the loss involved in dying to support her claims. To fill this gap in Tallman's account, I propose a view on the badness of death that I call 'Deprivationism'. I argue that this view explains why death is bad for those who die, and that it has some advantages over Tallman's complete lives view in the context of scarce resource allocation. Finally, I consider some objections to the relevance of Deprivationism to resource allocation, and offer my responses.

Determination of structure and properties of molecular crystals from first principles.

Science.gov (United States)

Szalewicz, Krzysztof

2014-11-18

CONSPECTUS: Until recently, it had been impossible to predict structures of molecular crystals just from the knowledge of the chemical formula for the constituent molecule(s). A solution of this problem has been achieved using intermolecular force fields computed from first principles. These fields were developed by calculating interaction energies of molecular dimers and trimers using an ab initio method called symmetry-adapted perturbation theory (SAPT) based on density-functional theory (DFT) description of monomers [SAPT(DFT)]. For clusters containing up to a dozen or so atoms, interaction energies computed using SAPT(DFT) are comparable in accuracy to the results of the best wave function-based methods, whereas the former approach can be applied to systems an order of magnitude larger than the latter. In fact, for monomers with a couple dozen atoms, SAPT(DFT) is about equally time-consuming as the supermolecular DFT approach. To develop a force field, SAPT(DFT) calculations are performed for a large number of dimer and possibly also trimer configurations (grid points in intermolecular coordinates), and the interaction energies are then fitted by analytic functions. The resulting force fields can be used to determine crystal structures and properties by applying them in molecular packing, lattice energy minimization, and molecular dynamics calculations. In this way, some of the first successful determinations of crystal structures were achieved from first principles, with crystal densities and lattice parameters agreeing with experimental values to within about 1%. Crystal properties obtained using similar procedures but empirical force fields fitted to crystal data have typical errors of several percent due to low sensitivity of empirical fits to interactions beyond those of the nearest neighbors. The first-principles approach has additional advantages over the empirical approach for notional crystals and cocrystals since empirical force fields can only be

Novel phases of lithium-aluminum binaries from first-principles structural search

Energy Technology Data Exchange (ETDEWEB)

Sarmiento-Pérez, Rafael; Cerqueira, Tiago F. T.; Botti, Silvana; Marques, Miguel A. L., E-mail: marques@tddft.org [Institut Lumière Matière (UMR5306) and ETSF, Université Lyon 1-CNRS, Université de Lyon, F-69622 Villeurbanne Cedex (France); Valencia-Jaime, Irais [Institut Lumière Matière (UMR5306) and ETSF, Université Lyon 1-CNRS, Université de Lyon, F-69622 Villeurbanne Cedex (France); Centro de Investigación y Estudios Avanzados del IPN, MX-76230 Querétaro (Mexico); Amsler, Maximilian; Goedecker, Stefan [Department of Physics, Universität Basel, Klingelbergstr. 82, 4056 Basel (Switzerland); Romero, Aldo H. [Physics Department, West Virginia University, Morgantown, West Virginia 26506-6315 (United States)

2015-01-14

Intermetallic Li–Al compounds are on the one hand key materials for light-weight engineering, and on the other hand, they have been proposed for high-capacity electrodes for Li batteries. We determine from first-principles the phase diagram of Li–Al binary crystals using the minima hopping structural prediction method. Beside reproducing the experimentally reported phases (LiAl, Li{sub 3}Al{sub 2}, Li{sub 9}Al{sub 4}, LiAl{sub 3}, and Li{sub 2}Al), we unveil a structural variety larger than expected by discovering six unreported binary phases likely to be thermodynamically stable. Finally, we discuss the behavior of the elastic constants and of the electric potential profile of all Li–Al stable compounds as a function of their stoichiometry.

Implementation of utaut model to understand the use of virtual classroom principle in higher education

Science.gov (United States)

Aditya, B. R.; Permadi, A.

2018-03-01

This paper describes implementation of Unified Theory of Acceptance and User of Technology (UTAUT) model to assess the use of virtual classroom in support of teaching and learning in higher education. The purpose of this research is how virtual classroom that has fulfilled the basic principle can be accepted and used by students positively. This research methodology uses the quantitative and descriptive approach with a questionnaire as a tool for measuring the height of virtual classroom principle acception. This research uses a sample of 105 students in D3 Informatics Management at Telkom University. The result of this research is that the use of classroom virtual principle are positive and relevant to the students in higher education.

First-principles molecular dynamics study of Al/Alq3 interfaces

Directory of Open Access Journals (Sweden)

Kousuke Takeuchi et al

2007-01-01

Full Text Available We have carried out first-principles molecular dynamics simulations of Al deposition on tris (8-hydroxyquinoline aluminum (Alq3 layers to investigate atomic geometries and electronic properties of Al/Alq3 interfaces. Al atoms were ejected to Alq3 one by one with the kinetic energy of 37.4 kJ/mol, which approximately corresponds to the average kinetic energy of Al at the boiling temperature of metal Al. The first Al atom interacts with two of the three O atoms of meridional Alq3. Following Al atoms interact with Alq3 rather weakly and they tend to aggregate each other to form Al clusters. During the deposition process, Alq3 was not broken and its molecular structure remained essentially intact. At the interface, weak bonds between deposited Al atoms and N and C atoms were formed. The projected density of states (PDOS onto the Alq3 molecular orbitals shows gap states in between the highest occupied molecular orbitals (HOMOs and the lowest unoccupied molecular orbitals (LUMOs, which were experimentally observed by ultraviolet photoelectron spectroscopy (UPS and metastable atom electron spectroscopy (MAES. Our results show that even though the Alq3 molecular structure is retained, weak N–Al and C–Al bonds induce gap states.

First-principles assessment of potential ultrafast laser-induced structural transition in Ni

Energy Technology Data Exchange (ETDEWEB)

Bévillon, E.; Colombier, J.P., E-mail: jean.philippe.colombier@univ-st-etienne.fr; Stoian, R.

2016-06-30

Highlights: • First-principles theory calculations in nonequilibrium conditions. • Electronic temperatures fully and consistently taken into account. • Evaluation of an ultrafast laser-induced solid-to-solid transition in Ni. • Relative energies, phonon spectra and energy path are evaluated. • Discussion on the generation of non-thermal forces in metals. - Abstract: The possibility to trigger ultrafast solid-to-solid transitions in transition metals under femtosecond laser irradiation is investigated by means of first-principles calculations. Electronic heating can drastically modify screening, charge distribution and atomic binding features, potentially determining new structural relaxation paths in the solid phase, before thermodynamic solid-to-liquid transformations set in. Consequently, we evaluate here the effect of electronic excitation on structural stability and conditions for structural transitions. Ni is chosen as a case study for the probability of a solid transition, and the stability of its FCC phase is compared to the non-standard HCP structure while accounting for the heating of the electronic subsystem. From a phonon spectra analysis, we show that the thermodynamic stability order reverses at an electronic temperature of around 10{sup 4} K. Both structures exhibit a dynamic stability, indicating they present a metastability depending on the heating. However, the general hardening of phonon modes with the increase of the electronic temperature points out that no transformation will occur, as confirmed by the study of a typical FCC to HCP diffusionless transformation path, showing an increasing energy barrier. Finally, based on electronic density of states interpretation, the tendency of different metal categories to undergo or not an ultrafast laser-induced structural transition is discussed.

Copper atoms embedded in hexagonal boron nitride as potential catalysts for CO oxidation: A first-principles investigation

KAUST Repository

Liu, Xin; Duan, Ting; Sui, Yanhui; Meng, Changgong; Han, Yu

2014-01-01

We addressed the electronic structure of Cu atoms embedded in hexagonal boron nitride (h-BN) and their catalytic role in CO oxidation by first-principles-based calculations. We showed that Cu atoms prefer to bind directly with the localized defects

Anomalous doping effect in black phosphorene using first-principles calculations.

Science.gov (United States)

Yu, Weiyang; Zhu, Zhili; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu

2015-07-07

Using first-principles density functional theory calculations, we investigate the geometries, electronic structures, and thermodynamic stabilities of substitutionally doped phosphorene sheets with group III, IV, V, and VI elements. We find that the electronic properties of phosphorene are drastically modified by the number of valence electrons in dopant atoms. The dopants with an even number of valence electrons enable the doped phosphorenes to have a metallic feature, while the dopants with an odd number of valence electrons retain a semiconducting feature. This even-odd oscillating behavior is attributed to the peculiar bonding characteristics of phosphorene and the strong hybridization of sp orbitals between dopants and phosphorene. Furthermore, the calculated formation energies of various substitutional dopants in phosphorene show that such doped systems can be thermodynamically stable. These results propose an intriguing route to tune the transport properties of electronic and photoelectronic devices based on phosphorene.

The elastic and thermodynamic properties of ZrMo2 from first principles calculations

International Nuclear Information System (INIS)

Liu, Xian-Kun; Zhou, Wei; Zheng, Zhou; Peng, Shu-Ming

2014-01-01

Highlights: • Elastic and thermodynamic properties of ZrMo 2 under high temperature and pressure are calculated by first principles. • Mechanical stability is testified from elastic constants at zero pressure. • Phonon scattering of ZrMo 2 under different temperature are obtained. - Abstract: The elastic and thermodynamic properties of ZrMo 2 under high temperature and pressure are investigated by first-principles calculations based on pseudopotential plane-wave density functional theory (DFT) within the generalized gradient approximation (GGA) and quasi-harmonic Debye model. The calculated lattice parameters are in good agreement with the available experimental data. The calculated elastic constants of ZrMo 2 increase monotonically with increasing pressure, and the relationship between the elastic constants and pressure show that ZrMo 2 satisfies the mechanical stability criteria under applied pressure (0–65 GPa). The related mechanical properties such as bulk modulus (B), shear modulus (G), Young’s modulus (E), and Poisson’s ratio (v) are also studied for polycrystalline of ZrMo 2 . The calculated B/G value shows that ZrMo 2 behaves in a ductile manner, and higher pressure can significantly improve the ductility of ZrMo 2 . The pressure and temperature dependencies of the relative volume, the bulk modulus, the elastic constants, the heat capacity and the thermal expansion coefficient, as well as the Grüneisen parameters are obtained and discussed by the quasi-harmonic Debye model in the ranges of 0–1800 K and 0–65 GPa

First principles of Hamiltonian medicine.

Science.gov (United States)

Crespi, Bernard; Foster, Kevin; Úbeda, Francisco

2014-05-19

We introduce the field of Hamiltonian medicine, which centres on the roles of genetic relatedness in human health and disease. Hamiltonian medicine represents the application of basic social-evolution theory, for interactions involving kinship, to core issues in medicine such as pathogens, cancer, optimal growth and mental illness. It encompasses three domains, which involve conflict and cooperation between: (i) microbes or cancer cells, within humans, (ii) genes expressed in humans, (iii) human individuals. A set of six core principles, based on these domains and their interfaces, serves to conceptually organize the field, and contextualize illustrative examples. The primary usefulness of Hamiltonian medicine is that, like Darwinian medicine more generally, it provides novel insights into what data will be productive to collect, to address important clinical and public health problems. Our synthesis of this nascent field is intended predominantly for evolutionary and behavioural biologists who aspire to address questions directly relevant to human health and disease.

Advertisement without Ethical Principles?

Directory of Open Access Journals (Sweden)

Wojciech Słomski

2007-10-01

Full Text Available The article replies to the question, whether the advertisement can exist without ethical principles or ethics should be the basis of the advertisement. One can say that the ethical opinion of the advertisement does not depend on content and the form of advertising content exclusively, but also on recipients consciousness. The advertisement appeals to the emotions more than to the intellect, thus restricting the area of conscious and based on rational premises choice, so it is morally bad. It is not that the moral evil immanently underlines the advertisement, but it concerns the mechanisms which cause that the advertisement turns out to be effective. The only admissible form of the advertisement would be the reliable full information about the advantages and flaws of the concrete advertised product. The only admissible form of the advertisement would be the reliable full information about the advantages and defects of the concrete advertised product. The most serious difficulty connected with the ethical opinion of the advertisement is the fact that the advertisement is the indispensable link of the present economy, and everyone who accepts the free market and perceives the positives of the economic growth, should also accept the advertisement. The advertisement constitutes the element of the economic activity, so in consequence the responsibility first of all lies with enterprises for its far-reaching results.

The precautionary principle and high-level nuclear waste policy

International Nuclear Information System (INIS)

Frishman, S.

1999-01-01

The 'Precautionary Principle' has grown from the broadening observation that there is compelling evidence that damage to humans and the world-wide environment is of such a magnitude and seriousness that new principles for conducting human activities are necessary. One of the various statements of the Precautionary Principle is: when an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically. The use of a precautionary principle was a significant recommendation emerging from the 1992 United Nations Conference on Environment and Development, held in Rio de Janeiro, Brazil, and it is gaining acceptance in discussions ranging from global warming to activities that affect the marine environment, and far beyond. In the US high-level nuclear waste policy, there is a growing trend on the part of geologic repository proponents and regulators to shift the required safety evaluation from a deterministic analysis of natural and engineered barriers and their interactions to risk assessments and total system waste containment and isolation performance assessment. This is largely a result of the realisation that scientific 'proof' of safety cannot be demonstrated to the level repository proponents have led the American public to expect. Therefore, they are now developing other methods in an attempt to effectively lower the repository safety expectations of the public. Implicit in this shift in demonstration of 'proof' is that levels of uncertainty far larger than those generally taken as scientifically acceptable must be accepted in repository safety, simply because greater certainty is either too costly, in time and money, or impossible to achieve at the potential Yucca Mountain repository site. In the context of the Precautionary Principle, the repository proponent must bear the burden of providing 'Acceptable' proof, established by an open

Tailoring spin injection and magnetoresistance in ferromagnet/graphene junctions from first principles

Science.gov (United States)

Lazic, Predrag; Sipahi, Guilherme; Kawakami, Roland; Zutic, Igor

2013-03-01

Recent experimental advances in graphene suggest intriguing opportunities for novel spintronic applications which could significantly exceed the state-of-the art performance of their conventional charge-based counterparts. However, for reliable operation of such spintronic devices it is important to achieve an efficient spin injection and large magnetoresistive effects. We use the first principles calculations to guide the choice of a ferromagnetic region and its relative orientation to optimize the desired effects. We propose structures which could enable uniform spin injection, one of the key factors in implementing scalable spintronic circuits. Supported by NSF-NRI, SRC, ONR, Croatian Ministry of Science, Education, and Sports, and CCR at SUNY UB.

First-principles calculations of bulk and interfacial thermodynamic properties for fcc-based Al-Sc alloys

International Nuclear Information System (INIS)

Asta, M.; Foiles, S.M.; Quong, A.A.

1998-01-01

The configurational thermodynamic properties of fcc-based Al-Sc alloys and coherent Al/Al 3 Sc interphase-boundary interfaces have been calculated from first principles. The computational approach used in this study combines the results of pseudopotential total-energy calculations with a cluster-expansion description of the alloy energetics. Bulk and interface configurational-thermodynamic properties are computed using a low-temperature-expansion technique. Calculated values of the {100} and {111} Al/Al 3 Sc interfacial energies at zero temperature are, respectively, 192 and 226mJ/m 2 . The temperature dependence of the calculated interfacial free energies is found to be very weak for {100} and more appreciable for {111} orientations; the primary effect of configurational disordering at finite temperature is to reduce the degree of crystallographic anisotropy associated with calculated interfacial free energies. The first-principles-computed solid-solubility limits for Sc in bulk fcc Al are found to be underestimated significantly in comparison with experimental measurements. It is argued that this discrepancy can be largely attributed to nonconfigurational contributions to the entropy which have been neglected in the present thermodynamic calculations. copyright 1998 The American Physical Society

The Harm Principle as a Mid-level Principle? Three Problems from the Context of Infectious Disease Control

NARCIS (Netherlands)

Krom, A.

2011-01-01

Effective infectious disease control may require states to restrict the liberty of individuals. Since preventing harm to others is almost universally accepted as a legitimate (prima facie) reason for restricting the liberty of individuals, it seems plausible to employ a mid-level harm principle in

First-principles molecular dynamics simulation study on electrolytes for use in redox flow battery

Science.gov (United States)

Choe, Yoong-Kee; Tsuchida, Eiji; Tokuda, Kazuya; Ootsuka, Jun; Saito, Yoshihiro; Masuno, Atsunobu; Inoue, Hiroyuki

2017-11-01

Results of first-principles molecular dynamics simulations carried out to investigate structural aspects of electrolytes for use in a redox flow battery are reported. The electrolytes studied here are aqueous sulfuric acid solutions where its property is of importance for dissolving redox couples in redox flow battery. The simulation results indicate that structural features of the acid solutions depend on the concentration of sulfuric acid. Such dependency arises from increase of proton dissociation from sulfuric acid.

Xenon Defects in Uranium Dioxide From First Principles and Interatomic Potentials

Science.gov (United States)

Thompson, Alexander

In this thesis, we examine the defect energetics and migration energies of xenon atoms in uranium dioxide (UO2) from first principles and interatomic potentials. We also parameterize new, accurate interatomic potentials for xenon and uranium dioxide. To achieve accurate energetics and provide a foundation for subsequent calculations, we address difficulties in finding consistent energetics within Hubbard U corrected density functional theory (DFT+U). We propose a method of slowly ramping the U parameter in order to guide the calculation into low energy orbital occupations. We find that this method is successful for a variety of materials. We then examine the defect energetics of several noble gas atoms in UO2 for several different defect sites. We show that the energy to incorporate large noble gas atoms into interstitial sites is so large that it is energetically favorable for a Schottky defect cluster to be created to relieve the strain. We find that, thermodynamically, xenon will rarely ever be in the interstitial site of UO2. To study larger defects associated with the migration of xenon in UO 2, we turn to interatomic potentials. We benchmark several previously published potentials against DFT+U defect energetics and migration barriers. Using a combination of molecular dynamics and nudged elastic band calculations, we find a new, low energy migration pathway for xenon in UO2. We create a new potential for xenon that yields accurate defect energetics. We fit this new potential with a method we call Iterative Potential Refinement that parameterizes potentials to first principles data via a genetic algorithm. The potential finds accurate energetics for defects with relatively low amounts of strain (xenon in defect clusters). It is important to find accurate energetics for these sorts of low-strain defects because they essentially represent small xenon bubbles. Finally, we parameterize a new UO2 potential that simultaneously yields accurate vibrational properties

First-principles study of thermodynamical properties of random magnetic overlayers on fcc-Cu(001) substrate

Czech Academy of Sciences Publication Activity Database

Mašín, Martin; Bergqvist, L.; Kudrnovský, Josef; Kotrla, Miroslav; Drchal, Václav

2013-01-01

Roč. 87, č. 7 (2013), "075452-1"-"075452-7" ISSN 1098-0121 R&D Projects: GA ČR GA202/09/0775 Institutional support: RVO:68378271 Keywords : Curie temperature * random overlayer * Heisenberg Hamiltonian * first principles * Monte Carlo simulations * magnon spectra Subject RIV: BE - Theoretical Physics Impact factor: 3.664, year: 2013 http://prb.aps.org/abstract/PRB/v87/i7/e075452

First-principles approach to the dynamic magnetoelectric couplings for the non-reciprocal directional dichroism in BiFeO3

International Nuclear Information System (INIS)

Lee, Jun Hee; Fishman, Randy S; Kézsmáki, István

2016-01-01

Due to the complicated magnetic and crystallographic structures of BiFeO 3 , its magnetoelectric (ME) couplings and microscopic model Hamiltonian remain poorly understood. By employing a first-principles approach, we uncover all possible ME couplings associated with the spin-current (SC) and exchange-striction (ES) polarizations, and construct an appropriate Hamiltonian for the long-range spin-cycloid in BiFeO 3 . First-principles calculations are used to understand the microscopic origins of the ME couplings. We find that inversion symmetries broken by ferroelectric and antiferroelectric distortions induce the SC and the ES polarizations, which cooperatively produce the dynamic ME effects in BiFeO 3 . A model motivated by first principles reproduces the absorption difference of counter-propagating light beams called non-reciprocal directional dichroism. The current paper focuses on the spin-driven (SD) polarizations produced by a dynamic electric field, i.e. the dynamic ME couplings. Due to the inertial properties of Fe, the dynamic SD polarizations differ significantly from the static SD polarizations. Our systematic approach can be generally applied to any multiferroic material, laying the foundation for revealing hidden ME couplings on the atomic scale and for exploiting optical ME effects in the next generation of technological devices such as optical diodes. (paper)

Quantum-mechanical calculation of H on Ni(001) using a model potential based on first-principles calculations

DEFF Research Database (Denmark)

Mattsson, T.R.; Wahnström, G.; Bengtsson, L.

1997-01-01

First-principles density-functional calculations of hydrogen adsorption on the Ni (001) surface have been performed in order to get a better understanding of adsorption and diffusion of hydrogen on metal surfaces. We find good agreement with experiments for the adsorption energy, binding distance...

Monolayer II-VI semiconductors: A first-principles prediction

Science.gov (United States)

Zheng, Hui; Chen, Nian-Ke; Zhang, S. B.; Li, Xian-Bin

A systematic study of 32 honeycomb monolayer II-VI semiconductors is carried out by first-principles methods. It appears that BeO, MgO, CaO, ZnO, CdO, CaS, SrS, SrSe, BaTe, and HgTe honeycomb monolayers have a good dynamic stability which is revealed by phonon calculations. In addition, from the molecular dynamic (MD) simulation of other unstable candidates, we also find two extra monolayers dynamically stable, which are tetragonal BaS and orthorhombic HgS. The honeycomb monolayers exist in form of either a planar perfect honeycomb or a low-buckled 2D layer, all of which possess a band gap and most of them are in the ultraviolet region. Interestingly, the dynamically stable SrSe has a gap near visible light, and displays exotic electronic properties with a flat top of the valence band, and hence has a strong spin polarization upon hole doping. The honeycomb HgTe has been reported to achieve a topological nontrivial phase under appropriate in-plane tensile strain and spin-orbital coupling (SOC). Some II-VI partners with less than 5% lattice mismatch may be used to design novel 2D heterojunction devices. If synthesized, potential applications of these 2D II-VI families could include optoelectronics, spintronics, and strong correlated electronics. Distinguished Student (DS) Program of APS FIP travel funds.

Regulatory Acceptance of Alternative Methods in the Development and Approval of Pharmaceuticals.

Science.gov (United States)

Beken, Sonja; Kasper, Peter; van der Laan, Jan-Willem

Animal studies may be carried out to support first administration of a new medicinal product to either humans or the target animal species, or before performing clinical trials in even larger populations, or before marketing authorisation, or to control quality during production. Ethical and animal welfare considerations require that animal use is limited as much as possible. Directive 2010/63/EU on the protection of animals used for scientific purposes unambiguously fosters the application of the principle of the 3Rs when considering the choice of methods to be used.As such, today, the 3Rs are embedded in the relevant regulatory guidance both at the European (European Medicines Agency (EMA)) and (Veterinary) International Conference on Harmonization ((V)ICH) levels. With respect to non-clinical testing requirements for human medicinal products, reduction and replacement of animal testing has been achieved by the regulatory acceptance of new in vitro methods, either as pivotal, supportive or exploratory mechanistic studies. Whilst replacement of animal studies remains the ultimate goal, approaches aimed at reducing or refining animal studies have also been routinely implemented in regulatory guidelines, where applicable. The chapter provides an overview of the implementation of 3Rs in the drafting of non-clinical testing guidelines for human medicinal products at the level of the ICH. In addition, the revision of the ICH S2 guideline on genotoxicity testing and data interpretation for pharmaceuticals intended for human use is discussed as a case study.In October 2010, the EMA established a Joint ad hoc Expert Group (JEG 3Rs) with the mandate to improve and foster the application of 3Rs principles to the regulatory testing of medicinal products throughout their lifecycle. As such, a Guideline on regulatory acceptance of 3R testing approaches was drafted that defines regulatory acceptance and provides guidance on the scientific and technical criteria for regulatory

A Principles-Based Approach to Teaching International Financial Reporting Standards (IFRS)

Science.gov (United States)

Persons, Obeua

2014-01-01

This article discusses the principles-based approach that emphasizes a "why" question by using the International Accounting Standards Board (IASB) "Conceptual Framework for Financial Reporting" to question and understand the basis for specific differences between IFRS and U.S. generally accepted accounting principles (U.S.…

First Stage Acceptance Test

Science.gov (United States)

1960-01-01

This photograph shows the intense smoke and fire created by the five F-1 engines from a test firing of the Saturn V first stage (S-1C) in the S-1C test stand at the Marshall Space Flight Center. The towering 363-foot Saturn V was a multi-stage, multi-engine launch vehicle standing taller than the Statue of Liberty. Altogether, the Saturn V engines produced as much power as 85 Hoover Dams.

