Hybrid functional pseudopotentials
Yang, Jing; Tan, Liang Z.; Rappe, Andrew M.
2018-02-01
The consistency between the exchange-correlation functional used in pseudopotential construction and in the actual density functional theory calculation is essential for the accurate prediction of fundamental properties of materials. However, routine hybrid density functional calculations at present still rely on generalized gradient approximation pseudopotentials due to the lack of hybrid functional pseudopotentials. Here, we present a scheme for generating hybrid functional pseudopotentials, and we analyze the importance of pseudopotential density functional consistency for hybrid functionals. For the PBE0 hybrid functional, we benchmark our pseudopotentials for structural parameters and fundamental electronic gaps of the Gaussian-2 (G2) molecular dataset and some simple solids. Our results show that using our PBE0 pseudopotentials in PBE0 calculations improves agreement with respect to all-electron calculations.
Ab initio pseudopotential theory
International Nuclear Information System (INIS)
Yin, M.T.; Cohen, M.L.
1982-01-01
The ab initio norm-conserving pseudopotential is generated from a reference atomic configuration in which the pseudoatomic eigenvalues and wave functions outside the core region agree with the corresponding ab initio all-electron results within the density-functional formalism. This paper explains why such pseudopotentials accurately reproduce the all-electron results in both atoms and in multiatomic systems. In particular, a theorem is derived to demonstrate the energy- and perturbation-independent properties of ab initio pseudopotentials
Xα method with pseudopotentials
International Nuclear Information System (INIS)
Szasz, L.
1980-01-01
The Xα method for an atom or molecule is transformed into an all-electron pseudopotential formalism. The equations of the Xα method are exactly transformed into pseudo-orbital equations and the resulting pseudopotentials are replaced by simple density-dependent potentials derived from Thomas-Fermi model. It is shown that the new formalism satisfies the virial theorem. As the first application it is shown that the model explains the shell-structure of atoms by the property that the pseudo-orbitals for the (ns), (np), (nd) etc. electrons are, in a very good approximation, the solutions of the same equation and have their maxima at the same point thereby creating the peaks in the radial density characterizing the shell structure. (orig.)
Pseudopotential theory of atoms and molecules
International Nuclear Information System (INIS)
Szasz, L.
1985-01-01
This book reviews the pseudopotential theory of atoms and molecules. It refers to the quantum mechanical technique in which the Pauli exclusion principle is replaced by operators and potential functions, jointly called pseudopotentials. The book describes the development of the theory up to the state-of-the-art techniques. It discusses exact pseudopotentials for one-valence electron systems, density-dependent pseudopotentials for one-valence electron systems, and model pseudopotentials for one-valence electron systems
Mixed ultrasoft/norm-conserved pseudopotential scheme
DEFF Research Database (Denmark)
Stokbro, Kurt
1996-01-01
A variant of the Vanderbilt ultrasoft pseudopotential scheme, where the norm conservation is released for only one or a few angular channels, is presented. Within this scheme some difficulties of the truly ultrasoft pseudopotentials are overcome without sacrificing the pseudopotential softness. (...
Short-range correlations with pseudopotentials
International Nuclear Information System (INIS)
Osman, A.
1976-01-01
Short-range correlations in nuclei are considered on an unitary-model operator approach. Short-range pseudopotentials have been added to achieve healing in the correlated wave functions. With the introduction of the pseudopotentials, correlated basis wave functions are constructed. The matrix element for effective interaction in nuclei is developed. The required pseudopotentials have been calculated for the Hamda-Johnston, Yale and Reid potentials and for the nuclear nucleon-nucleon potential A calculated by us according to meson exchange between nucleons. (Osman, A.)
Pseudopotentials for quantum-Monte-Carlo-calculations
International Nuclear Information System (INIS)
Burkatzki, Mark Thomas
2008-01-01
The author presents scalar-relativistic energy-consistent Hartree-Fock pseudopotentials for the main-group and 3d-transition-metal elements. The pseudopotentials do not exhibit a singularity at the nucleus and are therefore suitable for quantum Monte Carlo (QMC) calculations. The author demonstrates their transferability through extensive benchmark calculations of atomic excitation spectra as well as molecular properties. In particular, the author computes the vibrational frequencies and binding energies of 26 first- and second-row diatomic molecules using post Hartree-Fock methods, finding excellent agreement with the corresponding all-electron values. The author shows that the presented pseudopotentials give superior accuracy than other existing pseudopotentials constructed specifically for QMC. The localization error and the efficiency in QMC are discussed. The author also presents QMC calculations for selected atomic and diatomic 3d-transitionmetal systems. Finally, valence basis sets of different sizes (VnZ with n=D,T,Q,5 for 1st and 2nd row; with n=D,T for 3rd to 5th row; with n=D,T,Q for the 3d transition metals) optimized for the pseudopotentials are presented. (orig.)
Revised Huang-Yang multipolar pseudopotential
International Nuclear Information System (INIS)
Derevianko, Andrei
2005-01-01
A number of authors have recently pointed out inconsistencies of results obtained with the Huang-Yang multipolar pseudopotential for low-energy scattering [K. Huang and K. C. Yang, Phys. Rev. 105, 767 (1957); later revised by Huang, Statistical Mechanics (Wiley, New York, 1963)]. The conceptual validity of their original derivation has been questioned. Here I show that these inconsistencies are rather due to an algebraic mistake made by Huang and Yang. With the corrected error, I present the revised version of the multipolar pseudopotential
Pseudopotential transformation of correlated-pair equations
International Nuclear Information System (INIS)
Szasz, L.; Brown, L.
1975-01-01
A pseudopotential transformation for correlated-pair equations is derived that yields solutions that are pseudowavefunctions, i.e., they do not have to be orthogonal to the core functions. The approximate solutions for the transformation will be much simpler to compute, but they do not involve a loss of accuracy
X. cap alpha. method with pseudopotentials
Energy Technology Data Exchange (ETDEWEB)
Szasz, L. (Fordham Univ., New York (USA). Dept. of Physics)
1980-06-01
The X..cap alpha.. method for an atom or molecule is transformed into an all-electron pseudopotential formalism. The equations of the X..cap alpha.. method are exactly transformed into pseudo-orbital equations and the resulting pseudopotentials are replaced by simple density-dependent potentials derived from Thomas-Fermi model. It is shown that the new formalism satisfies the virial theorem. As the first application, it is shown that the model explains the shell-structure of atoms by the property that the pseudo-orbitals for the (ns), (np), (nd), etc. electrons are, in a very good approximation, the solutions of the same equation and have their maxima at the same point thereby creating the peaks in the radial density characterizing the shell structure.
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
Tan's distributions and Fermi-Huang pseudopotential in momentum space
DEFF Research Database (Denmark)
Valiente, Manuel
2012-01-01
form of the Fourier-transformed pseudopotential remains very simple. Operator forms for the so-called Tan's selectors, which, together with Fermi-Huang pseudopotential, largely simplify the derivation of Tan's universal relations for the Fermi gas, are here derived and are also very simple. A momentum...
Directory of Open Access Journals (Sweden)
Pablo Rivero
2015-06-01
Full Text Available We present in this article a pseudopotential (PP database for DFT calculations in the context of the SIESTA code [1–3]. Comprehensive optimized PPs in two formats (psf files and input files for ATM program are provided for 20 chemical elements for LDA and GGA exchange-correlation potentials. Our data represents a validated database of PPs for SIESTA DFT calculations. Extensive transferability tests guarantee the usefulness of these PPs.
The Fermi pseudo-potential in one dimension
International Nuclear Information System (INIS)
Coutinho, F A B; Nogami, Y; Tomio, Lauro; Toyama, F M
2004-01-01
Wu and Yu recently examined point interactions in one dimension in the form of the Fermi pseudo-potential. On the other hand there are point interactions in the form of self-adjoint extensions (SAEs) of the kinetic energy operator. We examine the relationship between the point interactions in these two forms in the one-channel and two-channel cases. In the one-channel case the pseudo-potential leads to the standard three-parameter family of SAEs. In the two-channel case the pseudo-potential furnishes a ten-parameter family of SAEs
Pseudopotentials for calculating the bulk and surface properties of solids
International Nuclear Information System (INIS)
Cohen, M.L.
1983-01-01
A survey is presented describing research in condensed matter physics using pseudopotentials to calculate electronic, structural, and vibrational properties of solids. Semiconductors are emphasized, and both bulk and surface calculations are discussed. (author) [pt
Study of the electrons elastic scattering by atoms through pseudopotentials
International Nuclear Information System (INIS)
Bettega, M.H.F.
1990-01-01
Pseudopotentials allow an extraordinary simplification in the calculation of the electronic structure of atoms, molecules and crystals. Though they have been used extensively for electronic structure calculations, little is known of their applicability to scattering. A study of the pseudopotentials of Bachelet, Hamann and Schuter in the electron scattering by atoms was made, calculating phase-shifts and cross sections for angular momenta 1=0,1 and 2 and energy up to 5 R y. The results for the pseudopotential were compared all-electron calculations. The agreement is very good in a broad energy band. A simplification of the calculation of scattering by complex molecules where an all-electron calculation is impossible is aimed. (author)
Actinides and lanthanides under pressure: the pseudopotential approach
International Nuclear Information System (INIS)
Richard, N.
2002-01-01
In the Density Functional Theory Framework, the pseudopotential formalism offers a broader scope of study than other theoretical methods such as global relaxation of the parameters of the cell or ab initio molecular dynamics simulations. This method has been widely used to study light elements or transition metals but never to study f elements. We have generated two non local norm conserving Trouillier-Martins pseudopotentials (one in LDA and one in GGA) for the cerium. To check the validity of the pseudopotentials, we have calculated the equilibrium volume and the incompressibility modulus and compared our results to previous all-electron calculations. If the GGA and non linear core corrections are used, the equation of state is in a good agreement with the experimental equation of state. A static study of the previously proposed high pressure phases give a transitions fcc-a''(I)-bct. Using the pseudopotentials we have generated, an ab initio molecular dynamics simulation at constant pressure, in the region between 5 and 12 GPa where the stable phase of cerium is not well defined, lead us to predict that a centred monoclinic structure, as the a''(I) phase previously observed in some experiments, is the most stable phase. We have also generated pseudopotentials for the light actinides (Th, Pa, U and Np). We have study their phase transitions under pressure at zero temperature. We compared our results with all electron results. The structure parameters have always been relaxed in this study. And for the first time in pseudopotential calculation, the spin-orbit coupling has been taken into account. The curves describing the variation of the volume or the incompressibility modulus depending on the elements and the phase transitions are always in agreement with the one found in the all electron calculations. (author)
Relativity and pseudopotentials in the Hartree-Fock-Slater method
International Nuclear Information System (INIS)
Snijders, J.G.
1979-01-01
The methodological problems involved in electronic structure determinations of compounds containing heavy elements by the Hartree-Fock-Slater scheme are investigated. It is shown that the effect of the inner electrons can be simulated by a so called pseudopotential, so that only the valence electrons have to be treated explicitly which constitutes a considerable reduction of computation time. It is further shown that a pseudopotential calculation is able to achieve an accuracy that is comparable to the results of a calculation including the core. (Auth.)
Phase stability of random brasses: pseudopotential theory revisited
International Nuclear Information System (INIS)
Rahman, S.M.M.
1987-06-01
We review the theoretical development concerning the phase stability of random brasses. The introductory discussion of the subject embraces the rules of metallurgy in general, but we emphasize on the roles of electron-per-atom ratio in the major bulk of our discussion. Starting from the so-called rigid-band model the discussion goes up to the recent higher-order pseudopotential theory. The theoretical refinements within the pseudopotential framework are discussed briefly. The stability criteria of the random phases are analysed both in the static lattice and dynamic lattice approximations. (author). 71 refs, figs and tabs
Correlated electron pseudopotentials for 3d-transition metals
International Nuclear Information System (INIS)
Trail, J. R.; Needs, R. J.
2015-01-01
A recently published correlated electron pseudopotentials (CEPPs) method has been adapted for application to the 3d-transition metals, and to include relativistic effects. New CEPPs are reported for the atoms Sc − Fe, constructed from atomic quantum chemical calculations that include an accurate description of correlated electrons. Dissociation energies, molecular geometries, and zero-point vibrational energies of small molecules are compared with all electron results, with all quantities evaluated using coupled cluster singles doubles and triples calculations. The CEPPs give better results in the correlated-electron calculations than Hartree-Fock-based pseudopotentials available in the literature
Empirical pseudo-potential studies on electronic structure
Indian Academy of Sciences (India)
Theoretical investigations of electronic structure of quantum dots is of current interest in nanophase materials. Empirical theories such as effective mass approximation, tight binding methods and empirical pseudo-potential method are capable of explaining the experimentally observed optical properties. We employ the ...
Forcing scheme in pseudopotential lattice Boltzmann model for multiphase flows.
Li, Q; Luo, K H; Li, X J
2012-07-01
The pseudopotential lattice Boltzmann (LB) model is a widely used multiphase model in the LB community. In this model, an interaction force, which is usually implemented via a forcing scheme, is employed to mimic the molecular interactions that cause phase segregation. The forcing scheme is therefore expected to play an important role in the pseudoepotential LB model. In this paper, we aim to address some key issues about forcing schemes in the pseudopotential LB model. First, theoretical and numerical analyses will be made for Shan-Chen's forcing scheme [Shan and Chen, Phys. Rev. E 47, 1815 (1993)] and the exact-difference-method forcing scheme [Kupershtokh et al., Comput. Math. Appl. 58, 965 (2009)]. The nature of these two schemes and their recovered macroscopic equations will be shown. Second, through a theoretical analysis, we will reveal the physics behind the phenomenon that different forcing schemes exhibit different performances in the pseudopotential LB model. Moreover, based on the analysis, we will present an improved forcing scheme and numerically demonstrate that the improved scheme can be treated as an alternative approach to achieving thermodynamic consistency in the pseudopotential LB model.
Use of pseudopotentials in atom-atom (or molecule) collisions
International Nuclear Information System (INIS)
Pascale, J.
1985-09-01
Knowledge of interactions between ions, atoms or molecules is fundamental for interpretating or predicting collisional processes which may occur under various circumstances. The aim of this paper is to demonstrate the usefulness of using semiempirical effective interactions (more particularly, emphasis will be put on the pseudopotential approach) in the study of atom-atom (or molecule) collisions. We would like to show that if the semiempirical effective interactions are carefully defined, their use in molecular-structure calculations and in collision problems can give quite accurate results. We will limit our examples to one-electron systems. We consider the M-atom-He systems as a first example. For these systems, recent molecular-structure calculations have been carried out using an 1-dependent semiempirical pseudopotential approach and they have been tested against numerous experimental data in extensive calculations of cross sections for intra-and-inter-doublet transitions in the M-atom in collisions with He. Our second example will concern the M-H 2 systems, for which semiempirical pseudopotential molecular-structure calculations have been performed very recently using an one-electron two-center model. The results of these calculations are quite encouraging and we foresee the use of the pseudopotential approach in future studies of some reactive scattering processes
Full Development Of Pseudopotentials That Work For All Elements ...
African Journals Online (AJOL)
(1982) as well as the prescription of Pattnaik et al.(1979) which eliminated the numerical instability problems. The liquid metal resistivity is evaluated using Simpson's rule. Keywords: Pseudopotential, liquid metal resistivity, matrix element, linear coefficients, inverse orthogonality transformation. Nigerian Journal of Physics ...
Pseudopotential calculations of AlSb under pressure
Algarni, H.; Al-Hagan, O. A.; Bouarissa, N.; Khan, M. A.; Alhuwaymel, T. F.
2018-02-01
The dependence on hydrostatic pressure of the electronic and optical properties of zinc-blende AlSb semiconducting material in the pressure range of 0-20 kbar has been reported using a pseudopotential approach. At zero pressure, our findings showed that the electron and heavy hole effective masses are 0.11 and 0.38 m0, respectively. Moreover, our results yielded values of 3.3289 and 11.08 for refractive index and high frequency dielectric constant, respectively. These results are found to be in good accord with experiment. Upon compression, all physical parameters of interest showed a monotonic behavior. The pressure-induced energy shifts for the optical transition related to band-gaps indicated that AlSb remains an indirect (D-X) band-gap semiconductor at pressures from 0 to 20 kbar. The trend in all features of interest versus pressure has been presented and discussed. It is found that the lattice parameter is reduced from 0.61355 to 0.60705 nm when pressure is raised from 0 to 20 kbar. The present investigation may be useful for mid-infrared lasers applications, detectors and communication devices.
Dielectric functions, pseudopotentials and applications to lattice dynamics
International Nuclear Information System (INIS)
Sinha, S.K.
1975-01-01
An attempt has been made to review the method of calculating the phonon spectra of crystals in terms of the basic electronic structure. Solids with defects, disordered solids and anharmonic effects have been excluded. The most general technique, viz. the Born-Oppenheimer perturbation theory has been discussed. The structure of the dynamic matrix has been discussed and the manifestations of the Fermi surface in the phonon spectrum explained. A pseudopotential concept for the free electron like metals has been justified and a brief account of these potentials from the point of view of the OPW method as well as from that of the phase shift analysis is included. The formalism of the basic results of the phenomenological dipolar models and their recent generalizations have been reviewed. It has pointed out that this could be derived from the microscopic theory by factorization approximation for the dielectric matrix, and the same method could lead even to more general models and the dielectric properties of the crystal could be obtained from such a microscopic theory. It is expected that the results may be applied to optical properties of the crystal. (K.B.)
Pseudopotential approach to superconductivity in MgB2
International Nuclear Information System (INIS)
Sharma, K.S.; Bhargava, Nidhi; Jain, Ritu; Goyal, Varsha; Sharma, Ritu; Sharma, Smita
2010-01-01
Superconductivity in MgB 2 has been re-examined in BCS-Eliashberg framework by employing Mc-Millan's T c -equation and form factors of MgB 2 computed from the form factors of component metals (Model-I). The empty core model pseudopotential due to Ashcroft and random phase approximation form of dielectric screening due to Gellmann and Brueckner are used in the present work. An excellent agreement between the present values and other theoretically computed values of T c and with the relevant experimental data for MgB 2 confirms the validity of the present approach. The explicit dependence of λ and T c on the isotopic masses of Mg and B, as revealed from the present work, confirms the role of lattice vibrations in the superconducting behaviour of MgB 2 and the high value of T c in it may be attributed to the phonon mediated e-e interaction coupled with higher values of phonon frequencies due to light mass of B atoms. It has also been observed that the pseudo-atom model (Model-II) with appropriate choice of the potential parameter r c successfully explains high value of T c and isotope effect in MgB 2 , confirming the prominent role played by electron-phonon interaction in the high-T c superconductivity observed in MgB 2 . The isotope effect exponent α-values obtained from the two models are in complete agreement with each other and the present value α = 0.46 is also much closer to the BCS value of 0.5. Interaction strength N 0 V values obtained from the two models are also in perfect agreement with each other and the present value N 0 V = 0.48 suggests that MgB 2 is a strong coupling superconductor. (author)
The PSEUDODOJO: Training and grading a 85 element optimized norm-conserving pseudopotential table
van Setten, M. J.; Giantomassi, M.; Bousquet, E.; Verstraete, M. J.; Hamann, D. R.; Gonze, X.; Rignanese, G.-M.
2018-05-01
First-principles calculations in crystalline structures are often performed with a planewave basis set. To make the number of basis functions tractable two approximations are usually introduced: core electrons are frozen and the diverging Coulomb potential near the nucleus is replaced by a smoother expression. The norm-conserving pseudopotential was the first successful method to apply these approximations in a fully ab initio way. Later on, more efficient and more exact approaches were developed based on the ultrasoft and the projector augmented wave formalisms. These formalisms are however more complex and developing new features in these frameworks is usually more difficult than in the norm-conserving framework. Most of the existing tables of norm-conserving pseudopotentials, generated long ago, do not include the latest developments, are not systematically tested or are not designed primarily for high precision. In this paper, we present our PSEUDODOJO framework for developing and testing full tables of pseudopotentials, and demonstrate it with a new table generated with the ONCVPSP approach. The PSEUDODOJO is an open source project, building on the ABIPY package, for developing and systematically testing pseudopotentials. At present it contains 7 different batteries of tests executed with ABINIT, which are performed as a function of the energy cutoff. The results of these tests are then used to provide hints for the energy cutoff for actual production calculations. Our final set contains 141 pseudopotentials split into a standard and a stringent accuracy table. In total around 70,000 calculations were performed to test the pseudopotentials. The process of developing the final table led to new insights into the effects of both the core-valence partitioning and the non-linear core corrections on the stability, convergence, and transferability of norm-conserving pseudopotentials. The PSEUDODOJO hence provides a set of pseudopotentials and general purpose tools
Energy Technology Data Exchange (ETDEWEB)
Burkatzki, Mark Thomas
2008-07-01
The author presents scalar-relativistic energy-consistent Hartree-Fock pseudopotentials for the main-group and 3d-transition-metal elements. The pseudopotentials do not exhibit a singularity at the nucleus and are therefore suitable for quantum Monte Carlo (QMC) calculations. The author demonstrates their transferability through extensive benchmark calculations of atomic excitation spectra as well as molecular properties. In particular, the author computes the vibrational frequencies and binding energies of 26 first- and second-row diatomic molecules using post Hartree-Fock methods, finding excellent agreement with the corresponding all-electron values. The author shows that the presented pseudopotentials give superior accuracy than other existing pseudopotentials constructed specifically for QMC. The localization error and the efficiency in QMC are discussed. The author also presents QMC calculations for selected atomic and diatomic 3d-transitionmetal systems. Finally, valence basis sets of different sizes (VnZ with n=D,T,Q,5 for 1st and 2nd row; with n=D,T for 3rd to 5th row; with n=D,T,Q for the 3d transition metals) optimized for the pseudopotentials are presented. (orig.)
The PSML format and library for norm-conserving pseudopotential data curation and interoperability
García, Alberto; Verstraete, Matthieu J.; Pouillon, Yann; Junquera, Javier
2018-06-01
Norm-conserving pseudopotentials are used by a significant number of electronic-structure packages, but the practical differences among codes in the handling of the associated data hinder their interoperability and make it difficult to compare their results. At the same time, existing formats lack provenance data, which makes it difficult to track and document computational workflows. To address these problems, we first propose a file format (PSML) that maps the basic concepts of the norm-conserving pseudopotential domain in a flexible form and supports the inclusion of provenance information and other important metadata. Second, we provide a software library (libPSML) that can be used by electronic structure codes to transparently extract the information in the file and adapt it to their own data structures, or to create converters for other formats. Support for the new file format has been already implemented in several pseudopotential generator programs (including ATOM and ONCVPSP), and the library has been linked with SIESTA and ABINIT, allowing them to work with the same pseudopotential operator (with the same local part and fully non-local projectors) thus easing the comparison of their results for the structural and electronic properties, as shown for several example systems. This methodology can be easily transferred to any other package that uses norm-conserving pseudopotentials, and offers a proof-of-concept for a general approach to interoperability.
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.
Energy Technology Data Exchange (ETDEWEB)
Richard, N
2002-07-01
In the Density Functional Theory Framework, the pseudopotential formalism offers a broader scope of study than other theoretical methods such as global relaxation of the parameters of the cell or ab initio molecular dynamics simulations. This method has been widely used to study light elements or transition metals but never to study f elements. We have generated two non local norm conserving Trouillier-Martins pseudopotentials (one in LDA and one in GGA) for the cerium. To check the validity of the pseudopotentials, we have calculated the equilibrium volume and the incompressibility modulus and compared our results to previous all-electron calculations. If the GGA and non linear core corrections are used, the equation of state is in a good agreement with the experimental equation of state. A static study of the previously proposed high pressure phases give a transitions fcc-a''(I)-bct. Using the pseudopotentials we have generated, an ab initio molecular dynamics simulation at constant pressure, in the region between 5 and 12 GPa where the stable phase of cerium is not well defined, lead us to predict that a centred monoclinic structure, as the a''(I) phase previously observed in some experiments, is the most stable phase. We have also generated pseudopotentials for the light actinides (Th, Pa, U and Np). We have study their phase transitions under pressure at zero temperature. We compared our results with all electron results. The structure parameters have always been relaxed in this study. And for the first time in pseudopotential calculation, the spin-orbit coupling has been taken into account. The curves describing the variation of the volume or the incompressibility modulus depending on the elements and the phase transitions are always in agreement with the one found in the all electron calculations. (author)
Energy Technology Data Exchange (ETDEWEB)
Rakhecha, Shalu, E-mail: shalurakhecha@yahoo.com; Vyas, P. R.; Gohel, V. B. [Department of Physics, School of Sciences, Gujarat University, Ahmedabad - 380009, Gujarat (India); Bhatt, N. K. [Department of Physics, Sardar Patel University, Vallabh Vidyanagar - 388120, Gujarat (India)
2016-05-06
In the present communication, we have computed static and dynamic properties (binding energy-E, bulk modulus-B and second moment- <ω{sup 2}>) as well as first order pressure induced phase transition (FCC-BCC) using local form of pseudopotential for Calcium and Strontium. The form of pseudopotential used for the computation is directly extracted from Generalized Pseudopotential Theory (GPT) which contains three parameters (r{sub c}, r{sub d} and β). We have suggested a simple method using which pseudopotential is determined by single parameter (β). Our computed results for binding energy and bulk modulii are in excellent agreement with experimental findings and are better than other theoretical results. The present study confirms that s-d hybridization is accounted properly in the presently used pseudopotential and can be extended for the study of lattice mechanical properties of these metals.
Effect of the forcing term in the pseudopotential lattice Boltzmann modeling of thermal flows.
Li, Qing; Luo, K H
2014-05-01
The pseudopotential lattice Boltzmann (LB) model is a popular model in the LB community for simulating multiphase flows. Recently, several thermal LB models, which are based on the pseudopotential LB model and constructed within the framework of the double-distribution-function LB method, were proposed to simulate thermal multiphase flows [G. Házi and A. Márkus, Phys. Rev. E 77, 026305 (2008); L. Biferale, P. Perlekar, M. Sbragaglia, and F. Toschi, Phys. Rev. Lett. 108, 104502 (2012); S. Gong and P. Cheng, Int. J. Heat Mass Transfer 55, 4923 (2012); M. R. Kamali et al., Phys. Rev. E 88, 033302 (2013)]. The objective of the present paper is to show that the effect of the forcing term on the temperature equation must be eliminated in the pseudopotential LB modeling of thermal flows. First, the effect of the forcing term on the temperature equation is shown via the Chapman-Enskog analysis. For comparison, alternative treatments that are free from the forcing-term effect are provided. Subsequently, numerical investigations are performed for two benchmark tests. The numerical results clearly show that the existence of the forcing-term effect will lead to significant numerical errors in the pseudopotential LB modeling of thermal flows.
Fully local orbital-free calculation of electronic structure using pseudopotentials
Pino, R.; Markvoort, Albert. J.; Santen, van R.A.; Hilbers, P.A.J.
2003-01-01
An exactly solvable orbital-free technique is applied to the calculation of the electronic structure of polyatomic systems. The Thomas–Fermi kinetic energy, local exchange, local electrostatic energy functionals, and pseudopotentials are used. Given the potential, the cost of the calculation of the
Bhatia, K. G.; Vyas, S. M.; Patel, A. B.; Bhatt, N. K.; Vyas, P. R.; Gohel, V. B.
2018-05-01
Using parameter-free (first principles local) pseudopotential, in the present communication we have calculated dynamical elastic constants (C11, C12 and C44), bulk modulus (B), shear modulus (µp), Young's modulus (Y) and Poisson's ratio (σ) in long wavelength limit. Our computed results are well agreed for C44 and B with experiment and with other theoretical results obtained within framework of second order perturbation pseudopotential theory. From the present study we conclude that pseudopotential used contain s-p hybridization and no extra term is required to account core-core repulsion.
Electronic structure prediction via data-mining the empirical pseudopotential method
Energy Technology Data Exchange (ETDEWEB)
Zenasni, H; Aourag, H [LEPM, URMER, Departement of Physics, University Abou Bakr Belkaid, Tlemcen 13000 (Algeria); Broderick, S R; Rajan, K [Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011-2230 (United States)
2010-01-15
We introduce a new approach for accelerating the calculation of the electronic structure of new materials by utilizing the empirical pseudopotential method combined with data mining tools. Combining data mining with the empirical pseudopotential method allows us to convert an empirical approach to a predictive approach. Here we consider tetrahedrally bounded III-V Bi semiconductors, and through the prediction of form factors based on basic elemental properties we can model the band structure and charge density for these semi-conductors, for which limited results exist. This work represents a unique approach to modeling the electronic structure of a material which may be used to identify new promising semi-conductors and is one of the few efforts utilizing data mining at an electronic level. (Abstract Copyright [2010], Wiley Periodicals, Inc.)
Pseudo-potential method for taking into account the Pauli principle in cluster systems
International Nuclear Information System (INIS)
Krasnopol'skii, V.M.; Kukulin, V.I.
1975-01-01
In order to take account of the Pauli principle in cluster systems (such as 3α, α + α + n) a convenient method of renormalization of the cluster-cluster deep attractive potentials with forbidden states is suggested. The renormalization consists of adding projectors upon the occupied states with an infinite coupling constant to the initial deep potential which means that we pass to pseudo-potentials. The pseudo-potential approach in projecting upon the noneigenstates is shown to be equivalent to the orthogonality condition model of Saito et al. The orthogonality of the many-particle wave function to the forbidden states of each two-cluster sub-system is clearly demonstrated
Del Rio, Beatriz G; Dieterich, Johannes M; Carter, Emily A
2017-08-08
The accuracy of local pseudopotentials (LPSs) is one of two major determinants of the fidelity of orbital-free density functional theory (OFDFT) simulations. We present a global optimization strategy for LPSs that enables OFDFT to reproduce solid and liquid properties obtained from Kohn-Sham DFT. Our optimization strategy can fit arbitrary properties from both solid and liquid phases, so the resulting globally optimized local pseudopotentials (goLPSs) can be used in solid and/or liquid-phase simulations depending on the fitting process. We show three test cases proving that we can (1) improve solid properties compared to our previous bulk-derived local pseudopotential generation scheme; (2) refine predicted liquid and solid properties by adding force matching data; and (3) generate a from-scratch, accurate goLPS from the local channel of a non-local pseudopotential. The proposed scheme therefore serves as a full and improved LPS construction protocol.
Electrical resistivity of noble-metal alloys: Roles of pseudopotential refinements
International Nuclear Information System (INIS)
Mujibar Rahman, S.M.
1983-08-01
The electrical resistivity of liquid noble-metal alloys i.e. CuAu and AgAu is calculated as a function of concentration. The calculations employ transition-metal-pseudopotentials that include nonlocal effects, hybridization and corrections due to orthogonalization hole and use the hard-sphere structure factors; the optimal values of the hard-sphere diameters are being determined by variational calculations. The calculated resistivities are comparable to the experimental values and to the available theoretical results. (author)
Magnitude of pseudopotential localization errors in fixed node diffusion quantum Monte Carlo.
Krogel, Jaron T; Kent, P R C
2017-06-28
Growth in computational resources has lead to the application of real space diffusion quantum Monte Carlo to increasingly heavy elements. Although generally assumed to be small, we find that when using standard techniques, the pseudopotential localization error can be large, on the order of an electron volt for an isolated cerium atom. We formally show that the localization error can be reduced to zero with improvements to the Jastrow factor alone, and we define a metric of Jastrow sensitivity that may be useful in the design of pseudopotentials. We employ an extrapolation scheme to extract the bare fixed node energy and estimate the localization error in both the locality approximation and the T-moves schemes for the Ce atom in charge states 3+ and 4+. The locality approximation exhibits the lowest Jastrow sensitivity and generally smaller localization errors than T-moves although the locality approximation energy approaches the localization free limit from above/below for the 3+/4+ charge state. We find that energy minimized Jastrow factors including three-body electron-electron-ion terms are the most effective at reducing the localization error for both the locality approximation and T-moves for the case of the Ce atom. Less complex or variance minimized Jastrows are generally less effective. Our results suggest that further improvements to Jastrow factors and trial wavefunction forms may be needed to reduce localization errors to chemical accuracy when medium core pseudopotentials are applied to heavy elements such as Ce.
International Nuclear Information System (INIS)
Shan Ming-Lei; Zhu Chang-Ping; Yao Cheng; Yin Cheng; Jiang Xiao-Yan
2016-01-01
The dynamics of the cavitation bubble collapse is a fundamental issue for the bubble collapse application and prevention. In the present work, the modified forcing scheme for the pseudopotential multi-relaxation-time lattice Boltzmann model developed by Li Q et al. [Li Q, Luo K H and Li X J 2013 Phys. Rev. E 87 053301] is adopted to develop a cavitation bubble collapse model. In the respects of coexistence curves and Laplace law verification, the improved pseudopotential multi-relaxation-time lattice Boltzmann model is investigated. It is found that the thermodynamic consistency and surface tension are independent of kinematic viscosity. By homogeneous and heterogeneous cavitation simulation, the ability of the present model to describe the cavitation bubble development as well as the cavitation inception is verified. The bubble collapse between two parallel walls is simulated. The dynamic process of a collapsing bubble is consistent with the results from experiments and simulations by other numerical methods. It is demonstrated that the present pseudopotential multi-relaxation-time lattice Boltzmann model is applicable and efficient, and the lattice Boltzmann method is an alternative tool for collapsing bubble modeling. (paper)
International Nuclear Information System (INIS)
Ehvarestov, R.A.; Panin, A.I.; Bandura, A.V.
2008-01-01
Account of relativistic effects on the properties of uranium hexafluoride is testified. Detailed comparison of single electron energies spectrum revealed in nonrelativistic (by Hartree-Fock method), relativistic (by Dirac-Fock method), and scalar-relativistic (using relativistic potential of atomic uranium frame) has been conducted. Optimization procedures of atomic basis in LCAO calculations of molecules and crystals permissive taking into account distortion of atomic orbitals when chemical bonding are discussed, and optimization effect of atomic basis on the results of scalar-relativistic calculations of UF 6 molecule properties is analyzed. Calculations of electronic structure and properties of UO 2 crystal having relativistic and nonrelativistic pseudopotentials have been realized [ru
Band structure calculation of GaSe-based nanostructures using empirical pseudopotential method
International Nuclear Information System (INIS)
Osadchy, A V; Obraztsova, E D; Volotovskiy, S G; Golovashkin, D L; Savin, V V
2016-01-01
In this paper we present the results of band structure computer simulation of GaSe- based nanostructures using the empirical pseudopotential method. Calculations were performed using a specially developed software that allows performing simulations using cluster computing. Application of this method significantly reduces the demands on computing resources compared to traditional approaches based on ab-initio techniques and provides receiving the adequate comparable results. The use of cluster computing allows to obtain information for structures that require an explicit account of a significant number of atoms, such as quantum dots and quantum pillars. (paper)
Pseudopotential description of rare earths in oxides: The case of Er2Si2O7
DEFF Research Database (Denmark)
Lægsgaard, Jesper; Stokbro, Kurt
2001-01-01
The applicability of ultrasoft pseudopotentials to the problem of rare-earth incorporation in silicates is investigated using the compound Er2Si2O7 as a test case. It is found that density-functional theory within the generalized gradient approximation provides a good description of the structural...... parameters, when treating the Er 4f states as a partially occupied core shell. The density of states and the distribution of electronic charge are analyzed, and it is concluded that the presence of Er tends to increase the covalency of neighboring Si-O bonds....
Temperature dependence of residual electrical resistivity of Cu-Au in pseudopotential approximation
International Nuclear Information System (INIS)
Khwaja, F.A.; Ahmed, I.; Shaukat, A.
1986-08-01
The problem of temperature dependence of residual electrical resistivity of Cu-Au system is re-examined in the light of static distortion and thermal vibration of the lattice along with the short-range-order of atoms above critical temperature. The extended version of Ziman's formula for resistivity obtained yields a unified version for the calculation of resistivity in pseudopotential approximation. The temperature dependence of the quantity Δρ/ρ in this framework for Cu-Au system is found to be in better agreement with the experimental data as compared to previous calculation. (author)
Spin-orbit interaction effects in zincblende semiconductors: Ab initio pseudopotential calculations
International Nuclear Information System (INIS)
Li, Ming-Fu; Surh, M.P.; Louie, S.G.
1988-06-01
Ab initio band structure calculations have been performed for the spin-orbit interaction effects at the top of the valence bands for GaAs and InSb. Relativistic, norm-conserving pseudopotentials are used with no correction made for the gaps from the local density approximation. The spin-orbit splitting at Γ and linear terms in the /rvec char/k dependence of the splitting are found to be in excellent agreement with existing experiments and previous theoretical results. The effective mass and the cubic splitting terms are also examined. 6 refs., 1 fig., 2 tabs
Energy Technology Data Exchange (ETDEWEB)
Ghoshal, S. K.; Sahar, M. R.; Rohani, M. S. [Universiti Teknologi Malaysia, Johor (Malaysia)
2011-02-15
A computer simulation using a pseudopotential approach has been carried out to investigate the band gap as a function of the size and the shape of small silicon (Si) dots having 3 to 44 atoms per dot with and without surface passivation. We used an empirical pseudo-potential Hamiltonian, a plane-wave basis expansion and a basic tetrahedral structure with undistorted local bonding configurations. In our simulation, the structures of the quantum dots were relaxed and optimized before and after passivation. We found that the gap increased more for an oxygenated surface than a hydrogenated one. Thus, both quantum confinement and surface passivation determined the optical and the electronic properties of Si quantum dots. Visible luminescence was probably due to radiative recombination of electrons and holes in the quantum-confined nanostructures. The effect of passivation of the surface dangling bonds by hydrogen and oxygen atoms and the role of surface states on the gap energy was also examined. We investigated the entire energy spectrum starting from the very low-lying ground state to the very high-lying excited states. The results for the sizes of the gap, the density of states, the oscillator strength and the absorption coefficient as functions of the size are presented. The importance of the confinement and the role of surface passivation on the optical effects are also discussed.
Eliminating cubic terms in the pseudopotential lattice Boltzmann model for multiphase flow
Huang, Rongzong; Wu, Huiying; Adams, Nikolaus A.
2018-05-01
It is well recognized that there exist additional cubic terms of velocity in the lattice Boltzmann (LB) model based on the standard lattice. In this work, elimination of these cubic terms in the pseudopotential LB model for multiphase flow is investigated, where the force term and density gradient are considered. By retaining high-order (≥3 ) Hermite terms in the equilibrium distribution function and the discrete force term, as well as introducing correction terms in the LB equation, the additional cubic terms of velocity are entirely eliminated. With this technique, the computational simplicity of the pseudopotential LB model is well maintained. Numerical tests, including stationary and moving flat and circular interface problems, are carried out to show the effects of such cubic terms on the simulation of multiphase flow. It is found that the elimination of additional cubic terms is beneficial to reduce the numerical error, especially when the velocity is relatively large. Numerical results also suggest that these cubic terms mainly take effect in the interfacial region and that the density-gradient-related cubic terms are more important than the other cubic terms for multiphase flow.
Energy Technology Data Exchange (ETDEWEB)
Battat, M E [Los Alamos Scientific Laboratory, University of California, Los Alamos, NM (United States)
1962-03-15
1 megavatt, aktivnaya zona kotorogo soderzhit rasplavlennyj splav plutoniya i zheleza (90 atomnykh protsentov plutoniya, 10 atomnykh protsentov zheleza pri tochke plavleniya v 410{sup o} TS). Regulirovka reaktivnosti obespechena putem ispol'zovaniya otrazhatelya iz nerzhaveyushchej stali i chetyrekh nikelievykh reguliruyushchikh sterzhnej, raspolozhennykh vne aktivnoj zony. Byli provedeny opyty pri temperaturakh aktivnoj zony v 80, 160 i 480 deg. TS s tem, chtoby opredelit' kriticheskuyu massu i tsennost' otrazhatelya pri kazhdoj iz ehtikh temperatur. Byli izmereny temperaturnyj koehffitsient reaktivnosti, a takzhe tsennost' reguliruyushchikh sterzhnej po izmereniyam perioda. Byli sdelany raschety s ispol'zovaniem metoda S{sub n} dlya resheniya problemy perenosa nejtronov, chtoby opredelit' osnovnye yadernye parametry sistemy. Sravnenie mezhdu raschetnymi i izmerennymi velichinami parametrov takikh kak temperaturnyj koehffitsient, tsennost' reguliruyushchikh ehlementov i kriticheskaya massa predstavlyayut takzhe interes v otsenke nadezhnosti proektnykh raschetov. (author)
International Nuclear Information System (INIS)
Mo, O.; Riera, A.; Yaez, M.
1985-01-01
We present an extension of the analytical method of Macias and Riera to calculate radial couplings, to include model potentials or (local and nonlocal) pseudopotentials, in the Hamiltonian. As an illustration, energies, couplings, and momentum matrix elements are presented and discussed for the two-effective-electron NaH quasimolecule, as a stringent test case
Energy Technology Data Exchange (ETDEWEB)
Mo, O.; Riera, A.; Yaez, M.
1985-06-01
We present an extension of the analytical method of Macias and Riera to calculate radial couplings, to include model potentials or (local and nonlocal) pseudopotentials, in the Hamiltonian. As an illustration, energies, couplings, and momentum matrix elements are presented and discussed for the two-effective-electron NaH quasimolecule, as a stringent test case.
International Nuclear Information System (INIS)
Munukutla, L.V.; Cappelletti, R.L.
1980-01-01
Normal-state specific heats between 1 and 4.4 K and superconducting transition temperatures of pure indium and In-Tl alloys have been measured. Excellent agreement with previous results was found. N/sub bs/(0) was extracted using our γ values and Dynes's lambda values and shows a large variation. The measured variation of lambda 2 > was also obtained from Dynes's results and found to be nearly linear in spite of the large variation of N/sub bs/(0). This is shown to be a consequence of the fact that the ratio of the calculated average screened pseudopotential form factor to electron density of states, 2 /sub s/>/N/sub bs/(0), is nearly constant across the alloy series for each element. No anomaly was found in the specific heat of In/sub 0.69/Tl/sub 0.31/ at the expected martensitic transition temperature
Energy Technology Data Exchange (ETDEWEB)
Zaitsevskii, Andrei V [Institute of Hydrogen Energetics and Plasma Technologies, Russian Research Centre ' Kurchatov Institute' (Russian Federation); Wuellen, C van [Technische Universitaet Kaiserslautern (Germany); Titov, A V [B P Konstantinov Petersburg Nuclear Physics Institute, Russian Academy of Sciences (Russian Federation)
2009-12-31
Relativistic pseudopotential approach to the electronic structure simulation of superheavy elements (SHE) compounds is presented. Advanced formulations of this approach leaving both valence and outer-core electronic shells for explicit treatment give rise to simple and efficient computational techniques ensuring highly accurate description of most chemical properties of SHE. At present, the errors due to the use of approximate methods for solving the correlation problem for a subsystem of valence electrons are much larger than those stemming from the pseudopotential approximation itself. Recent applications to the studies of the chemistry of elements 112 (eka-Hg) and 114 (eka-Pb) are reviewed; properties of these elements and their lighter homologues, Hg and Pb, are compared.
International Nuclear Information System (INIS)
Harchaoui, N; Hellal, S; Grosdidier, B; Gasser, J G
2008-01-01
The physical properties of disordered matter depend on the 'atomic structure' i.e. the arrangement of the atoms. This arrangement is described by the structure factor S (q) in reciprocal space and by the pair correlation function g(r) in real space. The structure factor is obtained experimentally while the numerical simulation enables us to obtain the pair correlation function. Liquid sodium is one of the elements the most studied and one can wonder about new scientific contribution appropriateness. The majority of theoretical calculations are compared with the experiment of Waseda. However two other posterior measurements have been published and give different results, in particular with regard to the height of the first peak of the structure factor. Three models of pseudopotential are considered to describe the electron-ion interaction. The first is a local pseudopotential with the alternative known as 'individual' of the model suggested by Fiolhais et al. The second model considered is that of Bachelet et al. This one, ab-initio and 'norm conserving', is non local. The last model is that proposed by Shaw known as 'first principles' and 'energy dependent'. Various static dielectric functions characteristic of the effects of exchange and correlation have been used and developed by Hellal et al. We calculated the form factors (pseudopotential in reciprocal space) and deduce the normalized energy-wave-number characteristic F N (q), the interatomic pair potential V eff (r), then the pair correlation function g(r) by molecular dynamics. The structure factor S(q) is obtained by Fourier transform and is compared with the experiment. Our calculations with the Bachelet and Shaw pseudopotentials are close to the last experiments of Greenfield et al. and of Huijben et al. Our results are discussed
Contact angle adjustment in equation-of-state-based pseudopotential model.
Hu, Anjie; Li, Longjian; Uddin, Rizwan; Liu, Dong
2016-05-01
The single component pseudopotential lattice Boltzmann model has been widely applied in multiphase simulation due to its simplicity and stability. In many studies, it has been claimed that this model can be stable for density ratios larger than 1000. However, the application of the model is still limited to small density ratios when the contact angle is considered. The reason is that the original contact angle adjustment method influences the stability of the model. Moreover, simulation results in the present work show that, by applying the original contact angle adjustment method, the density distribution near the wall is artificially changed, and the contact angle is dependent on the surface tension. Hence, it is very inconvenient to apply this method with a fixed contact angle, and the accuracy of the model cannot be guaranteed. To solve these problems, a contact angle adjustment method based on the geometry analysis is proposed and numerically compared with the original method. Simulation results show that, with our contact angle adjustment method, the stability of the model is highly improved when the density ratio is relatively large, and it is independent of the surface tension.
Pala, M. G.; Esseni, D.
2018-03-01
This paper presents the theory, implementation, and application of a quantum transport modeling approach based on the nonequilibrium Green's function formalism and a full-band empirical pseudopotential Hamiltonian. We here propose to employ a hybrid real-space/plane-wave basis that results in a significant reduction of the computational complexity compared to a full plane-wave basis. To this purpose, we provide a theoretical formulation in the hybrid basis of the quantum confinement, the self-energies of the leads, and the coupling between the device and the leads. After discussing the theory and the implementation of the new simulation methodology, we report results for complete, self-consistent simulations of different electron devices, including a silicon Esaki diode, a thin-body silicon field effect transistor (FET), and a germanium tunnel FET. The simulated transistors have technologically relevant geometrical features with a semiconductor film thickness of about 4 nm and a channel length ranging from 10 to 17 nm. We believe that the newly proposed formalism may find applications also in transport models based on ab initio Hamiltonians, as those employed in density functional theory methods.
Study of Thermodynamics of Liquid Noble-Metals Alloys Through a Pseudopotential Theory
International Nuclear Information System (INIS)
Vora, Aditya M.
2010-01-01
The Gibbs-Bogoliubov (GB) inequality is applied to investigate the thermodynamic properties of some equiatomic noble metal alloys in liquid phase such as Au-Cu, Ag-Cu, and Ag-Au using well recognized pseudopotential formalism. For description of the structure, well known Percus-Yevick (PY) hard sphere model is used as a reference system. By applying a variation method the best hard core diameters have been found which correspond to minimum free energy. With this procedure the thermodynamic properties such as entropy and heat of mixing have been computed. The influence of local field correction function viz; Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F), and Sarkar et al. (S) is also investigated. The computed results of the excess entropy compares favourably in the case of liquid alloys while the agreement with experiment is poor in the case of heats of mixing. This may be due to the sensitivity of the heats of mixing with the potential parameters and the dielectric function. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Scalable real space pseudopotential density functional codes for materials in the exascale regime
Lena, Charles; Chelikowsky, James; Schofield, Grady; Biller, Ariel; Kronik, Leeor; Saad, Yousef; Deslippe, Jack
Real-space pseudopotential density functional theory has proven to be an efficient method for computing the properties of matter in many different states and geometries, including liquids, wires, slabs, and clusters with and without spin polarization. Fully self-consistent solutions using this approach have been routinely obtained for systems with thousands of atoms. Yet, there are many systems of notable larger sizes where quantum mechanical accuracy is desired, but scalability proves to be a hindrance. Such systems include large biological molecules, complex nanostructures, or mismatched interfaces. We will present an overview of our new massively parallel algorithms, which offer improved scalability in preparation for exascale supercomputing. We will illustrate these algorithms by considering the electronic structure of a Si nanocrystal exceeding 104 atoms. Support provided by the SciDAC program, Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences. Grant Numbers DE-SC0008877 (Austin) and DE-FG02-12ER4 (Berkeley).
Temperature dependent empirical pseudopotential theory for self-assembled quantum dots.
Wang, Jianping; Gong, Ming; Guo, Guang-Can; He, Lixin
2012-11-28
We develop a temperature dependent empirical pseudopotential theory to study the electronic and optical properties of self-assembled quantum dots (QDs) at finite temperature. The theory takes the effects of both lattice expansion and lattice vibration into account. We apply the theory to InAs/GaAs QDs. For the unstrained InAs/GaAs heterostructure, the conduction band offset increases whereas the valence band offset decreases with increasing temperature, and there is a type-I to type-II transition at approximately 135 K. Yet, for InAs/GaAs QDs, the holes are still localized in the QDs even at room temperature, because the large lattice mismatch between InAs and GaAs greatly enhances the valence band offset. The single-particle energy levels in the QDs show a strong temperature dependence due to the change of confinement potentials. Because of the changes of the band offsets, the electron wavefunctions confined in QDs increase by about 1-5%, whereas the hole wavefunctions decrease by about 30-40% when the temperature increases from 0 to 300 K. The calculated recombination energies of excitons, biexcitons and charged excitons show red shifts with increasing temperature which are in excellent agreement with available experimental data.
Parallel Implementation of Gamma-Point Pseudopotential Plane-Wave DFT with Exact Exchange
International Nuclear Information System (INIS)
Bylaska, Eric J.; Tsemekhman, Kiril L.; Baden, Scott B.; Weare, John H.; Jonsson, Hannes
2011-01-01
One of the more persistent failures of conventional density functional theory (DFT) methods has been their failure to yield localized charge states such as polarons, excitons and solitons in solid-state and extended systems. It has been suggested that conventional DFT functionals, which are not self-interaction free, tend to favor delocalized electronic states since self-interaction creates a Coulomb barrier to charge localization. Pragmatic approaches in which the exchange correlation functionals are augmented with small amount of exact exchange (hybrid-DFT, e.g. B3LYP and PBE0) have shown promise in localizing charge states and predicting accurate band gaps and reaction barriers. We have developed a parallel algorithm for implementing exact exchange into pseudopotential plane-wave density functional theory and we have implemented it in the NWChem program package. The technique developed can readily be employed in plane-wave DFT programs. Furthermore, atomic forces and stresses are straightforward to implement, making it applicable to both confined and extended systems, as well as to Car-Parrinello ab initio molecular dynamic simulations. This method has been applied to several systems for which conventional DFT methods do not work well, including calculations for band gaps in oxides and the electronic structure of a charge trapped state in the Fe(II) containing mica, annite.
Fermi surface changes in dilute magnesium alloys: a pseudopotential band structure model
International Nuclear Information System (INIS)
Fung, W.K.
1976-01-01
The de Haas-van Alphen effect has been used to study the Fermi surface of pure magnesium and its dilute alloys containing lithium and indium. The quantum oscillations in magnetization were detected by means of a torque magnetometer in magnetic field up to 36 kilogauss and temperature range of 4.2 0 to 1.7 0 K. The results provide information on the effects of lithium and indium solutes on the Fermi surface of magnesium in changes of extremal cross sections and effective masses as well as the relaxation times associated with the orbits. The nonlocal pseudopotential model proposed by Kimball, Stark and Mueller has been fitted to the Fermi surface of magnesium and extended to include the dilute alloys, fitting all the observed de Haas-van Alphen frequencies with an accuracy of better than 1 percent. A modified rigid band interpretation including both Fermi energy and local band edge changes computed from the model, gives an overall satisfactory description of the observed frequency shifts. With the pseudo-wavefunctions provided by the nonlocal model, the relaxation times in terms of Dingle temperatures for several orbits have been predicted using Sorbello's multiple-plane-wave phase shift model. The calculation with phase shifts obtained from a model potential yields a greater anisotropy than has been observed experimentally, while a two-parameter phase shift model provides a good fit to the experimental results
International Nuclear Information System (INIS)
White, W.T. III.
1985-01-01
We have studied two-photon absorption in solids theoretically and experimentally. We have shown that it is possible to use accurate band structure techniques to compute two-photon absorption spectra within 15% of measured values in a wide band-gap material, ZnS. The empirical pseudopotential technique that we used is significantly more accurate than previous models of two-photon absorption in zinc blende materials, including present tunneling theories (which are essentially parabolic-band results in disguise) and the nonparabolic-band formalism of Pidgeon et al. and Weiler. The agreement between our predictions and previous measurements allowed us to use ZnS as a reference material in order to validate a technique for measuring two-photon absorption that was previously untried in solids, pulsed dual-beam thermal lensing. With the validated technique, we examined nonlinear absorption in one other crystal (rutile) and in several glasses, including silicates, borosilicates, and one phosphate glass. Initially, we believed that the absorption edges of all the materials were comparable; however, subsequent evidence suggested that the effective band-gap energies of the glasses were above the energy of two photons in our measurement. Therefore, we attribute the nonlinear absorption that we observed in glasses to impurities or defects. The measured nonlinear absorption coefficients were of the order of a few cm/TW in the glasses and of the order of 10 cm/GW in the crystals, four orders of magnitude higher than in glasses. 292 refs
Energy Technology Data Exchange (ETDEWEB)
White, W.T. III
1985-11-04
We have studied two-photon absorption in solids theoretically and experimentally. We have shown that it is possible to use accurate band structure techniques to compute two-photon absorption spectra within 15% of measured values in a wide band-gap material, ZnS. The empirical pseudopotential technique that we used is significantly more accurate than previous models of two-photon absorption in zinc blende materials, including present tunneling theories (which are essentially parabolic-band results in disguise) and the nonparabolic-band formalism of Pidgeon et al. and Weiler. The agreement between our predictions and previous measurements allowed us to use ZnS as a reference material in order to validate a technique for measuring two-photon absorption that was previously untried in solids, pulsed dual-beam thermal lensing. With the validated technique, we examined nonlinear absorption in one other crystal (rutile) and in several glasses, including silicates, borosilicates, and one phosphate glass. Initially, we believed that the absorption edges of all the materials were comparable; however, subsequent evidence suggested that the effective band-gap energies of the glasses were above the energy of two photons in our measurement. Therefore, we attribute the nonlinear absorption that we observed in glasses to impurities or defects. The measured nonlinear absorption coefficients were of the order of a few cm/TW in the glasses and of the order of 10 cm/GW in the crystals, four orders of magnitude higher than in glasses. 292 refs.
Ab initio pseudopotential studies of cubic BC2N under high pressure
International Nuclear Information System (INIS)
Pan Zicheng; Sun Hong; Chen Changfeng
2005-01-01
We present the results of a systematic study of the structural, electronic, and vibrational properties of various cubic BC 2 N phases under high pressure. Ab initio pseudopotential total-energy and phonon calculations have been carried out to examine the changes in the structural parameters, bonding behaviours, band structures, and dynamic instabilities caused by phonon softening in these phases. We find that an experimentally synthesized high-density phase of cubic BC 2 N exhibits outstanding stability in the structural and electronic properties up to very high pressures. On the other hand, another experimentally identified phase with lower density and lower symmetry undergoes a dramatic structural transformation with a volume and bond-length collapse and a concomitant semi-metal to semiconductor transition. A third phase is predicted to be favourable over the above-mentioned lower-density phase by the enthalpy calculations. However, the dynamic phonon calculations reveal that it develops imaginary phonon modes and, therefore, is unstable in the experimental pressure range. The calculations indicate that its synthesis may be achieved at reduced pressures. These results provide a comprehensive understanding for the high-pressure behaviour of the cubic BC 2 N phases and reveal their interesting properties that can be verified by experiments
International Nuclear Information System (INIS)
Zunger, A.; Cohen, M.L.
