Benchmarking density-functional-theory calculations of rotational g tensors and magnetizabilities using accurate coupled-cluster calculations.

Science.gov (United States)

Lutnaes, Ola B; Teale, Andrew M; Helgaker, Trygve; Tozer, David J; Ruud, Kenneth; Gauss, Jürgen

2009-10-14

An accurate set of benchmark rotational g tensors and magnetizabilities are calculated using coupled-cluster singles-doubles (CCSD) theory and coupled-cluster single-doubles-perturbative-triples [CCSD(T)] theory, in a variety of basis sets consisting of (rotational) London atomic orbitals. The accuracy of the results obtained is established for the rotational g tensors by careful comparison with experimental data, taking into account zero-point vibrational corrections. After an analysis of the basis sets employed, extrapolation techniques are used to provide estimates of the basis-set-limit quantities, thereby establishing an accurate benchmark data set. The utility of the data set is demonstrated by examining a wide variety of density functionals for the calculation of these properties. None of the density-functional methods are competitive with the CCSD or CCSD(T) methods. The need for a careful consideration of vibrational effects is clearly illustrated. Finally, the pure coupled-cluster results are compared with the results of density-functional calculations constrained to give the same electronic density. The importance of current dependence in exchange-correlation functionals is discussed in light of this comparison.

MODY - calculation of ordered structures by symmetry-adapted functions

Science.gov (United States)

Białas, Franciszek; Pytlik, Lucjan; Sikora, Wiesława

2016-01-01

In this paper we focus on the new version of computer program MODY for calculations of symmetryadapted functions based on the theory of groups and representations. The choice of such a functional frame of coordinates for description of ordered structures leads to a minimal number of parameters which must be used for presentation of such structures and investigations of their properties. The aim of this work is to find those parameters, which are coefficients of a linear combination of calculated functions, leading to construction of different types of structure ordering with a given symmetry. A spreadsheet script for simplification of this work has been created and attached to the program.

Evaluation of exchange-correlation functionals for time-dependent density functional theory calculations on metal complexes.

Science.gov (United States)

Holland, Jason P; Green, Jennifer C

2010-04-15

The electronic absorption spectra of a range of copper and zinc complexes have been simulated by using time-dependent density functional theory (TD-DFT) calculations implemented in Gaussian03. In total, 41 exchange-correlation (XC) functionals including first-, second-, and third-generation (meta-generalized gradient approximation) DFT methods were compared in their ability to predict the experimental electronic absorption spectra. Both pure and hybrid DFT methods were tested and differences between restricted and unrestricted calculations were also investigated by comparison of analogous neutral zinc(II) and copper(II) complexes. TD-DFT calculated spectra were optimized with respect to the experimental electronic absorption spectra by use of a Matlab script. Direct comparison of the performance of each XC functional was achieved both qualitatively and quantitatively by comparison of optimized half-band widths, root-mean-squared errors (RMSE), energy scaling factors (epsilon(SF)), and overall quality-of-fit (Q(F)) parameters. Hybrid DFT methods were found to outperform all pure DFT functionals with B1LYP, B97-2, B97-1, X3LYP, and B98 functionals providing the highest quantitative and qualitative accuracy in both restricted and unrestricted systems. Of the functionals tested, B1LYP gave the most accurate results with both average RMSE and overall Q(F) 0.990) for the copper complexes. The XC functional performance in spin-restricted TD-DFT calculations on the zinc complexes was found to be slightly worse. PBE1PBE, mPW1PW91 and B1LYP gave the most accurate results with typical RMSE and Q(F) values between 5.3 and 7.3%, and epsilon(SF) around 0.930. These studies illustrate the power of modern TD-DFT calculations for exploring excited state transitions of metal complexes. 2009 Wiley Periodicals, Inc.

Green's function Monte Carlo calculations of /sup 4/He

Energy Technology Data Exchange (ETDEWEB)

Carlson, J.A.

1988-01-01

Green's Function Monte Carlo methods have been developed to study the ground state properties of light nuclei. These methods are shown to reproduce results of Faddeev calculations for A = 3, and are then used to calculate ground state energies, one- and two-body distribution functions, and the D-state probability for the alpha particle. Results are compared to variational Monte Carlo calculations for several nuclear interaction models. 31 refs.

Calculation of neutron importance function in fissionable assemblies using Monte Carlo method

International Nuclear Information System (INIS)

Feghhi, S. A. H.; Afarideh, H.; Shahriari, M.

2007-01-01

The purpose of the present work is to develop an efficient solution method to calculate neutron importance function in fissionable assemblies for all criticality conditions, using Monte Carlo Method. The neutron importance function has a well important role in perturbation theory and reactor dynamic calculations. Usually this function can be determined by calculating adjoint flux through out solving the Adjoint weighted transport equation with deterministic methods. However, in complex geometries these calculations are very difficult. In this article, considering the capabilities of MCNP code in solving problems with complex geometries and its closeness to physical concepts, a comprehensive method based on physical concept of neutron importance has been introduced for calculating neutron importance function in sub-critical, critical and supercritical conditions. For this means a computer program has been developed. The results of the method has been benchmarked with ANISN code calculations in 1 and 2 group modes for simple geometries and their correctness has been approved for all three criticality conditions. Ultimately, the efficiency of the method for complex geometries has been shown by calculation of neutron importance in MNSR research reactor

Calculation of neutron importance function in fissionable assemblies using Monte Carlo method

International Nuclear Information System (INIS)

Feghhi, S.A.H.; Shahriari, M.; Afarideh, H.

2007-01-01

The purpose of the present work is to develop an efficient solution method for the calculation of neutron importance function in fissionable assemblies for all criticality conditions, based on Monte Carlo calculations. The neutron importance function has an important role in perturbation theory and reactor dynamic calculations. Usually this function can be determined by calculating the adjoint flux while solving the adjoint weighted transport equation based on deterministic methods. However, in complex geometries these calculations are very complicated. In this article, considering the capabilities of MCNP code in solving problems with complex geometries and its closeness to physical concepts, a comprehensive method based on the physical concept of neutron importance has been introduced for calculating the neutron importance function in sub-critical, critical and super-critical conditions. For this propose a computer program has been developed. The results of the method have been benchmarked with ANISN code calculations in 1 and 2 group modes for simple geometries. The correctness of these results has been confirmed for all three criticality conditions. Finally, the efficiency of the method for complex geometries has been shown by the calculation of neutron importance in Miniature Neutron Source Reactor (MNSR) research reactor

Calculation of the pion-nucleon double spectral functions and applications

International Nuclear Information System (INIS)

Grether, D.

1986-01-01

In the present thesis the latest results from pion-pion and pion-nucleon phase analyses are applied in order to calculate the pion-nucleon double spectral functions which belong to the elastic unitarity in the t-channel. The equivalence of the partial wave projection of these spectral functions in the s-channel with the elastic t-channel unitarity is extensively discussed. After we summarize the aspects of the pion-nucleon system seeming in this connection interesting we discuss the Mandelstam method for the calculation of the spectral functions by means of the elastic t-channel unitarity as well as the applied input and present the results. Thereafter we use these results in order to calculate by means of a fixed t-channel dispersion relation the real parts of the t-channel cuts. Partial wave projections into the t-channel are proved as equivalent to the elastic t-channel unitarity. We study the compatibility of the asymptotic behaviour of the spectral functions relative to the energy with current Regge pole models. Finally we use our results in order to calculate the pion-nucleon partial waves by means of their Froissart-Gribov representations which follow from their analyticity at fixed energy. (orig./HSI) [de

Hybrid functional calculation of electronic and phonon structure of BaSnO3

International Nuclear Information System (INIS)

Kim, Bog G.; Jo, J.Y.; Cheong, S.W.

2013-01-01

Barium stannate, BaSnO 3 (BSO), with a cubic perovskite structure, has been highlighted as a promising host material for the next generation transparent oxide electrodes. This study examined theoretically the electronic structure and phonon structure of BSO using hybrid density functional theory based on the HSE06 functional. The electronic structure results of BSO were corrected by extending the phonon calculations based on the hybrid density functional. The fundamental thermal properties were also predicted based on a hybrid functional calculation. Overall, a detailed understanding of the electronic structure, phonon modes and phonon dispersion of BSO will provide a theoretical starting-point for engineering applications of this material. - Graphical Abstract: (a) Crystal structure of BaSnO 3 . The center ball is Ba and small (red) ball on edge is oxygen and SnO 6 octahedrons are plotted as polyhedron. (b) Electronic band structure along the high symmetry point in the Brillouin zone using the HSE06 hybrid functional. (c) The phonon dispersion curve calculated using the HSE06 hybrid functional (d) Zone center lowest energy F 1u phonon mode. Highlights: ► We report the full hybrid functional calculation of not only the electronic structure but also the phonon structure for BaSnO 3 . ► The band gap calculation of HSE06 revealed an indirect gap with 2.48 eV. ► The effective mass at the conduction band minimum and valence band maximum was calculated. ► In addition, the phonon structure of BSO was calculated using the HSE06 functional. ► Finally, the heat capacity was calculated and compared with the recent experimental result.

Calculating scattering matrices by wave function matching

International Nuclear Information System (INIS)

Zwierzycki, M.; Khomyakov, P.A.; Starikov, A.A.; Talanana, M.; Xu, P.X.; Karpan, V.M.; Marushchenko, I.; Brocks, G.; Kelly, P.J.; Xia, K.; Turek, I.; Bauer, G.E.W.