First-principles prediction of phononic thermal conductivity of silicene: A comparison with graphene

International Nuclear Information System (INIS)

Gu, Xiaokun; Yang, Ronggui

2015-01-01

There has been great interest in two-dimensional materials, beyond graphene, for both fundamental sciences and technological applications. Silicene, a silicon counterpart of graphene, has been shown to possess some better electronic properties than graphene. However, its thermal transport properties have not been fully studied. In this paper, we apply the first-principles-based phonon Boltzmann transport equation to investigate the thermal conductivity of silicene as well as the phonon scattering mechanisms. Although both graphene and silicene are two-dimensional crystals with similar crystal structure, we find that phonon transport in silicene is quite different from that in graphene. The thermal conductivity of silicene shows a logarithmic increase with respect to the sample size due to the small scattering rates of acoustic in-plane phonon modes, while that of graphene is finite. Detailed analysis of phonon scattering channels shows that the linear dispersion of the acoustic out-of-plane (ZA) phonon modes, which is induced by the buckled structure, makes the long-wavelength longitudinal acoustic phonon modes in silicene not as efficiently scattered as that in graphene. Compared with graphene, where most of the heat is carried by the acoustic out-of-plane (ZA) phonon modes, the ZA phonon modes in silicene only have ∼10% contribution to the total thermal conductivity, which can also be attributed to the buckled structure. This systematic comparison of phonon transport and thermal conductivity of silicene and graphene using the first-principle-based calculations shed some light on other two-dimensional materials, such as two-dimensional transition metal dichalcogenides

Safeguards First Principles Initiative at the Nevada Test Site

International Nuclear Information System (INIS)

Johnson, Geneva

2007-01-01

The Material Control and Accountability (MC and A) program at the Nevada Test Site (NTS) was selected as a test bed for the Safeguards First Principles Initiative (SFPI). The implementation of the SFPI is evaluated using the system effectiveness model and the program is managed under an approved MC and A Plan. The effectiveness model consists of an evaluation of the critical elements necessary to detect, deter, and/or prevent the theft or diversion of Special Nuclear Material (SNM). The modeled results indicate that the MC and A program established under this variance is still effective, without creating unacceptable risk. Extensive performance testing is conducted through the duration of the pilot to ensure the protection system is effective and no material is at an unacceptable risk. The pilot was conducted from January 1, 2007, through May 30, 2007. This paper will discuss the following activities in association with SFPI: (1) Development of Timeline; (2) Crosswalk of DOE Order and SFPI; (3) Peer Review; (4) Deviation; (5) MC and A Plan and Procedure changes; (6) Changes implemented at NTS; (7) Training; and (8) Performance Test

Adsorption of methanol molecule on graphene: Experimental results and first-principles calculations

Science.gov (United States)

Zhao, X. W.; Tian, Y. L.; Yue, W. W.; Chen, M. N.; Hu, G. C.; Ren, J. F.; Yuan, X. B.

2018-04-01

Adsorption properties of methanol molecule on graphene surface are studied both theoretically and experimentally. The adsorption geometrical structures, adsorption energies, band structures, density of states and the effective masses are obtained by means of first-principles calculations. It is found that the electronic characteristics and conductivity of graphene are sensitive to the methanol molecule adsorption. After adsorption of methanol molecule, bandgap appears. With the increasing of the adsorption distance, the bandgap, adsorption energy and effective mass of the adsorption system decreased, hence the resistivity of the system decreases gradually, these results are consistent with the experimental results. All these calculations and experiments indicate that the graphene-based sensors have a wide range of applications in detecting particular molecules.

Polytypism in ZnS, ZnSe, and ZnTe: First-principles study

KAUST Repository

Boutaiba, F.

2014-06-23

We report results of first-principles calculations based on the projector augmented wave (PAW) method to explore the structural, thermodynamic, and electronic properties of cubic (3C) and hexagonal (6H, 4H, and 2H) polytypes of II-VI compounds: ZnS, ZnSe, and ZnTe. We find that the different bond stacking in II-VI polytypes remarkably influences the resulting physical properties. Furthermore, the degree of hexagonality is found to be useful to understand both the ground-state properties and the electronic structure of these compounds. The resulting lattice parameters, energetic stability, and characteristic band energies are in good agreement with available experimental data. Trends with hexagonality of the polytype are investigated.

Polytypism in ZnS, ZnSe, and ZnTe: First-principles study

KAUST Repository

Boutaiba, F.; Belabbes, Abderrezak; Ferhat, M.; Bechstedt, F.

2014-01-01

We report results of first-principles calculations based on the projector augmented wave (PAW) method to explore the structural, thermodynamic, and electronic properties of cubic (3C) and hexagonal (6H, 4H, and 2H) polytypes of II-VI compounds: ZnS, ZnSe, and ZnTe. We find that the different bond stacking in II-VI polytypes remarkably influences the resulting physical properties. Furthermore, the degree of hexagonality is found to be useful to understand both the ground-state properties and the electronic structure of these compounds. The resulting lattice parameters, energetic stability, and characteristic band energies are in good agreement with available experimental data. Trends with hexagonality of the polytype are investigated.

Nano-sized graphene flakes: insights from experimental synthesis and first principles calculations.

Science.gov (United States)

Lin, Pin-Chun; Chen, Yi-Rui; Hsu, Kuei-Ting; Lin, Tzu-Neng; Tung, Kuo-Lun; Shen, Ji-Lin; Liu, Wei-Ren

2017-03-01

In this study, we proposed a cost-effective method for preparing graphene nano-flakes (GNFs) derived from carbon nanotubes (CNTs) via three steps (pressing, homogenization and sonication exfoliation processes). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), laser scattering, as well as ultraviolet-visible and photoluminescence (PL) measurements were carried out. The results indicated that the size of as-synthesized GNFs was approximately 40-50 nm. Furthermore, we also used first principles calculations to understand the transformation from CNTs to GNFs from the viewpoints of the edge formation energies of GNFs in different shapes and sizes. The corresponding photoluminescence measurements of GNFs were carried out in this work.

First-Principles Study of Lithium and Sodium Atoms Intercalation in Fluorinated Graphite

Directory of Open Access Journals (Sweden)

Fengya Rao

2015-06-01

Full Text Available The structure evolution of fluorinated graphite (CFx upon the Li/Na intercalation has been studied by first-principles calculations. The Li/Na adsorption on single CF layer and intercalated into bulk CF have been calculated. The better cycling performance of Na intercalation into the CF cathode, comparing to that of Li intercalation, is attributed to the different strength and characteristics of the Li-F and Na-F interactions. The interactions between Li and F are stronger and more localized than those between Na and F. The strong and localized Coulomb attraction between Li and F atoms breaks the C−F bonds and pulls the F atoms away, and graphene sheets are formed upon Li intercalation.

Culture of safety. Indicators of culture of safety. Stage of culture of safety. Optimization of radiating protection. Principle of precaution. Principle ALARA. Procedure ALARA

International Nuclear Information System (INIS)

Mursa, E.

2006-01-01

Object of research: is the theory and practice of optimization of radiating protection according to recommendations of the international organizations, realization of principle ALARA and maintenance of culture of safety (SC) on the nuclear power plant. The purpose of work - to consider the general aspects of realization of principle ALARA, conceptual bases of culture of safety, as principle of management, and practice of their introduction on the nuclear power plant. The work has the experts' report character in which the following questions are presented: The recommendations materials of the IAEA and other international organizations have been assembled, systematized and analyzed. The definitions, characteristics and universal SC features, and also indicators as a problem of parameters and quantitative SC measurements are described in details advanced. The ALARA principles - principle of precaution; not acceptance of zero risk; choice of a principle ALARA; model of acceptable radiation risk are described. The methodology of an estimation of culture of safety level and practical realization of the ALARA principle in separate organization is shown on a practical example. The SC general estimation at a national level in Republic of Moldova have been done. Taking into consideration that now Safety Culture politics are introduced only in relation to APS, in this paper the attempt of application of Safety Culture methodology to Radiological Objects have been made (Oncological Institute of the Republic of Moldova and Special Objects No.5101 and 5102 for a long time Storage of the Radioactive Waste). (authors)

Analysis of electron-positron momentum spectra of metallic alloys as supported by first-principles calculations

OpenAIRE

Folegati, P.; Makkonen, I.; Ferragut, R.; Puska, Martti J.

2007-01-01

Electron-positron momentum distributions measured by the coincidence Doppler broadening method can be used in the chemical analysis of the annihilation environment, typically a vacancy-impurity complex in a solid. In the present work, we study possibilities for a quantitative analysis, i.e., for distinguishing the average numbers of different atomic species around the defect. First-principles electronic structure calculations self-consistently determining electron and positron densities and i...

First principles calculation on the adsorption of water on lithium-montmorillonite (Li-MMT)

International Nuclear Information System (INIS)

Wungu, Triati Dewi Kencana; Agusta, Mohammad Kemal; Saputro, Adhitya Gandaryus; Kasai, Hideaki; Dipojono, Hermawan Kresno

2012-01-01

The interaction of water molecules and lithium-montmorillonite (Li-MMT) is theoretically investigated using density functional theory (DFT) based first principles calculation. The mechanism of water adsorption at two different water concentrations on Li-MMT as well as their structural and electronic properties are investigated. It is found that the adsorption stability in Li-MMT is higher in higher water concentration. It is also found that an adsorbed water molecule on Li-MMT causes the Li to protrude from the MMT surface, so it is expected that Li may be mobile on H 2 O/Li-MMT.

First principles calculation on the adsorption of water on lithium-montmorillonite (Li-MMT).

Science.gov (United States)

Wungu, Triati Dewi Kencana; Agusta, Mohammad Kemal; Saputro, Adhitya Gandaryus; Dipojono, Hermawan Kresno; Kasai, Hideaki

2012-11-28

The interaction of water molecules and lithium-montmorillonite (Li-MMT) is theoretically investigated using density functional theory (DFT) based first principles calculation. The mechanism of water adsorption at two different water concentrations on Li-MMT as well as their structural and electronic properties are investigated. It is found that the adsorption stability in Li-MMT is higher in higher water concentration. It is also found that an adsorbed water molecule on Li-MMT causes the Li to protrude from the MMT surface, so it is expected that Li may be mobile on H(2)O/Li-MMT.

Multiferroic BiFeO3-BiMnO3 Nanocheckerboard From First Principles

OpenAIRE

Palova, L.; Chandra, P.; Rabe, K. M.

2010-01-01

We present a first principles study of an unusual heterostructure, an atomic-scale checkerboard of BiFeO3-BiMnO3, and compare its properties to the two bulk constituent materials, BiFeO3 and BiMnO3. The "nanocheckerboard" is found to have a multiferroic ground state with the desired properties of each constituent: polar and ferrimagnetic due to BiFeO3 and BiMnO3, respectively. The effect of B-site cation ordering on magnetic ordering in the BiFeO3-BiMnO3 system is studied. The checkerboard ge...

First -principles calculations of the crystal structure, electronic structure, and thermodynamic stability of Be(BH4)2

NARCIS (Netherlands)

van Setten, Michiel J.; de Wijs, Gilles A.; Brocks, G.

2008-01-01

Alanates and boranates are intensively studied because of their potential use as hydrogen storage materials. In this paper, we present a first-principles study of the electronic structure and the energetics of beryllium boranate BeBH42. From total energy calculations, we show that—in contrast to the

Crosscheck Principle in Pediatric Audiology Today: A 40-Year Perspective.

Science.gov (United States)

Hall, James W

2016-09-01

The crosscheck principle is just as important in pediatric audiology as it was when first described 40 years ago. That is, no auditory test result should be accepted and used in the diagnosis of hearing loss until it is confirmed or crosschecked by one or more independent measures. Exclusive reliance on only one or two tests, even objective auditory measures, may result in a auditory diagnosis that is not clear or perhaps incorrect. On the other hand, close and careful analysis of findings for a test battery consisting of objective procedures and behavioral tests whenever feasible usually leads to prompt and accurate diagnosis of auditory dysfunction. This paper provides a concise review of the crosscheck principle from its introduction to its clinical application today. The review concludes with a description of a modern test battery for pediatric hearing assessment that supplements traditional behavioral tests with a variety of independent objective procedures including aural immittance measures, otoacoustic emissions, and auditory evoked responses.

Crosscheck Principle in Pediatric Audiology Today: A 40-Year Perspective

Science.gov (United States)

2016-01-01

The crosscheck principle is just as important in pediatric audiology as it was when first described 40 years ago. That is, no auditory test result should be accepted and used in the diagnosis of hearing loss until it is confirmed or crosschecked by one or more independent measures. Exclusive reliance on only one or two tests, even objective auditory measures, may result in a auditory diagnosis that is not clear or perhaps incorrect. On the other hand, close and careful analysis of findings for a test battery consisting of objective procedures and behavioral tests whenever feasible usually leads to prompt and accurate diagnosis of auditory dysfunction. This paper provides a concise review of the crosscheck principle from its introduction to its clinical application today. The review concludes with a description of a modern test battery for pediatric hearing assessment that supplements traditional behavioral tests with a variety of independent objective procedures including aural immittance measures, otoacoustic emissions, and auditory evoked responses. PMID:27626077

36 CFR 219.2 - Principles.

Science.gov (United States)

2010-07-01

... 36 Parks, Forests, and Public Property 2 2010-07-01 2010-07-01 false Principles. 219.2 Section 219... Forest System Land and Resource Management Planning Purpose and Principles § 219.2 Principles. The planning regulations in this subpart are based on the following principles: (a) The first priority for...

Jump rates for surface diffusion of large molecules from first principles

Energy Technology Data Exchange (ETDEWEB)

Shea, Patrick, E-mail: patrick.shea@dal.ca; Kreuzer, Hans Jürgen [Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 3J5 (Canada)

2015-04-21

We apply a recently developed stochastic model for the surface diffusion of large molecules to calculate jump rates for 9,10-dithioanthracene on a Cu(111) surface. The necessary input parameters for the stochastic model are calculated from first principles using density functional theory (DFT). We find that the inclusion of van der Waals corrections to the DFT energies is critical to obtain good agreement with experimental results for the adsorption geometry and energy barrier for diffusion. The predictions for jump rates in our model are in excellent agreement with measured values and show a marked improvement over transition state theory (TST). We find that the jump rate prefactor is reduced by an order of magnitude from the TST estimate due to frictional damping resulting from energy exchange with surface phonons, as well as a rotational mode of the diffusing molecule.

Towards a mulitphase equation of state of Carbon from first principles

Science.gov (United States)

Correa, Alfredo; Benedict, Lorin; Schwegler, Eric

2007-03-01

Ab initio molecular dynamics and electronic structure calculation had become one of the most useful tools to investigate properties of materials. Unfortunately these atomistic detailed results are rarely reused in calculations at a higher level of description, such as fluid dynamics and finite elements calculations. In this talk we present a concrete example showing the way that first principles results can be expressed in a way that is useful for hydrodynamics calculations, in particular we show how to build a analytic equation of state for Carbon that involves solid (diamond and BC8) and liquid phases. Applications of this newly obtained equation of state will be presented. This work was performed under the auspices of the U.S. Dept. of Energy at the University of California/Lawrence Livermore National Laboratory under contract no. W-7405-Eng-48.

Insight into point defects and impurities in titanium from first principles

Science.gov (United States)

Nayak, Sanjeev K.; Hung, Cain J.; Sharma, Vinit; Alpay, S. Pamir; Dongare, Avinash M.; Brindley, William J.; Hebert, Rainer J.

2018-03-01

Titanium alloys find extensive use in the aerospace and biomedical industries due to a unique combination of strength, density, and corrosion resistance. Decades of mostly experimental research has led to a large body of knowledge of the processing-microstructure-properties linkages. But much of the existing understanding of point defects that play a significant role in the mechanical properties of titanium is based on semi-empirical rules. In this work, we present the results of a detailed self-consistent first-principles study that was developed to determine formation energies of intrinsic point defects including vacancies, self-interstitials, and extrinsic point defects, such as, interstitial and substitutional impurities/dopants. We find that most elements, regardless of size, prefer substitutional positions, but highly electronegative elements, such as C, N, O, F, S, and Cl, some of which are common impurities in Ti, occupy interstitial positions.

Dispersion-corrected first-principles calculation of terahertz vibration, and evidence for weak hydrogen bond formation

Science.gov (United States)

Takahashi, Masae; Ishikawa, Yoichi; Ito, Hiromasa

2013-03-01

A weak hydrogen bond (WHB) such as CH-O is very important for the structure, function, and dynamics in a chemical and biological system WHB stretching vibration is in a terahertz (THz) frequency region Very recently, the reasonable performance of dispersion-corrected first-principles to WHB has been proven. In this lecture, we report dispersion-corrected first-principles calculation of the vibrational absorption of some organic crystals, and low-temperature THz spectral measurement, in order to clarify WHB stretching vibration. The THz frequency calculation of a WHB crystal has extremely improved by dispersion correction. Moreover, the discrepancy in frequency between an experiment and calculation and is 10 1/cm or less. Dispersion correction is especially effective for intermolecular mode. The very sharp peak appearing at 4 K is assigned to the intermolecular translational mode that corresponds to WHB stretching vibration. It is difficult to detect and control the WHB formation in a crystal because the binding energy is very small. With the help of the latest intense development of experimental and theoretical technique and its careful use, we reveal solid-state WHB stretching vibration as evidence for the WHB formation that differs in respective WHB networks The research was supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan (Grant No. 22550003).

Dissociation of water and Acetic acid on PbS from first principles

Science.gov (United States)

Satta, Alessandra; Ruggerone, Paolo; de Giudici, Giovanni

2008-03-01

The adsorption of complex molecules at mineral surfaces are crucial ingredients for understanding the mechanisms that rule the interaction between minerals and the biosphere and for predicting both the stability and the reactivity of minerals. The present work focuses mainly on the early stages of different adsorption reactions occurring at both the cleavage surface and a high-index vicinal surface of galena (PbS). We have studied the dissociation mechanism of water and acetic acid on the galena surfaces by means of ab initio calculations within the framework of the density functional theory in the generalized gradient approximation and of pseudopotential approach. The calculated adsorption energies of the molecules indicate the stepped surface as the most reactive, as expected. The free energy surface during the reaction process has been explored via metadynamics[1]. The optimized configurations of both reactants and products obtained, were then used to accurately calculate the dissociation energy via the Nudge Elastic Band method[2]. [1] A. Laio and M. Parrinello, PNAS 99, 12562 (2002). [2] G. Mills and H. Jonsson, Phys. Rev. Lett. 72, 1124 (1994).

The Mindful Way Through the Semester: An Investigation of the Effectiveness of an Acceptance-Based Behavioral Therapy Program on Psychological Wellness in First-Year Students.

Science.gov (United States)

Danitz, Sara B; Orsillo, Susan M

2014-07-01

First-year students in higher education deal with an increasing number of mental health issues. Cost-effective and time-efficient programs that ease transitions and reduce risk of depression are needed. To date, programs informed by both cognitive-behavioral and acceptance-based-behavioral therapy (ABBT) approaches have produced some positive outcomes, but methodological limitations limit their utility. The aim of the present study was to address some of these limitations, by developing and preliminary testing the efficacy of a one-session ABBT intervention with first-year undergraduates and first-year law students. Ninety-eight first-year students were randomly assigned to receive either a single-session 90-min ABBT workshop within their first month of school or to a waitlist control condition. Students who received the intervention reported significantly less depression and more acceptance. Moreover, increase in acceptance over the course of the semester was associated with reductions in depression. Implications of these findings for future interventions are discussed. © The Author(s) 2014.

Elastic properties of cubic perovskite BaRuO{sub 3} from first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Han Deming; Liu Xiaojuan; Lv Shuhui; Li Hongping [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Meng Jian, E-mail: jmeng@ciac.jl.c [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China)

2010-08-01

We present first-principles investigations on the structural and elastic properties of the cubic perovskite BaRuO{sub 3} using density-functional theory within both local density approximation (LDA) and generalized gradient approximation (GGA). Basic physical properties, such as lattice constant, shear modulus, elastic constants (C{sub ij}) are calculated. The calculated energy band structures show that the cubic perovskite BaRuO{sub 3} is metallic. We have also predicted the Young's modulus (Y), Poisson's ratio ({upsilon}), and Anisotropy factor (A).

First-principles study of lithium adsorption and diffusion on graphene: the effects of strain

International Nuclear Information System (INIS)

Hao, Feng; Chen, Xi

2015-01-01

Large strain is produced within graphene sheets, which serve as a critical component in lithium-ion batteries, due to the expansion of the electrodes. First-principles calculations are therefore employed to investigate the interaction of Li with strained single-layer graphene. It is found that tensile strain enhances Li binding on graphene and significantly reduces the formation energy of divacancies. In addition, Li diffusion through graphene with defects is facilitated by tensile strain, whereas diffusion parallel to the plane of pristine graphene is slightly hindered. (paper)

Time-dependent first-principles study of angle-resolved secondary electron emission from atomic sheets

Science.gov (United States)

Ueda, Yoshihiro; Suzuki, Yasumitsu; Watanabe, Kazuyuki

2018-02-01

Angle-resolved secondary electron emission (ARSEE) spectra were analyzed for two-dimensional atomic sheets using a time-dependent first-principles simulation of electron scattering. We demonstrate that the calculated ARSEE spectra capture the unoccupied band structure of the atomic sheets. The excitation dynamics that lead to SEE have also been revealed by the time-dependent Kohn-Sham decomposition scheme. In the present study, the mechanism for the experimentally observed ARSEE from atomic sheets is elucidated with respect to both energetics and the dynamical aspects of SEE.

Using Axline's Eight Principles of Play Therapy with Mexican-American Children

Science.gov (United States)

Ramirez, Sylvia Z.; Flores-Torres, Leila L.; Kranz, Peter L.; Lund, Nick L.

2005-01-01

There is a paucity of literature on the application of client-centered play therapy to diverse cultures. In this regard, the purpose of the article is to discuss considerations related to using Axline's eight principles of play therapy with Mexican-American children. The principles involve multicultural acceptance and understanding, relationship…

Clean intermittent self-catheterisation - principles and practice

Directory of Open Access Journals (Sweden)

Arun Narayanaswamy

2000-01-01

Full Text Available This review of the literature on the principles and prac-tice of clean intermittent self-catheterisation includes the role of antiseptics/antibiotics, and outcome. It covers ac-ceptance of the technique, urinary tract infection, conti-nence, and preservation of upper urinary tract.

Development of food acceptance patterns in the first years of life.