1978-01-01
We present a method for obtaining first-principles nonlocal atomic pseudopotentials in the density-functional formalism by direct inversion of the pseudopotential eigenvalue problem, where the pseudo-wave-functions are represented as a unitary rotation of the exact all-electron wave functions. The usual pseudopotential nonuniqueness of the orbitals is fixed by imposing the physically appealing constraints of maximum similarity to the all-electron wave functions and minimum radial kinetic energy. These potentials are shown to yield very accurate energy eigenvalues, total energy differences, and wave-function moments over a wide range of excited atomic configurations. We have calculated the potentials for 68 transition and nontransition elements of rows 1--5 in the Periodic Table. Their characteristic features, such as classical turning points and minimum potential radii, faithfully reflect the chemical regularities of the Periodic Table. The nonempirical nature of these potentials permits both an analysis of their dominant features in terms of the underlying interelectronic potentials and the systematic improvement of their predictions through inclusion of appropriate correlation terms. As these potentials accurately reproduce both energy eigenvalues and wave functions and can be readily fit to analytic forms with known asymptotic behavior, they can be used directly for studies of many structural and electronic properties of solids
Sohrabi, Salman; Liu, Yaling
2018-03-01
Pseudopotential lattice Boltzmann methods (LBMs) can simulate a phase transition in high-density ratio multiphase flow systems. If coupled with thermal LBMs through equation of state, they can be used to study instantaneous phase transition phenomena with a high-temperature gradient where only one set of formulations in an LBM system can handle liquid, vapor, phase transition, and heat transport. However, at lower temperatures an unrealistic spurious current at the interface introduces instability and limits its application in real flow system. In this study, we proposed new modifications to the LBM system to minimize a spurious current which enables us to study nucleation dynamic at room temperature. To demonstrate the capabilities of this approach, the thermal ejection process is modeled as one example of a complex flow system. In an inkjet printer, a thermal pulse instantly heats up the liquid in a microfluidic chamber and nucleates bubble vapor providing the pressure pulse necessary to eject droplets at high speed. Our modified method can present a more realistic model of the explosive vaporization process since it can also capture a high-temperature/density gradient at nucleation region. Thermal inkjet technology has been successfully applied for printing cells, but cells are susceptible to mechanical damage or death as they squeeze out of the nozzle head. To study cell deformation, a spring network model, representing cells, is connected to the LBM through the immersed boundary method. Looking into strain and stress distribution of a cell membrane at its most deformed state, it is found that a high stretching rate effectively increases the rupture tension. In other words, membrane deformation energy is released through creation of multiple smaller nanopores rather than big pores. Overall, concurrently simulating multiphase flow, phase transition, heat transfer, and cell deformation in one unified LB platform, we are able to provide a better insight into the
Exact exchange plane-wave-pseudopotential calculations for slabs: Extending the width of the vacuum
Engel, Eberhard
2018-04-01
Standard plane-wave pseudopotential (PWPP) calculations for slabs such as graphene become extremely demanding, as soon as the exact exchange (EXX) of density functional theory is applied. Even if the Krieger-Li-Iafrate (KLI) approximation for the EXX potential is utilized, such EXX-PWPP calculations suffer from the fact that an accurate representation of the occupied states throughout the complete vacuum between the replicas of the slab is required. In this contribution, a robust and efficient extension scheme for the PWPP states is introduced, which ensures the correct exponential decay of the slab states in the vacuum for standard cutoff energies and therefore facilitates EXX-PWPP calculations for very wide vacua and rather thick slabs. Using this scheme, it is explicitly verified that the Slater component of the EXX/KLI potential decays as -1 /z over an extended region sufficiently far from the surface (assumed to be perpendicular to the z direction) and from the middle of the vacuum, thus reproducing the asymptotic behavior of the exact EXX potential of a single slab. The calculations also reveal that the orbital-shift component of the EXX/KLI potential is quite sizable in the asymptotic region. In spite of the long-range exchange potential, the replicas of the slab decouple rather quickly with increasing width of the vacuum. Relying on the identity of the work function with the Fermi energy obtained with a suitably normalized total potential, the present EXX/KLI calculations predict work functions for both graphene and the Si(111) surface which are substantially larger than the corresponding experimental data. Together with the size of the orbital-shift potential in the asymptotic region, the very large EXX/KLI work functions indicate a failure of the KLI approximation for nonmetallic slabs.
Sohrabi, Salman; Liu, Yaling
2018-03-01
Pseudopotential lattice Boltzmann methods (LBMs) can simulate a phase transition in high-density ratio multiphase flow systems. If coupled with thermal LBMs through equation of state, they can be used to study instantaneous phase transition phenomena with a high-temperature gradient where only one set of formulations in an LBM system can handle liquid, vapor, phase transition, and heat transport. However, at lower temperatures an unrealistic spurious current at the interface introduces instability and limits its application in real flow system. In this study, we proposed new modifications to the LBM system to minimize a spurious current which enables us to study nucleation dynamic at room temperature. To demonstrate the capabilities of this approach, the thermal ejection process is modeled as one example of a complex flow system. In an inkjet printer, a thermal pulse instantly heats up the liquid in a microfluidic chamber and nucleates bubble vapor providing the pressure pulse necessary to eject droplets at high speed. Our modified method can present a more realistic model of the explosive vaporization process since it can also capture a high-temperature/density gradient at nucleation region. Thermal inkjet technology has been successfully applied for printing cells, but cells are susceptible to mechanical damage or death as they squeeze out of the nozzle head. To study cell deformation, a spring network model, representing cells, is connected to the LBM through the immersed boundary method. Looking into strain and stress distribution of a cell membrane at its most deformed state, it is found that a high stretching rate effectively increases the rupture tension. In other words, membrane deformation energy is released through creation of multiple smaller nanopores rather than big pores. Overall, concurrently simulating multiphase flow, phase transition, heat transfer, and cell deformation in one unified LB platform, we are able to provide a better insight into the
Qin, Feifei; Mazloomi Moqaddam, Ali; Kang, Qinjun; Derome, Dominique; Carmeliet, Jan
2018-03-01
An entropic multiple-relaxation-time lattice Boltzmann approach is coupled to a multirange Shan-Chen pseudopotential model to study the two-phase flow. Compared with previous multiple-relaxation-time multiphase models, this model is stable and accurate for the simulation of a two-phase flow in a much wider range of viscosity and surface tension at a high liquid-vapor density ratio. A stationary droplet surrounded by equilibrium vapor is first simulated to validate this model using the coexistence curve and Laplace's law. Then, two series of droplet impact behavior, on a liquid film and a flat surface, are simulated in comparison with theoretical or experimental results. Droplet impact on a liquid film is simulated for different Reynolds numbers at high Weber numbers. With the increase of the Sommerfeld parameter, onset of splashing is observed and multiple secondary droplets occur. The droplet spreading ratio agrees well with the square root of time law and is found to be independent of Reynolds number. Moreover, shapes of simulated droplets impacting hydrophilic and superhydrophobic flat surfaces show good agreement with experimental observations through the entire dynamic process. The maximum spreading ratio of a droplet impacting the superhydrophobic flat surface is studied for a large range of Weber numbers. Results show that the rescaled maximum spreading ratios are in good agreement with a universal scaling law. This series of simulations demonstrates that the proposed model accurately captures the complex fluid-fluid and fluid-solid interfacial physical processes for a wide range of Reynolds and Weber numbers at high density ratios.
Study of the atomic ordering in the alloys Ni-Ir using diffuse X-ray scattering and pseudopotentials
International Nuclear Information System (INIS)
Abbas, T.
1982-06-01
Experiments were performed on the Ni-Ir alloys to measure the diffuse X-ray scattering intensity after annealing from high temperatures. It was established that the short-range order exists in these alloys when the samples are quenched from 1200 0 C and 1400 0 C. The ordering potentials for various concentrations of Ir in Ni were calculated using the pseudopotentials of Animalu. The method of incorporating the d electrons in the dielectric screening function was proposed. It was shown that the ordering potential is severely affected by the new type of screening. (author)
International Nuclear Information System (INIS)
Green, Timothy F. G.; Yates, Jonathan R.
2014-01-01
We present a method for the first-principles calculation of nuclear magnetic resonance (NMR) J-coupling in extended systems using state-of-the-art ultrasoft pseudopotentials and including scalar-relativistic effects. The use of ultrasoft pseudopotentials is allowed by extending the projector augmented wave (PAW) method of Joyce et al. [J. Chem. Phys. 127, 204107 (2007)]. We benchmark it against existing local-orbital quantum chemical calculations and experiments for small molecules containing light elements, with good agreement. Scalar-relativistic effects are included at the zeroth-order regular approximation level of theory and benchmarked against existing local-orbital quantum chemical calculations and experiments for a number of small molecules containing the heavy row six elements W, Pt, Hg, Tl, and Pb, with good agreement. Finally, 1 J(P-Ag) and 2 J(P-Ag-P) couplings are calculated in some larger molecular crystals and compared against solid-state NMR experiments. Some remarks are also made as to improving the numerical stability of dipole perturbations using PAW
Petruzielo, F R; Toulouse, Julien; Umrigar, C J
2011-02-14
A simple yet general method for constructing basis sets for molecular electronic structure calculations is presented. These basis sets consist of atomic natural orbitals from a multiconfigurational self-consistent field calculation supplemented with primitive functions, chosen such that the asymptotics are appropriate for the potential of the system. Primitives are optimized for the homonuclear diatomic molecule to produce a balanced basis set. Two general features that facilitate this basis construction are demonstrated. First, weak coupling exists between the optimal exponents of primitives with different angular momenta. Second, the optimal primitive exponents for a chosen system depend weakly on the particular level of theory employed for optimization. The explicit case considered here is a basis set appropriate for the Burkatzki-Filippi-Dolg pseudopotentials. Since these pseudopotentials are finite at nuclei and have a Coulomb tail, the recently proposed Gauss-Slater functions are the appropriate primitives. Double- and triple-zeta bases are developed for elements hydrogen through argon. These new bases offer significant gains over the corresponding Burkatzki-Filippi-Dolg bases at various levels of theory. Using a Gaussian expansion of the basis functions, these bases can be employed in any electronic structure method. Quantum Monte Carlo provides an added benefit: expansions are unnecessary since the integrals are evaluated numerically.
Moriarty, John A.
1988-08-01
The first-principles, density-functional version of the generalized pseudopotential theory (GPT) developed in papers I and II of this series [Phys. Rev. B 16, 2537 (1977); 26, 1754 (1982)] for empty- and filled-d-band metals is here extended to pure transition metals with partially filled d bands. The present focus is on a rigorous, real-space expansion of the bulk total energy in terms of widely transferable, structure-independent interatomic potentials, including both central-force pair interactions and angular-force triplet and quadruplet interactions. To accomplish this expansion, a specialized set of starting equations is derived from the basic local-density formalism for a pure metal, including refined expansions for the exchange-correlation terms and a simplified yet accurate representation of the cohesive energy. The parent pseudo-Green's-function formalism of the GPT is then used to develop these equations in a plane-wave, localized-d-state basis. In this basis, the cohesive energy divides quite naturally into a large volume component and a smaller structural component. The volume component,which includes all one-ion intra-atomic energy contributions, already gives a good description of the cohesion in lowest order. The structural component is expanded in terms of weak interatomic matrix elements and gives rise to a multi-ion series which establishes the interatomic potentials. Special attention is focused on the dominant d-electron contributions to this series and complete formal results for the two-ion, three-ion, and four-ion d-state potentials (vd2, vd3, and vd4) are derived. In addition, a simplified model is used to demonstrate that while vd3 can be of comparable importance to vd2, vd4 is inherently small and the series is rapidly convergent beyond three-ion interactions. Analytic model forms are also derived for vd2 and vd3 in the case of canonical d bands. In this limit, vd2 is purely attractive and varies with interatomic distance as r-10, while
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Shulenburger, Luke [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Mattsson, Thomas Kjell Rene [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Desjarlais, Michael Paul [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2015-01-01
Motivated by the disagreement between recent diffusion Monte Carlo calculations of the phase transition pressure between the ambient and beta-Sn phases of silicon and experiments, we present a study of the HCP to BCC phase transition in beryllium. This lighter element provides an opportunity for directly testing many of the approximations required for calculations on silicon and may suggest a path towards increasing the practical accuracy of diffusion Monte Carlo calculations of solids in general. We demonstrate that the single largest approximation in these calculations is the pseudopotential approximation and after removing this we find excellent agreement with experiment for the ambient HCP phase and results similar to careful calculations using density functional theory for the phase transition pressure.
International Nuclear Information System (INIS)
Beckman, S.P.; Chelikowsky, James R.
2007-01-01
The structure and properties of vacancies in a 2 nm Si nano-crystal are studied using a real space density functional theory/pseudopotential method. It is observed that a vacancy's electronic properties and energy of formation are directly related to the local symmetry of the vacancy site. The formation energy for vacancies and Frenkel pair are calculated. It is found that both defects have lower energy in smaller crystals. In a 2 nm nano-crystal the energy to form a Frenkel pair is 1.7 eV and the energy to form a vacancy is no larger than 2.3 eV. The energy barrier for vacancy diffusion is examined via a nudged elastic band algorithm
Simulated non-contact atomic force microscopy for GaAs surfaces based on real-space pseudopotentials
International Nuclear Information System (INIS)
Kim, Minjung; Chelikowsky, James R.
2014-01-01
We simulate non-contact atomic force microscopy (AFM) with a GaAs(1 1 0) surface using a real-space ab initio pseudopotential method. While most ab initio simulations include an explicit model for the AFM tip, our method does not introduce the tip modeling step. This approach results in a considerable reduction of computational work, and also provides complete AFM images, which can be directly compared to experiment. By analyzing tip-surface interaction forces in both our results and previous ab initio simulations, we find that our method provides very similar force profile to the pure Si tip results. We conclude that our method works well for systems in which the tip is not chemically active.
Energy Technology Data Exchange (ETDEWEB)
Fang, Jingtian, E-mail: jingtian.fang@utdallas.edu; Vandenberghe, William G.; Fu, Bo; Fischetti, Massimo V. [Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080 (United States)
2016-01-21
We present a formalism to treat quantum electronic transport at the nanometer scale based on empirical pseudopotentials. This formalism offers explicit atomistic wavefunctions and an accurate band structure, enabling a detailed study of the characteristics of devices with a nanometer-scale channel and body. Assuming externally applied potentials that change slowly along the electron-transport direction, we invoke the envelope-wavefunction approximation to apply the open boundary conditions and to develop the transport equations. We construct the full-band open boundary conditions (self-energies of device contacts) from the complex band structure of the contacts. We solve the transport equations and present the expressions required to calculate the device characteristics, such as device current and charge density. We apply this formalism to study ballistic transport in a gate-all-around (GAA) silicon nanowire field-effect transistor with a body-size of 0.39 nm, a gate length of 6.52 nm, and an effective oxide thickness of 0.43 nm. Simulation results show that this device exhibits a subthreshold slope (SS) of ∼66 mV/decade and a drain-induced barrier-lowering of ∼2.5 mV/V. Our theoretical calculations predict that low-dimensionality channels in a 3D GAA architecture are able to meet the performance requirements of future devices in terms of SS swing and electrostatic control.
International Nuclear Information System (INIS)
Holzwarth, N.A.; Matthews, G.E.; Dunning, R.B.; Tackett, A.R.; Zeng, Y.
1997-01-01
The projector augmented-wave (PAW) method was developed by Bloechl as a method to accurately and efficiently calculate the electronic structure of materials within the framework of density-functional theory. It contains the numerical advantages of pseudopotential calculations while retaining the physics of all-electron calculations, including the correct nodal behavior of the valence-electron wave functions and the ability to include upper core states in addition to valence states in the self-consistent iterations. It uses many of the same ideas developed by Vanderbilt in his open-quotes soft pseudopotentialclose quotes formalism and in earlier work by Bloechl in his open-quotes generalized separable potentials,close quotes and has been successfully demonstrated for several interesting materials. We have developed a version of the PAW formalism for general use in structural and dynamical studies of materials. In the present paper, we investigate the accuracy of this implementation in comparison with corresponding results obtained using pseudopotential and linearized augmented-plane-wave (LAPW) codes. We present results of calculations for the cohesive energy, equilibrium lattice constant, and bulk modulus for several representative covalent, ionic, and metallic materials including diamond, silicon, SiC, CaF 2 , fcc Ca, and bcc V. With the exception of CaF 2 , for which core-electron polarization effects are important, the structural properties of these materials are represented equally well by the PAW, LAPW, and pseudopotential formalisms. copyright 1997 The American Physical Society
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Silva, Cleuton de Souza [Instituto de Química, Universidade Estadual de Campinas, Barão Geraldo, P.O. Box 6154, 13083-970 Campinas, São Paulo (Brazil); Instituto de Ciências Exatas e Tecnologia, Universidade Federal do Amazonas, Campus de Itacoatiara, 69100-021 Itacoatiara, Amazonas (Brazil); Pereira, Douglas Henrique [Departamento de Ciências Exatas e Biotecnológicas, Universidade Federal do Tocantins, Campus de Gurupi, 77410-530 Gurupi, Tocantins (Brazil); Custodio, Rogério, E-mail: roger@iqm.unicamp.br [Instituto de Química, Universidade Estadual de Campinas, Barão Geraldo, P.O. Box 6154, 13083-970 Campinas, São Paulo (Brazil)
2016-05-28
The G4CEP composite method was developed from the respective G4 all-electron version by considering the implementation of compact effective pseudopotential (CEP). The G3/05 test set was used as reference to benchmark the adaptation by treating in this work atoms and compounds from the first and second periods of the periodic table, as well as representative elements of the third period, comprising 440 thermochemical data. G4CEP has not reached a so high level of accuracy as the G4 all-electron theory. G4CEP presented a mean absolute error around 1.09 kcal mol{sup −1}, while the original method presents a deviation corresponding to 0.83 kcal mol{sup −1}. The similarity of the optimized molecular geometries between G4 and G4CEP indicates that the core-electron effects and basis set adjustments may be pointed out as a significant factor responsible for the large discrepancies between the pseudopotential results and the experimental data, or even that the all-electron calculations are more efficient either in its formulation or in the cancellation of errors. When the G4CEP mean absolute error (1.09 kcal mol{sup −1}) is compared to 1.29 kcal mol{sup −1} from G3CEP, it does not seem so efficient. However, while the G3CEP uncertainty is ±4.06 kcal mol{sup −1}, the G4CEP deviation is ±2.72 kcal mol{sup −1}. Therefore, the G4CEP theory is considerably more reliable than any previous combination of composite theory and pseudopotential, particularly for enthalpies of formation and electron affinities.
Skripnikov, L V
2016-12-07
A precise theoretical study of the electronic structure of heavy atom diatomic molecules is of key importance to interpret the experiments in the search for violation of time-reversal (T) and spatial-parity (P) symmetries of fundamental interactions in terms of the electron electric dipole moment, eEDM, and dimensionless constant, k T,P , characterizing the strength of the T,P-odd pseudoscalar-scalar electron-nucleus neutral current interaction. The ACME collaboration has recently improved limits on these quantities using a beam of ThO molecules in the electronic H 3 Δ 1 state [J. Baron et al., Science 343, 269 (2014)]. We apply the combined direct relativistic 4-component and two-step relativistic pseudopotential/restoration approaches to a benchmark calculation of the effective electric field, E eff , parameter of the T,P-odd pseudoscalar-scalar interaction, W T,P , and hyperfine structure constant in Δ13 state of the ThO molecule. The first two parameters are required to interpret the experimental data in terms of the eEDM and k T,P constant. We have investigated the electron correlation for all of the 98 electrons of ThO simultaneously up to the level of the coupled cluster with single, double, and noniterative triple amplitudes, CCSD(T), theory. Contributions from iterative triple and noniterative quadruple cluster amplitudes for the valence electrons have been also treated. The obtained values are E eff = 79.9 GV/cm, W T,P = 113.1 kHz. The theoretical uncertainty of these values is estimated to be about two times smaller than that of our previous study [L. V. Skripnikov and A. V. Titov, J. Chem. Phys., 142, 024301 (2015)]. It was found that the correlation of the inner- and outer-core electrons contributes 9% to the effective electric field. The values of the molecule frame dipole moment of the Δ13 state and the H 3 Δ 1 →X 1 Σ + transition energy of ThO calculated within the same methods are in a very good agreement with the experiment.
International Nuclear Information System (INIS)
Smardon, R.D.; Srivastava, G.P.
2004-01-01
Using a first principles pseudopotential method we have studied the adsorption of H on the high index Si(1 1 4)-(2x1) surface within the local density approximation. This stable surface is found to be both chemically and electronically passivated by two different coverages of hydrogen: 1.0 ML and 1.5 ML. For the 1.0 ML coverage all the A- and B-type dimer bond lengths have equalised to 2.40 Angst and the rebonded lengths are slightly longer at 2.48 Angst. Hydrogen passivation, for both coverages, leads the surface bands of the clean Si(1 1 4)-(2x1) surface to move into the bulk valence and conduction bands. Differences in the density of states for the clean, 1.0 ML and 1.5 ML coverages were observed and are discussed
International Nuclear Information System (INIS)
Khwaja, F.A.
1980-08-01
The calculations for the temperature dependence of the first shell short-range order (SRO) parameter for Ni 3 Fe using the cubic approximation of Tahir Kheli, and the concentration dependence of order-disorder temperature Tsub(c) for Ni-Fe and Ni-Pt systems using the linear approximation, have been carried out in the framework of pseudopotential theory. It is shown that the cubic approximation yields a good agreement between the theoretical prediction of the α 1 and the experimental data. Results for the concentration dependence of the Tsub(c) show that improvements in the statistical pseudo-potential approach are essential to achieve a good agreement with experiment. (author)
International Nuclear Information System (INIS)
Fares, Nour El-Houda; Bouarissa, Nadir
2016-01-01
Highlights: • Electron band structure and related properties in Al_xIn_1_−_xSb. • Positron characteristics in Al_xIn_1_−_xSb. • Differences and similarities between electronic and positronic properties in Al_xIn_1_−_xSb. • Investigation of positron annihilation in Al_xIn_1_−_xSb semiconductor alloys. - Abstract: Based on a pseudopotential approach under the virtual-crystal approximation, the electron and positron band structures and their derived properties have been investigated for zinc-blende Al_xIn_1_−_xSb ternary semiconductor alloys. The effect of compositional disorder on electron and positron band structures has been examined and discussed. Moreover, the differences and the similarities between electron and positron characteristics in the material system of interest have been analyzed. The present study reveals possibilities for the investigation of the positron annihilation in Al_xIn_1_−_xSb.
Duan, Xiaofeng F; Burggraf, Larry W; Huang, Lingyu
2013-07-22
To find low energy Si(n)C(n) structures out of hundreds to thousands of isomers we have developed a general method to search for stable isomeric structures that combines Stochastic Potential Surface Search and Pseudopotential Plane-Wave Density Functional Theory Car-Parinello Molecular Dynamics simulated annealing (PSPW-CPMD-SA). We enhanced the Sunders stochastic search method to generate random cluster structures used as seed structures for PSPW-CPMD-SA simulations. This method ensures that each SA simulation samples a different potential surface region to find the regional minimum structure. By iterations of this automated, parallel process on a high performance computer we located hundreds to more than a thousand stable isomers for each Si(n)C(n) cluster. Among these, five to 10 of the lowest energy isomers were further optimized using B3LYP/cc-pVTZ method. We applied this method to Si(n)C(n) (n = 4-12) clusters and found the lowest energy structures, most not previously reported. By analyzing the bonding patterns of low energy structures of each Si(n)C(n) cluster, we observed that carbon segregations tend to form condensed conjugated rings while Si connects to unsaturated bonds at the periphery of the carbon segregation as single atoms or clusters when n is small and when n is large a silicon network spans over the carbon segregation region.
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Larry W. Burggraf
2013-07-01
Full Text Available To find low energy SinCn structures out of hundreds to thousands of isomers we have developed a general method to search for stable isomeric structures that combines Stochastic Potential Surface Search and Pseudopotential Plane-Wave Density Functional Theory Car-Parinello Molecular Dynamics simulated annealing (PSPW-CPMD-SA. We enhanced the Sunders stochastic search method to generate random cluster structures used as seed structures for PSPW-CPMD-SA simulations. This method ensures that each SA simulation samples a different potential surface region to find the regional minimum structure. By iterations of this automated, parallel process on a high performance computer we located hundreds to more than a thousand stable isomers for each SinCn cluster. Among these, five to 10 of the lowest energy isomers were further optimized using B3LYP/cc-pVTZ method. We applied this method to SinCn (n = 4–12 clusters and found the lowest energy structures, most not previously reported. By analyzing the bonding patterns of low energy structures of each SinCn cluster, we observed that carbon segregations tend to form condensed conjugated rings while Si connects to unsaturated bonds at the periphery of the carbon segregation as single atoms or clusters when n is small and when n is large a silicon network spans over the carbon segregation region.
Hill, J. Grant; Peterson, Kirk A.
2017-12-01
New correlation consistent basis sets based on pseudopotential (PP) Hamiltonians have been developed from double- to quintuple-zeta quality for the late alkali (K-Fr) and alkaline earth (Ca-Ra) metals. These are accompanied by new all-electron basis sets of double- to quadruple-zeta quality that have been contracted for use with both Douglas-Kroll-Hess (DKH) and eXact 2-Component (X2C) scalar relativistic Hamiltonians. Sets for valence correlation (ms), cc-pVnZ-PP and cc-pVnZ-(DK,DK3/X2C), in addition to outer-core correlation [valence + (m-1)sp], cc-p(w)CVnZ-PP and cc-pwCVnZ-(DK,DK3/X2C), are reported. The -PP sets have been developed for use with small-core PPs [I. S. Lim et al., J. Chem. Phys. 122, 104103 (2005) and I. S. Lim et al., J. Chem. Phys. 124, 034107 (2006)], while the all-electron sets utilized second-order DKH Hamiltonians for 4s and 5s elements and third-order DKH for 6s and 7s. The accuracy of the basis sets is assessed through benchmark calculations at the coupled-cluster level of theory for both atomic and molecular properties. Not surprisingly, it is found that outer-core correlation is vital for accurate calculation of the thermodynamic and spectroscopic properties of diatomic molecules containing these elements.
Hill, J Grant; Peterson, Kirk A
2017-12-28
New correlation consistent basis sets based on pseudopotential (PP) Hamiltonians have been developed from double- to quintuple-zeta quality for the late alkali (K-Fr) and alkaline earth (Ca-Ra) metals. These are accompanied by new all-electron basis sets of double- to quadruple-zeta quality that have been contracted for use with both Douglas-Kroll-Hess (DKH) and eXact 2-Component (X2C) scalar relativistic Hamiltonians. Sets for valence correlation (ms), cc-pVnZ-PP and cc-pVnZ-(DK,DK3/X2C), in addition to outer-core correlation [valence + (m-1)sp], cc-p(w)CVnZ-PP and cc-pwCVnZ-(DK,DK3/X2C), are reported. The -PP sets have been developed for use with small-core PPs [I. S. Lim et al., J. Chem. Phys. 122, 104103 (2005) and I. S. Lim et al., J. Chem. Phys. 124, 034107 (2006)], while the all-electron sets utilized second-order DKH Hamiltonians for 4s and 5s elements and third-order DKH for 6s and 7s. The accuracy of the basis sets is assessed through benchmark calculations at the coupled-cluster level of theory for both atomic and molecular properties. Not surprisingly, it is found that outer-core correlation is vital for accurate calculation of the thermodynamic and spectroscopic properties of diatomic molecules containing these elements.
Energy Technology Data Exchange (ETDEWEB)
Ukhov, S B
1975-01-01
This book presents the analytical methods which are used to describe the processes of the deformation and collapse of the rock-dirt foundations of dams, and techniques are presented for experimentally determining the mechanical properties of fissured rock-dirt under natural conditions. A determination is made of the required complex of engineering-geological, geophysical and geomechanical methods of investigation for calculating the interaction of the structure and the foundation, and a report is also given on the main assumptions of such calculations by using the method of finite elements. Methods are recommended for estimating the effect of engineering actions on the change in mechanical properties of the rock-dirt foundation. The book is intended for engineering dealing with the search and design of dam structures constructed on rock foundations. 126 refs.
Energy Technology Data Exchange (ETDEWEB)
Profio, A. E.; Koppel, J. U. [General Atomic Division of General Dynamics Corporation, John Jay Hopkins Laboratory for Pure and Applied Science, San Diego, CA (United States); Adamantiades, A. [Massachusetts Institute of Technology, Cambridge, MA (United States)
1965-08-15
The mean time and variance in time for neutrons from an impulse source to slow down and migrate to the energy, angle and position of observation are important quantities in many experiments. The mean time is a correction in time-of-flight measurements of neutron spectra in bulk media, and the variance limits the ultimate resolution of such experiments. These parameters are equally significant in detectors which depend on moderation, in time-of-flight experiments where low energy neutrons are provided by a moderator placed near the pulsed source, and in slowing-down-time spectrometry. Various analytical and numerical methods have been developed to calculate the space-energy-angle-time . dependence, or integrals thereof. It is shown that the time moments, Empty-Set {sup (n)} (r, {Omega}, v, t) = {integral}{sub 0}{sup {infinity}}t{sup n} Empty-Set (r, {Omega}, v, t)dt, can be calculated by repeated application of a steady state transport code. The source term for the calculation of the n{sup -tb} moment is equal to nv{sup -1} Empty-Set {sup (n-1)}. Results are presented for multiplying and non-multiplying mockups of the TRIGA reactor. Another powerful calculational method is the time-dependent Monte Carlo code. Results of a calculation of leakage flux from a thin lead slab are presented. Measurements have been made of the slowing-down time to the cadmium edge and to the 1.46-eV resonance of indium in water and in toluene. Capture gamma rays are detected by a scintillation counter. The technique requires a fairly intense source and efficient detector because of the low duty cycle (short burst width for resolution of the slowing-down time, large interpulse period for thermal neutron die-away) and the small probability for capture. (author) [French] Dans le phenomene de ralentissement et de migration des neutrons puises, amenes a l'enetgie, a l'angle et S la position d'observation, le temps moyen et la variance en temps sont des grandeurs importantes pour beaucoup d'experiences. Le temps moyen est une correction pour les mesures par la methode du temps de vol des spectres de neutrons dans des milieux de grande diffusion, et la variance a pour effet d'imposer une limite a la resolution des experiences. La grandeur de ces parametres est egalement importante pour les detecteurs qui dependent du ralentissement, dans les experiences par | la methode du temps de vol des spectres de neutrons de faible energie sont fournis par un ralentisseur place pres de la source puisee, et en spectrometrie du temps de ralentissement. Diverses methodes analytiques et numeriques ont ete mises au point pour calculer la fonction espaceenergie- angle-temps ou des integrales de cette fonction. Les auteurs montrent que les moments Empty-Set {sup (n)} (r, {Omega}, v, t) = {integral}{sub 0}{sup {infinity}}t{sup n} Empty-Set (r, {Omega}, v, t)dt peuvent etre calcules par application repetee d'un code de transport pour un etat stationnaire. Le terme de la source pour le calcul du nieme moment est egal a nv{sup -1} Empty-Set {sup (n-1)}. Les auteurs presentent des resultats pour des modeles multiplicateurs et non multiplicateurs du reacteur Triga. Une autre methode de calcul tres utile est le code de Monte-Carlo variable dans le temps. Les auteurs presentent les resultats d'un calcul de flux de fuite a partir d'une mince plaque de plomb. Les auteurs ont mesure le temps de ralentissement jusqu 'au seuil cadmium et jusqu 'a la resonance 1,46 eV de l'indium dans l'eau et dans le toluene. Ils ont deceleles rayonsgamma de capture avec un compteura scintillation. La methode necessite l'utilisation d'une source assez intense et d'un detecteur efficace a cause de la brievete du cycle de fonctionnement (petite largeur de bouffee pour la resolution du temps de ralentissement, grand intervalle entre les bouffees pour l'evanouissement des neutrons thermiques) et de la faible probabilite de capture. (author) [Spanish] En muchos experimentos, reviste gran importancia el tiempo medio que transcurre hasta que la velocidad de los neutrones pulsados disminuya en la medida necesaria para que estos alcancen la energia, el angulo y la posicion de observacion apetecidas. El tiempo medio es una correccion de las mediciones de espectros neutronicos en la masa hechas segun el metodo del tiempo de vuelo, y la variacion impone limites al poder de resolucion efectivo de tales experimentos. Estos parametros son igualmente importantes en los detectores cuyo funcionamiento se base en la moderacion, en los experimentos con el metodo de tiempo de vuelo en los que un moderador situado cerca de la fuente de neutrones pulsados proporciona neutrones de baja energia, y en la espectrometria del tiempo de moderacion. Se han ideado diversos metodos analfticos y numericos para calcular la distribucion espacio-energia angulo-tiempo o sus integrales. Ha podido demostrarse que los momentos temporales Empty-Set {sup (n)} (r, {Omega}, v, t) = {integral}{sub 0}{sup {infinity}}t{sup n} Empty-Set (r, {Omega}, v, t)dt, pueden calcularse aplicando repetidamente una clave de transporte en regimen estacionario. El termino de la fuente para el calculo del momento 'n'es igual a nv{sup -1} Empty-Set {sup (n-1)}. Los autores presentan los resultados correspondientes a maquetas del reactor TRIGA en las que se emplean medios multiplicadores y no multiplicadores. Otro valioso metodo de calculo consiste en emplear una clave de Monte Cario en funcion del tiempo. Los autores exponen los resultados del calculo de un flujo que escapa de una delgada placa de plomo. Se han hecho mediciones del tiempo de moderacion hasta la energia de corte del Cd y hasta la resonancia de 1,46 eV del In en agua y en tolueno. Los rayos gamma de captura se detectaron con un contador de centelleo. Esta tecnica exige disponer de una fuente de suficiente intensidad y de un detector eficaz debido a la brevedad del ciclo de trabajo (escasa anchura de las rafagas para la resolucion del tiempo de moderacion y amplio intervalo entre los impulsos para observar la atenuacion neutronica de caracter termico) y a las escasas probabilidades de captura. (author) [Russian] Srednee vremja i izmenenie vo vremeni zhizni nejtronov, poluchaemyh ot impul'snogo istochnika, s cel'ju ih zamedlenija i migracii do velichiny energii, ugla i polozhenija, udobnogo dlja nabljudenija, javljajutsja sushhestvennymi kolichestvennymi velichinami vo mnogih jeksperimentah. Srednee vremja javljaetsja popravkoj v izmerenijah nejtronnyh spektrov po metodu vremeni proleta v bol'shih ob{sup e}mah materialov, a izmenenie ogranichivaet maksimal'nuju razreshajushhuju spo- sobnost' takih jeksperimentov. Jeti parametry odinakovo vazhny v detektorah, zavisjashhih ot zamedlenija, v jeksperimentah po vremeni proleta, gde nejtrony s maloj energiej postu- pajut iz zamedlitelja, nahodjashhegosja vblizi pul'sirujushhego istochnika, a takzhe spektrometrii vremeni zamedlenija. Razrabotany razlichnye analiticheskie i cifrovye sposoby dlja vychislenija zavisimosti prostranstvennogo-energeticheskogo-uglovogo i vremennogo raspredelenija ili integralov po nim. Pokazano, chto momenty vremeni Empty-Set {sup (n)} (r, {Omega}, v, t) = {integral}{sub 0}{sup {infinity}}t{sup n} Empty-Set (r, {Omega}, v, t)dt, mozhno vyschitat' putem povtornogo primenenija programmy rascheta dlja stacionarnogo so- stojanija perenosa. Uslovie istochnika dlja vychislenija momenta ''p'' ravno nv{sup -1} Empty-Set {sup (n-1)}. Pri- vodjatsja rezul'taty dlja razmnozhajushhih i nerazmnozhajushih modelej reaktora {sup T}riga{sup .} Dru- gim metodom energeticheskogo rascheta javljaetsja metod vremennoj zavisimosti Monte Karlo. Dajutsja takzhe rezul'taty vychislenija potoka utechki iz tonkoj svincovoj plastiny. Izmerenija provodili na zamedlenii po vremeni po otnosheniju kadmievoj grani i re- zonansa v 1,46 jev indija v vode i toluole. Zahvatnoe gamma-izluchenie detektiruetsja s po- moshh'ju scintilljacionnogo schetchika. Jetot metod trebuet iskljuchitel'no intensivnogo is- tochnika i jeffektivnogo detektora v svjazi s nizkoj polezno ispol'zuemoj dolej vremeni cikla (korotkaja prodolzhitel'nost' vspyshki dlja razreshajushhej sposobnosti zamedlenija bol'- shoj period promezhutochnogo pul'sa dlja zatuhanija teplovyh nejtronov) i nebol'shoj verojat- nosti dlja zahvata. (author)
Massobrio, C
2003-01-01
Density functional theory, in combination with a) a careful choice of the exchange-correlation part of the total energy and b) localized basis sets for the electronic orbital, has become the method of choice for calculating the exchange-couplings in magnetic molecular complexes. Orbital expansion on plane waves can be seen as an alternative basis set especially suited to allow optimization of newly synthesized materials of unknown geometries. However, little is known on the predictive power of this scheme to yield quantitative values for exchange coupling constants J as small as a few hundredths of eV (50-300 cm sup - sup 1). We have used density functional theory and a plane waves basis set to calculate the exchange couplings J of three homodinuclear Cu-based molecular complexes with experimental values ranging from +40 cm sup - sup 1 to -300 cm sup - sup 1. The plane waves basis set proves as accurate as the localized basis set, thereby suggesting that this approach can be reliably employed to predict and r...
International Nuclear Information System (INIS)
Massobrio, C.; Ruiz, E.
2003-01-01
Density functional theory, in combination with a) a careful choice of the exchange-correlation part of the total energy and b) localized basis sets for the electronic orbital, has become the method of choice for calculating the exchange-couplings in magnetic molecular complexes. Orbital expansion on plane waves can be seen as an alternative basis set especially suited to allow optimization of newly synthesized materials of unknown geometries. However, little is known on the predictive power of this scheme to yield quantitative values for exchange coupling constants J as small as a few hundredths of eV (50-300 cm -1 ). We have used density functional theory and a plane waves basis set to calculate the exchange couplings J of three homodinuclear Cu-based molecular complexes with experimental values ranging from +40 cm -1 to -300 cm -1 . The plane waves basis set proves as accurate as the localized basis set, thereby suggesting that this approach can be reliably employed to predict and rationalize the magnetic properties of molecular-based materials. (author)
Density functional theory and pseudopotentials: A panacea for calculating properties of materials
International Nuclear Information System (INIS)
Cohen, M.L.; Lawrence Berkeley Lab., CA
1995-09-01
Although the microscopic view of solids is still evolving, for a large class of materials one can construct a useful first-principles or ''Standard Model'' of solids which is sufficiently robust to explain and predict many physical properties. Both electronic and structural properties can be studied and the results of the first-principles calculations can be used to predict new materials, formulate empirical theories and simple formulae to compute material parameters, and explain trends. A discussion of the microscopic approach, applications, and empirical theories is given here, and some recent results on nanotubes, hard materials, and fullerenes are presented
Phosphorus {delta}-doped silicon: mixed-atom pseudopotentials and dopant disorder effects
Energy Technology Data Exchange (ETDEWEB)
Carter, Damien J; Marks, Nigel A [Nanochemistry Research Institute, Curtin University, PO Box U1987, Perth WA 6845 (Australia); Warschkow, Oliver; McKenzie, David R, E-mail: d.carter@curtin.edu.au [Centre for Quantum Computer Technology, School of Physics, University of Sydney, Sydney, NSW 2006 (Australia)
2011-02-11
Within a full density functional theory framework we calculate the band structure and doping potential for phosphorus {delta}-doped silicon. We compare two different representations of the dopant plane; pseudo-atoms in which the nuclear charge is fractional between silicon and phosphorus, and explicit arrangements employing distinct silicon and phosphorus atoms. While the pseudo-atom approach offers several computational advantages, the explicit model calculations differ in a number of key points, including the valley splitting, the Fermi level and the width of the doping potential. These findings have implications for parameters used in device modelling.
Zou, Wenli; Cai, Ziyu; Wang, Jiankang; Xin, Kunyu
2018-04-29
Based on two-component relativistic atomic calculations, a free electron density function (EDF) library has been developed for nearly all the known ECPs of the elements Li (Z = 3) up to Ubn (Z = 120), which can be interfaced into modern quantum chemistry programs to save the .wfx wavefunction file. The applicability of this EDF library is demonstrated by the analyses of the quantum theory of atoms in molecules (QTAIM) and other real space functions on HeCuF, PtO42+, OgF 4 , and TlCl 3 (DMSO) 2 . When a large-core ECP is used, it shows that the corrections by EDF may significantly improve the properties of some density-derived real space functions, but they are invalid for the wavefunction-depending real space functions. To classify different chemical bonds and especially some nonclassical interactions, a list of universal criteria has also been proposed. © 2018 Wiley Periodicals, Inc. © 2018 Wiley Periodicals, Inc.
International Nuclear Information System (INIS)
Pyykkoe, P.; Li, J.; Runeberg, N.
1994-01-01
The calculated trends of geometries and vibrational frequencies of several uranyl isoelectronic species, like the known NUN and CUO, and the unknown CUN - , NUO + , and NUF 2+ , are reported. The NUN and CUO results support the matrix spectroscopic assignments. The simplest example of equatorial coordination to uranyl is the C 2d species UO 3 . Its calculated vibrational frequencies also support matrix spectroscopic ones. We earlier suggested that the large range of uranyl bond lengths in UO 6 6- -type systems could be interpreted in terms of a open-quotes frozen, soft e g vibrational modeclose quotes. Further studies on UF 6 , U(OH) 6 , [(OUO)(F eq ) n ] (n-2) -, [(OUO)(NO 3 ) 3 ] - , and [(OUO)(CO 3 ) 3 ] 4- show only small variation of R ax as function of R eq . Thus, the all-oxide case is a special one, where all ligands are capable of single and multiple bonding. 44 refs., 10 figs., 7 tabs
Thermodynamics properties of lanthanide series near melting point-A pseudopotential approach
Suthar, P. H.; Gajjar, P. N.
2018-04-01
The present paper deals with computational study of thermodynamics properties for fifteen elements of lanthanide series. The Helmholtz free energy (F), Internal energy (E) and Entropy (S)have been computed using variational method based on the Gibbs-Bogoliubov (GB) along with Percus-Yevick hard sphere reference system and Gajjar's model potential. The local field correction function proposed by Taylor is applied to introduce the exchange and correlation effects in the study of thermodynamics of these metals. The present results in comparison with available theoretical and experimental are found to be in good agreement and confirm the ability of the model potential.
Structure of thallium and lead calculated from Shaw local pseudopotential and molecular dynamics
Directory of Open Access Journals (Sweden)
Gasser J. G.
2011-05-01
Full Text Available Recently, we (Es Sbihi Phil. Mag 2010 have successfully calculated, by molecular dynamics, the static structure factor of liquid bismuth at different temperatures. Our results were in very good agreement with the Waseda experimental data. Our assumption was to consider the true density of states which presents a gap as measured by Indlekofer (J. Non-Cryst. Solids 1989 and calculated by Hafner-Jank (Phys. Rev. B 1990 for liquid bismuth. The number of electrons at the Fermi energy has been calculated with three conduction electrons for bismuth (number of p electrons. With this assumption, the structures were determined with an effective ion-ion potential constructed from the Shaw local Optimised Model Potential (OMP and the Ichimaru-Utsumi dielectric function. In the present paper, we generalize our assumptions to liquid thallium and lead which also present such a gap. Their calculated structures are also very close to the experimental ones. This confirms that the number of conduction electrons on the Fermi sphere is consistent with the number of p electrons as has been even shown for our electronic transport properties of liquid lead (A. Ben Abdellah, Phys. Rev. B 2003.
Lattice Dynamics of Beryllium from a First-Principles Nonlocal Pseudopotential Approach
DEFF Research Database (Denmark)
Walter, F. King; Cutler, P. H.
1970-01-01
dielectric-screening function employing the Kohn-Sham approximation for exchange among the conduction electrons. The energy-wave-number characteristic F(q) is constructed from the Hartree-Fock-Slater (HFS) wave function for Be++; this is used to calculate the phonon dispersion relations in the [0001], [011̅...
Energy Technology Data Exchange (ETDEWEB)
Killeen, J.; Neil, V. K.; Heckrotte, W. [Lawrence Radiation Laboratory, Livermore, CA (United States)
1966-04-15
High intensity beams of relativistic electrons injected into the Astron device can be trapped in part by the action of coherent electromagnetic self-forces. Through the appropriate design of external passive circuitry, axial electrostatic blow-up of the azimuthally injected beam can be prevented or inhibited. The self-forces result in a spread of particles in z-P{sub z} phase space, and part of the beam is trapped at the expense of the loss of the rest. In addition to this effect, for sufficiently high beam currents, the coupling of the relativistic beam to the passive circuitry can lead to significant loss of axial momentum through energy dissipation. A one-dimensional model of the actual Astron geometry has been investigated theoretically. Green's functions for the self-electric and self-magnetic fields have been calculated analytically and incorporated into the Vlasov equation governing the axial motion of the electrons. Results of the calculation allow some qualitative comparison with experimental results from the Astron experiment. As envisioned, the trapped electrons will form a cylindrical layer of sufficient intensity so that the self-magnetic field is comparable to the applied field. The mathematical model for the build-up of the electron layer and the self-field is the time-dependent Vlasov equation coupled with Maxwell's equations. The system is axially symmetric and complete neutralization is assumed. The field components Br and B{sub z} can be derived from a stream function {psi}( r, z, t). The canonical angular momentum is a constant of the motion, hence we can consider an electron distribution function f{sub e}( r, z, P{sub r}, P{sub z}). The partial differential equations for f{sub e} and {psi} are solved numerically by using finite difference methods. The phase space consists of over 160 000 points, that is 81 in z, 12 in r, 19 in P{sub z} and 9 in P{sub r}. At each step an integration of f{sub e} over momentum space yields the current density j{sub {theta}}(r, z, t); the self-field is then computed by solving the equation for {psi}(r, z, t). In this paper a number of runs are presented, corresponding to several vacuum magnetic fields and various injection conditions. The electron distributions obtained differ widely according to the applied mirror field that is used. In all these runs, minimum-B regions are formed and some have been carried for enough to achieve field reversal. (author) [French] Des faisceaux de forte intensite d'electrons relativistes, injectes dans 1*Astron, peuvent etre pieges en partie par l'action de forces propres electromagnetiques coherentes. Par un schema approprie de circuits passifs externes, il est possible d'empecher ou d'inhiber une explosion electrostatique axiale du faisceau injecte par voie azimutale. Les forces propres donnent lieu a une diffusion de particules dans l'espace des phases z- Pz; une partie du faisceau est piegee au prix de la perte de la partie restante. En plus de cet effet, il est possible, dans le cas de courants de faisceau suffisamment eleves, que le couplage du faisceau relativiste aux circuits passifs entraine, par dissipation d'energie, une perte considerable de quantite de mouvement axiale. Les. auteurs ont etudie, du point de vue theorique, un modele unidimensionnel de la geometrie de 1*Astron. Ils ont calcule analytiquement les fonctions de Green pour les champs electriques et magnetiques propres et les ont incorporees dans l'equation de Vlassov qui regit le mouvement axial des electrons. Les resultats du calcul permettent de proceder a une comparaison qualitative avec les resultats experimentaux obtenus dans l'installation Astron. Conformement aux previsions, les electrons pieges formeront une couche cylindrique d'une intensite telle que le champ magnetique propre puisse etre compare au champ applique. Le modele mathematique expliquant la formation de la couche d'electrons et du champ propre est l'equation de Vlassov (qui est fonction du temps) couplee aux equations de Maxwell. Le systeme possede une symetrie axiale et on le suppose electriquement neutre. Les composantes du champ B{sub r} et B{sub z} peuvent etre derivees d'une fonction d'ecoulement {psi}(r, z, t). Le moment cinetique canonique est une constante du mouvement, ce qui permet de considerer une fonction de distribution des electrons du type f{sub e} (r, z, Pr, Pz). Les equations differentielles partielles pour f{sub e} et {psi} sont resolues numeriquement par des methodes de differences finies. L'espace des phases se compose de plus de 160 000 points, soit 81 dans z, 12 dans r, 19 dans P{sub z} et 9 dans P{sub r}. A chaque stade, une integration de fe sur l'espace des quantites de mouvement donne la densite du courant j{sub {theta}} (r, z, t); on calcule ensuite le champ propre en resolvant l'equation pour {psi} (r, z, t). Les auteurs presentent un certain nombre d'essais qui correspondent a plusieurs champs magnetiques dans le vide et a diverses conditions d'injection. Les distributions d'electrons obtenues different sensiblement selon le champ de miroir applique. Dans tous ces essais, il se forme des regions de B minimum, dont certaines ont ete poussees assez loin pour donner lieu a une inversion de champ. (author) [Spanish] Los haces de alta intensidad de electrones inyectados con velocidades relativistas en el dispositivo Astron,pueden ser atrapados en parte por la aceion de fuerzas propias electromagneticas coherentes. Proyectando adecuadamente los circuitos pasivos externos es posible impedir o inhibir la explosion electrostatica axial del haz inyectado en direccion azimutal. Las fuerzas propias originan una dispersion de particulas en el espacio de fases z-P{sub z}, y parte del haz es atrapado a expensas de la perdida del resto. Ademas de este efecto, para corrientes de haz suficientemente intensas el acoplamiento del haz.relativista con los circuitos pasivos puede provocar una perdida significativa de cantidad de movimiento axial debida a disipacion de energia. Los autores estudiaron teoricamente un modelo unidimensional del dispositivo Astron. Calcularon analiticamente las funciones de Green representativas de los campos propios electrico y magnetico, y las incorporaron a la ecuacion de Vlasov que rige el movimiento axial de los electrones. Los resultados de los calculos permiten establecer una comparacion cualitativa con los resultados experimentales obtenidos mediante la instalacion Astron. Tal como se suponia, los electrones atrapados forman una capa cilindrica de intensidad suficiente para que el campo magnetico propio sea comparable con el campo aplicado. El modelo matematico que explica la formacion de la capa electronica y del campo propio es la ecuacion de Vlasov en funcion del tiempo, unida a las ecuaciones de Maxwell. El.sistema tiene simetria axial y se supone electricamente neutro. Los componentes del campo B{sub r} y B{sub z} pueden deducirse a partir de una funcion de flujo {psi} (r, z, t). El momento angular canonico es una constante del movimiento, lo que permite considerar una funcion de distribucion de los electrones del tipo f{sub e} (r, z, P{sub r}, P{sub z}). Las ecuaciones diferenciales parciales en f{sub e} y {psi} se resuelven numericamente usando el metodo de las diferencias finitas. El espacio de las fases consiste en mas de 160 000 puntos, a saber 81 en z, 12 en r, 19 en P{sub z} y 9 en P{sub r} . En cada paso, la integracion de f{sub e} en el espacio de las cantidades de movimiento da la densidad de corriente j{sub {theta}} (r, z, t); el campo propio se calcula luego resolviendo la ecuacion para {psi} (r, z, t). Los autores presentan una serie de experimentos correspondientes a varios campos magneticos en el vacio y distintas condiciones de inyeccion. Las distribuciones de electrones obtenidas difieren sensiblemente segun cual sea el campo de espejo aplicado. En todos estos experimentos se forman regiones de B mfnimo y algunos se han desarrollado lo suficiente como para lograr la inversion del campo. (author) [Russian] Zahvat vysoko intensivnyh puchkov reljativistskih jelektronov, inzhektiruemyh v ustanovku Astron, mozhet chastichno osushhestvljat'sja za schet kogerentnyh jelektromagnitnyh sil. Osevoe jelektrostaticheskoe razmytie azimutal'no inzhektiruemogo puchka mozhet byt' predotvrashheno ili podavleno blagodarja sootvetstvujushhej konstrukcii vneshnej passivnoj shemy. Pod dejstviem sobstvennyh sil chasticy rasprostranjajutsja v fazovom prostranstve z-Pz, i chast' puchka zahvatyvaetsja za schet poter' drugoj chasti. V dopolnenie k jetomu jeffektu dlja dostatochno vysokih tokov v puchke svjaz' reljativistskogo puchka s passivnoj shemoj mozhet privesti k znachitel'noj potere osevogo momenta iz-za dissipacii jEhnergii. Teoreticheski byla izuchena odnomernaja model' real'noj geometrii Astrona. Funkcii Grina dlja sobstvennyh jelektricheskih i magnitnyh polej byli rasschitany analiticheskim sposobom i vvedeny v uravnenie Vlasova, kotoroe opredeljaet osevoe dvizhenie jelektronov. Rezul'taty raschetov pozvoljajut provesti nekotorye kachestvennye sravnenija s jeksperimental'nymi rezul'tatami, poluchennymi v jeksperimente na Astrone. Kak i predpolagalos', zahvachennye jelektrony obrazujut cilindricheskij sloj dostatochnoj intensivnosti, tak chto sobstvennoe magnitnoe pole sravnimo s prilozhennym polem. Matematicheskaja model' dlja narastanija jelektronnogo sloja i sobstvennogo polja javljaetsja zavisimym ot vremeni uravneniem Vlasova sovmestno s uravnenijami Maksvella. Sistema javljaetsja aksial'no-simmetrichnoj, i predpolagaetsja polnaja nejtralizacija. Komponenty polja Vg i B z mozhno vyvesti na osnovanii funkcii potoka {psi}(r, z, t). Kanonicheskij uglovoj moment javljaetsja konstantoj dvizhenija, i pojetomu my mozhem rassmatrivat' funkciju jelektronnogo raspredelenija f{sub e} (r, z, R{sub g}, R{sub g}). Differencial'nye uravnenija dlja f{sub e} i {psi} reshajutsja chislenno s ispol'zovaniem metodov konechnyh raznostej. Fazovoe prostranstvo soderzhit bolee 160 000 tochek, naprimer 81 v prostranstve g, 12 v g, 19 v P z i 9 v Rg. Na kazhdoj stupeni integracija fe po prostranstvu momenta daet plotnost' toka j{sub {theta}} (r, z, t)j sobstvennoe pole zatem vychisljaetsja putem reshenija uravnenija dlja {psi} (r, z, t). V nastojashhem doklade privoditsja celaja serija opytov, otnosjashhihsja v razlichnym vakuumnym poljam i k razlichnym uslovijam inzhekcii. Poluchennye jelektronnye raspredelenija sil'no otlichajutsja drug ot druga v zavisimosti ot primenjaemogo probochnogo polja. Vo vseh sluchajah imelo mesto obrazovanie oblastej minimal'nogo-V i v nekotoryh iz nih bylo dostignuto reversirovanie polja. (author)
Xia, Junfeng; Yue, Zhenyu; Di, Yunqiang; Zhu, Xiaolei; Zheng, Chun-Hou
2016-01-01
The identification of hot spots, a small subset of protein interfaces that accounts for the majority of binding free energy, is becoming more important for the research of drug design and cancer development. Based on our previous methods (APIS and KFC2), here we proposed a novel hot spot prediction method. For each hot spot residue, we firstly constructed a wide variety of 108 sequence, structural, and neighborhood features to characterize potential hot spot residues, including conventional ones and new one (pseudo hydrophobicity) exploited in this study. We then selected 3 top-ranking features that contribute the most in the classification by a two-step feature selection process consisting of minimal-redundancy-maximal-relevance algorithm and an exhaustive search method. We used support vector machines to build our final prediction model. When testing our model on an independent test set, our method showed the highest F1-score of 0.70 and MCC of 0.46 comparing with the existing state-of-the-art hot spot prediction methods. Our results indicate that these features are more effective than the conventional features considered previously, and that the combination of our and traditional features may support the creation of a discriminative feature set for efficient prediction of hot spots in protein interfaces. PMID:26934646
Energy Technology Data Exchange (ETDEWEB)
Brammer, H. A.; Jacobson, J. [General Electric Company, San Jose, CA (United States)
1964-06-15
A control blade design, incorporating boron-carbide (B{sub 4}C) in stainless-steel tubes, was introduced into service in boiling water reactors in April 1961. Since that time this blade has become the standard reference control element in General Electric boiling-water reactors, replacing the 2% boron-stainless-steel blades previously used. The blades consist of a sheathed, cruciform array of small vertical stainless-steel tubes filled with compacted boron-carbide powder. The boron-carbide powder is confined longitudinally into several independent compartments by swaging over ball bearings located inside the tubes. The development and use of boron-carbide control rods is discussed in five phases: 1. Summary of experience with boron-steel blades and reasons for transition to boron-carbide control; 2. Design of the boron-carbide blade, beginning with developmental experiments, including early measurements performed in the AEC ''Control Rod Material and Development Program'' at the Vallecitos Atomic Laboratory, through a description of the final control blade configuration; 3. Fabrication of the blades and quality control procedures; 4. Results of confirmatory pre-operational mechanical and reactivity testing; and 5. Post-operational experience with the blades, including information on the results of mechanical inspection and reactivity testing after two years of reactor service. (author) [French] Un modele de lame de commande en carbure de bore (B{sub 4}C) a ete mis en place dans des reacteurs a eau bouillante en avril 1961. Depuis lors, cette lame est devenue l 'element de commande temoin classique dans les reacteurs a eau bouillante de la General Electric et a remplace les lames en acier inoxydable a 2% de bore utilisees auparavant. Ces lames consistent en un assemblage gaine cruciforme comprenant de petits tubes d'acier inoxydable verticaux remplis de poudre de carbure de bore agglomeree. Dans le sens de la longueur, cette poudre est enfermee dans plusieurs compartiments independants par tassement sur des supports spheriques situes a l'interieur des tubes. Les auteurs etudient la mise au point et l'utilisation des lames de commande en carbure de bore sous les cinq rubriques suivantes: 1. Apercu de l'experience acquise avec l'acier au bore et raisons de son remplacement par du carbure de bore. 2. Etudes de la lame en carbure de bore depuis le debut des experiences de mise au point, y compris les premieres mesures effectuees dans le cadre du ' Programme de mise au point de materiaux pour barres de controle' de la CEA au Laboratoire atomique de Vallecitos, et description de la configuration definitive de la lame de controle. 3. Fabrication des lames et methodes de controle de la qualite. 4. Resultats des essais confirmatoires avant mise en service (essais mecaniques et essais de reactivites). 5. Experience apres mise en service, y compris les resultats d'essais mecaniques et d'essais'de reactivites effectues apres deux annees d'utilisation dans le reacteur. (author) [Spanish] En abril de 1961 se comenzo a utilizar en los reactores de agua hirviente un nuevo modelo de elemento de control de carburo de boro (B{sub 4}C) en tubos de acero inoxidable. Desde entonces, este elemento se ha convertido en el elemento de control normal de referencia en los reactores de agua hirviente de la General Electric, y ha sustituido a las placas de acero inoxidable con 2% de boro que se utilizaban con anterioridad. Los nuevos elementos consisten en pequenos tubos verticales de acero inoxidable, dispuestos de manera cruciforme,, con un revestimiento, que estan llenos de polvo de carburo de boro compactado. El polvo de carburo de boro queda confinado longitudinalmente en varios compartimentos independientes estampandolo sobre bolas de acero de cojinetes situadas en el interior de los tubos. La memoria discute en cinco fases el perfeccionamiento, y el empleo de las barras de control de carburo de boro. 1. Resumen de los experimentos realizados con placas de acero al boro y motivos por los que se abandonaron en favor del carburo de boro. 2. Desarrollo progresivo del elemento de carburo de boro, comenzando con los primeros experimentos y las mediciones iniciales llevadas a cabo en el Vallecitos Atomic Laboratory en el marco del programa de desarrollo de materiales para barras de control de la AEC, hasta llegar a una descripcion de la configuracion definitiva de la barra de control. 3. Elaboracion de los elementos y procedimientos de control de calidad. 4. Resultados de los ensayos para determinar las caracteristicas mecanicas y la reactividad. 5. Experiencia adquirida Con los elementos y datos sobre los resultados de la inspeccion mecanica y de los ensayos de la reactividad al cabo de 2 aflos de utilizacion en los reactores. (author) [Russian] Regulirujushhee ustrojstvo s ispol'zovaniem krestoobraznoj kasety, Sostojashhej iz trubok iz nerzhavejushhej stali, zapolnennyh karbidom bora (B{sub 4}C), stali primenjat' v re aktorah s kipjashhej vodoj v aprele 1961 goda. S jetogo vremeni kasety stali standartnym jetalonom upravljajushhih sterzhnej v reaktorah s kipjashhej vodoj kompanii {sup D}zhene- ral Jelektrik{sup .} Oni zamenili kasety iz nerzhavejushhej stali s 2%-nym soderzhaniem bo r a . Jeti krestoobraznye kasety sostojat iz nabora nebol'shih vertikal'nyh trub iz nerzhavejushhej stali, zapolnennyh plotnym poroshkom karbida bora. Poroshok karbida bora pomeshhen v prodol'nom napravlenii v nezavisimyh otdalenijah putem gorjachej pakovki nad sharikopodshipnikami, razmeshhennymi, razmeshhennymi vnutri trub. R azr abotka i ispol'zovanie regulirujushhih sterzhnej iz karbida bora obsuzhdaetsja po sledujushhim pjati fazam: 1. Kratkoe opisanie opyta s pomoshh'ju stal'nyh kaset, soderzhashhih bor, i prichiny perehoda k regulirujushhim sterzhnjam iz karbida bora. 2 . Ustrojstvo kaset iz karbida bora, nachinaja s jeksperimentov po ra zrab otke i vkljuchaja samye pervye meroprijatija, provedennye v KAJe po ''Materialam dlja regulirujushhih sterzhnej i programme razrabotki'' v atomnoj laboratorii Valesitos, a takzhe opisanie okonchatel'nyh form regulirujushhih kaset I 3 . Izgotovlenie kaset j metody kontrolja ih kachestva. 4. Rezul'taty opytov po proverke predjekspluatacionnyh mehanicheskih svojstv i reaktivnosti. 5 . Opyt, poluchennyj posle jekspluatacii kaset, vkljuchaja i dannye o rezul'tatah obsledovanija mehanicheskoj chasti i ispytanie na reaktivnost' posle dvuh l e t raboty reaktora. (author)
Energy Technology Data Exchange (ETDEWEB)
Bobbitt, N. Scott; Kim, Minjung [Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States); Sai, Na [Department of Physics, The University of Texas at Austin, Austin, Texas 78712 (United States); Marom, Noa [Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana, 70118 (United States); Chelikowsky, James R. [Center for Computational Materials, Institute for Computational Engineering and Sciences, Departments of Physics and Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States)
2014-09-07
Zinc oxide is often used as a popular inexpensive transparent conducting oxide. Here, we employ density functional theory and local density approximation to examine the effects of quantum confinement in doped nanocrystals of this material. Specifically, we examine the addition of Ga and Al dopants to ZnO nanocrystals on the order of 1.0 nm. We find that the inclusion of these dopants is energetically less favorable in smaller particles and that the electron binding energy, which is associated with the dopant activation, decreases with the nanocrystal size. We find that the introduction of impurities does not alter significantly the Kohn-Sham eigenspectrum for small nanocrystals of ZnO. The added electron occupies the lowest existing state, i.e., no new bound state is introduced in the gap. We verify this assertion with hybrid functional calculations.