2008-01-01

The conductance of nanoscale structures can be conveniently related to their scattering properties expressed in terms of transmission and reflection coefficients. Wave function matching (WFM) is a transparent technique for calculating transmission and reflection matrices for any Hamiltonian that can be represented in tight-binding form. A first-principles Kohn-Sham Hamiltonian represented on a localized orbital basis or on a real space grid has such a form. WFM is based upon direct matching of the scattering-region wave function to the Bloch modes of ideal leads used to probe the scattering region. The purpose of this paper is to give a pedagogical introduction to WFM and present some illustrative examples of its use in practice. We briefly discuss WFM for calculating the conductance of atomic wires, using a real space grid implementation. A tight-binding muffin-tin orbital implementation very suitable for studying spin-dependent transport in layered magnetic materials is illustrated by looking at spin-dependent transmission through ideal and disordered interfaces. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Introduction to Density Functional Theory: Calculations by Hand on the Helium Atom

Science.gov (United States)

Baseden, Kyle A.; Tye, Jesse W.

2014-01-01

Density functional theory (DFT) is a type of electronic structure calculation that has rapidly gained popularity. In this article, we provide a step-by-step demonstration of a DFT calculation by hand on the helium atom using Slater's X-Alpha exchange functional on a single Gaussian-type orbital to represent the atomic wave function. This DFT…

Development of Calculation Module for Intake Retention Functions based on Occupational Intakes of Radionuclides

Energy Technology Data Exchange (ETDEWEB)

Noh, Siwan; Kwon, Tae-Eun; Lee, Jai-Ki [Hanyang Univ., Seoul (Korea, Republic of); Lee, Jong-Il; Kim, Jang-Lyul [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2014-10-15

In internal dosimetry, intake retention and excretion functions are essential to estimate intake activity using bioassay sample such as whole body counter, lung counter, and urine sample. Even though ICRP (International Commission on Radiological Protection)provides the functions in some ICRP publications, it is needed to calculate the functions because the functions from the publications are provided for very limited time. Thus, some computer program are generally used to calculate intake retention and excretion functions and estimate intake activity. OIR (Occupational Intakes of Radionuclides) will be published soon by ICRP, which totally replaces existing internal dosimetry models and relevant data including intake retention and excretion functions. Thus, the calculation tool for the functions is needed based on OIR. In this study, we developed calculation module for intake retention and excretion functions based on OIR using C++ programming language with Intel Math Kernel Library. In this study, we developed the intake retention and excretion function calculation module based on OIR using C++ programing language.

Development of Calculation Module for Intake Retention Functions based on Occupational Intakes of Radionuclides

International Nuclear Information System (INIS)

Noh, Siwan; Kwon, Tae-Eun; Lee, Jai-Ki; Lee, Jong-Il; Kim, Jang-Lyul

2014-01-01

In internal dosimetry, intake retention and excretion functions are essential to estimate intake activity using bioassay sample such as whole body counter, lung counter, and urine sample. Even though ICRP (International Commission on Radiological Protection)provides the functions in some ICRP publications, it is needed to calculate the functions because the functions from the publications are provided for very limited time. Thus, some computer program are generally used to calculate intake retention and excretion functions and estimate intake activity. OIR (Occupational Intakes of Radionuclides) will be published soon by ICRP, which totally replaces existing internal dosimetry models and relevant data including intake retention and excretion functions. Thus, the calculation tool for the functions is needed based on OIR. In this study, we developed calculation module for intake retention and excretion functions based on OIR using C++ programming language with Intel Math Kernel Library. In this study, we developed the intake retention and excretion function calculation module based on OIR using C++ programing language

Actuarial values calculated using the incomplete Gamma function

Directory of Open Access Journals (Sweden)

Giovanni Mingari Scarpello

2013-03-01

Full Text Available The complete expectation-of-life for a person and the actuarial present value of continuous life annuities are defined by integrals. In all of them at least one of the factors is a survival function value ratio. If de Moivre’s law of mortality is chosen, such integrals can easily be evaluated; but if the Makeham survival function is adopted, they are used to be calculated numerically. For the above actuarial figures, closed form integrations are hereafter provided by means of the incomplete Gamma function.

Development of NRESP98 Monte Carlo codes for the calculation of neutron response functions of neutron detectors. Calculation of the response function of spherical BF{sub 3} proportional counter

Energy Technology Data Exchange (ETDEWEB)

Hashimoto, M.; Saito, K.; Ando, H. [Power Reactor and Nuclear Fuel Development Corp., Oarai, Ibaraki (Japan). Oarai Engineering Center

1998-05-01

The method to calculate the response function of spherical BF{sub 3} proportional counter, which is commonly used as neutron dose rate meter and neutron spectrometer with multi moderator system, is developed. As the calculation code for evaluating the response function, the existing code series NRESP, the Monte Carlo code for the calculation of response function of neutron detectors, is selected. However, the application scope of the existing NRESP is restricted, the NRESP98 is tuned as generally applicable code, with expansion of the geometrical condition, the applicable element, etc. The NRESP98 is tested with the response function of the spherical BF{sub 3} proportional counter. Including the effect of the distribution of amplification factor, the detailed evaluation of the charged particle transportation and the effect of the statistical distribution, the result of NRESP98 calculation fit the experience within {+-}10%. (author)

Correlation functions for fully or partially state-resolved reactive scattering calculations

International Nuclear Information System (INIS)

Manthe, Uwe; Welsch, Ralph

2014-01-01

Flux correlation functions and the quantum transition state concept are important tools for the accurate description of polyatomic reaction processes. Combined with the multi-configurational time-dependent Hartree approach, they facilitate rigorous full-dimensional calculations of cumulative and initial-state selected reaction probabilities for six atom reactions. In recent work [R. Welsch, F. Huarte-Larrañaga, and U. Manthe, J. Chem. Phys. 136, 064117 (2012)], an approach which allows one to calculate also state-to-state reaction probabilities within the quantum transition state concept has been introduced. This article presents further developments. Alternative generalized flux correlation functions are introduced and discussed. Equations for the calculation of fully state-resolved differential cross section using arbitrary definitions of the body fixed frame are derived. An approach for the efficient calculation of partially state-resolved observables as a function of the collision energy is introduced. Finally, numerical test studying the D + H 2 reaction illustrate important aspects of the formalism

The calculation of isotopic partition function ratios by a perturbation theory technique

International Nuclear Information System (INIS)

Singh, G.; Wolfsberg, M.

1975-01-01

The vibrational Hamiltonian of a molecule in the harmonic approximation, H = (1/2) Σ (g/subi/jp/subi/p/subj/ + f/subi/jq/subi/q/subj/), has been divided into a diagonal part (terms with i=j) and an off-diagonal part (inot-equalj), which is regarded as the perturbation. The vibrational partition function of the molecule is then calculated by Schwinger perturbation theory as the partition function of the unperturbed problem, corresponding to a collection of oscillators with frequencies 2πν/subi/' = (f/subi/ig/subi/i)/sup 1 / 2 /, plus perturbation correction terms which are calculated to second order. With the usual assumptions of isotope effect calculations that the molecular translations and rotations are classical and separable from the vibrations, the perturbation formulation of the vibrational partition function is easily transformed into a perturbation theory formulation of (reduced) isotopic partition function ratios. If, for example, the molecular potential function is expressed in terms of the displacements of bond stretches and bond angle bends from their respective equilibrium values, the unperturbed partition function ratio corresponds to the isotope effect expected for noninteracting bond-stretch and bond-angle-bend oscillators. Detailed comparison is made for a number of molecular systems of perturbation theory calculations of partition functions and isotopic partition function ratios with exact calculations carried out by actually obtaining the normal mode vibrational frequencies of the vibrational Hamiltonian. Good agreement is found. The utility of the perturbation theory formulation resides in the fact that it permits one to look at isotope effects in a very simple manner; some demonstrations are given

Nodewise analytical calculation of the transfer function

International Nuclear Information System (INIS)

Makai, Mihaly

1994-01-01

The space dependence of neutron noise has so far been mostly investigated in homogeneous core models. Application of core diagnostic methods to locate a malfunction requires however that the transfer function be calculated for real, inhomogeneous cores. A code suitable for such purpose must be able to handle complex arithmetic and delta-function source. Further requirements are analytical dependence in one spatial variable and fast execution. The present work describes the TIDE program written to fulfil the above requirements. The core is subdivided into homogeneous, square assemblies. An analytical solution is given, which is a generalisation of the inhomogeneous response matrix method. (author)

Self-consistent green function calculations for isospin asymmetric nuclear matter

International Nuclear Information System (INIS)

Mansour, Hesham; Gad, Khalaf; Hassaneen, Khaled S.A.

2010-01-01

The one-body potentials for protons and neutrons are obtained from the self-consistent Green-function calculations of asymmetric nuclear matter, in particular their dependence on the degree of proton/neutron asymmetry. Results of the binding energy per nucleon as a function of the density and asymmetry parameter are presented for the self-consistent Green function approach using the CD-Bonn potential. For the sake of comparison, the same calculations are performed using the Brueckner-Hartree-Fock approximation. The contribution of the hole-hole terms leads to a repulsive contribution to the energy per nucleon which increases with the nuclear density. The incompressibility for asymmetric nuclear matter has been also investigated in the framework of the self-consistent Green-function approach using the CD-Bonn potential. The behavior of the incompressibility is studied for different values of the nuclear density and the neutron excess parameter. The nuclear symmetry potential at fixed nuclear density is also calculated and its value decreases with increasing the nucleon energy. In particular, the nuclear symmetry potential at saturation density changes from positive to negative values at nucleon kinetic energy of about 200 MeV. For the sake of comparison, the same calculations are performed using the Brueckner-Hartree-Fock approximation. The proton/neutron effective mass splitting in neutron-rich matter has been studied. The predicted isospin splitting of the proton/neutron effective mass splitting in neutron-rich matter is such that m n * ≥ m p * . (author)

Affordable and accurate large-scale hybrid-functional calculations on GPU-accelerated supercomputers

Science.gov (United States)

Ratcliff, Laura E.; Degomme, A.; Flores-Livas, José A.; Goedecker, Stefan; Genovese, Luigi

2018-03-01

Performing high accuracy hybrid functional calculations for condensed matter systems containing a large number of atoms is at present computationally very demanding or even out of reach if high quality basis sets are used. We present a highly optimized multiple graphics processing unit implementation of the exact exchange operator which allows one to perform fast hybrid functional density-functional theory (DFT) calculations with systematic basis sets without additional approximations for up to a thousand atoms. With this method hybrid DFT calculations of high quality become accessible on state-of-the-art supercomputers within a time-to-solution that is of the same order of magnitude as traditional semilocal-GGA functionals. The method is implemented in a portable open-source library.