Science.gov (United States)

Birch, L L

1998-11-01

As young omnivores, children make the transition from the exclusive milk diet of infancy to consuming a variety of foods. They must learn to accept a set of the foods available in their environmental niche, and they 'come equipped' with a set of predispositions that facilitate the development of food acceptance patterns, constrained by predisposition and limited by what is offered to them. While children are predisposed to like sweet or salty foods and to avoid sour or bitter foods, their preferences for the majority of foods are shaped by repeated experience. The predispositions that shape food acceptance patterns also include neophobia and the predisposition to learn to prefer and accept new foods when they are offered repeatedly. In addition, the predisposition for associative conditioning affects children's developing food acceptance patterns, resulting in preferences for foods offered in positive contexts, while foods presented in negative contexts will become more disliked via the learning of associations with the social and environmental contexts. Children also learn to prefer energy-dense foods when consumption of those foods is followed by positive post-ingestive consequences, such as those produced when high-energy-density foods are eaten when hungry. Although children are predisposed to be responsive to the energy content of foods in controlling their intake, they are also responsive to parents' control attempts. We have seen that these parental control attempts can refocus the child away from responsiveness to internal cues of hunger and satiety and towards external factors such as the presence of palatable foods. This analysis suggests that taking a closer look at what children are learning about food and eating may provide clues regarding the formation of children's food acceptance patterns, and that this approach also suggests potential causative factors implicated in the aetiology of obesity and the emergence of weight concerns. Current data

Acceptance of Others, Feeling of Being Accepted and Striving for Being Accepted Among the Representatives of Different Kinds of Occupations

Directory of Open Access Journals (Sweden)

Gergana Stanoeva

2012-05-01

Full Text Available This paper deals with an important issue related to the human attitudes and needs in interpersonal and professional aspects. The theoretical part deals with several psychological components of the self-esteem and esteem of the others – acceptance of the others, feeling of being accepted, need for approval. Some gender differences in manifestations of acceptance and feeling of being accepted at the workplace are discussed. This article presents some empirical data for the degree of acceptance of others, feeling of being accepted and the strive for being accepted among the representatives of helping, pedagogical, administrative and economic occupations, as well as non-qualified workers. The goals of the study were to reveal the interdependency between these constructs and to be found some significant differences between the representatives of the four groups of occupations. The methods of the first study were W. Fey’s scales “Acceptance of others”, and “How do I feel accepted by others”. The method of the second study was Crown and Marlowe Scale for Social Desirability. The results indicated some significant differences in acceptance of others and feeling of being accepted between the non-qualified workers and the representatives of helping, administrative and economic occupations. There were not any significant difference in strive for being accepted between the fouroccupational groups.

Anisotropy and temperature dependence of structural, thermodynamic, and elastic properties of crystalline cellulose Iβ: a first-principles investigation

Science.gov (United States)

ShunLi Shang; Louis G. Hector Jr.; Paul Saxe; Zi-Kui Liu; Robert J. Moon; Pablo D. Zavattieri

2014-01-01

Anisotropy and temperature dependence of structural, thermodynamic and elastic properties of crystalline cellulose Iβ were computed with first-principles density functional theory (DFT) and a semi-empirical correction for van der Waals interactions. Specifically, we report the computed temperature variation (up to 500...

First-Principles Prediction of Spin-Polarized Multiple Dirac Rings in Manganese Fluoride

Science.gov (United States)

Jiao, Yalong; Ma, Fengxian; Zhang, Chunmei; Bell, John; Sanvito, Stefano; Du, Aijun

2017-07-01

Spin-polarized materials with Dirac features have sparked great scientific interest due to their potential applications in spintronics. But such a type of structure is very rare and none has been fabricated. Here, we investigate the already experimentally synthesized manganese fluoride (MnF3 ) as a novel spin-polarized Dirac material by using first-principles calculations. MnF3 exhibits multiple Dirac cones in one spin orientation, while it behaves like a large gap semiconductor in the other spin channel. The estimated Fermi velocity for each cone is of the same order of magnitude as that in graphene. The 3D band structure further reveals that MnF3 possesses rings of Dirac nodes in the Brillouin zone. Such a spin-polarized multiple Dirac ring feature is reported for the first time in an experimentally realized material. Moreover, similar band dispersions can be also found in other transition metal fluorides (e.g., CoF3 , CrF3 , and FeF3 ). Our results highlight a new interesting single-spin Dirac material with promising applications in spintronics and information technologies.

First-Principles Prediction of Spin-Polarized Multiple Dirac Rings in Manganese Fluoride.

Science.gov (United States)

Jiao, Yalong; Ma, Fengxian; Zhang, Chunmei; Bell, John; Sanvito, Stefano; Du, Aijun

2017-07-07

Spin-polarized materials with Dirac features have sparked great scientific interest due to their potential applications in spintronics. But such a type of structure is very rare and none has been fabricated. Here, we investigate the already experimentally synthesized manganese fluoride (MnF_{3}) as a novel spin-polarized Dirac material by using first-principles calculations. MnF_{3} exhibits multiple Dirac cones in one spin orientation, while it behaves like a large gap semiconductor in the other spin channel. The estimated Fermi velocity for each cone is of the same order of magnitude as that in graphene. The 3D band structure further reveals that MnF_{3} possesses rings of Dirac nodes in the Brillouin zone. Such a spin-polarized multiple Dirac ring feature is reported for the first time in an experimentally realized material. Moreover, similar band dispersions can be also found in other transition metal fluorides (e.g., CoF_{3}, CrF_{3}, and FeF_{3}). Our results highlight a new interesting single-spin Dirac material with promising applications in spintronics and information technologies.

Temperature effects on the generalized planar fault energies and twinnabilities of Al, Ni and Cu: First principles calculations

KAUST Repository

Liu, Lili

2014-06-01

Based on the quasiharmonic approach from first-principles phonon calculations, the volume versus temperature relations for Al, Ni and Cu are obtained. Using the equilibrium volumes at temperature T, the temperature dependences of generalized planar fault energies have also been calculated by first-principles calculations. It is found that the generalized planar fault energies reduce slightly with increasing temperature. Based on the calculated generalized planar fault energies, the twinnabilities of Al, Ni and Cu are discussed with the three typical criteria for crack tip twinning, grain boundary twinning and inherent twinning at different temperatures. The twinnabilities of Al, Ni and Cu also decrease slightly with increasing temperature. Ni and Cu have the inherent twinnabilities. But, Al does not exhibit inherent twinnability. These results are in agreement with the previous theoretical studies at 0 K and experimental observations at ambient temperature. © 2014 Elsevier B.V. All rights reserved.

Temperature effects on the generalized planar fault energies and twinnabilities of Al, Ni and Cu: First principles calculations

KAUST Repository

Liu, Lili; Wang, Rui; Wu, Xiaozhi; Gan, Liyong; Wei, Qunyi

2014-01-01

Based on the quasiharmonic approach from first-principles phonon calculations, the volume versus temperature relations for Al, Ni and Cu are obtained. Using the equilibrium volumes at temperature T, the temperature dependences of generalized planar fault energies have also been calculated by first-principles calculations. It is found that the generalized planar fault energies reduce slightly with increasing temperature. Based on the calculated generalized planar fault energies, the twinnabilities of Al, Ni and Cu are discussed with the three typical criteria for crack tip twinning, grain boundary twinning and inherent twinning at different temperatures. The twinnabilities of Al, Ni and Cu also decrease slightly with increasing temperature. Ni and Cu have the inherent twinnabilities. But, Al does not exhibit inherent twinnability. These results are in agreement with the previous theoretical studies at 0 K and experimental observations at ambient temperature. © 2014 Elsevier B.V. All rights reserved.

Defect physics and electronic properties of Cu3PSe4 from first principles

Science.gov (United States)

Foster, D. H.; Barras, F. L.; Vielma, J. M.; Schneider, G.

2013-11-01

The p-type semiconductor Cu3PSe4 has recently been established to have a direct band gap of 1.4 eV and an optical absorption spectrum similar to GaAs [Foster , Appl. Phys. Lett.APPLAB0003-695110.1063/1.3656760 99, 181903 (2011)], suggesting a possible application as a solar photovoltaic absorber. Here we calculate the thermodynamic stability, defect energies and concentrations, and several material properties of Cu3PSe4 using a wholly GGA+U method (the generalized gradient approximation of density functional theory with a Hubbard U term included for the Cu-d orbitals). We find that two low energy acceptor defects, the copper vacancy VCu and the phosphorus-on-selenium antisite PSe, establish the p-type behavior and likely prevent any n-type doping near thermal equilibrium. The GGA+U defect calculation method is shown to yield more accurate results than the more standard method of applying post-calculation GGA+U-based band-gap corrections to strictly GGA defect calculations.

Effects of hydrogen on Mn-doped GaN: A first principles calculation

International Nuclear Information System (INIS)

Wu, M.S.; Xu, B.; Liu, G.; Lei, X.L.; Ouyang, C.Y.

2013-01-01

First-principles calculations based on spin density functional theory are performed to study the effects of H on the structural, electronic and magnetic properties of the Mn-doped GaN dilute magnetic semiconductors. Our results show that the interstitial H atom prefers to bond with N atom rather than Mn atom, which means that H favors to form the N–H complex rather than Mn–H complex in the Mn-doped GaN. After introducing one H atom in the system, the total magnetic moment of the Mn-doped GaN increases by 25%, from 4.0μ B to 5.0μ B . The physics mechanism of the increase of magnetic moment after hydrogenation in Mn-doped GaN is discussed

Thermal conductivity of hexagonal Si and hexagonal Si nanowires from first-principles

Science.gov (United States)

Raya-Moreno, Martí; Aramberri, Hugo; Seijas-Bellido, Juan Antonio; Cartoixà, Xavier; Rurali, Riccardo

2017-07-01

We calculate the thermal conductivity, κ, of the recently synthesized hexagonal diamond (lonsdaleite) Si using first-principles calculations and solving the Boltzmann Transport Equation. We find values of κ which are around 40% lower than in the common cubic diamond polytype of Si. The trend is similar for [111] Si nanowires, with reductions of the thermal conductivity that are even larger than in the bulk in some diameter range. The Raman active modes are identified, and the role of mid-frequency optical phonons that arise as a consequence of the reduced symmetry of the hexagonal lattice is discussed. We also show briefly that popular classic potentials used in molecular dynamics might not be suited to describe hexagonal polytypes, discussing the case of the Tersoff potential.

The interaction of oxygen with TiC(001): Photoemission and first-principles studies

International Nuclear Information System (INIS)

Rodriguez, J.A.; Liu, P.; Dvorak, J.; Jirsak, T.; Gomes, J.; Takahashi, Y.; Nakamura, K.

2004-01-01

High-resolution photoemission and first-principles density-functional slab calculations were used to study the interaction of oxygen with a TiC(001) surface. Atomic oxygen is present on the TiC(001) substrate after small doses of O 2 at room temperature. A big positive shift (1.5-1.8 eV) was detected for the C 1s core level. These photoemission studies suggest the existence of strong O↔C interactions. A phenomenon corroborated by the results of first-principles calculations, which show a CTiTi hollow as the most stable site for the adsorption of O. Ti and C atoms are involved in the adsorption and dissociation of the O 2 molecule. In general, the bond between O and the TiC(001) surface contains a large degree of ionic character. The carbide→O charge transfer is substantial even at high coverages (>0.5 ML) of oxygen. At 500 K and large doses of O 2 , oxidation of the carbide surface occurs with the removal of C and formation of titanium oxides. There is an activation barrier for the exchange of Ti-C and Ti-O bonds which is overcome only by the formation of C-C or C-O bonds on the surface. The mechanism for the removal of a C atom as CO gas involves a minimum of two O adatoms, and three O adatoms are required for the formation of CO 2 gas. Due to the high stability of TiC, an O adatom alone cannot induce the generation of a C vacancy in a flat TiC(001) surface

Temperature-dependent dielectric function of germanium in the UV–vis spectral range: A first-principles study

International Nuclear Information System (INIS)

Yang, J.Y.; Liu, L.H.; Tan, J.Y.

2014-01-01

The study of temperature dependence of thermophysical parameter dielectric function is key to understanding thermal radiative transfer in high-temperature environments. Limited by self-radiation and thermal oxidation, however, it is difficult to directly measure the high-temperature dielectric function of solids with present experimental technologies. In this work, we implement two first-principles methods, the ab initio molecular dynamics (AIMD) and density functional perturbation theory (DFPT), to study the temperature dependence of dielectric function of germanium (Ge) in the UV–vis spectral range in order to provide data of high-temperature dielectric function for radiative transfer study in high-temperature environments. Both the two methods successfully predict the temperature dependence of dielectric function of Ge. Moreover, the good agreement between the calculated results of the AIMD approach and experimental data at 825 K enables us to predict the high-temperature dielectric function of Ge with the AIMD method in the UV–vis spectral range. - Highlights: • The temperature dependence of dielectric function of germanium (Ge) is investigated with two first-principles methods. • The temperature effect on dielectric function of Ge is discussed. • The high-temperature dielectric function of Ge is predicted

First-principles study of the electronic transport properties of the anthraquinone-based molecular switch

Energy Technology Data Exchange (ETDEWEB)

Zhao, P., E-mail: ss_zhaop@ujn.edu.c [School of Science, University of Jinan, Jinan 250022 (China); Liu, D.S. [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Department of Physics, Jining University, Qufu 273155 (China); Wang, P.J.; Zhang, Z. [School of Science, University of Jinan, Jinan 250022 (China); Fang, C.F.; Ji, G.M. [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China)

2011-02-15

By applying non-equilibrium Green's function (NEGF) formalism combined with first-principles density functional theory (DFT), we have investigated the electronic transport properties of the anthraquinone-based molecular switch. The molecule that comprises the switch can be converted between the hydroquinone (HQ) and anthraquinone (AQ) forms via redox reactions. The transmission spectra of these two forms are remarkably distinctive. Our results show that the current through the HQ form is significantly larger than that through the AQ form, which suggests that this system has attractive potential application in future molecular switch technology.

First-principles study of the electronic transport properties of the anthraquinone-based molecular switch

International Nuclear Information System (INIS)

Zhao, P.; Liu, D.S.; Wang, P.J.; Zhang, Z.; Fang, C.F.; Ji, G.M.

2011-01-01

By applying non-equilibrium Green's function (NEGF) formalism combined with first-principles density functional theory (DFT), we have investigated the electronic transport properties of the anthraquinone-based molecular switch. The molecule that comprises the switch can be converted between the hydroquinone (HQ) and anthraquinone (AQ) forms via redox reactions. The transmission spectra of these two forms are remarkably distinctive. Our results show that the current through the HQ form is significantly larger than that through the AQ form, which suggests that this system has attractive potential application in future molecular switch technology.

Liquid Water from First Principles: Validation of Different Sampling Approaches

Energy Technology Data Exchange (ETDEWEB)

Mundy, C J; Kuo, W; Siepmann, J; McGrath, M J; Vondevondele, J; Sprik, M; Hutter, J; Parrinello, M; Mohamed, F; Krack, M; Chen, B; Klein, M

2004-05-20

A series of first principles molecular dynamics and Monte Carlo simulations were carried out for liquid water to assess the validity and reproducibility of different sampling approaches. These simulations include Car-Parrinello molecular dynamics simulations using the program CPMD with different values of the fictitious electron mass in the microcanonical and canonical ensembles, Born-Oppenheimer molecular dynamics using the programs CPMD and CP2K in the microcanonical ensemble, and Metropolis Monte Carlo using CP2K in the canonical ensemble. With the exception of one simulation for 128 water molecules, all other simulations were carried out for systems consisting of 64 molecules. It is found that the structural and thermodynamic properties of these simulations are in excellent agreement with each other as long as adiabatic sampling is maintained in the Car-Parrinello molecular dynamics simulations either by choosing a sufficiently small fictitious mass in the microcanonical ensemble or by Nos{acute e}-Hoover thermostats in the canonical ensemble. Using the Becke-Lee-Yang-Parr exchange and correlation energy functionals and norm-conserving Troullier-Martins or Goedecker-Teter-Hutter pseudopotentials, simulations at a fixed density of 1.0 g/cm{sup 3} and a temperature close to 315 K yield a height of the first peak in the oxygen-oxygen radial distribution function of about 3.0, a classical constant-volume heat capacity of about 70 J K{sup -1} mol{sup -1}, and a self-diffusion constant of about 0.1 Angstroms{sup 2}/ps.

First-principles investigation of U doping in ZrO2

International Nuclear Information System (INIS)

Huang, H.W.; Pan, Y.; Yu, C.; Yang, J.; Wang, H.; Yi, W.; Peng, J.C.

2014-01-01

Highlights: • U-doped system with cubic structure is more stable than the monoclinic structure. • The elastic modulus of cubic structure is higher than the monoclinic structure. • U-doped weakens the resistance to shear deformation of ZrO 2 . • U-doped enhances the resistance to shape deformation for monoclinic structure. -- Abstract: The formation energies, elastic properties, Debye temperature and electronic structure of U-doped ZrO 2 within cubic and monoclinic structures are investigated by first-principles approach. The calculated formation energies show that the U-doped with cubic structure is more stable than that of monoclinic structure. The U-doped weakens the resistance to shear deformation whether cubic structure or monoclinic structure. However, the U-doped decreases the shape deformation of cubic structure in contrast to enhances the shape deformation for monoclinic structure. The Debye temperature of U-doped system is lower than the corresponding ZrO 2 . We found that the calculated electronic structure of these systems are consistent with the variation of formation energies

Alcohol molecules adsorption on graphane nanosheets - A first-principles investigation

Science.gov (United States)

Nagarajan, V.; Chandiramouli, R.

2018-05-01

The geometric structure, electronic and adsorption properties of methanol, ethanol and 1-propanol molecules on hydrogenated graphene (graphane) were investigated using first-principles calculations. The stability of graphane base material is confirmed using formation energy and phonon band structures. The adsorption of alcohol molecules on bare graphane and hydrogen vacant graphane nanosheet is found to be prominent and the selectivity of alcohol molecules can be achieved using bare or hydrogen vacant graphane nanosheet. Moreover, the interaction of alcohol molecules on bare and hydrogen vacant graphane nanosheets is studied using the adsorption energy, energy band gap variation, Bader charge transfer and average energy band gap variation. The adsorption energy ranges from -0.149 to -0.383 eV upon alcohol adsorption. The energy gap varies from 4.71 to 2.62 eV for bare graphane and from 4.02 to 3.60 eV for hydrogen vacant graphane nanosheets upon adsorption of alcohol molecules. The adsorption properties of alcohol molecules provide useful information for the possible application of graphane nanosheet as a base material for the detection of alcohol molecules.

Communication: Towards first principles theory of relaxation in supercooled liquids formulated in terms of cooperative motion

Energy Technology Data Exchange (ETDEWEB)

Freed, Karl F., E-mail: freed@uchicago.edu [James Franck Institute and Department of Chemistry, University of Chicago, 929 East 57 Street, Chicago, Illinois 60637 (United States)

2014-10-14

A general theory of the long time, low temperature dynamics of glass-forming fluids remains elusive despite the almost 20 years since the famous pronouncement by the Nobel Laureate P. W. Anderson, “The deepest and most interesting unsolved problem in solid state theory is probably the theory of the nature of glass and the glass transition” [Science 267, 1615 (1995)]. While recent work indicates that Adam-Gibbs theory (AGT) provides a framework for computing the structural relaxation time of supercooled fluids and for analyzing the properties of the cooperatively rearranging dynamical strings observed in low temperature molecular dynamics simulations, the heuristic nature of AGT has impeded general acceptance due to the lack of a first principles derivation [G. Adam and J. H. Gibbs, J. Chem. Phys. 43, 139 (1965)]. This deficiency is rectified here by a statistical mechanical derivation of AGT that uses transition state theory and the assumption that the transition state is composed of elementary excitations of a string-like form. The strings are assumed to form in equilibrium with the mobile particles in the fluid. Hence, transition state theory requires the strings to be in mutual equilibrium and thus to have the size distribution of a self-assembling system, in accord with the simulations and analyses of Douglas and co-workers. The average relaxation rate is computed as a grand canonical ensemble average over all string sizes, and use of the previously determined relation between configurational entropy and the average cluster size in several model equilibrium self-associating systems produces the AGT expression in a manner enabling further extensions and more fundamental tests of the assumptions.

Communication: Towards first principles theory of relaxation in supercooled liquids formulated in terms of cooperative motion.

Science.gov (United States)

Freed, Karl F

2014-10-14

A general theory of the long time, low temperature dynamics of glass-forming fluids remains elusive despite the almost 20 years since the famous pronouncement by the Nobel Laureate P. W. Anderson, "The deepest and most interesting unsolved problem in solid state theory is probably the theory of the nature of glass and the glass transition" [Science 267, 1615 (1995)]. While recent work indicates that Adam-Gibbs theory (AGT) provides a framework for computing the structural relaxation time of supercooled fluids and for analyzing the properties of the cooperatively rearranging dynamical strings observed in low temperature molecular dynamics simulations, the heuristic nature of AGT has impeded general acceptance due to the lack of a first principles derivation [G. Adam and J. H. Gibbs, J. Chem. Phys. 43, 139 (1965)]. This deficiency is rectified here by a statistical mechanical derivation of AGT that uses transition state theory and the assumption that the transition state is composed of elementary excitations of a string-like form. The strings are assumed to form in equilibrium with the mobile particles in the fluid. Hence, transition state theory requires the strings to be in mutual equilibrium and thus to have the size distribution of a self-assembling system, in accord with the simulations and analyses of Douglas and co-workers. The average relaxation rate is computed as a grand canonical ensemble average over all string sizes, and use of the previously determined relation between configurational entropy and the average cluster size in several model equilibrium self-associating systems produces the AGT expression in a manner enabling further extensions and more fundamental tests of the assumptions.

Substitutional Co dopant on the GaAs(110) surface: A first principles study

Energy Technology Data Exchange (ETDEWEB)

Fang, Zhou; Yi, Zhijun, E-mail: zhijunyi@cumt.edu.cn

2016-12-01

Using the first principles ground state method, the electronic properties of single Co dopant replacing one Ga atom on the GaAs(110) surface are studied. Our calculated local density of states (LDOS) at Co site presents several distinct peaks above the valence band maximum (VBM), and this agrees with recent experiments. Moreover, the calculated STM images at bias voltages of 2 eV and −2 eV also agree with experiments. We discussed the origin of Co impurity induced distinct peaks, which can be characterized with the hybridization between Co d orbitals and p-like orbitals of surface As and Ga atoms.

The Interface between Gd and Monolayer MoS2: A First-Principles Study

KAUST Repository

Zhang, Xuejing

2014-12-08

We analyze the electronic structure of interfaces between two-, four- and six-layer Gd(0001) and monolayer MoS2 by first-principles calculations. Strong chemical bonds shift the Fermi energy of MoS2 upwards into the conduction band. At the surface and interface the Gd f states shift to lower energy and new surface/interface Gd d states appear at the Fermi energy, which are strongly hybridized with the Mo 4d states and thus lead to a high spin-polarization (ferromagnetically ordered Mo magnetic moments of 0.15 μB). Gd therefore is an interesting candidate for spin injection into monolayer MoS2.

First principles study of CaTIO3 crystal in paraelectric and ferroelectric phases

International Nuclear Information System (INIS)

Hashemi, H.; Kompany, A.; Hosseini, M.

2005-01-01

Electronic properties of CaTiO 3 crystal in paraelectric and ferroelectric phases have been studied by first principles, using Hohenberg-kohn-sham density functional theory. In paraelectric phase the results show an indirect band gap of about at 2eV at Γ-R direction in the Brillouin zone and a strong hybridization between Ti-3d an O-2P orbital. In ferroelectric phase a direct band gap of about 1 eV is seen at ***Γ point. Up to our knowledge no data has been reported on the ferroelectric phase so far, therefore our results might be useful for the future works

A first-principles study of group IV and VI atoms doped blue phosphorene

Science.gov (United States)

Bai, Ruimin; Chen, Zheng; Gou, Manman; Zhang, Yixin

2018-02-01

Using first-principles calculations, we have systematically investigated the structural, electronic and magnetic properties of blue phosphorene doped by group IV and VI atoms, including C, Si, Ge, Sn, O, S, Se and Te. All the doped systems are energetically stable. Only C, Si, Ge and O-substituted systems show the characteristics of spin polarization and the magnetic moments are all 1.0 μB. Moreover, we found that C, Si, Ge and O doped systems are indirect bandgap semiconductors, while Sn, S, Se and Te doped systems present metallic property. These results show that blue phosphorene can be used prospectively in optoelectronic and spintronic devices.