Czech Academy of Sciences Publication Activity Database
Burda, J. V.; Zeizinger, M.; Šponer, Jiří; Leszczynski, J.
2000-01-01
Roč. 113, č. 6 (2000), s. 2224-2232 ISSN 0021-9606 Grant - others:GA UK(XC) 156/1999/B; VW(DE) AA114/99 Institutional research plan: CEZ:AV0Z4040901; CEZ:A54/98:Z4-040-9-ii Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.301, year: 2000
International Nuclear Information System (INIS)
Bobbitt, N. Scott; Kim, Minjung; Sai, Na; Marom, Noa; Chelikowsky, James R.
2014-01-01
Zinc oxide is often used as a popular inexpensive transparent conducting oxide. Here, we employ density functional theory and local density approximation to examine the effects of quantum confinement in doped nanocrystals of this material. Specifically, we examine the addition of Ga and Al dopants to ZnO nanocrystals on the order of 1.0 nm. We find that the inclusion of these dopants is energetically less favorable in smaller particles and that the electron binding energy, which is associated with the dopant activation, decreases with the nanocrystal size. We find that the introduction of impurities does not alter significantly the Kohn-Sham eigenspectrum for small nanocrystals of ZnO. The added electron occupies the lowest existing state, i.e., no new bound state is introduced in the gap. We verify this assertion with hybrid functional calculations
International Nuclear Information System (INIS)
Imai, Yoji; Imai, Motoharu
2011-01-01
Research highlights: → This paper reports the results of electronic structural calculations of Si clathrate, M 8 Si 38 Ga 8 (M: the encapsulated guest alkali atom; Na, K, Rb, and Cs). → All of them are found to be indirect semiconductors with the calculated gaps (E g ) from 0.45 to 0.89 eV, which should be compared to the calculated gap of 0.65 eV of crystalline Si with the diamond structure. The gaps become wider with the promotion to the heavier guest alkali atoms and the reasons of gap widening are discussed using the calculated dependence of E g on the cell-volume of guest-free silicon clathrate (Si 46 ). Effect of the substitutional elements in the clathrate framework (Al and In in place of Ga) was also discussed. - Abstract: We have calculated the band structures of Si clathrate, M 8 Si 38 Ga 8 (M = Na, K, Rb, and Cs), using the density-functional theory under the generalized gradient corrected local density approximation, where M is the encapsulated guest alkali atom. They are found to be indirect semiconductors with the calculated gaps (E g ) from 0.45 to 0.89 eV, which should be compared to the calculated gap of 0.65 eV of crystalline Si with the diamond structure. The gaps become wider with the promotion to the heavier guest alkali atoms and the reasons of gap widening are discussed using the calculated dependence of E g on the cell-volume of guest-free silicon clathrate (Si 46 ). Effect of the substitutional elements in the clathrate framework (Al and In in place of Ga) was also discussed.
A novel method of including Landau level mixing in numerical studies of the quantum Hall effect
International Nuclear Information System (INIS)
Wooten, Rachel; Quinn, John; Macek, Joseph
2013-01-01
Landau level mixing should influence the quantum Hall effect for all except the strongest applied magnetic fields. We propose a simple method for examining the effects of Landau level mixing by incorporating multiple Landau levels into the Haldane pseudopotentials through exact numerical diagonalization. Some of the resulting pseudopotentials for the lowest and first excited Landau levels will be presented
About relaxation phenomena and transport processing in a fully ionized non-ideal plasma
International Nuclear Information System (INIS)
Baimbetov, F.B.; Iztleuov, N.T.
1999-01-01
In this report correlation effects for non-ideal plasma are accounted in the so called pseudopotentials. The accounting of high order correlation influences in the pseudopotential lead to the strongly screened potential. Kinetic equation with pseudopotential is cited. The equations which describe the relaxation of the difference of directed velocities of plasma particles, and frequency of particle collision which determines relaxation of temperature for non-ideal plasma are obtained. On basis of mentioned kinetic equation the transport equation is obtained as well
Ionic core effects on the Mie resonance in lithium clusters
International Nuclear Information System (INIS)
Yabana, K.
1994-01-01
We investigate effects of atomic cores on the Mie resonance in lithium metal clusters, perturbing a helium Hamiltonian with zero-range pseudopotentials. The resonance is red-shifted with respect to the classical formula by core effects, most important of which is the increased effective mass due to the core potentials. Much of the large shift seen in lithium clusters is thereby explained if the strength of the Pseudopotentials is taken from band structure calculations. However, such pseudopotentials cause the resonance to be greatly broadened, contrary to observation
Ab-Initio Simulation of a/2 Screw Dislocations Gamma-TiAl
National Research Council Canada - National Science Library
Woodward, C; Rao, S. I
2004-01-01
...The equilibrium core structure of an isolated a/2screw dislocations is calculated using a first-principles pseudopotential-planewave method within the Local Density Approximation of Density Functional Theory...
International Nuclear Information System (INIS)
Bellan, P. M.
2013-01-01
The interaction between a circularly polarized wave and an energetic gyrating particle is described using a relativistic pseudo-potential that is a function of the frequency mismatch. Analysis of the pseudo-potential provides a means for interpreting numerical results. The pseudo-potential profile depends on the initial mismatch, the normalized wave amplitude, and the initial angle between the wave magnetic field and the particle perpendicular velocity. For zero initial mismatch, the pseudo-potential consists of only one valley, but for finite mismatch, there can be two valleys separated by a hill. A large pitch angle scattering of the energetic electron can occur in the two-valley situation but fast scattering can also occur in a single valley. Examples relevant to magnetospheric whistler waves show that the energetic electron pitch angle can be deflected 5°towards the loss cone when transiting a 10 ms long coherent wave packet having realistic parameters.
Molecular dynamics of liquid alkaline-earth metals near the melting ...
Indian Academy of Sciences (India)
Results of the studies of the properties like binding energy, the pair distrib- ... of the pseudopotential used from solid to liquid environment in the case of .... In this expression, Eeg represents the ground state energy of the electron gas, for.
Image charge forces inside conducting boundaries
International Nuclear Information System (INIS)
Tinkle, Mark D.; Barlow, S. E.
2001-01-01
The common description of the electrostatic force, F(x)=-q∇φ(x), provides an incomplete description of the force on the charge q at a point x when the charge itself induces additional fields, e.g., image charges, polarizations, etc. The equation may be corrected through the introduction of a ''pseudopotential'' formalism. Exploration of some of the elementary properties of the pseudopotential demonstrates its essential simplicity. This simplicity allows it to be incorporated directly into dynamics calculations. We explicitly evaluate the pseudopotential in a number of simple but important cases including the sphere, parallel plates, the rectangular prism, and the cylindrical box. The pseudopotential formalism may be expanded to include extended charge distributions; in this latter form we are able to directly apply the results to experimental measurements
Atomic displacements due to interstitial hydrogen in Cu and Pd
Indian Academy of Sciences (India)
2015-11-27
Nov 27, 2015 ... Atomic displacements; density functional theory; Kanzaki method. ... pseudopotentials for H, Cu and Pd are generated self-consistently. ... Both Cu and Pd lattices show lattice expansion due to the presence of hydrogen and ...
Goumri-Said, Souraya; Kanoun, Mohammed
2010-01-01
In this Letter we investigate the electronic properties of the bulk and the nanofilm BeO in wurtzite structure. We performed a first-principles pseudo-potential method within the generalized gradient approximation. We will give more importance
Indian Academy of Sciences (India)
Electrical resistivity of NaPb compound-forming liquid alloy using ab initio pseudopotentials ... Ultrasonic studies of aluminium-substituted Bi(Pb)-2223 superconduc- tors. M B Solunke, P U .... electrochemical studies for lithium secondary cells.
Defect complexes in carbon and boron nitride nanotubes
CSIR Research Space (South Africa)
Mashapa, MG
2012-05-01
Full Text Available The effect of defect complexes on the stability, structural and electronic properties of single-walled carbon nanotubes and boron nitride nanotubes is investigated using the ab initio pseudopotential density functional method implemented...
International Nuclear Information System (INIS)
Verheest, Frank
2011-01-01
Large dust-acoustic waves are investigated in a multispecies plasma model consisting of cold negative dust in the presence of cooler Boltzmann and hotter nonthermal Cairns positive ions, in a Sagdeev pseudopotential formalism. Use of the pseudopotential at the acoustic speed itself yields in a systematic way compositional parameter values where negative/positive solitons interchange polarities and also where both polarities coexist. The latter requires that solitons at the acoustic speed exist, with finite amplitudes, compared to superacoustic solitons of the opposite polarity. The coexistence region starts when the pseudopotential at the acoustic speed has a negative root at the limit of infinite dust compression and ends when a positive double root is encountered. Outside the coexistence domain, only negative or positive superacoustic solitons can exist. Thus, the discussion and numerical evaluations are guided by precise physical and analytic arguments rather than mere numerical experimentation. Graphs of relevant Sagdeev pseudopotentials illustrate the link with the analytical constraints.
African Journals Online (AJOL)
ADOWIE PERE
ABSTRACT: An ab initio plane-wave Pseudopotential calculations using the density functional theory (DFT) ... From these computations the lattice constants, crystal structures, phonon ..... frequency modes of optical branch at Γ point are in.
Energy Technology Data Exchange (ETDEWEB)
Verheest, Frank [Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, B-9000 Gent, Belgium and School of Physics, University of KwaZulu-Natal, Private Bag X54001, Durban 4000 (South Africa)
2011-08-15
Large dust-acoustic waves are investigated in a multispecies plasma model consisting of cold negative dust in the presence of cooler Boltzmann and hotter nonthermal Cairns positive ions, in a Sagdeev pseudopotential formalism. Use of the pseudopotential at the acoustic speed itself yields in a systematic way compositional parameter values where negative/positive solitons interchange polarities and also where both polarities coexist. The latter requires that solitons at the acoustic speed exist, with finite amplitudes, compared to superacoustic solitons of the opposite polarity. The coexistence region starts when the pseudopotential at the acoustic speed has a negative root at the limit of infinite dust compression and ends when a positive double root is encountered. Outside the coexistence domain, only negative or positive superacoustic solitons can exist. Thus, the discussion and numerical evaluations are guided by precise physical and analytic arguments rather than mere numerical experimentation. Graphs of relevant Sagdeev pseudopotentials illustrate the link with the analytical constraints.
Energy Technology Data Exchange (ETDEWEB)
Kheloufi, Nawal; Bouzid, Abderrazak, E-mail: a_bouzid34@hotmail.com
2016-06-25
We present band gap calculations of zinc-blende ternary CdS{sub x}Te{sub 1-x} semiconductors within the standard DFT and quasiparticle calculations employing pseudopotential method. The DFT, the local density approximation (LDA) and the Generalized Gradient Approximation (GGA) based calculations have given very poor results compared to experimental data. The quasiparticle calculations have been investigated via the one-shot GW approximation. The present paper discuses and confirms the effect of inclusion of the semicore states in the cadmium (Cd) pseudopotential. The obtained GW quasiparticle band gap using Cd{sup +20} pseudopotential has been improved compared to the obtained results from the available pseudopotential without the treatment of semicore states. Our DFT and quasiparticle band gap results are discussed and compared to the available theoretical calculations and experimental data. - Graphical abstract: Band gaps improvement concerning the binary and ternary alloys using the GW approximation and Cd{sup 20+} pseudopotential with others levels of approximations (the LDA and GGA approximation employing the Cd{sup 12+} and the LDA within Cd{sup 20+} pseudopotential). - Highlights: • The direct Γ- Γ and indirect Γ- X and Γ- L bands gaps show a nonlinear behavior when S content is enhanced. • The quasiparticle band gap result for the investigated semiconductors is improved using the GW approximation. • All CdS{sub x}Te{sub 1-x} compounds in all compositions range from 0 to 1 are direct band gap semiconductors.
CdS_xTe_1_-_x ternary semiconductors band gaps calculation using ground state and GW approximations
International Nuclear Information System (INIS)
Kheloufi, Nawal; Bouzid, Abderrazak
2016-01-01
We present band gap calculations of zinc-blende ternary CdS_xTe_1_-_x semiconductors within the standard DFT and quasiparticle calculations employing pseudopotential method. The DFT, the local density approximation (LDA) and the Generalized Gradient Approximation (GGA) based calculations have given very poor results compared to experimental data. The quasiparticle calculations have been investigated via the one-shot GW approximation. The present paper discuses and confirms the effect of inclusion of the semicore states in the cadmium (Cd) pseudopotential. The obtained GW quasiparticle band gap using Cd"+"2"0 pseudopotential has been improved compared to the obtained results from the available pseudopotential without the treatment of semicore states. Our DFT and quasiparticle band gap results are discussed and compared to the available theoretical calculations and experimental data. - Graphical abstract: Band gaps improvement concerning the binary and ternary alloys using the GW approximation and Cd"2"0"+ pseudopotential with others levels of approximations (the LDA and GGA approximation employing the Cd"1"2"+ and the LDA within Cd"2"0"+ pseudopotential). - Highlights: • The direct Γ- Γ and indirect Γ- X and Γ- L bands gaps show a nonlinear behavior when S content is enhanced. • The quasiparticle band gap result for the investigated semiconductors is improved using the GW approximation. • All CdS_xTe_1_-_x compounds in all compositions range from 0 to 1 are direct band gap semiconductors.
Energy Technology Data Exchange (ETDEWEB)
Yu, Jaehyung [Department of Mechanical Science and Engineering, 1206 W Green Street, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Wagner, Lucas K. [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Ertekin, Elif, E-mail: ertekin@illinois.edu [Department of Mechanical Science and Engineering, 1206 W Green Street, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); International Institute for Carbon Neutral Energy Research - WPI-I" 2CNER, Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395 (Japan)
2015-12-14
The fixed node diffusion Monte Carlo (DMC) method has attracted interest in recent years as a way to calculate properties of solid materials with high accuracy. However, the framework for the calculation of properties such as total energies, atomization energies, and excited state energies is not yet fully established. Several outstanding questions remain as to the effect of pseudopotentials, the magnitude of the fixed node error, and the size of supercell finite size effects. Here, we consider in detail the semiconductors ZnSe and ZnO and carry out systematic studies to assess the magnitude of the energy differences arising from controlled and uncontrolled approximations in DMC. The former include time step errors and supercell finite size effects for ground and optically excited states, and the latter include pseudopotentials, the pseudopotential localization approximation, and the fixed node approximation. We find that for these compounds, the errors can be controlled to good precision using modern computational resources and that quantum Monte Carlo calculations using Dirac-Fock pseudopotentials can offer good estimates of both cohesive energy and the gap of these systems. We do however observe differences in calculated optical gaps that arise when different pseudopotentials are used.
Effective interactions in dilute mixtures of 3He in 4He
International Nuclear Information System (INIS)
Hsu, W.; Pines, D.
1985-01-01
Nonlocal pseudopotentials which describe the effective interaction between 3 He quasiparticles, and between these quasiparticles and the background 4 He liquid, are obtained as a function of concentration and pressure by generalizing the Aldrich--Pines pseudopotentials for pure 3 He and 4 He to dilute mixtures. The hierarchy of physical effects which determine these pseudopotentials is established. Interaction-induced short-range correlations are the dominant physical feature; next in order of importance is the greater zero point motion associated with the replacement of a 4 He atom by a 3 He atom, while spin-duced ''Pauli principle'' correlations play a significantly smaller, albeit still important role. We find a consistent trend in the change of the effective direct quasiparticle interactions with increasing concentration, and show how the Aldrich-Pines pseudopotentials for pure 3 He quasiparticles represent a natural extension of our results for dilute mixtures. Our calculated nonlocal pseudopotential for 3 He quasiparticles is qualitatively similar to that proposed by Bardeen, Baym, and Pines; it changes sign at somewhat lower momentum transfers than the BBP result, varies little with concentration, and provides a physical basis for understanding the BBP result. The effective interaction between quasiparticles of parallel spin, here determined for the first time, is essentially repulsive in the very dilute limit; as the concentration increases, it becomes increasingly attractive at low momentum transfers, and resembles closely that between antiparallel spin quasiparticles at 5% concentration. The concentration-dependent transport properties calculated from these pseudopotentials (which involve only one phenomenological parameter) are in good agreement with experiment at saturated vapor pressure (SVP), 10 atm, and 20 atm
Ab initio phonon dispersions of face centered cubic Pb: effects of spin-orbit coupling
International Nuclear Information System (INIS)
Dal Corso, Andrea
2008-01-01
I present the ab initio phonon dispersions of face centered cubic Pb calculated within the framework of density functional perturbation theory, with plane waves and a fully relativistic ultrasoft pseudopotential which includes spin-orbit coupling effects. I find that, within the local density approximation, the theory gives phonon frequencies close to the experimental inelastic neutron scattering data. Many of the anomalies present in these dispersions are well reproduced by the fully relativistic pseudopotential theory and can be shown to appear only for small values of the smearing parameter that controls the sharpness of the Fermi surface.
Electronic band structure of lithium, sodium and potassium fluorides
International Nuclear Information System (INIS)
Jouanin, C.; Albert, J.P.; Gout, C.
1975-01-01
A mixed tight-binding, pseudopotential method is proposed to calculate the energy band structure of large-gap crystals and is tested here on LiF, NaF and KF. Three-centre terms are included in the determination of the valence bands by the tight-binding method and for the conduction bands we use a pseudopotential model proposed by Bassani and Giuliano, modified for the positive ions. By taking into account the polarization corrections, transitions calculated from the energy band structures are compared with experimental data and the agreement is generally good
DEFF Research Database (Denmark)
Valiente, Manuel
2012-01-01
We prove the equivalence between the hard-sphere Bose gas and a system with momentum-dependent zero-range interactions in one spatial dimension, which we call extended hard-sphere Bose gas. The two-body interaction in the latter model has the advantage of being a regular pseudopotential. The most...
Modes of oscillation in radiofrequency Paul traps
DEFF Research Database (Denmark)
Landa, H.; Reznik, B.; Drewsen, M.
2012-01-01
We examine the time-dependent dynamics of ion crystals in radiofrequency traps. The problem of stable trapping of general threedimensional crystals is considered and the validity of the pseudopotential approximation is discussed. We analytically derive the micromotion amplitude of the ions...
Optical properties of nano-silicon
Indian Academy of Sciences (India)
Unknown
the surface of the dot was passivated with the hydrogen atoms incorporating proper hydrogen pseudopotential. 2. Experimental. PL measurements were performed on the Si-doped SiO2 thin films deposited on p-type Si (100) substrates by. *Author for correspondence. †Paper presented at the 5th IUMRS ICA98, October ...
2015-08-24
for initiation. We have used first principle calculations (plane wave Density Functional Theory with projector augmented-wave (PAW) pseudopotentials...RDX -what are conformers?- • Estimation of energy barriers using the Nudged Elastic Band method. • Various conformations stabilized by the Grant
Adhesion of ultrathin ZrO2(111) films on Ni(111) from first principles
DEFF Research Database (Denmark)
Christensen, Asbjørn; Carter, Emily A.
2001-01-01
We have studied the ZrO2(111)/Ni(111) interface using the ultrasoft pseudopotential formalism within density functional theory. We find that ZrO2(111) adheres relatively strongly at the monolayer level but thicker ceramic films interact weakly with the Ni-substrate. We argue that the cohesion cha...
Calculation of inelastic cross-sections for: H++Cs→H(n=2)+Cs+
International Nuclear Information System (INIS)
Valance, A.; Spiess, G.
1975-01-01
The cross sections for the processes H + + Cs→H(2p and 2s) + Cs + were calculated in the center of mass energy range 250-2400eV using a pseudo-potential formalism for the potential curves and coupling matrix elements and a perturbated stationary state formulation for the calculation of the cross sections [fr
Ab-initio theoretical predictions of structure properties of semiconductors
International Nuclear Information System (INIS)
Rodriguez, C.O.; Peltzer y Blanca, E.L.; Cappannini, O.M.
1983-01-01
In this paper, calculations of the total energies and related structural properties of Si, GaP and C are presented showing good agreement with experimental values. The total energy is calculated within the local-density functional formalism using first principles non-local pseudopotentials. (A.C.A.S.) [pt
Bulletin of Materials Science | Indian Academy of Sciences
Indian Academy of Sciences (India)
First-principles pseudopotential-based density functional theory calculations of atomic and electronic structures, full phonon dispersions and thermal properties of zigzag single wall carbon nanotubes (SWCNTs) are presented. By determining the correlation between vibrational modes of a graphene sheet and of the ...
Pseudo potentials and model potentials in atomic collisions
International Nuclear Information System (INIS)
Reyes, O.; Jouin, H.; Fuentealba, P.
1988-01-01
In this work, it is discussed the main differences between the use of pseudo-potentials and model potentials in collision problems . It is shown the potential energy curves for distinct systems obtained with both kinds of potentials. (A.C.A.S.) [pt
Energy Technology Data Exchange (ETDEWEB)
2015-05-26
Octopus is a scientific program aimed at the ab initio virtual experimentation on a hopefully ever-increasing range of system types. Electrons are described quantum-mechanically within density-functional theory (DFT), in its time-dependent form (TDDFT) when doing simulations in time. Nuclei are described classically as point particles. Electron-nucleus interaction is described within the pseudopotential approximation.
Hiroshi Uno
2007-01-01
This paper proposes a new class of potential games, the nested potential games, which generalize the potential games defined in Monderer and Shapley (1996), as well as the pseudo-potential games defined in Dubey et al. (2006). We show that each maximizer of a nested potential is a Nash equilibrium.
Czech Academy of Sciences Publication Activity Database
Holub, Josef; Melichar, Petr; Růžičková, Z.; Vrána, J.; Wann, D. A.; Fanfrlík, Jindřich; Hnyk, Drahomír; Růžička, A.
2017-01-01
Roč. 46, č. 40 (2017), s. 13714-13719 ISSN 1477-9226 R&D Projects: GA ČR(CZ) GA17-08045S Institutional support: RVO:61388980 ; RVO:61388963 Keywords : adjusted pseudopotentials * derivates * halogen * carboranes * chalcogen Subject RIV: CA - Inorganic Chemistry OBOR OECD: Inorganic and nuclear chemistry Impact factor: 4.029, year: 2016
Electronic properties and charge density of BexZn1− xTe alloys
Indian Academy of Sciences (India)
Electronic band structure calculations are performed for the BeZn1−Te (0 ≤ ≤ 1 in steps of 0.2) alloys following the empirical pseudopotential method. The alloying effects are modelled through the modified virtual crystal approximation. Throughout the composition, valence band maximum resides at the point.
Electrical resistivity of liquid Ag-Au alloy
International Nuclear Information System (INIS)
Anis Alam, M.; Tomak, M.
1983-01-01
Calculations of the dependence of the electrical resistivity in liquid Ag-Au binary alloy on composition are reported. The structure of the binary alloy is described as a hard-sphere system. A one-parameter local pseudopotential, which incorporates s-d hybridization effects phenomenologically, is employed in the resistivity calculation. A reasonable agreement with experimental trend is observed. (author)
Large amplitude solitary waves in a multicomponent plasma with negative ions
International Nuclear Information System (INIS)
Nakamura, Y.; Tsukabayashi, I.; Ludwig, G.O.; Ferreira, J.L.
1987-09-01
When the concentration of negative ions is larger than a critical value, a small compressive pulse evolves into a subsonic wave train and a large pulse develops into a solitary wave. The threshold amplitude and velocity of the solitary waves are measured and compared with predictions using the pseudopotential method. (author) [pt
International Nuclear Information System (INIS)
Mookerjee, A.; Chaudhry, V.
1980-09-01
Using the chemical pseudopotential approach of Anderson and Bullett we have generated from first principles pseudo-Hamiltonians for heteropolar alloys. The one-electron density of states has been generated for Gasub(x)Insub(1-x)As using a self-consistent cluster CPA introduced earlier by one of us. Off-diagonal disorder has also been incorporated. (author)
Pramana – Journal of Physics | News
Indian Academy of Sciences (India)
However, it can be used with an additional term known as Born–Mayer (BM) core term. The influence of the BM core term on the phonon dispersion is discussed. The same pseudo-potential formalism has been employed to obtain the dispersion relation in liquid Li0.61Na0.39 alloy. Apart from the phonon spectra, the ...
Large-amplitude double layers in a dusty plasma with an arbitrary ...
Indian Academy of Sciences (India)
Formation of large-amplitude double layers in a dusty plasma whose constituents are electrons, ions, warm dust grains and positive ion beam are studied using Sagdeev's pseudopotential technique. Existence of double layers is investigated. It is found that both the temperature of dust particles and ion beam temperature ...
Neutron radiography with ultracold neutrons
International Nuclear Information System (INIS)
Bates, J.C.
1981-01-01
The neutron transmission factor of very thin films may be low if the neutron energy is comparable to the pseudo-potential of the film material. Surprisingly, perhaps, it is relatively easy to obtain neutrons with such low energies in sufficient numbers to produce neutron radiographs. (orig.)
1990-12-01
in the cylindrical coordinate 9. L. Szasz , Pseudopotential Theory ofAtoms and Mole- s y s t e m . ul e s , P e y , N e Y o rr (1 9 8 5) . In summary...test calculations were carried out to cu/es, Wiley, New York (1985). evaluate a proposed semiclassical correction rule. The 10. L. Szasz
International Nuclear Information System (INIS)
Krauss, M.; Stevens, W.J.; Julienne, P.S.; Mies, F.H.
1979-11-01
The included summaries are divided into three categories. First, the theoretical analyses of Raman processes in intense fields are described. Second, the electronic structure calculations are presented with a brief description of pseudopotential code development. Third, the analysis of absorption processes, both collision-induced and photoionization, and energy transfer processes is presented
Effect of three-body forces on the lattice dynamics of noble metals
Indian Academy of Sciences (India)
A simple method to generate an effective electron–ion interaction pseudopotential from the energy wave number characteristic obtained by ﬁrst principles calculations has been suggested. This effective potential has been used, in third order perturbation, to study the effect of three-body forces on the lattice dynamics of ...
Bulletin of Materials Science | Indian Academy of Sciences
Indian Academy of Sciences (India)
An extensive computer simulation using empirical pseudopotential method ... Two- and three-dimensional models for analysis of optical absorption in ... Study on growth factors of intermetallic layer within hot-dipped 25%Al-Zn alloy coating on steel ... Cellular automaton simulation of microstructure evolution during austenite ...
Study of Atoms and Molecules with Auxiliary-Field Quantum Monte Carlo
Purwanto, Wirawan; Suewattana, Malliga; Krakauer, Henry; Zhang, Shiwei; Walter, Eric J.
2006-03-01
We study the ground-state properties of second-row atoms and molecules using the phaseless auxiliary-field quantum Monte Carlo (AF QMC) method. This method projects the many-body ground state from a trial wave function by means of random walks in the Slater-determinant space. We use a single Slater-determinant trial wave function obtained from density-functional theory (DFT) or Hartree-Fock (HF) calculations. The calculations were done with a plane-wave basis and supercells with periodic boundary condition. We investigate the finite-size effects and the accuracy of pseudopotentials within DFT, HF, and AF QMC frameworks. Pseudopotentials generated from both LDA (OPIUM) and HF are employed. We find that the many-body QMC calculations show a greater sensitivity to the accuracy of the pseudopotentials. With reliable pseudopotentials, the ionization potentials and dissociation energies obtained using AF QMC are in excellent agreement with the experimental results. S. Zhang and H. Krakauer, Phys. Rev. Lett. 90, 136401 (2003) http://opium.sourceforge.net I. Ovcharenko, A. Aspuru-Guzik, and W. A. Lester, J. Chem. Phys. 114, 7790 (2001)
A localized orbital description of ideal vacancies in GaP and GaSb
International Nuclear Information System (INIS)
Erbarut, E.; Tomak, M.
1986-10-01
Gaussian orbitals of s and p symmetry and an empirical pseudopotential Hamiltonian is employed for the study of electronic structures of ideal vacancies in GaP and GaSb. A reasonably accurate description of band structures and densities of states are attained. (author)
Symmetry properties of some nonlinear field theory models
International Nuclear Information System (INIS)
Shvachka, A.B.
1984-01-01
Various approaches towards the study of symmetry properties of some nonlinear evolution equations as well as possible ways of their computer implementation using the computer algebra systems langage are discussed. Special attention is paid to the method of pseudopotential investigation of formal integrability and isovector method for the equations of balance
Calculations of H+ + Cs→H(2s or 2p) + Cs+ reaction cross sections
International Nuclear Information System (INIS)
Valance, A.; Spiess, G.
1975-01-01
The H(2s) and H(2p) atom production cross-sections are calculated and compared with experimental results in the incident proton energy range 250-2400eV. The calculation method used involves a perturbation of the stationary molecular states, these adiabatic potentials being obtained from a pseudo-potential describing the core of cesium [fr
Pramana – Journal of Physics | Indian Academy of Sciences
Indian Academy of Sciences (India)
Pseudopotential plane-wave method (PP–PW) based on density functional theory (DFT) and density functional perturbation theory (DFPT) within the Teter and Pade exchangecorrelation functional form of the local spin density approximation (LSDA) is applied to study the effect of pressure on the elastic and piezoelectric ...
On the theory of elastic scattering of spin polarized electrons from ferromagnets
International Nuclear Information System (INIS)
Helman, J.S.
1984-01-01
The first Born approximation supposedly inadequate for dealing with elastic scattering of spin polarized electrons on ferromagnets is reconsidered. It is found that when used in conjunction with a spin dependent pseudopotential, it can describe the gross features of the ansisotropy. (Author) [pt
On the theory of elastic scattering of spin polarized electrons from ferromagnets
International Nuclear Information System (INIS)
Helman, J.S.; Baltenspenger, W.
1984-01-01
The first Born approximation supposedly inadequate for dealing with the elastic scattering of spin polarized electrons on ferromagnets is reconsidered. It is found that when used in conjunction with a spin dependent pseudo-potential, it can describe the gross features of the anisotropy. (author) [pt
Modeling of inter-ribbon tunneling in graphene
Van de Put, Maarten L.; Vandenberghe, William G.; Sorée, Bart; Magnus, Wim; Fischetti, Massimo
2015-01-01
The tunneling current between two crossed graphene ribbons is described invoking the empirical pseudopotential approximation and the Bardeen transfer Hamiltonian method. Results indicate that the density of states is the most important factor determining the tunneling current between small (nm) ribbons. The quasi-one dimensional nature of graphene nanoribbons is shown to result in resonant tunneling.
Benchmark density functional theory calculations for nanoscale conductance
DEFF Research Database (Denmark)
Strange, Mikkel; Bækgaard, Iben Sig Buur; Thygesen, Kristian Sommer
2008-01-01
We present a set of benchmark calculations for the Kohn-Sham elastic transmission function of five representative single-molecule junctions. The transmission functions are calculated using two different density functional theory methods, namely an ultrasoft pseudopotential plane-wave code...
Czech Academy of Sciences Publication Activity Database
Novák, Vít; Dendisová, M.; Matějka, P.; Bouř, Petr
2016-01-01
Roč. 120, č. 32 (2016), s. 18275-18280 ISSN 1932-7447 R&D Projects: GA ČR GA13-03978S; GA ČR(CZ) GA16-05935S Institutional support: RVO:61388963 Keywords : SERS spectroscopy * consistent pseudopotentials * Ag nanoparticles Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.536, year: 2016
Interparticle interaction and transport processes in dense semiclassical plasmas
International Nuclear Information System (INIS)
Baimbetov, F.B.; Giniyatova, Sh.G.
2005-01-01
On the basis of the density response formalism an expression for the pseudopotential of dense semiclassical plasma, which takes account of quantum-mechanical effects, local field corrections, and electronic screening effects is obtained. The static structure factors taking into account both local fields and quantum-mechanical effects are calculated. An electrical conductivity, thermal conductivity, and viscosity of dense semiclassical plasma are studied
Czech Academy of Sciences Publication Activity Database
Abdel-Rahman, O. S.; Maurer, J.; Záliš, Stanislav; Winter, R. F.
2015-01-01
Roč. 34, č. 14 (2015), s. 3611-3628 ISSN 0276-7333 R&D Projects: GA MŠk LD14129 Institutional support: RVO:61388955 Keywords : BRIDGED DIRUTHENIUM COMPLEXES * AB-INITIO PSEUDOPOTENTIALS * IRON SIGMA-ACETYLIDES Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.186, year: 2015
Electronic structure calculations on nitride semiconductors and their alloys
International Nuclear Information System (INIS)
Dugdale, D.
2000-09-01
Calculations of the electronic properties of AIN, GaN, InN and their alloys are presented. Initial calculations are performed using the first principles pseudopotential method to obtain accurate lattice constants. Further calculations then investigate bonding in the nitrides through population analysis and density of state calculations. The empirical pseudopotential method is also used in this work. Pseudopotentials for each of the nitrides are constructed using a functional form that allows strained material and alloys to be studied. The conventional k.p valence band parameters for both zincblende and wurtzite are obtained from the empirical band structure using two different methods. A Monte-Carlo fitting of the k.p band structure to the pseudopotential data (or an effective mass method for the zincblende structure) is used to produce one set. Another set is obtained directly from the momentum matrix elements and energy eigenvalues at the centre of the Brillouin zone. Both methods of calculating k.p parameters produce band structure in excellent agreement with the original empirical band calculations near the centre of the Brillouin zone. The advantage of the direct method is that it produces consistent sets of parameters, and can be used in studies involving a series of alloy compositions. Further empirical pseudopotential method calculations are then performed for alloys of the nitrides. In particular, the variation of the band gap with alloy composition is investigated, and good agreement with theory and experiment is found. The direct method is used to obtain k.p parameters for the alloys, and is contrasted with the fitting approach. The behaviour of the nitrides under strain is also studied. In particular. valence band offsets for nitride heterojunctions are calculated, and a strong forward- backward asymmetry in the band offset is found, in good agreement with other results in the literature. (author)
Energy Technology Data Exchange (ETDEWEB)
Codd, J; James, M F; Mann, J E [United Kingdom Atomic Energy Authority, Reactor Group (United Kingdom)
1962-03-15
The characteristics of a system using an iron-based oxide cermet as fuel material are discussed. A transport theory investigation to develop methods of predicting the effect of core heterogeneity on reactivity and flux distribution is described. Some preliminary calculations are also given of resonance self-shielding and Doppler temperature effects in a cermet system. (author) [French] Les auteurs etudient les caracteristique s d'un reacteur utilisant comme combustible un cermet d'oxydes a armature de fer. Ils exposent une application de la theorie du transport a la mise au point des methodes permettant de prevoir l'effet de l'heterogeneite du coeur sur la reactivite et sur la distribution du flux. Ils donnent egalement quelques calculs preliminaires d'effets d'autoprotection due a la resonance et d'effet Doppler du a la chaleur dans un reacteur utilisant un cermet. (author) [Spanish] La memoria discute las caracteristicas de un sistema que emplea como combustible un oxido tipo cermet a base de hierro. Describe una investigacion de la teoria de transporte con miras a desarrollar metodos para evaluar el efecto de la heterogeneidad del cuerpo sobre la reactividad y la distribucion de flujo. Tambien da algunos calculos preliminares de los efectos del autoblindaje por resonancia y de la temperatura de Doppler en un sistema de tipo cermet. (author) [Russian] Obsuzhdayutsya kharakteristiki sistemy, ispol'zuyushchej v kachestve toplivnogo materiala oksidnye kermety, razrabotannye na osnove zheleza. Opisyvaetsya issledovanie teorii perenosa, chtoby razvit' metody predskazaniya vliyaniya geterogennosti aktivnoj zony na reaktivnost' i raspredelenie potoka. Dayutsya takzhe nekotorye predvaritel'nye raschety ehffektov rezonansnoj samozashchity i temperaturnogo ehffekta Dopplera v kermetnoj sisteme. (author)
Energy Technology Data Exchange (ETDEWEB)
Coekelbergs, R.; Crucq, A.; Decot, J.; Degols, L.; Frennet, A.; Lienard, G.; Timmerman, L. [Laboratoire de Chimie Nucleaire, Institut Interuniversitaire des Sciences Nucleaires et Ecole Royale Militaire, Bruxelles (Belgium)
1963-11-15
] Avtory obsuzhdayut protsessy kataliza, indutsirovannye radiatsiej v prisutstvii nemetallicheskikh tverdykh tel. Oni rassmatrivayut isklyuchitel'no tol'ko dejstviya, svyazannye s izmeneniem postoyannoj kontsentratsii nositelej zaryada. Vliyanie ehtogo izmeneniya na kinetiku i ravnovesie geterogennykh reaktsij rasschityvaetsya kolichestvenno v ramkakh ehlektronnoj teorii kataliza i uchityvaya ehlektronnye kharakteristiki poverkhnosti tverdogo tela. Nakonets, oni rassmatrivayut sootnoshenie, sushchestvuyushchee mezhdu ehtimi yavleniyami, aktivatsiej katalizatorov i peredachej ehnergii, opisannymi ranee. (author)
Energy Technology Data Exchange (ETDEWEB)
Makin, S M [Wantage Research Laboratory, Wantage, Berks (United Kingdom)
1962-01-15
radioizotopov v metallurgii. V khode ehtoj raboty byli sozdany novye avtoradiograficheskie metody. Oni vklyuchayut obluchenie i avtoradiografiyu ehkstraktsionnykh modelej, podobno ispol'zuemym v ehlektronnoj mikroskopii, i protsess dvukhtsvetnogo perekhoda, pri kotorom tsvetnye kopii chertezhej avtoradiografa pokazyvayutsya s sootvetstvuyushchimi nalozhennymi dannymi mikrografov. EHti metody ispol'zuyutsya pri izuchenii primesej v stali i urane i pri issledovanii segregatsii sery i fosfora pri svarke v nerzhaveyushchej stali. (author)
Hamaguchi, Chihiro
2017-01-01
This book presents a detailed description of basic semiconductor physics. The text covers a wide range of important phenomena in semiconductors, from the simple to the advanced. Four different methods of energy band calculations in the full band region are explained: local empirical pseudopotential, non-local pseudopotential, KP perturbation and tight-binding methods. The effective mass approximation and electron motion in a periodic potential, Boltzmann transport equation and deformation potentials used for analysis of transport properties are discussed. Further, the book examines experiments and theoretical analyses of cyclotron resonance in detail. Optical and transport properties, magneto-transport, two-dimensional electron gas transport (HEMT and MOSFET) and quantum transport are reviewed, while optical transition, electron-phonon interaction and electron mobility are also addressed. Energy and electronic structure of a quantum dot (artificial atom) are explained with the help of Slater determinants. The...
Nonlinear Waves in the Terrestrial Quasiparallel Foreshock.
Hnat, B; Kolotkov, D Y; O'Connell, D; Nakariakov, V M; Rowlands, G
2016-12-02
We provide strongly conclusive evidence that the cubic nonlinearity plays an important part in the evolution of the large amplitude magnetic structures in the terrestrial foreshock. Large amplitude nonlinear wave trains at frequencies above the proton cyclotron frequency are identified after nonharmonic slow variations are filtered out by applying the empirical mode decomposition. Numerical solutions of the derivative nonlinear Schrödinger equation, predicted analytically by the use of a pseudopotential approach, are found to be consistent with the observed wave forms. The approximate phase speed of these nonlinear waves, indicated by the parameters of numerical solutions, is of the order of the local Alfvén speed. We suggest that the feedback of the large amplitude fluctuations on background plasma is reflected in the evolution of the pseudopotential.
Molecular potentials and relaxation dynamics
International Nuclear Information System (INIS)
Karo, A.M.
1981-01-01
The use of empirical pseudopotentials, in evaluating interatomic potentials, provides an inexpensive and convenient method for obtaining highly accurate potential curves and permits the modeling of core-valence correlation, and the inclusion of relativistic effects when these are significant. As an example, recent calculations of the chi 1 Σ + and a 3 Σ + states of LiH, NaH, KH, RbH, and CsH and the chi 2 Σ + states of their anions are discussed. Pseudopotentials, including core polarization terms, have been used to replace the core electrons, and this has been coupled with the development of compact, highly-optimized basis sets for the corresponding one- and two-electron atoms. Comparisons of the neutral potential curves with experiment and other ab initio calculations show good agreement (within 1000 cm -1 over most of the potential curves) with the difference curves being considerably more accurate
Ab initio study on structural stability of uranium carbide
International Nuclear Information System (INIS)
Sahoo, B.D.; Joshi, K.D.; Gupta, Satish C.
2013-01-01
First principles calculations have been performed using plane wave pseudopotential and full potential linearized augmented plane wave (FP-LAPW) methods to analyze structural, elastic and dynamic stability of UC under hydrostatic compression. Our calculations within pseudopotential method suggest that the rocksalt (B1) structure will transform to body centered orthorhombic (bco) structure at ∼21.5 GPa. The FP-LAPW calculations put this transition at 23 GPa. The transition pressures determined from our calculations though agree reasonably with the experimental value of 27 GPa, the high pressure bco structure suggested by theory differs slightly from the experimentally reported pseudo bco phase. The elastic stability analysis of B1 phase suggests that the B1 to bco transition is driven by the failure of C 44 modulus. This finding is further substantiated by the lattice dynamic calculations which demonstrate that the B1 phase becomes dynamically unstable around the transition pressure and the instability is of long wavelength nature
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.)
Simulating condensation on microstructured surfaces using Lattice Boltzmann Method
Alexeev, Alexander; Vasyliv, Yaroslav
2017-11-01
We simulate a single component fluid condensing on 2D structured surfaces with different wettability. To simulate the two phase fluid, we use the athermal Lattice Boltzmann Method (LBM) driven by a pseudopotential force. The pseudopotential force results in a non-ideal equation of state (EOS) which permits liquid-vapor phase change. To account for thermal effects, the athermal LBM is coupled to a finite volume discretization of the temperature evolution equation obtained using a thermal energy rate balance for the specific internal energy. We use the developed model to probe the effect of surface structure and surface wettability on the condensation rate in order to identify microstructure topographies promoting condensation. Financial support is acknowledged from Kimberly-Clark.
Pereira, Douglas Henrique; Rocha, Carlos Murilo Romero; Morgon, Nelson Henrique; Custodio, Rogério
2015-08-01
The compact effective potential (CEP) pseudopotential was adapted to the G3(MP2) theory, herein referred to as G3(MP2)-CEP, and applied to the calculation of enthalpies of formation, ionization energies, atomization energies, and electron and proton affinities for 446 species containing elements of the 1st, 2nd, and 3rd rows of the periodic table. A total mean absolute deviation of 1.67 kcal mol(-1) was achieved with G3(MP2)-CEP, compared with 1.47 kcal mol(-1) for G3(MP2). Electron affinities and enthalpies of formation are the properties exhibiting the lowest deviations with respect to the original G3(MP2) theory. The use of pseudopotentials and composite theories in the framework of the G3 theory is feasible and compatible with the all electron approach. Graphical Abstract Application of composite methods in high-level ab initio calculations.
Structural study of the AlP, GaAs and AlAs semiconductors with wurtzite structure
International Nuclear Information System (INIS)
Bautista H, A.; Perez A, L.; Pal, U.; Rivas S, J.F.
2003-01-01
In this work we present ab initio calculations of optimization geometries, lattice constant and electronic structure for semiconductors wurtzite type, like AIN, CdS, Zn S, Zn Se, Ga N and GaAs. For this, we used the CASTEP program of CERUIS with LDA and GGA approximations, in the framework of Functional Density Theory. The used pseudopotentials are available in that program and were generated using the optimization scheme of Troullier-Martins. With the lattice constant just optimized, we calculate then the X-ray spectra for studied semiconductors.We analyzed the effect of used pseudopotentials on function of the results obtained. Finally, we predicted the geometry and X-ray pattern for AIP, AlAs and GaAs with wurtzite structure, giving evidence about the semiconductor character of these materials. (Author)
High-temperature electronic structure with the Korringa-Kohn-Rostoker Green's function method
Starrett, C. E.
2018-05-01
Modeling high-temperature (tens or hundreds of eV), dense plasmas is challenging due to the multitude of non-negligible physical effects including significant partial ionization and multisite effects. These effects cause the breakdown or intractability of common methods and approximations used at low temperatures, such as pseudopotentials or plane-wave basis sets. Here we explore the Korringa-Kohn-Rostoker Green's function method at these high-temperature conditions. The method is all electron, does not rely on pseudopotentials, and uses a spherical harmonic basis set, and so avoids the aforementioned limitations. It is found to be accurate for solid density aluminum and iron plasmas when compared to a plane-wave method at low temperature, while being able to access high temperatures.
Studies in the electronic structure of matter
International Nuclear Information System (INIS)
Swarts, C.A.
1979-01-01
The results of various theories for the angular distribution of electrons photoemitted from the outermost p-shell of rare gas atoms are compared. The theories compared are the local density theories of Slater (X/sub α/) and of Hohenberg, Kohn and Sham, the pseudopotential method, Hartree-Fock theory as evaluated by Kennedy and Manson, and Amusia's random phase approximation with exchange (RPAE). Extended Huekel theory is applied to GaAs, GaP, and to the nitrogen isoelectronic trap in GaAs and GaP. The computer perfect crystal band structures are found to be in reasonable agreement with those computed with empirical pseudopotentials. Nitrogen impurity levels in GaAs and GaP are calculated using a cluster model. By means of model calculations for an independent electron metal, exact lineshapes are obtained for the photon absorption, emission and photoemission spectra of deep core states. 97 references
Theoretical study of pressure dependence of transition temperature of In and Pb
Energy Technology Data Exchange (ETDEWEB)
Kumar, Priyank, E-mail: priyank-kumar2007@yahoo.co.in [Department of Science, Government Polytechnic, Gandhinagar -382024, Gujarat (India); Bhatt, N. K. [Department of Physics, Sardar Patel University, Vallabh Vidyanagar - 388120, Gujarat (India); Vyas, P. R.; Gohel, V. B. [Department of Physics, School of Science, Gujarat University, Ahmedabad - 380009, Gujarat (India)
2015-08-28
Recently proposed structured local pseudopotential (PP) by Fiolhais et al. has been successfully used to compute superconducting state parameters (SSP): electron-phonon coupling strength (λ), Coulomb pseudopotential (μ*), critical temperature (T{sub c}), effective interaction strength (N{sub 0}V), isotopic effect parameter (α) and their pressure dependence of non-transition metals In and Pb as a test case. Pressure dependence of the Debye temperature has been computed by Gruneisen model. Present results are in good agreement with experimental and other theoretical results. Present study has been further extended to estimate volume (critical volume) at which λ=μ*, where Tc and N{sub 0}V becomes zero. The presently used model is found to be transferable at the extreme environment without any adjustment of parameters further alongwith its simplicity and predictivity.
Nonlinear acoustic waves in nonthermal plasmas with negative and positive dust
International Nuclear Information System (INIS)
Verheest, Frank
2009-01-01
Using a Sagdeev pseudopotential formalism where nonlinear structures are stationary in a co-moving frame, large dust-acoustic solitary waves and double layers have been studied in plasmas with negative and positive cold dust, in the presence of nonthermal electrons and ions. This has been done in a systematic way, to delimit the compositional parameter space in which such modes can be found. The existence domain of negative/positive solitary waves is limited by infinite compression of the negative/positive dust or by the occurrence of negative/positive double layers. These double layers require a sufficient nonthermality of the electrons/ions and the presence of enough positive/negative dust. There are parameter ranges where both negative and positive solitary structures coexist, sometimes both of the solitary wave type, sometimes one a solitary wave and the other a double layer. Typical Sagdeev pseudopotentials and solitary wave profiles have been presented.
Compressive and rarefactive solitary waves in nonthermal two-component plasmas
International Nuclear Information System (INIS)
Verheest, Frank; Hellberg, Manfred A.
2010-01-01
Using a Sagdeev pseudopotential formalism where nonlinear structures are stationary in a comoving frame, large ion-acoustic solitary waves and double layers have been studied in plasmas with positive ions and nonthermal electrons. The velocity range of positive, compressive solitary waves is limited by the ion density reaching infinite compression, whereas negative, rarefactive solitary waves and double layers can exist when the electron nonthermality exceeds a certain minimum. There are even regions of coexistence, the limits of which can be elucidated by considering the properties of the special Sagdeev pseudopotential at the acoustic speed. In particular, when the compositional parameters and Mach numbers admit only compressive or rarefactive solitary structures, these have to be superacoustic, their amplitude vanishing at the acoustic speed. When both compressive and rarefactive modes can occur, one of them is Korteweg-de Vries (KdV)-like, the other having a non-KdV character, with a finite amplitude at the acoustic speed.
Ideal flux field dielectric concentrators.
García-Botella, Angel
2011-10-01
The concept of the vector flux field was first introduced as a photometrical theory and later developed in the field of nonimaging optics; it has provided new perspectives in the design of concentrators, overcoming standard ray tracing techniques. The flux field method has shown that reflective concentrators with the geometry of the field lines achieve the theoretical limit of concentration. In this paper we study the role of surfaces orthogonal to the field vector J. For rotationally symmetric systems J is orthogonal to its curl, and then a family of surfaces orthogonal to the lines of J exists, which can be called the family of surfaces of constant pseudopotential. Using the concept of the flux tube, it is possible to demonstrate that refractive concentrators with the shape of these pseudopotential surfaces achieve the theoretical limit of concentration.
Electrical resistivity of liquid noble metal alloys
International Nuclear Information System (INIS)
Anis Alam, M.; Tomak, M.
1983-08-01
Calculations of the dependence of the electrical resistivity in liquid Ag-Au, Cu-Ag, Cu-Au binary alloys on composition are reported. The structure of the binary alloy is described as a hard sphere system. A one-parameter local pseudopotential, which incorporates s-d hybridization effects phenomenologically, is employed in the resistivity calculation. A reasonable agreement with experimental trends is observed in cases where experimental information is available. (author)
Prolongation structure and linear eigenvalue equations for Einstein-Maxwell fields
International Nuclear Information System (INIS)
Kramer, D.; Neugebauer, G.
1981-01-01
The Einstein-Maxwell equations for stationary axisymmetric exterior fields are shown to be the integrability conditions of a set of linear eigenvalue equations for pseudopotentials. Using the method of Wahlquist and Estabrook (J. Math Phys.; 16:1 (1975)) it is shown that the prolongation structure of the Einstein-Maxwell equations contains the SU(2,1) Lie algebra. A new mapping of known solutions to other solutions has been found. (author)
Electron removal from H and He atoms in collisions with C q+ , O q+ ions
Janev, R. K.; McDowell, M. R. C.
1984-06-01
Cross sections for electron capture and ionisation in collision of partially and completely stripped C q+ , N q+ and O q+ ions with hydrogen and helium atoms have been calculated at selected energies. The classical trajectory Monte Carlo method was used with a variable-charge pseudopotential to describe the interaction of the active electron with the projectile ion. A scalling relationship has been derived for the electron removal (capture and ionisation) cross section which allows a unifield representation of the data.
Fractional Quantum Hall Effect in n = 0 Landau Band of Graphene with Chern Number Matrix
Kudo, Koji; Hatsugai, Yasuhiro
2018-06-01
Fully taking into account the honeycomb lattice structure, fractional quantum Hall states of graphene are considered by a pseudopotential projected into the n = 0 Landau band. By using chirality as an internal degree of freedom, the Chern number matrices are defined and evaluated numerically. Quantum phase transition induced by changing a range of the interaction is demonstrated that is associated with chirality ferromagnetism. The chirality-unpolarized ground state is consistent with the Halperin 331 state of the bilayer quantum Hall system.
Atomistic simulation of the mechanical properties of β-SiC based on the first-principles
Energy Technology Data Exchange (ETDEWEB)
Zhang, Renhui, E-mail: zrh_111@126.com [Research Center of Material and Chemical Engineering, School of Material and Chemical Engineering, Tongren University, Tongren 554300 (China); Leng, Senlin, E-mail: 764546880@qq.com [Research Center of Material and Chemical Engineering, School of Material and Chemical Engineering, Tongren University, Tongren 554300 (China); Yang, Yingchang; Shi, Wei [Research Center of Material and Chemical Engineering, School of Material and Chemical Engineering, Tongren University, Tongren 554300 (China); Lu, Zhibin, E-mail: zblu@licp.cas.cn [Lanzhou Institute of Chemical Physics, Lanzhou 730000 (China)
2017-05-01
On the basis of the pseudopotential plane-wave method and the local-density-functional theory, this work studied the energetics and stress-strain relationship of β-SiC, where uniform uniaxial compression and tension were considered along (001), (110) and (111) planes. The calculated results were in consistence with the experimental data. The present work should be conducive to understanding the mechanical property of β-SiC.