The calculations of small molecular conformation energy differences by density functional method

Science.gov (United States)

Topol, I. A.; Burt, S. K.

1993-03-01

The differences in the conformational energies for the gauche (G) and trans(T) conformers of 1,2-difluoroethane and for myo-and scyllo-conformer of inositol have been calculated by local density functional method (LDF approximation) with geometry optimization using different sets of calculation parameters. It is shown that in the contrast to Hartree—Fock methods, density functional calculations reproduce the correct sign and value of the gauche effect for 1,2-difluoroethane and energy difference for both conformers of inositol. The results of normal vibrational analysis for1,2-difluoroethane showed that harmonic frequencies calculated in LDF approximation agree with experimental data with the accuracy typical for scaled large basis set Hartree—Fock calculations.

Calculating the knowledge-based similarity of functional groups using crystallographic data

Science.gov (United States)

Watson, Paul; Willett, Peter; Gillet, Valerie J.; Verdonk, Marcel L.

2001-09-01

A knowledge-based method for calculating the similarity of functional groups is described and validated. The method is based on experimental information derived from small molecule crystal structures. These data are used in the form of scatterplots that show the likelihood of a non-bonded interaction being formed between functional group A (the `central group') and functional group B (the `contact group' or `probe'). The scatterplots are converted into three-dimensional maps that show the propensity of the probe at different positions around the central group. Here we describe how to calculate the similarity of a pair of central groups based on these maps. The similarity method is validated using bioisosteric functional group pairs identified in the Bioster database and Relibase. The Bioster database is a critical compilation of thousands of bioisosteric molecule pairs, including drugs, enzyme inhibitors and agrochemicals. Relibase is an object-oriented database containing structural data about protein-ligand interactions. The distributions of the similarities of the bioisosteric functional group pairs are compared with similarities for all the possible pairs in IsoStar, and are found to be significantly different. Enrichment factors are also calculated showing the similarity method is statistically significantly better than random in predicting bioisosteric functional group pairs.

Optical rotation calculated with time-dependent density functional theory: the OR45 benchmark.

Science.gov (United States)

Srebro, Monika; Govind, Niranjan; de Jong, Wibe A; Autschbach, Jochen

2011-10-13

Time-dependent density functional theory (TDDFT) computations are performed for 42 organic molecules and three transition metal complexes, with experimental molar optical rotations ranging from 2 to 2 × 10(4) deg cm(2) dmol(-1). The performances of the global hybrid functionals B3LYP, PBE0, and BHLYP, and of the range-separated functionals CAM-B3LYP and LC-PBE0 (the latter being fully long-range corrected), are investigated. The performance of different basis sets is studied. When compared to liquid-phase experimental data, the range-separated functionals do, on average, not perform better than B3LYP and PBE0. Median relative deviations between calculations and experiment range from 25 to 29%. A basis set recently proposed for optical rotation calculations (LPol-ds) on average does not give improved results compared to aug-cc-pVDZ in TDDFT calculations with B3LYP. Individual cases are discussed in some detail, among them norbornenone for which the LC-PBE0 functional produced an optical rotation that is close to available data from coupled-cluster calculations, but significantly smaller in magnitude than the liquid-phase experimental value. Range-separated functionals and BHLYP perform well for helicenes and helicene derivatives. Metal complexes pose a challenge to first-principles calculations of optical rotation.

Non-invasive mapping of calculation function by repetitive navigated transcranial magnetic stimulation.

Science.gov (United States)

Maurer, Stefanie; Tanigawa, Noriko; Sollmann, Nico; Hauck, Theresa; Ille, Sebastian; Boeckh-Behrens, Tobias; Meyer, Bernhard; Krieg, Sandro M

2016-11-01

Concerning calculation function, studies have already reported on localizing computational function in patients and volunteers by functional magnetic resonance imaging and transcranial magnetic stimulation. However, the development of accurate repetitive navigated TMS (rTMS) with a considerably higher spatial resolution opens a new field in cognitive neuroscience. This study was therefore designed to evaluate the feasibility of rTMS for locating cortical calculation function in healthy volunteers, and to establish this technique for future scientific applications as well as preoperative mapping in brain tumor patients. Twenty healthy subjects underwent rTMS calculation mapping using 5 Hz/10 pulses. Fifty-two previously determined cortical spots of the whole hemispheres were stimulated on both sides. The subjects were instructed to perform the calculation task composed of 80 simple arithmetic operations while rTMS pulses were applied. The highest error rate (80 %) for all errors of all subjects was observed in the right ventral precentral gyrus. Concerning division task, a 45 % error rate was achieved in the left middle frontal gyrus. The subtraction task showed its highest error rate (40 %) in the right angular gyrus (anG). In the addition task a 35 % error rate was observed in the left anterior superior temporal gyrus. Lastly, the multiplication task induced a maximum error rate of 30 % in the left anG. rTMS seems feasible as a way to locate cortical calculation function. Besides language function, the cortical localizations are well in accordance with the current literature for other modalities or lesion studies.

An efficient method for hybrid density functional calculation with spin-orbit coupling

Science.gov (United States)

Wang, Maoyuan; Liu, Gui-Bin; Guo, Hong; Yao, Yugui

2018-03-01

In first-principles calculations, hybrid functional is often used to improve accuracy from local exchange correlation functionals. A drawback is that evaluating the hybrid functional needs significantly more computing effort. When spin-orbit coupling (SOC) is taken into account, the non-collinear spin structure increases computing effort by at least eight times. As a result, hybrid functional calculations with SOC are intractable in most cases. In this paper, we present an approximate solution to this problem by developing an efficient method based on a mixed linear combination of atomic orbital (LCAO) scheme. We demonstrate the power of this method using several examples and we show that the results compare very well with those of direct hybrid functional calculations with SOC, yet the method only requires a computing effort similar to that without SOC. The presented technique provides a good balance between computing efficiency and accuracy, and it can be extended to magnetic materials.

A J matrix engine for density functional theory calculations

International Nuclear Information System (INIS)

White, C.A.; Head-Gordon, M.

1996-01-01

We introduce a new method for the formation of the J matrix (Coulomb interaction matrix) within a basis of Cartesian Gaussian functions, as needed in density functional theory and Hartree endash Fock calculations. By summing the density matrix into the underlying Gaussian integral formulas, we have developed a J matrix open-quote open-quote engine close-quote close-quote which forms the exact J matrix without explicitly forming the full set of two electron integral intermediates. Several precomputable quantities have been identified, substantially reducing the number of floating point operations and memory accesses needed in a J matrix calculation. Initial timings indicate a speedup of greater than four times for the (pp parallel pp) class of integrals with speedups increasing to over ten times for (ff parallel ff) integrals. copyright 1996 American Institute of Physics

Lagrange polynomial interpolation method applied in the calculation of the J({xi},{beta}) function

Energy Technology Data Exchange (ETDEWEB)

Fraga, Vinicius Munhoz; Palma, Daniel Artur Pinheiro [Centro Federal de Educacao Tecnologica de Quimica de Nilopolis, RJ (Brazil)]. E-mails: munhoz.vf@gmail.com; dpalma@cefeteq.br; Martinez, Aquilino Senra [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Coordenacao dos Programas de Pos-graduacao de Engenharia (COPPE) (COPPE). Programa de Engenharia Nuclear]. E-mail: aquilino@lmp.ufrj.br

2008-07-01

The explicit dependence of the Doppler broadening function creates difficulties in the obtaining an analytical expression for J function . The objective of this paper is to present a method for the quick and accurate calculation of J function based on the recent advances in the calculation of the Doppler broadening function and on a systematic analysis of its integrand. The methodology proposed, of a semi-analytical nature, uses the Lagrange polynomial interpolation method and the Frobenius formulation in the calculation of Doppler broadening function . The results have proven satisfactory from the standpoint of accuracy and processing time. (author)

Lagrange polynomial interpolation method applied in the calculation of the J(ξ,β) function

International Nuclear Information System (INIS)

Fraga, Vinicius Munhoz; Palma, Daniel Artur Pinheiro; Martinez, Aquilino Senra

2008-01-01

The explicit dependence of the Doppler broadening function creates difficulties in the obtaining an analytical expression for J function . The objective of this paper is to present a method for the quick and accurate calculation of J function based on the recent advances in the calculation of the Doppler broadening function and on a systematic analysis of its integrand. The methodology proposed, of a semi-analytical nature, uses the Lagrange polynomial interpolation method and the Frobenius formulation in the calculation of Doppler broadening function . The results have proven satisfactory from the standpoint of accuracy and processing time. (author)

Molecular structures from density functional calculations with simulated annealing

International Nuclear Information System (INIS)

Jones, R.O.