A first principle approach for encapsulated type composite detectors

International Nuclear Information System (INIS)

Kshetri, R

2012-01-01

A first principle approach is presented for modeling a composite detector consisting of several high-purity germanium detector modules. Without making assumptions, if we consider the full energy peak counts from single and multiple detector module interactions, and the decomposition of background counts to counts corresponding to the escaping γ-rays and counts for γ-rays which could be recovered in addback mode, it is observed that the addback mode of a composite detector could be described in terms of four probability amplitudes only. Expressions for peak-to-total and peak-to-background ratios are obtained. Considering details of the scattering and absorption processes in a composite detector, a formalism is introduced for understanding the probability amplitudes. Detailed investigation has been performed on the effect of shape and size of composite detectors on peak-to-total and peak-to-background ratios. In accordance with isoperimetric inequality for hexagonal shapes, we have discussed about the optimal design of detector layout for extremely large values of detector modules. Using experimental data on relative single crystal efficiency, addback factor and peak-to-total ratio at 1332 keV for cluster detector, the peak-to-total and peak-to-background ratios have been calculated for several composite detectors.

Development of a first-principles code based on the screened KKR method for large super-cells

International Nuclear Information System (INIS)

Doi, S; Ogura, M; Akai, H

2013-01-01

The procedures of performing first-principles electronic structure calculation using the Korringa-Kohn-Rostoker (KKR) and the screened KKR methods are reviewed with an emphasis put on their numerical efficiency. It is shown that an iterative matrix inversion combined with a suitable preconditioning greatly improves the computational time of screened KKR method. The method is well parallelized and also has an O(N) scaling property

First principles study of the optical contrast in phase change materials

Energy Technology Data Exchange (ETDEWEB)

Caravati, S; Parrinello, M [Department of Chemistry and Applied Biosciences, ETH Zurich, USI Campus, Via Giuseppe Buffi 13, 6900 Lugano (Switzerland); Bernasconi, M, E-mail: marco.bernasconi@mater.unimib.i [Dipartimento di Scienza dei Materiali, Universita di Milano-Bicocca, Via R Cozzi 53, I-20125, Milano (Italy)

2010-08-11

We study from first principles the optical properties of the phase change materials Ge{sub 2}Sb{sub 2}Te{sub 5} (GST), GeTe and Sb{sub 2}Te{sub 3} in the crystalline phase and in realistic models of the amorphous phase generated by quenching from the melt in ab initio molecular dynamics simulations. The calculations reproduce the strong optical contrast between the crystalline and amorphous phases measured experimentally and exploited in optical data storage. It is demonstrated that the optical contrast is due to a change in the optical matrix elements across the phase change in all the compounds. It is concluded that the reduction of the optical matrix elements in the amorphous phases is due to angular disorder in p-bonding which dominates the amorphous network in agreement with previous proposals (Huang and Robertson 2010 Phys. Rev. B 81 081204) based on calculations on crystalline models.

Elastic and thermal properties of silicon compounds from first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Hou, Haijun; Zhu, H.J. [Yancheng Institute of Technology (China). School of Materials Engineering; Cheng, W.H. [Yancheng Institute of Technology (China). Dept. of Light Chemical Engineering; Xie, L.H. [Sichuan Normal Univ., Chengdu (China). Inst. of Solid State Physics and School of Physics and Electronic Engineering

2016-11-01

The structural and elastic properties of V-Si (V{sub 3}Si, VSi{sub 2}, V{sub 5}Si{sub 3}, and V{sub 6}Si{sub 5}) compounds are studied by using first-principles method. The calculated equilibrium lattice parameters and formation enthalpy are in good agreement with the available experimental data and other theoretical results. The calculated results indicate that the V-Si compounds are mechanically stable. Elastic properties including bulk modulus, shear modulus, Young's modulus, and Poisson's ratio are also obtained. The elastic anisotropies of V-Si compounds are investigated via the three-dimensional (3D) figures of directional dependences of reciprocals of Young's modulus. Finally, based on the quasi-harmonic Debye model, the internal energy, Helmholtz free energy, entropy, heat capacity, thermal expansion coefficient, Grueneisen parameter, and Debye temperature of V-Si compounds have been calculated.

A first-principles study of sodium adsorption and diffusion on phosphorene.

Science.gov (United States)

Liu, Xiao; Wen, Yanwei; Chen, Zhengzheng; Shan, Bin; Chen, Rong

2015-07-07

The structural, electronic, electrochemical as well as diffusion properties of Na doped phosphorene have been investigated based on first-principles calculations. The strong binding energy between Na and phosphorene indicates that Na could be stabilized on the surface of phosphorene without clustering. By comparing the adsorption of Na atoms on one side and on both sides of phosphorene, it has been found that Na-Na exhibits strong repulsion at the Na-Na distance of less than 4.35 Å. The Na intercalation capacity is estimated to be 324 mA h g(-1) and the calculated discharge curve indicates quite a low Na(+)/Na voltage of phosphorene. Moreover, the diffusion energy barrier of Na atoms on the phosphorene surface at both low and high Na concentrations is as low as 40-63 meV, which implies the high mobility of Na during the charge/discharge process.

Wobbled electronic properties of lithium clusters: Deterministic approach through first principles

Science.gov (United States)

Kushwaha, Anoop Kumar; Nayak, Saroj Kumar

2018-03-01

The innate tendency to form dendritic growth promoted through cluster formation leading to the failure of a Li-ion battery system have drawn significant attention of the researchers towards the effective destabilization of the cluster growth through selective implementation of electrolytic media such as acetonitrile (MeCN). In the present work, using first principles density functional theory and continuum dielectric model, we have investigated the origin of oscillatory nature of binding energy per atom of Lin (n ≤ 8) under the influence of MeCN. In the gas phase, we found that static mean polarizability is strongly correlated with binding energy and shows oscillatory nature with cluster size due to the open shell of Lin cluster. However, in acetonitrile medium, the binding energy has been correlated with electrostatic Lin -MeCN interaction and it has been found that both of them possess wobbled behavior characterized by the cluster size.

Common principles and multiculturalism.

Science.gov (United States)

Zahedi, Farzaneh; Larijani, Bagher

2009-01-01

Judgment on rightness and wrongness of beliefs and behaviors is a main issue in bioethics. Over centuries, big philosophers and ethicists have been discussing the suitable tools to determine which act is morally sound and which one is not. Emerging the contemporary bioethics in the West has resulted in a misconception that absolute westernized principles would be appropriate tools for ethical decision making in different cultures. We will discuss this issue by introducing a clinical case. Considering various cultural beliefs around the world, though it is not logical to consider all of them ethically acceptable, we can gather on some general fundamental principles instead of going to the extremes of relativism and absolutism. Islamic teachings, according to the presented evidence in this paper, fall in with this idea.

Common Principles and Multiculturalism

Science.gov (United States)

Zahedi, Farzaneh; Larijani, Bagher

2009-01-01

Judgment on rightness and wrongness of beliefs and behaviors is a main issue in bioethics. Over centuries, big philosophers and ethicists have been discussing the suitable tools to determine which act is morally sound and which one is not. Emerging the contemporary bioethics in the West has resulted in a misconception that absolute westernized principles would be appropriate tools for ethical decision making in different cultures. We will discuss this issue by introducing a clinical case. Considering various cultural beliefs around the world, though it is not logical to consider all of them ethically acceptable, we can gather on some general fundamental principles instead of going to the extremes of relativism and absolutism. Islamic teachings, according to the presented evidence in this paper, fall in with this idea. PMID:23908720

First-principles calculations on thermodynamic properties of BaTiO3 rhombohedral phase.

Science.gov (United States)

Bandura, Andrei V; Evarestov, Robert A

2012-07-05

The calculations based on the linear combination of atomic orbitals have been performed for the low-temperature phase of BaTiO(3) crystal. Structural and electronic properties, as well as phonon frequencies were obtained using hybrid PBE0 exchange-correlation functional. The calculated frequencies and total energies at different volumes have been used to determine the equation of state and thermal contribution to the Helmholtz free energy within the quasiharmonic approximation. For the first time, the bulk modulus, volume thermal expansion coefficient, heat capacity, and Grüneisen parameters in BaTiO(3) rhombohedral phase have been estimated at zero pressure and temperatures form 0 to 200 K, based on the results of first-principles calculations. Empirical equation has been proposed to reproduce the temperature dependence of the calculated quantities. The agreement between the theoretical and experimental thermodynamic properties was found to be satisfactory. Copyright © 2012 Wiley Periodicals, Inc.

Vibrational and mechanical properties of single layer MXene structures: a first-principles investigation

Science.gov (United States)

Yorulmaz, Uğur; Özden, Ayberk; Perkgöz, Nihan K.; Ay, Feridun; Sevik, Cem

2016-08-01

MXenes, carbides, nitrides and carbonitrides of early transition metals are the new members of two dimensional materials family given with a formula of {{{M}}}n+1 X n . Recent advances in chemical exfoliation and CVD growth of these crystals together with their promising performance in electrochemical energy storage systems have triggered the interest in these two dimensional structures. In this work, we employ first principles calculations for n = 1 structures of Sc, Ti, Zr, Mo and Hf pristine MXenes and their fully surface terminated forms with F and O. We systematically investigated the dynamical and mechanical stability of both pristine and fully terminated MXene structures to determine the possible MXene candidates for experimental realization. In conjunction with an extensive stability analysis, we report Raman and infrared active mode frequencies for the first time, providing indispensable information for the experimental elaboration of MXene field. After determining dynamically stable MXenes, we provide their phonon dispersion relations, electronic and mechanical properties.

First-principles study on electronic structures and magnetic properties of Eu-doped phosphorene

Science.gov (United States)

Luan, Zhaohui; Zhao, Lei; Chang, Hao; Sun, Dan; Tan, Changlong; Huang, Yuewu

2017-11-01

The structural, electronic and magnetic properties of Eu-doped phosphorene with different doping concentrations were investigated by first-principles calculations for the first time. The calculations show that Eu-doped phosphorene systems are stable and have the large magnetic moments of more than 6 μB by 2.7, 6.25 and 12.5 at.% doping concentrations. The major contribution to the magnetic moment stems from the 4f states of Eu-doped atom. Meanwhile, Eu-doped atom introduces the impurity bands which can be changed by different doping concentrations. In order to determine the magnetic interaction, the different configurations for two Eu atoms doping in 3 × 3 × 1 phosphorene supercell were studied, which reveals that all of the configurations tend to form ferromagnetic. These results can provide references for inducing large magnetism of two-dimensional phosphorene, which are valuable for their applications in spintronic devices and novel semiconductor materials.

High-Performance First-Principles Molecular Dynamics for Predictive Theory and Modeling

Energy Technology Data Exchange (ETDEWEB)

Gygi, Francois [Univ. of California, Davis, CA (United States). Dept. of Computer Science; Galli, Giulia [Univ. of Chicago, IL (United States); Schwegler, Eric [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

2017-12-03

This project focused on developing high-performance software tools for First-Principles Molecular Dynamics (FPMD) simulations, and applying them in investigations of materials relevant to energy conversion processes. FPMD is an atomistic simulation method that combines a quantum-mechanical description of electronic structure with the statistical description provided by molecular dynamics (MD) simulations. This reliance on fundamental principles allows FPMD simulations to provide a consistent description of structural, dynamical and electronic properties of a material. This is particularly useful in systems for which reliable empirical models are lacking. FPMD simulations are increasingly used as a predictive tool for applications such as batteries, solar energy conversion, light-emitting devices, electro-chemical energy conversion devices and other materials. During the course of the project, several new features were developed and added to the open-source Qbox FPMD code. The code was further optimized for scalable operation of large-scale, Leadership-Class DOE computers. When combined with Many-Body Perturbation Theory (MBPT) calculations, this infrastructure was used to investigate structural and electronic properties of liquid water, ice, aqueous solutions, nanoparticles and solid-liquid interfaces. Computing both ionic trajectories and electronic structure in a consistent manner enabled the simulation of several spectroscopic properties, such as Raman spectra, infrared spectra, and sum-frequency generation spectra. The accuracy of the approximations used allowed for direct comparisons of results with experimental data such as optical spectra, X-ray and neutron diffraction spectra. The software infrastructure developed in this project, as applied to various investigations of solids, liquids and interfaces, demonstrates that FPMD simulations can provide a detailed, atomic-scale picture of structural, vibrational and electronic properties of complex systems

First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material

Directory of Open Access Journals (Sweden)

Donato Belmonte

2017-09-01

Full Text Available Ab initio thermodynamic properties, equation of state and phase stability of periclase (MgO, B1-type structure have been investigated in a broad P–T range (0–160 GPa; 0–3000 K in order to set a model reference system for phase equilibria simulations under deep Earth conditions. Phonon dispersion calculations performed on large supercells using the finite displacement method and in the framework of quasi-harmonic approximation highlight the performance of the Becke three-parameter Lee-Yang-Parr (B3LYP hybrid density functional in predicting accurate thermodynamic functions (heat capacity, entropy, thermal expansivity, isothermal bulk modulus and phase reaction boundaries at high pressure and temperature. A first principles Mie–Grüneisen equation of state based on lattice vibrations directly provides a physically-consistent description of thermal pressure and P–V–T relations without any need to rely on empirical parameters or other phenomenological formalisms that could give spurious anomalies or uncontrolled extrapolations at HP–HT. The post-spinel phase transformation, Mg2SiO4 (ringwoodite = MgO (periclase + MgSiO3 (bridgmanite, is taken as a computational example to illustrate how first principles theory combined with the use of hybrid functionals is able to provide sound results on the Clapeyron slope, density change and P–T location of equilibrium mineral reactions relevant to mantle dynamics.

Microstructure investigation and first-principle analysis of die-cast AZ91 alloy with calcium addition

International Nuclear Information System (INIS)

Lin, L.; Wang, F.; Yang, L.; Chen, L.J.; Liu, Z.; Wang, Y.M.

2011-01-01

Highlights: → Die-cast AZ91 with Ca addition was investigated experimentally and theoretically. → Precipitation sequence was confirmed with increasing Ca addition. → Phase stability difference was verified by first-principle calculation. → Valence configurations were associated with alloying effects of Al, Mg and Ca. - Abstract: In order to get improved mechanical properties of die-cast AZ91 alloy under elevated temperatures, Ca element was added as a cost-effective alloying constituent. It appeared that minor Ca addition less than 0.5 wt% would result in no apparent change in microstructure, but the tensile strength at elevated temperatures was improved considerably. When increasing Ca addition to more than 1.0 wt%, Al 2 Ca phase will precipitate during solidification, no Mg 2 Ca phase was discovered. Homogeneous microstructure and high temperature stability in tensile strength of die-cast AZ91 alloy with Ca addition was mainly attributed to the precipitation of Al 2 Ca phase, which considerably refined the bulky β-Mg 17 Al 12 phase distributed originally at the grain boundaries of die-cast AZ91 alloy with no Ca addition. The priority of Al 2 Ca phase compared to Mg 2 Ca phase in precipitation sequence was verified by first-principle calculation of their cohesive energy and formation enthalpy, and can also be associated with more bounding electrons between Al and Ca atoms.

Electro-oxidation of water on hematite: Effects of surface termination and oxygen vacancies investigated by first-principles

DEFF Research Database (Denmark)

Hellman, Anders; Iandolo, Beniamino; Wickman, Bjorn

2015-01-01

The oxygen evolution reaction on hydroxyl- and oxygen-terminated hematite was investigated using first-principle calculations within a theoretical electrochemical framework. Both pristine hematite and hematite containing oxygen vacancies were considered. The onset potential was determined to be 1...... on hematite occurs on the oxygen-terminated hematite, containing oxygen vacancies. (C) 2015 Elsevier B.V. All rights reserved....

Acceptability of the Conceptions of Higher Education Quality to First Year Students of the Study Field of Pedagogy

Science.gov (United States)

Žibeniene, Gintaute; Savickiene, Izabela

2014-01-01

The article presents which conceptions of higher education quality are most acceptable to first-year students of the study field of pedagogy. It is significant to analyse students' opinions as more than 10 years ago the EU member states agreed that higher education institutions bear responsibility for the quality of higher education. Being members…

The distribution trends and site preferences of alloying elements in precipitates within a Zr alloy: A combined first-principles and experimental study

Energy Technology Data Exchange (ETDEWEB)

Luan, B.F., E-mail: bfluan@cqu.edu.cn [College of Materials Science and Engineering, Chongqing University, Chongqing 400044 (China); Wang, J.M.; Qiu, R.S.; Tao, B.R.; He, W.J. [College of Materials Science and Engineering, Chongqing University, Chongqing 400044 (China); Zhang, X.Y.; Liu, R.P. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Liu, Q., E-mail: qingliu@cqu.edu.cn [College of Materials Science and Engineering, Chongqing University, Chongqing 400044 (China)

2016-09-05

Energy dispersive X-ray spectroscopy in scanning transmission electron microscope (STEM-EDS) technique and first-principles calculation are jointly utilized to investigate the distribution trends and site preferences of alloying elements in the precipitates within Zr-1.0Cr-0.4Fe-0.4Mo-0.4Bi alloy. Based on selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS) results, the precipitates within the studied alloy are confirmed to be ZrCr{sub 2}-based Laves phase with FCC (C15) type structure. The STEM-EDS elemental mapping is acquired to clarify the distribution trends of alloying elements in precipitates, i.e. Fe>Mo>Bi. To better verify this distribution behavior, substitutional formation energies and equilibrium concentrations of ternary alloying elements in ZrCr{sub 2} Laves phase are calculated by first-principles. The calculated results show a good consistence with the STEM-EDS results. In addition, the site preferences of ternary alloying elements in ZrCr{sub 2} Laves phase are predicted by the calculation of transfer energies. Finally, the reasons accounting for different distribution trends and site preferences of alloying elements in ZrCr{sub 2} Laves phase are discussed in terms of density of states, which attributed to the pseudogap effect and hybridizations between atoms. - Highlights: • Clarified the distribution trends of Fe>Mo>Bi in precipitates by STEM-EDS. • Verified the experimental results by first-principles calculation. • Predicted the site preferences of alloying elements by first-principles calculation. • Hybridization and pseudogap lead to the strong distribution and site preferences.

First-principles calculation for the effect of hydrogen atoms on the mobility of a screw dislocation in BCC iron

International Nuclear Information System (INIS)

Itakura, Mitsuhiro; Kaburaki, Hideo; Yamaguchi, Masatake; Endo, Tatsuro; Higuchi, Kenji; Ogata, Shigenobu; Kimizuka, Hajime

2012-01-01

Effect of hydrogen atoms on the mobility of a screw dislocation in BCC iron has been evaluated using the first-principles calculation. The stable position of a hydrogen atom is found to be near the screw dislocation core and inside the core respectively when the dislocation is at the easy-core or hard-core configuration in BCC iron. The intrinsically unstable hard-core configuration of the screw dislocation is stabilized when a hydrogen atom is trapped inside the core. On the basis of this first-principles result, an elastic string model of a dislocation is developed to predict the kink motion in the presence of a hydrogen atom. It is found that a double-kink formation is facilitated when a hydrogen atom is located near a dislocation line, however, a kink motion is retarded when a hydrogen atom is behind the kink. (author)

Pt atoms stabilized on hexagonal boron nitride as efficient single-atom catalysts for CO oxidation: A first-principles investigation

KAUST Repository

Liu, Xin; Duan, Ting; Meng, Changgong; Han, Yu

2015-01-01

Taking CO oxidation as a probe, we investigated the electronic structure and reactivity of Pt atoms stabilized by vacancy defects on hexagonal boron nitride (h-BN) by first-principles-based calculations. As a joint effect of the high reactivity

First-principles investigations of the physical properties of binary uranium silicide alloys

International Nuclear Information System (INIS)

Yang, Jin; Long, Jianping; Yang, Lijun; Li, Dongmei

2013-01-01

Graphical abstract: Total density of states for USi 2 . Display Omitted -- Abstract: The structural, elastic properties and the Debye temperature of binary Uranium Silicide (U-Si) alloys are investigated by using the first-principles plane-wave pseudopotential density function theory within the generalized gradient approximation (GGA). The ground states properties are found to agree with the available experimental data. The mechanical properties like shear modulus, Young’s modulus, Poisson’s ratio σ and ratio B/G are also calculated. Finally, The averaged sound velocity (v m ), the longitudinal sound velocity (v l ), transverse sound velocity (v t ) and the Debye temperature (θ D ) are obtained. However, the theoretical values are slightly different from few existed experiment data because the latter was obtained at room temperature while the former one at 0 K

First Principles Modeling and Interpretation of Ionization-Triggered Charge Migration in Molecules

Science.gov (United States)

Bruner, Adam; Hernandez, Sam; Mauger, Francois; Abanador, Paul; Gaarde, Mette; Schafer, Ken; Lopata, Ken

Modeling attosecond coherent charge migration in molecules is important for understanding initial steps of photochemistry and light harvesting processes. Ionization triggered hole migration can be difficult to characterize and interpret as the dynamics can be convoluted with excited states. Here, we introduce a real-time time-dependent density functional theory (RT-TDDFT) approach for modeling such dynamics from first principles. To isolate the specific hole dynamics from excited states, Fourier transform analysis and orbital occupations are used to provide a spatial hole representation in the frequency domain. These techniques are applied to hole transfer across a thiophene dimer as well as core-hole triggered valence motion in nitrosobenzene. This work was supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award No. DE-SC0012462.

First-principles study of Cu adsorption on vacancy-defected/Au-doped graphene

Science.gov (United States)

Liu, Yang; An, Libao; Gong, Liang

2018-04-01

To enhance the interaction between Cu and graphene in graphene reinforced Cu matrix composites, the first principles calculation was carried out to study the adsorption of Cu atoms on graphene. P-type doping and n-type doping were formed, respectively, on vacancy-defected and Au-doped graphene based on band structure analysis, and this was verified by subsequent investigation on density of states. A computation on charge transfer confirmed that p-type doping could promote the electron transport between Cu and graphene, while n-type doping would prevent it. In addition, adsorption energy and Mulliken population analysis revealed that both vacancy defects and Au doping could improve the stability of the Cu-graphene system. The research conducted in this paper provides useful guidance for the preparation of Cu/graphene composites.

Risk reduction and the privatization option: First principles

International Nuclear Information System (INIS)

Bjornstad, D.J.; Jones, D.W.; Russell, M.; Cummings, R.C.; Valdez, G.; Duemmer, C.L.

1997-01-01

The Department of Energy's Office of Environmental Restoration and Waste Management (EM) faces a challenging mission. To increase efficiency, EM is undertaking a number of highly innovative initiatives--two of which are of particular importance to the present study. One is the 2006 Plan, a planning and budgeting process that seeks to convert the clean-up program from a temporally and fiscally open-ended endeavor to a strictly bounded one, with firm commitments over a decade-long horizon. The second is a major overhauling of the management and contracting practices that define the relationship between the Department and the private sector, aimed at cost reduction by increasing firms' responsibilities and profit opportunities and reducing DOE's direct participation in management practices and decisions. The goal of this paper is to provide an independent perspective on how EM should create new management practices to deal with private sector partners that are motivated by financial incentives. It seeks to ground this perspective in real world concerns--the background of the clean-up effort, the very difficult technical challenges it faces, the very real threats to environment, health and safety that have now been juxtaposed with financial drivers, and the constraints imposed by government's unique business practices and public responsibilities. The approach is to raise issues through application of first principles. The paper is targeted at the EM policy officer who must implement the joint visions of the 2006 plan and privatization within the context of the tradeoff between terminal risk reduction and interim risk management

Risk reduction and the privatization option: First principles

Energy Technology Data Exchange (ETDEWEB)

Bjornstad, D.J.; Jones, D.W.; Russell, M. [Joint Inst. for Energy and Environment, Knoxville, TN (United States); Cummings, R.C.; Valdez, G. [Georgia State Univ., Atlanta, GA (United States); Duemmer, C.L. [Hull, Duemmer and Garland (United States)

1997-06-25

The Department of Energy`s Office of Environmental Restoration and Waste Management (EM) faces a challenging mission. To increase efficiency, EM is undertaking a number of highly innovative initiatives--two of which are of particular importance to the present study. One is the 2006 Plan, a planning and budgeting process that seeks to convert the clean-up program from a temporally and fiscally open-ended endeavor to a strictly bounded one, with firm commitments over a decade-long horizon. The second is a major overhauling of the management and contracting practices that define the relationship between the Department and the private sector, aimed at cost reduction by increasing firms` responsibilities and profit opportunities and reducing DOE`s direct participation in management practices and decisions. The goal of this paper is to provide an independent perspective on how EM should create new management practices to deal with private sector partners that are motivated by financial incentives. It seeks to ground this perspective in real world concerns--the background of the clean-up effort, the very difficult technical challenges it faces, the very real threats to environment, health and safety that have now been juxtaposed with financial drivers, and the constraints imposed by government`s unique business practices and public responsibilities. The approach is to raise issues through application of first principles. The paper is targeted at the EM policy officer who must implement the joint visions of the 2006 plan and privatization within the context of the tradeoff between terminal risk reduction and interim risk management.