Calculation of inelastic cross sections for H+ + Cs → H(n=2) + Cs+
International Nuclear Information System (INIS)
Valance, A.; Spiess, G.
1975-01-01
The cross sections for the processes H + +Cs → H(2p and 2s) +Cs + were calculated in the center of mass energy range 250--2400 eV using a simple pseudopotential formalism for the potential curves and coupling matrix elements and a perturbed stationary state (pss) formulation for the calculation of the cross sections. The results are found to be in reasonable agreement with experiment. (auth)
Phonon spectrum, mechanical and thermophysical properties of thorium carbide
International Nuclear Information System (INIS)
Pérez Daroca, D.; Jaroszewicz, S.; Llois, A.M.; Mosca, H.O.
2013-01-01
In this work, we study, by means of density functional perturbation theory and the pseudopotential method, mechanical and thermophysical properties of thorium carbide. These properties are derived from the lattice dynamics in the quasi-harmonic approximation. The phonon spectrum of ThC presented in this article, to the best authors’ knowledge, have not been studied, neither experimentally, nor theoretically. We compare mechanical properties, volume thermal expansion and molar specific capacities with previous results and find a very good agreement
Theoretical x-ray absorption investigation of high pressure ice and compressed graphite
International Nuclear Information System (INIS)
Shaw, Dawn M; Tse, John S
2007-01-01
The x-ray absorption spectra (XAS) of high pressure ices II, VIII, and IX have been computed with the Car-Parrinello plane wave pseudopotential method. XAS for the intermediate structures obtained from uniaxial compression of hexagonal graphite along the c-axis are also studied. Whenever possible, comparisons to available experimental results are made. The reliability of the computational methods for the XAS for these structures is discussed
Phonon spectrum, mechanical and thermophysical properties of 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 (Argentina); Consejo Nacional de Investigaciones Cientı´ficas y Técnicas (Argentina); Jaroszewicz, S. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Consejo Nacional de Investigaciones Cientı´ficas 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)
2013-06-15
In this work, we study, by means of density functional perturbation theory and the pseudopotential method, mechanical and thermophysical properties of thorium carbide. These properties are derived from the lattice dynamics in the quasi-harmonic approximation. The phonon spectrum of ThC presented in this article, to the best authors’ knowledge, have not been studied, neither experimentally, nor theoretically. We compare mechanical properties, volume thermal expansion and molar specific capacities with previous results and find a very good agreement.
Indian Academy of Sciences (India)
Charge density calculations and electronic band structures for GaAl1- = 1.0, 0.5 and 0.0 are presented in this work. The calculations are performed using the empirical pseudopotential method. The charge density is computed for a number of planes, i.e. = 0:0, 0.125 and 0.25 0 by generating the potential through a ...
Energy Technology Data Exchange (ETDEWEB)
Wagner, Jan-Martin
2004-10-14
In this dissertation, ab-initio investigations of the strain influence on vibrational properties of GaN and AlN as well as of short-period GaN/AlN superlattices are presented. Based on densityfunctional theory and density-functional perturbation theory, for differently strained structures complete phonon spectra and related properties are calculated using the local-density approximation and norm-conserving pseudopotentials. (orig.)
Electronic states in Li/sub c/Mg/sub l-c/ alloys: soft x-ray emission spectra
International Nuclear Information System (INIS)
Stocks, G.M.; Tagle, J.A.; Callcott, T.A.; Arakawa, E.T.
1980-01-01
A first principles theory is developed for Li-Mg alloy systems which avoids the use of pseudo-potentials and, more importantly, low-order perturbation theory and which can be checked quantitatively against detailed probes of the electronic structure such as soft x-ray spectroscopy. These calculations can then be used as a base against which the psuedo-potential methods can, in the future, be checked
Introduction Of Computational Materials Science
International Nuclear Information System (INIS)
Lee, Jun Geun
2006-08-01
This book gives, descriptions of computer simulation, computational materials science, typical three ways of computational materials science, empirical methods ; molecular dynamics such as potential energy, Newton's equation of motion, data production and analysis of results, quantum mechanical methods like wave equation, approximation, Hartree method, and density functional theory, dealing of solid such as pseudopotential method, tight-binding methods embedded atom method, Car-Parrinello method and combination simulation.
International Nuclear Information System (INIS)
Garrett, W.R.
1979-01-01
Through the use of a molecular pseudopotential method, we determine the a approximate magnitudes of errors that result when electron affinity determinations of polar negative ions are made through ab initio calculations in which the use of a given basis set yields inappropriate values for permanent and induced dipole moments of the neutral molecule. These results should prove useful in assessing the adequacy of basis sets in ab initio calculations of molecular electron affinities for simple linear polar molecules
Valence and atomic size dependent exchange barriers in vacancy-mediated dopant diffusion
International Nuclear Information System (INIS)
Nelson, J.S.; Schultz, P.A.; Wright, A.F.
1998-01-01
First-principles pseudopotential calculations of dopant-vacancy exchange barriers indicate a strong dependency on dopant valence and atomic size, in contrast to current models of vacancy-mediated dopant diffusion. First-row elements (B, C, N) are found to have exchange barriers which are an order of magnitude larger than the assumed value of 0.3 eV (the Si vacancy migration energy). copyright 1998 American Institute of Physics
International Nuclear Information System (INIS)
Kukulin, V.I.; Pomerantsev, V.N.
1976-01-01
Method of rearrangement of the Born series in scattering theory is proposed which uses the corthogonal projecting pseudopotentials (OPP) proposed recently. It is proved vigorously that the rearranged Born series will converge for all negative and small positive energy value seven in the presence of bound states. Method of correct introduction of scattering operators in orthogonal subspaces is displayed. Comparison of the OPP method with the projection technique developed by Feschbach is given. Physical applications of the method formulated are discussed
Cesium under pressure: First-principles calculation of the bcc-to-fcc phase transition
Carlesi, S.; Franchini, A.; Bortolani, V.; Martinelli, S.
1999-05-01
In this paper we present the ab initio calculation of the structural properties of cesium under pressure. The calculation of the total energy is done in the local-density approximation of density-functional theory, using a nonlocal pseudopotential including the nonlinear core corrections proposed by Louie et al. The calculation of the pressure-volume diagram for both bcc and fcc structures allows us to prove that the transition from bcc to fcc structure is a first-order transition.
Asymptotic elastic energy in simple metals
International Nuclear Information System (INIS)
Khalifeh, J.M.
1983-07-01
The asymptotic form of the elastic binding energy ΔEsup(as)(R) between two Mg atoms in Al is expressed as a product of a lattice Green function and the dipole force tensor P. The quantity P is obtained by a nearly free electron model in which the impurity effect is introduced by a screened Ashcroft pseudopotential characterized by an excess charge ΔZ and a core radius rsub(j). (author)
Studies in the electronic structure of matter
International Nuclear Information System (INIS)
Miller, D.L.
1979-01-01
KLL Auger transition rates for helium are computed using simple atomic orbital wavefunctions which take into account the difference in average electron--electron repulsion of initial and final states. The results are consistent with transition rates computed by other authors using a variety of many-electron techniques. It is suggested that wavefunctions determined in the manner described provide a useful representation of the autoionizing state within the first Bohr radius. A method for extracting atomic pseudopotentials from photoelectron angular distributions is described and applied photoionization of the outermost p shells of Ar, Kr, and Xe and to the 4d shell of Xe. The pseudopotentials obtained reproduce the data, and also predict accurate cross sections and phase shifts for photoelectron energies up to 100 eV. It is suggested that the pseudopotentials aptly mimic the effects of intrashell electron--electron correlations in the photoionization process. The extended Hueckel theory is applied to the nitrogen trap in GaAs and GaP. Perfect crystal band structures are computed and are shown to be in reasonable agreement with those computed with empirical pseudopotentials. Nitrogen impurity levels in GaAs and GaP are computed using an extended Hueckel cluster model. In each case the model predicts two states within the band gap, in contrast to experiment which detects one impurity state in GaP and none in GaAs. It is suggested that the choice of cluster used unrealistically concentrates states near the conduction band edge on the central atom
Nonlinear Excitations in Strongly-Coupled Fermi-Dirac Plasmas
Akbari-Moghanjoughi, M.
2012-01-01
In this paper we use the conventional quantum hydrodynamics (QHD) model in combination with the Sagdeev pseudopotential method to explore the effects of Thomas-Fermi nonuniform electron distribution, Coulomb interactions, electron exchange and ion correlation on the large-amplitude nonlinear soliton dynamics in Fermi-Dirac plasmas. It is found that in the presence of strong interactions significant differences in nonlinear wave dynamics of Fermi-Dirac plasmas in the two distinct regimes of no...
Energy Technology Data Exchange (ETDEWEB)
Kumar, J [Agra Coll. (India). Dept. of Physics
1977-03-01
In the present work, a local model pseudopotential has been proposed to study the lattice dynamics of thorium. The model potential depends on the core and ionic radii, and accounts for the s-d-f hybridization effects in a phenomenological way. When this form of potential is applied to derive the photon dispersion curves of Th, sufficiently good agreement is found between the computed and experimental results.
Optical transitions and nature of Stokes shift in spherical CdS quantum dots
Demchenko, D. O.; Wang, Lin-Wang
2006-01-01
We study the structure of the energy spectra along with the character of the states participating in optical transitions in colloidal CdS quantum dots (QDs) using the {\\sl ab initio} accuracy charge patching method combined with the %pseudopotential based folded spectrum calculations of electronic structure of thousand-atom nanostructures. In particular, attention is paid to the nature of the large resonant Stokes shift observed in CdS quantum dots. We find that the top of the valence band st...
Potentials for the Modified Cam-Clay model
Zouain , Nestor; Pontes , Ivaldo; Vaunat , Jean
2009-01-01
Abstract Energy and dissipation pseudo-potentials are employed to derive constitutive relationships, in the context of thermodynamic concepts, for the widely used Modified Cam-Clay (MCC) model for soil mechanics. A variational formulation of the MCC evolution equations is proposed in this paper. Since plastic collapse of MCC soils cannot be embedded in the classical limit analysis theory, finding the critical amplification of the load that produces plastic collapse is formulated in...
International Nuclear Information System (INIS)
Ginejtite, V.L.; Balyavichyus, L.Z.
1979-01-01
Some shortcomings of the semiempirical method CNDO/1 (complete naglect of differential overlap) taking into account wave function orthogonalities of outer valence electrons to inner shells are being explained. To avoid these shortcomings the introduction of pseudopotential is recommended. Addition of the potential excludes overestimation of attraction among chemically unbounded atoms, corrects underestimation of the single, double and triple S-S coupling, gives reasons for some suppositions of the semiempirical methods, gives a truthful distribution of the electronic levels
Screening of ionic cores in partially ionized plasmas within linear response
International Nuclear Information System (INIS)
Gericke, D. O.; Vorberger, J.; Wuensch, K.; Gregori, G.
2010-01-01
We employ a pseudopotential approach to investigate the screening of ionic cores in partially ionized plasmas. Here, the effect of the tightly bound electrons is condensed into an effective potential between the (free) valence electrons and the ionic cores. Even for weak electron-ion coupling, the corresponding screening clouds show strong modifications from the Debye result for elements heavier than helium. Modifications of the theoretically predicted x-ray scattering signal and implications on measurements are discussed.
A new electron gas model for lattice vibrations in metals I : development of the model
International Nuclear Information System (INIS)
Ramamurthy, V.; Neelkandan, K.
1978-01-01
The theoretical study of the lattice dynamics of metals is generally based on either the phenomenological force constant method or the pseudopotential method. However, it has been found that all the existing phenomenological models are inconsistent. Hence a new model based on the deformation potential approximation has been developed. By comparing this model with the existing models, its salient features and limitations are discussed. (author)
International Nuclear Information System (INIS)
Rossi, F.N.
1986-10-01
The adiabatic potential lines are first obtained through the use of a pseudo-potential, depending on the electronic orbital moment. A perturbative method is then used to generate the potential surfaces, according to the potential lines. A quantum calculation in the thermal energy domain is realized, for the cross-sections concerning the structure transitions of the Rubidium, induced by the collision with hydrogen or deuterium molecules. This allowed the interpretation of the experimentally observed isotopic effect [fr
Electronic structure of the rotation twin stacking fault in β-ZnS
International Nuclear Information System (INIS)
Northrup, J.E.; Cohen, M.L.
1981-01-01
The electronic structure of the rotation twin stacking fault in β-ZnS is calculated with the self-consistent pseudopotential method. The stacking fault creates a potential barrier of approx.0.07 eV and induces the localization of stacking-fault resonances near the top of the valence band. Stacking-fault states are also predicted to exist in the various gaps in the projected valence-band structure
International Nuclear Information System (INIS)
Tian, F.; Tian, H.; Whitmore, L.; Ye, L.Y.
2015-01-01
The energy dependent on volume of hexagonal close-packed (hcp) nickel with different magnetism is calculated by full-potential linearized augmented plane wave method. Based on the calculation ferromagnetic state is found to be the most stable state. The magnetic moment of hcp Ni is calculated and compared to those calculated by different pseudo-potential methods. Furthermore, it is also compared to that of face-centered cubic (fcc) one with the reason discussed
Scattering of charged particles by a multicenter potential
International Nuclear Information System (INIS)
Gerasimov, O.I.; Stienko, A.G.
1994-01-01
Exact expressions are obtained for the amplitude and elastic cross section in the case of scattering of charged particles by a multicenter pseudopotential that includes the Coulomb potential and an arbitrary number of short-range potentials (modeled by zero-range potentials). Asymptotic limits are calculated and explicit expressions are found for the amplitudes of scattering by few-nucleon complexes modeled by superpositions of the Coulomb potential and purely point potentials
Directory of Open Access Journals (Sweden)
Muhammady Shibghatullah
2018-03-01
Full Text Available We report structural, electronic, and magnetic properties of SrCoO3 in Pm3̅m and P4/mbm space groups, which are calculated by using generalized gradient approximation corrected with on-site Coulomb repulsion U and exchange energies J. The cubic lattice parameter a and local magnetic moments of Co (μCo are optimized by varying U at Co 3d site. Employing ultrasoft pseudopotential, the values of U = 8 eV and J = 0.75 eV are the best choice for Pm3̅m space group. We found the value of μCo = 2.56 μB, which is consistent with the previous results. It was also found that Co 3d, hybridized with O 2p, is the main contributor to ferromagnetic metallic properties. Besides, norm-conserving pseudopotential promotes a, which is in good agreement with experimental result. However, it is not suitable for P4/mbm space group. By using ultrasoft pseudopotential, the value of U = 3 eV (J = 0.75 is the most suitable for P4/mbm group. Ferromagnetic metallic properties, Jahn-Teller distortion, and reasonable lattice parameters have been obtained. This study shows that U has significant contribution to the calculated properties and also points out that P4/mbm space group with US-PP is suitable to describe experimental results.
Structure factors and phonon dispersion in liquid Li0.61Na0.39 alloy
International Nuclear Information System (INIS)
Pratap, Arun; Lad, Kirit N.; Raval, K.G.
2004-01-01
The phonon spectra for liquid Li and Na have been computed through the phenomenological model of Bhatia and Singh for disordered systems like liquids and glasses and the obtained results have been compared with the available data obtained by inelastic neutron scattering (INS) and inelastic X-ray scattering (IXS) experiments. The effective pair potentials and their space derivatives are important ingredients in the computation of the dispersion curves. The pair potentials are obtained using the pseudo-potential theory. The empty core model proposed by Ashcroft is widely used for pseudo-potential calculations for alkali metals. But, it is thought to be unsuitable for Li because of its simple 1s electronic structure. However, it can be used with an additional term known as Born-Mayer (BM) core term. The influence of the BM core term on the phonon dispersion is discussed. The same pseudo-potential formalism has been employed to obtain the dispersion relation in liquid Li 0.61 Na 0.39 alloy. Apart from the phonon spectra, the Ashcroft-Langreth structure factors in the alloy are derived in the Percus-Yevick approximation. (author)
Theoretical study of the aluminum melting curve to very high pressure
International Nuclear Information System (INIS)
Moriarty, J.A.; Young, D.A.; Ross, M.
1984-01-01
A detailed theoretical study of the Al melting curve from normal melting conditions to pressures in the vicinity of 2 Mbar is presented. The analysis is based on two parallel, but distinct, treatments of the metal: the first from rigorous generalized pseudopotential theory involving first-principles nonlocal pseudopotentials and the second from a parametrized local pseudopotential model which has been accurately fit to first-principles band-theory and experimental equation-of-state data. Both treatments utilize full lattice-dynamical calculations of the phonon free energy in the solid, within the harmonic approximation, and fluid variational theory to obtain the free energy of the liquid. Particular attention is focused on the choice of the reference system in implementing the fluid variational theory. It is shown that in Al the soft-sphere model of Ross produces a lower (and hence more accurate) liquid free energy than either the hard-sphere or one-component-plasma reference systems, and is, moreover, necessary to obtain a reasonable quantitative description of the melting properties. With the soft-sphere system, the two theoretical treatments give results in good overall agreement with each other and with experiment. In particular, melting on the shock Hugoniot is predicted to begin at about 1.2 Mbar and to end at about 1.55 Mbar, in excellent agreement with the recent preliminary measurements of McQueen
International Nuclear Information System (INIS)
Hsu, W.
1984-01-01
A unified theory of effective interaction, elementary excitations, transport properties, and possible superfluidity of 3 He- 4 He mixtures was developed. The basic approach is patterned after that of Aldrich and Pines (AP) for pure 4 He and 3 He, in which the consequence of the strong interactions in 3 He and 4 He is described in terms of self-consistent fields. The strength of these fields are determined by physical arguments, static measurement, and sum rule considerations. A set of pseudopotentials was developed to describe the 3 He- 3 He and 3 He- 4 He interactions. In the long wavelength and zero concentration limit, these potentials are obtained by the thermodynamic argument of Bardeen, Baym, and Pines. At finite concentration and finite momentum transfer, these potentials are obtained with the aids of a scaling law and the AP pseudopotential theory. From these pseudopotentials, the scattering amplitudes, transport coefficients, and normal-superfluid transition temperature are calculated as functions of 3 He concentration. Good agreement is obtained between theory and experiment for low temperature transport coefficients, and the 3 He superfluid transition temperature is predicted to be approx. -80 K. The change in the density fluctuation excitation spectrum of 4 He atoms in 3 He- 4 He mixtures is calculated
Vonroos, O. H.
1982-01-01
A theory of deep point defects imbedded in otherwise perfect semiconductor crystals is developed with the aid of pseudopotentials. The dominant short-range forces engendered by the impurity are sufficiently weakened in all cases where the cancellation theorem of the pseudopotential formalism is operative. Thus, effective-mass-like equations exhibiting local effective potentials derived from nonlocal pseudopotentials are shown to be valid for a large class of defects. A two-band secular determinant for the energy eigenvalues of deep defects is also derived from the set of integral equations which corresponds to the set of differential equations of the effective-mass type. Subsequently, the theory in its simplest form, is applied to the system Al(x)Ga(1-x)As:Se. It is shown that the one-electron donor level of Se within the forbidden gap of Al(x)Ga(1-x)As as a function of the AlAs mole fraction x reaches its maximum of about 300 meV (as measured from the conduction band edge) at the cross-over from the direct to the indirect band-gap at x = 0.44 in agreement with experiments.
Molecular potentials and relaxation dynamics
International Nuclear Information System (INIS)
Karo, A.M.
1981-01-01
The use of empirical pseudopotentials, in evaluating interatomic potentials, provides an inexpensive and convenient method for obtaining highly accurate potential curves and permits the modeling of core-valence correlation, and the inclusion of relativistic effects when these are significant. Recent calculations of the X 1 Σ + and a 3 Σ + states of LiH, NaH, KH, RbH, and CsH and the X 2 Σ + states of their anions are discussed. Pseudopotentials, including core polarization terms, have been used to replace the core electrons, and this has been coupled with the development of compact, higly-optimized basis sets for the corresponding one- and two-electron atoms. Comparisons of the neutral potential curves with experiment and other ab initio calculations show good agreement (within 1000 cm -1 over most of the potential curves) with the difference curves being considerably more accurate. In the method of computer molecular dynamics, the force acting on each particle is the resultant of all interactions with other atoms in the neighborhood and is obtained as the derivative of an effective many-body potential. Exploiting the pseudopotential approach, in obtaining the appropriate potentials may be very fruitful in the future. In the molecular dynamics example considered here, the conventional sum-of-pairwise-interatomic-potentials (SPP) approximation is used with the potentials derived either from experimental spectroscopic data or from Hartree-Fock calculations. The problem is the collisional de-excitation of vibrationally excited molecular hydrogen at an Fe surface. The calculations have been carried out for an initial vibrotational state v = 8, J = 1 and a translational temperature corresponding to a gas temperature of 500 0 K. Different angles of approach and different initial random impact points on the surface have been selected. For any given collision with the wall, the molecule may pick up or lose vibrotatonal and translational energy
Studies in the electronic structure of matter
International Nuclear Information System (INIS)
Swarts, C.A.
1979-01-01
Chapter I: Here the results of various theories for the angular distribution of electrons photoemitted from the outermost p-shell of rare gas atoms are compared. The theories compared are (I) the local density theories of Slater (X/sub α/) and of Hohenberg, Kohn and Sham, (II) the pseudopotential method, (III) Hartree-Fock theory as evaluated by Kennedy and Manson, and (IV) Amusia's Random Phase Approximation with Exchange (RPAE). It is shown that the local density theories, although simple, generally fail to produce reliable cross section; the more complicated Hartree-Fock method is no more reliable; the a priori RPAE method is most reliable, but tedious; and the phenomenological pseudopotential method offers a good combination of reliability and simplicity. The muffin-tin approximation, widely used in molecular and condensed matter physics, is examined and found to be adequate. Chapter II: Extended Hueckel theory is applied to GaAs, GaP and to the nitrogen isoelectronic trap in GaAs and GaP. The computed perfect crystal band structures are found to be in reasonable agreement with those computed with empirical pseudopotentials. Nitrogen impurity levels in GaAs and GaP are calculated using a cluster model. Chapter III: By means of model calculations for an independent electron metal, we obtain exact lineshapes for the photon absorption, emission and photoemission spectra of deep core states. We find in each case an X-ray edge anomaly as pedicted by Nozieres and De Dominicis. Sumrules are used as a general check on the calculations and to explain the deviations of the exact theory from the exciton theory away from threshold
International Nuclear Information System (INIS)
Dardouri, Riadh; Habli, Héla; Oujia, Brahim; Gadéa, Florent Xavier
2012-01-01
Graphical abstract: We present the resulting 12 1 Σ + diabatic potential energy curves where they are labeled D 1 for the ionic Li − K + and D 2 to D 12 for other. Highlights: ► Our ab initio study has been conducted for 48 electronic states of LiK molecule. ► We use pseudo-potential for the core and large basis sets for the Rydberg states. ► The calculations rely on ab initio pseudo-potential and full valence CI approaches. ► Diabatic potentials are analyzed, revealing the strong imprint of the ionic 1 Σ + state. - Abstract: For all states dissociating below the ionic limit Li − K + , we perform an adiabatic and diabatic study for 1 Σ + electronic states dissociating into K (4s, 4p, 4d, 5s, 5p, 5d, 6s) + Li (2s, 2p, 3s). Furthermore, we present the adiabatic results for the 1–11 3 Σ, 1–8 1,3 Π and 1–4 1,3 Δ states. The present calculations on the KLi molecule are complementary to previous theoretical work on this system, including recently observed electronic states that had not been calculated previously. The calculations rely on an ab initio pseudo-potential, Core Polarization Potential operators for the core–valence correlation and full valence CI approaches, combined to an efficient diabatization procedure. For the low-lying states, our spectroscopic constants and vibrational level spacing are in good agreement with the available experimental data. Diabatic potentials and permanent dipole moments are analyzed, revealing the strong imprint of the ionic state in the 1 Σ + adiabatic states.
Energy Technology Data Exchange (ETDEWEB)
Dardouri, Riadh, E-mail: dardouririad@yahoo.fr [Laboratoire de Physique Quantique, Faculte des Sciences de Monastir, Avenue de l' Environnement, 5019 Monastir (Tunisia); Habli, Hela [Laboratoire de Physique Quantique, Faculte des Sciences de Monastir, Avenue de l' Environnement, 5019 Monastir (Tunisia); Oujia, Brahim; Gadea, Florent Xavier [Laboratoire de Chimie et Physique Quantique, UMR 5626 du CNRS, Universite de Toulouse, UPS, 118 route de Narbonne, 31062 Toulouse Cedex 4 (France)
2012-05-03
Graphical abstract: We present the resulting 12 {sup 1}{Sigma}{sup +} diabatic potential energy curves where they are labeled D{sub 1} for the ionic Li{sup -}K{sup +} and D{sub 2} to D{sub 12} for other. Highlights: Black-Right-Pointing-Pointer Our ab initio study has been conducted for 48 electronic states of LiK molecule. Black-Right-Pointing-Pointer We use pseudo-potential for the core and large basis sets for the Rydberg states. Black-Right-Pointing-Pointer The calculations rely on ab initio pseudo-potential and full valence CI approaches. Black-Right-Pointing-Pointer Diabatic potentials are analyzed, revealing the strong imprint of the ionic {sup 1}{Sigma}{sup +} state. - Abstract: For all states dissociating below the ionic limit Li{sup -}K{sup +}, we perform an adiabatic and diabatic study for {sup 1}{Sigma}{sup +} electronic states dissociating into K (4s, 4p, 4d, 5s, 5p, 5d, 6s) + Li (2s, 2p, 3s). Furthermore, we present the adiabatic results for the 1-11 {sup 3}{Sigma}, 1-8 {sup 1,3}{Pi} and 1-4 {sup 1,3}{Delta} states. The present calculations on the KLi molecule are complementary to previous theoretical work on this system, including recently observed electronic states that had not been calculated previously. The calculations rely on an ab initio pseudo-potential, Core Polarization Potential operators for the core-valence correlation and full valence CI approaches, combined to an efficient diabatization procedure. For the low-lying states, our spectroscopic constants and vibrational level spacing are in good agreement with the available experimental data. Diabatic potentials and permanent dipole moments are analyzed, revealing the strong imprint of the ionic state in the {sup 1}{Sigma}{sup +} adiabatic states.
Motamarri, Phani; Gavini, Vikram
2018-04-01
We derive the expressions for configurational forces in Kohn-Sham density functional theory, which correspond to the generalized variational force computed as the derivative of the Kohn-Sham energy functional with respect to the position of a material point x . These configurational forces that result from the inner variations of the Kohn-Sham energy functional provide a unified framework to compute atomic forces as well as stress tensor for geometry optimization. Importantly, owing to the variational nature of the formulation, these configurational forces inherently account for the Pulay corrections. The formulation presented in this work treats both pseudopotential and all-electron calculations in a single framework, and employs a local variational real-space formulation of Kohn-Sham density functional theory (DFT) expressed in terms of the nonorthogonal wave functions that is amenable to reduced-order scaling techniques. We demonstrate the accuracy and performance of the proposed configurational force approach on benchmark all-electron and pseudopotential calculations conducted using higher-order finite-element discretization. To this end, we examine the rates of convergence of the finite-element discretization in the computed forces and stresses for various materials systems, and, further, verify the accuracy from finite differencing the energy. Wherever applicable, we also compare the forces and stresses with those obtained from Kohn-Sham DFT calculations employing plane-wave basis (pseudopotential calculations) and Gaussian basis (all-electron calculations). Finally, we verify the accuracy of the forces on large materials systems involving a metallic aluminum nanocluster containing 666 atoms and an alkane chain containing 902 atoms, where the Kohn-Sham electronic ground state is computed using a reduced-order scaling subspace projection technique [P. Motamarri and V. Gavini, Phys. Rev. B 90, 115127 (2014), 10.1103/PhysRevB.90.115127].
Incipient localization and tight-binding superconductivity: Tsub(c) calculation
International Nuclear Information System (INIS)
Kolley, E.; Kolley, W.
1984-01-01
Localization effects on the superconducting transition temperature Tsub(c) are examined in strongly disordered three-dimensional systems. A tight-binding formulation of strong-coupling superconductivity is combined, after configuration averaging, with the self-consistent treatment of Anderson localization developed by Vollhardt and Woelfle. The Coulomb interaction becomes retarded via the joint local local density of states, giving rise to an enhancement of the pseudopotential. Numerical Tsub(c) results as a function of disorder are compared with another theoretical work and experimental values for some high-Tsub(c) materials. (orig.)
Saidi, F.; Sebaa, N.; Mahmoudi, A.; Aourag, H.; Merad, G.; Dergal, M.
2018-06-01
We performed first-principle calculations to investigate structural, phase stability, electronic and mechanical properties for the Laves phases YM2 (M = Mn, Fe, Co) with C15, C14 and C36 structures. We used the density functional theory within the framework of both pseudo-potentials and plane wave basis using VASP (Vienna Ab Initio Software Package). The calculated equilibrium structural parameters are in accordance with available theoretical values. Mechanical properties were calculated, discussed, and analyzed with data mining approach in terms of structure stability. The results reveal that YCo2 is harder than YFe2 and YMn2.
Surface modelling on heavy atom crystalline compounds: HfO2 and UO2 fluorite structures
International Nuclear Information System (INIS)
Evarestov, Robert; Bandura, Andrei; Blokhin, Eugeny
2009-01-01
The study of the bulk and surface properties of cubic (fluorite structure) HfO 2 and UO 2 was performed using the hybrid Hartree-Fock density functional theory linear combination of atomic orbitals simulations via the CRYSTAL06 computer code. The Stuttgart small-core pseudopotentials and corresponding basis sets were used for the core-valence interactions. The influence of relativistic effects on the structure and properties of the systems was studied. It was found that surface properties of Mott-Hubbard dielectric UO 2 differ from those found for other metal oxides with the closed-shell configuration of d-electrons
Surface modelling on heavy atom crystalline compounds: HfO{sub 2} and UO{sub 2} fluorite structures
Energy Technology Data Exchange (ETDEWEB)
Evarestov, Robert [Department of Quantum Chemistry, St. Petersburg State University, 26 Universitetsky Prospect, Peterhof, St. Petersburg 198504 (Russian Federation)], E-mail: re1973@re1973.spb.edu; Bandura, Andrei; Blokhin, Eugeny [Department of Quantum Chemistry, St. Petersburg State University, 26 Universitetsky Prospect, Peterhof, St. Petersburg 198504 (Russian Federation)
2009-01-15
The study of the bulk and surface properties of cubic (fluorite structure) HfO{sub 2} and UO{sub 2} was performed using the hybrid Hartree-Fock density functional theory linear combination of atomic orbitals simulations via the CRYSTAL06 computer code. The Stuttgart small-core pseudopotentials and corresponding basis sets were used for the core-valence interactions. The influence of relativistic effects on the structure and properties of the systems was studied. It was found that surface properties of Mott-Hubbard dielectric UO{sub 2} differ from those found for other metal oxides with the closed-shell configuration of d-electrons.
Energy Technology Data Exchange (ETDEWEB)
Chauhan, Mamta; Gupta, Dinesh C., E-mail: sosfizix@gmail.com, E-mail: mamta-physics@yahoo.co.in [Condensed Matter Theory Group, School of Studies in Physics, Jiwaji University, Gwalior – 474 011 (India)
2016-05-23
First-principles pseudo-potential calculations have been performed to analyze the stability of Ti{sub 1-x}Zr{sub 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{sub 1-x}Zr{sub 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.
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.
Microscopic mechanism of stability in yttria-doped zirconia
Ostanin, S A
2001-01-01
The relaxed configurations of yttria-stabilized zirconia (YSZ) between 3 and 10 mol. % Y sub 2 O sub 3 were modeled within the pseudopotential technique. The vibration mode corresponding to the soft phonon in pure c-ZrO sub 2 has been calculated for each Y sub 2 O sub 3 composition. These anharmonic vibrations, associated with stabilization of YSZ, have been investigated within the self-consistent phonon approximation that makes obtainable the fine structure in spectral density. In studying the phonon dynamics, it is proposed to use the displacement probability density which can quantify very accurately the transition temperature needed to stabilize the YSZ cubic phase
The surface chemistry of metal-oxygen interactions
DEFF Research Database (Denmark)
Stokbro, Kurt; Baroni, Stefano
1997-01-01
We report on a computational study of the clean and oxygen-covered Rh(110) surface, based on density-functional theory within the local-density approximation. We have used plane-wave basis sets and Vanderbilt ultra-soft pseudopotentials. For the clean surface, we present results for the equilibrium...... structure, surface energy and surface stress of the unreconstructed and (1 x 2) reconstructed structures. For the oxygen-covered surface we have performed a geometry optimization at 0.5, 1, and 2 monolayer oxygen coverages, and we present results for the equilibrium configurations, workfunctions and oxygen...
International Nuclear Information System (INIS)
Miotto, R; Ferraz, A C
2009-01-01
In this work we employ the state of the art pseudopotential method, within a generalized gradient approximation to the density functional theory, to investigate the adsorption process of furan on the silicon (001) surface. A direct comparison of different adsorption structures with x-ray photoelectron spectroscopy (XPS), ultra-violet photoelectron spectroscopy (UPS), high resolution electron energy loss spectroscopy (HREELS), near edge x-ray absorption fine structure (NEXAFS), and high resolution spectroscopy experimental data allows us to identify the [4+2 ] cycloaddition reaction as the most probable adsorbate. In addition, theoretical scanning tunnelling microscopy (STM) images are presented, with a view to contributing to further experimental investigations.
Detection and study of photo-generated spin currents in nonmagnetic semiconductor materials
International Nuclear Information System (INIS)
Miah, M. Idrish; Kityk, I.V.; Gray, E. MacA.
2007-01-01
The longitudinal current in Si-doped gallium arsenide was spin-polarized using circularly polarized light. The spin current was detected by the extraordinary Hall effect. An enhancement of Hall conductivity with increasing moderately Si-doping was found, indicating that the introduction of dopants increases the electronic spin polarization. This finding may provide an opportunity for controlling and manipulating nonmagnetic semiconductors via electron spin for operating device applications. Band energy calculations using pseudopotentials confirm the influence of Si content and electron-phonon interaction on the behaviour of the spin current and hence on the spin-dependent Hall voltage
Electronic properties of bromine-doped carbon nanotubes
Jhi, S H; Cohen, M L
2002-01-01
Intercalation of bromine molecules (Br2) into single-wall carbon nanotube (SWNT) ropes is studied using the ab initio pseudopotential density functional method. Electronic and vibrational properties of the SWNT and Br2 are studied for various bromine concentrations. A drastic change in the charge transfer, bromine stretching-mode, and bromine bond-length is observed when the bromine-bromine distance decreases. Calculated electronic structures show that, at high bromine concentrations, the bromine ppsigma level broadens due to the interbromine interaction. These states overlap with the electronic bands of the SWNT near the Fermi level which results in a substantial charge transfer from carbon to bromine.
Optical Second Harmonic Spectroscopy of Boron-Reconstructed Si(001)
International Nuclear Information System (INIS)
Lim, D.; Downer, M. C.; Ekerdt, J. G.; Arzate, N.; Mendoza, Bernardo S.; Gavrilenko, V. I.; Wu, R. Q.
2000-01-01
Optical second harmonic generation (SHG) spectroscopy is used to probe Si(001) following thermal decomposition of diborane at the surface. Incorporation of boron (B) at second layer substitutional sites at H-free Si(001) intensifies and redshifts the E 1 SHG spectral peak, while subsequent H termination further intensifies and blueshifts E 1 , in sharp contrast to the effect of bulk B doping or nonsubstitutional B. Ab initio pseudopotential and semiempirical tight binding calculations independently reproduce these unique trends, and attribute them to the surface electric field associated with charge transfer to electrically active B acceptors, and rehybridization of atomic bonds. (c) 2000 The American Physical Society
Detection and study of photo-generated spin currents in nonmagnetic semiconductor materials
Energy Technology Data Exchange (ETDEWEB)
Miah, M. Idrish [Nanoscale Science and Technology Centre, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); Department of Physics, University of Chittagong, Chittagong 4331 (Bangladesh)], E-mail: m.miah@griffith.edu.au; Kityk, I.V. [Institute of Physics, J. Dlugosz University Czestochowa, PL-42201 Czestochowa (Poland); Gray, E. MacA. [Nanoscale Science and Technology Centre, Griffith University, Nathan, Brisbane, QLD 4111 (Australia)
2007-10-15
The longitudinal current in Si-doped gallium arsenide was spin-polarized using circularly polarized light. The spin current was detected by the extraordinary Hall effect. An enhancement of Hall conductivity with increasing moderately Si-doping was found, indicating that the introduction of dopants increases the electronic spin polarization. This finding may provide an opportunity for controlling and manipulating nonmagnetic semiconductors via electron spin for operating device applications. Band energy calculations using pseudopotentials confirm the influence of Si content and electron-phonon interaction on the behaviour of the spin current and hence on the spin-dependent Hall voltage.
Study of an F center in molten KCl
Energy Technology Data Exchange (ETDEWEB)
Parrinello, M.; Rahman, A.
1984-01-15
It is shown that a discretized version of Feynman's path integral provides a convenient tool for the numerical investigation of the properties of an electron solvated in molten KCl. The binding energy, the magnetic susceptibility, and the pair correlation functions are calculated. The local structure around the solute electron appears to be different from that of an F center in the solid. The Feynman path of the electron dissolved in molten KCl is highly localized thus justifying the F center model. The effect of varying the e/sup -/-K/sup +/ pseudopotential is also reported.
Energy Technology Data Exchange (ETDEWEB)
Kim, Minjung; Scott Bobbitt, N. [Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States); Marom, Noa [Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana 70118 (United States); Chelikowsky, James R. [Center for Computational Materials, Institute for Computational Engineering and Sciences, Departments of Physics and Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States)
2015-01-28
We examine the electronic properties of Sb and F doped SnO{sub 2} nanocrystals up to 2.4 nm in diameter. A real-space pseudopotential implementation of density functional theory is employed within the local density approximation. We calculate electron binding energies and dopant formation energies as function of nanocrystal size, dopant concentration, and dopant species. Structural changes for different dopant species are also investigated. Our study should provide useful information for the design of transparent conducting oxides at the nanoscale.
International Nuclear Information System (INIS)
Goumri-Said, Souraya; Kanoun, Mohammed Benali
2010-01-01
In this Letter we investigate the electronic properties of the bulk and the nanofilm BeO in wurtzite structure. We performed a first-principles pseudo-potential method within the generalized gradient approximation. We will give more importance to the changes in band structure and density of states between the bulk structure and its derived nanofilms. The bonding characterization will be investigated via the analysis Mulliken population and charge density contours. It is found that the nanofilm retains the same properties as its bulk structure with slight changes in electronic properties and band structure which may offer some unusual transport properties.
The first principles study of elastic and thermodynamic properties of ZnSe
Khatta, Swati; Kaur, Veerpal; Tripathi, S. K.; Prakash, Satya
2018-05-01
The elastic and thermodynamic properties of ZnSe are investigated using thermo_pw package implemented in Quantum espresso code within the framework of density functional theory. The pseudopotential method within the local density approximation is used for the exchange-correlation potential. The physical parameters of ZnSe bulk modulus and shear modulus, anisotropy factor, Young's modulus, Poisson's ratio, Pugh's ratio and Frantsevich's ratio are calculated. The sound velocity and Debye temperature are obtained from elastic constant calculations. The Helmholtz free energy and internal energy of ZnSe are also calculated. The results are compared with available theoretical calculations and experimental data.
Band structure and dielectric function of TlInTe2
International Nuclear Information System (INIS)
Wakita, K.; Shim, Y.; Orudzhev, G.; Mamedov, N.; Hashimzade, F.
2006-01-01
The band structure of ternary chain TlInTe 2 was calculated with allowance for non-locality of ionic pseudo-potentials. The dielectric function, as well as the effective masses of holes and electrons, the effective number of valence electrons, and the function of characteristic losses were determined. The results of comparison between the calculated dielectric function and the one obtained ellipsometrically in the spectral range from 0.85 to 6 eV are quite favorable. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (Abstract Copyright [2006], Wiley Periodicals, Inc.)
Half-lives of proton emitters using relativistic mean field theory
International Nuclear Information System (INIS)
Sahu, Bidhubhusan; Patra, S. K.; Agarwalla, S. K.
2011-01-01
The proton radioactivity lifetimes of proton emitters from the ground and the isomeric states are calculated using the microscopic M3Y + Ex and R3Y + Ex (proposed) nucleon-nucleus interaction potentials. These interaction potentials are obtained by single folding the densities of the daughter nuclei supplemented by a zero-range pseudopotential. The quantum-mechanical-tunneling probability is calculated within the WKB approximation. The calculated results are found to be in good agreement with the experimental data for both the M3Y and R3Y interactions.
Atomic structures of Cd Te and Cd Se (110) surfaces
International Nuclear Information System (INIS)
Watari, K.; Ferraz, A.C.
1996-01-01
Results are reported based on the self-consistent density-functional theory, within the local-density approximation using ab-initio pseudopotentials of clean Cd Te and Cd Se (110) surfaces. We analyzed the trends for the equilibrium atomic structures, and the variations of the bond angles at the II-VI (110). The calculations are sensitive to the ionicity of the materials and the results are in agreement with the arguments which predict that the relaxed zinc-blend (110) surfaces should depend on ionicity. (author). 17 refs., 1 figs., 3 tabs
International Nuclear Information System (INIS)
Nejoh, Y.N.
1997-01-01
The nonlinear wave structures of large amplitude ion-acoustic waves are studied in a plasma with positrons. We have presented the region of existence of the ion-acoustic waves by analysing the structure of the pseudopotential. The region of existence sensitively depends on the positron to electron density ratio, the ion to electron mass ratio and the positron to electron temperature ratio. It is shown that the maximum Mach number increases as the positron temperature increases and the region of existence of the ion-acoustic waves spreads as the positron temperature increases. 12 refs., 6 figs
Positron-acoustic waves in an electron-positron plasma with an electron beam
International Nuclear Information System (INIS)
Nejoh, Y.N.
1996-01-01
The nonlinear wave structures of large-amplitude positron-acoustic waves are studied in an electron-positron plasma in the presence of an electron beam with finite temperature and hot electrons and positrons. The region where positron-acoustic waves exist is presented by analysing the structure of the pseudopotential. The region depends sensitively on the positron density, the positron temperature and the electron beam temperature. It is shown that the maximum amplitude of the wave decreases as the positron temperature increases, and the region of positron-acoustic waves spreads as the positron temperature increases. 11 refs., 5 figs
Band structure and phonon properties of lithium fluoride at high pressure
Energy Technology Data Exchange (ETDEWEB)
Panchal, J. M., E-mail: amitjignesh@yahoo.co.in [Government Engineering College, Gandhinagar 382028, Gujarat (India); Department of Physics, University School of Sciences, Gujarat University, Ahmedabad 380009, Gujarat (India); Joshi, Mitesh [Government Polytechnic for Girls, Athwagate, Surat395001, Gujarat (India); Gajjar, P. N., E-mail: pngajjar@rediffmail.com [Department of Physics, University School of Sciences, Gujarat University, Ahmedabad 380009, Gujarat (India)
2016-05-23
High pressure structural and electronic properties of Lithium Fluoride (LiF) have been studied by employing an ab-initio pseudopotential method and a linear response scheme within the density functional theory (DFT) in conjunction with quasi harmonic Debye model. The band structure and electronic density of states conforms that the LiF is stable and is having insulator behavior at ambient as well as at high pressure up to 1 Mbar. Conclusions based on Band structure, phonon dispersion and phonon density of states are outlined.
Structural and electronic properties of GaAs and GaP semiconductors
Energy Technology Data Exchange (ETDEWEB)
Rani, Anita [Guru Nanak College for girls, Sri Muktsar Sahib, Punjab (India); Kumar, Ranjan [Department of Physics, Panjab University, Chandigarh-160014 (India)
2015-05-15
The Structural and Electronic properties of Zinc Blende phase of GaAs and GaP compounds are studied using self consistent SIESTA-code, pseudopotentials and Density Functional Theory (DFT) in Local Density Approximation (LDA). The Lattice Constant, Equillibrium Volume, Cohesive Energy per pair, Compressibility and Band Gap are calculated. The band gaps calcultated with DFT using LDA is smaller than the experimental values. The P-V data fitted to third order Birch Murnaghan equation of state provide the Bulk Modulus and its pressure derivatives. Our Structural and Electronic properties estimations are in agreement with available experimental and theoretical data.
TiAl doping by vanadium: ab initio study
International Nuclear Information System (INIS)
Smirnova, E.A.; Isaev, Eh.I.; Vekilov, Yu.Kh.
2004-01-01
Tetragonality degree in TiAl and vanadium doping effect on it were studied using the methods of calculation based on approximation of coherent potential and ab initio pseudopotentials. It is shown that vanadium substitution for Ti sublattice atoms entails increase in tetragonality degree but with substitution of the atoms in aluminium sublattice the tetragonality of the TiAl:V alloy decreases and at the content of vanadium about 8 at. % the lattice becomes actually cubical. In its turn, it may result in increase in TiAl ductility, the alloy being brittle at low temperatures [ru
Integral equations for composite-particle scattering taking the Pauli principle into account
International Nuclear Information System (INIS)
Kukulin, V.I.; Neudatchin, V.G.; Pomerantsev, V.N.
1978-01-01
An approximate description of a system of three composite particles in terms of the Saito (Prog. Theor. Phys.; 41:705 (1969)) orthogonality condition model is proposed. The orthogonalising pseudopotential technique is used to derive a modified set of Fadde'ev equations where the two- and three-body exchanges due to the Pauli principle are included by orthogonalising to two-and three-body forbidden states. The scope of applicability of and the method for solving the derived equations are discussed briefly. (author)
Simulation of YBa{sub 2}Cu{sub 3}O{sub 7}/MgO surface growth
Energy Technology Data Exchange (ETDEWEB)
Mohammadizadeh, M.R. [Superconductivity Research Laboratory (SRL), Department of Physics, University of Tehran, North Karegar Ave., P.O. Box 14395-547, Tehran (Iran); Computational Physical Sciences Research Laboratory, Department of Nano-Science, Institute for Studies in Theoretical Physics and Mathematics (IPM), P.O. Box 19395-5531, Tehran (Iran); Safari, N.; Kia, M.; Savaloni, H. [Superconductivity Research Laboratory (SRL), Department of Physics, University of Tehran, North Karegar Ave., P.O. Box 14395-547, Tehran (Iran)
2006-09-15
For surface growth simulation of YBa{sub 2}Cu{sub 3}O{sub 7} on MgO substrate, binding energies between each two different Y, Ba, Cu, O, and Mg atoms were calculated by ab initio pseudopotential density functional theory approach. Then, simulation of YBa{sub 2}Cu{sub 3}O{sub 7} growth was performed by a simple two dimensional model based on the ballistic aggregation of hard discs. By increasing the substrate temperature, the atomic layers distribution is more condensed and the nanometric surface roughness decreases. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Electronic structure and formation energy of a vacancy in aluminum
International Nuclear Information System (INIS)
Chakraborty, B.; Siegel, R.W.
1981-11-01
The electronic structure of a vacancy in Al was calculated self-consistently using norm-conserving ionic pseudopotentials obtained from ab initio atomic calculations. A 27-atom-site supercell containing 1 vacancy and 26 atoms was used to simulate the environment of the vacancy. A vacancy formation energy of 1.5 eV was also calculated (cf. the experimental value of 0.66 eV). The effects of the supercell and the nature of the ionic potential on the resulting electronic structure and formation energy are discussed. Results for the electronic structure of a divacancy are also presented. 3 figures
Parameter-free calculation of K alpha chemical shifts for Al, Si, and Ge oxides
DEFF Research Database (Denmark)
Lægsgaard, Jesper
2001-01-01
The chemical shifts of the K alpha radiation line from Al, Si, and Ge ions between their elemental and oxide forms are calculated within the framework of density functional theory using ultrasoft pseudopotentials. It is demonstrated that this theoretical approach yields quantitatively accurate...... results fur the systems investigated, provided that relaxations of the valence electrons upon the core-hole transition are properly accounted for. Therefore, such calculations provide a powerful tool for identification of impurity states based on x-ray fluorescence data. Results for an Al impurity...
Properties of heavy alkali metals under pressure
International Nuclear Information System (INIS)
Eremenko, T.M.; Zarochentsev, E.V.
1980-01-01
Zero isotherms, polymorphic phase body-centered cubic (BCC)-faced-centered cubic (FCC) transitions and K, Rb and Cs phonon spectra have been calculated within the framework of a pseudopotential model added with a short-range repulsion of frames in the Born-Mayer form. It is shown that taking into account Esub(SR) zero isotherms and phonon frequencies change insignificantly; microscopic Grueneisen parameters change by 10-20 % and BCC-FCC transition pressure decreases several times. The agreement of theoretic and experimentally observed characteristics of the transition in Cs and K and Rb phonon spectra is quite satisfactory
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
Ion-acoustic supersolitons and double layers in plasmas with nonthermal electrons
Gao, D.-N.; Zhang, J.; Yang, Y.; Duan, W.-S.
2017-08-01
Supersoliton (SS) can be mainly featured in two ways, namely, by focusing on subsidiary maxima on its electric field or by meeting the requirement that the appropriate Sagdeev pseudopotential (SP) has three local extrema between the equilibrium conditions and its amplitude. In this paper, by using the SP method, double layers and ion-acoustic SSs are studied in a plasma with Maxwellian cold electrons, nonthermal hot electrons, and fluid ions. The existence of the SS regime in parameter space is obtained in a methodical fashion. The existence domains for positive solitary waves are also presented. It is found that there is no SSs at the acoustic speed.
International Nuclear Information System (INIS)
Litvinchuk, A.P.; Vitrikhovskii, N.I.
1983-01-01
Studies are presented of photoluminescence spectra of the quaternary ZnTe/sub 1-2x/S/sub x/Se/sub x/ alloy (x = 0.05, 0.10, and 0.20). The determination of the energy gap variation with composition at 85 K is given. The nonlinear variation of the energy gap E/sub g/ with composition for the quaternary ZnTe/sub 1-2x/S/sub x/Se/sub x/ alloy may be interpreted in the framework of the pseudopotential theory based on the nonlinear crystal field properties
Ab-initio calculation of the valence-band offset at strained GaAs/InAs (001) heterojunction
International Nuclear Information System (INIS)
Tit, N.; Peressi, M.
1993-06-01
We present a self consistent pseudopotential calculation of the valence band offset (VBO) at GaAs/InAs (001) strained heterojunction, which is chose as an example of the isovalent polar with common-anion lattice mismatched heterojunctions. The effects of strain are studied by looking at the variation of the VBO versus the in plane lattice constant, which is imposed by the substrate. Our results show that the VBO can be tuned by about 0.17 eV going from GaAs to InAs substrates. Comparison of our work with the available experimental and theoretical results is also discussed. (author). 25 refs, 3 figs, 5 tabs
Energy of formation for AgIn liquid binary alloys along the line of phase separation
Bhuiyan, G M; Ziauddin-Ahmed, A Z
2003-01-01
We have investigated the energy of formation for AgIn liquid binary alloys along the solid-liquid phase separation line. A microscopic theory based on the first order perturbation has been applied. The interionic interaction and a reference liquid are the fundamental components of the theory. These are described by a local pseudopotential and the hard sphere liquids, respectively. The results of calculations reveal a characteristic feature that the energy of formation becomes minimum at the equiatomic composition, and thus indicates maximal mix-ability at this concentration. The energy of formation at a particular thermodynamic state that is at T 1173 K predicts the experimental trends fairly well.
Spectroscopic Constants for Selected Homonuclear Diatomic Molecules. Volume 2. K through Z
1976-02-16
Radiative Transfer 8, 1431-6 Theory, L. Szasz and G. McGinn, "Atomic and Molecular Calculations With the Pseudopotential Method. III. The Theory...Configuration Interaction. " J. Chem. Phy». 48, 434-9 (68. 48) L. Szasz and G. McGinn, "Atomic and Molecular Calculations With the...Singh and D. K. Rai. Indian J. Pure Appl. Phys. 2.475-8 (66. 38) L. Szasz and G. McGinn, "Atomic and Molecular Calculations With the
Statistical mechanics of dense plasmas and implications for the plasma polarization shift
International Nuclear Information System (INIS)
Rogers, F.J.
1984-01-01
A brief description of the statistical mechanics of reacting, dense, plasmas is given. The results do not support a Debye-like polarization shift at low density. It is shown that the electronic charge density factors into a strongly quantum mechanical part, that is not much affected by many body correlations and a weakly quantum mechanical part, that is considerably effected by many body correlations. The few body charge density is obtained from direct solution of the Schroedinger equation and the many body charge density is obtained from the hypernetted chain equation through the introduction of a pseudopotential
Equation of state and transport measurements on expanded liquid metals up to 80000K and 0.4 GPa
International Nuclear Information System (INIS)
Hodgson, W.M.
1978-05-01
Equilibrium measurements of pressure, enthalpy, density, temperature and resistivity have been made on liquid lead, platinum, gold-copper, uranium, niobium, and niobium-hafnium at high temperatures and pressures. A unique method of determining sample temperatures from multi-channel fast radiation pyrometry has been developed and used to calculate temperatures between 1600 and 8000 K without definitive emissivity information. Pseudo-potential theory has been used to model the lead resistivity and equation of state measurements and t-matrix theory has been applied to the uranium resistivity data
Energy Technology Data Exchange (ETDEWEB)
Emadi, E.; Zahed, H. [Physics Department, Faculty of Science, Sahand University of Technology, 51335–1996 Tabriz (Iran, Islamic Republic of)
2016-08-15
The behavior of linear and nonlinear dust ion acoustic (DIA) solitary waves in an unmagnetized quantum dusty plasma, including inertialess electrons and positrons, ions, and mobile negative dust grains, are studied. Reductive perturbation and Sagdeev pseudopotential methods are employed for small and large amplitude DIA solitary waves, respectively. A minimum value of the Mach number obtained for the existence of solitary waves using the analytical expression of the Sagdeev potential. It is observed that the variation on the values of the plasma parameters such as different values of Mach number M, ion to electron Fermi temperature ratio σ, and quantum diffraction parameter H can lead to the creation of compressive solitary waves.
Wavelets in self-consistent electronic structure calculations
International Nuclear Information System (INIS)
Wei, S.; Chou, M.Y.
1996-01-01
We report the first implementation of orthonormal wavelet bases in self-consistent electronic structure calculations within the local-density approximation. These local bases of different scales efficiently describe localized orbitals of interest. As an example, we studied two molecules, H 2 and O 2 , using pseudopotentials and supercells. Considerably fewer bases are needed compared with conventional plane-wave approaches, yet calculated binding properties are similar. Our implementation employs fast wavelet and Fourier transforms, avoiding evaluating any three-dimensional integral numerically. copyright 1996 The American Physical Society
Theoretical study of the electron stopping power in ion planar channeling
International Nuclear Information System (INIS)
Haymann, P.
1974-01-01
A theory recently developed by the authors for slow and fast electrons is shown to be also applicable to channeled ions and to explain the experimental results about electron loss phenomena as a whole. The theory is based on the fundamental hypothesis of the nonadiabaticity of the ion-target interactions. How essential an exponential form of the interaction pseudo-potential is in explaining the energy exchange mechanism at the walls may be deduced from a quasi-classical development of the quantum model. The theory also allows a number of new experiments to be envisaged in the field of surface electron states [fr
Goumri-Said, Souraya
2010-08-01
In this Letter we investigate the electronic properties of the bulk and the nanofilm BeO in wurtzite structure. We performed a first-principles pseudo-potential method within the generalized gradient approximation. We will give more importance to the changes in band structure and density of states between the bulk structure and its derived nanofilms. The bonding characterization will be investigated via the analysis Mulliken population and charge density contours. It is found that the nanofilm retains the same properties as its bulk structure with slight changes in electronic properties and band structure which may offer some unusual transport properties. © 2010 Elsevier B.V. All rights reserved.
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
Band structure and phonon properties of lithium fluoride at high pressure
International Nuclear Information System (INIS)
Panchal, J. M.; Joshi, Mitesh; Gajjar, P. N.
2016-01-01
High pressure structural and electronic properties of Lithium Fluoride (LiF) have been studied by employing an ab-initio pseudopotential method and a linear response scheme within the density functional theory (DFT) in conjunction with quasi harmonic Debye model. The band structure and electronic density of states conforms that the LiF is stable and is having insulator behavior at ambient as well as at high pressure up to 1 Mbar. Conclusions based on Band structure, phonon dispersion and phonon density of states are outlined.
Castin, Yvan
2004-04-01
A unitary quantum gas is a gas of quantum particles with a binary interaction of infinite scattering length and negligible range. It has been produced in recent experiments with gases of fermionic atoms by means of a Feshbach resonance. Using the Fermi pseudo-potential model for the atomic interaction, we show that the time evolution of such a gas in an isotropic three-dimensional time dependent harmonic trap is exactly given by a gauge and scaling transform. To cite this article: Y. Castin, C. R. Physique 5 (2004).