1991-01-01

The geometrical structure of any aggregate of atoms is one of its basic properties and, in principle, straightforward to predict. One chooses a structure, determines the total energy E of the system of electrons and ions, and repeats the calculation for all possible geometries. The ground state structure is that with the lowest energy. A quantum mechanical calculation of the exact wave function Ψ would lead to the total energy, but this is practicable only in very small molecules. Furthermore, the number of local minima in the energy surface increases dramatically with increasing molecular size. While traditional ab initio methods have had many impressive successes, the difficulties have meant that they have focused on systems with relatively few local minima, or have used experiments or experience to limit the range of geometries studied. On the other hand, calculations for much larger molecules and extended systems are often forced to use simplifying assumptions about the interatomic forces that limit their predictive capability. The approach described here avoids both of these extremes: Total energies of predictive value are calculated without using semi-empirical force laws, and the problem of multiple minima in the energy surface is addressed. The density functional formalism, with a local density approximation for the exchange-correlation energy, allows one to calculate the total energy for a given geometry in an efficient, if approximate, manner. Calculations for heavier elements are not significantly more difficult than for those in the first row and provide an ideal way to study bonding trends. When coupled with finite-temperature molecular dynamics, this formalism can avoid many of the energetically unfavorable minima in the energy surface. We show here that the method leads to surprising and exciting results. (orig.)

Calculating kaon fragmentation functions from the Nambu-Jona-Lasinio jet model

International Nuclear Information System (INIS)

Matevosyan, Hrayr H.; Thomas, Anthony W.; Bentz, Wolfgang

2011-01-01

The Nambu-Jona-Lasinio (NJL)-jet model provides a sound framework for calculating the fragmentation functions in an effective chiral quark theory, where the momentum and isospin sum rules are satisfied without the introduction of ad hoc parameters. Earlier studies of the pion fragmentation functions using the NJL model within this framework showed qualitative agreement with the empirical parametrizations. Here we extend the NJL-jet model by including the strange quark. The corrections to the pion fragmentation functions and corresponding kaon fragmentation functions are calculated using the elementary quark to quark-meson fragmentation functions from NJL. The results for the kaon fragmentation functions exhibit a qualitative agreement with the empirical parametrizations, while the unfavored strange quark fragmentation to pions is shown to be of the same order of magnitude as the unfavored light quark. The results of these studies are expected to provide important guidance for the analysis of a large variety of semi-inclusive data.

Measurement of human advanced brain function in calculation processing using functional magnetic resonance imaging (fMRI)

International Nuclear Information System (INIS)

Hashida, Masahiro; Yamauchi, Syuichi; Wu, Jing-Long

2001-01-01

Using functional magnetic resonance imaging (fMRI), we investigated the activated areas of the human brain related with calculation processing as an advanced function of the human brain. Furthermore, we investigated differences in activation between visual and auditory calculation processing. The eight subjects (all healthy men) were examined on a clinical MR unit (1.5 tesla) with a gradient echo-type EPI sequence. SPM99 software was used for data processing. Arithmetic problems were used for the visual stimulus (visual image) as well as for the auditory stimulus (audible voice). The stimuli were presented to the subjects as follows: no stimulation, presentation of random figures, and presentation of arithmetic problems. Activated areas of the human brain related with calculation processing were the inferior parietal lobule, middle frontal gyrus, and inferior frontal gyrus. Comparing the arithmetic problems with the presentation of random figures, we found that the activated areas of the human brain were not differently affected by visual and auditory systems. The areas activated in the visual and auditory experiments were observed at nearly the same place in the brain. It is possible to study advanced functions of the human brain such as calculation processing in a general clinical hospital when adequate tasks and methods of presentation are used. (author)

Generating bessel functions in mie scattering calculations using continued fractions.

Science.gov (United States)

Lentz, W J

1976-03-01

A new method of generating the Bessel functions and ratios of Bessel functions necessary for Mie calculations is presented. Accuracy is improved while eliminating the need for extended precision word lengths or large storage capability. The algorithm uses a new technique of evaluating continued fractions that starts at the beginning rather than the tail and has a built-in error check. The continued fraction representations for both spherical Bessel functions and ratios of Bessel functions of consecutive order are presented.

Further Stable methods for the calculation of partition functions

International Nuclear Information System (INIS)

Wilson, B G; Gilleron, F; Pain, J

2007-01-01

The extension to recursion over holes of the Gilleron and Pain method for calculating partition functions of a canonical ensemble of non-interacting bound electrons is presented as well as a generalization for the efficient computation of collisional line broadening

Next-to-leading QCD calculation of the heavy quark fragmentation function

International Nuclear Information System (INIS)

Mele, B.; Nason, P.

1990-01-01

We present the results of a next-to-leading order QCD calculation of the fragmentation function of b flavoured hadrons at LEP. We find that the addition of the next-to-leading effects improves the stability of the result under changes of the evolution scale and does not alter drastically the leading order prediction. Our next-to-leading calculation suggests that, if we neglect non-perturbative effects, the b fragmentation function is peaked at fairly large values of x, even if the average value of x is not necessarily large. (orig.)

Self-interaction corrected density functional calculations of molecular Rydberg states

International Nuclear Information System (INIS)

Gudmundsdóttir, Hildur; Zhang, Yao; Weber, Peter M.; Jónsson, Hannes

2013-01-01

A method is presented for calculating the wave function and energy of Rydberg excited states of molecules. A good estimate of the Rydberg state orbital is obtained using ground state density functional theory including Perdew-Zunger self-interaction correction and an optimized effective potential. The total energy of the excited molecule is obtained using the Delta Self-Consistent Field method where an electron is removed from the highest occupied orbital and placed in the Rydberg orbital. Results are presented for the first few Rydberg states of NH 3 , H 2 O, H 2 CO, C 2 H 4 , and N(CH 3 ) 3 . The mean absolute error in the energy of the 33 molecular Rydberg states presented here is 0.18 eV. The orbitals are represented on a real space grid, avoiding the dependence on diffuse atomic basis sets. As in standard density functional theory calculations, the computational effort scales as NM 2 where N is the number of orbitals and M is the number of grid points included in the calculation. Due to the slow scaling of the computational effort with system size and the high level of parallelism in the real space grid approach, the method presented here makes it possible to estimate Rydberg electron binding energy in large molecules

FPSPH DFPSPF, Line Shape Function for Doppler Broadened Resonance Cross-Sections Calculation

International Nuclear Information System (INIS)

Ribon, P.

1982-01-01

1 - Description of problem or function: In the computation of Doppler- broadened resonance cross sections, use is made of the symmetric and anti-symmetric line shape functions. These functions usually denoted as Psi and Phi (Psi and Chi in Anglo-Saxon formalism) are defined in terms of the real and imaginary parts of the error function for complex arguments. They are the product of the convolution of a Gaussian function with the symmetric and anti-symmetric Breit-Wigner functions, respectively. FPSPH and DFPSPH compute these functions. 2 - Method of solution: For (1+x 2 ) > 20 Beta 2 , the calculation is based upon the asymptotic expansion: Psi+(i*Phi) = 1/(1-ix)*(1-t+3t 2 -3.5t 3 +3.5+7t 4 ---), with: t = 1/(2z 2 ); z = (1-ix)/Beta. The half-plane (Beta,x) is split in several parts, and use is made of PADE approximants. For 1 + x 2 2 , the calculation is based upon the relation with the erf function: Psi + i*Phi = SQRT(Pi)/Beta*(e (z 2 ) )*(1-erf(z)) (z = (1-ix)/Beta, and erf(z) being calculated from its analytic expansion: erf(z) = 2/SQRT(Pi)*z*e (-z 2 ) *(1+z 2 /3+z 4 /(3*5) + z 6 /(3*5*7)+---). PADE approximants are used to compute the expansion and e z 2

Calculation of parton fragmentation functions from jet calculus: gluon applications

International Nuclear Information System (INIS)

Lassila, K.E.; Ng, A.

1985-01-01

A method is presented for calculation of general parton fragmentation functions based on jet calculus plus meson and baryon wave functions. Results for gluon fragmentation into mesons and baryons are discussed and related to recent information on upsilon decay into gluons. The expressions derived can be used directly in e + e - cross section predictions and will need to be folded in with baryon parton distribution functions when used in p-barp collisions. (author)

Analytic calculations of hyper-Raman spectra from density functional theory hyperpolarizability gradients

Energy Technology Data Exchange (ETDEWEB)

Ringholm, Magnus; Ruud, Kenneth [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø – The Arctic University of Norway, 9037 Tromsø (Norway); Bast, Radovan [Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology, AlbaNova University Center, S-10691 Stockholm (Sweden); PDC Center for High Performance Computing, Royal Institute of Technology, S-10044 Stockholm (Sweden); Oggioni, Luca [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø – The Arctic University of Norway, 9037 Tromsø (Norway); Department of Physics G. Occhialini, University of Milano Bicocca, Piazza della scienza 3, 20126 Milan (Italy); Ekström, Ulf [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, 0315 Oslo (Norway)

2014-10-07

We present the first analytic calculations of the geometrical gradients of the first hyperpolarizability tensors at the density-functional theory (DFT) level. We use the analytically calculated hyperpolarizability gradients to explore the importance of electron correlation effects, as described by DFT, on hyper-Raman spectra. In particular, we calculate the hyper-Raman spectra of the all-trans and 11-cis isomers of retinal at the Hartree-Fock (HF) and density-functional levels of theory, also allowing us to explore the sensitivity of the hyper-Raman spectra on the geometrical characteristics of these structurally related molecules. We show that the HF results, using B3LYP-calculated vibrational frequencies and force fields, reproduce the experimental data for all-trans-retinal well, and that electron correlation effects are of minor importance for the hyper-Raman intensities.