First-principles calculation of optical absorption spectra in conjugated polymers: Role of electron-hole interaction

International Nuclear Information System (INIS)

Rohlfing, Michael; Tiago, M.L.; Louie, Steven G.

2000-01-01

Experimental and theoretical studies have shown that excitonic effects play an important role in the optical properties of conjugated polymers. The optical absorption spectrum of trans-polyacetylene, for example, can be understood as completely dominated by the formation of exciton bound states. We review a recently developed first-principles method for computing the excitonic effects and optical spectrum, with no adjustable parameters. This theory is used to study the absorption spectrum of two conjugated polymers: trans-polyacetylene and poly-phenylene-vinylene(PPV)

First-principles calculation of optical absorption spectra in conjugated polymers: Role of electron-hole interaction

Energy Technology Data Exchange (ETDEWEB)

Rohlfing, Michael; Tiago, M.L.; Louie, Steven G.

2000-03-20

Experimental and theoretical studies have shown that excitonic effects play an important role in the optical properties of conjugated polymers. The optical absorption spectrum of trans-polyacetylene, for example, can be understood as completely dominated by the formation of exciton bound states. We review a recently developed first-principles method for computing the excitonic effects and optical spectrum, with no adjustable parameters. This theory is used to study the absorption spectrum of two conjugated polymers: trans-polyacetylene and poly-phenylene-vinylene(PPV).

First principles study the stability and mechanical properties of MC (M = Ti, V, Zr, Nb, Hf and Ta) compounds

International Nuclear Information System (INIS)

Liu, YangZhen; Jiang, YeHua; Zhou, Rong; Feng, Jing

2014-01-01

Highlights: • The stability and elastic constants of carbides are studied by first principles. • The rules of modulus of MC compounds are discussed by their group. • The hardness of carbides is estimated in this paper at the first time. -- Abstract: The first principles calculations based on density functional theory (DFT) were adopted to investigate the stability, elastic constants, chemical bonding, Debye temperature and hardness of MC (M = Ti, V, Zr, Nb, Hf and Ta) compounds. The cohesive energy and formation enthalpy of these carbides indicate that they are thermodynamically stable structures. The population analysis was used to discuss the chemical bonding of these carbides. The elastic constants and moduli of these compounds were calculated. The results show that the bulk moduli of the carbides of transition metals from the fourth group (TiC, ZrC, HfC) are lower than the fifth group (VC, NbC, TaC). However, the Young’s moduli of the carbides from fourth group are higher than the fifth group. The hardness of compounds was estimated using a semi empirical hardness theory

Novel structures of oxygen adsorbed on a Zr(0001) surface predicted from first principles

Energy Technology Data Exchange (ETDEWEB)

Gao, Bo [State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012 (China); Beijing computational science research center, Beijing,100084 (China); Wang, Jianyun [State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012 (China); Lv, Jian [State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012 (China); College of Materials Science and Engineering, Jilin University, Changchun, 130012 (China); Gao, Xingyu [Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics, Beijing, 100088 (China); CAEP Software Center for High Performance Numerical Simulation, Beijing, 100088 (China); Zhao, Yafan [CAEP Software Center for High Performance Numerical Simulation, Beijing, 100088 (China); Wang, Yanchao, E-mail: wyc@calypso.cn [State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012 (China); Beijing computational science research center, Beijing,100084 (China); College of Materials Science and Engineering, Jilin University, Changchun, 130012 (China); Song, Haifeng, E-mail: song_haifeng@iapcm.ac.cn [Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics, Beijing, 100088 (China); CAEP Software Center for High Performance Numerical Simulation, Beijing, 100088 (China); Ma, Yanming [State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012 (China); Beijing computational science research center, Beijing,100084 (China)

2017-01-30

Highlights: • Two stable structures of O adsorbed on a Zr(0001) surface are predicted with SLAM. • A stable structure of O adsorbed on a Zr(0001) surface is proposed with MLAM. • The calculated work function change is agreement with experimental value. - Abstract: The structures of O atoms adsorbed on a metal surface influence the metal properties significantly. Thus, studying O chemisorption on a Zr surface is of great interest. We investigated O adsorption on a Zr(0001) surface using our newly developed structure-searching method combined with first-principles calculations. A novel structural prototype with a unique combination of surface face-centered cubic (SFCC) and surface hexagonal close-packed (SHCP) O adsorption sites was predicted using a single-layer adsorption model (SLAM) for a 0.5 and 1.0 monolayer (ML) O coverage. First-principles calculations based on the SLAM revealed that the new predicted structures are energetically favorable compared with the well-known SFCC structures for a low O coverage (0.5 and 1.0 ML). Furthermore, on basis of our predicted SFCC + SHCP structures, a new structure within multi-layer adsorption model (MLAM) was proposed to be more stable at the O coverage of 1.0 ML, in which adsorbed O atoms occupy the SFCC + SHCP sites and the substitutional octahedral sites. The calculated work functions indicate that the SFCC + SHCP configuration has the lowest work function of all known structures at an O coverage of 0.5 ML within the SLAM, which agrees with the experimental trend of work function with variation in O coverage.

SU-E-T-191: First Principle Calculation of Quantum Yield in Photodynamic Therapy

Energy Technology Data Exchange (ETDEWEB)

Abolfath, R; Guo, F; Chen, Z; Nath, R [Yale New Haven Hospital, New Haven, CT (United States)

2014-06-01

Purpose: We present a first-principle method to calculate the spin transfer efficiency in oxygen induced by any photon fields especially in MeV energy range. The optical pumping is mediated through photosensitizers, e.g., porphyrin and/or ensemble of quantum dots. Methods: Under normal conditions, oxygen molecules are in the relatively non-reactive triplet state. In the presence of certain photosensitizer compounds such as porphyrins, electromagnetic radiation of specific wavelengths can excite oxygen to highly reactive singlet state. With selective uptake of photosensitizers by certain malignant cells, photon irradiation of phosensitized tumors can lead to selective killing of cancer cells. This is the basis of photodynamic therapy (PDT). Despite several attempts, PDT has not been clinically successful except in limited superficial cancers. Many parameters such as photon energy, conjugation with quantum dots etc. can be potentially combined with PDT in order to extend the role of PDT in cancer management. The key quantity for this optimization is the spin transfer efficiency in oxygen by any photon field. The first principle calculation model presented here, is an attempt to fill this need. We employ stochastic density matrix description of the quantum jumps and the rate equation methods in quantum optics based on Markov/Poisson processes and calculate time evolution of the population of the optically pumped singlet oxygen. Results: The results demonstrate the feasibility of our model in showing the dependence of the optical yield in generating spin-singlet oxygen on the experimental conditions. The adjustable variables can be tuned to maximize the population of the singlet oxygen hence the efficacy of the photodynamic therapy. Conclusion: The present model can be employed to fit and analyze the experimental data and possibly to assist researchers in optimizing the experimental conditions in photodynamic therapy.

First-principles electronic functionalization of silicene and germanene by adatom chemisorption

Energy Technology Data Exchange (ETDEWEB)

Broek, B. van den; Houssa, M.; Scalise, E. [Semiconductor Physics Laboratory, Department of Physics and Astronomy, University of Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium); Pourtois, G. [IMEC, 75 Kapeldreef, B-3001 Leuven (Belgium); Department of Chemistry, Plasmant Research Group, University of Antwerp, B-2610 Wilrijk-Antwerp (Belgium); Afanas‘ev, V.V.; Stesmans, A. [Semiconductor Physics Laboratory, Department of Physics and Astronomy, University of Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium)

2014-02-01

This study presents first-principles results on the electronic functionalization of silicene and germanene monolayers by means of chemisorption of adatom species H, Li, F, Sc, Ti, V. Three general adatom-monolayer configurations are considered, each having its distinct effect on the electronic structure, yielding metallic or semiconducting dispersions depending on the adatom species and configuration. The induced bandgap is a (in)direct Γ gap ranging from 0.2 to 2.3 eV for both silicene and germanene. In general the alternating configuration was found to be the most energetically stable. The boatlike and chairlike conformers are degenerate with the former having anisotropic effective carrier masses. The top configuration leads to the planar monolayer and predominately to a gapped dispersion. The hollow configuration with V adatoms retains the Dirac cone, but with strong orbital planar hybridization at the Fermi level. We also observe a planar surface state the Fermi level for the latter systems.

A method of orbital analysis for large-scale first-principles simulations

Energy Technology Data Exchange (ETDEWEB)

Ohwaki, Tsukuru [Advanced Materials Laboratory, Nissan Research Center, Nissan Motor Co., Ltd., 1 Natsushima-cho, Yokosuka, Kanagawa 237-8523 (Japan); Otani, Minoru [Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Ozaki, Taisuke [Research Center for Simulation Science (RCSS), Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292 (Japan)

2014-06-28

An efficient method of calculating the natural bond orbitals (NBOs) based on a truncation of the entire density matrix of a whole system is presented for large-scale density functional theory calculations. The method recovers an orbital picture for O(N) electronic structure methods which directly evaluate the density matrix without using Kohn-Sham orbitals, thus enabling quantitative analysis of chemical reactions in large-scale systems in the language of localized Lewis-type chemical bonds. With the density matrix calculated by either an exact diagonalization or O(N) method, the computational cost is O(1) for the calculation of NBOs associated with a local region where a chemical reaction takes place. As an illustration of the method, we demonstrate how an electronic structure in a local region of interest can be analyzed by NBOs in a large-scale first-principles molecular dynamics simulation for a liquid electrolyte bulk model (propylene carbonate + LiBF{sub 4})

A method of orbital analysis for large-scale first-principles simulations

International Nuclear Information System (INIS)

Ohwaki, Tsukuru; Otani, Minoru; Ozaki, Taisuke

2014-01-01

An efficient method of calculating the natural bond orbitals (NBOs) based on a truncation of the entire density matrix of a whole system is presented for large-scale density functional theory calculations. The method recovers an orbital picture for O(N) electronic structure methods which directly evaluate the density matrix without using Kohn-Sham orbitals, thus enabling quantitative analysis of chemical reactions in large-scale systems in the language of localized Lewis-type chemical bonds. With the density matrix calculated by either an exact diagonalization or O(N) method, the computational cost is O(1) for the calculation of NBOs associated with a local region where a chemical reaction takes place. As an illustration of the method, we demonstrate how an electronic structure in a local region of interest can be analyzed by NBOs in a large-scale first-principles molecular dynamics simulation for a liquid electrolyte bulk model (propylene carbonate + LiBF 4 )

On possibility of superconductivity in SnSb: A first principle study

Energy Technology Data Exchange (ETDEWEB)

Dabhi, Shweta D. [Department of Physics, M. K. Bhavnagar University, Bhavnagar 364001 (India); Shrivastava, Deepika [Department of Physics, Barkatullah University, Bhopal 462026 (India); Jha, Prafulla K., E-mail: prafullaj@yahoo.com [Department of Physics, Faculty of Science, The M. S. University of Baroda, Vadodara 390002 (India); Sanyal, Sankar P. [Department of Physics, Barkatullah University, Bhopal 462026 (India)

2016-09-15

Highlights: • Superconducting property of SnSb is predicted by ab-initio calculations. • Electronic properties of SnSb in RS phase shows metallic behaviour similar to SnAs. • Phonon dispersion confirms the dynamical stability of SnSb in RS phase. • Superconducting transition temperature is 3.1 K, slightly lower than that of SnAs. • Calculated thermodynamic properties are also reported. - Abstract: The electronic, phonon structure and superconducting properties of tin antimonide (SnSb) in rock-salt (RS) structure are calculated using first-principles density functional theory. The electronic band structure and density of states show metallic behavior. The phonon frequencies are positive throughout the Brillouin zone in rock-salt structure indicating its stability in that phase. Superconductivity of SnSb in RS phase is discussed in detail by calculating phonon linewidths, Eliashberg spectral function, electron-phonon coupling constant and superconducting transition temperature. SnSb is found to have a slightly lower T{sub C} (3.1 K), as compared to SnAs.

Introduction to First-Principles Electronic Structure Methods: Application to Actinide Materials

International Nuclear Information System (INIS)

Klepeis, J E

2006-01-01

This paper provides an introduction for non-experts to first-principles electronic structure methods that are widely used in condensed-matter physics. Particular emphasis is placed on giving the appropriate background information needed to better appreciate the use of these methods to study actinide and other materials. Specifically, I describe the underlying theory sufficiently to enable an understanding of the relative strengths and weaknesses of the methods. I also explain the meaning of commonly used terminology, including density functional theory (DFT), local density approximation (LDA), and generalized gradient approximation (GGA), as well as linear muffin-tin orbital (LMTO), linear augmented plane wave (LAPW), and pseudopotential methods. I also briefly discuss methodologies that extend the basic theory to address specific limitations. Finally, I describe a few illustrative applications, including quantum molecular dynamics (QMD) simulations and studies of surfaces, impurities, and defects. I conclude by addressing the current controversy regarding magnetic calculations for actinide materials

From Acceptance to Rejection: Food Contamination in the Classroom.

Science.gov (United States)

Rajecki, D. W.

1989-01-01

Describes a classroom exercise to explain design and measurement principles in methodology and statistics courses. This demonstration which involves measurement of a shift from food acceptance to food rejection produces meaningful data sets. The realism of the exercise gives students a view of problems that emerge in research. (KO)

Canadian nuclear power principles for beyond design basis events - supporting rationale

International Nuclear Information System (INIS)

Elliott, M.; Newman, G.; Bhaloo, A.

2014-01-01

The development of the following principles and their rationale began during a special Chief Nuclear Engineers forum held on March 25th, 2013 in Toronto. These principles are intended to provide guidance to the Canadian Nuclear Power Industry in developing responses to the lessons learned from the Fukushima event of March 2011. These principles were accepted and signed off by the Chief Nuclear Officers of each of the three utilities in August 2013 and were presented to the CNSC at a public hearing on August 21, 2013. This document provides the underlying rationale for the principles. (author)

Canadian nuclear power principles for beyond design basis events - supporting rationale

Energy Technology Data Exchange (ETDEWEB)

Elliott, M. [OPG Nuclear, Ontario (Canada); Newman, G. [Bruce Power, Ontario (Canada); Bhaloo, A. [New Brunswick Power, New Brunswick (Canada)

2014-09-15

The development of the following principles and their rationale began during a special Chief Nuclear Engineers forum held on March 25th, 2013 in Toronto. These principles are intended to provide guidance to the Canadian Nuclear Power Industry in developing responses to the lessons learned from the Fukushima event of March 2011. These principles were accepted and signed off by the Chief Nuclear Officers of each of the three utilities in August 2013 and were presented to the CNSC at a public hearing on August 21, 2013. This document provides the underlying rationale for the principles. (author)

Canadian nuclear power principles for beyond design basis events - supporting rationale

Energy Technology Data Exchange (ETDEWEB)

Elliott, M. [Ontario Power Generation Nuclear, Pickering, ON (Canada); Newman, G. [Bruce Power, Tiverton, ON (Canada); Bhaloo, A. [New Brunswick Power, Fredericton, NB (Canada)

2014-07-01

The development of the following principles and their rationale began during a special Chief Nuclear Engineers forum held on March 25th, 2013 in Toronto. These principles are intended to provide guidance to the Canadian Nuclear Power Industry in developing responses to the lessons learned from the Fukushima event of March 2011. These principles were accepted and signed off by the Chief Nuclear Officers of each of the three utilities in August 2013 and were presented to the CNSC at a public hearing on August 21, 2013. This document provides the underlying rationale for the principles. (author)

Near-infrared radiation absorption properties of covellite (CuS using first-principles calculations

Directory of Open Access Journals (Sweden)

Lihua Xiao

2016-08-01

Full Text Available First-principles density functional theory was used to investigate the electronic structure, optical properties and the origin of the near-infrared (NIR absorption of covellite (CuS. The calculated lattice constant and optical properties are found to be in reasonable agreement with experimental and theoretical findings. The electronic structure reveals that the valence and conduction bands of covellite are determined by the Cu 3d and S 3p states. By analyzing its optical properties, we can fully understand the potential of covellite (CuS as a NIR absorbing material. Our results show that covellite (CuS exhibits NIR absorption due to its metal-like plasma oscillation in the NIR range.

Experimental and first-principles study of ferromagnetism in Mn-doped zinc stannate nanowires

KAUST Repository

Deng, Rui; Zhou, Hang; Li, Yong-Feng; Wu, Tao; Yao, Bin; Qin, Jie-Ming; Wan, Yu-Chun; Jiang, Da-Yong; Liang, Qing-Cheng; Liu, Lei

2013-01-01

Room temperature ferromagnetism was observed in Mn-doped zinc stannate (ZTO:Mn) nanowires, which were prepared by chemical vapor transport. Structural and magnetic properties and Mn chemical states of ZTO:Mn nanowires were investigated by X-ray diffraction, superconducting quantum interference device (SQUID) magnetometry and X-ray photoelectron spectroscopy. Manganese predominantly existed as Mn2+ and substituted for Zn (Mn Zn) in ZTO:Mn. This conclusion was supported by first-principles calculations. MnZn in ZTO:Mn had a lower formation energy than that of Mn substituted for Sn (MnSn). The nearest neighbor MnZn in ZTO stabilized ferromagnetic coupling. This observation supported the experimental results. © 2013 AIP Publishing LLC.

First principles and phonon calculations of ZrCo and ZrCo-H systems

International Nuclear Information System (INIS)

Chattaraj, D.; Parida, S.C.; Dash, Smruti; Majumder, C.

2012-01-01

The intermetallic ZrCo is a potential material for the storage and release of hydrogen isotopes because of its high gravimetric capacity and its low hydrogen equilibrium pressure. This intermetallic is a proposed material for the safe storage, supply and delivery of hydrogen isotope in the ITER project. To investigate the suitability of ZrCo as a getter material for the storage of hydrogen isotope it is essential to know in detail the structure-property relationships in both ZrCo and its hydride. Hence, in this study, we have investigated the structural, electronic, vibrational and thermodynamic properties of ZrCo and ZrCoH 3 using the first principles and phonon calculations

Experimental and first-principles study of ferromagnetism in Mn-doped zinc stannate nanowires

KAUST Repository

Deng, Rui

2013-07-17

Room temperature ferromagnetism was observed in Mn-doped zinc stannate (ZTO:Mn) nanowires, which were prepared by chemical vapor transport. Structural and magnetic properties and Mn chemical states of ZTO:Mn nanowires were investigated by X-ray diffraction, superconducting quantum interference device (SQUID) magnetometry and X-ray photoelectron spectroscopy. Manganese predominantly existed as Mn2+ and substituted for Zn (Mn Zn) in ZTO:Mn. This conclusion was supported by first-principles calculations. MnZn in ZTO:Mn had a lower formation energy than that of Mn substituted for Sn (MnSn). The nearest neighbor MnZn in ZTO stabilized ferromagnetic coupling. This observation supported the experimental results. © 2013 AIP Publishing LLC.

TEFI principles in action: reflections on the first year of the Global TEFI Courses

DEFF Research Database (Denmark)

Liburd, Janne J.; Gretzel, Ulrike; Lund-Durlacher, Dagmar

2011-01-01

a fraction of what it once was. A degree was a passport to a good job. Now, at best, it's a visa. It only gives you provisional residence in the job market". Concerned that few undergraduate and graduate tourism programs are preparing students to meet the challenges of the present and be instrumental......) and the implementation of the Global TEFI courses. First the context for the creation of five values-based principles (TEFI, 2009) that tourism students must imbibe upon graduation will be outlined in brief. Next, as a critical component of this initiative the INNOTOUR portal will be introduced before the conditions...

First-principles calculations of GaN:Gd nanowires: Carbon-dopants-induced room-temperature ferromagnetism

Directory of Open Access Journals (Sweden)

Ruikuan Xie

2017-11-01

Full Text Available First-principle calculations of the electronic structure and magnetic interaction of C-Gd co-doped GaN nanowires have been performed. The room-temperature ferromagnetism in GaN:Gd nanowires is observed after the substitution of N atoms by C atoms. A p-d coupling is considered as the reason of the observed ferromagnetism. The striking feature is that such coupling is effected greatly by the position where the C atoms dope in. As the C-Gd distance increases this coupling decreases and the system won’t gain enough energy to stabilize the ferromagnetism.

Phonon-limited mobility in n-type single-layer MoS2 from first principles

DEFF Research Database (Denmark)

Kaasbjerg, Kristen; Thygesen, Kristian S.; Jacobsen, Karsten W.

2012-01-01

We study the phonon-limited mobility in intrinsic n-type single-layer MoS2 for temperatures T > 100 K. The materials properties including the electron-phonon interaction are calculated from first principles and the deformation potentials and Frohlich interaction in single-layer MoS2 are established...... to recent experimental findings for the mobility in single-layer MoS2 (similar to 200 cm(2)V(-1)s(-1)), our results indicate that mobilities close to the intrinsic phonon-limited mobility can be achieved in two-dimensional materials via dielectric engineering that effectively screens static Coulomb...

The effects of the impurity distribution on the electrical and optical properties of Cr2+:ZnSe nanowires: First-principles study

Directory of Open Access Journals (Sweden)

Shenyu Dai

2018-03-01

Full Text Available The structural, electrical and mid-infrared optical properties of wurtzite structured ZnSe nanowires with different Chromium impurity distribution are investigated using first-principles calculation based on density-functional theory (DFT. The formation energies have been calculated to study the relative stabilities of different Cr doping positions. It is shown that when the Cr doping position shifted from the center to the edge, the splitting energy between 5T2 and 5E levels of Cr d-orbitals is decreased and a redshift is observed in the calculated infrared absorption spectra. A probable reason for these effects of the impurity distribution is discussed. Keywords: First-principles, Nanowires, Impurity distribution, Cr-doped ZnSe

Operations Acceptance Management

OpenAIRE

Suchá, Ivana

2010-01-01

This paper examines the process of Operations Acceptance Management, whose main task is to control Operations Acceptance Tests (OAT). In the first part the author focuses on the theoretical ground for the problem in the context of ITSM best practices framework ITIL. Benefits, process pitfalls and possibilities for automation are discussed in this part. The second part contains a case study of DHL IT Services (Prague), where a solution optimizing the overall workflow was implemented using simp...

First principles simulations

International Nuclear Information System (INIS)

Palummo, M.; Reining, L.; Ballone, P.

1993-01-01

In this paper we outline the major features of the ''ab-initio'' simulation scheme of Car and Parrinello, focusing on the physical ideas and computational details at the basis of its efficiency and success. We briefly review the main applications of the method. We discuss the limitations of the standard scheme, as well as recent developments proposed in order to extend the reach of the method. Moreover, we consider more in detail two specific subjects. First, we describe a simple improvement (Gradient Corrections) on the basic approximation of the ''ab-initio'' simulation, i.e. the Local Density Approximation. These corrections can be easily and efficiently included in the Car-Parrinello code, bringing computed structural and cohesive properties significantly closer to their experimental values. Finally, we discuss the choice of the pseudopotential, with special attention to the possibilities and limitations of the last generation of soft pseudopotentials. (orig.)