Structural energetics of noble metals
International Nuclear Information System (INIS)
Mujibur Rahman, S.M.
1982-06-01
Structural energetics of the noble metals, namely Cu, Ag, and Au are investigated by employing a single-parameter pseudopotential. The calculations show that the lowest energy for all of these metals corresponds to FCC - their observed crystal structure. The one-electron contribution to the free energy is found to dominate the structural prediction for these metals. The present investigation strongly emphasizes that the effects due to band hybridization and core-core exchange play a significant role on the structural stability of the noble metals. (author)
An h-adaptive finite element solver for the calculations of the electronic structures
International Nuclear Information System (INIS)
Bao Gang; Hu Guanghui; Liu Di
2012-01-01
In this paper, a framework of using h-adaptive finite element method for the Kohn–Sham equation on the tetrahedron mesh is presented. The Kohn–Sham equation is discretized by the finite element method, and the h-adaptive technique is adopted to optimize the accuracy and the efficiency of the algorithm. The locally optimal block preconditioned conjugate gradient method is employed for solving the generalized eigenvalue problem, and an algebraic multigrid preconditioner is used to accelerate the solver. A variety of numerical experiments demonstrate the effectiveness of our algorithm for both the all-electron and the pseudo-potential calculations.
International Nuclear Information System (INIS)
Woicik, J.C.; Nelson, E.J.; Kronik, Leeor; Jain, Manish; Chelikowsky, James R.; Heskett, D.; Berman, L.E.; Herman, G.S.
2002-01-01
We have determined the Ti and O components of the rutile TiO 2 valence band using the method of site-specific x-ray photoelectron spectroscopy. Comparisons with calculations based on pseudopotentials within the local density approximation reveal the hybridization of the Ti 3d, 4s, and 4p states, and the O 2s and 2p states on each site. These chemical effects are observed due to the large differences between the angular-momentum dependent matrix elements of the photoelectron process
General theory of the transverse dielectric constant of III-V semiconducting compounds
Kahen, K. B.; Leburton, J. P.
1985-01-01
A general model of the transverse dielectric constant of III-V compounds is developed using a hybrid method which combines the kp method with a nonlocal pseudopotential calculation. In this method the Brillouin zone is partitioned into three regions by expanding the energy bands and matrix elements about the F, X, and L symmetry points. The real and imaginary parts of the dielectric constant are calculated as a sum of the individual contributions of each region. By using this partition method, it is possible to get good insight into the dependence of the dielectric constant on the shape of the band structure.
First-principles calculations for elastic properties of OsB{sub 2} under pressure
Energy Technology Data Exchange (ETDEWEB)
Yang Junwei [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); Chen Xiangrong, E-mail: x.r.chen@tom.co [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016 (China); Luo Fen [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); Ji Guangfu [Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, Chinese Academy of Engineering Physics, Mianyang 621900 (China)
2009-11-01
The structure, elastic properties and elastic anisotropy of orthorhombic OsB{sub 2} are investigated by density functional theory method with the ultrasoft pseudopotential scheme in the frame of the generalized gradient approximation (GGA) as well as local density approximation (LDA). The obtained structural parameters, elastic constants, elastic anisotropy and Debye temperature for OsB{sub 2} under pressure are consistent with the available experimental data and other theoretical results. It is found that the elastic constants, bulk modulus and Debye temperature of OsB{sub 2} tend to increase with increasing pressure. It is predicted that OsB{sub 2} is not a superhard material from our calculations.
First-principles calculations for elastic properties of OsB2 under pressure
International Nuclear Information System (INIS)
Yang Junwei; Chen Xiangrong; Luo Fen; Ji Guangfu
2009-01-01
The structure, elastic properties and elastic anisotropy of orthorhombic OsB 2 are investigated by density functional theory method with the ultrasoft pseudopotential scheme in the frame of the generalized gradient approximation (GGA) as well as local density approximation (LDA). The obtained structural parameters, elastic constants, elastic anisotropy and Debye temperature for OsB 2 under pressure are consistent with the available experimental data and other theoretical results. It is found that the elastic constants, bulk modulus and Debye temperature of OsB 2 tend to increase with increasing pressure. It is predicted that OsB 2 is not a superhard material from our calculations.
First-principles calculations for elastic properties of OsB 2 under pressure
Yang, Jun-Wei; Chen, Xiang-Rong; Luo, Fen; Ji, Guang-Fu
2009-11-01
The structure, elastic properties and elastic anisotropy of orthorhombic OsB 2 are investigated by density functional theory method with the ultrasoft pseudopotential scheme in the frame of the generalized gradient approximation (GGA) as well as local density approximation (LDA). The obtained structural parameters, elastic constants, elastic anisotropy and Debye temperature for OsB 2 under pressure are consistent with the available experimental data and other theoretical results. It is found that the elastic constants, bulk modulus and Debye temperature of OsB 2 tend to increase with increasing pressure. It is predicted that OsB 2 is not a superhard material from our calculations.
A first principles study of native defects in alpha-quartz
Roma, G
2003-01-01
We present a study of several neutral and charged oxygen and silicon defects in alpha-quartz. We performed plane waves pseudopotential calculations in the framework of density functional theory in the local density approximation. We will show the structures that we obtained for vacancies and interstitials in several charge states and the corresponding formation energies. We discuss the reciprocal dependence of formation energies of charged defects (and thus concentrations) and the electron chemical potential on each other and we determine the latter by iterative self-consistent solution of the equation imposing charge neutrality. Results on defect concentrations, their dependence on oxygen partial pressure, and self-doping effects are presented.
Positron effective mass in silicon
International Nuclear Information System (INIS)
Panda, B.K.; Shan, Y.Y.; Fung, S.; Beling, C.D.
1995-01-01
The positron effective mass in Si is obtained from the first-principles calculations along various crystallographic directions. The effect of electron-positron correlation on the band mass is examined in this work. A positron pseudopotential scheme is worked out to calculate the isotropic band mass without explicitly solving the band energy. The effective mass 1.46m obtained as a sum of band mass and the positron-plasmon interaction compares very well with 1.5m obtained from the positron mobility data
Umari, P; Gonze, Xavier; Pasquarello, Alfredo
2003-01-17
Using a first-principles approach, we calculate Raman spectra for a model structure of vitreous silica. We develop a perturbational method for calculating the dielectric tensor in an ultrasoft pseudopotential scheme and obtain Raman coupling tensors by finite differences with respect to atomic displacements. For frequencies below 1000 cm(-1), the parallel-polarized Raman spectrum of vitreous silica is dominated by oxygen bending motions, showing a strong sensitivity to the intermediate range structure. By modeling the Raman coupling, we derive estimates for the concentrations of three- and four-membered rings from the experimental intensities of the Raman defect lines.
The Electronic and Optical Properties of Au Doped Single-Layer Phosphorene
Zhu, Ziqing; Chen, Changpeng; Liu, Jiayi; Han, Lu
2018-01-01
The electronic properties and optical properties of single and double Au-doped phosphorene have been comparatively investigated using the first-principles plane-wave pseudopotential method based on density functional theory. The decrease from direct band gap 0.78 eV to indirect band gap 0.22 and 0.11 eV are observed in the single and double Au-doped phosphorene, respectively. The red shifts of absorbing edge occur in both doped systems, which consequently enhance the absorbing of infrared light in phosphorene. Band gap engineering can, therefore, be used to directly tune the optical absorption of phosphorene system by substitutional Au doping.
Theoretical modelling of semiconductor surfaces microscopic studies of electrons and photons
Srivastava, G P
1999-01-01
The state-of-the-art theoretical studies of ground state properties, electronic states and atomic vibrations for bulk semiconductors and their surfaces by the application of the pseudopotential method are discussed. Studies of bulk and surface phonon modes have been extended by the application of the phenomenological bond charge model. The coverage of the material, especially of the rapidly growing and technologically important topics of surface reconstruction and chemisorption, is up-to-date and beyond what is currently available in book form. Although theoretical in nature, the book provides
Tabular equation of state of lithium for laser-fusion reactor studies
International Nuclear Information System (INIS)
Young, D.A.; Ross, M.; Rogers, F.J.
1979-01-01
A tabular lithium equation of state was formulated from three separate equation-of-state models to carry out hydrodynamic simulations of a lithium-waterfall laser-fusion reactor. The models we used are: ACTEX for the ionized fluid, soft-sphere for the liquid and vapor, and pseudopotential for the hot, dense liquid. The models are smoothly joined over the range of density and temperature conditions appropriate for a laser-fusion reactor. We also fitted the models into two forms suitable for hydrodynamic calculations
Knock-on type exchange and the density dependence of an effective interaction
International Nuclear Information System (INIS)
Jeukenne, J.P.; Mahaux, C.
1981-01-01
We investigate the origin of the density-dependence of the strength of an effective interaction previously derived from a Brueckner-Hartree-Fock calculation of the optical-model potential in nuclear matter. From the analysis of a model based on the Hartree-Fock approximation and on a Yukawa interaction with a Majorana exchange component, we study to what extent this dependence derives from the momentum-dependence of the exchange contribution of the knock-on type. The model is also used to discuss zero-range pseudopotential methods for including this knock-on contribution. (orig.)
Wilson, F.; Neukirch, T.
2018-01-01
We present new analytical three-dimensional solutions of the magnetohydrostatic equations, which are applicable to the co-rotating frame of reference outside a rigidly rotating cylindrical body, and have potential applications to planetary magnetospheres and stellar coronae. We consider the case with centrifugal force only, and use a transformation method in which the governing equation for the "pseudo-potential" (from which the magnetic field can be calculated) becomes the Laplace partial differential equation. The new solutions extend the set of previously found solutions to those of a "fractional multipole" nature, and offer wider possibilities for modelling than before. We consider some special cases, and present example solutions.
Structural and electronic properties of lithium intercalated graphite LiC6
CSIR Research Space (South Africa)
Kganyago, KR
2003-11-01
Full Text Available Thomas-Fermi plus gradient approximation,44 the Korringa-Kohn-Rostoker45,46 ~KKR! method,47 the FLAPW method,26,37,48 full potential linear muf?n-tin-orbital~FLMTO! method,49?51 the ab initio pseudopotential ~PP! method,52?57 linear muf... excess near a. This delocalization of the electrons in the interplanar region was reported by Charlier et al.90 and is used in our study to evaluate the corrections to the exchange- correlation term of the Kohn-Sham equations and under- standing...
Link between structural and mechanical stability of fcc- and bcc-based ordered MgeLi alloys
CSIR Research Space (South Africa)
Phasha, MJ
2010-06-01
Full Text Available ) pseudopotential method, embodied in the CASTEP code [10]. The Hohenberg-Kohn-Sham density functional theory (DFT) [11] was used 5 within the GGA formalism [12] to describe the electronic exchange-correlation interactions. We used the recent PBE form..., Int. J. Quantum Chem. 77 (2000) 895. [11] P. Hohenberg and W. Kohn, Phys. Rev. 136, B 864 (1964), W. Kohn and L.J. Sham, Phys. Rev. 140 (1965) A 1133. [12] J.P. Perdew and Y. Wang, Phys. Rev. B 45 (1992) 13244. [13] J.P. Perdew, K. Burke and M...
CSIR Research Space (South Africa)
Ouma, CNM
2016-06-01
Full Text Available defects and defect complexes. Very few theoretical studies have attempted to investigate defect metastability[23,24]. 2.0 Computational details All DFT calculations were done based on the generalized Kohn-Sham approach[25] and the projector... (2014) 141–143. [25] W. Kohn, L.J. Sham, Self-Consistent Equations Including Exchange and Correlation Effects, Phys. Rev. 140 (1965) A1133–A1138. doi:10.1103/PhysRev.140.A1133. [26] G. Kresse, D. Joubert, From ultrasoft pseudopotentials...
Structure and transport properties of atomic chains and molecules
DEFF Research Database (Denmark)
Strange, Mikkel
2008-01-01
general in the literature, a set of benchmark calculations for the Kohn-Sham elastic transmission function of representative single-molecule junctions has been performed. The transmission functions are calculated using two different density functional theory methods, namely an ultrasoft pseudopotential...... by direct visualization of Kohn-Sham eigenchannel states. The possibility of non-carbon based nanotubes is also discussed. Both calculations of the strain energy of infinite PtO2 nanotubes that this material could be a candidate for non-carbon based nanotubes, as was recently suggested [6]....
Wang, Wei; Sun, Jiafa; Li, Bin; He, Junqi
2017-09-01
First-principles pseudopotential calculations on phonon and electronic properties of β -pyrochlore superconductor KOs2O6 are performed. The imaginary soft-phonon modes with a special double-well potential for the lowest Eu(1) mode and the second lowest T1u(1) mode are reported, which indicates the dynamical instability in KOs2O6. However, the double wells are too small to induce a structural phase transformation in KOs2O6. The strong anharmonicity especially for K T2g(1) phonon mode is got, which is approved to be from the strong electron-phonon coupling that supports the superconductivity in KOs2O6.
Tabular equation of state of lithium for laser-fusion reactor studies
Energy Technology Data Exchange (ETDEWEB)
Young, D.A.; Ross, M.; Rogers, F.J.
1979-01-19
A tabular lithium equation of state was formulated from three separate equation-of-state models to carry out hydrodynamic simulations of a lithium-waterfall laser-fusion reactor. The models we used are: ACTEX for the ionized fluid, soft-sphere for the liquid and vapor, and pseudopotential for the hot, dense liquid. The models are smoothly joined over the range of density and temperature conditions appropriate for a laser-fusion reactor. We also fitted the models into two forms suitable for hydrodynamic calculations.
International Nuclear Information System (INIS)
Yao Qiang; Zhu Yuhong; Wang Yan
2011-01-01
Ultrasoft pseudopotential within a generalized gradient approximation was employed to study the structural stability, electronic structure, and elastic properties of ternary Co 3 (Ga,W) precipitate. The Young's and shear moduli of the polycrystals containing the Co 3 (Ga,W) precipitate were calculated using the Voigt-Reuss-Hill averaging scheme. Results show that the stable ternary Co 3 (Ga,W) compound has the L1 2 structure, and is ductile in nature. The structural stability of the Co 3 (Ga,W) compound is discussed together with the calculated electronic structure.
Application of the stochastic variational method to the calculation of 3α- and 4α-systems
International Nuclear Information System (INIS)
Kukulin, V.I.; Krasnopol'skii, V.M.
1975-01-01
The results of calculations of the properties of 3α- and 4α-systems carried out within the framework of the recently suggested stochastic variational method are presented. As the α-α potentials, two different types of potentials are used: the Ali-Bodmer repulsive core potential and the deep attractive α-α potential with forbidden states. In the latter case the pseudopotential approach we have earlier suggested is used. The energies of levels, (r 2 ) and form-factors of the ground state F(q 2 ) are calculated
The use of bulk states to accelerate the band edge state calculation of a semiconductor quantum dot
International Nuclear Information System (INIS)
Voemel, Christof; Tomov, Stanimire Z.; Wang, Lin-Wang; Marques, Osni A.; Dongarra, Jack J.
2007-01-01
We present a new technique to accelerate the convergence of the folded spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We use bulk band states of the materials constituent of the quantum dot to construct initial vectors and a preconditioner. We apply these to accelerate the convergence of the folded spectrum method for the interior states at the top of the valence and the bottom of the conduction band. For large CdSe quantum dots, the number of iteration steps until convergence decreases by about a factor of 4 compared to previous calculations
Electron–phonon superconductivity in YIn3
International Nuclear Information System (INIS)
Billington, D; Llewellyn-Jones, T M; Maroso, G; Dugdale, S B
2013-01-01
First-principles calculations of the electron–phonon coupling were performed on the cubic intermetallic compound YIn 3 . The electron–phonon coupling constant was found to be λ ep = 0.42. Using the Allen–Dynes formula with a Coulomb pseudopotential of μ* = 0.10, a T c of approximately 0.77 K is obtained which is reasonably consistent with the experimentally observed temperature (between 0.8 and 1.1 K). The results indicate that conventional electron–phonon coupling is capable of producing the superconductivity in this compound. (paper)
Electron-phonon superconductivity in YIn3
Billington, D.; Llewellyn-Jones, T. M.; Maroso, G.; Dugdale, S. B.
2013-08-01
First-principles calculations of the electron-phonon coupling were performed on the cubic intermetallic compound YIn3. The electron-phonon coupling constant was found to be λep = 0.42. Using the Allen-Dynes formula with a Coulomb pseudopotential of μ* = 0.10, a Tc of approximately 0.77 K is obtained which is reasonably consistent with the experimentally observed temperature (between 0.8 and 1.1 K). The results indicate that conventional electron-phonon coupling is capable of producing the superconductivity in this compound.
CO tip functionalization in subatomic resolution atomic force microscopy
International Nuclear Information System (INIS)
Kim, Minjung; Chelikowsky, James R.
2015-01-01
Noncontact atomic force microscopy (nc-AFM) employing a CO-functionalized tip displays dramatically enhanced resolution wherein covalent bonds of polycyclic aromatic hydrocarbon can be imaged. Employing real-space pseudopotential first-principles calculations, we examine the role of CO in functionalizing the nc-AFM tip. Our calculations allow us to simulate full AFM images and ascertain the enhancement mechanism of the CO molecule. We consider two approaches: one with an explicit inclusion of the CO molecule and one without. By comparing our simulations to existing experimental images, we ascribe the enhanced resolution of the CO functionalized tip to the special orbital characteristics of the CO molecule
International Nuclear Information System (INIS)
Kim, Minjung; Scott Bobbitt, N.; Marom, Noa; Chelikowsky, James R.
2015-01-01
We examine the electronic properties of Sb and F doped SnO 2 nanocrystals up to 2.4 nm in diameter. A real-space pseudopotential implementation of density functional theory is employed within the local density approximation. We calculate electron binding energies and dopant formation energies as function of nanocrystal size, dopant concentration, and dopant species. Structural changes for different dopant species are also investigated. Our study should provide useful information for the design of transparent conducting oxides at the nanoscale
Energy Technology Data Exchange (ETDEWEB)
Radeka, V [Institut Rudjer Boskovic, Zagreb, Yugoslavia (Croatia)
1962-04-15
continu non stabilise. (author) [Spanish] Se dan soluciones nuevas para circuitos deflectores de haz que permiten montar circuitos contadores sencillos y seguros. La precision con que tiene que ser desviado el haz es deducida por el autor partiendo de investigaciones teoricas del proceso de contaje publicadas anteriormente. Calcula la disminucion de los limites de error en la deflexion que resulta de la diferencia entre las caracteristicas real e ideal de la valvula. Se demuestra que el limite de error en la deflexion es maximo hasta unos 3x10{sup 5} impulsos por segundo, e independiente de la velocidad de contaje, por lo que es posible disenar circuitos mas simples. Para contar hasta 10{sup 6} impulsos por segundo, se requieren circuitos deflectores de mayor precision. La memoria describe dos circuitos que se pueden emplear hasta estos limites de velocidad de recuento. No es necesario que los componentes del circuito sean muy estables o muy exactos. Solamente se precisa una tension continua de alimentacion no estabilizada. (author) [Russian] Dayutsya novye resheniya dlya polucheniya otklonyayushchikh puchek luchej konturov, chto pozvolyaet osushchestvlyat' prostye i nadezhnye schetnye kontury. Trebovaniya tochnosti otkloneniya puchka luchej vyvedeny iz teoreticheskikh izyskanij schetnykh protsessov, opublikovannykh avtorom ranee. Podschityvaetsya umen'shenie predela pogreshnosti otkloneniya, vytekayushchej iz raznitsy mezhdu dejstvitel'noj i teoreticheskoj kharakteristikami ehlektronnoj lampy. Dokazyvaetsya, chto priblizitel'no okolo 3 x 10{sup 5} impul'sov v sekundu predel pogreshnosti otkloneniya dostigaet svoego maksimal'nogo znacheniya; on ne zavisit ot skorosti scheta, chto daet vozmozhnost' uprostit' konstruktsiyu konturov. Dlya otscheta do 10{sup 6} impul'sov v sekundu trebuyutsya bolee tochnye kontury otkloneniya. Opisyvayutsya dva kontura dlya ispol'zovaniya ikh do ehtikh predelov skorosti scheta. Trebovaniya, pred{sup y}avlyaemye k sostavnym chastyam kontura v
Energy Technology Data Exchange (ETDEWEB)
Stia, C.R.; Fojon, O.A. [Instituto de Fisica Rosario - CONICET-Universidad Nacional de Rosario, Rosario (Argentina); Gaigeot, M.P. [Laboratoire Analyse et Modelisation pour la Biologie et l' Environnement, LAMBE, UMR-CNRS 8587, Universite d' Evry-Val-d' Essonne, 91 - Evry (France); Institut Universitaire de France, 75 - Paris (France); Vuilleumier, R. [Departement de chimie, Ecole Normale Superieure, 75 - Paris (France); Herve du Penhoat, M.A.; Politis, M.F. [Institut de Mineralogie et de Physique des Milieux Condenses, IMPMC, UMR-CNRS 7590, Universite Pierre et Marie Curie, 75 - Paris (France)
2010-10-15
We present a series of ab initio density functional based calculations of the fragmentation dynamics of core-ionized biomolecules. The computations are performed for pure liquid water, aqueous and isolated Uracil. Core ionization is described by replacing the 1s{sup 2} pseudopotential of one atom of the target molecule (C, N or O) with a pseudopotential for a 1s{sup 1} core-hole state. Our results predict that the dissociation of core-ionized water molecules may be reached during the lifetime of inner-shell vacancy (less than 10 fs), leading to OH bond breakage as a primary outcome. We also observe a second fragmentation channel in which total Coulomb explosion of the ionized water molecule occurs. Fragmentation pathways are found similar for pure water or when the water molecule is in the primary hydration shell of the uracil molecule. In the latter case, the proton may be transferred towards the uracil oxygen atoms. When the core hole is located on the uracil molecule, ultrafast dissociation is only observed in the aqueous environment and for nitrogen-K vacancies, resulting in proton transfers towards the hydrogen-bonded water molecule. (authors)
Precise positioning of an ion in an integrated Paul trap-cavity system using radiofrequency signals
Kassa, Ezra; Takahashi, Hiroki; Christoforou, Costas; Keller, Matthias
2018-03-01
We report a novel miniature Paul ion trap design with an integrated optical fibre cavity which can serve as a building block for a fibre-linked quantum network. In such cavity quantum electrodynamic set-ups, the optimal coupling of the ions to the cavity mode is of vital importance and this is achieved by moving the ion relative to the cavity mode. The trap presented herein features an endcap-style design complemented with extra electrodes on which additional radiofrequency voltages are applied to fully control the pseudopotential minimum in three dimensions. This method lifts the need to use three-dimensional translation stages for moving the fibre cavity with respect to the ion and achieves high integrability, mechanical rigidity and scalability. Not based on modifying the capacitive load of the trap, this method leads to precise control of the pseudopotential minimum allowing the ion to be moved with precisions limited only by the ion's position spread. We demonstrate this by coupling the ion to the fibre cavity and probing the cavity mode profile.
Turi, László
2016-04-01
We evaluate the applicability of a hierarchy of quantum models in characterizing the binding energy of excess electrons to water clusters. In particular, we calculate the vertical detachment energy of an excess electron from water cluster anions with methods that include one-electron pseudopotential calculations, density functional theory (DFT) based calculations, and ab initio quantum chemistry using MP2 and eom-EA-CCSD levels of theory. The examined clusters range from the smallest cluster size (n = 2) up to nearly nanosize clusters with n = 1000 molecules. The examined cluster configurations are extracted from mixed quantum-classical molecular dynamics trajectories of cluster anions with n = 1000 water molecules using two different one-electron pseudopotenial models. We find that while MP2 calculations with large diffuse basis set provide a reasonable description for the hydrated electron system, DFT methods should be used with precaution and only after careful benchmarking. Strictly tested one-electron psudopotentials can still be considered as reasonable alternatives to DFT methods, especially in large systems. The results of quantum chemistry calculations performed on configurations, that represent possible excess electron binding motifs in the clusters, appear to be consistent with the results using a cavity structure preferring one-electron pseudopotential for the hydrated electron, while they are in sharp disagreement with the structural predictions of a non-cavity model.
Ab initio investigation of superconductivity in orthorhombic MgPtSi
Energy Technology Data Exchange (ETDEWEB)
Tütüncü, H.M., E-mail: tutuncu@sakarya.edu.tr [Sakarya Üniversitesi, Fen-Edebiyat Fakültesi, Fizik Bölümü, 54187, Adapazarı (Turkey); Sakarya Üniversitesi, BIMAYAM Biyomedikal, Manyetik ve Yarıiletken Malzemeler Araştırma Merkezi, 54187, Adapazarı (Turkey); Ertuǧrul Karaca [Sakarya Üniversitesi, Fen-Edebiyat Fakültesi, Fizik Bölümü, 54187, Adapazarı (Turkey); Srivastava, G.P. [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom)
2016-07-15
We have performed an ab initio study of electronic, vibrational and superconducting properties of the orthorhombic MgPtSi by employing the density functional theory, a linear-response formalism, and the plane-wave pseudopotential method. Our electronic results suggest that the density of states at the Fermi level is primarily contributed by Pt 5d and Si 3p states with much smaller contribution from Mg electronic states. Phonon anomalies have been found for all three acoustic branches. Due to these phonon anomalies, the acoustic branches make large contributions to the average electron-phonon coupling parameter. From the Eliashberg spectral function, the value of average electron-phonon coupling parameter is found to 0.707. Using this value, the superconducting critical temperature is obtained to be 2.4 K, in excellent accordance with its experimental value of 2.5 K. - Highlights: • The electronic structure of MgPtSi is studied using ab initio pseudopotential method. • Phonons and electron–phonon interaction in MgPtSi are studied using a linear response theory. • The acoustic phonon modes couple more strongly with electrons. • The value of λ is found to be 0.707 which shows that MgPtSi is a conventional honon-mediated superconductor. • The calculated T{sub c} of 2.4 K is in excellent accordance with its experimental value of 2.5 K.
Mean-field potential approach for thermodynamic properties of lanthanide: Europium as a prototype
Kumar, Priyank; Bhatt, N. K.; Vyas, P. R.; Gohel, V. B.
2018-03-01
In the present paper, a simple conjunction scheme [mean-field potential (MFP) + local pseudopotential] is used to study the thermodynamic properties of divalent lanthanide europium (Eu) at extreme environment. Present study has been carried out due to the fact that divalent nature of Eu arises because of stable half-filled 4f-shell at ambient condition, which has great influence on the thermodynamic properties at extreme environment. Due to such electronic structure, it is different from remaining lanthanides having incomplete 4f-shell. The presently computed results of thermodynamic properties of Eu are in good agreement with the experimental results. Looking to such success, it seems that the concept of MFP approach is successful to account contribution due to nuclear motion to the total Helmholtz free energy at finite temperatures and pressure-induced inter-band transfer of electrons for condensed state of matter. The local pseudopotential is used to evaluate cold energy and hence MFP accounts the s-p-d-f hybridization properly. Looking to the reliability and transferability along with its computational and conceptual simplicity, we would like to extend the present scheme for the study of thermodynamic properties of remaining lanthanides and actinides at extreme environment.
International Nuclear Information System (INIS)
Izquierdo, J.; Vega, A.; Balbas, L. C.; Sanchez-Portal, Daniel; Junquera, Javier; Artacho, Emilio; Soler, Jose M.; Ordejon, Pablo
2000-01-01
We present a theoretical study of the electronic and magnetic properties of iron systems in different environments: pure iron systems [dimer, bcc bulk, (100) surface, and free-standing iron monolayer], and low-dimensional iron systems deposited on Ag (100) surface (monoatomic linear wires, iron monolayer, planar, and three-dimensional clusters). Electronic and magnetic properties have been calculated using a recently developed total-energy first-principles method based on density-functional theory with numerical atomic orbitals as a basis set for the description of valence electrons and nonlocal pseudopotentials for the atomic core. The Kohn-Sham equations are solved self-consistently within the generalized gradient approximation for the exchange-correlation potential. Tests on the pseudopotential, the basis set, grid spacing, and k sampling are carefully performed. This technique, which has been proved to be very efficient for large nonmagnetic systems, is applied in this paper to calculate electronic and magnetic properties of different iron nanostructures. The results compare well with previous ab initio all-electron calculations and with experimental data. The method predicts the correct trends in the magnetic moments of Fe systems for a great variety of environments and requires a smaller computational effort than other ab initio methods. (c) 2000 The American Physical Society
Ab initio study of C14 laves phases in Fe-based systems
Directory of Open Access Journals (Sweden)
Pavlu J.
2012-01-01
Full Text Available Structural properties and energetics of Fe-based C14 Laves phases at various compositions (i.e. Fe2Fe, Fe2X, X2Fe, X2X, where X stands for Si, Cr, Mo, W, Ta were investigated using the pseudopotential VASP (Vienna Ab initio Simulation Package code employing the PAW-PBE (Projector Augmented Wave - Perdew Burke-Ernzerhof pseudopotentials. Full relaxation was performed for all structures studied including the reference states of elemental constituents and the equilibrium structure parameters as well as bulk moduli were found. The structure parameters of experimentally found structures were very well reproduced by our calculations. It was also found that the lattice parameters and volumes of the unit cell decrease with increasing molar fraction of iron. Thermodynamic analysis shows that the Fe2X configurations of Laves phases are more stable than the X2Fe ones. Some of the X2Fe configurations are even unstable with respect to the weighted average of the Laves phases of elemental constituents. Our calculations predict the stability of Fe2Ta. On the other hand, Fe2Mo and Fe2W are slightly unstable (3.19 and 0.68 kJ.mol-1, respectively and hypothetical structures Fe2Cr and Fe2Si are found unstable as well.
Quasiparticle semiconductor band structures including spin-orbit interactions.
Malone, Brad D; Cohen, Marvin L
2013-03-13
We present first-principles calculations of the quasiparticle band structure of the group IV materials Si and Ge and the group III-V compound semiconductors AlP, AlAs, AlSb, InP, InAs, InSb, GaP, GaAs and GaSb. Calculations are performed using the plane wave pseudopotential method and the 'one-shot' GW method, i.e. G(0)W(0). Quasiparticle band structures, augmented with the effects of spin-orbit, are obtained via a Wannier interpolation of the obtained quasiparticle energies and calculated spin-orbit matrix. Our calculations explicitly treat the shallow semicore states of In and Ga, which are known to be important in the description of the electronic properties, as valence states in the quasiparticle calculation. Our calculated quasiparticle energies, combining both the ab initio evaluation of the electron self-energy and the vector part of the pseudopotential representing the spin-orbit effects, are in generally very good agreement with experimental values. These calculations illustrate the predictive power of the methodology as applied to group IV and III-V semiconductors.
Morales-Cifuentes, Josue; Wang, Yilin; Reutt-Robey, Janice; Einstein, T. L.
2014-03-01
An effective pseudopotential mechanism for breaking the inherent sub-lattice symmetry of graphene has been studied using DFT calculations on hexagonal boron nitride. Electrical detection of CF3Cl phase transitions on graphene shows the existence of a commensurate ordered phase in which this can be tested. We study the electronic properties of this phase using VASP ver 5.3.3, with ab initio van der Waals density functionals (vdW-DF1 and vdW-DF2). Consistent with a physisorbed phase, binding energies and charge transfer per CF3Cl molecule are calculated to be on the order of 280meV and 0.01e, respectively. By exploring different coverages and orientations of this ordered phase we are able to open a band gap in some configurations; said gap is in the range of 8 to 80meV depending on the strength of the effective pseudopotential. Furthermore, we calculate the screening of these effects in bi-layer and tri-layer graphene. Work supported by NSF-MRSEC at UMD, grant DMR 05-20471 and NSF-CHE 13-05892.
International Nuclear Information System (INIS)
Jones, Wesley B; Bester, Gabriel; Canning, Andrew; Franceschetti, Alberto; Graf, Peter A; Kim, Kwiseon; Langou, Julien; Wang Linwang; Dongarra, Jack; Zunger, Alex
2005-01-01
Researchers at the National Renewable Energy Laboratory and their collaborators have developed over the past ∼10 years a set of algorithms for an atomistic description of the electronic structure of nanostructures, based on plane-wave pseudopotentials and configurationinteraction. The present contribution describes the first step in assembling these various codes into a single, portable, integrated set of software packages. This package is part of an ongoing research project in the development stage. Components of NanoPSE include codes for atomistic nanostructure generation and passivation, valence force field model for atomic relaxation, code for potential field generation, empirical pseudopotential method solver, strained linear combination of bulk bands method solver, configuration interaction solver for excited states, selection of linear algebra methods, and several inverse band structure solvers. Although not available for general distribution at this time as it is being developed and tested, the design goal of the NanoPSE software is to provide a software context for collaboration. The software package is enabled by fcdev, an integrated collection of best practice GNU software for open source development and distribution augmented to better support FORTRAN
Calculated Electronic Behavior and Spectrum of Mg+@C60 Using a Simple Jellium-shell Model
Directory of Open Access Journals (Sweden)
H. A. Schuessler
2004-11-01
Full Text Available Abstract: We present a method for calculating the energy levels and wave functions of any atom or ion with a single valence electron encapsulated in a Fullerene cage using a jelluim-shell model. The valence electron-core interaction is represented by a one-body pseudo-potential obtained through density functional theory with strikingly accurate parameters for Mg+ and which reduces to a purely Coulombic interaction in the case of H. We find that most energy states are affected little by encapsulation. However, when either the electron in the non-encapsulated species has a high probability of being near the jellium cage, or when the cage induces a maximum electron probability density within it, the energy levels shift considerably. Mg+ shows behavior similar to that of H, but since its wave functions are broader, the changes in its energy levels from encapsulation are slightly more pronounced. Agreement with other computational work as well as experiment is excellent and the method presented here is generalizable to any encapsulated species where a one-body electronic pseudo-potential for the free atom (or ion is available. Results are also presented for off-center hydrogen, where a ground state energy minimum of -14.01 eV is found at a nuclear displacement of around 0.1 ÃƒÂ….
Pacheco, Alexander B.; Reyes, Andrés; Micha, David A.
2006-12-01
Collision-induced light emission during the interaction of an alkali-metal atom and a noble-gas atom is treated within a first-principles, or direct, dynamics approach that calculates a time-dependent electric dipole for the whole system, and spectral emission cross sections from its Fourier transform. These cross sections are very sensitive to excited diatomic potentials and a source of information on their shape. The coupling between electronic transitions and nuclear motions is treated with atomic pseudopotentials and an electronic density matrix coupled to trajectories for the nuclei. A recently implemented pseudopotential parametrization scheme is used here for the ground and excited states of the LiHe system, and to calculate state-to-state dipole moments. To verify the accuracy of our new parameters, we recalculate the integral cross sections for the LiHe system in the keV energy regime and obtain agreement with other results from theory and experiment. We further present results for the emission spectrum from 10keV Li(2s)+He collisions, and compare them to experimental values available in the region of light emitted at 300-900nm .
Pacheco, Alexander B; Reyes, Andrés; Micha, David A
2006-10-21
The absorption of light during atomic collisions is treated by coupling electronic excitations, treated quantum mechanically, to the motion of the nuclei described within a short de Broglie wavelength approximation, using a density matrix approach. The time-dependent electric dipole of the system provides the intensity of light absorption in a treatment valid for transient phenomena, and the Fourier transform of time-dependent intensities gives absorption spectra that are very sensitive to details of the interaction potentials of excited diatomic states. We consider several sets of atomic expansion functions and atomic pseudopotentials, and introduce new parametrizations to provide light absorption spectra in good agreement with experimentally measured and ab initio calculated spectra. To this end, we describe the electronic excitation of the valence electron of excited alkali atoms in collisions with noble gas atoms with a procedure that combines l-dependent atomic pseudopotentials, including two- and three-body polarization terms, and a treatment of the dynamics based on the eikonal approximation of atomic motions and time-dependent molecular orbitals. We present results for the collision induced absorption spectra in the Li-He system at 720 K, which display both atomic and molecular transition intensities.
Self-consistent field with pseudowavefunctions
International Nuclear Information System (INIS)
Szasz, L.
1976-01-01
A computational method is given in which the energy of an atom is computed by using pseudowavefunctions only. The method centers on a model energy expression E/sub M/ which is similar to the Hartree--Fock energy expression, but contains only pseudowavefunctions. A theorem is proved according to which the Hartree--Fock orbitals can be transformed by a linear transformation into a set of uniquely defined pseudowavefunctions which have the property that, when substituted into E/sub M/, this quantity will closely approximate the Hartree--Fock energy E/sub F/. The new method is then formulated by identifying the total energy of an atom with the minimum of E/sub M/. Application of the energy minimum principle leads to a set of equations for the pseudowavefunctions which are similar to but simpler than the Hartree--Fock equations. These equations contain pseudopotentials for which explicit expressions are derived. The possibility of replacing these pseudopotentials by simpler model potentials is discussed, and the criteria for the selection of the model potential are outlined
Energy Technology Data Exchange (ETDEWEB)
Izquierdo, J. [Departamento de Fisica Teorica, Universidad de Valladolid, E-47011 Valladolid, (Spain); Vega, A. [Departamento de Fisica Teorica, Universidad de Valladolid, E-47011 Valladolid, (Spain); Balbas, L. C. [Departamento de Fisica Teorica, Universidad de Valladolid, E-47011 Valladolid, (Spain); Sanchez-Portal, Daniel [Department of Physics and Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 (United States); Junquera, Javier [Departamento de Fisica de la Materia Condensada, C-III, and Institut Nicolas Cabrera, Universidad Autonoma de Madrid, 28049 Madrid, (Spain); Artacho, Emilio [Departamento de Fisica de la Materia Condensada, C-III, and Institut Nicolas Cabrera, Universidad Autonoma de Madrid, 28049 Madrid, (Spain); Soler, Jose M. [Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Ordejon, Pablo [Institut de Ciencia de Materials de Barcelona (CSIC), Campus de la U.A.B., Bellaterra, E-08193 Barcelona, (Spain)
2000-05-15
We present a theoretical study of the electronic and magnetic properties of iron systems in different environments: pure iron systems [dimer, bcc bulk, (100) surface, and free-standing iron monolayer], and low-dimensional iron systems deposited on Ag (100) surface (monoatomic linear wires, iron monolayer, planar, and three-dimensional clusters). Electronic and magnetic properties have been calculated using a recently developed total-energy first-principles method based on density-functional theory with numerical atomic orbitals as a basis set for the description of valence electrons and nonlocal pseudopotentials for the atomic core. The Kohn-Sham equations are solved self-consistently within the generalized gradient approximation for the exchange-correlation potential. Tests on the pseudopotential, the basis set, grid spacing, and k sampling are carefully performed. This technique, which has been proved to be very efficient for large nonmagnetic systems, is applied in this paper to calculate electronic and magnetic properties of different iron nanostructures. The results compare well with previous ab initio all-electron calculations and with experimental data. The method predicts the correct trends in the magnetic moments of Fe systems for a great variety of environments and requires a smaller computational effort than other ab initio methods. (c) 2000 The American Physical Society.
International Nuclear Information System (INIS)
Block de Priego, R.A.
1977-11-01
The structure factor S(Q) of liquid rubidium has been measured for temperatures between 450 K and 1400 K and pressures up to 200 atm. The corresponding densities varied between 1.42 and 0.98 g cm -3 . The incident energy of the neutrons was 3.4 MeV, the momentum transfer Q being 0.2 - 2.5 A -1 . A significant change in the order of the liquid has been registrated. Compressibility and electrical conductivity were derived from the structure factors and compared with the direct measured quantities, showing a good agreement. Further interpretation of the data was done by means of a hard core and a square well potential. Using these models it was already possible to get some information about the interactions between the rubidium atoms. A more exact calculation with a modified STLS model and a pseudopotential leads to a good description of the measured S(Q). In order to describe at high temperatures S(Q) for smaller values a new term had to be added to the pseudopotential. (orig.) [de
Importance of unit cells in accurate evaluation of the characteristics of graphene
Energy Technology Data Exchange (ETDEWEB)
Sabzyan, Hassan; Sadeghpour, Narges [Isfahan Univ. (Iran, Islamic Republic of). Dept. of Chemistry
2016-08-01
Effects of the size of the unit cell on energy, atomic charges, and phonon frequencies of graphene at the Γ point of the Brillouin zone are studied in the absence and presence of an electric field using density functional theory (DFT) methods (LDA and DFT-PBE functionals with Goedecker-Teter-Hutter (GTH) and Troullier-Martins (TM) norm-conserving pseudopotentials). Two types of unit cells containing n{sub c}=4-28 carbon atoms are considered. Results show that stability of graphene increases with increasing size of the unit cell. Energy, atomic charges, and phonon frequencies all converge above n{sub c}=24 for all functional-pseudopotentials used. Except for the LDA-GTH calculations, application of an electric field of 0.4 and 0.9 V/nm strengths does not change the trends with the size of the unit cell but instead slightly decreases the binding energy of graphene. Results of this study show that the choice of unit cell size and type is critical for calculation of reliable characteristics of graphene.
International Nuclear Information System (INIS)
Choi, Sunghwan; Hong, Kwangwoo; Kim, Jaewook; Kim, Woo Youn
2015-01-01
We developed a self-consistent field program based on Kohn-Sham density functional theory using Lagrange-sinc functions as a basis set and examined its numerical accuracy for atoms and molecules through comparison with the results of Gaussian basis sets. The result of the Kohn-Sham inversion formula from the Lagrange-sinc basis set manifests that the pseudopotential method is essential for cost-effective calculations. The Lagrange-sinc basis set shows faster convergence of the kinetic and correlation energies of benzene as its size increases than the finite difference method does, though both share the same uniform grid. Using a scaling factor smaller than or equal to 0.226 bohr and pseudopotentials with nonlinear core correction, its accuracy for the atomization energies of the G2-1 set is comparable to all-electron complete basis set limits (mean absolute deviation ≤1 kcal/mol). The same basis set also shows small mean absolute deviations in the ionization energies, electron affinities, and static polarizabilities of atoms in the G2-1 set. In particular, the Lagrange-sinc basis set shows high accuracy with rapid convergence in describing density or orbital changes by an external electric field. Moreover, the Lagrange-sinc basis set can readily improve its accuracy toward a complete basis set limit by simply decreasing the scaling factor regardless of systems
International Nuclear Information System (INIS)
Johansson, B.; Rosengren, A.
1975-01-01
A ''generalized'' phase diagram is constructed empirically for the lanthanides. This diagram makes it possible, not only in one picture, to assemble a lot of information but also to predict phase transitions not yet experimentally accessible. Further, it clearly illustrates the close relation between the members of the lanthanide group. To account for some of its features, the pseudopotential method is applied. The trend in crystal structure through the lanthanide series can thereby be qualitatively accounted for, as can the trend in crystal structure for an individual element, when compressed. A scaling procedure makes it possible to extend the treatment to elements neighboring the lanthanides in the Periodic Table. In total 25 elements are considered. An atomic parameter f (relatable to the pseudopotential) is introduced, by means of which different phase transitions, both for an individual rare-earth element and intra-rare-earth alloys, can be correlated to certain critical values of this parameter. A nonmagnetic rare-earth series (Sc, Lu, Y, La, and Ac) is introduced and the occurrence of superconductivity is discussed with special emphasis on the pressure dependence of the transition temperature. This temperature can be correlated to the above-mentioned parameter f, both for intra-rare-earth alloys and pure elements at different pressures. The correlation implies that actinium is a superconductor with a critical temperature which could be as high as (11--12) degree K
Electronic properties of the layer III-VI semiconductors. A comparative study
International Nuclear Information System (INIS)
Depeursinge, Y.
1981-01-01
The electronic properties of the family of layer compounds InSe, GaSe and GaS by the empirical pseudopotential method have been studied. Both atomic positions, which are not accurately known from experiment, and atomic pseudopotentials are adjusted to fit the main optical and photoemission data with the further constraint that the same Se potential should be valid for InSe and GaSe, and the same Ga potential for GaS and GaSe. The charge densities have also been calculated and show that the ionicity of InSe is greater than that of GaS and GaSe, in good agreement with the Phillips electronegativity scale which predicts that InSe is 1.2 and 1.3 times more ionic than GaS and GaSe, respectively. The calculated band structures and charge densities allow a detailed discussion of the integrated and angle-resolved photoemission data as well as of the optical properties of these compounds. (author)
International Nuclear Information System (INIS)
Poleshchuk, O. K.; Branchadell, V.; Ritter, R. A.; Fateev, A. V.
2008-01-01
We have analyzed by means of Density functional theory calculations the nuclear quadrupole coupling constants of a range of gold, antimony, platinum, niobium and tantalum compounds. The geometrical parameters and halogen nuclear quadrupole coupling constants obtained by these calculations substantially corresponded to the data of microwave and nuclear quadrupole resonance spectroscopy. An analysis of the quality of the calculations that employ pseudo-potentials and all-electron basis sets for the halogen compounds was carried out. The zero order regular approximation (ZORA) method is shown to be a viable alternative for the calculation of halogen coupling constants in molecules. In addition, the ZORA model, in contrast to the pseudo-potential model, leads to realistic values of all metal nuclear quadrupole coupling constants. From Klopman's approach, it follows that the relationship between the electrostatic bonding and covalent depends on the nature of the central atom. The results on Moessbauer chemical shifts are also in a good agreement with the coordination number of the central atom.
International Nuclear Information System (INIS)
Sabry, R.
2009-01-01
A finite amplitude theory for ion-acoustic solitary waves and double layers in multicomponent plasma consisting of hot positrons, cold ions, and electrons with two-electron temperature distributions is presented. Conditions are obtained under which large amplitude stationary ion-acoustic solitary waves and double layers can exist. For the physical parameters of interest, the ion-acoustic solitary wave (double layers) profiles and the relationship between the maximum soliton (double layers) amplitude and the Mach number are found. Also, we have presented the region of existence of the large amplitude ion-acoustic waves by analyzing the structure of the pseudopotential. For the selected range of parameters, it is found that only positive solitary waves and double layers can exist. An analysis for the small amplitude limit through the Sagdeev pseudopotential analysis and the reductive perturbation theory shows the existence of positive and negative ion-acoustic solitary waves and double layers. The effects of positron concentration and temperature ratio on the characteristics of the solitary ion-acoustic waves and double layers (namely, the amplitude and width) are discussed in detail. The relevance of this investigation to space and laboratory plasmas is pointed out.
High-temperature study of superconducting hydrogen and deuterium sulfide
Energy Technology Data Exchange (ETDEWEB)
Durajski, A.P. [Institute of Physics, Czestochowa University of Technology, Ave. Armii Krajowej 19, 42-200 Czestochowa (Poland); Szczesniak, R. [Institute of Physics, Czestochowa University of Technology, Ave. Armii Krajowej 19, 42-200 Czestochowa (Poland); Institute of Physics, Jan Dlugosz University, Ave. Armii Krajowej 13/15, 42-200 Czestochowa (Poland); Pietronero, L. [Sapienza, Universita di Roma, Dip. Fisica, P. le A. Moro 2, 00185 Roma (Italy); Institute of Complex Systems, CNR, Via dei Taurini 19 Roma (Italy); London Institute for Mathematical Sciences, South Street 22, Mayfair London (United Kingdom)
2016-05-15
Hydrogen-rich compounds are extensively explored as candidates for a high-temperature superconductors. Currently, the measured critical temperature of 203 K in hydrogen sulfide (H{sub 3}S) is among the highest over all-known superconductors. In present paper, using the strong-coupling Eliashberg theory of superconductivity, we compared in detail the thermodynamic properties of two samples containing different hydrogen isotopes H{sub 3}S and D{sub 3}S at 150 GPa. Our research indicates that it is possible to reproduce the measured values of critical temperature 203 K and 147 K for H{sub 3}S and D{sub 3}S by using a Coulomb pseudopotential of 0.123 and 0.131, respectively. However, we also discuss a scenario in which the isotope effect is independent of pressure and the Coulomb pseudopotential for D{sub 3}S is smaller than for H{sub 3}S. For both scenarios, the energy gap, specific heat, thermodynamic critical field and related dimensionless ratios are calculated and compared with other conventional superconductors. We shown that the existence of the strong-coupling and retardation effects in the systems analysed result in significant differences between values obtained within the framework of the Eliashberg formalism and the prediction of the Bardeen-Cooper-Schrieffer theory. (copyright 2015 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Energy Technology Data Exchange (ETDEWEB)
Turi, László, E-mail: turi@chem.elte.hu [Department of Physical Chemistry, Eötvös Loránd University, P.O. Box 32, H-1518 Budapest 112 (Hungary)
2016-04-21
We evaluate the applicability of a hierarchy of quantum models in characterizing the binding energy of excess electrons to water clusters. In particular, we calculate the vertical detachment energy of an excess electron from water cluster anions with methods that include one-electron pseudopotential calculations, density functional theory (DFT) based calculations, and ab initio quantum chemistry using MP2 and eom-EA-CCSD levels of theory. The examined clusters range from the smallest cluster size (n = 2) up to nearly nanosize clusters with n = 1000 molecules. The examined cluster configurations are extracted from mixed quantum-classical molecular dynamics trajectories of cluster anions with n = 1000 water molecules using two different one-electron pseudopotenial models. We find that while MP2 calculations with large diffuse basis set provide a reasonable description for the hydrated electron system, DFT methods should be used with precaution and only after careful benchmarking. Strictly tested one-electron psudopotentials can still be considered as reasonable alternatives to DFT methods, especially in large systems. The results of quantum chemistry calculations performed on configurations, that represent possible excess electron binding motifs in the clusters, appear to be consistent with the results using a cavity structure preferring one-electron pseudopotential for the hydrated electron, while they are in sharp disagreement with the structural predictions of a non-cavity model.
Electrostatic supersolitons and double layers at the acoustic speed
International Nuclear Information System (INIS)
Verheest, Frank; Hellberg, Manfred A.
2015-01-01
Supersolitons are characterized by subsidiary extrema on the sides of a typical bipolar electric field signature or by association with a root beyond double layers in the fully nonlinear Sagdeev pseudopotential description. It has been proven that supersolitons may exist in several plasmas having at least three constituent species, but they cannot be found in weakly nonlinear theory. Another recent aspect of pseudopotential theory is that in certain plasma models and parameter regimes solitons and/or double layers can exist at the acoustic speed, having no reductive perturbation counterparts. Importantly, they signal coexistence between solitons having positive and negative polarity, in that one solution can be realized at a time, depending on infinitesimal perturbations from the equilibrium state. Weaving the two strands together, we demonstrate here that one can even find supersolitons and double layers at the acoustic speed, as illustrated using the model of cold positive and negative ions, in the presence of nonthermal electrons following a Cairns distribution. This model has been discussed before, but the existence and properties of supersolitons at the acoustic speed were not established at the time of publication
Electrostatic supersolitons and double layers at the acoustic speed
Energy Technology Data Exchange (ETDEWEB)
Verheest, Frank, E-mail: frank.verheest@ugent.be [Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, B–9000 Gent (Belgium); School of Chemistry and Physics, University of KwaZulu-Natal, Durban 4000 (South Africa); Hellberg, Manfred A., E-mail: hellberg@ukzn.ac.za [School of Chemistry and Physics, University of KwaZulu-Natal, Durban 4000 (South Africa)
2015-01-15
Supersolitons are characterized by subsidiary extrema on the sides of a typical bipolar electric field signature or by association with a root beyond double layers in the fully nonlinear Sagdeev pseudopotential description. It has been proven that supersolitons may exist in several plasmas having at least three constituent species, but they cannot be found in weakly nonlinear theory. Another recent aspect of pseudopotential theory is that in certain plasma models and parameter regimes solitons and/or double layers can exist at the acoustic speed, having no reductive perturbation counterparts. Importantly, they signal coexistence between solitons having positive and negative polarity, in that one solution can be realized at a time, depending on infinitesimal perturbations from the equilibrium state. Weaving the two strands together, we demonstrate here that one can even find supersolitons and double layers at the acoustic speed, as illustrated using the model of cold positive and negative ions, in the presence of nonthermal electrons following a Cairns distribution. This model has been discussed before, but the existence and properties of supersolitons at the acoustic speed were not established at the time of publication.
Energy Technology Data Exchange (ETDEWEB)
Poleshchuk, O. K., E-mail: poleshch@tspu.edu.ru [Tomsk State Pedagogical University (Russian Federation); Branchadell, V. [Universitat Autonoma de Barcelona, Departament de Quimica (Spain); Ritter, R. A.; Fateev, A. V. [Tomsk State Pedagogical University (Russian Federation)
2008-01-15
We have analyzed by means of Density functional theory calculations the nuclear quadrupole coupling constants of a range of gold, antimony, platinum, niobium and tantalum compounds. The geometrical parameters and halogen nuclear quadrupole coupling constants obtained by these calculations substantially corresponded to the data of microwave and nuclear quadrupole resonance spectroscopy. An analysis of the quality of the calculations that employ pseudo-potentials and all-electron basis sets for the halogen compounds was carried out. The zero order regular approximation (ZORA) method is shown to be a viable alternative for the calculation of halogen coupling constants in molecules. In addition, the ZORA model, in contrast to the pseudo-potential model, leads to realistic values of all metal nuclear quadrupole coupling constants. From Klopman's approach, it follows that the relationship between the electrostatic bonding and covalent depends on the nature of the central atom. The results on Moessbauer chemical shifts are also in a good agreement with the coordination number of the central atom.
Lee, Myoung-Jae; Jung, Young-Dae
2017-04-01
The collective nonideal effects on the nuclear fusion reaction process are investigated in partially ionized classical nonideal hydrogen plasmas. The effective pseudopotential model taking into account the collective and plasma shielding effects is applied to describe the interaction potential in nonideal plasmas. The analytic expressions of the Sommerfeld parameter, the fusion penetration factor, and the cross section for the nuclear fusion reaction in nonideal plasmas are obtained as functions of the nonideality parameter, Debye length, and relative kinetic energy. It is found that the Sommerfeld parameter is suppressed due to the influence of collective nonideal shielding. However, the collective nonideal shielding is found to enhance the fusion penetration factor in partially ionized classical nonideal plasmas. It is also found that the fusion penetration factors in nonideal plasmas represented by the pseudopotential model are always greater than those in ideal plasmas represented by the Debye-Hückel model. In addition, it is shown that the collective nonideal shielding effect on the fusion penetration factor decreases with an increase of the kinetic energy.
Nuclear Collective Hamiltonian and Deformations; Yadernyj kollektivnyj gamil'tonian i deformatsii
Energy Technology Data Exchange (ETDEWEB)
Kumar, Krishna [Niels Bohr Institute, University of Copenhagen, Copenhagen (Denmark)
1968-12-15
kollektivnom gamil'toniane Bora i modeli s parnym i kvadrupol'nym vzaimodejstviem. S pomoshh'ju chislennogo podbora velichiny svjazej mezhdu pjat'ju komponentami kvadrupol'nogo dvizhenija teorija mozhet ob{sup j}asnit' i predskazyvat' mnogie tendencii nizkolezhashhih urovnej i jelektromagnitnyh perehodov v oblasti W-Os-Pt. Nulevye kolebanija igrajut vazhnuju rol' v razmytii volnovoj funkcii jadra v ploskosti {beta}-{gamma}, tak chto povedenie jadra sushhestvenno zavisit ot po-vedenija kollektivnogo gamil'toniana vdali ot ravnovesnoj formy. Zavisimost' gamil'toniana ot u, i osobenno chlena v potenciale, otvechajushhego za raznicu vytjanutoj i spljusnutoj formy, igraet rjoshajushhuju rol' v rasshheplenii 2'{sup +} i 4{sup +} sostojanij i v sostojanijah I Not-Equal-To 0, s kvadrupol'nymi momentami, neravnymi nulju i imejushhimi mesto dazhe v sluchae sfericheskoj ravnovesnoj formy ili polnost'ju assimmetrichnoj s {gamma} = 30 Degree-Sign . Angarmonichnost' shesti inercionnyh funkcij gamil'toniana Bora vyzyvaet smeshivanie {beta}-{gamma} polos v protonah W, umen'shaet {beta}-{gamma} smeshivanie v izotopah Os i nejtralizuet razlichie v potenciale vytjanutoj i spljusnutoj formy. Takim obrazom, rasschitannyj spektr 196Pt okazalsja kolebatel'nym. Raschety dlja {sup 196}Pt dajut kak dostatochno bol'shoj otricatel'nyj kvadru- pol'nyj moment pervogo 2{sup +} sostojanija, tak i maluju verojatnost' prjamogo perehoda iz osnovnogo sostojanija na vtoroe 2{sup +} sostojanie. Odnako asschitannye 2+ (sostojanija {sup 192-196}Pt nahodjatsja na 0,1-0,2 Mjev vyshe. Velichiny V(E2; 2 Rightwards-Arrow 2'), rasschitannye dlja jetoj oblasti, bol'she nabljudaemyh priblizitel'no raza v dva. Ukazyvajutsja nekotorye vozmozhnye puti sovershenstvovanija metodiki. (author)
Energy Technology Data Exchange (ETDEWEB)
Ryabukhina, Yu. S.