Microhartree precision in density functional theory calculations

Science.gov (United States)

Gulans, Andris; Kozhevnikov, Anton; Draxl, Claudia

2018-04-01

To address ultimate precision in density functional theory calculations we employ the full-potential linearized augmented plane-wave + local-orbital (LAPW + lo) method and justify its usage as a benchmark method. LAPW + lo and two completely unrelated numerical approaches, the multiresolution analysis (MRA) and the linear combination of atomic orbitals, yield total energies of atoms with mean deviations of 0.9 and 0.2 μ Ha , respectively. Spectacular agreement with the MRA is reached also for total and atomization energies of the G2-1 set consisting of 55 molecules. With the example of α iron we demonstrate the capability of LAPW + lo to reach μ Ha /atom precision also for periodic systems, which allows also for the distinction between the numerical precision and the accuracy of a given functional.

Reducing Systematic Errors in Oxide Species with Density Functional Theory Calculations

DEFF Research Database (Denmark)

Christensen, Rune; Hummelshøj, Jens S.; Hansen, Heine Anton

2015-01-01

Density functional theory calculations can be used to gain valuable insight into the fundamental reaction processes in metal−oxygen systems, e.g., metal−oxygen batteries. Here, the ability of a range of different exchange-correlation functionals to reproduce experimental enthalpies of formation...

Calculation and applications of the frequency dependent neutron detector response functions

International Nuclear Information System (INIS)

Van Dam, H.; Van Hagen, T.H.J.J. der; Hoogenboom, J.E.; Keijzer, J.

1994-01-01

The theoretical basis is presented for the evaluation of the frequency dependent function that enables to calculate the response of a neutron detector to parametric fluctuations ('noise') or oscillations in reactor core. This function describes the 'field view' of a detector and can be calculated with a static transport code under certain conditions which are discussed. Two applications are presented: the response of an ex-core detector to void fraction fluctuations in a BWR and of both in and ex-core detectors to a rotating neutron absorber near or inside a research reactor core. (authors). 7 refs., 4 figs

Semi-classical calculation of the spin-isospin response functions

International Nuclear Information System (INIS)

Chanfray, G.

1987-03-01

We present a semi-classical calculation of the nuclear response functions beyond the Thomas-Fermi approximation. We apply our formalism to the spin-isospin responses and show that the surface peaked h/2π corrections considerably decrease the ratio longitudinal/transverse as obtained through hadronic probes

Combined hybrid functional and DFT+U calculations for metal chalcogenides

Energy Technology Data Exchange (ETDEWEB)

Aras, Mehmet; Kılıç, Çetin, E-mail: cetin-kilic@gyte.edu.tr [Department of Physics, Gebze Institute of Technology, Gebze, Kocaeli 41400 (Turkey)

2014-07-28

In the density-functional studies of materials with localized electronic states, the local/semilocal exchange-correlation functionals are often either combined with a Hubbard parameter U as in the LDA+U method or mixed with a fraction of exactly computed (Fock) exchange energy yielding a hybrid functional. Although some inaccuracies of the semilocal density approximations are thus fixed to a certain extent, the improvements are not sufficient to make the predictions agree with the experimental data. Here, we put forward the perspective that the hybrid functional scheme and the LDA+U method should be treated as complementary, and propose to combine the range-separated Heyd-Scuseria-Ernzerhof (HSE) hybrid functional with the Hubbard U. We thus present a variety of HSE+U calculations for a set of II-VI semiconductors, consisting of zinc and cadmium monochalcogenides, along with comparison to the experimental data. Our findings imply that an optimal value U{sup *} of the Hubbard parameter could be determined, which ensures that the HSE+U{sup *} calculation reproduces the experimental band gap. It is shown that an improved description not only of the electronic structure but also of the crystal structure and energetics is obtained by adding the U{sup *} term to the HSE functional, proving the utility of HSE+U{sup *} approach in modeling semiconductors with localized electronic states.

Configurational forces in electronic structure calculations using Kohn-Sham density functional theory

Science.gov (United 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].

Application of an excited state LDA exchange energy functional for the calculation of transition energy of atoms within time-independent density functional theory

Energy Technology Data Exchange (ETDEWEB)

Shamim, Md; Harbola, Manoj K, E-mail: sami@iitk.ac.i, E-mail: mkh@iitk.ac.i [Department of Physics, Indian Institute of Technology, Kanpur 208 016 (India)

2010-11-14

Transition energies of a new class of excited states (two-gap systems) of various atoms are calculated in time-independent density functional formalism by using a recently proposed local density approximation exchange energy functional for excited states. It is shown that the excitation energies calculated with this functional compare well with those calculated with exact exchange theories.

Application of an excited state LDA exchange energy functional for the calculation of transition energy of atoms within time-independent density functional theory

International Nuclear Information System (INIS)

Shamim, Md; Harbola, Manoj K

2010-01-01

Transition energies of a new class of excited states (two-gap systems) of various atoms are calculated in time-independent density functional formalism by using a recently proposed local density approximation exchange energy functional for excited states. It is shown that the excitation energies calculated with this functional compare well with those calculated with exact exchange theories.

Surface regulated arsenenes as Dirac materials: From density functional calculations

International Nuclear Information System (INIS)

Yuan, Junhui; Xie, Qingxing; Yu, Niannian; Wang, Jiafu

2017-01-01

Highlights: • The presence of Dirac cones in chemically decorated buckled arsenene AsX (X = CN, NC, NCO, NCS, and NCSe) has been revealed. • First-principles calculations show that all these chemically decorated arsenenes are kinetically stable in defending thermal fluctuations in room temperature. - Abstract: Using first principle calculations based on density functional theory (DFT), we have systematically investigated the structure stability and electronic properties of chemically decorated arsenenes, AsX (X = CN, NC, NCO, NCS and NCSe). Phonon dispersion and formation energy analysis reveal that all the five chemically decorated buckled arsenenes are energetically favorable and could be synthesized. Our study shows that wide-bandgap arsenene would turn into Dirac materials when functionalized by -X (X = CN, NC, NCO, NCS and NCSe) groups, rendering new promises in next generation high-performance electronic devices.

Conjugate-gradient optimization method for orbital-free density functional calculations.

Science.gov (United States)

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.

Particle-hole calculation of the longitudinal response function of 12C

International Nuclear Information System (INIS)

Dellafiore, A.; Lenz, F.; Brieva, F.A.

1985-01-01

The longitudinal response function of 12 C in the range of momentum transfers 200 MeV/c< or =q< or =550 MeV/c is calculated in the Tamm-Dancoff approximation. The particle-hole Green's function is evaluated by means of a doorway-state expansion. This method allows us to take into account finite-range residual interactions in the continuum, including exchange processes. At low momentum transfers, calculations agree qualitatively with the data. The data cannot be reproduced at momentum transfers around 450 MeV/c. This discrepancy can be accounted for neither by uncertainties in the residual interaction, nor by more complicated processes in the nuclear final states

Off-gas treatment carbon footprint calculator : form and function

Energy Technology Data Exchange (ETDEWEB)

Kessell, L. [Good EarthKeeping Organization Inc., Corona, CA (United States); Squire, J.; Crosby, K. [Haley and Aldrich Inc., Boston, MA (United States)

2008-07-01

Carbon footprinting is the measurement of the impact on the environment in terms of the amount of greenhouse gases produced, measured in units of carbon dioxide released directly and indirectly by an individual, organization, process, event or product. This presentation discussed an off-gas treatment carbon footprint calculator. The presentation provided a review of off-gas treatment technologies and presented a carbon footprint model. The model included: form and function; parameters; assumptions; calculations; and off-gas treatment applications. Parameters of the model included greenhouse gases listed in the Kyoto Protocol to the United Nations Framework Convention on Climate Change, such as carbon dioxide, methane, nitrous oxide, sulfur hexafluoride, hydrofluorocarbons, and perfluorocarbons. Assumptions of the model included stationary combustion emissions; mobile combustion emissions; indirect emissions; physical or chemical processing emissions; fugitive emissions; and de minimus emissions. The presentation also examined resource conservation and discussed three greenhouse gas footprint case studies. It was concluded that the model involved a calculator with standard calculations with clearly defined assumptions with boundaries. tabs., figs.

Subtleties in the beta-function calculation of N = 1 supersymmetric gauge theories

Energy Technology Data Exchange (ETDEWEB)

Cherchiglia, A.L. [ICEx, Universidade Federal de Minas Gerais, Departamento de Fisica, P.O. Box 702, Belo Horizonte, MG (Brazil); Universidad de Granada, Departamento de Fisica Teorica y del Cosmos and CAFPE, Granada (Spain); Sampaio, Marcos [ICEx, Universidade Federal de Minas Gerais, Departamento de Fisica, P.O. Box 702, Belo Horizonte, MG (Brazil); Hiller, B. [CFisUC, Universidade de Coimbra, Departamento de Fisica, Faculdade de Ciencias e Tecnologia, Coimbra (Portugal); Scarpelli, A.P.B. [Setor Tecnico-Cientifico, Departamento de Policia Federal, Sao Paulo (Brazil)

2016-02-15

We investigate some peculiarities in the calculation of the two-loop beta function of N = 1 supersymmetric models which are intimately related to the so-called ''anomaly puzzle''. There is an apparent paradox when the computation is performed in the framework of the covariant derivative background field method. In this formalism, there is obtained a finite two-loop effective action, although a non-null coefficient for the beta function is achieved by means of the renormalized two-point function in the background field. We show that if the standard background field method is used, this two-point function has a divergent part which allows for the calculation of the beta function via the renormalization constants, as usual. Therefore, we conjecture that this paradox has its origin in the covariant supergraph formalism itself, possibly being an artifact of the rescaling anomaly. (orig.)