Progress towards an effective model for FeSe from high-accuracy first-principles quantum Monte Carlo

Science.gov (United States)

Busemeyer, Brian; Wagner, Lucas K.

While the origin of superconductivity in the iron-based materials is still controversial, the proximity of the superconductivity to magnetic order is suggestive that magnetism may be important. Our previous work has suggested that first-principles Diffusion Monte Carlo (FN-DMC) can capture magnetic properties of iron-based superconductors that density functional theory (DFT) misses, but which are consistent with experiment. We report on the progress of efforts to find simple effective models consistent with the FN-DMC description of the low-lying Hilbert space of the iron-based superconductor, FeSe. We utilize a procedure outlined by Changlani et al.[1], which both produces parameter values and indications of whether the model is a good description of the first-principles Hamiltonian. Using this procedure, we evaluate several models of the magnetic part of the Hilbert space found in the literature, as well as the Hubbard model, and a spin-fermion model. We discuss which interaction parameters are important for this material, and how the material-specific properties give rise to these interactions. U.S. Department of Energy, Office of Science, Office of Advanced Scientific Computing Research, Scientific Discovery through Advanced Computing (SciDAC) program under Award No. FG02-12ER46875, as well as the NSF Graduate Research Fellowship Program.

A first-principles generic methodology for representing the knowledge base of a process diagnostic expert system

International Nuclear Information System (INIS)

Reifman, J.; Briggs, L.L.; Wei, T.Y.C.

1990-01-01

In this paper we present a methodology for identifying faulty component candidates of process malfunctions through basic physical principles of conservation, functional classification of components and information from the process schematics. The basic principles of macroscopic balance of mass, momentum and energy in thermal hydraulic control volumes are applied in a novel approach to incorporate deep knowledge into the knowledge base. Additional deep knowledge is incorporated through the functional classification of process components according to their influence in disturbing the macroscopic balance equations. Information from the process schematics is applied to identify the faulty component candidates after the type of imbalance in the control volumes is matched against the functional classification of the components. Except for the information from the process schematics, this approach is completely general and independent of the process under consideration. The use of basic first-principles, which are physically correct, and the process-independent architecture of the diagnosis procedure allow for the verification and validation of the system. A prototype process diagnosis expert system is developed and a test problem is presented to identify faulty component candidates in the presence of a single failure in a hypothetical balance of plant of a liquid metal nuclear reactor plant

First principles study of lithium insertion in bulk silicon

KAUST Repository

Wan, Wenhui

2010-09-23

Si is an important anode material for the next generation of Li ion batteries. Here the energetics and dynamics of Li atoms in bulk Si have been studied at different Li concentrations on the basis of first principles calculations. It is found that Li prefers to occupy an interstitial site as a shallow donor rather than a substitutional site. The most stable position is the tetrahedral (Td) site. The diffusion of a Li atom in the Si lattice is through a Td-Hex-Td trajectory, where the Hex site is the hexagonal transition site with an energy barrier of 0.58 eV. We have also systematically studied the local structural transition of a LixSi alloy with x varying from 0 to 0.25. At low doping concentration (x = 0-0.125), Li atoms prefer to be separated from each other, resulting in a homogeneous doping distribution. Starting from x = 0.125, Li atoms tend to form clusters induced by a lattice distortion with frequent breaking and reforming of Si-Si bonds. When x ≥ 0.1875, Li atoms will break some Si-Si bonds permanently, which results in dangling bonds. These dangling bonds create negatively charged zones, which is the main driving force for Li atom clustering at high doping concentration. © 2010 IOP Publishing Ltd.

First-principles modeling of titanate/ruthenate superlattices

Science.gov (United States)

Junquera, Javier

2013-03-01

The possibility to create highly confined two-dimensional electron gases (2DEG) at oxide interfaces has generated much excitement during the last few years. The most widely studied system is the 2DEG formed at the LaO/TiO2 polar interface between LaAlO3 and SrTiO3, where the polar catastrophe at the interface has been invoked as the driving force. More recently, partial or complete delta doping of the Sr or Ti cations at a single layer of a SrTiO3 matrix has also been used to generate 2DEG. Following this recipe, we report first principles characterization of the structural and electronic properties of (SrTiO3)5/(SrRuO3)1 superlattices, where all the Ti of a given layer have been replaced by Ru. We show that the system exhibits a spin-polarized two-dimensional electron gas extremely confined to the 4 d orbitals of Ru in the SrRuO3 layer, a fact that is independent of the level of correlation included in the simulations. For hybrid functionals or LDA+U, every interface in the superlattice behaves as minority-spin half-metal ferromagnet, with a magnetic moment of μ = 2.0 μB/SrRuO3 unit. The shape of the electronic density of states, half metallicity and magnetism are explained in terms of a simplified tight-binding model, considering only the t2 g orbitals plus (i) the bi-dimensionality of the system, and (ii) strong electron correlations. Possible applications are discussed, from their eventual role in thermoelectric applications to the possible tuning of ferromagnetic properties of the 2DEG with the polarization of the dielectric. Work done in collaboration with P. García, M. Verissimo-Alves, D. I. Bilc, and Ph. Ghosez. Financial support provided by MICINN Grant FIS2009-12721-C04-02, and by the European Union Grant No. CP-FP 228989-2 ``OxIDes.'' The authors thankfully acknowledge the computer resources, technical expertise and assistance provided by the BSC/RES.

Particle image velocimetry - Principles and first results

International Nuclear Information System (INIS)

Laporta, A.; Marechal, J.P.

1997-01-01

Particle Image Velocimetry (PIV) is a measurement technique elaborated towards the end of the 1970's, but which has developed considerably in recent years. The general principle of PIV is very simple and enables access to instantaneous velocity fields. It consists in recording images of tracer-particles injected into the flow and determining the distance covered by these particles. Since we know the time lapse between successive images of the same particle, we can derive the local fluid velocity. Among the many existing image acquisition and processing methods, the image inter-correlation analysis techniques, used with a pulsed laser source, is the most effective. Since we know the influence of different parameters (number of particles, beam power, time lapse between two successive images, size of query zones, etc.) on the quality of the final result, we can optimize practical adjustment of the PIV measurement scheme. The PIV was tested on the LAVITA hydraulic mockup (simulating the operation of a tangential fan). First results are, all in all, highly satisfactory. These have enabled the rapid drafting of instantaneous mean velocity field maps (20 images acquired in less than 90 seconds, with a post-processing time of about 10 minutes). Observation of the instantaneous fields has evidenced the presence of low frequency non-stationary phenomena which are not revealed by Laser Doppler Velocimetry (LDV). Quantitative comparison between LDV and PIV, concerning average fields, showed close results, with, however, local divergences which could be relatively marked. It must nevertheless be noted that the PIV measurements performed on LAVITA have not been optimized with a view to obtaining a consistently good accuracy level. Priority in the present case was given to the scope of the field explored, with a view to observing the large non-stationary structures within a flow. The PIV measurement technique is thus operational for prompt flow characterization. However

A first-principles study of gas molecule adsorption on borophene

Directory of Open Access Journals (Sweden)

Tingting Liu

2017-12-01

Full Text Available Borophene, a new two-dimensional material, was recently synthesized. The unique anisotropic structure and excellent properties of borophene have attracted considerable research interest. This paper presents a first-principles study of the adsorption of gas molecules (CO, CO2, NH3, NO, NO2 and CH4 on borophene. The adsorption configurations, adsorption energies and electronic properties of the gas molecules absorpted on borophene are determined, and the mechanisms of the interactions between the gas molecules and borophene are evaluated. We find that CO, CO2, NH3, NO and NO2 are chemisorbed on borophene, while CH4 is physisorbed on borophene. Furthermore, our calculation also indicate that CO and CO2 are chemisorbed on borophene with moderate adsorption energy and NO, NO2 and NH3 are chemisorbed on borophene via strong covalent bonds. Moreover, CO is found as an electron donor, while CO2 an electron acceptor. The chemisorption of CO and CO2 on borophene increases the electrical conductivity, so It seems that borophene has the potential to be used in high-sensitivity CO and CO2 gas sensors.

Electric field effect of GaAs monolayer from first principles

Directory of Open Access Journals (Sweden)

Jiongyao Wu

2017-03-01

Full Text Available Using first-principle calculations, we investigate two-dimensional (2D honeycomb monolayer structures composed of group III-V binary elements. It is found that such compound like GaAs should have a buckled structure which is more stable than graphene-like flat structure. This results a polar system with out-of-plane dipoles arising from the non-planar structure. Here, we optimized GaAs monolayer structure, then calculated the electronic band structure and the change of buckling height under external electric field within density functional theory using generalized gradient approximation method. We found that the band gap would change proportionally with the electric field magnitude. When the spin-orbit coupling (SOC is considered, we revealed fine spin-splitting at different points in the reciprocal space. Furthermore, the valence and conduction bands spin-splitting energies due to SOC at the K point of buckled GaAs monolayers are found to be weakly dependent on the electric field strength. Finally electric field effects on the spin texture and second harmonic generation are discussed. The present work sheds light on the control of physical properties of GaAs monolayer by the applied electric field.

Communicating with Muslim parents: "the four principles" are not as culturally neutral as suggested

NARCIS (Netherlands)

A.E. Westra (Anna); D.L. Willems (Dick); B.J. Smit (Bert)

2009-01-01

textabstractThe "four principles approach" has been popularly accepted as a set of universal guidelines for biomedical ethics. Based on four allegedly trans-cultural principles (respect for autonomy, nonmaleficence, beneficence and justice), it is supposed to fulfil the need of a 'culturally neutral

Different dynamic behaviors of the dissociation and recombination reactions in a model calculation of polyethylene by first-principles steered molecular dynamics simulation

International Nuclear Information System (INIS)

Higuchi, Yuji; Ishikawa, Takeshi; Ozawa, Nobuki; Chazeau, Laurent; Cavaillé, Jean-Yves; Kubo, Momoji

2015-01-01

Highlights: • We study the different dynamics of dissociation and recombination processes. • Hydrogen at the chain ends collides each other in the recombination process. • Dissociation and recombination processes take different pathway. - Abstract: We investigate the different dynamics of the stress-induced dissociation and recombination reactions in a model of polyethylene by a first-principles molecular dynamics simulation at the B3LYP/6-31g(d) level. The dissociation under external forces acting on the chemical reaction site at 300 K follows the same pathway as the one calculated by the static first-principles method because it has a similar activation barrier to that of the static first-principles calculation. On the other hand, in the recombination process, thermal fluctuations causes collisions between hydrogen atoms at the chain ends. Furthermore, when external forces do not directly act on the chemical reaction site, two different dissociation processes are observed. On the other hand, recombination process is not observed due to rarely contact of the radical carbon. These results indicate that dissociation and recombination dynamics are very different, showing the importance of the dynamic calculation.

Principles for School Drug Education

Science.gov (United States)

Meyer, Lois

2004-01-01

This document presents a revised set of principles for school drug education. The principles for drug education in schools comprise an evolving framework that has proved useful over a number of decades in guiding the development of effective drug education. The first edition of "Principles for Drug Education in Schools" (Ballard et al.…

Assignment of solid-state 13C and 1H NMR spectra of paramagnetic Ni(II) acetylacetonate complexes aided by first-principles computations

DEFF Research Database (Denmark)

Rouf, Syed Awais; Jakobsen, Vibe Boel; Mareš, Jiří

2017-01-01

Recent advances in computational methodology allowed for first-principles calculations of the nuclear shielding tensor for a series of paramagnetic nickel(II) acetylacetonate complexes, [Ni(acac)2L2] with L = H2O, D2O, NH3, ND3, and PMe2Ph have provided detailed insight into the origin of the par......Recent advances in computational methodology allowed for first-principles calculations of the nuclear shielding tensor for a series of paramagnetic nickel(II) acetylacetonate complexes, [Ni(acac)2L2] with L = H2O, D2O, NH3, ND3, and PMe2Ph have provided detailed insight into the origin...

First-principles investigation of quantum transport through an endohedral N@C60 in the Coulomb blockade regime.

Science.gov (United States)

Yu, Zhizhou; Chen, Jian; Zhang, Lei; Wang, Jian

2013-12-11

We report an investigation of Coulomb blockade transport through an endohedral N@C60 weakly coupled with aluminum leads, employing the first-principles method combined with the Keldysh non-equilibrium Green's function derived from the equation of motion beyond the Hartree-Fock approximation. The differential conductance characteristics of the molecular device are calculated within the Coulomb blockade regime, which shows the Coulomb diamond as observed experimentally. When the gate voltage is less than that of the degeneracy point, there are two peaks in the differential conductance with an excited state induced by the change of the exchange interaction between the spin of C60 and the encapsulated nitrogen atom due to the transition from N@C(1-)(60) to N@C(2-)(60), while for a gate voltage larger than that of the degeneracy point, no excited state is available due to the quenching of exchange energy. As a result, there is only one Coulomb blockade peak in the differential conductance from the electron tunneling through the highest energy level below the Fermi level. Our first-principles results are in good agreement with experimental data obtained by an endohedral N@C60 molecular device.

Tailoring graphene magnetism by zigzag triangular holes: A first-principles thermodynamics study

Directory of Open Access Journals (Sweden)

Muhammad Ejaz Khan

2016-03-01

Full Text Available We discuss the thermodynamic stability and magnetic property of zigzag triangular holes (ZTHs in graphene based on the results of first-principles density functional theory calculations. We find that ZTHs with hydrogen-passivated edges in mixed sp2/sp3 configurations (z211 could be readily available at experimental thermodynamic conditions, but ZTHs with 100% sp2 hydrogen-passivation (z1 could be limitedly available at high temperature and ultra-high vacuum conditions. Graphene magnetization near the ZTHs strongly depends on the type and the size of the triangles. While metallic z1 ZTHs exhibit characteristic edge magnetism due to the same-sublattice engineering, semiconducting z211 ZTHs do show characteristic corner magnetism when the size is small <2 nm. Our findings could be useful for experimentally tailoring metal-free carbon magnetism by simply fabricating triangular holes in graphene.

First-principles study of ternary fcc solution phases from special quasirandom structures

International Nuclear Information System (INIS)

Shin Dongwon; Wang Yi; Liu Zikui; Walle, Axel van de

2007-01-01

In the present work, ternary special quasirandom structures (SQSs) for a fcc solid solution phase are generated at different compositions, x A =x B =x C =(1/3) and x A =(1/2), x B =x C =(1/4), whose correlation functions are satisfactorily close to those of a random fcc solution. The generated SQSs are used to calculate the mixing enthalpy of the fcc phase in the Ca-Sr-Yb system. It is observed that first-principles calculations of all the binary and ternary SQSs in the Ca-Sr-Yb system exhibit very small local relaxation. It is concluded that the fcc ternary SQSs can provide valuable information about the mixing behavior of the fcc ternary solid solution phase. The SQSs presented in this work can be widely used to study the behavior of ternary fcc solid solutions

Pressure induced structural phase transition of OsB 2: First-principles calculations

Science.gov (United States)

Ren, Fengzhu; Wang, Yuanxu; Lo, V. C.

2010-04-01

Orthorhombic OsB 2 was synthesized at 1000 °C and its compressibility was measured by using the high-pressure X-ray diffraction in a Diacell diamond anvil cell from ambient pressure to 32 GPa [R.W. Cumberland, et al. (2005)]. First-principles calculations were performed to study the possibility of the phase transition of OsB 2. An analysis of the calculated enthalpy shows that orthorhombic OsB 2 can transfer to the hexagonal phase at 10.8 GPa. The calculated results with the quasi-harmonic approximation indicate that this phase transition pressure is little affected by the thermal effect. The calculated phonon band structure shows that the hexagonal P 6 3/ mmc structure (high-pressure phase) is stable for OsB 2. We expect the phase transition can be further confirmed by the experimental work.

Lattice dynamics and thermal conductivity of lithium fluoride via first-principles calculations

Science.gov (United States)

Liang, Ting; Chen, Wen-Qi; Hu, Cui-E.; Chen, Xiang-Rong; Chen, Qi-Feng

2018-04-01

The lattice thermal conductivity of lithium fluoride (LiF) is accurately computed from a first-principles approach based on an iterative solution of the Boltzmann transport equation. Real-space finite-difference supercell approach is employed to generate the second- and third-order interatomic force constants. The related physical quantities of LiF are calculated by the second- and third- order potential interactions at 30 K-1000 K. The calculated lattice thermal conductivity 13.89 W/(m K) for LiF at room temperature agrees well with the experimental value, demonstrating that the parameter-free approach can furnish precise descriptions of the lattice thermal conductivity for this material. Besides, the Born effective charges, dielectric constants and phonon spectrum of LiF accord well with the existing data. The lattice thermal conductivities for the iterative solution of BTE are also presented.

First-principles study on electron transport properties of carbon-silicon mixed chains

Science.gov (United States)

Hu, Wei; Zhou, Qinghua; Liang, Yan; Liu, Wenhua; Wang, Tao; Wan, Haiqing

2018-03-01

In this paper, the transport properties of carbon-silicon mixed chains are studied by using the first-principles. We studied five atomic chain models. In these studies, we found that the equilibrium conductances of atomic chains appear to oscillate, the maximum conductance and the minimum conductance are more than twice the difference. Their I-V curves are linear and show the behavior of metal resistance, M5 system and M2 system current ratio is the largest in 0.9 V, which is 3.3, showing a good molecular switch behavior. In the case of bias, while the bias voltage increases, the transmission peaks move from the Fermi level. The resonance transmission peak height is reduced near the Fermi level. In the higher energy range, a large resonance transmission peak reappears, there is still no energy cut-off range.

Detection of nucleic acids by graphene-based devices: A first-principles study

Energy Technology Data Exchange (ETDEWEB)

Zhang, Hua [School of Physics and Electronics, Central South University, Changsha 410083 (China); School of Physics and Electronic Science, Changsha University of Science and Technology, Changsha 410114 (China); Xu, Hui, E-mail: xuhui@csu.edu.cn, E-mail: ouyangfp06@tsinghua.org.cn; Ni, Xiang; Lin Peng, Sheng; Liu, Qi; Ping OuYang, Fang, E-mail: xuhui@csu.edu.cn, E-mail: ouyangfp06@tsinghua.org.cn [School of Physics and Electronics, Central South University, Changsha 410083 (China)

2014-04-07

Based on first-principles quantum transport calculations, we design a graphene-based biosensor device, which is composed of graphene nanoribbons electrodes and a biomolecule. It is found that when different nucleobases or poly nucleobase chains are located in the nanogap, the device presents completely different transport properties, showing different current informations. And the change of currents from 2 to 5 orders of magnitude for four different nucleobases suggests a great ability of discrimination by utilizing such a device. The physical mechanism of this phenomenon originates from their different chemical composition and structure. Moreover, we also explore the coupling effect of several neighboring bases and the size effect of the nanogap on transport properties. Our results show the possibility of rapid sequencing DNA by measuring such a transverse-current of the device, and provide a new idea for sequencing DNA.

Promising half-metallicity in ductile NbF3: a first-principles prediction.

Science.gov (United States)

Yang, Bo; Wang, Junru; Liu, Xiaobiao; Zhao, Mingwen

2018-02-14

Materials with half-metallicity are long desired in spintronics. Using first-principles calculations, we predicted that the already-synthesized NbF 3 crystal is a promising half-metal with a large exchange splitting and stable ferromagnetism. The mechanical stability, ductility and softness of the NbF 3 crystal were confirmed by its elastic constants and moduli. The Curie temperature (T C = 120 K) estimated from the Monte Carlo simulations based on the 3D Ising model is above the liquid nitrogen temperature (78 K). The ferromagnetism and half-metallicity can be preserved on the surfaces of NbF 3 . The NbOF 2 formed by substituting F with O atoms, however, has an antiferromagnetic ground state and a normal metallic band structure. This work opens an avenue for half-metallic materials and may find applications in spintronic devices.

Thermal conductivities of phosphorene allotropes from first-principles calculations: a comparative study.

Science.gov (United States)

Zhang, J; Liu, H J; Cheng, L; Wei, J; Liang, J H; Fan, D D; Jiang, P H; Shi, J

2017-07-04

Phosphorene has attracted tremendous interest recently due to its intriguing electronic properties. However, the thermal transport properties of phosphorene, especially for its allotropes, are still not well-understood. In this work, we calculate the thermal conductivities of five phosphorene allotropes (α-, β-, γ-, δ- and ζ-phase) by using phonon Boltzmann transport theory combined with first-principles calculations. It is found that the α-phosphorene exhibits considerable anisotropic thermal transport, while it is less obvious in the other four phosphorene allotropes. The highest thermal conductivity is found in the β-phosphorene, followed by the δ-, γ- and ζ-phase. The much lower thermal conductivity of the ζ-phase can be attributed to its relatively complex atomic configuration. It is expected that the rich thermal transport properties of phosphorene allotropes can have potential applications in the thermoelectrics and thermal management.

A theoretical study of blue phosphorene nanoribbons based on first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Xie, Jiafeng; Si, M. S., E-mail: sims@lzu.edu.cn; Yang, D. Z.; Zhang, Z. Y.; Xue, D. S. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China)

2014-08-21

Based on first-principles calculations, we present a quantum confinement mechanism for the band gaps of blue phosphorene nanoribbons (BPNRs) as a function of their widths. The BPNRs considered have either armchair or zigzag shaped edges on both sides with hydrogen saturation. Both the two types of nanoribbons are shown to be indirect semiconductors. An enhanced energy gap of around 1 eV can be realized when the ribbon's width decreases to ∼10 Å. The underlying physics is ascribed to the quantum confinement effect. More importantly, the parameters to describe quantum confinement are obtained by fitting the calculated band gaps with respect to their widths. The results show that the quantum confinement in armchair nanoribbons is stronger than that in zigzag ones. This study provides an efficient approach to tune the band gap in BPNRs.

A Variation on Uncertainty Principle and Logarithmic Uncertainty Principle for Continuous Quaternion Wavelet Transforms

Directory of Open Access Journals (Sweden)

Mawardi Bahri

2017-01-01

Full Text Available The continuous quaternion wavelet transform (CQWT is a generalization of the classical continuous wavelet transform within the context of quaternion algebra. First of all, we show that the directional quaternion Fourier transform (QFT uncertainty principle can be obtained using the component-wise QFT uncertainty principle. Based on this method, the directional QFT uncertainty principle using representation of polar coordinate form is easily derived. We derive a variation on uncertainty principle related to the QFT. We state that the CQWT of a quaternion function can be written in terms of the QFT and obtain a variation on uncertainty principle related to the CQWT. Finally, we apply the extended uncertainty principles and properties of the CQWT to establish logarithmic uncertainty principles related to generalized transform.

Adherence to Principles of Medical Ethics Among Physicians in Mazandaran Province, Iran.

Science.gov (United States)

Ghaderi, Ahmad; Malek, Farhad; Mohammadi, Mohammad; Rostami Maskopaii, Somayeh; Hamta, Amir; Madani, Seyyed Abdollah

2018-01-01

Considering that medical ethics is an applied subject providing systematic solutions to help physicians with moral issues, this research aimed to evaluate adherence to the principles of medical ethics among physicians on the basis of attitude of physicians of Mazandaran province. This cross-sectional study was conducted in Mazandaran province, Iran during 2015. A researcher-made questionnaire was used for data collection. The questionnaire was first completed by 40 physicians and its reliability was confirmed by obtaining a Cronbach's alpha coefficient equal to 0.818. Its validity was confirmed by medical ethics experts. Therefore, the questionnaire was reliable and valid. Analytical and descriptive analysis were performed. According to our findings, there is a significant correlation between some of variables of medical ethics principles. The results show that adherence to indicators of beneficence, non-maleficence and justice has been almost good; however, physicians' ethical behaviors which pertain towards the principle of autonomy have not been acceptable. There was not any significant difference in adherence to the principles of autonomy, beneficence and non-maleficence, and justice on the basis of sex, residency, education and occupation. According to the present study, more training is required to improve physicians' adherence to the principles of medical ethics . 2018 The Author(s). This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Communicating with Muslim parents: "the four principles" are not as culturally neutral as suggested

NARCIS (Netherlands)

Westra, A.E.; Willems, D.L.; Smit, B.J.