1963-11-15
vybrany kontury na zhidkikh pri komnatnoj temperature splavakh indiya. Bylo izucheno povedenie dvukh ehvtekticheskikh splavov indiya po otnosheniyu k nekotorym konstruktivnym materialam, i v nachale 1960 g. byl zapushchen pervyj stendovyj indij-gallievyj kontur. V rezul'tate dal'nejshikh rabot byli zapushcheny model'nyj indij-galdievyj kontur s aktivnost'yu v obluchatele do {approx} 100 g. eh k v radiya pri reaktore IRT AN Gruzinskoj SSR i stendovyj indij-gallij-olovyannyj kontur v kanale reaktora IRT IAEH AN SSSR. Nakonets, v 1962 g. byl zapushen rabochij indij-gallij-olovyannyj kontur pri reaktore IRT AN Latvijskoj SSR dlya provedeniya polupromyshlennykh radiatsionnykh protsessov. Maksimal'naya aktivnost' obluchatelya kontura 30 000 g. eh k v radiya. Doklad sostoit iz 4 razdelov: 1. Raschety radiatsionnykh konturov. Obobshchaetsya prodelannaya rabota po metodam rascheta radiatsionnykh konturov. 2. Model' radiatsionnogo indij-gallievogo kontura reaktora IRT-2000 v Tbilisi. Opisyvaetsya dejstvuyushchij kontur. 3. Indij-gallij-olovyannyj radiatsionnyj kontur yadernogo reaktora IRT AN Latvijskoj SSR. Opisyvaetsya dejstvuyushchij kontur. 4. Perspektivy dal'nejshego razvitiya radiatsionnykh konturov. Opisyvayutsya ehksperimenty, skhemy i privodyatsya raschety, na osnovanii kotorykh predstavlyaetsya vozmozhnym sozdanie konturov na tverdom margantse i mobil'nykh konturov na zhidkikh splavakh indiya. (author)
Energy Technology Data Exchange (ETDEWEB)
Jezowska-Trzeblatowska, B; Ziolkowski, J [University of Wroclaw (Poland)
1962-03-15
central y la capa p del atomo de nitrogeno. (author) [Russian] V kachestve slozhnogo svyazuyushchego zvena nitrozilovaya gruppa predstavlyaet osobyj interes kak po svoej strukture, tak i blagodarya svoemu svojstvu obrazovyvat' gruppy NO{sup -} i NO{sup +}. Dlya issledovaniya ehlektronnoj struktury K{sub 3}Mn(CN){sub 6} i K{sub 3}Mn(CN){sub 6}NO, valentnosti metalla i kharaktera soedinenij byli proizvedeny issledovaniya pri pomoshchi metoda radioizotopnogo obmena, a takzhe i drugikh fiziko-khimicheskikh metodov. Bylo obnaruzheno, chto dobavlenie nitrozilovoj gruppy k ionam geksatsionata znachitel'no uvelichivaet ustojchivost' soedineniya kak v tverdom sostoyanii, tak i v rastvore. EHto nablyudenie bylo podtverzhdeno issledovaniem kinetiki obmena v sistemakh: (I) K{sub 3}Mn(CN){sub 6} + KC{sup 14}N; (II) K{sub 3}Mn(CN){sub 5}NO + KC{sup 14}N. V oboikh sluchayakh reaktsii obmena v funktsii vremeni yavlyayutsya reaktsiyami pervogo poryadka, no oni znachitel'no otlichayutsya drug ot druga po skorosti. EHnergii aktivatsii ehtikh reaktsij ravny E{sub 1}=8,5 kilokalorij na molekulu i E{sub 11}=22,8 kilokalorij na molekulu. Anion Mn(CN){sub 5}NO{sub 3} svetochuvstvitelen, tak chto reaktsiya obmena nosit fotokhimicheskij kharakter. Sootnoshenie postoyannykh skorostej obmena v temnote i pri standartizirovannom osveshchenii ravno 1:100. Pervaya reaktsiya obmena (I) proiskhodit po tipu assotsiatsii, togda kak vtoraya reaktsiya (II) sleduet slozhnomu mekhanizmu assotsiatsii i dissotsiatsii. Analiz raspredeleniya aktivnosti mezhdu tsianistymi gruppami, podvergayushchimisya obmenu v sostoyanii izotopnogo ravnovesiya, obnaruzhil identichnost' po men'shej mere chetyrekh tsianistykh grupp. Bol'shaya ustojchivost' nitrozilovykh soedinenij po sravneniyu s geksatsianatami, a takzhe otsutstvie vtorichnykh dissotsiatsij byli podtverzhdeny razlichnymi metodami. Vse ehto ukazyvaet na strukturu NO{sup -} kompleksa. Predydushchie issledovaniya pokazali, chto nitrozilovaya gruppa koordiniruetsya v
Predictions For New, Exotic Actinide Species
International Nuclear Information System (INIS)
Pyykko, P.
2002-01-01
The approach. New, simple chemical species can be predicted by studying isoelectronic series using ab initio quantum chemistry. We currently use in most cases relativistic pseudopotentials and handle the electron correlation using density functional theory (DFT) or wave-function-based methods, from MP2 to CCSD(T). Typical codes are Gaussian 98, Turbomole or MolCas. For full four-component Dirac-Fock calculations, the DREAMS code of K. G. Dyall has been utilized. For mapping out the possible new species, complete maps of all possibilities are made, whenever possible, and the new species typically occur along the coast-line of the 'island of stability' of already known species
Ab initio transmission electron microscopy image simulations of coherent Ag-MgO interfaces
International Nuclear Information System (INIS)
Mogck, S.; Kooi, B.J.; Hosson, J.Th.M. de; Finnis, M.W.
2004-01-01
Density-functional theory calculations, within the plane-wave-ultrasoft pseudopotential framework, were performed in the projection for MgO and for the coherent (111) Ag-MgO polar interface. First-principles calculations were incorporated in high-resolution transmission electron microscopy (HRTEM) simulations by converting the charge density into electron scattering factors to examine the influence of charge transfer, charge redistribution at the interface, and ionicity on the dynamical electron scattering and on calculated HRTEM images. It is concluded that the ionicity of oxides and the charge redistribution at interfaces play a significant role in HRTEM image simulations. In particular, the calculations show that at oxygen-terminated (111) Ag-MgO interfaces the first oxygen layer at the interface is much brighter than that in calculations with neutral atoms, in agreement with experimental observations
Nonlinear low frequency electrostatic structures in a magnetized two-component auroral plasma
Energy Technology Data Exchange (ETDEWEB)
Rufai, O. R., E-mail: rajirufai@gmail.com [University of the Western Cape, Bellville 7535, Cape-Town (South Africa); Scientific Computing, Memorial University of Newfoundland, St John' s, Newfoundland and Labrador A1C 5S7 (Canada); Bharuthram, R., E-mail: rbharuthram@uwc.ac.za [University of the Western Cape, Bellville 7535, Cape-Town (South Africa); Singh, S. V., E-mail: satyavir@iigs.iigm.res.in; Lakhina, G. S., E-mail: lakhina@iigs.iigm.res.in [University of the Western Cape, Bellville 7535, Cape-Town (South Africa); Indian Institute of Geomagnetism, New Panvel (W), Navi Mumbai 410218 (India)
2016-03-15
Finite amplitude nonlinear ion-acoustic solitons, double layers, and supersolitons in a magnetized two-component plasma composed of adiabatic warm ions fluid and energetic nonthermal electrons are studied by employing the Sagdeev pseudopotential technique and assuming the charge neutrality condition at equilibrium. The model generates supersoliton structures at supersonic Mach numbers regime in addition to solitons and double layers, whereas in the unmagnetized two-component plasma case only, soliton and double layer solutions can be obtained. Further investigation revealed that wave obliqueness plays a critical role for the evolution of supersoliton structures in magnetized two-component plasmas. In addition, the effect of ion temperature and nonthermal energetic electron tends to decrease the speed of oscillation of the nonlinear electrostatic structures. The present theoretical results are compared with Viking satellite observations.
International Nuclear Information System (INIS)
Cortez, S.; Krebs, O.; Voisin, P.
2000-01-01
The recently discovered in-plane optical anisotropy of [001]-grown quantum wells offers a new theoretical and experimental insight into the electronic properties of semiconductor interfaces. We first discuss the coupling of X and Y valence bands due to the breakdown of rotation inversion symmetry at a semiconductor hetero-interface, with special attention to its dependence on effective parameters such as valence band offset. The intracell localization of Bloch functions is explained from simple theoretical arguments and evaluated numerically from a pseudo-potential microscopic model. The role of envelope functions is considered, and we discuss the specific case of non-common atom interfaces. Experimental results and applications to interface characterization are presented. These calculations give a microscopic justification, and establish the limits of the heuristic 'H BF ' model. (author)
Chen Chang Feng
1998-01-01
We have constructed an effective model Hamiltonian in the Hubbard formalism for the Cs/GaAs(110) surface at quarter-monolayer coverage with all of the parameters extracted from constrained local-density-approximation (LDA) pseudopotential calculations. The single-particle excitation spectrum of the model has been calculated using an exact-diagonalization technique to help determine the relevant interaction terms. It is shown that the intersite interaction between the nearest-neighbour Ga sites plays the key role in determining the insulating nature of the system and must be included in the model, in contrast to suggestions of some previous work. Our results show that a reliable mapping of LDA results onto an effective model Hamiltonian can be achieved by combining constrained LDA calculations for the Hamiltonian parameters and many-body calculations of the single-particle excitation spectrum for identifying relevant interaction terms. (author)
Structural properties of III-V zinc-blende semiconductors under pressure
International Nuclear Information System (INIS)
Froyen, S.; Cohen, M.L.
1983-01-01
The pseudopotential method within the local-density approximation is used to investigate the static and structural properties of some III-V compound semiconductors. Comparisons of calculated total energies as a function of volume and structure yield information about solid-solid phase transformations. At high pressures the results indicate that several metallic structures are lower in energy than the zinc-blende structure. From our results the compounds (AlP, AlAs, GaP, and GaAs) can be divided into two classes. In the Ga compounds, we find a pressure-induced phase transformation to either rocksalt, β-Sn, or NiAs, whereas in the Al compounds rocksalt and NiAs are stabilized with respect to β-Sn. All structures except zinc blende are metallic. We discuss the electronic structure of each phase and show how it relates to structural stability
Dilmi, S.; Saib, S.; Bouarissa, N.
2018-06-01
Structural, electronic, electron-phonon coupling and superconducting properties of the intermetallic compound LuC2 are investigated by means of ab initio pseudopotential plane wave method within the generalized gradient approximation. The calculated equilibrium lattice parameters yielded a very good accord with experiment. There is no imaginary phonon frequency in the whole Brillouin zone supporting thus the dynamical stability in the material of interest. The average electron-phonon coupling parameter is found to be 0.59 indicating thus a weak-coupling BCS superconductor. Using a reasonable value of μ* = 0.12 for the effective Coulomb repulsion parameter, the superconducting critical temperature Tc is found to be 3.324 which is in excellent agreement with the experimental value of 3.33 K. The effect of the spin-orbit coupling on the superconducting properties of the material of interest has been examined and found to be weak.
Pearsall, Thomas P
2017-01-01
This textbook employs a pedagogical approach that facilitates access to the fundamentals of Quantum Photonics. It contains an introductory description of the quantum properties of photons through the second quantization of the electromagnetic field, introducing stimulated and spontaneous emission of photons at the quantum level. Schrödinger’s equation is used to describe the behavior of electrons in a one-dimensional potential. Tunneling through a barrier is used to introduce the concept of nonlocality of an electron at the quantum level, which is closely-related to quantum confinement tunneling, resonant tunneling, and the origin of energy bands in both periodic (crystalline) and aperiodic (non-crystalline) materials. Introducing the concepts of reciprocal space, Brillouin zones, and Bloch’s theorem, the determination of electronic band structure using the pseudopotential method is presented, allowing direct computation of the band structures of most group IV, group III-V, and group II-VI semiconducto...
Optical properties of LiGaS{sub 2}: an ab initio study and spectroscopic ellipsometry measurement
Energy Technology Data Exchange (ETDEWEB)
Atuchin, V V [Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 90, 630090 (Russian Federation); Lin, Z S [Beijing Center for Crystal R and D, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, PO Box 2711, Beijing 100190 (China); Isaenko, L I; Lobanov, S I [Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, Novosibirsk 90, 630090 (Russian Federation); Kesler, V G [Laboratory of Physical Bases of Integrated Microelectronics, Institute of Semiconductor Physics, SB RAS, Novosibirsk 90, 630090 (Russian Federation); Kruchinin, V N, E-mail: zslin@mail.ipc.ac.c [Laboratory for Ellipsometry of Semiconductor Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 90, 630090 (Russian Federation)
2009-11-11
Electronic and optical properties of lithium thiogallate crystal, LiGaS{sub 2}, have been investigated by both experimental and theoretical methods. The plane-wave pseudopotential method based on DFT theory has been used for band structure calculations. The electronic parameters of Ga 3d orbitals have been corrected by the DFT+U methods to be consistent with those measured with x-ray photoemission spectroscopy. Evolution of optical constants of LiGaS{sub 2} over a wide spectral range was determined by developed first-principles theory and dispersion curves were compared with optical parameters defined by spectroscopic ellipsometry in the photon energy range 1.2-5.0 eV. Good agreement has been achieved between theoretical and experimental results.
Optical properties of LiGaS2: an ab initio study and spectroscopic ellipsometry measurement
International Nuclear Information System (INIS)
Atuchin, V V; Lin, Z S; Isaenko, L I; Lobanov, S I; Kesler, V G; Kruchinin, V N
2009-01-01
Electronic and optical properties of lithium thiogallate crystal, LiGaS 2 , have been investigated by both experimental and theoretical methods. The plane-wave pseudopotential method based on DFT theory has been used for band structure calculations. The electronic parameters of Ga 3d orbitals have been corrected by the DFT+U methods to be consistent with those measured with x-ray photoemission spectroscopy. Evolution of optical constants of LiGaS 2 over a wide spectral range was determined by developed first-principles theory and dispersion curves were compared with optical parameters defined by spectroscopic ellipsometry in the photon energy range 1.2-5.0 eV. Good agreement has been achieved between theoretical and experimental results.
Bonding xenon and krypton on the surface of uranium dioxide single crystal
Directory of Open Access Journals (Sweden)
Dąbrowski Ludwik
2014-08-01
Full Text Available We present density functional theory (DFT calculation results of krypton and xenon atoms interaction on the surface of uranium dioxide single crystal. A pseudo-potential approach in the generalised gradient approximation (GGA was applied using the ABINIT program package. To compute the unit cell parameters, the 25 atom super-cell was chosen. It has been revealed that close to the surface of a potential well is formed for xenon and krypton atom due to its interaction with the atoms of oxygen and uranium. Depth and shape of the well is the subject of ab initio calculations in adiabatic approximation. The calculations were performed both for the case of oxygenic and metallic surfaces. It has been shown that the potential well for the oxygenic surface is deeper than for the metallic surface. The thermal stability of immobilising the atoms of krypton and xenon in the potential wells were evaluated. The results are shown in graphs.
Variation of the energy gap of the SbSI crystals at ferroelectric phase transition
International Nuclear Information System (INIS)
Audzijonis, A.; Zaltauskas, R.; Zigas, L.; Vinokurova, I.V.; Farberovich, O.V.; Pauliukas, A.; Kvedaravicius, A.
2006-01-01
Variation of the forbidden gap of SbSI crystals in the phase transition region is analyzed on the pseudopotential method for antiferroelectric and ferroelectric phase. The band gap at several special points of the Brillouin zone and some characteristic parameters of the band are considered. During the phase transition, the most significant changes are observed with the valence band top at points Q, C, R, H, E and with the conduction band bottom at points H, T and E of the Brillouin zone. At the ferroelectric phase transition, the valence and conduction bands change due to displacement of Sb and S atoms with respect to I and with respect to each other as a result of order-disorder and displacement-type transition. The obtained band gap values agree quite well with the experiment. This is apparently due to application of neutral rather than ionic atomic functions and inclusion of sufficiently many plane waves in the basis set for calculation
International Nuclear Information System (INIS)
Audzijonis, A.; Zigas, L.; Vinokurova, I.V.; Farberovic, O.V.; Zaltauskas, R.; Cijauskas, E.; Pauliukas, A.; Kvedaravicius, A.
2006-01-01
The force constants of SbSI crystal have been calculated by the pseudo-potential method. The frequencies and normal coordinates of SbSI vibration modes along the c (z) direction have been determined in harmonic approximation. The potential energies of SbSI normal modes dependence on normal coordinates along the c (z) direction V(z) have been determined in anharmonic approximation, taking into account the interaction between the phonons. It has been found, that in the range of 30-120 cm -1 , the vibrational spectrum is determined by a V(z) double-well normal mode, but in the range of 120-350 cm -1 , it is determined by a V(z) single-well normal mode
Impurity-defect complexes in hydrogenated amorphous silicon
International Nuclear Information System (INIS)
Yang, L.H.; Fong, C.Y.; Nichols, C.S.
1991-01-01
The two most outstanding features observed for dopants in hydrogenated amorphous silicon (a-Si:H)-a shift in the Fermi level accompanied by an increase in the defect density and an absence of degenerate doping have previously been postulated to stem from the formation of substitutional dopant-dangling bond complexes. Using first-principles self-consistent pseudopotential calculations in conjunction with a supercell model for the amorphous network and the ability of network relaxation from the first-principles results. The authors have studied the electronic and structural properties of substitutional fourfold-coordinated phosphorus and boron at the second neighbor position to a dangling bond defect. This paper demonstrates that such impurity-defect complexes can account for the general features observed experimentally in doped a-Si:H
HREM investigation of the structure of the Σ5(310)/[001] symmetric tilt grain boundaries in Nb
International Nuclear Information System (INIS)
King, W.E.; Compbell, G.H.; Coombs, A.; Ruehle, M.
1991-01-01
This paper reports on atomistic simulations using interatomic potentials for Nb developed employing the embedded atom method (EAM) and the model generalized pseudopotential theory (MGPT) that have indicated a possible cusp at the Σ5 (310) orientation in the energy vs tilt angle curves for left-angle 001 right-angle symmetric tilt grain boundaries. In addition, the most stable structure predicted using EAM exhibits shifts of one crystal relative to the other along the tilt axis and along the direction perpendicular to the tilt axis lying in the boundary plane. The structure predicted using the MGPT was mirror symmetric across the plane of the grain boundary. This boundary has been prepared for experimental study using the ultra high vacuum diffusion bonding method. A segment of this boundary has been studied using high resolution electron microscopy
Continuum variational and diffusion quantum Monte Carlo calculations
International Nuclear Information System (INIS)
Needs, R J; Towler, M D; Drummond, N D; Lopez RIos, P
2010-01-01
This topical review describes the methodology of continuum variational and diffusion quantum Monte Carlo calculations. These stochastic methods are based on many-body wavefunctions and are capable of achieving very high accuracy. The algorithms are intrinsically parallel and well suited to implementation on petascale computers, and the computational cost scales as a polynomial in the number of particles. A guide to the systems and topics which have been investigated using these methods is given. The bulk of the article is devoted to an overview of the basic quantum Monte Carlo methods, the forms and optimization of wavefunctions, performing calculations under periodic boundary conditions, using pseudopotentials, excited-state calculations, sources of calculational inaccuracy, and calculating energy differences and forces. (topical review)
Simple formalism for efficient derivatives and multi-determinant expansions in quantum Monte Carlo
Energy Technology Data Exchange (ETDEWEB)
Filippi, Claudia, E-mail: c.filippi@utwente.nl [MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede (Netherlands); Assaraf, Roland, E-mail: assaraf@lct.jussieu.fr [Sorbonne Universités, UPMC Univ Paris 06, CNRS, Laboratoire de Chimie Théorique CC 137-4, place Jussieu F-75252 Paris Cedex 05 (France); Moroni, Saverio, E-mail: moroni@democritos.it [CNR-IOM DEMOCRITOS, Istituto Officina dei Materiali, and SISSA Scuola Internazionale Superiore di Studi Avanzati, Via Bonomea 265, I-34136 Trieste (Italy)
2016-05-21
We present a simple and general formalism to compute efficiently the derivatives of a multi-determinant Jastrow-Slater wave function, the local energy, the interatomic forces, and similar quantities needed in quantum Monte Carlo. Through a straightforward manipulation of matrices evaluated on the occupied and virtual orbitals, we obtain an efficiency equivalent to algorithmic differentiation in the computation of the interatomic forces and the optimization of the orbital parameters. Furthermore, for a large multi-determinant expansion, the significant computational gain afforded by a recently introduced table method is here extended to the local value of any one-body operator and to its derivatives, in both all-electron and pseudopotential calculations.
Electron-phonon contribution to the phonon and excited electron (hole) linewidths in bulk Pd
International Nuclear Information System (INIS)
Sklyadneva, I Yu; Leonardo, A; Echenique, P M; Eremeev, S V; Chulkov, E V
2006-01-01
We present an ab initio study of the electron-phonon (e-ph) coupling and its contribution to the phonon linewidths and to the lifetime broadening of excited electron and hole states in bulk Pd. The calculations, based on density-functional theory, were carried out using a linear-response approach in the plane-wave pseudopotential representation. The obtained results for the Eliashberg spectral function α 2 F(ω), e-ph coupling constant λ, and the contribution to the lifetime broadening, Γ e-ph , show strong dependence on both the energy and momentum of an electron (hole) state. The calculation of phonon linewidths gives, in agreement with experimental observations, an anomalously large broadening for the transverse phonon mode T 1 in the Σ direction. In addition, this mode is found to contribute most strongly to the electron-phonon scattering processes on the Fermi surface
First-principles study on the effect of high In doping on the conductivity of ZnO
International Nuclear Information System (INIS)
Hou Qing-Yu; Li Ji-Jun; Ying Chun; Zhao Chun-Wang; Zhao Er-Jun; Zhang Yue
2013-01-01
Based on the density functional theory (DFT), using first-principles plane-wave ultrasoft pseudopotential method, the models of the unit cell of pure ZnO and two highly In-doped supercells of Zn 0.9375 In 0.0625 O and Zn 0.875 In 0.125 O are constructed, and the geometry optimizations of the three models are carried out. The total density of states (DOS) and the band structures (BS) are also calculated. The calculation results show that in the range of high doping concentration, when the doping concentration is hihger than a specific value, the conductivity decreases with the increase of the doping concentration of In in ZnO, which is in consistence with the change trend of the experimental results
Infrared spectroscopy of copper-resveratrol complexes: A joint experimental and theoretical study
Energy Technology Data Exchange (ETDEWEB)
Chiavarino, B.; Crestoni, M. E.; Fornarini, S. [Dipartimento di Chimica e Tecnologie del Farmaco, Sapienza - Universita di Roma, Piazzale A. Moro 5, 00185 Rome (Italy); Taioli, S. [Interdisciplinary Laboratory for Computational Science, FBK-CMM and University of Trento, Via Sommarive 18, 38123 Trento (Italy); Department of Physics, University of Trento, Via Sommarive 14, 38123 Trento (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Perugia (Italy); Department of Chemistry, University of Bologna, Via F. Selmi 2, I-40126 Bologna (Italy); Mancini, I.; Tosi, P. [Department of Physics, University of Trento, Via Sommarive 14, 38123 Trento (Italy)
2012-07-14
Infrared multiple-photon dissociation spectroscopy has been used to record vibrational spectra of charged copper-resveratrol complexes in the 3500-3700 cm{sup -1} and 1100-1900 cm{sup -1} regions. Minimum energy structures have been determined by density functional theory calculations using plane waves and pseudopotentials. In particular, the copper(I)-resveratrol complex presents a tetra-coordinated metal bound with two carbon atoms of the alkenyl moiety and two closest carbons of the adjoining resorcinol ring. For these geometries vibrational spectra have been calculated by using linear response theory. The good agreement between experimental and calculated IR spectra for the selected species confirms the overall reliability of the proposed geometries.
Electronic structure and equation of state of Sm2Co17 from first-principles DFT+ U
Huang, Patrick; Butch, Nicholas P.; Jeffries, Jason R.; McCall, Scott K.
2013-03-01
Rare-earth intermetallics have important applications as permanent magnet materials, and the rational optimization of their properties would benefit greatly from guidance from ab initio modeling. However, these systems are particularly challenging for current electronic structure methods. Here, we present an ab initio study of the prototype material Sm2Co17 and related compounds, using density functional theory with a Hubbard correction for the Sm 4 f-electrons (DFT+ U method) and ultrasoft pseudopotentials. The Hubbard U parameter is derived from first principles [Cococcioni and de Gironcoli, PRB 71, 035105 (2005)], not fit to experiment. Our calculations are in good agreement with recent photoemission measurements at ambient pressure and the equation of state up to 40 GPa, thus supporting the validity of our DFT+ U model. Prepared by LLNL under Contract DE-AC52-07NA27344.
Energy Technology Data Exchange (ETDEWEB)
Sykora, Rudolf [Nanotechnology Centre, VSB-TU Ostrava (Czech Republic); Legut, Dominik [IT4Innovations Centre, VSB-TU Ostrava (Czech Republic); Rogl, Gerda [Institute of Physical Chemistry, University of Vienna (Austria); Institute of Solid State Physics, University of Technology, Wien (Austria); Faculty of Physics, University of Vienna (Austria); Mueller, Peter; Mueller, Herbert; Bauer, Ernst [Institute of Solid State Physics, University of Technology, Wien (Austria); Puchegger, Stephan [Faculty of Physics, University of Vienna (Austria); Rogl, Peter [Institute of Physical Chemistry, University of Vienna (Austria)
2015-07-01
Adopting the plane-wave pseudopotential VASP[1] DFT package, using a simple local density approximation for electronic exchange and correlation effects, and disregarding spin-orbit interaction we calculate (a necessarily naive) electronic structure of CePt{sub 3}Si and CePt{sub 3}B materials (the former being known as a heavy-fermion superconductor with no inversion centre) under several discrete values of stress and strain. For each such configuration we calculate its phonon spectrum with a direct (supercell) method as supplied by the Phonopy program. Combining the results we obtain materials' thermal and mechanical properties within the quasi-harmonic approximation, presumably applicable to temperatures above magnetic-ordering temperatures. Results are compared to experimental data.
Electronic Properties of Curved and Defective 2-D BN Nanostructures
Beach, Kory; Terrones, Humberto; Raeliarijaona, Aldo; Siegel, Ross; Florio, Fred
Density functional theory (DFT) with local density approximation (LDA) pseudopotentials is used to calculate the band structure and density of states of various novel 2-D BN nanostructures. Three types of systems are studied: Schwarzites, a Haeckelite, and an h-BN monolayer. Schwarzites are negatively curved structures in which the curvature is due to the introduction of octagonal rings of alternating boron and nitrogen atoms. In particular, three families of Schwarzites are analyzed: P, G and IWP. The Haeckelites on the other hand, are flat layers composed of squares and octagons of BN. It is found that all these BN allotropes are metastable in which the band gap is direct and smaller than the most stable system, h-BN. National Science Foundation (EFRI-1433311).
Polarizabilities and hyperpolarizabilities of the alkali metal atoms
Energy Technology Data Exchange (ETDEWEB)
Fuentealba, P. (Chile Univ., Santiago (Chile). Departamento de Fisica and Centro de Mecanica Cuantica Aplicada (CMCA)); Reyes, O. (Chile Univ., Santiago (Chile). Dept. de Fisica)
1993-08-14
The electric static dipole polarizability [alpha], quadrupole polarizability C, dipole-quadrupole polarizability B, and the second dipole hyperpolarizability [gamma] have been calculated for the alkali metal atoms in the ground state. The results are based on a pseudopotential which is able to incorporate the very important core-valence correlation effect through a core polarization potential, and, in an empirical way, the main relativistic effects. The calculated properties compare very well with more elaborated calculations for the Li atom, excepting the second hyperpolarizability [gamma]. For the other atoms, there is neither theoretical nor experimental information about most of the higher polarizabilities. Hence, the results of this paper should be seen as a first attempt to give a complete account of the series expansion of the interaction energy of an alkali metal atom and a static electric field. (author).
Energy gaps, effective masses and ionicity of AlxGa1-xSb ternary semiconductor alloys
Bouarissa, N.; Boucenna, M.; Saib, S.; Siddiqui, S. A.
2017-12-01
A pseudopotential calculation of the electronic structure of AlxGa1-xSb ternary alloys in the zinc-blende structure has been performed. The compositional dependence of energy gaps, electron and heavy hole effective masses and ionicity of the material system of interest have been examined and discussed. Special attention has been given to the effect of the alloy disorder on the direct (Γ-Γ) bandgap energy. It is found that all features of interest vary monotonically with increasing the Al concentration x. Besides, bandgap bowing parameters and extent of the direct-to-indirect bandgap transition have been determined. Our findings agree generally well with the data reported in the literature. Trends in ionicity are found to be consistent with the Phillips ionicity scale.
The structural, electronic and phonon behavior of CsPbI_3: A first principles study
International Nuclear Information System (INIS)
Bano, Amreen; Khare, Preeti; Parey, Vanshree; Shukla, Aarti; Gaur, N. K.
2016-01-01
Metal halide perovskites are optoelectronic materials that have attracted enormous attention as solar cells with power conversion efficiencies reaching 20%. The benefit of using hybrid compounds resides in their ability to combine the advantage of these two classes of compounds: the high mobility of inorganic materials and the ease of processing of organic materials. In spite of the growing attention of this new material, very little is known about the electronic and phonon properties of the inorganic part of this compounds. A theoretical study of structural, electronic and phonon properties of metal-halide cubic perovskite, CsPbI_3 is presented, using first-principles calculations with planewave pseudopotential method as personified in PWSCF code. In this approach local density approximation (LDA) is used for exchange-correlation potential.
Makinistian, Leonardo; Albanesi, Eduardo A.
2013-06-01
We present ab initio calculations of magnetoelectronic and transport properties of the interface of hcp Cobalt (001) and the intrinsic narrow-gap semiconductor germanium selenide (GeSe). Using a norm-conserving pseudopotentials scheme within DFT, we first model the interface with a supercell approach and focus on the spin-resolved densities of states and the magnetic moment (spin and orbital components) at the different atomic layers that form the device. We also report a series of cuts (perpendicular to the plane of the heterojunction) of the electronic and spin densities showing a slight magnetization of the first layers of the semiconductor. Finally, we model the device with a different scheme: using semiinfinite electrodes connected to the heterojunction. These latter calculations are based upon a nonequilibrium Green's function approach that allows us to explore the spin-resolved electronic transport under a bias voltage (spin-resolved I-V curves), revealing features of potential applicability in spintronics.
The dynamics of H absorption in and adsorption on Cu(111)
DEFF Research Database (Denmark)
Strömquist, J.; Bengtsson, L.; Persson, M.
1998-01-01
We have studied theoretically the dynamics of H adsorption on and adsorption in Cu(111) using a classical molecular dynamics approach. A key ingredient of this study is plane-wave and pseudopotential calculations of potential energy curves for the major high symmetry sites. These calculations...... by relaxation of the Cu atoms, these barriers are so low that, even in the rigid surface lattice situation, the absorption of an incident H atom is non-activated for impacts close to the so-called fcc and hep hollow sites. The model interaction potential that we have used in the dynamics calculations...... is determined from the calculated potential energy curves and its form is taken from a semi-empirical effective medium theory for binary compounds. The main results of the dynamics calculations are: the relaxations and thermal fluctuations of the Cu atom do not affect the absorption of H in the surface...
Effect of nitrogen doping of graphene oxide on hydrogen and hydroxyl adsorption
Energy Technology Data Exchange (ETDEWEB)
Min, Byeong June; Jeong, Hae Kyung [Daegu University, Kyungsan (Korea, Republic of)
2014-05-15
We investigate how nitrogen-doping affects the hydrogen (H) and the hydroxyl (OH) adsorption on graphene oxide (GO) and on nitrogen-doped GO (NGO) via pseudopotential plane wave density functional calculations within the local spin density approximation. We find that the nitrogen doping brings about drastic changes in the hydrogen and the hydroxyl adsorption energetics, but its effects depend sensitively on the nitrogen configuration in NGO. The H and the OH adsorption energies are comparable only for pyrrolic NGO. In GO and quarternary NGO, the H adsorption energy is greater than the OH adsorption energy while the trend is reversed in pyridinic NGO. Also, the OH adsorption process is less affected by nitrogen-doping than the H adsorption is.
Energy Technology Data Exchange (ETDEWEB)
Wang, Zhi [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Jiang, Xiang-Wei; Li, Shu-Shen [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Wang, Lin-Wang, E-mail: lwwang@lbl.gov [Material Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)
2014-03-24
We have presented a fully atomistic quantum mechanical simulation method on band-to-band tunneling (BTBT) field-effect transistors (FETs). Our simulation approach is based on the linear combination of bulk band method with empirical pseudopotentials, which is an atomist method beyond the effective-mass approximation or k.p perturbation method, and can be used to simulate real-size devices (∼10{sup 5} atoms) efficiently (∼5 h on a few computational cores). Using this approach, we studied the InAs dual-gate BTBT FETs. The I-V characteristics from our approach agree very well with the tight-binding non-equilibrium Green's function results, yet our method costs much less computationally. In addition, we have studied ways to increase the tunneling current and analyzed the effects of different mechanisms for that purpose.
International Nuclear Information System (INIS)
Wang, Zhi; Jiang, Xiang-Wei; Li, Shu-Shen; Wang, Lin-Wang
2014-01-01
We have presented a fully atomistic quantum mechanical simulation method on band-to-band tunneling (BTBT) field-effect transistors (FETs). Our simulation approach is based on the linear combination of bulk band method with empirical pseudopotentials, which is an atomist method beyond the effective-mass approximation or k.p perturbation method, and can be used to simulate real-size devices (∼10 5 atoms) efficiently (∼5 h on a few computational cores). Using this approach, we studied the InAs dual-gate BTBT FETs. The I-V characteristics from our approach agree very well with the tight-binding non-equilibrium Green's function results, yet our method costs much less computationally. In addition, we have studied ways to increase the tunneling current and analyzed the effects of different mechanisms for that purpose
Pair potentials in liquid metals
International Nuclear Information System (INIS)
Faber, T.E.
1980-01-01
The argument which justifies the use of a pair potential to describe the structure-dependent term in the energy of liquid metals is briefly reviewed. Because there is an additional term in the energy which depends upon volume rather than structure, and because the pair potential itself is volume-dependent, the relationship between pair potential and observable properties such as pressure, bulk modulus and pair distribution function is more complicated for liquid metals than it is for molecular liquids. Perhaps for this reason, the agreement between pair potentials inferred from observable properties and pair potentials calculated by means of pseudo-potential theory is still far from complete. The pair potential concept is applicable only to simple liquid metals, in which the electron-ion interaction is weak. No attempt is made to discuss liquid transition and rare-earth metals, which are not simple in this sense. (author)
Efficient G0W0 using localized basis sets: a benchmark for molecules
Koval, Petr; Per Ljungberg, Mathias; Sanchez-Portal, Daniel
Electronic structure calculations within Hedin's GW approximation are becoming increasingly accessible to the community. In particular, as it has been shown earlier and we confirm by calculations using our MBPT_LCAO package, the computational cost of the so-called G0W0 can be made comparable to the cost of a regular Hartree-Fock calculation. In this work, we study the performance of our new implementation of G0W0 to reproduce the ionization potentials of all 117 closed-shell molecules belonging to the G2/97 test set, using a pseudo-potential starting point provided by the popular density-functional package SIESTA. Moreover, the ionization potentials and electron affinities of a set of 24 acceptor molecules are compared to experiment and to reference all-electron calculations. PK: Guipuzcoa Fellow; PK,ML,DSP: Deutsche Forschungsgemeinschaft (SFB1083); PK,DSP: MINECO MAT2013-46593-C6-2-P.
Microscopic theory of the phonon frequencies in BCC barium
International Nuclear Information System (INIS)
Oli, B.A.
1988-09-01
The phonon dispersion frequencies are calculated from first principles for bbc barium using a resonance pseudopotential model which incorporates the effect of s-d hybridization. It was also possible using this scheme to account for the anomalous feature of the Ba dispersion curve observed experimentally in the (ξ,0,0) direction where the frequencies of the transverse branch are higher than the frequencies of the longitudinal branch. The frequencies obtained were also used to calculate the phonon density of states by the linear-analytic tetrahedra method of zone integration. The results of these calculations are qualitatively in good agreement with experimental data, and provide further support to the interpretation of the anomalous behaviour in the (ξ,0,0) direction as arising from s-d hybridization. (author). 27 refs, 4 figs, 3 tabs
International Nuclear Information System (INIS)
Bergeman, T.; Moore, M.G.; Olshanii, M.
2003-01-01
It was recently predicted [Phys. Rev. Lett. 81, 938 (1998)10.1103/PhysRevLett.81.938] that atom-atom scattering under transverse harmonic confinement is subject to a 'confinement-induced resonance' where the effective one-dimensional coupling strength diverges at a particular ratio of the confinement and scattering lengths. As the initial prediction made use of the zero-range pseudopotential approximation, we now report numerical results for finite-range interaction potentials that corroborate this resonance. In addition, we now present a physical interpretation of this effect as a novel type of Feshbach resonance in which the transverse modes of the confining potential assume the roles of 'open' and 'closed' scattering channels
Energetics of cyclohexane isomers: a density-functional study
International Nuclear Information System (INIS)
Lee, Chang Yol
1999-01-01
The binding energies and the geometric structures of conformational isomers of cyclohexane (C 6 H 12 ) are determined from the density-functional theory combined with ultrasoft pseudopotentials and gradient-corrected nonlocal exchange-correlation functionals. The ground-state chair conformation is found to have a binding energy of 99.457 eV, and the metastable twist-boat conformation has 99.161 eV. The chair conformation converts to another conformation via a half-chair conformation with an energy barrier of 0.507 eV whereas the twist-boat conformation converts to another twist-boat conformation via a boat conformation with a much smaller energy barrier of 0.015 eV
Ab initio interionic potentials for NaCl by multiple lattice inversion
International Nuclear Information System (INIS)
Zhang Shuo; Chen Nanxian
2002-01-01
Based on the Chen-Moebius lattice inversion and a series of pseudopotential total-energy curves, a different method is presented to derive the ab initio interionic pair potentials for B1-type ionic crystals. Comparing with the experimental data, the static properties of B1- and B2-type NaCl are well reproduced by the interionic potentials. Moreover, the phase stability of B1-NaCl has been described by the energy minimizations from the global deformed and disturbed states. The molecular-dynamics simulations for the molten NaCl indicate that the calculated mean-square displacements, radial distribution function, and diffusion coefficients gain good agreements with the experimental results. It can be concluded that the inversion pair potentials are valid over a wide range of interionic separations for describing the structural properties of B1-type ionic crystals
Stability and electronic structure of superlattices (IIIV)n/(IV2)n
International Nuclear Information System (INIS)
Casagrande, D.; Ferraz, A.C.
1996-01-01
Theoretical investigations of atomic relaxation and electronic states have been made for ultrathin superlattices (GaP) n /(Ge 2 ) n , (GaP) n /(Si 2 ) n , (In P) n /(Ge 2 ) n and (In P) n /(Si 2 ) n with period n ≤ 3 in growth directions (001) and (110). The calculations were performed within the momentum-space formalism of the self-consistent ab-initio pseudopotential method and the molecular dynamics approach as proposed by Car and Parrinello. The structures were found to be unstable with respect to the phase separation into the constituent bulk materials. The results for the enthalpy show a metastability as increasing the superlattice period n. The density of nonoctet wrong-bonds play an important role to determine the stability of the structures. (author). 13 refs., 2 figs., 3 tabs
Luo, Xiao-Feng; Fang, Chao; Li, Xin; Lai, Wen-Sheng; Sun, Li-Feng; Liang, Tong-Xiang
2013-06-01
The adsorption behaviors of radioactive strontium and silver nuclides on the graphite surface in a high-temperature gas-cooled reactor are studied by first-principles theory using generalized gradient approximation (GGA) and local density approximation (LDA) pseudo-potentials. It turns out that Sr prefers to be absorbed at the hollow of the carbon hexagonal cell by 0.54 eV (GGA), while Ag likes to sit right above the carbon atom with an adsorption energy of almost zero (GGA) and 0.45 eV (LDA). Electronic structure analysis reveals that Sr donates its partial electrons of the 4p and 5s states to the graphite substrate, while Ag on graphite is a physical adsorption without any electron transfer.
Structural, electronic, and magnetic properties of pristine and oxygen-adsorbed graphene nanoribbons
Energy Technology Data Exchange (ETDEWEB)
Miwa, R.H.; Veiga, R.G.A. [Instituto de Fisica, Universidade Federal de Uberlandia, Caixa Postal 593, CEP 38400-902, Uberlandia, MG (Brazil); Srivastava, G.P., E-mail: gps@excc.ex.ac.uk [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom)
2010-07-15
The structural, electronic and magnetic properties of pristine and oxygen-adsorbed (3,0) zigzag and (6,1) armchair graphene nanoribbons have been investigated theoretically, by employing the ab initio pseudopotential method within the density functional scheme. The zigzag nanoribbon is more stable with antiferromagnetically coupled edges, and is semiconducting. The armchair nanoribbon does not show any preference for magnetic ordering and is semiconducting. The oxygen molecule in its triplet state is adsorbed most stably at the edge of the zigzag nanoribbon. The Stoner metallic behaviour of the ferromagnetic nanoribbons and the Slater insulating (ground state) behaviour of the antiferromagnetic nanoribbons remain intact upon oxygen adsorption. However, the local magnetic moment of the edge carbon atom of the ferromagnetic zigzag ribbon is drastically reduced, due to the formation of a spin-paired C-O bond.
Atomic and electronic structure of clusters from car-Parrinello method
International Nuclear Information System (INIS)
Kumar, V.
1994-06-01
With the development of ab-initio molecular dynamics method, it has now become possible to study the static and dynamical properties of clusters containing up to a few tens of atoms. Here I present a review of the method within the framework of the density functional theory and pseudopotential approach to represent the electron-ion interaction and discuss some of its applications to clusters. Particular attention is focussed on the structure and bonding properties of clusters as a function of their size. Applications to clusters of alkali metals and Al, non-metal - metal transition in divalent metal clusters, molecular clusters of carbon and Sb are discussed in detail. Some results are also presented on mixed clusters. (author). 121 refs, 24 ifigs
First-principle study of the AlP/Si interfacial adhesion
Energy Technology Data Exchange (ETDEWEB)
Dai Hongshang [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, 73 Jingshi Road, Jinan 250061 (China); Du Jing [School of Science, Shandong Jianzhu University, Jinan 250101 (China); Wang Li; Peng Chuanxiao [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, 73 Jingshi Road, Jinan 250061 (China); Liu Xiangfa, E-mail: xfliu@sdu.edu.c [Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, 73 Jingshi Road, Jinan 250061 (China); Shandong Binzhou Bohai Piston Co. Ltd., Binzhou 256602, Shandong (China)
2010-01-15
AlP is heterogeneous nucleation substrate of primary Si in hypereutectic Al-Si alloys, while studies on the nucleation mechanism at atomic level are absent. The pseudopotential-based DFT calculations have been carried out to investigate the atomic and electronic structure, bonding and adhesion of the AlP/Si interface. In total, eight geometries have been investigated, in which the interfacial stacking sequence is different. The favorable interfaces can be deduced for the reason that adhesive interface energies (W{sub ad}) are different, which cannot be obtained from the traditional mismatch theory. The interfacial density of states and Mulliken population are also investigated. It is found that the main bond between AlP and Si is covalent Al-Si or P-Si bond, accompanying some ionic characteristic.
Influence of Sc doping concentration on electronic structure and optical properties of ZnO
International Nuclear Information System (INIS)
Wu Yuxi; Zhang Hao; Han Long; Qu Licheng; Gu Shulin; Li Teng
2011-01-01
In this paper, we adopt the density functional theory (DFT) plane wave pseudopotential method to study the crystal structure, electronic structure and optical property for the different concentrations of Sc doped ZnO system. We optimize the structure of Sc and get the basis of numerical simulation. The results show that with the adoption of Sc, the lattice constants of the system increase gradually, the energy of the system becomes larger, the Fermi level enters into the conduction band, the system shows Metallic gradually and the band gap becomes wider. On the other hand, certain changes of the optical properties of doped ZnO have taken place, i. e., a new absorption peak happens in ZnO absorption spectrum and the blue shift of absorption edge with the new peak occurs in the imagery part of dielectric function. (authors)
Electronic structure and optical properties of Al and Mg co-doped GaN
International Nuclear Information System (INIS)
Ji Yan-Jun; Du Yu-Jie; Wang Mei-Shan
2013-01-01
The electronic structure and optical properties of Al and Mg co-doped GaN are calculated from first principles using density function theory with the plane-wave ultrasoft pseudopotential method. The results show that the optimal form of p-type GaN is obtained with an appropriate Al:Mg co-doping ratio rather than with only Mg doping. Al doping weakens the interaction between Ga and N, resulting in the Ga 4s states moving to a high energy region and the system band gap widening. The optical properties of the co-doped system are calculated and compared with those of undoped GaN. The dielectric function of the co-doped system is anisotropic in the low energy region. The static refractive index and reflectivity increase, and absorption coefficient decreases. This provides the theoretical foundation for the design and application of Al—Mg co-doped GaN photoelectric materials
Lattice vibrations in K/sub c/Rb/sub 1-c/ alloys
International Nuclear Information System (INIS)
Kaplan, T.; Mostoller, M.; Gray, L.J.
1985-01-01
The authors have already studied this system theoretically using the mass defect coherent potential approximation (CPA) and the CPA-F. The deficiencies in the mass defect CPA and CPA-F theories have led them to apply a more sophisticated approximation which was developed by Kaplan, Leath, Gray and Diehl (KLGD). This approximation is a generalization of the CPA which is not restricted to single site averaging, but can include cluster scattering. More important, it can incorporate force constant changes without any restrictions. As a first application of KLGD, they have included nearest neighbor radial and tangential force constant changes with single site averaging. As in the previous cases, all longer range forces are included in a virtual crystal approximation. In this study they have not tried to fit the force constants. Instead they have used a pseudopotential approximation by Gruenewald and Scharnberg to determine the force constants in K-Rb alloys
Peculiarities of the momentum distribution functions of strongly correlated charged fermions
Larkin, A. S.; Filinov, V. S.; Fortov, V. E.
2018-01-01
New numerical version of the Wigner approach to quantum thermodynamics of strongly coupled systems of particles has been developed for extreme conditions, when analytical approximations based on different kinds of perturbation theories cannot be applied. An explicit analytical expression of the Wigner function has been obtained in linear and harmonic approximations. Fermi statistical effects are accounted for by effective pair pseudopotential depending on coordinates, momenta and degeneracy parameter of particles and taking into account Pauli blocking of fermions. A new quantum Monte-Carlo method for calculations of average values of arbitrary quantum operators has been developed. Calculations of the momentum distribution functions and the pair correlation functions of degenerate ideal Fermi gas have been carried out for testing the developed approach. Comparison of the obtained momentum distribution functions of strongly correlated Coulomb systems with the Maxwell-Boltzmann and the Fermi distributions shows the significant influence of interparticle interaction both at small momenta and in high energy quantum ‘tails’.
Directory of Open Access Journals (Sweden)
Gulebaglan Sinem Erden
2015-01-01
Full Text Available We performed first-principles calculations to obtain the electronic, optical, elastic, lattice-dynamical and thermodynamic properties of RbH compound with rock salt structure. The ground-state properties, i.e., the lattice constant and the band gap were investigated using a plane wave pseudopotential method within density functional theory. The calculated lattice constant, bulk modulus, energy band gap and elastic constants are reported and compared with previous theoretical and experimental results. Our calculated results and the previous results which are obtained from literature are in a good agreement. Moreover, real and imaginary parts of complex dielectric function, reflectivity spectrum, absorption, extinction coefficient and loss function as a function of photon energy and refractive index with respect to photon wavelength were calculated. In addition, temperature dependent thermodynamic properties such as Helmholtz free energy, internal energy, entropy and specific heat have been studied.
Lattice thermal conductivity of LaSe
Energy Technology Data Exchange (ETDEWEB)
Li, Wei, E-mail: tolwwt@163.com [School of Physics and Telecommunication Engineering, South China Normal University, 510006 Guangzhou (China); Pan, Zhong-liang; Chen, Jun-fang; He, Qin-yu [School of Physics and Telecommunication Engineering, South China Normal University, 510006 Guangzhou (China); Wang, Teng [School of Computer, South China Normal University, 510631 Guangzhou (China)
2015-07-15
The phonon dispersions and phonon density of states of LaSe are obtained, based on density functional perturbation theory and the norm-conserving pseudo-potential method. An anomaly in calculated phonon dispersion curves is presented and interpreted as a Kohn anomaly. The heat capacity of LaSe is calculated then. For the three-phonon process scattering, the lowest non-harmonic cubic terms of the interatomic potential are considered to obtain single-phonon relaxation rate by applying the Fermi's golden rule. For the boundary scattering, the average phonon relaxation time was obtained. Considering two kinds of phonon scattering mechanisms, we obtain the lattice thermal conductivity of LaSe.
Phonon spectra of elpasolites Cs{sub 2}NaRF{sub 6} (R=Y,Yb): Ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Chernyshev, Vladimir, E-mail: Vladimir.Chernyshev@urfu.ru; Petrov, Vladislav; Nikiforov, Anatoliy; Zakiryanov, Dmitriy [Ural Federal University, Ekaterinburg (Russian Federation)
2015-12-07
The influence of hydrostatic pressure on structure and dynamics of a crystal lattice of elpasolites Cs{sub 2}NaYbF{sub 6} and Cs{sub 2}NaYF{sub 6} (S.G. 225) within ab initio approach is investigated. Frequencies and irreducible representations (irreps) of phonon modes are determined. Elastic constants are calculated. The calculations are carried out within MO LCAO approach using DFT method with hybrid functionalities of B3LYP and PBE0 in CRYSTAL09 periodic code. For the description of rare earth ion the pseudopotential replacing internal orbitals including 4f orbitals was used. External 5s and 5p orbitals defining chemical bond were described by valence basis sets.
Energy Technology Data Exchange (ETDEWEB)
Prasad, K. Ganga; Niranjan, Manish K.; Asthana, Saket [Department of Physics, Indian Institute of Technology Hyderabad, India, 502205 (India)
2016-05-06
We report the electronic structure of the AgMO{sub 3}(M=Nb, Ta) within the frame work of density functional theory and calculations are performed within the generalized gradient approximation (GGA) by using ultrasoft pseudopotentials. The calculated equilibrium lattice parameters and volumes are extracted from fitting of Birch third order equation of state and which are reasonable agreement with the available experimental results. The density of states,band structure of Ag(Nb,Ta)O{sub 3} reveals that the valance bands mostly occupied with O-2p and O-2s states and whereas conduction band occupied with Nb (Ta) 4d(5d) states including less contribution from Ag 5s states.
Alekseeva, O. S.; Devdariani, A. Z.; Grigorian, G. M.; Lednev, M. G.; Zagrebin, A. L.
2017-02-01
This study is devoted to the theoretical investigation of the quasimolecular emission of Xe*-He and Kr*-He collision pairs near the Xe (5p 56s 1,3 P 1 - 5p 6 1 S 0) and Kr (4p 55s 1,3 P 1 - 4p 6 1 S 0) resonance atomic lines. The potential curves of the quasimolecules Xe(5p 56s) + He and Kr(4p 55s) + He have been obtained with the use of the effective Hamiltonian and pseudopotential methods. Based on these potential curves the processes of quasimolecular emission of Xe*+He and Kr*+He mixtures have been considered and the spectral distributions I(ħΔω) of photons emitted have been obtained in the framework of quasistatic approximation.
Ab initio Calculations of Electronic Fingerprints of DNA bases on Graphene
Ahmed, Towfiq; Rehr, John J.; Kilina, Svetlana; Das, Tanmoy; Haraldsen, Jason T.; Balatsky, Alexander V.
2012-02-01
We have carried out first principles DFT calculations of the electronic local density of states (LDOS) of DNA nucleotide bases (A,C,G,T) adsorbed on graphene using LDA with ultra-soft pseudo-potentials. We have also calculated the longitudinal transmission currents T(E) through graphene nano-pores as an individual DNA base passes through it, using a non-equilibrium Green's function (NEGF) formalism. We observe several dominant base-dependent features in the LDOS and T(E) in an energy range within a few eV of the Fermi level. These features can serve as electronic fingerprints for the identification of individual bases from dI/dV measurements in scanning tunneling spectroscopy (STS) and nano-pore experiments. Thus these electronic signatures can provide an alternative approach to DNA sequencing.
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)
Energy Technology Data Exchange (ETDEWEB)
Nyawere, P.W.O., E-mail: otienop98@yahoo.ca [Computational Materials Science Group, Department of Physics, University of Eldoret, P.O. Box 1125-30100 Eldoret (Kenya); Department of Computing, Kabarak University, P.O. - Private Bag - 20157 Kabarak (Kenya); The Abdus Salam International Centre for Theoretical Physics, Trieste (Italy); Makau, N.W., E-mail: wanimak@yahoo.com [Computational Materials Science Group, Department of Physics, University of Eldoret, P.O. Box 1125-30100 Eldoret (Kenya); Amolo, G.O., E-mail: georgeamolo862@gmail.com [Computational Materials Science Group, Department of Physics, University of Eldoret, P.O. Box 1125-30100 Eldoret (Kenya)
2014-02-01
All the elastic constants of cubic, orthorhombic and hexagonal phases of BaF{sub 2} have been calculated using first principles methods. We have employed density-functional theory within generalized gradient approximation (GGA) using a plane-wave pseudopotentials method and a plane-wave basis set. The calculated elastic constant values for a cubic phase compare well with recent theoretical and experimental calculations. The bulk modulus derived from the elastic constant calculations of orthorhombic phase of BaF{sub 2} is 94.5 GPa and those of hexagonal phase is 161 GPa. These values are in good agreement with experimental data available. Stability of these phases of BaF{sub 2} is also estimated in different crystallographic directions.
A dielectric matrix calculation of the surface-plasmon energy for the silicon (100) surface
International Nuclear Information System (INIS)
Forsyth, A.J.; Smith, A.E.; Josefsson, T.W.
1996-01-01
Full text: As an extension of previous work, we present preliminary calculations for the dielectric properties of the silicon (100) surface. In particular, the |q|→0 and |q|=2π/a(1,0,0) surface loss function, and corresponding surface plasmon energies have been calculated within a simple model for the silicon surface. The results have been obtained from the Adler and Wiser dielectric matrix (DM). The bandstructure used for the calculation was based on the highly successful empirical pseudopotential method of Cohen and Chelikovsky. We have used a 59 plane wave basis for the bandstructure, and have chosen a DM size of 59 x 59. Results are compared and contrasted with volume plasmon calculations, free electron calculations and experiment
Energy Technology Data Exchange (ETDEWEB)
Wei, Hai; Guo, Guang-Can; He, Lixin, E-mail: helx@ustc.edu.cn [Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei, Anhui 230026 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026 (China)
2014-11-28
We investigate the electric field tuning of the phonon-assisted hole spin relaxation in single self-assembled In{sub 1−x}Ga{sub x}As/GaAs quantum dots (QDs), using an atomistic empirical pseudopotential method. We find that the electric field along the growth direction can tune the hole spin relaxation time for more than one order of magnitude. The electric field can prolong or shorten the hole spin lifetime and the tuning shows an asymmetry in terms of the field direction. The asymmetry is more pronounced for the taller dot. The results show that the electric field is an effective way to tune the hole spin-relaxation in self-assembled QDs.
Mesoscopic electrohydrodynamic simulations of binary colloidal suspensions
Rivas, Nicolas; Frijters, Stefan; Pagonabarraga, Ignacio; Harting, Jens
2018-04-01
A model is presented for the solution of electrokinetic phenomena of colloidal suspensions in fluid mixtures. We solve the discrete Boltzmann equation with a Bhatnagar-Gross-Krook collision operator using the lattice Boltzmann method to simulate binary fluid flows. Solvent-solvent and solvent-solute interactions are implemented using a pseudopotential model. The Nernst-Planck equation, describing the kinetics of dissolved ion species, is solved using a finite difference discretization based on the link-flux method. The colloids are resolved on the lattice and coupled to the hydrodynamics and electrokinetics through appropriate boundary conditions. We present the first full integration of these three elements. The model is validated by comparing with known analytic solutions of ionic distributions at fluid interfaces, dielectric droplet deformations, and the electrophoretic mobility of colloidal suspensions. Its possibilities are explored by considering various physical systems, such as breakup of charged and neutral droplets and colloidal dynamics at either planar or spherical fluid interfaces.
Towards Scalable Entangled Photon Sources with Self-Assembled InAs /GaAs Quantum Dots
Wang, Jianping; Gong, Ming; Guo, G.-C.; He, Lixin
2015-08-01
The biexciton cascade process in self-assembled quantum dots (QDs) provides an ideal system for realizing deterministic entangled photon-pair sources, which are essential to quantum information science. The entangled photon pairs have recently been generated in experiments after eliminating the fine-structure splitting (FSS) of excitons using a number of different methods. Thus far, however, QD-based sources of entangled photons have not been scalable because the wavelengths of QDs differ from dot to dot. Here, we propose a wavelength-tunable entangled photon emitter mounted on a three-dimensional stressor, in which the FSS and exciton energy can be tuned independently, thereby enabling photon entanglement between dissimilar QDs. We confirm these results via atomistic pseudopotential calculations. This provides a first step towards future realization of scalable entangled photon generators for quantum information applications.