Subtleties in the beta-function calculation of N = 1 supersymmetric gauge theories

International Nuclear Information System (INIS)

Cherchiglia, A.L.; Sampaio, Marcos; Hiller, B.; Scarpelli, A.P.B.

2016-01-01

We investigate some peculiarities in the calculation of the two-loop beta function of N = 1 supersymmetric models which are intimately related to the so-called ''anomaly puzzle''. There is an apparent paradox when the computation is performed in the framework of the covariant derivative background field method. In this formalism, there is obtained a finite two-loop effective action, although a non-null coefficient for the beta function is achieved by means of the renormalized two-point function in the background field. We show that if the standard background field method is used, this two-point function has a divergent part which allows for the calculation of the beta function via the renormalization constants, as usual. Therefore, we conjecture that this paradox has its origin in the covariant supergraph formalism itself, possibly being an artifact of the rescaling anomaly. (orig.)

Bessel function expansion to reduce the calculation time and memory usage for cylindrical computer-generated holograms.

Science.gov (United States)

Sando, Yusuke; Barada, Daisuke; Jackin, Boaz Jessie; Yatagai, Toyohiko

2017-07-10

This study proposes a method to reduce the calculation time and memory usage required for calculating cylindrical computer-generated holograms. The wavefront on the cylindrical observation surface is represented as a convolution integral in the 3D Fourier domain. The Fourier transformation of the kernel function involving this convolution integral is analytically performed using a Bessel function expansion. The analytical solution can drastically reduce the calculation time and the memory usage without any cost, compared with the numerical method using fast Fourier transform to Fourier transform the kernel function. In this study, we present the analytical derivation, the efficient calculation of Bessel function series, and a numerical simulation. Furthermore, we demonstrate the effectiveness of the analytical solution through comparisons of calculation time and memory usage.

Performance Improvement of the Core Protection Calculator System (CPCS) by Introducing Optimal Function Sets

International Nuclear Information System (INIS)

Won, Byung Hee; Kim, Kyung O; Kim, Jong Kyung; Kim, Soon Young

2012-01-01

The Core Protection Calculator System (CPCS) is an automated device which is adopted to inspect the safety parameters such as Departure from Nuclear Boiling Ratio (DNBR) and Local Power Density (LPD) during normal operation. One function of the CPCS is to predict the axial power distributions using function sets in cubic spline method. Another function of that is to impose penalty when the estimated distribution by the spline method disagrees with embedded data in CPCS (i.e., over 8%). In conventional CPCS, restricted function sets are used to synthesize axial power shape, whereby it occasionally can draw a disagreement between synthesized data and the embedded data. For this reason, the study on improvement for power distributions synthesis in CPCS has been conducted in many countries. In this study, many function sets (more than 18,000 types) differing from the conventional ones were evaluated in each power shape. Matlab code was used for calculating/arranging the numerous cases of function sets. Their synthesis performance was also evaluated through error between conventional data and consequences calculated by new function sets

First-row diatomics: Calculation of the geometry and energetics using self-consistent gradient-functional approximations

International Nuclear Information System (INIS)

Kutzler, F.W.; Painter, G.S.

1992-01-01

A fully self-consistent series of nonlocal (gradient) density-functional calculations has been carried out using the augmented-Gaussian-orbital method to determine the magnitude of gradient corrections to the potential-energy curves of the first-row diatomics, Li 2 through F 2 . Both the Langreth-Mehl-Hu and the Perdew-Wang gradient-density functionals were used in calculations of the binding energy, bond length, and vibrational frequency for each dimer. Comparison with results obtained in the local-spin-density approximation (LSDA) using the Vosko-Wilk-Nusair functional, and with experiment, reveals that bond lengths and vibrational frequencies are rather insensitive to details of the gradient functionals, including self-consistency effects, but the gradient corrections reduce the overbinding commonly observed in the LSDA calculations of first-row diatomics (with the exception of Li 2 , the gradient-functional binding-energy error is only 50--12 % of the LSDA error). The improved binding energies result from a large differential energy lowering, which occurs in open-shell atoms relative to the diatomics. The stabilization of the atom arises from the use of nonspherical charge and spin densities in the gradient-functional calculations. This stabilization is negligibly small in LSDA calculations performed with nonspherical densities

Calculation of intensity factors using weight function theory for a transversely isotropic piezoelectric material

International Nuclear Information System (INIS)

Son, In Ho; An, Deuk Man

2012-01-01

In fracture mechanics, the weight function can be used for calculating stress intensity factors. In this paper, a two dimensional electroelastic analysis is performed on a transversely isotropic piezoelectric material with an open crack. A plane strain formulation of the piezoelectric problem is solved within the Leknitskii formalism. Weight function theory is extended to piezoelectric materials. The stress intensity factors and electric displacement intensity factor are calculated by the weight function theory

Green's function calculation of the satellite spectrum of neon

International Nuclear Information System (INIS)

Kheifets, A.S.

1995-01-01

The single-hole Green's function with the lowest-order self-energy part has been used to calculate energies and spectroscopic factors of the neon ion ground and excited states which originated from the removal of the 2s and 2p valence electrons. The simplest two-hole-one-electron ion sates were included explicitly to the self-energy. More complex (m+l)-hole-m-electron states were treated implicitly by using the experimental energy of the two holes in the simplest ion states. The results of the calculation are found to be consistent with experimental satellite line positions and intensities obtained from recent photoionization and electron impact ionization measurements. 20 refs., 5 tabs

Ab initio calculation atomics ground state wave function for interactions Ion- Atom

International Nuclear Information System (INIS)

Shojaee, F.; Bolori zadeh, M. A.

2007-01-01

Ab initio calculation atomics ground state wave function for interactions Ion- Atom Atomic wave function expressed in a Slater - type basis obtained within Roothaan- Hartree - Fock for the ground state of the atoms He through B. The total energy is given for each atom.

Method of the reduced-added Green function in the calculation of atomic polarizabilities

International Nuclear Information System (INIS)

Chernov, V.E.; Dorofeev, D.L.; Kretinin, I.Yu.; Zon, B.A.

2005-01-01

The Green function in the quantum defect theory provides an exact account for high-excited and continuum electronic states. We modify it by taking into account the ground and low-excited states using their wave functions calculated ab initio. As an application, we present a simple and efficient semianalytical method for the calculation of atomic electric frequency-dependent scalar dipole polarizability, for both real and imaginary frequencies. The polarizabilities calculated for some atoms (Li, Na, K, Be, Mg, Ca, Si, P, S, O, Al, Ge, C, N, F, He, Ne, Ar, Kr, and Xe) are compared with existing methods of computational quantum chemistry and with experiments; good accuracy of the proposed method is demonstrated

Wave resistance calculation method combining Green functions based on Rankine and Kelvin source

Directory of Open Access Journals (Sweden)

LI Jingyu

2017-12-01

Full Text Available [Ojectives] At present, the Boundary Element Method(BEM of wave-making resistance mostly uses a model in which the velocity distribution near the hull is solved first, and the pressure integral is then calculated using the Bernoulli equation. However,the process of this model of wave-making resistance is complex and has low accuracy.[Methods] To address this problem, the present paper deduces a compound method for the quick calculation of ship wave resistance using the Rankine source Green function to solve the hull surface's source density, and combining the Lagally theorem concerning source point force calculation based on the Kelvin source Green function so as to solve the wave resistance. A case for the Wigley model is given.[Results] The results show that in contrast to the thin ship method of the linear wave resistance theorem, this method has higher precision, and in contrast to the method which completely uses the Kelvin source Green function, this method has better computational efficiency.[Conclusions] In general, the algorithm in this paper provides a compromise between precision and efficiency in wave-making resistance calculation.

Green's function approach to calculate spin injection in quantum dot

International Nuclear Information System (INIS)

Tan, S.G.; Jalil, M.B.A.; Liew, Thomas; Teo, K.L.

2006-01-01

We present a theoretical model to study spin injection (η) through a quantum dot system sandwiched by two ferromagnetic contacts. The effect of contact magnetization on η was studied using Green's function descriptions of the density of states. Green's function models have the advantages that coherent effects of temperature, electron occupation in the QD, and lead perturbation on the state wave function and hence the current can be formally included in the calculations. In addition, self-consistent treatment of current with applied electrochemical potential or lead conductivity, a necessary step which has not been considered in previous works, has also been implemented in our model

Electronic Structure Calculation of Permanent Magnets using the KKR Green's Function Method

Science.gov (United States)

Doi, Shotaro; Akai, Hisazumi

2014-03-01

Electronic structure and magnetic properties of permanent magnetic materials, especially Nd2Fe14B, are investigated theoretically using the KKR Green's function method. Important physical quantities in magnetism, such as magnetic moment, Curie temperature, and anisotropy constant, which are obtained from electronics structure calculations in both cases of atomic-sphere-approximation and full-potential treatment, are compared with past band structure calculations and experiments. The site preference of heavy rare-earth impurities are also evaluated through the calculation of formation energy with the use of coherent potential approximations. Further, the development of electronic structure calculation code using the screened KKR for large super-cells, which is aimed at studying the electronic structure of realistic microstructures (e.g. grain boundary phase), is introduced with some test calculations.

Calculation of the Green functions by the coupling constant dispersion relations

International Nuclear Information System (INIS)

Bogomalny, E.B.

1977-01-01

The discontinuities of the Green functions on the cut in the complex plane of the coupling constant are calculated by the steepest descent method. The saddle points are given by the solutions of the classical field equations at those values of the coupling constant for which the classical theory has no ground state. The Green functions at the physical values of the coupling constant are determined by dispersion relations. (Auth.)