2009-01-01

The "four principles approach" has been popularly accepted as a set of universal guidelines for biomedical ethics. Based on four allegedly trans-cultural principles (respect for autonomy, nonmaleficence, beneficence and justice), it is supposed to fulfil the need of a 'culturally neutral approach to

First principle study of structural, electronic and magnetic properties of zigzag boron nitride nanoribbon: Role of vacancies

Energy Technology Data Exchange (ETDEWEB)

Kumar, Arun [Department of Physics, Govt. College Banjar, Kullu, Himanchal Pradesh, 175123 India (India); Bahadur, Amar, E-mail: abr.phys@gmail.com [Department of Physics, Kamla Nehru Institute of Physical and Social Sciences, Sultanpur, Uttar Pradesh, 228118 India (India); Mishra, Madhukar [Department of Physics, Birla Institute of Technology and Science, Pilani, Rajasthan, 333031 India (India); Vasudeva, Neena [Department of Physics, S. V. G. College, Ghumarwin, Bilaspur, Himanchal Pradesh, 1714021 India (India)

2015-05-15

We study the effect of vacancies on the structural, electronic and magnetic properties of zigzag boron nitride nanoribbon (ZBNNR) by using first principle calculations. We find that the shift of the vacancies with respect to the ribbon edges causes change in the structural geometry, electronic structure and magnetization of ZBNNR. These vacancies also produce band gap modulation and consequently results the magnetization of ZBNNR.

Ni/boride interfaces and environmental embrittlement in Ni-based superalloys: A first-principles study

International Nuclear Information System (INIS)

Sanyal, Suchismita; Waghmare, Umesh V.; Hanlon, Timothy; Hall, Ernest L.

2011-01-01

Highlights: ► Fracture strengths of Ni/boride interfaces through first-principles calculations. ► Fracture strengths of Ni/boride interfaces are higher than Ni/Ni 3 Al and NiΣ5 grain boundaries. ► Ni/boride interfaces have higher resistance to O-embrittlement than Ni/Ni 3 Al and NiΣ5 grain boundaries. ► CrMo-borides are more effective than Cr-borides in resisting O-embrittlement. ► Electronegativity differences between alloying elements correlate with fracture strengths. - Abstract: Motivated by the vital role played by boride precipitates in Ni-based superalloys in improving mechanical properties such as creep rupture strength, fatigue crack growth rates and improved resistance towards environmental embrittlement , we estimate fracture strength of Ni/boride interfaces through determination of their work of separation using first-principles simulations. We find that the fracture strength of Ni/boride interfaces is higher than that of other commonly occurring interfaces in Ni-alloys, such as Ni Σ-5 grain boundaries and coherent Ni/Ni 3 Al interfaces, and is less susceptible to oxygen-induced embrittlement. Our calculations show how the presence of Mo in Ni/M 5 B 3 (M = Cr, Mo) interfaces leads to additional reduction in oxygen-induced embrittlement. Through Electron-Localization-Function based analyses, we identify the electronic origins of effects of alloying elements on fracture strengths of these interfaces and observe that chemical interactions stemming from electronegativity differences between different atomic species are responsible for the trends in calculated strengths. Our findings should be useful towards designing Ni-based alloys with higher interfacial strengths and reduced oxygen-induced embrittlement.

Site preference and phase stability of Ti doping Ni–Mn–Ga shape memory alloys from first-principles calculations

International Nuclear Information System (INIS)

Gao, Zhiyong; Chen, Baishu; Meng, Xianglong; Cai, Wei

2013-01-01

Highlights: •Site preference and phase stability of NiMnGaTi are studied by first-principles. •The Ti atoms prefer to occupy the Ga sites in the Ni 2 MnGa austenitic phase. •The phase stability becomes worse when Ga is replaced by Ti. •The phase stability is discussed based on the densities of states. -- Abstract: The effects of Ti content on martensitic transformation and phase stability of Ni 50 Mn 25 Ga 25−x Ti x shape memory alloys were investigated from first-principles calculations based on density functional theory. The formation energy results indicate that the added Ti preferentially occupies the Ga sites in Ni 2 MnGa alloy due to the lowest formation energy. The total energy difference between austenite and martensite increases with Ti alloying, being relevant to the experimentally reported changes in martensitic transformation temperature. The phase stability of Ni 50 Mn 25 Ga 25−x Ti x austenite decreases with increasing Ti content, which results from the reduced Ni 3d–Mn 3d hybridization when Ga is replaced by Ti

Nuclear power development and public acceptance

International Nuclear Information System (INIS)

Yoda, Sunao; Yamada, Akihiko

1976-01-01

The public acceptance aimed at realizing the development of nuclear energy of 49,000,000 kW in 1985 in accordance with the basic policy of the combined energy measures in Japan determined by the cabinet meeting in December 1975 is discussed, and the three principles, namely democracy, independence and disclosures under Article 2 of the Atomic Energy Act, are reviewed. Stronger friction may occur owing to the following characteristics of nuclear power development: it is comprehensive but apt to be sectional, too large scale, very long term, military secrecy, and international relations. In addition, there are the sensibility to radioactivity and illogical refusal in Japan. As to the democracy, the participation of the people to the development of nuclear power has not so far been considered. For example, the holding of public hearings has not been legal obligation, but only a by-law of Atomic Energy Commission. As to the independence, serious troubles have been experienced because of the complete dependence of U.S. techniques. As to the disclosure, the opening to the public of the commercial secrecy attached to the application for the approval of reactor installations is apt to be much disputed. In conclusion, it is believed that there is no other way than the exertion of straight effort under the three principles, so that the formation of public acceptance will be accomplished. (Iwakiri, K.)

Understanding and applying principles of social cognition and ...

Science.gov (United States)

Environmental governance systems are under greater pressure to adapt and to cope with increased social and ecological uncertainty from stressors like climate change. We review principles of social cognition and decision making that shape and constrain how environmental governance systems adapt. We focus primarily on the interplay between key decision makers in society and legal systems. We argue that adaptive governance must overcome three cooperative dilemmas to facilitate adaptation: (1) encouraging collaborative problem solving, (2) garnering social acceptance and commitment, and (3) cultivating a culture of trust and tolerance for change and uncertainty. However, to do so governance systems must cope with biases in people’s decision making that cloud their judgment and create conflict. These systems must also satisfy people’s fundamental needs for self-determination, fairness, and security, ensuring that changes to environmental governance are perceived as legitimate, trustworthy, and acceptable. We discuss the implications of these principles for common governance solutions (e.g., public participation, enforcement) and conclude with methodological recommendations. We outline how scholars can investigate the social cognitive principles involved in cases of adaptive governance. Social-ecological stressors place significant pressure on major societal systems, triggering adaptive reforms in human governance and environmental law. Though potentially benefici

Electronic structures of N- and C-doped NiO from first-principles calculations

International Nuclear Information System (INIS)

Long, Run; English, Niall J.; Mooney, Damian A.

2010-01-01

The large intrinsic band gap of NiO has hindered severely its potential application under visible-light irradiation. In this Letter, we have performed first-principles calculations on the electronic properties of N- and C-doped NiO to ascertain if its band gap may be narrowed theoretically. It was found that impurity bands driven by N 2p or C 2p states appear in the band gap of NiO and that some of these locate at the conduction band minimum, which leads to a significant band gap narrowing. Our results show that N-doped NiO may serve as a potential photocatalyst relative to C-doped NiO, due to the presence of some recombination centres in C-doped NiO.

First-principles studies on vacancy-modified interstitial diffusion mechanism of oxygen in nickel, associated with large-scale atomic simulation techniques

International Nuclear Information System (INIS)

Fang, H. Z.; Shang, S. L.; Wang, Y.; Liu, Z. K.; Alfonso, D.; Alman, D. E.; Shin, Y. K.; Zou, C. Y.; Duin, A. C. T. van; Lei, Y. K.; Wang, G. F.

2014-01-01

This paper is concerned with the prediction of oxygen diffusivities in fcc nickel from first-principles calculations and large-scale atomic simulations. Considering only the interstitial octahedral to tetrahedral to octahedral minimum energy pathway for oxygen diffusion in fcc lattice, greatly underestimates the migration barrier and overestimates the diffusivities by several orders of magnitude. The results indicate that vacancies in the Ni-lattice significantly impact the migration barrier of oxygen in nickel. Incorporation of the effect of vacancies results in predicted diffusivities consistent with available experimental data. First-principles calculations show that at high temperatures the vacancy concentration is comparable to the oxygen solubility, and there is a strong binding energy and a redistribution of charge density between the oxygen atom and vacancy. Consequently, there is a strong attraction between the oxygen and vacancy in the Ni lattice, which impacts diffusion

First-principles study of the pentacene/Cu(1 1 1) interface: Adsorption states and vacuum level shifts

International Nuclear Information System (INIS)

Toyoda, Kenji; Nakano, Yosuke; Hamada, Ikutaro; Lee, Kyuho; Yanagisawa, Susumu; Morikawa, Yoshitada

2009-01-01

We have studied the interaction of pentacene with a Cu(1 1 1) surface using density functional theory (DFT) within a generalized gradient approximation (GGA) and the van der Waals density functional [vdW-DF, M. Dion, H. Rydberg, E. Schroeder, D.C. Langreth, B.I. Lundqvist, Phys. Rev. Lett. 92 (2004) 246401]. The adsorption energy is accurately predicted by vdW-DF, while the equilibrium distances between pentacene and the metal substrate (Z C ) are overestimated by both GGA and vdW-DF. The work function changes depend significantly on Z C . The experimental work function change can be successfully reproduced by GGA if the experimentally reported adsorption geometry is used, whereas the magnitude of the work function change is underestimated if calculated adsorption geometries are applied. We examined the IDIS model [H. Vazquez, R. Qszwaldowski, P. Pou, J. Ortega, R. Perez, F. Flores, A. Kahn, Europhys. Lett. 65 (2004) 802] to compare it with the GGA results. The interface dipoles estimated by the IDIS model fairly agree with the GGA results, provided that the adsorption distance is large. On the other hand, they tend to deviate from the GGA results as the adsorption distance becomes smaller, where back donation from the metal surface to the adsorbate occurs. Our analysis reveals that at experimentally reported metal-organic distance, back donation is significant enough to induce polarization of pentacene molecules perpendicular to the surface, which leads to a reduction of the work function. Thus, at the experimentally reported metal-organic distance, the work function change estimated by a simple IDIS model deviates from that calculated by self-consistent GGA calculations. We also found that at the experimentally reported metal-organic distance, the transferred electrons create weak chemical bonds between pentacene and the Cu(1 1 1) surface, illustrating the reactive nature of pentacene.

First-principles calculations of the II-VI semiconductor β-HgS: Metal or semiconductor

International Nuclear Information System (INIS)

Delin, A.

2002-06-01

Relativistic all-electron full-potential first-principles calculations have been performed in order to study the symmetry of the energy levels around the valence band maximum in the zinc blende II-VI semiconductors β-HgS, HgSe, and HgTe. It is demonstrated that in general, an inverted band-structure does not necessarily lead to a zero fundamental energy gap for systems with zinc blende symmetry. Specifically, β-HgS is found to have at the same time an inverted band structure, and a small, slightly indirect, fundamental energy gap. Possibly, the energy levels around the valence band maximum order differently in each of these systems. (author)

Piezoelectric, Mechanical and Acoustic Properties of KNaNbOF5 from First-Principles Calculations

Directory of Open Access Journals (Sweden)

Han Han

2015-12-01

Full Text Available Recently, a noncentrosymmetric crystal, KNaNbOF5, has attracted attention due to its potential to present piezoelectric properties. Although α- and β-KNaNbOF5 are similar in their stoichiometries, their structural frameworks, and their synthetic routes, the two phases exhibit very different properties. This paper presents, from first-principles calculations, comparative studies of the structural, electronic, piezoelectric, and elastic properties of the α and the β phase of the material. Based on the Christoffel equation, the slowness surface of the acoustic waves is obtained to describe its acoustic prosperities. These results may benefit further applications of KNaNbOF5.

First principles investigation of structural, vibrational and thermal properties of black and blue phosphorene

Science.gov (United States)

Arif Khalil, R. M.; Ahmad, Javed; Rana, Anwar Manzoor; Bukhari, Syed Hamad; Tufiq Jamil, M.; Tehreem, Tuba; Nissar, Umair

2018-05-01

In this investigation, structural, dynamical and thermal properties of black and blue phosphorene (P) are presented through the first principles calculations based on the density functional theory (DFT). These DFT calculations depict that due to the approximately same values of ground state energy at zero Kelvin and Helmholtz free energy at room-temperature, it is expected that both structures can coexist at transition temperature. Lattice dynamics of both phases were investigated by using the finite displacement supercell approach. It is noticed on the basis of harmonic approximation thermodynamic calculations that the blue phase is thermodynamically more stable than the black phase above 155 K.

Half-metallic ferromagnetism in Fe-doped Zn3P2 from first-principles calculations

International Nuclear Information System (INIS)

Jaiganesh, G.; Jaya, S. Mathi

2014-01-01

Using the first-principles calculations based on the density functional theory, we have studied the magnetism and electronic structure of Fe-doped Zinc Phosphide (Zn 3 P 2 ). Our results show that the half-metallic ground state and ferromagnetic stability for the small Fe concentrations considered in our study. The stability of the doped material has been studied by calculating the heat of formation and analyzing the minimum total energies in nonmagnetic and ferromagnetic phases. A large value of the magnetic moment is obtained from our calculations and our calculation suggests that the Fe-doped Zn 3 P 2 may be a useful material in semiconductor spintronics

Five charges against the precautionary principle

NARCIS (Netherlands)

Sandin, P.; Peterson, M.B.; Hanson, S.O.; Rudén, C.; Juthe, A.

2002-01-01

We defend the precautionary principle against five common charges, namely that it is ill-defined, absolutist, and a value judgement, increases risk-taking, and marginalizes science. We argue, first, that the precautionary principle is, in principle, no more vague or ill-defined than other decision

Supervision of nuclear safety - IAEA requirements, accepted solutions, trends

International Nuclear Information System (INIS)

Jurkowski, M.

2007-01-01

Ten principles of the nuclear safety, based on the IAEA's standards are presented. Convention on Nuclear Safety recommends for nuclear safety landscape, the control transparency, culture safety, legal framework and knowledge preservation. Examples of solutions accepted in France, Finland, and Czech Republic are discussed. New trends in safety fundamentals and Integration Regulatory Review are presented

High pressure stability analysis and chemical bonding of Ti1-xZrxN alloy: A first principle study

International Nuclear Information System (INIS)

Chauhan, Mamta; Gupta, Dinesh C.

2016-01-01

First-principles pseudo-potential calculations have been performed to analyze the stability of Ti 1-x Zr x N alloy under high pressures. The first order phase transition from B1 to B2 phase has been observed in this alloy at high pressure. The variation of lattice parameter with the change in concentration of Zr atom in Ti 1-x Zr x N is also reported in both the phases. The calculations for density of states have been performed to understand the alloying effects on chemical bonding of Ti-Zr-N alloy.

A first-principles study of He, Xe, Kr and O incorporation in thorium carbide

Energy Technology Data Exchange (ETDEWEB)

Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650 San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1033 Buenos Aires (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650 San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1033 Buenos Aires (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650 San Martín, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA, Av. General Paz 1499, 1650 San Martín, Buenos Aires (Argentina)

2015-05-15

Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. Understanding the incorporation of fission products and oxygen is very important to predict the behavior of nuclear fuels. A first approach to this goal is the study of the incorporation energies and stability of these elements in the material. By means of first-principles calculations within the framework of density functional theory, we calculate the incorporation energies of He, Xe, Kr and O atoms in Th and C vacancy sites, in tetrahedral interstitials and in Schottky defects along the 〈1 1 1〉 and 〈1 0 0〉 directions. We also analyze atomic displacements, volume modifications and Bader charges. This kind of results for ThC, to the best authors’ knowledge, have not been obtained previously, neither experimentally, nor theoretically. This should deal as a starting point towards the study of the complex behavior of fission products in irradiated ThC.

Corrosion Thermodynamics of Magnesium and Alloys from First Principles as a Function of Solvation

Science.gov (United States)

Limmer, Krista; Williams, Kristen; Andzelm, Jan

Thermodynamics of corrosion processes occurring on magnesium surfaces, such as hydrogen evolution and water dissociation, have been examined with density functional theory (DFT) to evaluate the effect of impurities and dilute alloying additions. The modeling of corrosion thermodynamics requires examination of species in a variety of chemical and electronic states in order to accurately represent the complex electrochemical corrosion process. In this study, DFT calculations for magnesium corrosion thermodynamics were performed with two DFT codes (VASP and DMol3), with multiple exchange-correlation functionals for chemical accuracy, as well as with various levels of implicit and explicit solvation for surfaces and solvated ions. The accuracy of the first principles calculations has been validated against Pourbaix diagrams constructed from solid, gas and solvated charged ion calculations. For aqueous corrosion, it is shown that a well parameterized implicit solvent is capable of accurately representing all but the first coordinating layer of explicit water for charged ions.

First-principle calculations of optical properties of monolayer arsenene and antimonene allotropes

Energy Technology Data Exchange (ETDEWEB)

Xu, Yuanfeng; Peng, Bo; Zhang, Hao; Zhang, Rongjun; Zhu, Heyuan [Shanghai Ultra-precision Optical Manufacturing Engineering Research Center and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, Fudan University, Shanghai 200433 (China); Shao, Hezhu [Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China)

2017-04-15

Recently a stable monolayer of antimony in buckled honeycomb structure called antimonene was successfully grown on 3D topological insulator Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3}, which displays novel semiconducting properties. By first-principle calculations, we systematically investigate the electronic and optical properties of α- and β-allotropes of monolayer arsenene/antimonene. The obtained electronic structures reveal that the direct band gap of α-arsenene/antimonene is much smaller than the indirect band gap of their β-counterpart, respectively. Significant absorption is observed in α-antimonene, which can be used as a broad saturable absorber. For β-arsenene/antimonene, the reflectivity is low and the absorption is negligible in the visible region when the polarization along the out-plane direction, indicating that β-arsenene/antimonene are polarizationally transparent materials. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

A first-principles study of the electronic structure of the sulvanite compounds

Energy Technology Data Exchange (ETDEWEB)

Osorio-Guillen, J.M., E-mail: jorge.osorio@fisica.udea.edu.co [Instituto de Fisica, Universidad de Antioquia, Medellin A.A. 1226 (Colombia); Espinosa-Garcia, W.F. [Instituto de Fisica, Universidad de Antioquia, Medellin A.A. 1226 (Colombia)

2012-03-15

We have investigated by means of first-principles total energy calculations the electronic structure of the sulvanite compounds: Cu{sub 3}VS{sub 4}, Cu{sub 3}NbS{sub 4} and Cu{sub 3}TaS{sub 4}; the later is a possible candidate as a p-type transparent conductor with potential applications in solar cells and electrochromic devices. The calculated electronic structure shows that these compounds are indirect band gap semiconductors, with the valence band maximum located at the R-point and the conduction band minimum located at the X-point. The character of the valence band maximum is dominated by Cu d-states and the character of the conduction band minimum is due to the d-states of the group five elements. From the calculated charge density and electron localisation function we can conclude that the sulvanite compounds are polar covalent semiconductors.

Study on the intrinsic defects in tin oxide with first-principles method

Science.gov (United States)

Sun, Yu; Liu, Tingyu; Chang, Qiuxiang; Ma, Changmin

2018-04-01

First-principles and thermodynamic methods are used to study the contribution of vibrational entropy to defect formation energy and the stability of the intrinsic point defects in SnO2 crystal. According to thermodynamic calculation results, the contribution of vibrational entropy to defect formation energy is significant and should not be neglected, especially at high temperatures. The calculated results indicate that the oxygen vacancy is the major point defect in undoped SnO2 crystal, which has a higher concentration than that of the other point defect. The property of negative-U is put forward in SnO2 crystal. In order to determine the most stable defects much clearer under different conditions, the most stable intrinsic defect as a function of Fermi level, oxygen partial pressure and temperature are described in the three-dimensional defect formation enthalpy diagrams. The diagram visually provides the most stable point defects under different conditions.

Atomistic properties of helium in hcp titanium: A first-principles study

International Nuclear Information System (INIS)

Wang Yongli; Liu, Shi; Rong Lijian; Wang Yuanming

2010-01-01

First-principles calculations based on density functional theory have been performed to investigate the behaviors of He in hcp-type Ti. The most favorable interstitial site for He is not an ordinary octahedral or tetrahedral site, but a novel interstitial site (called FC) with a formation energy as low as 2.67 eV, locating the center of the face shared by two adjacent octahedrons. The origin was further analyzed by composition of formation energy of interstitial He defects and charge density of defect-free hcp Ti. It has also been found that an interstitial He atom can easily migrate along direction with an activation energy of 0.34 eV and be trapped by another interstitial He atom with a high binding energy of 0.66 eV. In addition, the small He clusters with/without Ti vacancy have been compared in details and the formation energies of He n V clusters with a pre-existing Ti vacancy are even higher than those of He n clusters until n ≥ 3.

First principles DFT study of dye-sensitized CdS quantum dots

Energy Technology Data Exchange (ETDEWEB)

Jain, Kalpna; Singh, Kh. S. [Department of Physics, D. J. College, Baraut -250611, U.P. (India); Kishor, Shyam, E-mail: shyam387@gmail.com [Department of Chemistry, J. V. College, Baraut -250611, U.P. (India); Josefesson, Ida; Odelius, Michael [Fysikum, Albanova University Center, Stockholm University, S-106 91 Stockholm (Sweden); Ramaniah, Lavanya M. [High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai-400085 (India)

2014-04-24

Dye-sensitized quantum dots (QDs) are considered promising candidates for dye-sensitized solar cells. In order to maximize their efficiency, detailed theoretical studies are important. Here, we report a first principles density functional theory (DFT) investigation of experimentally realized dye - sensitized QD / ligand systems, viz., Cd{sub 16}S{sub 16}, capped with acetate molecules and a coumarin dye. The hybrid B3LYP functional and a 6−311+G(d,p)/LANL2dz basis set are used to study the geometric, energetic and electronic properties of these clusters. There is significant structural rearrangement in all the clusters studied - on the surface for the bare QD, and in the positions of the acetate / dye ligands for the ligated QDs. The density of states (DOS) of the bare QD shows states in the band gap, which disappear on surface passivation with the acetate molecules. Interestingly, in the dye-sensitised QD, the HOMO is found to be localized mainly on the dye molecule, while the LUMO is on the QD, as required for photo-induced electron injection from the dye to the QD.

First-principles study of hydrogen storage in non-stoichiometric TiCx

International Nuclear Information System (INIS)

Ding, Haimin; Fan, Xiaoliang; Li, Chunyan; Liu, Xiangfa; Jiang, Dong; Wang, Chunyang

2013-01-01

Highlights: ► The absorption of hydrogen in non-stoichiometric TiC x is thermally favorable. ► As many as four hydrogen atoms can be trapped by a carbon vacancy. ► The diffusion of hydrogen in TiC x is difficult, especially in TiC x with high x. - Abstract: In this work, the first principles calculation has been performed to study the hydrogen storage in non-stoichiometric TiC x . It is found that hydrogen absorption in stoichiometric TiC is energetically unfavorable, while it is favorable in non-stoichiometric TiC x . This indicates that the existence of carbon vacancies is essential for hydrogenation storage in TiC x . At the same time, multiple hydrogen occupancy of the vacancy has been confirmed and it is calculated that as many as four hydrogen atoms can be trapped by a carbon vacancy. These absorbed hydrogen atoms tend to uniformly distribute around the vacancy. However, it is also found that the diffusion of hydrogen atoms in TiC x is difficult, especially in TiC x with high x.