X-ray diffuse scattering study of height fluctuations at the liquid-vapor interface of gallium
Energy Technology Data Exchange (ETDEWEB)
Lin Binhua [CARS, University of Chicago, Chicago, IL 60637 (United States); Meron, Mati [CARS, University of Chicago, Chicago, IL 60637 (United States); Gebhardt, Jeff [CARS, University of Chicago, Chicago, IL 60637 (United States); Graber, Tim [CARS, University of Chicago, Chicago, IL 60637 (United States); Li Dongxu [Department of Chemistry and James Franck Institute, University of Chicago, Chicago, IL 60637 (United States); Yang Bin [Department of Chemistry and James Franck Institute, University of Chicago, Chicago, IL 60637 (United States); Rice, Stuart A. [Department of Chemistry and James Franck Institute, University of Chicago, Chicago, IL 60637 (United States)]. E-mail: s-rice@uchicago.edu
2005-02-28
We report an experimental study of wavelength dependent interfacial tension of liquid Ga using X-ray surface diffusion scattering. The observed surface tension can be explained by Mecke-Dietrich formalism derived from a microscopic density functional theory when the known stratified liquid-vapor interfacial density profile of Ga and a so-called individual local pseudo-potential for the pair-interaction potential of liquid metal are used. The quantitative behavior of the surface tension as a function of wavelength is very sensitive to the forms of both the interfacial density profile and the asymptotic part of the pair-potential, and is different from that observed from several dielectric liquids reported previously (Nature 403 (2000) 871; Phys. Rev. Lett. 90 (2003) 216101)
Wavelength dependence of liquid-vapor interfacial tension of Ga
International Nuclear Information System (INIS)
Li Dongxu; Yang Bin; Rice, Stuart A.; Lin Binhua; Meron, Mati; Gebhardt, Jeff; Graber, Tim
2004-01-01
The wave-vector dependence of the liquid-vapor interfacial tension of Ga, γ(q), has been determined from diffuse x-ray scattering measurements. The ratio γ(q)/γ(0)=1 for q -1 decreases to 0.5 near q=0.22 Angstrom -1 , and increases strongly for larger q. The observed form for γ(q)/γ(0) is consistent with the prediction from the Mecke-Dietrich theory when the known stratified liquid-vapor interfacial density profile of Ga and a pseudopotential based pair interaction with appropriate asymptotic (r→∞) behavior are used. The detailed behavior of γ(q)/γ(0) depends on the particular forms of both the interfacial density profile and the asymptotic falloff of the atomic pair interaction
Advanced capabilities for materials modelling with Quantum ESPRESSO
Giannozzi, P.; Andreussi, O.; Brumme, T.; Bunau, O.; Buongiorno Nardelli, M.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Cococcioni, M.; Colonna, N.; Carnimeo, I.; Dal Corso, A.; de Gironcoli, S.; Delugas, P.; DiStasio, R. A., Jr.; Ferretti, A.; Floris, A.; Fratesi, G.; Fugallo, G.; Gebauer, R.; Gerstmann, U.; Giustino, F.; Gorni, T.; Jia, J.; Kawamura, M.; Ko, H.-Y.; Kokalj, A.; Küçükbenli, E.; Lazzeri, M.; Marsili, M.; Marzari, N.; Mauri, F.; Nguyen, N. L.; Nguyen, H.-V.; Otero-de-la-Roza, A.; Paulatto, L.; Poncé, S.; Rocca, D.; Sabatini, R.; Santra, B.; Schlipf, M.; Seitsonen, A. P.; Smogunov, A.; Timrov, I.; Thonhauser, T.; Umari, P.; Vast, N.; Wu, X.; Baroni, S.
2017-11-01
Quantum EXPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches. Quantum EXPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.
Total energy calculations for structural phase transformations
International Nuclear Information System (INIS)
Ye, Y.Y.; Chan, C.T.; Ho, K.M.; Harmon, B.N.
1990-01-01
The structural integrity and physical properties of crystalline solids are frequently limited or enhanced by the occurrence of phase transformations. Martensitic transformations involve the collective displacement of atoms from one ordered state to another. Modern methods to determine the microscopic electronic changes as the atoms move are now accurate enough to evaluate the very small energy differences involved. Extensive first principles calculations for the prototypical martensitic transformation from body-centered cubic (bcc) to closepacked 9R structure in sodium metal are described. The minimum energy coordinate or configuration path between the bcc and 9R structures is determined as well as paths to other competing close-packed structures. The energy barriers and important anharmonic interactions are identified and general conclusions drawn. The calculational methods used to solve the Schrodinger equation include pseudopotentials, fast Fourier transforms, efficient matrix diagnonalization, and supercells with many atoms
Relationship between the electronic structure and the glide in the hexagonal close packed metals
International Nuclear Information System (INIS)
Legrand, B.; Le Hazif, R.
1983-06-01
In all hexagonal close-packed metals (HCP), deformation is performed by slip on a mean glide system (MGS) and on several secondary systems. There are no reliable predictions of the MGS choice. In this paper is shown the role played by the electronic structure on the choice of glide system in HCP metals. MGS is basal for all normal metals and is a function of the electron number in HCP transition metals. The different SFE's were calculated using appropriate total energy models, for different metals. Thus pseudopotentials were used (or empirical pair potentials) for normal metals, and a tight-binding model for transition metals. The most important results are the following: prismatic SFE (PSFE) is smaller than basal SFE (BSFE) for Y, Ti, Zr, Hf, Ru and Os; BSFE is smaller than PSFE for Co and all normal metals; BSFE and PSFe and about the same for RE and Tc
Ion-acoustic cnoidal waves in a quantum plasma
International Nuclear Information System (INIS)
Mahmood, S.; Haas, F.
2014-01-01
Nonlinear ion-acoustic cnoidal wave structures are studied in an unmagnetized quantum plasma. Using the reductive perturbation method, a Korteweg-de Vries equation is derived for appropriate boundary conditions and nonlinear periodic wave solutions are obtained. The corresponding analytical solution and numerical plots of the ion-acoustic cnoidal waves and solitons in the phase plane are presented using the Sagdeev pseudo-potential approach. The variations in the nonlinear potential of the ion-acoustic cnoidal waves are studied at different values of quantum parameter H e which is the ratio of electron plasmon energy to electron Fermi energy defined for degenerate electrons. It is found that both compressive and rarefactive ion-acoustic cnoidal wave structures are formed depending on the value of the quantum parameter. The dependence of the wavelength and frequency on nonlinear wave amplitude is also presented
Large amplitude ion-acoustic waves in a plasma with an electron beam
International Nuclear Information System (INIS)
Nejoh, Y.; Sanuki, H.
1995-01-01
The nonlinear wave structures of large amplitude ion-acoustic waves are studied in a plasma with an electron beam, by the pseudopotential method. The region of the existence of large amplitude ion-acoustic waves is examined, showing that the condition of the existence sensitively depends on the parameters such as the electron beam temperature, the ion temperature, the electrostatic potential, and the concentration of the electron beam density. It turns out that the region of the existence spreads as the beam temperature increases but the effect of the electron beam velocity is relatively small. New findings of large amplitude ion-acoustic waves in a plasma with an electron beam are predicted. copyright 1995 American Institute of Physics
Structural, electronic and vibrational properties of lanthanide monophosphide at high pressure
Energy Technology Data Exchange (ETDEWEB)
Panchal, J. M., E-mail: amitjignesh@yahoo.co.in [Government Engineering College, Gandhinagar382028, Gujarat (India); Department of Physics, University School of Sciences, Gujarat University, Ahmedabad 380009, Gujarat (India); Joshi, Mitesh [Government Polytechnic for Girls, Athwagate, Surat395001, Gujarat (India); Gajjar, P. N., E-mail: pngajjar@rediffmail.com [Department of Physics, University School of Sciences, Gujarat University, Ahmedabad 380009, Gujarat (India)
2016-05-06
A first-principles plane wave self-consistent method with the ultra-soft-pseudopotential scheme in the framework of the density functional theory (DFT) is performed to study structural, electronic and vibrational properties of LaP for Rock-salt (NaCl/Bl) and Cesium-chloride (CsCl/B2) phases. The instability of Rock-salt (NaCl/Bl) phases around the transition is discussed. Conclusions based on electronic energy band structure, density of state, phonon dispersion and phonon density of states in both phases are outlined. The calculated results are consistence and confirm the successful applicability of quasi-harmonic phonon theory for structural instability studies for the alloys.
Ab initio studies of magnetic anisotropy energy in highly Co-doped ZnO
Energy Technology Data Exchange (ETDEWEB)
Łusakowski, A., E-mail: lusak@ifpan.edu.pl [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, PL-02668 Warsaw (Poland); Szuszkiewicz, W. [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, PL-02668 Warsaw (Poland); Faculty of Mathematics and Natural Sciences, University of Rzeszów, ul. S. Pigonia 1, PL-35959 Rzeszów (Poland)
2017-03-15
Density functional theory (DFT) calculations of the energy of magnetic anisotropy for diluted magnetic semiconductor (Zn,Co)O were performed using OpenMX package with fully relativistic pseudopotentials. The analysis of the band spin-orbit interaction and the magnetic ion's surrounding on magnetic anisotropy have been provided. As a result, the calculations show that the magnetic anisotropy in (Zn,Co)O solid solution, mainly of the single ion anisotropy type has been caused by Co ions. - Highlights: • The magnetic anisotropy in (Zn,Co)O is mainly due to anisotropy of single cobalt ion. • The magnetic anisotropy of (Zn,Co)O strongly depends on the nearest neighborhood of magnetic ion including local lattice deformations. • For (Zn,Co)O the energy of magnetic anisotropy is described by second order terms in magnetization.
Electronic properties of liquid Hg-In alloys : Ab-initio molecular dynamics study
International Nuclear Information System (INIS)
Sharma, Nalini; Ahluwalia, P. K.; Thakur, Anil
2016-01-01
Ab-initio molecular dynamics simulations are performed to study the structural properties of liquid Hg-In alloys. The interatomic interactions are described by ab-initio pseudopotentials given by Troullier and Martins. Three liquid Hg-In alloys (Hg_1_0In_9_0, Hg_3_0In_7_0_,_. Hg_5_0In_5_0, Hg_7_0In_3_0, and Hg_9_0Pb_1_0) at 299 K are considered. The calculated results for liquid Hg (l-Hg) and lead (l-In) are also drawn. Along with the calculated results of considered five liquid alloys of Hg-In alloy. The results obtained from electronic properties namely total density of state and partial density of states help to find the local arrangement of Hg and In atoms and the presence of liquid state in the considered five alloys.
Electronic structure of GaAs with InAs (001) monolayer
International Nuclear Information System (INIS)
Tit, N.; Peressi, M.
1995-04-01
The effect on the electronic structure of an InAs monomolecular plane inserted in bulk GaAs is investigated theoretically. The (InAs) 1 (GaAs) n (001) strained superlattice is studied via ab-initio self-consistent pseudopotential calculations. Both electrons and holes are localized nearby the inserted InAs monolayer, which therefore acts as a quantum well for all the charge carriers. The small thickness of the inserted InAs slab is responsible of high confinement energies for the charge carriers, and therefore the interband electron-heavy-hole transition energy is close to the energy gap of the bulk GaAs, in agreement with recent experimental data. (author). 18 refs, 4 figs
Theoretical study of the elastic properties of titanium nitride
Institute of Scientific and Technical Information of China (English)
Jingdong CHEN; Yinglu ZHAO; Benhai YU; Chunlei WANG; Deheng SHI
2009-01-01
The equilibrium lattice parameter, relative volume V/Vo, elastic constants Cij, and bulk modulus of titanium nitride are successfully obtained using the ab initio plane-wave pseudopotential (PW-PP) method within the framework of density functional theory. The quasi-harmonic Debye model, using a set of total energy vs molar volume obtained with the PW-PP method, is applied to the study of the elastic properties and vibrational effects. We analyze the relationship between the bulk modulus and temperature up to 2000 K and obtain the relationship between bulk modulus B and pressure at different temperatures. It is found that the bulk modulus B increases monotonously with increasing pressure and decreases with increasing temperature. Moreover, the Debye temperature is determined from the non-equilibrium Gibbs func-tions.
Energy Technology Data Exchange (ETDEWEB)
Qi-Jun, Liu; Fu-Sheng, Liu, E-mail: qijunliu@home.swjtu.edu.cn [School of Physical Science and Technology, Southwest Jiaotong University, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Chengdu (China); Bond and Band Engineering Group, Sichuan Provincial Key Laboratory (for Universities) of High Pressure Science and Technology, Southwest Jiaotong University, Chengdu (China); Zheng-Tang, Liu [State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi' an, (China)
2015-08-15
Structural, elastic, mechanical, and electronic properties of monoclinic N{sub 2}H{sub 5}N{sub 3} at zero and high pressure have been investigated using the plane-wave ultrasoft pseudopotential method within the density-functional theory (DFT). The pressure dependences of structural parameters, elastic constants, mechanical properties, band gaps, and density of states of monoclinic N{sub 2}H{sub 5}N{sub 3} have been calculated and discussed. The obtained results show that monoclinic N{sub 2}H{sub 5}N{sub 3} is unstable at pressures exceeding the value 126.1 GPa. The ratio of B/G and the Cauchy’s pressure indicate that monoclinic N{sub 2}H{sub 5}N{sub 3} behaves in ductile nature with pressure ranging from 0 to 200 GPa. (author)
International Nuclear Information System (INIS)
Song, T.; Ma, Q.; Sun, X.W.; Liu, Z.J.; Fu, Z.J.; Wei, X.P.; Wang, T.; Tian, J.H.
2016-01-01
The phase transition, electronic band structure, and equation of state (EOS) of cubic TcN are investigated by first-principles pseudopotential method based on density-functional theory. The calculated enthalpies show that TcN has a transformation between zincblende and rocksalt phases and the pressure determined by the relative enthalpy is 32 GPa. The calculated band structure indicates the metallic feature and it might make cubic TcN a better candidate for hard materials. Particular attention is paid to the predictions of volume, bulk modulus and its pressure derivative which play a central role in the formulation of approximate EOSs using the quasi-harmonic Debye model. - Highlights: • The phase transition pressure and electronic band structure for cubic TcN are determined. • Particular attention is paid to investigate the equation of state parameters for cubic TcN. • The thermodynamic properties up to 80 GPa and 3000 K are successfully predicted.
Bonding and compressibility in molecular and polymeric phases of solid CO2
International Nuclear Information System (INIS)
Gracia, L; Marques, M; Beltran, A; Pendas, A Martin; Recio, J M
2004-01-01
We present the results of a theoretical study of the response of molecular CO 2 -I and CO 2 -III, and polymeric CO 2 -V polymorphs to hydrostatic pressure. Total energy calculations and geometry optimizations have been performed under the local density functional approximation combining a pseudopotential and planewave scheme as implemented in the VASP code. Using the atoms in molecules theory, the network of inter- and intra-molecular chemical bonds of the different phases are rigorously characterized in terms of the values of the electron density and the Laplacian at the bond critical points. The chemical graph of a hypothetical orthorhombic structure displays bonding features that are associated with a precursor geometry of polymeric carbon four-fold coordinated phases. In addition, the bulk compressibility is decomposed into atomic and molecular contributions with the aim of providing a better understanding of the reasons that explain the emergence of low compressible polymorphs at high pressures
Metastable He (n=2) - Ne potential interaction calculation
International Nuclear Information System (INIS)
Rahal, H.
1983-10-01
Diabatic potential terms corresponding to He (2 1 S)-Ne and He (2 3 S)-Ne interactions are calculated. These potentials reproduce the experimental results thermal metastable atom elastic scattering on Ne target. A model which reduces the interaction to a one-electron problem is proposed: the He excited electron. Its interaction with the He + center is reproduced by a ''l'' dependent potential model with a 1/2 behaviour at short range. The electron interaction facing the Ne is described by a l-dependent pseudopotential reproducing with accuracy the electron elastic scattering on a Ne atom. The importance of the corrective term related to the Ne polarizations by the electron and the He + ion is showed in this work. In the modelling problems, the accuracy cannot be better than 0.1 MeV [fr
Theory of Defects in Semiconductors
Drabold, David A
2007-01-01
Semiconductor science and technology is the art of defect engineering. The theoretical modeling of defects has improved dramatically over the past decade. These tools are now applied to a wide range of materials issues: quantum dots, buckyballs, spintronics, interfaces, amorphous systems, and many others. This volume presents a coherent and detailed description of the field, and brings together leaders in theoretical research. Today's state-of-the-art, as well as tomorrow’s tools, are discussed: the supercell-pseudopotential method, the GW formalism,Quantum Monte Carlo, learn-on-the-fly molecular dynamics, finite-temperature treatments, etc. A wealth of applications are included, from point defects to wafer bonding or the propagation of dislocation.
Inamdar, Shaukatali N; Ingole, Pravin P; Haram, Santosh K
2008-12-01
Band structure parameters such as the conduction band edge, the valence band edge and the quasi-particle gap of diffusing CdSe quantum dots (Q-dots) of various sizes were determined using cyclic voltammetry. These parameters are strongly dependent on the size of the Q-dots. The results obtained from voltammetric measurements are compared to spectroscopic and theoretical data. The fit obtained to the reported calculations based on the semi-empirical pseudopotential method (SEPM)-especially in the strong size-confinement region, is the best reported so far, according to our knowledge. For the smallest CdSe Q-dots, the difference between the quasi-particle gap and the optical band gap gives the electron-hole Coulombic interaction energy (J(e1,h1)). Interband states seen in the photoluminescence spectra were verified with cyclic voltammetry measurements.
Energy gaps, valence and conduction charge densities and optical properties of GaAs1‑xPx
Al-Hagan, O. A.; Algarni, H.; Bouarissa, N.; Alhuwaymel, T. F.; Ajmal Khan, M.
2018-04-01
The electronic structure and its derived valence and conduction charge distributions along with the optical properties of zinc-blende GaAs1‑xPx ternary alloys have been studied. The calculations are performed using a pseudopotential approach under the virtual crystal approximation (VCA) which takes into account the compositional disorder effect. Our findings are found to be generally in good accord with experiment. The composition dependence of direct and indirect bandgaps showed a clear bandgap bowing. The nature of the gap is found to depend on phosphorous content. The bonding and ionicity of the material of interest have been examined in terms of the anti-symmetric gap and charge densities. The variation in the optical constants versus phosphorous concentration has been discussed. The present investigation may give a useful applications in infrared and visible spectrum light emitters.
On the neutron diffraction in a crystal in the field of a standing laser wave
International Nuclear Information System (INIS)
Grigoryan, K.K.; Hayrapetyan, A.G.; Petrosyan, R.G.
2010-01-01
The possibility of high-energy neutron diffraction in a crystal is shown by applying the solution of time-dependent Schroedinger equation for a neutron in the field of a standing laser wave. The scattering picture is examined within the framework of non-stationary S-matrix theory, where the neutron-laser field interaction is considered exactly and the neutron-crystal interaction is considered as a perturbation described by Fermi pseudopotential (Farri representation). The neutron-crystal interaction is elastic, and the neutron-laser field interaction has both inelastic and elastic behaviors which results in the observation of an analogous to the Kapitza-Dirac effect for neutrons. The neutron scattering probability is calculated and the analysis of the results are adduced. Both inelastic and elastic diffraction conditions are obtained and the formation of a 'sublattice' is illustrated in the process of neutron-photon-phonon elastic interaction.
International Nuclear Information System (INIS)
Grosso, G.
1986-01-01
The aim of this chapter is to present, in detail, some theoretical methods used to calculate electronic band structures in crystals. The basic strategies employed to attack the problem of electronic-structure calculations are presented. Successive sections present the basic formulations of the tight-binding, orthogonalized-plane-wave, Green'sfunction, and pseudopotential methods with a discussion of their application to perfect solids. Exemplifications in the case of a few selected problems provide further insight by the author into the physical aspects of the different methods and are a guide to the use of their mathematical techniques. A discussion is offered of completely a priori Hartree-Fock calculations and attempts to extend them. Special aspects of the different methods are also discussed in light of recently published related work
International Nuclear Information System (INIS)
Qiu Feng; Shen Ping; Liu Tao; Lin Qiaoli; Jiang Qichuan
2010-01-01
Martensitic transformation, phase stability and electronic structure of Al-doped ZrCu intermetallics were investigated by experiments and first-principles calculations using the pseudopotentials plane wave method. The formation energy calculations indicate that the stability of the ZrCu phase increases with the increasing Al content. Al plays a decisive role in controlling the formation and microstructures of the martensite phases in Zr-Cu-Al alloys. The total energy difference between ZrCu (B2) austenite and ZrCu martensite plays an important role in the martensitic transformation. The phase stability is dependent on its electronic structure. The densities of states (DOS) of the intermetallics were discussed in detail.
International Nuclear Information System (INIS)
Ramos, L E; Degoli, Elena; Cantele, G; Ossicini, Stefano; Ninno, D; Furthmueller, J; Bechstedt, F
2007-01-01
We investigate the incorporation of group-III (B and Al), group-IV (C and Ge), and group-V (N and P) impurities in Si nanocrystallites. The structural features and electronic properties of doped Si nanocrystallites, which are faceted or spherical-like, are studied by means of an ab initio pseudopotential method including spin polarization. Jahn-Teller distortions occur in the neighborhood of the impurity sites and the bond lengths show a dependence on size and shape of the nanocrystallites. We find that the acceptor (group-III) and donor (group-V) levels become deep as the nanocrystallites become small. The energy difference between the spin-up and spin-down levels of group-III and group-V impurities decreases as the size of the Si nanocrystallite increases and tends to the value calculated for Si bulk. Doping with carbon introduces an impurity-related level in the energy gap of the Si nanocrystallites
International Nuclear Information System (INIS)
Chakraborty, Sudip; Rajesh, Ch.
2012-01-01
We have reported a first-principle investigation of the structural properties of monomer and dimer for group IV elements (C, Si, Ge, and Sn) adsorbed on the Au(111) and Ag(111) surfaces. The calculations were performed by means of a plane wave based pseudopotential method under the framework of density functional theory. The results reveal the preference of adatom to be adsorbed on the hexagonal closed packed site of the metal (111) surfaces with strong binding energy. The structures introduce interlayer forces in the adsorbate. The strong bonding with the surface atoms is a result of p–d hybridization. The adsorption energy follows a sequence as one goes down in the group IV elements which imply that the interaction of the group IV elements with Au/Ag is decreasing as the atomic number increases.
Electron-phonon interaction on an Al(001) surface
International Nuclear Information System (INIS)
Sklyadneva, I Yu; Chulkov, E V; Echenique, P M
2008-01-01
We report an ab initio study of the electron-phonon (e-ph) interaction and its contribution to the lifetime broadening of excited hole (electron) surface states on Al(001). The calculations based on density-functional theory were carried out using a linear response approach in the plane-wave pseudopotential representation. The obtained results show that both the electron-phonon coupling and the linewidth experience a weak variation with the energy and momentum position of a hole (electron) surface state in the energy band. An analysis of different contributions to the e-ph coupling reveals that bulk phonon modes turn out to be more involved in the scattering processes of excited electrons and holes than surface phonon modes. It is also shown that the role of the e-ph coupling in the broadening of the Rayleigh surface phonon mode is insignificant compared to anharmonic effects
Bond charge approximation for valence electron density in elemental semiconductors
International Nuclear Information System (INIS)
Bashenov, V.K.; Gorbachov, V.E.; Marvakov, D.I.
1985-07-01
The spatial valence electron distribution in silicon and diamond is calculated in adiabatic bond charge approximation at zero temperature when bond charges have the Gaussian shape and their tensor character is taken into account. An agreement between theory and experiment has been achieved. For this purpose Xia's ionic pseudopotentials and Schulze-Unger's dielectric function are used. By two additional parameters Asub(B) and Zsub(B)sup(') we describe the spatial extent of the bond charge and local-field corrections, respectively. The parameter Zsub(B)sup(') accounts for the ratio between the Coulomb and exchange correlation interactions of the valence electrons and its silicon and diamond values have different signs. (author)
Strained interface defects in silicon nanocrystals
Energy Technology Data Exchange (ETDEWEB)
Lee, Benjamin G.; Stradins, Paul [National Center for Photovoltaics, National Renewable Energy Laboratory, Golden, CO (United States); Hiller, Daniel; Zacharias, Margit [IMTEK - Faculty of Engineering, Albert-Ludwigs-University Freiburg (Germany); Luo, Jun-Wei; Beard, Matthew C. [Chemical and Materials Science, National Renewable Energy Laboratory, Golden, CO (United States); Semonin, Octavi E. [Chemical and Materials Science, National Renewable Energy Laboratory, Golden, CO (United States); Department of Physics, University of Colorado, Boulder, CO (United States)
2012-08-07
The surface of silicon nanocrystals embedded in an oxide matrix can contain numerous interface defects. These defects strongly affect the nanocrystals' photoluminescence efficiency and optical absorption. Dangling-bond defects are nearly eliminated by H{sub 2} passivation, thus decreasing absorption below the quantum-confined bandgap and enhancing PL efficiency by an order of magnitude. However, there remain numerous other defects seen in absorption by photothermal deflection spectroscopy; these defects cause non-radiative recombination that limits the PL efficiency to <15%. Using atomistic pseudopotential simulations, we attribute these defects to two specific types of distorted bonds: Si-Si and bridging Si-O-Si bonds between two Si atoms at the nanocrystal surface. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
International Nuclear Information System (INIS)
Zhou, M.; Andrews, L.
1999-01-01
Laser ablation produces metal atoms, cations, and electrons for reaction with CO during condensation in excess neon at 4 K. Infrared spectra are observed for the metal carbonyls, cations, and anions, which are identified from isotopic shifts ( 13 CO, C 18 O) and splittings using mixed isotopic precursors. Density functional calculations with pseudopotentials for Rh and Ir predict the observed carbonyl stretching frequencies within 1--2%. This characterization of the simple RhCO + , RhCO, and RhCO - (and Ir) species over a 350 cm -1 range provides a scale for comparison of larger catalytically active Rh and Ir carbonyl complexes in solution and on surfaces to estimate charge on the metal center. This work provides the first spectroscopic characterization of Rh and Ir carbonyl cations and anions except for the stable tetracarbonyl anions in solution
Lattice mechanical properties of some fcc f-shell metals
International Nuclear Information System (INIS)
Baria, J.K.; Jani, A.R.
2003-01-01
A pseudopotential depending on an effective core radius is proposed to study the binding energy, equation of state, ion-ion interaction, phonon dispersion curves (q-space and r-space analysis), mode Grueneisen parameters and dynamical elastic constants of some fcc f-shell metals La, Yb, Ce and Th. The contribution of the s-like electrons is calculated in the second-order perturbation theory for the potential while d- and f-like electron is taken into account by introducing repulsive short-range Born-Mayer term. The parameter of the potential is evaluated by zero pressure condition. An excellent agreement between theoretical investigations and experimental findings is achieved which confirms the present formalism. (author)
Thermal properties of UO2 from density functional theory: role of strong correlations
International Nuclear Information System (INIS)
Panigrahi, Puspamitra; Kaur Gurpreet; Valsakumar, M.C.
2011-01-01
We report a study of ground state magnetic structure of Uranium-dioxide (UO 2 ) using ab initio calculations employing PAW pseudopotentials and Dudarev's version of GGA+U formalism as implemented in VASP to take into account the strong on-site Coulomb correlation among the localized Uranium-5f electrons. By choosing the value of the Hubbard parameter U eff to be 4.0 eV, we have confirmed the experimental observation that the ground state of UO 2 is an insulator with an anti-ferromagnetic (AFM) ordering. We study systematically the ground state structural, electronic, and magnetic properties of UO 2 and focus on the structure sensitive thermal properties such as specific heat, thermal expansion and comment on the calculation of thermal conductivity. (author)
Nonlinear eigen-mode structures in complex astroclouds
International Nuclear Information System (INIS)
Karmakar, P K; Haloi, A
2017-01-01
The evolutionary dynamics of strongly nonlinear waves (of arbitrary amplitude) in an inhomogeneous complex astrophysical viscous cloud is investigated without recourse to any kind of swindle. It consists of warm lighter electrons and ions (Boltzmanian); and cold massive bi-polar dust grains (inertial fluids) alongside vigorous neutral dynamics in quasi-neural hydrodynamic equilibrium. Application of the Sagdeev pseudo-potential method transforms the analytic model into a conjugated pair of intermixed non-integrable energy integral laws. A natural excitation of electrostatic quasi-monotonic compressive dispersive shock-like eigen-modes is numerically demonstrated. In contrast, the self-gravitational waves grow purely as non-monotonic compressive oscillatory shock-like structures. The unique features of both the distinct classes are depicted. Their non-trivial significance in the astro-context is emphasized. (paper)
Nonlinear eigen-mode structures in complex astroclouds
Karmakar, P. K.; Haloi, A.
2017-05-01
The evolutionary dynamics of strongly nonlinear waves (of arbitrary amplitude) in an inhomogeneous complex astrophysical viscous cloud is investigated without recourse to any kind of swindle. It consists of warm lighter electrons and ions (Boltzmanian); and cold massive bi-polar dust grains (inertial fluids) alongside vigorous neutral dynamics in quasi-neural hydrodynamic equilibrium. Application of the Sagdeev pseudo-potential method transforms the analytic model into a conjugated pair of intermixed non-integrable energy integral laws. A natural excitation of electrostatic quasi-monotonic compressive dispersive shock-like eigen-modes is numerically demonstrated. In contrast, the self-gravitational waves grow purely as non-monotonic compressive oscillatory shock-like structures. The unique features of both the distinct classes are depicted. Their non-trivial significance in the astro-context is emphasized.
International Nuclear Information System (INIS)
Juo, J.W.; Franceschetti, A.; Zunger, A.
2009-01-01
Excitons in quantum dots manifest a lower-energy spin-forbidden 'dark' state below a spin-allowed 'bright' state; this splitting originates from electron-hole (e-h) exchange interactions, which are strongly enhanced by quantum confinement. The e-h exchange interaction may have both a short-range and a long-range component. Calculating numerically the e-h exchange energies from atomistic pseudopotential wave functions, we show here that in direct-gap quantum dots (such as InAs) the e-h exchange interaction is dominated by the long-range component, whereas in indirect-gap quantum dots (such as Si) only the short-range component survives. As a result, the exciton dark/bright splitting scales as 1/R 2 in InAs dots and 1/R 3 in Si dots, where R is the quantum-dot radius.
Search for basic properties of the nucleon-nucleon interaction
International Nuclear Information System (INIS)
Gersten, A.
1981-01-01
Extraction of N-N amplitudes directly from phase-shift analysis is described and the results are compared to those obtained via potential or pseudopotential models at low and intermediate energies and through Regge trajectory exchanges and diffraction models at high energies. While potential models fit the experimental data up to about 400 MeV lab energy, the information obtained directly by phase-shift analysis of N-N amplitudes is obtained from experiments in the 400-800 MeV range. At higher energies the real part of the amplitudes becomes better approximated by the first Born term. In this way one can get an insight into the meson exchange structure of the N-N amplitudes. (O.T.)
Electro-acoustic solitary waves in dusty plasmas
International Nuclear Information System (INIS)
Mamun, A.A.; Sayed, F.
2005-10-01
present a rigorous theoretical investigation of electro- acoustic [particularly, dust-ion acoustic (DIA) and dust-acoustic (DA)] solitary waves in dusty plasmas. We employ the reductive perturbation method for small but finite amplitude solitary waves as well as the pseudo-potential approach for arbitrary amplitude ones. We also analyze the effects of non-planar geometry and dust charge fluctuations on both DIA and DA solitary waves, the effect of finite ion-temperature on DIA solitary waves, and the effects of dust-fluid temperature and non-isothermal ion distributions on DA solitary waves. It has been reported that these effects do not only significantly modify the basic features of DIA or DA solitary waves, but also introduce some important new features. The basic features and the underlying physics of DIA and DA solitary waves, which are relevant to space and laboratory dusty plasmas, are briefly discussed. (author)
Arbitrary amplitude dust-acoustic solitary structures in a three-component dusty plasma
International Nuclear Information System (INIS)
Mamun, A.A.
1999-07-01
A rigorous theoretical investigation has been made of arbitrary amplitude dust-acoustic solitary structures in an unmagnetized three-component dusty plasma whose constituents are an inertial charged dust fluid and Boltzmann distributed ions and electrons. The pseudo-potential approach and the reductive perturbation technique are employed for this study. It is found from both weakly and highly nonlinear analyses that the dusty plasma model can support solitary waves only with negative potential but not with positive potential. The effects of equilibrium free electron density and its temperature on these solitary structures are discussed. The implications of these results to some astrophysical and space plasma systems, especially to planetary ring-systems and cometary tails, are briefly mentioned. (author)
Second-order phase transition at high-pressure in GeS crystal
Energy Technology Data Exchange (ETDEWEB)
Hashimzade, F.M.; Huseinova, D.A.; Jahangirli, Z.A.; Mehdiyev, B.H., E-mail: bachschi@yahoo.de
2014-12-01
In this paper we give a theoretical proof of the existence of a second-order structural phase transition in the GeS at a pressure of 35.4 GPa. We use the plane-wave pseudopotential approach to the density functional theory in the local density approximation. The evidence of the phase transition is the abrupt change in the bulk modulus as the volume of the unit cell of the crystal changes continuously. We show that the phase transition is caused by the softening of the low-frequency fully symmetric interlayer mode with increasing pressure. As a result, phase transition of a displacement type takes place with the change of translational symmetry of the crystal from the simple orthorhombic to the base-centered orthorhombic (P{sub bnm}(D{sub 2h}{sup 16})→C{sub mcm}(D{sub 2h}{sup 17}))
The Theory of High Energy Collision Processes - Final Report DOE/ER/40158-1
Energy Technology Data Exchange (ETDEWEB)
Wu, Tai, T.
2011-09-15
In 1984, DOE awarded Harvard University a new Grant DE-FG02-84ER40158 to continue their support of Tai Tsun Wu as Principal Investigator of research on the theory of high energy collision processes. This Grant was renewed and remained active continuously from June 1, 1984 through November 30, 2007. Topics of interest during the 23-year duration of this Grant include: the theory and phenomenology of collision and production processes at ever higher energies; helicity methods of QED and QCD; neutrino oscillations and masses; Yang-Mills gauge theory; Beamstrahlung; Fermi pseudopotentials; magnetic monopoles and dyons; cosmology; classical confinement; mass relations; Bose-Einstein condensation; and large-momentum-transfer scattering processes. This Final Report describes the research carried out on Grant DE-FG02-84ER40158 for the period June 1, 1984 through November 30, 2007. Two books resulted from this project and a total of 125 publications.
Magnetism at the V/Gd interface
International Nuclear Information System (INIS)
Mouketo, L; M'Passi-Mabiala, B; Binggeli, N
2010-01-01
Recent experimental investigations into the magnetic properties of V/Gd bilayers have shown that vanadium, which is nonmagnetic in the bulk, can acquire a magnetic moment in such systems. We have performed ab initio pseudopotential calculations to examine the magnetic behavior of V(110)/Gd(0001) bilayers for V layers with thicknesses up to 4 monolayers (ML). We considered both abrupt and atomic intermixed V/Gd interfaces. In both cases, the magnetic moment of the V layer is found to align antiparallel to the moment of the Gd layer, consistent with the experimental observation. However, the magnitude of the V moment at the abrupt interface is considerably smaller than the moments reported experimentally. In the presence of atomic intermixing, instead, substantially larger V moments are found, closer to the experimentally reported moments. On the basis of the calculated atomic and spin resolved density of states, we discuss the possible mechanism responsible for the observed Gd-V antiferromagnetic coupling.
Dielectric and vibrational properties of amino acids
Tulip, P. R.; Clark, S. J.
2004-09-01
We calculate polarizability tensors and normal mode frequencies for the amino acids alanine, leucine, isoleucine, and valine using density functional perturbation theory implemented within the plane wave pseudopotential framework. It is found that the behavior of the electron density under external fields depends to a large extent on the geometrical structure of the molecule in question, rather than simply on the constituent functional groups. The normal modes are able to help distinguish between the different types of intramolecular hydrogen bonding present, and help to explain why leucine is found in the zwitterionic form for the gaseous phase. Calculated IR spectra show a marked difference between those obtained for zwitterionic and nonzwitterionic molecules. These differences can be attributed to the different chemical and hydrogen bonds present. Effective dynamical charges are calculated, and compared to atomic charges obtained from Mulliken population analysis. It is found that disagreement exists, largely due to the differing origins of these quantities.
International Nuclear Information System (INIS)
Kahlert, H.; Boysen, H.; Frey, F.
1998-01-01
In situ neutron powder investigations of cubic stabilized zirconia [Zr 0.85 Ca 0.15 O 1.85 (CSZ15)] sinter material were performed at room temperature without an applied direct-current electric field and at 1100 K with and without an applied field, i.e. lasting ionic current. Experimental conditions (temperature, oxidizing atmosphere etc.) were chosen as close as possible to 'working conditions' of zirconia oxygen sensoric devices. To learn about field-induced structural changes and most probable ionic pathways, atomic displacement parameters were derived in the frame of a non-Gaussian Debye-Waller factor formalism for the oxygens. Probability-density-function maps and pseudo-potential (V eff ) maps indicate curved diffusion pathways of the oxygens close to the left angle 100 right angle directions. The action of the applied field is to lower the effective potential barriers. (orig.)
Relativistic effects on large amplitude nonlinear Langmuir waves in a two-fluid plasma
International Nuclear Information System (INIS)
Nejoh, Yasunori
1994-07-01
Large amplitude relativistic nonlinear Langmuir waves are analyzed by the pseudo-potential method. The existence conditions for nonlinear Langmuir waves are confirmed by considering relativistic high-speed electrons in a two-fluid plasma. The significant feature of this investigation is that the propagation of nonlinear Langmuir waves depends on the ratio of the electron streaming velocity to the velocity of light, the normalized potential and the ion mass to electron mass ratio. The constant energy is determined by the specific range of the relativistic effect. In the non-relativistic limit, large amplitude relativistic Langmuir waves do not exist. The present investigation predicts new findings of large amplitude nonlinear Langmuir waves in space plasma phenomena in which relativistic electrons are important. (author)
Attractive short-range interatomic potential in the lattice dynamics of niobium and tantalum
International Nuclear Information System (INIS)
Onwuagba, B.N.; Pal, S.
1987-01-01
It is shown in the framework of the pseudopotential approach that there is a sizable attractive short-range component of the interatomic potential due to the s-d interaction which has the same functional form in real space as the Born-Mayer repulsion due to the overlap of core electron wave functions centred on neighbouring ions. The magnitude of this attractive component is such as to completely cancel the conventional Born-Mayer repulsion, making the resultant short-range interatomic potential attractive rather than repulsive. Numerical calculations show that the attractive interatomics potential, which represents the local-field correction, leads to a better understanding of the occurrence of the soft modes in the phonon dispersion curves of niobium and tantalum
Empirical tight-binding parameters for solid C60
International Nuclear Information System (INIS)
Tit, N.; Kumar, V.
1993-01-01
We present a tight-binding model for the electronic structure of C 60 using four (1s and 3p) orbitals per carbon atom. The model has been developed by fitting the tight-binding parameters to the ab-initio pseudopotential calculation of Troullier and Martins (Phys. Rev. B46, 1754 (1992)) in the face-centered cubic (Fm3-bar) phase. Following this, calculations of the energy bands and the density of electronic states have been carried out as a function of the lattice constant. Good agreement has been obtained with the observed lattice-constant dependence of T c using McMillan's formula. Furthermore, calculations of the electronic structure are presented in the simple cubic (Pa3-bar) phase. (author). 43 refs, 3 figs, 1 tab
Intermetallic bonds and midgap interface states at epitaxial Al/GaAs(001) junctions
International Nuclear Information System (INIS)
Maxisch, T.; Baldereschi, A.; Binggeli, N.
2003-03-01
Using first-principles pseudopotential calculations, we have investigated the nature of the electronic states with energies within the semiconductor bandgap of abrupt, defect-free As-terminated Al/GaAs(001) junctions. While bonding-/antibonding-like semiconductor evanescent states occur near the valence-/conduction-band edges, the semiconductor midgap region is characterized by a new type of electronic states, not accounted for by commonly accepted models. These states, which correspond to intermetallic bonds between the outermost Ga cations of the semiconductor and Al atoms of the metal, occur near the Fermi energy. They are localized at the interface and are located around the J-point of the Brillouin zone. These new interface states derive from an interaction between localized states of the Al(001) surface and bulk GaAs conduction band states, mediated by localized states of the unreconstructed As-terminated GaAs(001) surface. (author)
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
Debye temperature, thermal expansion, and heat capacity of TcC up to 100 GPa
Energy Technology Data Exchange (ETDEWEB)
Song, T., E-mail: songting@mail.lzjtu.cn [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); School of Material Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 (China); Ma, Q. [School of Material Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 (China); Tian, J.H. [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Liu, X.B. [School of Physics and Information Science, Tianshui Normal University, Tianshui 741000 (China); Ouyang, Y.H.; Zhang, C.L.; Su, W.F. [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China)
2015-01-15
Highlights: • A number of thermodynamic properties of rocksalt TcC are investigated for the first time. • The quasi-harmonic Debye model is applied to take into account the thermal effect. • The pressure and temperature up to about 100 GPa and 3000 K, respectively. - Abstract: Debye temperature, thermal expansion coefficient, and heat capacity of ideal stoichiometric TcC in the rocksalt structure have been studied systematically by using ab initio plane-wave pseudopotential density functional theory method within the generalized gradient approximation. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of Debye temperature, thermal expansion coefficient, constant-volume heat capacity, and constant-pressure heat capacity on pressure and temperature are successfully predicted. All the thermodynamic properties of TcC with rocksalt phase have been predicted in the entire temperature range from 300 to 3000 K and pressure up to 100 GPa.
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 study of the effects of segregated Ga on an Al grain boundary
International Nuclear Information System (INIS)
Zhang Ying; Lu Guanghong; Wang Tianmin; Deng Shenghua; Shu Xiaolin; Kohyama, Masanori; Yamamoto, Ryoichi
2006-01-01
The effects of different amounts of segregated Ga (substitutional) on an Al grain boundary have been investigated by using a first-principles pseudopotential method. The segregated Ga is found to draw charge from the surrounding Al due to the electronegativity difference between Ga and Al, leading to a charge density reduction between Ga and Al as well as along the Al grain boundary. Such an effect can be enhanced by increasing the Ga segregation amount. With further Ga segregated, in addition to the charge-drawing effect that occurs in the Al-Ga interface, a heterogeneous α-Ga-like phase can form in the grain boundary, which greatly alters the boundary structure. These effects are suggested to be responsible for Ga-induced Al intergranular embrittlement
Fast plane wave density functional theory molecular dynamics calculations on multi-GPU machines
International Nuclear Information System (INIS)
Jia, Weile; Fu, Jiyun; Cao, Zongyan; Wang, Long; Chi, Xuebin; Gao, Weiguo; Wang, Lin-Wang
2013-01-01
Plane wave pseudopotential (PWP) density functional theory (DFT) calculation is the most widely used method for material simulations, but its absolute speed stagnated due to the inability to use large scale CPU based computers. By a drastic redesign of the algorithm, and moving all the major computation parts into GPU, we have reached a speed of 12 s per molecular dynamics (MD) step for a 512 atom system using 256 GPU cards. This is about 20 times faster than the CPU version of the code regardless of the number of CPU cores used. Our tests and analysis on different GPU platforms and configurations shed lights on the optimal GPU deployments for PWP-DFT calculations. An 1800 step MD simulation is used to study the liquid phase properties of GaInP
Determination of Surface Properties of Liquid Transition Metals
International Nuclear Information System (INIS)
Korkmaz, S. D.
2008-01-01
Certain surface properties of liquid simple metals are reported. Using the expression derived by Gosh and coworkers we investigated the surface entropy of liquid transition metals namely Fe, Co and Ni. We have also computed surface tensions of the metals concerned. The pair distribution functions are calculated from the solution of Ornstein-Zernike integral equation with Rogers-Young closure using the individual version of the electron-ion potential proposed by Fioalhais and coworkers which was originally developed for solid state. The predicted values of surface tension and surface entropy are in very good agreement with available experimental data. The present study results show that the expression derived by Gosh and coworkers is very useful for the surface entropy by using Fioalhais pseudopotential and Rogers-Young closure
Ab-initio calculation of ZnGeAs{sub 2} semiconductor
Energy Technology Data Exchange (ETDEWEB)
Tripathy, S. K., E-mail: susanta96@gmail.com; Kumar, V., E-mail: susanta96@gmail.com [Department of Electronics Engineering, Indian School of Mines, Dhanbad 826004 (India)
2014-04-24
The structural, electronic, optical and elastic properties of ZnGeAs{sub 2} semiconductor have been investigated using pseudopotential plane wave method within the density functional theory (DFT). The optimized lattice constants, energy gap and crystal field splitting parameter are calculated. The optical properties such as dielectric function, optical reflectivity,, extinction coefficient, absorption spectra, refractive index and electron energy loss spectrum have been studied. The values of bulk modulus (B), elastic constants (C{sub ij}), Young’s modulus (Y), Zener anisotropic factor (A), Poisson’s ratio (ν) and Debye temperature (Θ{sub D}) have been calculated. The calculated values of all these parameters are compared with the available experimental values and the values reported by different workers. A fairly good agreement has been found between them.
Energy Technology Data Exchange (ETDEWEB)
Juillet, O.; Gulminelli, F. [Caen Univ., Lab. de Physique Corpusculaire (LPC/ENSICAEN), 14 (France); Chomaz, Ph. [Grand Accelerateur National d' Ions Lourds (GANIL), 14 - Caen (France)
2003-11-01
The canonical thermodynamic properties of a one-dimensional system of interacting spin-1/2 fermions with an attractive zero-range pseudo-potential are investigated within an exact approach. The density operator is evaluated as the statistical average of dyadics formed from a stochastic mean-field propagation of independent Slater determinants. For an harmonically trapped Fermi gas and for fermions confined in a 1D-like torus, we observe the transition to a quasi-BCS state with Cooper-like momentum correlations and an algebraic long-range order. For few trapped fermions in a rotating torus, a dominant superfluid component with quantized circulation can be isolated. (author)
Mokhtari, Ali; Alidoosti, Mohammad
2014-11-01
In the present work, we have performed first principles calculations to study the structural and electronic properties of the MgFBrxCl1-x quaternary alloys using the pseudo-potential plane wave approach within the framework of density functional theory. By using the optimized initial parameters, we have obtained the physical quantities such as equilibrium lattice constants a and c, cohesive energy and band gap and then fitted the results by a quadratic expression for all x compositions. The results of bulk modulus exhibit nearly linear concentration dependence (LCD) but other quantities show nonlinear dependence. Finally, we have calculated the total and angular momentum decomposed (partial) density of states and determined the contributions of different orbitals of each atoms.
Temperature dependent structural and vibrational properties of liquid indium
Patel, A. B.; Bhatt, N. K.
2018-05-01
The influence of the temperature effect on both the structure factor and the phonon dispersion relation of liquid indium have been investigated by means of pseudopotential theory. The Percus-Yevick Hard Sphere reference system is applied to describe the structural calculation. The effective electron-ion interaction is explained by using modified empty core potential due to Hasegawa et al. along with a local field correction function due to Ichimaru-Utsumi (IU). The temperature dependence of pair potential needed at higher temperatures was achieved by multiplying the damping factor exp(- π/kBT2k F r ) in the pair potential. Very close agreement of static structure factor, particularly, at elevated temperatures confirms the validity of the local potential. A positive dispersion is found in low-q region and the correct trend of phonon dispersion branches like the experimental; shows all broad features of collective excitations in liquid metals.
Quantum-based Atomistic Simulation of Transition Metals
International Nuclear Information System (INIS)
Moriarty, J A; Benedict, L X; Glosli, J N; Hood, R Q; Orlikowski, D A; Patel, M V; Soderlind, P; Streitz, F H; Tang, M; Yang, L H
2005-01-01
First-principles generalized pseudopotential theory (GPT) provides a fundamental basis for transferable multi-ion interatomic potentials in d-electron transition metals within density-functional quantum mechanics. In mid-period bcc metals, where multi-ion angular forces are important to structural properties, simplified model GPT or MGPT potentials have been developed based on canonical d bands to allow analytic forms and large-scale atomistic simulations. Robust, advanced-generation MGPT potentials have now been obtained for Ta and Mo and successfully applied to a wide range of structural, thermodynamic, defect and mechanical properties at both ambient and extreme conditions of pressure and temperature. Recent algorithm improvements have also led to a more general matrix representation of MGPT beyond canonical bands allowing increased accuracy and extension to f-electron actinide metals, an order of magnitude increase in computational speed, and the current development of temperature-dependent potentials
Incremental binding free energies of aluminum (III) vs. magnesium (II) complexes
International Nuclear Information System (INIS)
Mercero, Jose M.; Mujika, Jon I.; Matxain, Jon M.; Lopez, Xabier; Ugalde, Jesus M.
2003-01-01
A sequential ligand addition to the aluminum (III) cation has been studied using the B3LYP functional and a combined all-electron/pseudopotentials basis set. The aluminum complexes are compared with analogous magnesium (II) complexes. Different thermodynamical data, such as incremental binding energies, enthalpies, entropies and free energies, are presented for these addition reactions. While the magnesium (II) cation can only accommodate three negatively charged ligands, aluminum (III) accommodates four even after including bulk solvent effects. The main differences between both cations complexing with the neutral ligands, is that aluminum (III) is not able to form complexes with methanol until the number of methanol ligands is equal to 3. Magnesium (II) prefers to bind methanol and formamide when the number of ligands is small, while aluminum prefers formamide. For the largest complexes both cations prefer to bind water
Structural, electronic and vibrational properties of lanthanide monophosphide at high pressure
International Nuclear Information System (INIS)
Panchal, J. M.; Joshi, Mitesh; Gajjar, P. N.
2016-01-01
A first-principles plane wave self-consistent method with the ultra-soft-pseudopotential scheme in the framework of the density functional theory (DFT) is performed to study structural, electronic and vibrational properties of LaP for Rock-salt (NaCl/Bl) and Cesium-chloride (CsCl/B2) phases. The instability of Rock-salt (NaCl/Bl) phases around the transition is discussed. Conclusions based on electronic energy band structure, density of state, phonon dispersion and phonon density of states in both phases are outlined. The calculated results are consistence and confirm the successful applicability of quasi-harmonic phonon theory for structural instability studies for the alloys.
International Nuclear Information System (INIS)
Chornodolskyy, Ya; Stryganyuk, G; Syrotyuk, S; Voloshinovskii, A; Rodnyi, P
2007-01-01
From luminescence spectroscopy of CsCaCl 3 , Rb 1-x Cs x CaCl 3 and K 1-x Cs x CaCl 3 crystals, we have found evidence for intrinsic and impurity core-valence luminescence due to the radiative recombination of valence electrons with the holes of intrinsic or impurity 5p Cs + core states. The structural similarity of core-valence luminescence spectra has been revealed for the A 1-x Cs x CaCl 3 (A = K,Rb) crystals investigated. The electron energy structure of the CsCaCl 3 crystal has been calculated using the pseudopotential approach taking into account the gradient corrections for the exchange-correlation energy. The calculated density of the electronic states of CsCaCl 3 has been compared with corresponding parameters obtained from the analysis of core-valence luminescence spectra
Yan, Hai-Yan; Zhang, Mei-Guang; Huang, Duo-Hui; Wei, Qun
2013-04-01
The first-principles study on the elastic properties, elastic anisotropy and thermodynamic properties of the orthorhombic OsB4 is reported using density functional theory method with the ultrasoft pseudopotential scheme in the frame of the generalized gradient approximation. The calculated equilibrium parameters are in good agreement with the available theoretical data. A complete elastic tensor and crystal anisotropies of the ultra-incompressible OsB4 are determined in the pressure range of 0-50 GPa. By the elastic stability criteria, it is predicted that the orthorhombic OsB4 is stable below 50 GPa. By using the quasi-harmonic Debye model, the heat capacity, the coefficient of thermal expansion, and the Grüneisen parameter of OsB4 are also successfully obtained in the present work.
Approximate treatment of semicore states in GW calculations with application to Au clusters.
Xian, Jiawei; Baroni, Stefano; Umari, P
2014-03-28
We address the treatment of transition metal atoms in GW electronic-structure calculations within the plane-wave pseudo-potential formalism. The contributions of s and p semi-core electrons to the self-energy, which are essential to grant an acceptable accuracy, are dealt with using a recently proposed scheme whereby the exchange components are treated exactly at the G0W0 level, whereas a suitable approximation to the correlation components is devised. This scheme is benchmarked for small gold nano-clusters, resulting in ionization potentials, electron affinities, and density of states in very good agreement with those obtained from calculations where s and p semicore states are treated as valence orbitals, and allowing us to apply this same scheme to clusters of intermediate size, Au20 and Au32, that would be otherwise very difficult to deal with.
Approximate treatment of semicore states in GW calculations with application to Au clusters
Energy Technology Data Exchange (ETDEWEB)
Xian, Jiawei [SISSA – Scuola Internazionale Superiore di Studi Avanzati, Via Bonomea 265, I-34136 Trieste (Italy); Baroni, Stefano [SISSA – Scuola Internazionale Superiore di Studi Avanzati, Via Bonomea 265, I-34136 Trieste (Italy); CNR-IOM Democritos, Theory-Elettra group, Trieste (Italy); Umari, P., E-mail: paolo.umari@unipd.it [CNR-IOM Democritos, Theory-Elettra group, Trieste (Italy); Dipartimento di Fisica e Astronomia, Università di Padova, Via Marzolo 8, I-35131 Padova (Italy)
2014-03-28
We address the treatment of transition metal atoms in GW electronic-structure calculations within the plane-wave pseudo-potential formalism. The contributions of s and p semi-core electrons to the self-energy, which are essential to grant an acceptable accuracy, are dealt with using a recently proposed scheme whereby the exchange components are treated exactly at the G{sub 0}W{sub 0} level, whereas a suitable approximation to the correlation components is devised. This scheme is benchmarked for small gold nano-clusters, resulting in ionization potentials, electron affinities, and density of states in very good agreement with those obtained from calculations where s and p semicore states are treated as valence orbitals, and allowing us to apply this same scheme to clusters of intermediate size, Au{sub 20} and Au{sub 32}, that would be otherwise very difficult to deal with.
Advanced capabilities for materials modelling with Quantum ESPRESSO.
Andreussi, Oliviero; Brumme, Thomas; Bunau, Oana; Buongiorno Nardelli, Marco; Calandra, Matteo; Car, Roberto; Cavazzoni, Carlo; Ceresoli, Davide; Cococcioni, Matteo; Colonna, Nicola; Carnimeo, Ivan; Dal Corso, Andrea; de Gironcoli, Stefano; Delugas, Pietro; DiStasio, Robert; Ferretti, Andrea; Floris, Andrea; Fratesi, Guido; Fugallo, Giorgia; Gebauer, Ralph; Gerstmann, Uwe; Giustino, Feliciano; Gorni, Tommaso; Jia, Junteng; Kawamura, Mitsuaki; Ko, Hsin-Yu; Kokalj, Anton; Küçükbenli, Emine; Lazzeri, Michele; Marsili, Margherita; Marzari, Nicola; Mauri, Francesco; Nguyen, Ngoc Linh; Nguyen, Huy-Viet; Otero-de-la-Roza, Alberto; Paulatto, Lorenzo; Poncé, Samuel; Giannozzi, Paolo; Rocca, Dario; Sabatini, Riccardo; Santra, Biswajit; Schlipf, Martin; Seitsonen, Ari Paavo; Smogunov, Alexander; Timrov, Iurii; Thonhauser, Timo; Umari, Paolo; Vast, Nathalie; Wu, Xifan; Baroni, Stefano
2017-09-27
Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudo-potential and projector-augmented-wave approaches. Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement theirs ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software. © 2017 IOP Publishing Ltd.
Approximate treatment of semicore states in GW calculations with application to Au clusters
International Nuclear Information System (INIS)
Xian, Jiawei; Baroni, Stefano; Umari, P.
2014-01-01
We address the treatment of transition metal atoms in GW electronic-structure calculations within the plane-wave pseudo-potential formalism. The contributions of s and p semi-core electrons to the self-energy, which are essential to grant an acceptable accuracy, are dealt with using a recently proposed scheme whereby the exchange components are treated exactly at the G 0 W 0 level, whereas a suitable approximation to the correlation components is devised. This scheme is benchmarked for small gold nano-clusters, resulting in ionization potentials, electron affinities, and density of states in very good agreement with those obtained from calculations where s and p semicore states are treated as valence orbitals, and allowing us to apply this same scheme to clusters of intermediate size, Au 20 and Au 32 , that would be otherwise very difficult to deal with
Observation of large-amplitude ion acoustic solitary waves in a plasma
International Nuclear Information System (INIS)
Nakamura, Yoshiharu
1987-01-01
Propagation of nonlinear ion acoustic waves in a multi-component plasma with negative ions is investigated in a double-plasma device. When the density of negative ions is larger than a critical value, a broad negative pulse evolves to rarefactive solitons, and a positive pulse whose amplitude is less than a certain threshold value becomes a subsonic wave train. In the same plasma, a positive pulse whose amplitude is larger than the threshold develops into a solitary wave. The critical amplitude is measured as a function of the density of negative ions and compared with predictions of the pseudo-potential method. The energy distribution of electrons in the solitary wave is also measured. (author)
Electronic, phonon and superconducting properties of LaPtBi half-Heusler compound
Shrivastava, Deepika; Sanyal, Sankar P.