Ballistic calculation of nonequilibrium Green's function in nanoscale devices using finite element method

International Nuclear Information System (INIS)

Kurniawan, O; Bai, P; Li, E

2009-01-01

A ballistic calculation of a full quantum mechanical system is presented to study 2D nanoscale devices. The simulation uses the nonequilibrium Green's function (NEGF) approach to calculate the transport properties of the devices. While most available software uses the finite difference discretization technique, our work opts to formulate the NEGF calculation using the finite element method (FEM). In calculating a ballistic device, the FEM gives some advantages. In the FEM, the floating boundary condition for ballistic devices is satisfied naturally. This paper gives a detailed finite element formulation of the NEGF calculation applied to a double-gate MOSFET device with a channel length of 10 nm and a body thickness of 3 nm. The potential, electron density, Fermi functions integrated over the transverse energy, local density of states and the transmission coefficient of the device have been studied. We found that the transmission coefficient is significantly affected by the top of the barrier between the source and the channel, which in turn depends on the gate control. This supports the claim that ballistic devices can be modelled by the transport properties at the top of the barrier. Hence, the full quantum mechanical calculation presented here confirms the theory of ballistic transport in nanoscale devices.

Fragment approach to constrained density functional theory calculations using Daubechies wavelets

International Nuclear Information System (INIS)

Ratcliff, Laura E.; Genovese, Luigi; Mohr, Stephan; Deutsch, Thierry

2015-01-01

In a recent paper, we presented a linear scaling Kohn-Sham density functional theory (DFT) code based on Daubechies wavelets, where a minimal set of localized support functions are optimized in situ and therefore adapted to the chemical properties of the molecular system. Thanks to the systematically controllable accuracy of the underlying basis set, this approach is able to provide an optimal contracted basis for a given system: accuracies for ground state energies and atomic forces are of the same quality as an uncontracted, cubic scaling approach. This basis set offers, by construction, a natural subset where the density matrix of the system can be projected. In this paper, we demonstrate the flexibility of this minimal basis formalism in providing a basis set that can be reused as-is, i.e., without reoptimization, for charge-constrained DFT calculations within a fragment approach. Support functions, represented in the underlying wavelet grid, of the template fragments are roto-translated with high numerical precision to the required positions and used as projectors for the charge weight function. We demonstrate the interest of this approach to express highly precise and efficient calculations for preparing diabatic states and for the computational setup of systems in complex environments

Fragment approach to constrained density functional theory calculations using Daubechies wavelets

Energy Technology Data Exchange (ETDEWEB)

Ratcliff, Laura E., E-mail: lratcliff@anl.gov [Argonne Leadership Computing Facility, Argonne National Laboratory, Lemont, Illinois 60439 (United States); Université de Grenoble Alpes, CEA, INAC-SP2M, L-Sim, F-38000 Grenoble (France); Genovese, Luigi; Mohr, Stephan; Deutsch, Thierry [Université de Grenoble Alpes, CEA, INAC-SP2M, L-Sim, F-38000 Grenoble (France)

2015-06-21

In a recent paper, we presented a linear scaling Kohn-Sham density functional theory (DFT) code based on Daubechies wavelets, where a minimal set of localized support functions are optimized in situ and therefore adapted to the chemical properties of the molecular system. Thanks to the systematically controllable accuracy of the underlying basis set, this approach is able to provide an optimal contracted basis for a given system: accuracies for ground state energies and atomic forces are of the same quality as an uncontracted, cubic scaling approach. This basis set offers, by construction, a natural subset where the density matrix of the system can be projected. In this paper, we demonstrate the flexibility of this minimal basis formalism in providing a basis set that can be reused as-is, i.e., without reoptimization, for charge-constrained DFT calculations within a fragment approach. Support functions, represented in the underlying wavelet grid, of the template fragments are roto-translated with high numerical precision to the required positions and used as projectors for the charge weight function. We demonstrate the interest of this approach to express highly precise and efficient calculations for preparing diabatic states and for the computational setup of systems in complex environments.

Calculation of nondiffused proximity functions from cloud-chamber data

International Nuclear Information System (INIS)

Zaider, M.

1987-01-01

To a large extent the cloud chamber is an ideal microdosimetric device: by measuring the positions of ionizing events in charged-particle tracks one can generate - with a flexibility matched only by Monte-Carlo simulations-any microdosimetric quantity of interest, ranging from lineal energy spectra (in volumes of practically arbitrary shape and size) to proximity functions, that is, distributions of distances between energy transfer points in the track. Cloud-chamber data analyzed in such ways have been indeed reported for a variety of radiations. In view of these clear advantages it is certainly surprising that, within the microdosimetric community, only one group (at Harwell, UK) is actively involved in such work and that, furthermore, cloud-chamber results are used essentially only as a testing ground for Monte-Carlo calculations. It appears that this reluctance can be traced to the fact that the tracks are distorted by the diffusion of droplets during their growth. This diffusion - which is of the order of several nanometers (in unit-density material), although rather insignificant vis-a-vis conventional microdosimetry, can be a serious limitation in view of modern theories of radiation action which emphasize energy deposition events at the nanometer level. The purpose of this research activity is to show that, using a rather straight-forward mathematical procedure, one can unfold the effect of diffusion from proximity functions. Since the nondiffused proximity function can be used to calculate other microdosimetric quantities an important limitation of the cloud-chamber data can thus be avoided

DFT calculations of electronic and optical properties of SrS with LDA, GGA and mGGA functionals

Energy Technology Data Exchange (ETDEWEB)

Sharma, Shatendra, E-mail: shatendra@gmai.com [University Science Instrumentation Centre, Jawaharlal Nehru University, New Delhi-110067 (India); Sharma, Jyotsna [School of Basic & Applied Sciences, K. R. Mangalam University, Sohna Road, Gurgaon-122103 (India); Sharma, Yogita [Department of Applied Sciences, KIIT, Sohna Road, Gurgaon-122103 (India)

2016-05-06

The theoretical investigations of electronic and optical properties of SrS are made using the first principle DFT calculations. The calculations are performed for the local-density approximation (LDA), generalized gradient approximation (GGA) and for an alternative form of GGA i.e. metaGGA for both rock salt type (B1, Fm3m) and cesium chloride (B2, Pm3m) structures. The band structure, density of states and optical spectra are calculated under various available functional. The calculations with LDA and GGA functional underestimate the values of band gaps with all functional, however the values with mGGA show reasonably good agreement with experimental and those calculated by using other methods.

Study on application of green's function method in thermal stress rapid calculation

International Nuclear Information System (INIS)

Zhang Guihe; Duan Yuangang; Xu Xiao; Chen Rong

2013-01-01

This paper presents a quick and accuracy thermal stress calculation method, the Green's Function Method, which is a combination of finite element method and numerical algorithm method. Thermal stress calculation of Safe Injection Nozzle of Reactor Coolant Line of PWR plant is performed with Green's function method for heatup and cooldown thermal transients as a demonstration example, and the result is compared with finite element method to verify the rationality and accuracy of this method. The advantage and disadvantage of the Green's function method and the finite element method are also compared. (authors)

A Pearson VII distribution function for fast calculation of dechanneling and angular dispersion of beams

International Nuclear Information System (INIS)

Shao Lin; Peng Luohan

2009-01-01

Although multiple scattering theories have been well developed, numerical calculation is complicated and only tabulated values have been available, which has caused inconvenience in practical use. We have found that a Pearson VII distribution function can be used to fit Lugujjo and Mayer's probability curves in describing the dechanneling phenomenon in backscattering analysis, over a wide range of disorder levels. Differentiation of the obtained function gives another function to calculate angular dispersion of the beam in the frameworks by Sigmund and Winterbon. The present work provides an easy calculation of both dechanneling probability and angular dispersion for any arbitrary combination of beam and target having a reduced thickness ≥0.6, which can be implemented in modeling of channeling spectra. Furthermore, we used a Monte Carlo simulation program to calculate the deflection probability and compared them with previously tabulated data. A good agreement was reached.

Hybrid functional band gap calculation of SnO6 containing perovskites and their derived structures

International Nuclear Information System (INIS)

Lee, Hyewon; Cheong, S.W.; Kim, Bog G.

2015-01-01

We have studied the properties of SnO 6 octahedra-containing perovskites and their derived structures using ab initio calculations with different density functionals. In order to predict the correct band gap of the materials, we have used B3LYP hybrid density functional, and the results of B3LYP were compared with those obtained using the local density approximation and generalized gradient approximation data. The calculations have been conducted for the orthorhombic ground state of the SnO 6 containing perovskites. We also have expended the hybrid density functional calculation to the ASnO 3 /A'SnO 3 system with different cation orderings. We propose an empirical relationship between the tolerance factor and the band gap of SnO 6 containing oxide materials based on first principles calculation. - Graphical abstract: (a) Structure of ASnO 3 for orthorhombic ground state. The green ball is A (Ba, Sr, Ca) cation and the small (red) ball on edge is oxygen. SnO 6 octahedrons are plotted as polyhedron. (b) Band gap of ASnO 3 as a function of the tolerance factor for different density functionals. The experimental values of the band gap are marked as green pentagons. (c) ASnO 3 /A'SnO 3 superlattices with two types cation arrangement: [001] layered structure and [111] rocksalt structure, respectively. (d) B3LYP hybrid functional band gaps of ASnO 3 , [001] ordered superlattices, and [111] ordered superlattices of ASnO 3 /A'SnO 3 as a function of the effective tolerance factor. Note the empirical linear relationship between the band gap and effective tolerance factor. - Highlights: • We report the hybrid functional band gap calculation of ASnO 3 and ASnO 3 /A'SnO 3 . • The band gap of ASnO 3 using B3LYP functional reproduces the experimental value. • We propose the linear relationship between the tolerance factor and the band gap

Calculation of spatial weighting functions for ex-core detectors of VVER-440 reactors by Monte Carlo method

International Nuclear Information System (INIS)

Berki, T.