A first-principles approach to total-dose hardness assurance

International Nuclear Information System (INIS)

Fleetwood, D.M.

1995-01-01

A first-principles approach to radiation hardness assurance was described that provides the technical background to the present US and European total-dose radiation hardness assurance test methods for MOS technologies, TM 1019.4 and BS 22900. These test methods could not have been developed otherwise, as their existence depends not on a wealth of empirical comparisons of IC data from ground and space testing, but on a fundamental understanding of MOS defect growth and annealing processes. Rebound testing should become less of a problem for advanced MOS small-signal electronics technologies for systems with total dose requirements below 50--100 krad(SiO 2 ) because of trends toward much thinner gate oxides. For older technologies with thicker gate oxides and for power devices, rebound testing is unavoidable without detailed characterization studies to assess the impact of interface traps on devices response in space. The QML approach is promising for future hardened technologies. A sufficient understanding of process effects on radiation hardness has been developed that should be able to reduce testing costs in the future for hardened parts. Finally, it is hoped that the above discussions have demonstrated that the foundation for cost-effective hardness assurance tests is laid with studies of the basic mechanisms of radiation effects. Without a diligent assessment of new radiation effects mechanisms in future technologies, one cannot be assured that the present generation of radiation test standards will continue to apply

A systematic first principle method to study magnetic properties of FeMo, CoMo and NiMo

International Nuclear Information System (INIS)

Bhattacharjee, Ashis Kumar; Touheed, Md.; Ahmed, Mesbahuddin; Halder, A.; Mookerjee, A.

2003-06-01

We use the first principle TB-LMTO (Tight-Binding Linear Muffin Tin Orbital) method combined with the ASM (Augmented Space Method) to take care of disorder beyond the mean field (CPA - Cohetent Potential Approximation) approximation. We analyze binary alloys between magnetic transition metals Fe, Co, Ni and non-magnetic Mo to find out the effect of disorder on electronic structure and consequently magnetic properties of the alloys. (author)

First-principles simulations of the streching and final breaking of Al nanowires: Mechanical properties and electrical conductance

Czech Academy of Sciences Publication Activity Database

Jelínek, Pavel; Pérez, R.; Ortega, J.; Flores, F.

2003-01-01

Roč. 68, č. 8 (2003), 085403/1-085403/6 ISSN 0163-1829 Grant - others:European Project(XE) HPRN-CT-2000-00154; DGI-MCyT(ES) MAT2001-0665; Consejera de Educacio de la Comunidad de Madrid(ES) 07N/0050/2001 Institutional research plan: CEZ:AV0Z1010914 Keywords : nanowires * transport properties * first principles simulations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.962, year: 2003

Is there a self-organization principle of river deltas?

Science.gov (United States)

Tejedor, Alejandro; Longjas, Anthony; Foufoula-Georgiou, Efi

2017-04-01

River deltas are known to possess a complex topological and flux-partitioning structure which has recently been quantified using spectral graph theory [Tejedor et al., 2015a,b]. By analysis of real and simulated deltas it has also been shown that there is promise in formalizing relationships between this topo-dynamic delta structure and the underlying delta forming processes [e.g., Tejedor et al., 2016]. The question we pose here is whether there exists a first order organizational principle behind the self-organization of river deltas and whether this principle can be unraveled from the co-evolving topo-dynamic structure encoded in the delta planform. To answer this question, we introduce a new metric, the nonlocal Entropy Rate (nER) that captures the information content of a delta network in terms of the degree of uncertainty in delivering fluxes from any point of the network to the shoreline. We hypothesize that if the "guiding principle" of undisturbed deltas is to efficiently and robustly build land by increasing the diversity of their flux pathways over the delta plane, then they would exhibit maximum nonlocal Entropy Rate at states at which geometry and flux dynamics are at equilibrium. At the same time, their nER would be non-optimal at transient states, such as before and after major avulsions during which topology and dynamics adjust to each other to reach a new equilibrium state. We will present our results for field and simulated deltas, which confirm this hypothesis and open up new ways of thinking about self-organization, complexity and robustness in river deltas. One particular connection of interest might have important implications since entropy rate and resilience are related by the fluctuation theorem [Demetrius and Manke, 2005], and therefore our results suggest that deltas might in fact self-organize to maximize their resilience to structural and dynamic perturbations. References: Tejedor, A., A. Longjas, I. Zaliapin, and E. Foufoula

Autonomous Robotic Weapons: US Army Innovation for Ground Combat in the Twenty-First Century

Science.gov (United States)

2015-05-21

1 Introduction Today the robot is an accepted fact, but the principle has not been pushed far enough. In the twenty-first century the...2013, accessed March 29, 2015, http://www.bbc.com/news/magazine-21576376?print=true. 113 Steven Kotler , “Say Hello to Comrade Terminator: Russia’s...of autonomous robotic weapons, black- marketed directed energy weapons, and or commercially available software, potential adversaries may find

Risk acceptance criteria of the Nuclear Regulatory Authority

International Nuclear Information System (INIS)

Felizia, Eduardo R.

2005-01-01

This report describes some of the regulatory and control functions legally conferred upon the Argentine Nuclear Regulatory Authority concerning radiological risks, as well as a critical analysis of the radiological risk acceptance criteria contained in the Argentine regulatory system. A summary of the application of regulatory standards AR 3.1.3. - 'Radiological criteria related to accidents in nuclear power reactors' and AR 4.1.3. - 'Radiological criteria related to accidents in research reactors' to concrete cases is made, while the favourable and unfavourable aspects of the risk acceptance criteria are discussed. The conclusion is that the Argentine regulatory system contains adequate radiological risk acceptance criteria, that the latter are consistent with the radiological protection principles applicable to man and that, for the moment, there is no need to perform any modifications that would broaden the conceptual framework on which such criteria are based. (author) [es

LANDSCAPE PLANNING IN UKRAINE: THE FIRST LANDSCAPE-PLANNING PROGRAM

Directory of Open Access Journals (Sweden)

Leonid Rudenko

2013-01-01

Full Text Available The paper presents the results of the first, in Ukraine; project on landscape planning widely accepted in European countries. Under the project implemented in 2010–2013, a landscape-planning program has been developed for the Cherkassy oblast. This is the first document of this kind in Ukraine. The program is mainly based on the experience of the German and Russian schools of landscape planning and on research and assessment conducted by the authors, which allowed identifying approaches to landscape planning, principles of the national policy, and characteristics and potential of environmentally friendly planning in Ukraine. The paper discusses the main phases of the work on the development of the landscape program for the oblast. It also identifies the main stages and key concepts and principles of landscape planning. The paper presents the results of integrated research on the identification and classification of conflicts in land use and the integral concept of the developmental goals for the oblast. The results can be the foundation for adopting management decisions and development of action plans for the lower hierarchal branches.

Charge transfer of edge states in zigzag silicene nanoribbons with Stone–Wales defects from first-principles

Energy Technology Data Exchange (ETDEWEB)

Ting, Xie [College of Mathematics and Statistics, Chongqing University, Chongqing 401331 (China); School of Mathematics and Statistic, Chongqing University of Technology, Chongqing 400054 (China); Rui, Wang, E-mail: rcwang@cqu.edu.cn [Institute for Structure and Function and Department of Physics, Chongqing University, Chongqing 400044 (China); State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Science, Beijing 100190 (China); Shaofeng, Wang [Institute for Structure and Function and Department of Physics, Chongqing University, Chongqing 400044 (China); Xiaozhi, Wu, E-mail: xiaozhiwu@cqu.edu.cn [Institute for Structure and Function and Department of Physics, Chongqing University, Chongqing 400044 (China)

2016-10-15

Highlights: • The properties of SW defects in silicene and ZSNRs are obtained. • The SW defects at the edge of ZSNRs induce a sizable gap. • The charge transfer of edge states is resulted from SW defects in ZSNRS. - Abstract: Stone–Wales (SW) defects are favorably existed in graphene-like materials with honeycomb lattice structure and potentially employed to change the electronic properties in band engineering. In this paper, we investigate structural and electronic properties of SW defects in silicene sheet and its nanoribbons as a function of their concentration using the methods of periodic boundary conditions with first-principles calculations. We first calculate the formation energy, structural properties, and electronic band structures of SW defects in silicene sheet, with dependence on the concentration of SW defects. Our results show a good agreement with available values from the previous first-principles calculations. The energetics, structural aspects, and electronic properties of SW defects with dependence on defect concentration and location in edge-hydrogenated zigzag silicene nanoribbons are obtained. For all calculated concentrations, the SW defects prefer to locate at the edge due to the lower formation energy. The SW defects at the center of silicene nanoribbons slightly influence on the electronic properties, whereas the SW defects at the edge of silicene nanoribbons split the degenerate edge states and induce a sizable gap, which depends on the concentration of defects. It is worth to find that the SW defects produce a perturbation repulsive potential, which leads the decomposed charge of edge states at the side with defect to transfer to the other side without defect.

First-Principles Study of Superconductivity in Ultra- thin Pb Films

Science.gov (United States)

Noffsinger, Jesse; Cohen, Marvin L.

2010-03-01

Recently, superconductivity in ultrathin layered Pb has been confirmed in samples with as few as two atomic layers [S. Qin, J. Kim, Q. Niu, and C.-K. Shih, Science 2009]. Interestingly, the prototypical strong-coupling superconductor exhibits different Tc's for differing surface reconstructions in samples with only two monolayers. Additionally, Tc is seen to oscillate as the number of atomic layers is increased. Using first principles techniques based on Wannier functions, we analyze the electronic structure, lattice dynamics and electron-phonon coupling for varying thicknesses and surface reconstructions of layered Pb. We discuss results as they relate to superconductivity in the bulk, for which accurate calculations of superconducting properties can be compared to experiment [W. L. McMillan and J.M. Rowell, PRL 1965]. This work was supported by National Science Foundation Grant No. DMR07-05941, the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Computational resources have been provided by the Lawrencium computational cluster resource provided by the IT Division at the Lawrence Berkeley National Laboratory (Supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231)

An application of first-principles diagnosis to a thermalhydraulic system

International Nuclear Information System (INIS)

Lapointe, P.A.; Chung, J.

1990-03-01

Recent advances in computer technology, such as artificial intelligence and interactive multimedia, offer significant new opportunities to enhance nuclear plant safety and improve the performance of the operations staff. Atomic Energy of Canada Limited is developing a framework on which newer approaches to operator support systems will be implemented. A prototype system has been developed for plant information access and display, on-line advice and diagnosis, and interactive operating procedures; it is called the Operator Companion. This paper describes the work performed for the development of the fault detection and diagnostic module within the Operator Companion. An early prototype of the module was developed for a small heat transfer circuit. A qualitative physics representation coupled with first-principles diagnosis using constraint suspension was utilized. Temporal information was required; it was integrated into the diagnosis using a type of directed graph to record event dependencies. This graph dynamically altered the qualitative model to reflect changes in the system over time. Although not completely formal, out method has successfully integrated the time diagnostic information to permit the identification of the faulty components and limit the number of spurious candidates in the tests performed. This paper summarizes the qualitative diagnosis concepts, describes the special temporal reasoning scheme developed, and presents a summary of the results obtained

Interpretation Principles of Jus Cogens Principles as Public Order in International Practice

Directory of Open Access Journals (Sweden)

Claudia Andritoi

2010-07-01

Full Text Available What is happening if the custom is founded on the coincidence of interests, or even worse, on error? If we rapport specific problems of international customary law to the principles of judicial interpretation it results that a common error (including opinio juris does not disturb the process of legality proper to the principle error communis facit jus. According to the principle of equity, a common error operates only if the victim’s interests are not affected in an irreparable manner. In this case, the error is insuperable and represents a vice for judicial nullity. Error cannot be accepted when it results from the actions of the state, realized with bad intention, as coercion is. Pacta sunt servanda as a jus cogens norm protects nor only good faith. Thus, through interpretation theories in the Anglo-American environment we will use the refinement of a traditional position in continental interpretation, arguing a general method of interpretation based on the recovery of the legislator’s intentions, had at the moment of an edition of a juridical norm. We will use of this application thedialectics between meanings expressed by the text and those the interpret advances with the role of interpretative hypothesis in order to find its meaning.

Towards first principle medical diagnostics: on the importance of disease-disease and sign-sign interactions

Science.gov (United States)

Ramezanpour, Abolfazl; Mashaghi, Alireza

2017-07-01

A fundamental problem in medicine and biology is to assign states, e.g. healthy or diseased, to cells, organs or individuals. State assignment or making a diagnosis is often a nontrivial and challenging process and, with the advent of omics technologies, the diagnostic challenge is becoming more and more serious. The challenge lies not only in the increasing number of measured properties and dynamics of the system (e.g. cell or human body) but also in the co-evolution of multiple states and overlapping properties, and degeneracy of states. We develop, from first principles, a generic rational framework for state assignment in cell biology and medicine, and demonstrate its applicability with a few simple theoretical case studies from medical diagnostics. We show how disease-related statistical information can be used to build a comprehensive model that includes the relevant dependencies between clinical and laboratory findings (signs) and diseases. In particular, we include disease-disease and sign-sign interactions and study how one can infer the probability of a disease in a patient with given signs. We perform comparative analysis with simple benchmark models to check the performances of our models. We find that including interactions can significantly change the statistical importance of the signs and diseases. This first principles approach, as we show, facilitates the early diagnosis of disease by taking interactions into accounts, and enables the construction of consensus diagnostic flow charts. Additionally, we envision that our approach will find applications in systems biology, and in particular, in characterizing the phenome via the metabolome, the proteome, the transcriptome, and the genome.

Generally accepted accounting principles according to the IFRS and the czech legislation

OpenAIRE

Markéta Bartoňová; Olga Malíková

2011-01-01

Accounting as a system provides quantitative information for users about economic processes which proceed in an accounting unit. The main objective of accounting is to observe and describe financial position, efficiency and cash flow of a given entity. This information should be compiled and presented so that users would be able to make qualified decisions. That is why it is necessary that accounting has to be based on the same methods and principles that should ensure that the outputs from a...

Pedagogical Principles in Online Teaching

DEFF Research Database (Denmark)

Beckmann, Suzanne C.; Uth Thomsen, Thyra; von Wallpach, Sylvia

of the seven pedagogical principles that govern the teaching at our university. We also present a case study that illustrates how both opportunities and challenges were met in two “first-mover” fully online courses during Fall 2014. The experiences from this case study are discussed in terms of to what extent...... they met the pedagogical principles and observations unrelated to the pedagogical principle are shared....

Electronic and optical properties of RESn{sub 3} (RE=Pr & Nd) intermetallics: A first principles study

Energy Technology Data Exchange (ETDEWEB)

Pagare, G., E-mail: gita-pagare@yahoo.co.in [Department of Physics, Government M. L. B. Girls P. G. Autonomous College, Bhopal-462002 (India); Abraham, Jisha A. [Department of Physics, Government M. L. B. Girls P. G. Autonomous College, Bhopal-462002 (India); Department of Physics, National Defence Academy, Pune-411023 (India); Sanyal, S. P. [Department of Physics, Barkatullah University, Bhopal-462026 (India)

2015-06-24

A theoretical study of structural, electronic and optical properties of RESn{sub 3} (RE = Pr & Nd) intermetallics have been investigated systematically using first principles density functional theory. The calculations are carried out within the PBE-GGA and LSDA for the exchange correlation potential. The ground state properties such as lattice parameter (a{sub 0}), bulk modulus (B) and its pressure derivative (B′) are calculated and the calculated lattice parameters show well agreement with the experimental results. We first time predict elastic constants for these compounds. From energy dispersion curves, it is found that these compounds are metallic in nature. The linear optical response of these compounds are also studied and the higher value of static dielectric constant shows the possibility to use them as good dielectric materials.

Fe magnetic moment formation and exchange interaction in Fe{sub 2}P: A first-principles study

Energy Technology Data Exchange (ETDEWEB)

Liu, X.B., E-mail: liuxubo@uta.edu [Department of Physics, University of Texas at Arlington, Arlington, TX 76019 (United States); Ping Liu, J.; Zhang, Qiming [Department of Physics, University of Texas at Arlington, Arlington, TX 76019 (United States); Altounian, Z. [Center for the Physics of Materials and Department of Physics, McGill University, 3600 University Street, Montreal, Quebec, H3A 2T8 (Canada)

2013-03-15

Electronic structure and magnetic properties of Fe{sub 2}P have been studied by a first-principles density functional theory calculation. The ground state is ferromagnetic and the calculated magnetic moments for Fe{sub 1} (3f) and Fe{sub 2} (3g) are 0.83 and 2.30μ{sub B}, respectively. The nearest neighbor inter-site magnetic exchange coupling parameter at the Fe{sub 1} layer (0.02 mRy) is much smaller than that at the Fe{sub 2} layer (1.29 mRy). The Fe moment at the 3f site is metastable and sensitive to the inter-site exchange interaction with its magnetic neighbors, which is responsible for the first order magnetic transition and large magneto-caloric effect around T{sub C}.

First-principles study on band structures and electrical transports of doped-SnTe

Directory of Open Access Journals (Sweden)

Xiao Dong

2016-06-01

Full Text Available Tin telluride is a thermoelectric material that enables the conversion of thermal energy to electricity. SnTe demonstrates a great potential for large-scale applications due to its lead-free nature and the similar crystal structure to PbTe. In this paper, the effect of dopants (i.e., Mg, Ca, Sr, Ba, Eu, Yb, Zn, Cd, Hg, and In on the band structures and electrical transport properties of SnTe was investigated based on the first-principles density functional theory including spin–orbit coupling. The results show that Zn and Cd have a dominant effect of band convergence, leading to power factor enhancement. Indium induces obvious resonant states, while Hg-doped SnTe exhibits a different behavior with defect states locating slightly above the Fermi level.

First-Principles Propagation of Geoelectric Fields from Ionosphere to Ground using LANLGeoRad

Science.gov (United States)

Jeffery, C. A.; Woodroffe, J. R.; Henderson, M. G.

2017-12-01

A notable deficiency in the current SW forecasting chain is the propagation of geoelectric fields from ionosphere to ground using Biot-Savart integrals, which ignore the localized complexity of lithospheric electrical conductivity and the relatively high conductivity of ocean water compared to the lithosphere. Three-dimensional models of Earth conductivity with mesoscale spatial resolution are being developed, but a new approach is needed to incorporate this information into the SW forecast chain. We present initial results from a first-principles geoelectric propagation model call LANLGeoRad, which solves Maxwell's equations on an unstructured geodesic grid. Challenges associated with the disparate response times of millisecond electromagnetic propagation and 10-second geomagnetic fluctuations are highlighted, and a novel rescaling of the ionosphere/ground system is presented that renders this geoelectric system computationally tractable.

Point defect thermodynamics and diffusion in Fe3C: A first-principles study

International Nuclear Information System (INIS)

Chao Jiang; Uberuaga, B.P.; Srinivasan, S.G.

2008-01-01

The point defect structure of cementite (Fe 3 C) is investigated using a combination of the statistical mechanical Wagner-Schottky model and first-principles calculations within the generalized gradient approximation. Large 128-atom supercells are employed to obtain fully converged point defect formation energies. The present study unambiguously shows that carbon vacancies and octahedral carbon interstitials are the structural defects in C-depleted and C-rich cementite, respectively. The dominant thermal defects in C-depleted and stoichiometric cementite are found to be carbon Frenkel pairs. In C-rich cementite, however, the primary thermal excitations are strongly temperature-dependent: interbranch, Schottky and Frenkel defects dominate successively with increasing temperature. Using the nudged elastic band technique, the migration barriers of major point defects in cementite are also determined and compared with available experiments in the literature

Adsorption configuration of magnesium on wurtzite gallium nitride surface using first-principles calculations

International Nuclear Information System (INIS)

Yan Han; Gan Zhiyin; Song Xiaohui; Chen Zhaohui; Xu Jingping; Liu Sheng

2009-01-01

First-principles calculations of magnesium adsorption at the Ga-terminated and N-terminated {0 0 0 1} basal plane wurtzite gallium nitride surfaces have been carried out to explain the atomic-scale insight into the initial adsorption processes of magnesium doping in gallium nitride. The results reveal that magnesium adsorption on N-terminated surfaces is preferred than that on Ga-terminated surfaces. Furthermore, the surface diffusivity of magnesium atom on the N-terminated surface is much lower than that on the Ga-terminated surface, which is due to both the larger average adsorption energies and the lower adsorption distance on N-terminated surface than that on Ga-terminated surface. The results indicate that the p-type doping on the Ga-terminated surface will be better distributed than that on the N-terminated surface.

Strength of FePd/MgO and FePt/MgO interfaces from first principles

Science.gov (United States)

Černý, M.

2018-04-01

Cleavage characteristics such as the cleavage energy and the cleavage stress of FePd/MgO and FePt/MgO interfaces are computed from first principles. Considering several possible cleavage planes, the weakest link in these systems is found as the plane with the lowest cleavage stress. This weakest plane is identified in both systems with the interface plane, where the cohesion is reduced by 30% compared to the MgO bulk. Two distinct models of tensile test are employed to verify the results and convergence of computed values with respect to size of the simulation cell is discussed.

The application of the ALARA principle: a first assessment

International Nuclear Information System (INIS)

Lochard, J.; Webb, G.A.M.

1984-01-01

What can we learn from practical ALARA studies. On the methodological point of view the different works developed these last years rely upon the two basic ICRP assumptions, i.e.: the linearity of the dose-risk relationship and the optimal resource allocation principle. Furthermore, most authors seem now to assume the multidimensionality of radiological protection problems. This leads to envisage for decision-aiding techniques the enlargement of the cost-benefit method. As for the quantification process of ALARA principle, assessment techniques for both protection costs and levels of exposures of the various groups at risk are well established. Some differences can be however pointed out between authors concerning the monetary valuation of the detriment cost as well as the way to cope with time, probabilistic events and ''other factors'' not directly linked to protection costs and radiological detriment. Further consideration must be given to the exact role ALARA studies have to play in the decision-making process concerning conception and operation of installations. Particular efforts have to be put on the development of adequate data bases and also decision-aiding techniques able to take into account the multidimensionnality of factors involved in practical protection [fr

Structural, Mechanical and Thermodynamic Properties under Pressure Effect of Rubidium Telluride: First Principle Calculations

Directory of Open Access Journals (Sweden)

Bidai K.

2017-06-01

Full Text Available First-principles density functional theory calculations have been performed to investigate the structural, elastic and thermodynamic properties of rubidium telluride in cubic anti-fluorite (anti-CaF2-type structure. The calculated ground-state properties of Rb2Te compound such as equilibrium lattice parameter and bulk moduli are investigated by generalized gradient approximation (GGA-PBE that are based on the optimization of total energy. The elastic constants, Young’s and shear modulus, Poisson ratio, have also been calculated. Our results are in reasonable agreement with the available theoretical and experimental data. The pressure dependence of elastic constant and thermodynamic quantities under high pressure are also calculated and discussed.

First-principles study of Dirac and Dirac-like cones in phononic and photonic crystals

KAUST Repository

Mei, Jun; Wu, Ying; Chan, C. T.; Zhang, Zhao-Qing

2012-01-01

By using the k•p method, we propose a first-principles theory to study the linear dispersions in phononic and photonic crystals. The theory reveals that only those linear dispersions created by doubly degenerate states can be described by a reduced Hamiltonian that can be mapped into the Dirac Hamiltonian and possess a Berry phase of -π. Linear dispersions created by triply degenerate states cannot be mapped into the Dirac Hamiltonian and carry no Berry phase, and, therefore should be called Dirac-like cones. Our theory is capable of predicting accurately the linear slopes of Dirac and Dirac-like cones at various symmetry points in a Brillouin zone, independent of frequency and lattice structure. © 2012 American Physical Society.