2018-05-01
In the framework of density functional theory based on plane wave pseudopotential method and linear response technique, we have studied the electronic, phonon and superconducting properties of LaPtBi half-Heusler compound. The electronic band structure and density of states show that it is gapless semiconductor which is consistent with previous results. The positive phonon frequencies confirm the stability of this compound in cubic MgAgAs phase. Superconductivity is studied in terms of Eliashberg spectral function (α2F(ω)), electron-phonon coupling constants (λ). The value of electron-phonon coupling parameter is found to be 0.41 and the superconducting transition temperature is calculated to be 0.76 K, in excellent agreement with the experimentally reported values.
Conjugate-gradient optimization method for orbital-free density functional calculations.
Jiang, Hong; Yang, Weitao
2004-08-01
Orbital-free density functional theory as an extension of traditional Thomas-Fermi theory has attracted a lot of interest in the past decade because of developments in both more accurate kinetic energy functionals and highly efficient numerical methodology. In this paper, we developed a conjugate-gradient method for the numerical solution of spin-dependent extended Thomas-Fermi equation by incorporating techniques previously used in Kohn-Sham calculations. The key ingredient of the method is an approximate line-search scheme and a collective treatment of two spin densities in the case of spin-dependent extended Thomas-Fermi problem. Test calculations for a quartic two-dimensional quantum dot system and a three-dimensional sodium cluster Na216 with a local pseudopotential demonstrate that the method is accurate and efficient. (c) 2004 American Institute of Physics.
Stability of gold atoms and dimers adsorbed on graphene
International Nuclear Information System (INIS)
Varns, R; Strange, P
2008-01-01
We report density functional theory (DFT) calculations for gold atoms and dimers on the surface of graphene. The calculations were performed using the plane wave pseudopotential method. Calculations were performed for a variety of geometries, and both the graphene surface and gold atoms were allowed to fully relax. In agreement with experiment, our results show that the gold-gold interaction is considerably stronger than the gold-graphene interaction, implying that uniform coverage could not be attained. The minimum energy configuration for a single gold atom is found to be directly above a carbon atom, while for the dimer it is perpendicular to the surface and directly above a carbon-carbon bond. Our results are consistent with previous similar calculations
International Nuclear Information System (INIS)
Lepkowski, S.P.; Majewski, J.A.
2004-01-01
We studied the nonlinear elasticity effects for the case of III-N compounds. Particularly, we determined the pressure dependences of elastic constants, in zinc-blende InN, GaN, and AlN by performing ab initio calculations in the framework of plane-wave pseudopotential implementation of the density-functional theory. We found significant and almost linear increase in C 11 , C 12 with pressure for considered nitrides compounds. Much weaker dependences on pressure was observed for C 44 . We also discussed pressure dependences of two-dimensional Poisson's ratio and elastic anisotropy coefficient. Finally, we showed that the pressure dependence of elastic constants results in significant reduction of the pressure coefficient of the energy emission in cubic InGaN/GaN quantum well and essentially improves the agreement between experimental and theoretical values. (author)
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
Quantum molecular dynamics of warm dense iron and a five-phase equation of state
Sjostrom, Travis; Crockett, Scott
2018-05-01
Through quantum molecular dynamics (QMD), utilizing both Kohn-Sham (orbital-based) and orbital-free density functional theory, we calculate the equation of state of warm dense iron in the density range 7 -30 g/cm 3 and temperatures from 1 to 100 eV. A critical examination of the iron pseudopotential is made, from which we find a significant improvement at high pressure to the previous QMD calculations of Wang et al. [Phys. Rev. E 89, 023101 (2014), 10.1103/PhysRevE.89.023101]. Our results also significantly extend the ranges of density and temperature that were attempted in that prior work. We calculate the shock Hugoniot and find very good agreement with experimental results to pressures over 20 TPa. These results are then incorporated with previous studies to generate a five-phase equation of state for iron.
Flexible 2D layered material junctions
Balabai, R.; Solomenko, A.
2018-03-01
Within the framework of the methods of the electron density functional and the ab initio pseudopotential, we have obtained the valence electron density spatial distribution, the densities of electron states, the widths of band gaps, the charges on combined regions, and the Coulomb potentials for graphene-based flexible 2D layered junctions, using author program complex. It is determined that the bending of the 2D layered junctions on the angle α leads to changes in the electronic properties of these junctions. In the graphene/graphane junction, there is clear charge redistribution with different signs in the regions of junctions. The presence in the heterojunctions of charge regions with different signs leads to the formation of potential barriers. The greatest potential jump is in the graphene/fluorographene junction. The greatest value of the band gap width is in the graphene/graphane junction.
International Nuclear Information System (INIS)
Schaefer, Sascha; Mehring, Max; Schaefer, Rolf; Schwerdtfeger, Peter
2007-01-01
The dielectric response to an inhomogeneous electric field has been investigated for Ba and Ba 2 within a molecular beam experiment. The ratio of the polarizabilities per atom of Ba 2 and Ba is determined to be 1.30±0.13. The experimental result is compared to a high level ab initio quantum chemical coupled cluster calculation with an energy-consistent scalar relativistic small-core pseudopotential for Ba. For the barium atom a polarizability of 40.82 A 3 is obtained and the isotropic value of the polarizability calculated for Ba 2 is 97.88 A 3 , which is in good agreement with the experimental results, demonstrating that a quantitative understanding of the interaction between two closed-shell heavy element metal atoms has been achieved
Calculation of the superconducting transition temperature in niobium
International Nuclear Information System (INIS)
Perlov, C.M.
1982-01-01
The author presents calculations of the superconducting transition temperature, T/sub c/, the electron-phonon coupling constant, lambda, and the spectral function, α 2 f(ω), for niobium. The author's calculations are based on an empirical pseudopotential method (EPM) band structure. Phonon linewidths are also given for longitudinal and transverse branches along different directions. The necessary electron-phonon matrix elements are evaluated using only the rigid-ion approximation by applying Green's theorem. The calculated value of T/sub c/ is 8.4 K which differs from the measured value by only 9%; the calculated lambda is 1.02. The spectral function and linewidths are compared to experimental and previous theoretical results
Laser operated optical features in β-BaTeMo{sub 2}O{sub 9}:Cr{sup 3+} nanocrystallites
Energy Technology Data Exchange (ETDEWEB)
Majchrowski, A.; Jaroszewicz, L.R. [Institute of Applied Physics, Military University of Technology, Kaliskiego 2, 00-908 Warsaw (Poland); Fedorchuk, A.O. [Lviv National University of Veterinary Medicine and Biotechnologies, Department of Inorganic and Organic Chemistry, Lviv (Ukraine); Kityk, I.V., E-mail: iwank74@gmail.com [Faculty of Electrical Engineering, Czestochowa University Technology, Armii Krajowej 17, Czestochowa (Poland)
2015-11-15
An increase of second order nonlinear optical efficiency was established for Cr{sup 3+} doped β-BaTeMo{sub 2}O{sub 9} (BTMO) nanocrystallites (with sizes varying within up to 150 nm range) under influence of two coherent beams of 532 nm nanosecond pulsed lasers at power densities up to 600 MW/cm{sup 2}. It was found that maximal enhancement of optical second harmonic generation was achieved for BTMO:Cr{sup 3+} nanocrystallites possessing sizes about 60–80 nm. Occurrence of some quasi-periodic space radial grating was observed as well. This is a consequence of competition between the photo-polarization and photo-thermal effects. Band structure simulations within a framework of the norm-conserving pseudopotential were performed. - Highlights: • BMTO nanocrystallites with the sizes 60 nm–120 nm were synthesized. • Photoinduced SHG is found. • The effect is caused by additional photopolarization.
Laser operated optical features in β-BaTeMo2O9:Cr3+ nanocrystallites
International Nuclear Information System (INIS)
Majchrowski, A.; Jaroszewicz, L.R.; Fedorchuk, A.O.; Kityk, I.V.
2015-01-01
An increase of second order nonlinear optical efficiency was established for Cr 3+ doped β-BaTeMo 2 O 9 (BTMO) nanocrystallites (with sizes varying within up to 150 nm range) under influence of two coherent beams of 532 nm nanosecond pulsed lasers at power densities up to 600 MW/cm 2 . It was found that maximal enhancement of optical second harmonic generation was achieved for BTMO:Cr 3+ nanocrystallites possessing sizes about 60–80 nm. Occurrence of some quasi-periodic space radial grating was observed as well. This is a consequence of competition between the photo-polarization and photo-thermal effects. Band structure simulations within a framework of the norm-conserving pseudopotential were performed. - Highlights: • BMTO nanocrystallites with the sizes 60 nm–120 nm were synthesized. • Photoinduced SHG is found. • The effect is caused by additional photopolarization
Electron capture in pseudo-two-electron systems: Ar8++He
International Nuclear Information System (INIS)
Kimura, M.; Olson, R.E.
1985-01-01
Molecular-structure calculations using the pseudopotential method have been performed on the (ArHe) 8+ system. The cross section for single-electron capture in Ar 8+ +He collisions was calculated for energies from 20 eV to 10 keV/amu. The perturbed-stationary-state method [M. Kimura, H. Sato, and R. E. Olson, Phys. Rev. A 28, 2085 (1983)], modified to include electron translation factors appropriate to two-electron systems, was used. The total cross section is relatively energy independent with a value of approximately 2.5 x 10 -15 cm 2 . The n = 4 level of Ar 7+ is found to be preferentially populated, with the 4f level being dominant
International Nuclear Information System (INIS)
Song, Mi-Young; Jung, Young-Dae
2003-01-01
Quantum screening effects on the occurrence scattering time advance for elastic electron-ion collisions in strongly coupled semiclassical plasmas are investigated using the second-order eikonal analysis. The electron-ion interaction in strongly coupled semiclassical plasmas is obtained by the pseudopotential model taking into account the plasma screening and quantum effects. It is found that the quantum-mechanical effects significantly reduce the occurrence scattering time advance. It is also found that the occurrence scattering time advance increases with increasing Debye length. It is quite interesting to note that the domain of the maximum occurrence time advance is localized for the forward scattering case. The region of the scaled thermal de Broglie wave length (λ-bar) for the maximum occurrence time advance is found to be 0.4≤λ-bar≤1.4
Lattice dynamics of Ru2FeX (X = Si, Ge) Full Heusler alloys
Rizwan, M.; Afaq, A.; Aneeza, A.
2018-05-01
In present work, the lattice dynamics of Ru2FeX (X = Si, Ge) full Heusler alloys are investigated using density functional theory (DFT) within generalized gradient approximation (GGA) in a plane wave basis, with norm-conserving pseudopotentials. Phonon dispersion curves and phonon density of states are obtained using first-principles linear response approach of density functional perturbation theory (DFPT) as implemented in Quantum ESPRESSO code. Phonon dispersion curves indicates for both Heusler alloys that there is no imaginary phonon in whole Brillouin zone, confirming dynamical stability of these alloys in L21 type structure. There is a considerable overlapping between acoustic and optical phonon modes predicting no phonon band gap exists in dispersion curves of alloys. The same result is shown by phonon density of states curves for both Heusler alloys. Reststrahlen band for Ru2FeSi is found smaller than Ru2FeGe.
Phonon Spectrum in Hydroxyapatite: Calculations and EPR Study at Low Temperatures
Biktagirov, Timur; Gafurov, Marat; Iskhakova, Kamila; Mamin, Georgy; Orlinskii, Sergei
2016-12-01
Density functional theory-based calculations within the framework of the plane-wave pseudopotential approach are carried out to define the phonon spectrum of hydroxyapatite Ca_{10}(PO4)6(OH)2 (HAp). It allows to describe the temperature dependence of the electronic spin-lattice relaxation time T_{1e} of the radiation-induced stable radical NO3^{2-} in HAp, which was measured in X-band (9 GHz, magnetic field strength of 0.34 T) in the temperature range T = (10-300) K. It is shown that the temperature behavior of T_{1e} at T> 20 K can be fitted via two-phonon Raman type processes with the Debye temperature Θ D ≈ 280 {K} evaluated from the phonon spectrum.
Orientation and alignment of the first excited p state in Li+He and Na+He scattering
International Nuclear Information System (INIS)
Archer, B.J.; Lane, N.F.; Kimura, M.
1990-01-01
Orientation and alignment parameters for the first excited p state of Li and Na in collisions with He through direct excitation from the ground state are studied theoretically in the energy region up to E c.m. =100 keV by using a quasi-one-electron theory. Scattering states are expanded in terms of molecular orbitals, which are calculated by using the pseudopotential method and include electron translation factors. The approach appears to work well for Li+He, giving good agreement for the 2p excitation probability and orientation. For alignment, the situation is less clear because of difficulty in experimental measurement. Two-electron effects and cascades from more highly excited states cause our description of Na+He collisions to be less satisfactory. However, agreement with the experimental 3p excitation probability and orientation parameters where all data are available is fairly good at lower energies (E c.m. 1.25 a.u.)
Haghighi Mood, Kaveh; Lüchow, Arne
2017-08-17
Diffusion quantum Monte Carlo calculations with partial and full optimization of the guide function are carried out for the dissociation of the FeS molecule. For the first time, quantum Monte Carlo orbital optimization for transition metal compounds is performed. It is demonstrated that energy optimization of the orbitals of a complete active space wave function in the presence of a Jastrow correlation function is required to obtain agreement with the experimental dissociation energy. Furthermore, it is shown that orbital optimization leads to a 5 Δ ground state, in agreement with experiments but in disagreement with other high-level ab initio wave function calculations which all predict a 5 Σ + ground state. The role of the Jastrow factor in DMC calculations with pseudopotentials is investigated. The results suggest that a large Jastrow factor may improve the DMC accuracy substantially at small additional cost.
Ab initio thermodynamic properties of stoichiometric phases in the Ni-Al system
International Nuclear Information System (INIS)
Arroyave, R.; Shin, D.; Liu, Z.-K.
2005-01-01
In this work the thermodynamic properties of Al, Ni, NiAl and Ni 3 Al were obtained through ab initio methods. Through the use of density functional theory within the generalized gradient approximation and projector augmented-wave (PAW) pseudopotentials, the 0 K energetics of the structures were calculated. The supercell method was used to calculate the vibrational contributions to the free energy. The contribution of electronic degrees of freedom to the total free energy was also included in the calculations. The resulting free energy was used to calculate the enthalpies and entropies of the structures investigated. The comparison with experimental data is satisfactory, and the calculations compare well with recent results using linear response theory
Structure and stability of ZrSiO4 under hydrostatic pressure
DEFF Research Database (Denmark)
Marques, M.; Florez, M.; Recio, J.M.
2006-01-01
-anvil cell using energy-dispersive synchrotron x-ray diffraction with emphasis on the pressure range 0-15 GPa. Static total-energy calculations have been performed within the density functional theory at local density and generalized gradient approximation levels using a plane-wave pseudopotential scheme....... Our quantum-mechanical simulations explore the pressure response of the two observed tetragonal structures (zircon- and scheelite-type reidite) as well as of other potential post-scheelite polymorphs up to about 60 GPa. We find very good agreement between our experimental and calculated pressure......-volume values for the low-pressure phase of ZrSiO4. A microscopic analysis of the bulk compressibility of zircon and reidite in terms of polyhedral and atomic contributions is proposed to clarify some of the discrepancies found in recent theoretical and experimental studies. Our results show the relevant role...
Polarizabilities and hyperpolarizabilities of the alkali metal atoms
International Nuclear Information System (INIS)
Fuentealba, P.; Reyes, O.
1993-01-01
The electric static dipole polarizability α, quadrupole polarizability C, dipole-quadrupole polarizability B, and the second dipole hyperpolarizability γ have been calculated for the alkali metal atoms in the ground state. The results are based on a pseudopotential which is able to incorporate the very important core-valence correlation effect through a core polarization potential, and, in an empirical way, the main relativistic effects. The calculated properties compare very well with more elaborated calculations for the Li atom, excepting the second hyperpolarizability γ. For the other atoms, there is neither theoretical nor experimental information about most of the higher polarizabilities. Hence, the results of this paper should be seen as a first attempt to give a complete account of the series expansion of the interaction energy of an alkali metal atom and a static electric field. (author)
Reliability evaluation of thermophysical properties from first-principles calculations.
Palumbo, Mauro; Fries, Suzana G; Dal Corso, Andrea; Kürmann, Fritz; Hickel, Tilmann; Neugebauer, Jürg
2014-08-20
Thermophysical properties, such as heat capacity, bulk modulus and thermal expansion, are of great importance for many technological applications and are traditionally determined experimentally. With the rapid development of computational methods, however, first-principles computed temperature-dependent data are nowadays accessible. We evaluate various computational realizations of such data in comparison to the experimental scatter. The work is focussed on the impact of different first-principles codes (QUANTUM ESPRESSO and VASP), pseudopotentials (ultrasoft and projector augmented wave) as well as phonon determination methods (linear response and direct force constant method) on these properties. Based on the analysis of data for two pure elements, Cr and Ni, consequences for the reliability of temperature-dependent first-principles data in computational thermodynamics are discussed.
Short-range order in alloys of nickel with the elements of group VIII of the periodic table
International Nuclear Information System (INIS)
Khwaja, F.A.
1981-08-01
Experimental measurements of the diffuse X-ray scattering intensity were performed on alloys of Ni with Rh and Os. The atomic short-range order (SRO) parameters αsub(i) and the size-effect parameters βsub(i) were calculated from these measurements. It is established that SRO and size-effect exist in Ni-Rh and Ni-Os alloys analogously as in a few other alloys of Ni with the elements of group VIII of the periodic table. The experimental data was interpreted theoretically by calculating the interaction energies from the pseudo-potentials and the effective valencies of the individual components of the systems studied. It was found that theoretically calculated values of the interaction energies for these alloys are inconsistent with the experimentally determined sign of the SRO parameter. (author)
Low frequency solitons and double layers in a magnetized plasma with two temperature electrons
Energy Technology Data Exchange (ETDEWEB)
Rufai, O. R. [Department of Physics, University of the Western Cape, Private Bag X17, Bellville 7535 (South Africa); Bharuthram, R. [Office of the Deputy Vice Chancellor (Academic), University of the Western Cape, Bellville (South Africa); Singh, S. V. [Indian Institute of Geomagnetism, New Panvel (W), Navi Mumbai-410218 (India); School of Chemistry and Physics, University of Kwa-Zulu Natal, Durban (South Africa); Lakhina, G. S. [Indian Institute of Geomagnetism, New Panvel (W), Navi Mumbai-410218 (India)
2012-12-15
Finite amplitude non-linear ion-acoustic solitary waves and double layers are studied in a magnetized plasma with cold ions fluid and two distinct groups of Boltzmann electrons, using the Sagdeev pseudo-potential technique. The conditions under which the solitary waves and double layers can exist are found both analytically and numerically. We have shown the existence of negative potential solitary waves and double layers for subsonic Mach numbers, whereas in the unmagnetized plasma they can only in the supersonic Mach number regime. For the plasma parameters in the auroral region, the electric field amplitude of the solitary structures comes out to be 49 mV/m which is in agreement of the Viking observations in this region.
Low frequency solitons and double layers in a magnetized plasma with two temperature electrons
International Nuclear Information System (INIS)
Rufai, O. R.; Bharuthram, R.; Singh, S. V.; Lakhina, G. S.
2012-01-01
Finite amplitude non-linear ion-acoustic solitary waves and double layers are studied in a magnetized plasma with cold ions fluid and two distinct groups of Boltzmann electrons, using the Sagdeev pseudo-potential technique. The conditions under which the solitary waves and double layers can exist are found both analytically and numerically. We have shown the existence of negative potential solitary waves and double layers for subsonic Mach numbers, whereas in the unmagnetized plasma they can only in the supersonic Mach number regime. For the plasma parameters in the auroral region, the electric field amplitude of the solitary structures comes out to be 49 mV/m which is in agreement of the Viking observations in this region.
Levin, Alan R.; Zhang, Deyin; Polizzi, Eric
2012-11-01
In a recent article Polizzi (2009) [15], the FEAST algorithm has been presented as a general purpose eigenvalue solver which is ideally suited for addressing the numerical challenges in electronic structure calculations. Here, FEAST is presented beyond the “black-box” solver as a fundamental modeling framework which can naturally address the original numerical complexity of the electronic structure problem as formulated by Slater in 1937 [3]. The non-linear eigenvalue problem arising from the muffin-tin decomposition of the real-space domain is first derived and then reformulated to be solved exactly within the FEAST framework. This new framework is presented as a fundamental and practical solution for performing both accurate and scalable electronic structure calculations, bypassing the various issues of using traditional approaches such as linearization and pseudopotential techniques. A finite element implementation of this FEAST framework along with simulation results for various molecular systems is also presented and discussed.
Quantum memory Write, read and reset
Wu Tai Tsun; Wu, Tai Tsun; Yu, Ming Lun
2002-01-01
A model is presented for the quantum memory, the content of which is a pure quantum state. In this model, the fundamental operations of writing on, reading, and resetting the memory are performed through scattering from the memory. The requirement that the quantum memory must remain in a pure state after scattering implies that the scattering is of a special type, and only certain incident waves are admissible. An example, based on the Fermi pseudo-potential in one dimension, is used to demonstrate that the requirements on the scattering process are consistent and can be satisfied. This model is compared with the commonly used model for the quantum memory; the most important difference is that the spatial dimensions and interference play a central role in the present model.
International Nuclear Information System (INIS)
Kang Lei; Luo Siyang; Huang Hongwei; Lin, Z S; Chen, C T; Zheng Tao
2012-01-01
Electronic structures of the deep ultraviolet nonlinear optical crystals of the KBe 2 BO 3 F 2 (KBBF) family, including KBBF, RbBe 2 BO 3 F 2 and CsBe 2 BO 3 F 2 , have been investigated based on a plane-wave pseudopotential method. Their linear and nonlinear optical coefficients are also calculated, and are in good agreement with the experimental results. A real-space atom-cutting method is adopted to analyze the respective contributions of the alkali metal cations and anionic groups to optical response. The results show that the contributions of anionic groups to the nonlinear optical anisotropic responses are dominant, but the influence of the A-site alkali metal cations becomes slightly more pronounced with the increase of their radius. Moreover, the birefringence difference among these crystals strongly depends on the volume effect, i.e., the spatial density of the (BO 3 ) 3- anionic groups. (paper)
Effect of pressure on some physical properties of gallium based semiconductors
International Nuclear Information System (INIS)
Vyas, P S; Thakore, B Y; Jani, A R; Gajjar, P N
2012-01-01
The gallium based semiconductor compounds are very useful materials for optical spectroscopy and optoelectronic applications, we have studied the effect of pressure on various physical properties like total energy, static bulk modulus, energy band gap at the point X on the Jones-zone face, pressure derivative of bulk modulus and equation of state of gallium based binary compounds GaSb, GaAs, GaP and GaN using pseudopotential theory beyond second order with our well established single parametric model potential. We have incorporated Nagy's static local field correction function to include exchange and correlation effects. The results are compared with those obtained using few other local field correction functions. The present results agree satisfactorily with available experimental and other such theoretical data confirming the application.
Electronic band structure calculations for GaxIn1−xASyP1−y alloys lattice matched to InP
International Nuclear Information System (INIS)
Bechiri, A; Benmakhlouf, F; Allouache, H; Bacha, S; Bouarissa, N
2012-01-01
A pseudopotential formalism coupled with the virtual crystal approximation are applied to study the effect of compositional disorder upon electronic band structure of cubic Ga x In 1−x As y P 1−y quarternary alloys lattice matched to InP. The effects of compositional variations are properly included in the calculations. Very good agreement is obtained between the calculated values and the available experimental data for the lattice–matched alloy to InP. The absorption at the fundamental optical gaps is found to be direct within a whole range of the y composition whatever the lattice-matching to the substrate of interest. The alloy system Ga x In 1−x As y P 1−y lattice matched to InP is suggested to be suitable for an efficient light emitting device (ELED) material.
Impact ionization in GaAs: A screened exchange density-functional approach
International Nuclear Information System (INIS)
Picozzi, S.; Asahi, R.; Geller, C.B.; Continenza, A.; Freeman, A.J.
2001-01-01
Results are presented of a fully ab initio calculation of impact ionization rates in GaAs within the density functional theory framework, using a screened-exchange formalism and the highly precise all-electron full-potential linearized augmented plane wave method. The calculated impact ionization rates show a marked orientation dependence in k space, indicating the strong restrictions imposed by the conservation of energy and momentum. This anisotropy diminishes as the impacting electron energy increases. A Keldysh type fit performed on the energy-dependent rate shows a rather soft edge and a threshold energy greater than the direct band gap. The consistency with available Monte Carlo and empirical pseudopotential calculations shows the reliability of our approach and paves the way to ab initio calculations of pair production rates in new and more complex materials
Infrared spectroscopy of copper-resveratrol complexes: A joint experimental and theoretical study
International Nuclear Information System (INIS)
Chiavarino, B.; Crestoni, M. E.; Fornarini, S.; Taioli, S.; Mancini, I.; Tosi, P.
2012-01-01
Infrared multiple-photon dissociation spectroscopy has been used to record vibrational spectra of charged copper-resveratrol complexes in the 3500–3700 cm −1 and 1100–1900 cm −1 regions. Minimum energy structures have been determined by density functional theory calculations using plane waves and pseudopotentials. In particular, the copper(I)-resveratrol complex presents a tetra-coordinated metal bound with two carbon atoms of the alkenyl moiety and two closest carbons of the adjoining resorcinol ring. For these geometries vibrational spectra have been calculated by using linear response theory. The good agreement between experimental and calculated IR spectra for the selected species confirms the overall reliability of the proposed geometries.
Transitioning NWChem to the Next Generation of Manycore Machines
Energy Technology Data Exchange (ETDEWEB)
Bylaska, Eric J.; Apra, Edoardo; Kowalski, Karol; Jacquelin, Mathias; De Jong, Wibe A.; Vishnu, Abhinav; Palmer, Bruce J.; Daily, Jeffrey A.; Straatsma, Tjerk P.; Hammond, Jeff R.; Klemm, Michael
2017-11-09
The NorthWest Chemistry (NWChem) modeling software is a popular molecular chemistry simulation software that was designed from the start to work on massively parallel processing supercomputers[6, 28, 49]. It contains an umbrella of modules that today includes Self Consistent Field (SCF), second order Mller-Plesset perturbation theory (MP2), Coupled Cluster, multi-conguration selfconsistent eld (MCSCF), selected conguration interaction (CI), tensor contraction engine (TCE) many body methods, density functional theory (DFT), time-dependent density functional theory (TDDFT), real time time-dependent density functional theory, pseudopotential plane-wave density functional theory (PSPW), band structure (BAND), ab initio molecular dynamics, Car-Parrinello molecular dynamics, classical molecular dynamics (MD), QM/MM, AIMD/MM, GIAO NMR, COSMO, COSMO-SMD, and RISM solvation models, free energy simulations, reaction path optimization, parallel in time, among other capabilities[ 22]. Moreover new capabilities continue to be added with each new release.
Modeling the photosensitizing properties of thiolate-protected gold nanoclusters.
Azarias, Cloé; Adamo, Carlo; Perrier, Aurélie
2016-03-21
An accurate computational strategy for studying the structural, redox and optical properties of thiolated gold nanoclusters (GNCs) using (Time-Dependent) Density Functional Theory is proposed. The influence of the pseudopotential/basis set, solvent description and the choice of the functional has been investigated to model the structural and electronic properties of the Au25(SR)18(-) system, with R being an organic ligand. This study aims to describe with a comparable precision both the GNC and the organic ligands and rationalize the effect of coating on different GNC properties. Two differently coated GNCs have been considered: the system with R = CH2CH2Ph and the GNC coated with 17 alkyl chains (C6H13) and functionalized by one fluorophore pyrene derivative (CH2CH2(NH)(CO)Py). The computational protocol we propose should then be used to design more efficient metal cluster-sensitized solar cells.
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
Atomistic modelling study of lanthanide incorporation in the crystal lattice of an apatite
International Nuclear Information System (INIS)
Louis-Achille, V.
1999-01-01
Studies of natural and synthetic apatites allow to propose such crystals as matrix for nuclear waste storage. The neodymium substituted britholite, Ca 9 Nd(PO 4 ) 5 (SiO 4 )F 2 . is a model for the trivalent actinide storage Neodymium can be substituted in two types of sites. The aim of this thesis is to compare the chemical nature of this two sites in fluoro-apatite Ca 9 (PO 4 ) 6 F 2 and then in britholite, using ab initio atomistic modeling. Two approaches are used: one considers the infinite crystals and the second considers clusters. The calculations of the electronic structure for both were performed using Kohn and Sham density functional theory in the local approximation. For solids, pseudopotentials were used, and wave functions are expanded in plane waves. For clusters, a frozen core approximation was used, and the wave functions are expanded in a linear combination of Slater type atomic orbitals. The pseudopotential is semi-relativistic for neodymium, and the Hamiltonian is scalar relativistic for the clusters. The validation of the solid approach is performed using two test cases: YPO 4 and ScPO 4 . Two numerical tools were developed to compute electronic deformation density map, and calculate partial density of stases. A full optimisation of the lattice parameters with a relaxation of the atomic coordinates leads to correct structural and thermodynamic properties for the fluoro-apatite, compared to experience. The electronic deformation density maps do not show any significant differences. between the two calcium sites. but Mulliken analysis on the solid and on the clusters point out the more ionic behavior of the calcium in site 2. A neodymium substituted britholite is then studied. Neodymium location only induces local modifications in; the crystalline structure and few changes in the formation enthalpy. The electronic study points out an increase of the covalent character the bonding involving neodymium compared with the one related to calcium
Wavelet-based linear-response time-dependent density-functional theory
International Nuclear Information System (INIS)
Natarajan, Bhaarathi; Genovese, Luigi; Casida, Mark E.; Deutsch, Thierry; Burchak, Olga N.
2012-01-01
Highlights: ► We has been implemented LR-TD-DFT in the pseudopotential wavelet-based program. ► We have compared the results against all-electron Gaussian-type program. ► Orbital energies converges significantly faster for BigDFT than for DEMON2K. ► We report the X-ray crystal structure of the small organic molecule flugi6. ► Measured and calculated absorption spectrum of flugi6 is also reported. - Abstract: Linear-response time-dependent (TD) density-functional theory (DFT) has been implemented in the pseudopotential wavelet-based electronic structure program BIGDFT and results are compared against those obtained with the all-electron Gaussian-type orbital program DEMON2K for the calculation of electronic absorption spectra of N 2 using the TD local density approximation (LDA). The two programs give comparable excitation energies and absorption spectra once suitably extensive basis sets are used. Convergence of LDA density orbitals and orbital energies to the basis-set limit is significantly faster for BIGDFT than for DEMON2K. However the number of virtual orbitals used in TD-DFT calculations is a parameter in BIGDFT, while all virtual orbitals are included in TD-DFT calculations in DEMON2K. As a reality check, we report the X-ray crystal structure and the measured and calculated absorption spectrum (excitation energies and oscillator strengths) of the small organic molecule N-cyclohexyl-2-(4-methoxyphenyl)imidazo[1, 2-a]pyridin-3-amine.
Bouamama, Kh.; Djemia, P.; Benhamida, M.
2015-09-01
First-principles pseudo-potentials calculations of the mixing enthalpy, of the lattice constants a0 and of the single-crystal elastic constants cij for ternary metal nitrides TaxMe1-xN (Me=Mo or W) alloys considering the cubic B1-rocksalt structure is carried out. For disordered ternary alloys, we employ the virtual crystal approximation VCA in which the alloy pseudopotentials are constructed within a first-principles VCA scheme. The supercell method SC is also used for ordered structures in order to evaluate clustering effects. We find that the mixing enthalpy still remains negative for TaxMe1-xN alloys in the whole composition range which implies these cubic TaxMo1-xN and TaxW1-xN ordered solid solutions are stable. We investigate the effect of Mo and W alloying on the trend of the mechanical properties of TaN. The effective shear elastic constant c44, the Cauchy pressure (c12-c44), and the shear to bulk modulus G/B ratio are used to discuss, respectively, the mechanical stability of the ternary structure and the brittle/ductile behavior in reference to TaN, MeN alloys. We determine the onset transition from the unstable structure to the stable one B1-rocksalt from the elastic stability criteria when alloying MeN with Ta. In a second stage, in the frame of anisotropic elasticity, we estimate by one homogenization method the averaged constants of the polycrystalline TaxMe1-xN alloys considering the special case of an isotropic medium with no crystallographic texture.
Energy Technology Data Exchange (ETDEWEB)
Vetere, V
2002-09-15
This thesis is related to comparative studies of the chemical properties of molecular complexes containing lanthanide or actinide trivalent cations, in the context of the nuclear waste disposal. More precisely, our aim was a quantum chemical analysis of the metal-ligand bonding in such species. Various theoretical approaches were compared, for the inclusion of correlation (density functional theory, multiconfigurational methods) and of relativistic effects (relativistic scalar and 2-component Hamiltonians, relativistic pseudopotentials). The performance of these methods were checked by comparing computed structural properties to published experimental data, on small model systems: lanthanide and actinide tri-halides and on X{sub 3}M-L species (X=F, Cl; M=La, Nd, U; L = NH{sub 3}, acetonitrile, CO). We have thus shown the good performance of density functionals combined with a quasi-relativistic method, as well as of gradient-corrected functionals associated with relativistic pseudopotentials. In contrast, functionals including some part of exact exchange are less reliable to reproduce experimental trends, and we have given a possible explanation for this result . Then, a detailed analysis of the bonding has allowed us to interpret the discrepancies observed in the structural properties of uranium and lanthanides complexes, based on a covalent contribution to the bonding, in the case of uranium(III), which does not exist in the lanthanide(III) homologues. Finally, we have examined more sizeable systems, closer to experimental species, to analyse the influence of the coordination number, of the counter-ions and of the oxidation state of uranium, on the metal-ligand bonding. (author)
The quasiparticle band structure of zincblende and rocksalt ZnO.
Dixit, H; Saniz, R; Lamoen, D; Partoens, B
2010-03-31
We present the quasiparticle band structure of ZnO in its zincblende (ZB) and rocksalt (RS) phases at the Γ point, calculated within the GW approximation. The effect of the p-d hybridization on the quasiparticle corrections to the band gap is discussed. We compare three systems, ZB-ZnO which shows strong p-d hybridization and has a direct band gap, RS-ZnO which is also hybridized but includes inversion symmetry and therefore has an indirect band gap, and ZB-ZnS which shows a weaker hybridization due to a change of the chemical species from oxygen to sulfur. The quasiparticle corrections are calculated with different numbers of valence electrons in the Zn pseudopotential. We find that the Zn(20+) pseudopotential is essential for the adequate treatment of the exchange interaction in the self-energy. The calculated GW band gaps are 2.47 eV and 4.27 eV respectively, for the ZB and RS phases. The ZB-ZnO band gap is underestimated compared to the experimental value of 3.27 by ∼ 0.8 eV. The RS-ZnO band gap compares well with the experimental value of 4.5 eV. The underestimation for ZB-ZnO is correlated with the strong p-d hybridization. The GW band gap for ZnS is 3.57 eV, compared to the experimental value of 3.8 eV.
Structure and stability of small Li2 +(X2Σ+ g )-Xen (n = 1-6) clusters
Saidi, Sameh; Ghanmi, Chedli; Berriche, Hamid
2014-04-01
We have studied the structure and stability of the Li2 +(X2Σ+ g )Xe n ( n = 1-6) clusters for special symmetry groups. The potential energy surfaces of these clusters, are described using an accurate ab initio approach based on non-empirical pseudopotential, parameterized l-dependent polarization potential and analytic potential forms for the Li+Xe and Xe-Xe interactions. The pseudopotential technique has reduced the number of active electrons of Li2 +(X2Σ+ g )-Xe n ( n = 1-6) clusters to only one electron, the Li valence electron. The core-core interactions for Li+Xe are included using accurate CCSD(T) potential fitted using the analytical form of Tang and Toennies. For the Xe-Xe potential interactions we have used the analytical form of Lennard Jones (LJ6 - 12). The potential energy surfaces of the Li2 +(X2Σ+ g )Xe n ( n = 1-6) clusters are performed for a fixed distance of the Li2 +(X2Σ+ g ) alkali dimer, its equilibrium distance. They are used to extract information on the stability of the Li2 +(X2Σ+ g Xe n ( n = 1-6) clusters. For each n, the stability of the different isomers is examined by comparing their potential energy surfaces. Moreover, we have determined the quantum energies ( D 0), the zero-point-energies (ZPE) and the ZPE%. To our best knowledge, there are neither experimental nor theoretical works realized for the Li2 +(X2Σ+ g Xe n ( n = 1-6) clusters, our results are presented for the first time.
Excess electrons in methanol clusters: Beyond the one-electron picture
Pohl, Gábor; Mones, Letif; Turi, László
2016-10-01
We performed a series of comparative quantum chemical calculations on various size negatively charged methanol clusters, ("separators=" CH 3 OH ) n - . The clusters are examined in their optimized geometries (n = 2-4), and in geometries taken from mixed quantum-classical molecular dynamics simulations at finite temperature (n = 2-128). These latter structures model potential electron binding sites in methanol clusters and in bulk methanol. In particular, we compute the vertical detachment energy (VDE) of an excess electron from increasing size methanol cluster anions using quantum chemical computations at various levels of theory including a one-electron pseudopotential model, several density functional theory (DFT) based methods, MP2 and coupled-cluster CCSD(T) calculations. The results suggest that at least four methanol molecules are needed to bind an excess electron on a hydrogen bonded methanol chain in a dipole bound state. Larger methanol clusters are able to form stronger interactions with an excess electron. The two simulated excess electron binding motifs in methanol clusters, interior and surface states, correlate well with distinct, experimentally found VDE tendencies with size. Interior states in a solvent cavity are stabilized significantly stronger than electron states on cluster surfaces. Although we find that all the examined quantum chemistry methods more or less overestimate the strength of the experimental excess electron stabilization, MP2, LC-BLYP, and BHandHLYP methods with diffuse basis sets provide a significantly better estimate of the VDE than traditional DFT methods (BLYP, B3LYP, X3LYP, PBE0). A comparison to the better performing many electron methods indicates that the examined one-electron pseudopotential can be reasonably used in simulations for systems of larger size.
Theoretical study of the electronic structure of f-element complexes by quantum chemical methods
International Nuclear Information System (INIS)
Vetere, V.
2002-09-01
This thesis is related to comparative studies of the chemical properties of molecular complexes containing lanthanide or actinide trivalent cations, in the context of the nuclear waste disposal. More precisely, our aim was a quantum chemical analysis of the metal-ligand bonding in such species. Various theoretical approaches were compared, for the inclusion of correlation (density functional theory, multiconfigurational methods) and of relativistic effects (relativistic scalar and 2-component Hamiltonians, relativistic pseudopotentials). The performance of these methods were checked by comparing computed structural properties to published experimental data, on small model systems: lanthanide and actinide tri-halides and on X 3 M-L species (X=F, Cl; M=La, Nd, U; L = NH 3 , acetonitrile, CO). We have thus shown the good performance of density functionals combined with a quasi-relativistic method, as well as of gradient-corrected functionals associated with relativistic pseudopotentials. In contrast, functionals including some part of exact exchange are less reliable to reproduce experimental trends, and we have given a possible explanation for this result . Then, a detailed analysis of the bonding has allowed us to interpret the discrepancies observed in the structural properties of uranium and lanthanides complexes, based on a covalent contribution to the bonding, in the case of uranium(III), which does not exist in the lanthanide(III) homologues. Finally, we have examined more sizeable systems, closer to experimental species, to analyse the influence of the coordination number, of the counter-ions and of the oxidation state of uranium, on the metal-ligand bonding. (author)
Zhang, Yachao; Yang, Yang; Jiang, Hong
2013-12-12
The 3d-4f exchange interaction plays an important role in many lanthanide based molecular magnetic materials such as single-molecule magnets and magnetic refrigerants. In this work, we study the 3d-4f magnetic exchange interactions in a series of Cu(II)-Gd(III) (3d(9)-4f(7)) dinuclear complexes based on the numerical atomic basis-norm-conserving pseudopotential method and density functional theory plus the Hubbard U correction approach (DFT+U). We obtain improved description of the 4f electrons by including the semicore 5s5p states in the valence part of the Gd-pseudopotential. The Hubbard U correction is employed to treat the strongly correlated Cu-3d and Gd-4f electrons, which significantly improve the agreement of the predicted exchange constants, J, with experiment, indicating the importance of accurate description of the local Coulomb correlation. The high efficiency of the DFT+U approach enables us to perform calculations with molecular crystals, which in general improve the agreement between theory and experiment, achieving a mean absolute error smaller than 2 cm(-1). In addition, through analyzing the physical effects of U, we identify two magnetic exchange pathways. One is ferromagnetic and involves an interaction between the Cu-3d, O-2p (bridge ligand), and the majority-spin Gd-5d orbitals. The other one is antiferromagnetic and involves Cu-3d, O-2p, and the empty minority-spin Gd-4f orbitals, which is suppressed by the planar Cu-O-O-Gd structure. This study demonstrates the accuracy of the DFT+U method for evaluating the 3d-4f exchange interactions, provides a better understanding of the exchange mechanism in the Cu(II)-Gd(III) complexes, and paves the way for exploiting the magnetic properties of the 3d-4f compounds containing lanthanides other than Gd.
The relation between the Gross-Pitaevskii and Bogoliubov descriptions of a dilute Bose gas
International Nuclear Information System (INIS)
Leggett, A J
2003-01-01
I formulate a 'pseudo-paradox' in the theory of a dilute Bose gas with repulsive interactions: the standard expression for the ground state energy within the Gross-Pitaevskii (GP) approximation is lower than that in the Bogoliubov approximation, and hence, by the standard variational argument, the former should prima facie be a better approximation than the latter to the true ground state - a conclusion which is of course opposite to the established wisdom concerning this problem. It is shown that the pseudo-paradox is (unsurprisingly) resolved by a correct transcription of the two-body scattering theory to the many-body case; however, contrary to what appears to be a widespread belief, the resolution has nothing to do with any spurious ultraviolet divergences which result from the replacement of the true interatomic potential by a delta-function pseudopotential. Rather, it relates to an infrared divergence which has the consequence that (a) the most obvious form of the GP 'approximation' actually does not correspond to any well-defined ansatz for the many-body wavefunction, and (b) that the 'best shot' at such a wavefunction always produces an energy which exceeds, or at best equals, that calculated in the Bogoliubov approximation. In fact, the necessity of the latter may be seen as a consequence of the need to reduce the Fock term in the energy, which is absent in the two-particle problem but dominant in the many-body case; it does this by increasing the density correlations, at distances less than or approximately equal to the correlation length ξ, above the value extrapolated from the two-body case. As a by-product I devise an alternative formulation of the Bogoliubov approximation which does not require the explicit replacement of the true interatomic potential by a delta-function pseudopotential
The relation between the Gross-Pitaevskii and Bogoliubov descriptions of a dilute Bose gas
Energy Technology Data Exchange (ETDEWEB)
Leggett, A J [Department of Physics, University of Illinois at Urbana-Champaign, IL 61801-3080 (United States)
2003-07-01
I formulate a 'pseudo-paradox' in the theory of a dilute Bose gas with repulsive interactions: the standard expression for the ground state energy within the Gross-Pitaevskii (GP) approximation is lower than that in the Bogoliubov approximation, and hence, by the standard variational argument, the former should prima facie be a better approximation than the latter to the true ground state - a conclusion which is of course opposite to the established wisdom concerning this problem. It is shown that the pseudo-paradox is (unsurprisingly) resolved by a correct transcription of the two-body scattering theory to the many-body case; however, contrary to what appears to be a widespread belief, the resolution has nothing to do with any spurious ultraviolet divergences which result from the replacement of the true interatomic potential by a delta-function pseudopotential. Rather, it relates to an infrared divergence which has the consequence that (a) the most obvious form of the GP 'approximation' actually does not correspond to any well-defined ansatz for the many-body wavefunction, and (b) that the 'best shot' at such a wavefunction always produces an energy which exceeds, or at best equals, that calculated in the Bogoliubov approximation. In fact, the necessity of the latter may be seen as a consequence of the need to reduce the Fock term in the energy, which is absent in the two-particle problem but dominant in the many-body case; it does this by increasing the density correlations, at distances less than or approximately equal to the correlation length {xi}, above the value extrapolated from the two-body case. As a by-product I devise an alternative formulation of the Bogoliubov approximation which does not require the explicit replacement of the true interatomic potential by a delta-function pseudopotential.
Electronic and structural properties of {beta}-Be{sub 3}N{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Mokhtari, A.; Akbarzadeh, H
2002-12-01
We report the results of a theoretical study of the electronic and structural properties of the hexagonal beryllium nitride, using first principle pseudopotential plane wave (PP-PW) as well as full potential linearized augmented plane wave (FP-LAPW) methods within density functional theory. In the case of PP-PW we generated the pseudopotential by the highly optimized Q{sub c}-tuning method and used the local density approximation and generalized gradient approximation (GGA) for the exchange-correlation potential. We applied pressure on the unit cell by the Wentzcovitch and traditional methods. In the FP-LAPW approach only the GGA was used for the exchange-correlation potential. Our calculated values for structural properties, based on both approaches are in reasonable agreement with experimental and other theoretical (Hartree Fock) results. By applying the above two approaches and also the Tight Binding Linear Muffin Thin Orbital method, the ground state Kohn-Sham eigenvalues were calculated. The energy bands in three cases were similar and except for the energy gap values they were in good agreement with other theoretical results. Various versions of GGA functionals are usually obtained by optimizing the exchange correlation energy E{sub XC} rather than the corresponding potential V{sub XC}. As these functionals are not able to simultaneously reproduce E{sub XC} and V{sub XC}, hence they cannot obtain an accurate value for the band gap which mainly depends on the potential. Engel and Vosko (Phys. Rev. B 47 (1993) 13164) have proposed an alternate form of GGA which is based on optimizing V{sub XC} instead of the integral quantity E{sub XC}. We used this functional to calculate the band gap and the result seems to be more reasonable. Finally the total and partial densities of states were calculated for each atom.
Lou, Qin; Zang, Chenqiang; Yang, Mo; Xu, Hongtao
In this work, the immiscible displacement in a cavity with different channel configurations is studied using an improved pseudo-potential lattice Boltzmann equation (LBE) model. This model overcomes the drawback of the dependence of the fluid properties on the grid size, which exists in the original pseudo-potential LBE model. The approach is first validated by the Laplace law. Then, it is employed to study the immiscible displacement process. The influences of different factors, such as the surface wettability, the distance between the gas cavity and liquid cavity and the surface roughness of the channel are investigated. Numerical results show that the displacement efficiency increases and the displacement time decreases with the increase of the surface contact angle. On the other hand, the displacement efficiency increases with increasing distance between the gas cavity and the liquid cavity at first and finally reaches a constant value. As for the surface roughness, two structures (a semicircular cavity and a semicircular bulge) are studied. The comprehensive results show that although the displacement processes for both the structures depend on the surface wettability, they present quite different behaviors. Specially, for the roughness structure constituted by the semicircular cavity, the displacement efficiency decreases and displacement time increases evidently with the size of the semicircular cavity for the small contact angle. The trend slows down as the increase of the contact angle. Once the contact angle exceeds a certain value, the size of the semicircular cavity almost has no influence on the displacement process. While for the roughness structure of a semicircular bulge, the displacement efficiency increases with the size of bulge first and then it decreases for the small contact angle. The displacement efficiency increases first and finally reaches a constant for the large contact angle. The results also show that the displacement time has an
Energetics and dynamics of excess electrons in simple fluids
International Nuclear Information System (INIS)
Space, B.
1992-01-01
Excess electronic dynamical and equilibrium properties are modeled in both polarizable and nonpolarizable noble gas fluids. Explicit dynamical calculations are carried out for excess electrons in fluid helium, where excess electronic eigenstates are localized. Energetics and dynamics are considered for fluids which span the entire range of polarizability present in the rare gases. Excess electronic eigenstates and eigenvalues are calculated for fluids of helium, argon and xenon. Both equilibrium and dynamical information is obtained from the calculation of these wavefunctions. A surface hopping trajectory method for studying nonadiabatic excess electronic relaxation in condensed systems is used to explore the nonadiabatic relaxation after photoexciting an equilibrated excess electron in dense fluid helium. The different types on nonadiabatic phenomena which are important in excess electronic relaxation are surveyed. The same surface hopping trajectory method is also used to study the rapid nonadiabatic relaxation after an excess electron is injected into unperturbed fluid helium. Several distinctively different relaxation processes, characterized by their relative importance at different times during the relaxation to a localized equilibrium state, are detailed. Though the dynamical properties of excess electrons under the conditions considered here have never been studied before, the behavior is remarkably similar to that observed in both experimental and theoretical studies of electron hydration dynamics, indicating that the processes described may be very general relaxation mechanisms for localization and trapping in fluids. Additionally, ground state energies of an excess electron, e 0 , are computed as a function of solvent density using model electron-atom pseudopotentials in fluid helium, argon, and xenon. The nonuniqueness of the pseudopotential description of electron-molecule interactions is demonstrated
International Nuclear Information System (INIS)
Caravaca, M A; Casali, R A
2005-01-01
The SIESTA approach based on pseudopotentials and a localized basis set is used to calculate the electronic, elastic and equilibrium properties of P 2 1 /c, Pbca, Pnma, Fm3m, P4 2 nmc and Pa3 phases of HfO 2 . Using separable Troullier-Martins norm-conserving pseudopotentials which include partial core corrections for Hf, we tested important physical properties as a function of the basis set size, grid size and cut-off ratio of the pseudo-atomic orbitals (PAOs). We found that calculations in this oxide with the LDA approach and using a minimal basis set (simple zeta, SZ) improve calculated phase transition pressures with respect to the double-zeta basis set and LDA (DZ-LDA), and show similar accuracy to that determined with the PPPW and GGA approach. Still, the equilibrium volumes and structural properties calculated with SZ-LDA compare better with experiments than the GGA approach. The bandgaps and elastic and structural properties calculated with DZ-LDA are accurate in agreement with previous state of the art ab initio calculations and experimental evidence and cannot be improved with a polarized basis set. These calculated properties show low sensitivity to the PAO localization parameter range between 40 and 100 meV. However, this is not true for the relative energy, which improves upon decrease of the mentioned parameter. We found a non-linear behaviour in the lattice parameters with pressure in the P 2 1 /c phase, showing a discontinuity of the derivative of the a lattice parameter with respect to external pressure, as found in experiments. The common enthalpy values calculated with the minimal basis set give pressure transitions of 3.3 and 10.8?GPa for P2 1 /c → Pbca and Pbca → Pnma, respectively, in accordance with different high pressure experimental values
Studies in the electronic structure of matter
International Nuclear Information System (INIS)
Miller, D.L.
1979-01-01
KLL Auger transition rates for helium are computed using simple atomic orbital wavefunctions which take into account the difference in average electron-electron repulsion of initial and final states. The results are consistent with transition rates computed by other authors using a variety of many-electron techniques. It is suggested that wavefunctions determined in the manner described provide a useful representation of the autoionizing state within the first Bohr radius. A method for extracting atomic psuedopotentials from photoelectron angular distributions is described and applied photoionization of the outermost p shells of Ar, Kr, and Xe and to the 4d shell of Xe. The pseudopotentials obtained reproduce the data, and also predict accurate cross sections and phase shifts for photoelectron energies up to 100 eV. It is suggested that the pseudopotentials aptly mimic the effects of intrashell electron-electron correlations in the photoionization process. The extended Hueckel theory is applied to the nitrogen trap in GaAs and GaP. Perfect crystal band structures are computed and are shown to be in reasonable agreement with those computed with empirical psuedopotentials. Nitrogen impurity levles in GaAs and GaP are computed using an extended Hueckel cluster model. In each case the model predicts two states within the band gap, in contrast to experiment which detects one impurity state in GaP and none in GaAs. It is suggested that the choice of cluster used unrealistically concentrates states near the conduction band edge on the central atom
Energy Technology Data Exchange (ETDEWEB)
Caravaca, M A [Facultad de Ingenieria, Universidad Nacional del Nordeste, Avenida Las Heras 727, 3500-Resistencia (Argentina); Casali, R A [Facultad de Ciencias Exactas y Naturales y Agrimensura, Universidad Nacional del Nordeste, Avenida Libertad, 5600-Corrientes (Argentina)
2005-09-21
The SIESTA approach based on pseudopotentials and a localized basis set is used to calculate the electronic, elastic and equilibrium properties of P 2{sub 1}/c, Pbca, Pnma, Fm3m, P4{sub 2}nmc and Pa3 phases of HfO{sub 2}. Using separable Troullier-Martins norm-conserving pseudopotentials which include partial core corrections for Hf, we tested important physical properties as a function of the basis set size, grid size and cut-off ratio of the pseudo-atomic orbitals (PAOs). We found that calculations in this oxide with the LDA approach and using a minimal basis set (simple zeta, SZ) improve calculated phase transition pressures with respect to the double-zeta basis set and LDA (DZ-LDA), and show similar accuracy to that determined with the PPPW and GGA approach. Still, the equilibrium volumes and structural properties calculated with SZ-LDA compare better with experiments than the GGA approach. The bandgaps and elastic and structural properties calculated with DZ-LDA are accurate in agreement with previous state of the art ab initio calculations and experimental evidence and cannot be improved with a polarized basis set. These calculated properties show low sensitivity to the PAO localization parameter range between 40 and 100 meV. However, this is not true for the relative energy, which improves upon decrease of the mentioned parameter. We found a non-linear behaviour in the lattice parameters with pressure in the P 2{sub 1}/c phase, showing a discontinuity of the derivative of the a lattice parameter with respect to external pressure, as found in experiments. The common enthalpy values calculated with the minimal basis set give pressure transitions of 3.3 and 10.8?GPa for P2{sub 1}/c {yields} Pbca and Pbca {yields} Pnma, respectively, in accordance with different high pressure experimental values.
International Nuclear Information System (INIS)
Albrecht, Stefan
1999-01-01
A method for the inclusion of self-energy and excitonic effects in first-principle calculations of absorption spectra, within the state-of-the-art plane wave pseudopotential approach, is presented. Starting from a ground state calculation, using density functional theory (DFT) in the local density approximation (LDA), we correct the exchange-correlation potential of DFT-LDA with the self-energy applying Hedin's GW approximation to obtain the physical quasiparticles states. The electron-hole interaction is treated solving an effective two-particle equation, which we derive from Hedin's coupled integral equations, leading to the fundamental Bethe-Salpeter equation in an intermediate step. The interaction kernel contains the screened electron-hole Coulomb interaction and the electron-hole exchange effects, which reflect the microscopic structure of the system and are thus also called local-field effects. We obtain the excitonic eigenstates through diagonalization. This allows us a detailed analysis of the optical properties. The application of symmetry properties enables us to reduce the size of the two-particle Hamiltonian matrix, thus minimizing the computational effort. We apply our method to silicon, diamond, lithium oxide and the sodium tetramer. Good agreement with experiment is obtained for the absorption spectra of Si and diamond, the static dielectric constant of diamond, and for the onset of optical absorption of Li 2 O due to discrete bound excitons. We discuss various approximations of our method and show the strong mixing of independent particle transitions to a bound excitonic state in the Na 4 cluster. The influence of ground state calculations on optical spectra is investigated under particular consideration of the pseudopotential generation and we discuss the use of different Brillouin zone point sampling schemes for spectral calculations. (author) [fr
Directory of Open Access Journals (Sweden)
W. C. Kreye
2010-01-01
Full Text Available Quantum-mechanical and semi-classical spectral-line shapes are computed at =400, 800, and 1000 K for the line core of the 5802 Å line of the Ar-Perturbed/K-Radiator system. HWHMs ('s are measured from computed full spectral-line shapes. The final-state pseudopotential is for the 721/2 state, and the initial-state potential is for the 423/2,3/2 state. Three high-pressure (P log(—versus—log( curves, corresponding to the non-impact region, intersect a similar set of low-P, impact-region curves at intersections, 0's. Similarly, for two sets of log(—versus—log( curves, which yield intersections, 0's, where is the perturber density. These 0's and 0's separate the two regions and represent the upper limits of the impact regions. A specific validity condition for the impact region is given by the equation ≤0. From an earlier spectroscopic, Fabry-Perot paper, expt=0.021 cm−1 at =400 K and =10 torr. Two theoretical values, theor=0.025 and 0.062 cm−1 corresponding to two different pseudo-potentials, are reported. Two -dependent figures are given, in which the first shows an increase in the impact region with , based on as the basic parameter, and the second which shows a decrease in the impact region with , based on as the basic parameter.