2003-01-01

The signal of ex-core detectors depends not only on the total power of a reactor but also on the power distribution. The spatial weighting function establishes correspondence between the power distribution and the detector signal. The weighting function is independent of the power distribution. The weighting function is used for detector-response analyses, for example in the case of rod-drop experiments. (1) The paper describes the calculation and analysis of the weighting function of a VVER-440. The three-dimensional Monte Carlo code MCNP is used for the evaluation. Results from forward and adjoint calculations are compared. The effect of the change in the concentration of boric acid is also investigated. The evaluation of the spatial weighting function is a fixed-source neutron transport problem, which can be solved much faster by adjoint calculation, however forward calculations provide more detailed results. It is showed that the effect of boric acid upon the weighting function is negligible. (author)

Approximated calculation of the vacuum wave function and vacuum energy of the LGT with RPA method

International Nuclear Information System (INIS)

Hui Ping

2004-01-01

The coupled cluster method is improved with the random phase approximation (RPA) to calculate vacuum wave function and vacuum energy of 2 + 1 - D SU(2) lattice gauge theory. In this calculating, the trial wave function composes of single-hollow graphs. The calculated results of vacuum wave functions show very good scaling behaviors at weak coupling region l/g 2 >1.2 from the third order to the sixth order, and the vacuum energy obtained with RPA method is lower than the vacuum energy obtained without RPA method, which means that this method is a more efficient one

Calculation of parameters of radial-piston reducer based on the use of functional semantic networks

Directory of Open Access Journals (Sweden)

Pashkevich V.M.

2016-12-01

Full Text Available The questions of сalculation of parameters of radial-piston reducer are considered in this article. It is used the approach which is based technologies of functional semantic networks. It is considered possibility applications of functional se-mantic networks for calculation of parameters of radial-piston reducer. Semantic networks to calculate the mass of the radial piston reducer are given.

Efficient Ab-Initio Electron Transport Calculations for Heterostructures by the Nonequilibrium Green’s Function Method

Directory of Open Access Journals (Sweden)

Hirokazu Takaki

2014-01-01

Full Text Available We present an efficient computation technique for ab-initio electron transport calculations based on density functional theory and the nonequilibrium Green’s function formalism for application to heterostructures with two-dimensional (2D interfaces. The computational load for constructing the Green’s functions, which depends not only on the energy but also on the 2D Bloch wave vector along the interfaces and is thus catastrophically heavy, is circumvented by parallel computational techniques with the message passing interface, which divides the calculations of the Green’s functions with respect to energy and wave vectors. To demonstrate the computational efficiency of the present code, we perform ab-initio electron transport calculations of Al(100-Si(100-Al(100 heterostructures, one of the most typical metal-semiconductor-metal systems, and show their transmission spectra, density of states (DOSs, and dependence on the thickness of the Si layers.

The statistic-thermodynamically calculations of magnetic thermodynamically functions for nuclear magnetic moments

International Nuclear Information System (INIS)

Zhu Zhenghe; Luo Deli; Feng Kaiming

2013-01-01

The present work is to calculate the magnetic thermodynamically functions, i.e. energy, the intensity of magnetization, enthalpy, entropy and Gibbs function for nuclear magnetic moments of T, D and neutron n at 2 T and 1, 50, 100 and 150 K from partition functions. It is shown that magnetic saturation of thermonuclear plasma does not easily occur for nuclear magneton is only of 10 -3 of Bohr magneton. The work done by magnetic field is considerable. (authors)

Analytic calculations of trial wave functions of the fractional quantum Hall effect on the sphere

Energy Technology Data Exchange (ETDEWEB)

Souza Batista, C.L. de [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil); Dingping Li [Perugia Univ. (Italy). Dipt. di Fisica

1996-07-01

We present a framework for the analytic calculations of the hierarchical wave functions and the composite fermion wave functions in the fractional quantum Hall effect on the sphere by using projective coordinates. Then we calculate the overlaps between these two wave functions at various fillings and small numbers of electrons. We find that the overlaps are most equal to one. This gives a further evidence that two theories of the fractional quantum Hall effect, the hierarchical theory, are physically equivalent. (author). 31 refs., 2 tabs.

Density functional calculations of elastic properties of portlandite, Ca(OH)(2)

DEFF Research Database (Denmark)

Laugesen, Jakob Lund

2005-01-01

The elastic constants of portlandite, Ca(OH)(2), are calculated by use of density functional theory. A lattice optimization of an infinite (periodic boundary conditions) lattice is performed on which strains are applied. The elastic constants are extracted by minimizing Hooke's law of linear...

Calculation of the spin-isospin response functions in an extended semi-classical theory

International Nuclear Information System (INIS)

Chanfray, G.

1987-01-01

We present a semi-classical calculation of the spin isospin response-functions beyond Thomas-Fermi theory. We show that surface-peaked ℎ 2 corrections reduce the collective effects predicted by Thomas-Fermi calculations. These effects, small for a volume response, become important for surface responses probed by hadrons. This yields a considerable improvement of the agreement with the (p, p') Los Alamos data

Benchmark calculations of excess electrons in water cluster cavities: balancing the addition of atom-centered diffuse functions versus floating diffuse functions.

Science.gov (United States)

Zhang, Changzhe; Bu, Yuxiang

2016-09-14

Diffuse functions have been proved to be especially crucial for the accurate characterization of excess electrons which are usually bound weakly in intermolecular zones far away from the nuclei. To examine the effects of diffuse functions on the nature of the cavity-shaped excess electrons in water cluster surroundings, both the HOMO and LUMO distributions, vertical detachment energies (VDEs) and visible absorption spectra of two selected (H2O)24(-) isomers are investigated in the present work. Two main types of diffuse functions are considered in calculations including the Pople-style atom-centered diffuse functions and the ghost-atom-based floating diffuse functions. It is found that augmentation of atom-centered diffuse functions contributes to a better description of the HOMO (corresponding to the VDE convergence), in agreement with previous studies, but also leads to unreasonable diffuse characters of the LUMO with significant red-shifts in the visible spectra, which is against the conventional point of view that the more the diffuse functions, the better the results. The issue of designing extra floating functions for excess electrons has also been systematically discussed, which indicates that the floating diffuse functions are necessary not only for reducing the computational cost but also for improving both the HOMO and LUMO accuracy. Thus, the basis sets with a combination of partial atom-centered diffuse functions and floating diffuse functions are recommended for a reliable description of the weakly bound electrons. This work presents an efficient way for characterizing the electronic properties of weakly bound electrons accurately by balancing the addition of atom-centered diffuse functions and floating diffuse functions and also by balancing the computational cost and accuracy of the calculated results, and thus is very useful in the relevant calculations of various solvated electron systems and weakly bound anionic systems.

Time-dependent importance sampling in semiclassical initial value representation calculations for time correlation functions.

Science.gov (United States)

Tao, Guohua; Miller, William H

2011-07-14

An efficient time-dependent importance sampling method is developed for the Monte Carlo calculation of time correlation functions via the initial value representation (IVR) of semiclassical (SC) theory. A prefactor-free time-dependent sampling function weights the importance of a trajectory based on the magnitude of its contribution to the time correlation function, and global trial moves are used to facilitate the efficient sampling the phase space of initial conditions. The method can be generally applied to sampling rare events efficiently while avoiding being trapped in a local region of the phase space. Results presented in the paper for two system-bath models demonstrate the efficiency of this new importance sampling method for full SC-IVR calculations.

A computer program for calculation of reliable pair distribution functions of non-crystalline materials from limited diffraction data. III

International Nuclear Information System (INIS)

Hansen, F.Y.

1978-01-01

This program calculates the final pair distribution functions of non-crystalline materials on the basis of the experimental structure factor as calculated in part I and the parameters of the small distance part of the pair distribution function as calculated in part II. In this way, truncation error may be eliminated from the final pair distribution function. The calculations with this program depend on the results of calculations with the programs described in parts I and II. The final pair distribution function is calculated by a Fourier transform of a combination of an experimental structure factor and a model structure factor. The storage requirement depends on the number of data points in the structure factor, the number of data points in the final pair distribution function and the number of peaks necessary to resolve the small distance part of the pair distribution function. In the present set-up a storage requirement is set to 8860 words which is estimated to be satisfactory for a large number of cases. (Auth.)

Fast Time-Dependent Density Functional Theory Calculations of the X-ray Absorption Spectroscopy of Large Systems.

Science.gov (United States)

Besley, Nicholas A

2016-10-11

The computational cost of calculations of K-edge X-ray absorption spectra using time-dependent density functional (TDDFT) within the Tamm-Dancoff approximation is significantly reduced through the introduction of a severe integral screening procedure that includes only integrals that involve the core s basis function of the absorbing atom(s) coupled with a reduced quality numerical quadrature for integrals associated with the exchange and correlation functionals. The memory required for the calculations is reduced through construction of the TDDFT matrix within the absorbing core orbitals excitation space and exploiting further truncation of the virtual orbital space. The resulting method, denoted fTDDFTs, leads to much faster calculations and makes the study of large systems tractable. The capability of the method is demonstrated through calculations of the X-ray absorption spectra at the carbon K-edge of chlorophyll a, C 60 and C 70 .

Density-density functionals and effective potentials in many-body electronic structure calculations

International Nuclear Information System (INIS)

Reboredo, Fernando A.; Kent, Paul R.

2008-01-01

We demonstrate the existence of different density-density functionals designed to retain selected properties of the many-body ground state in a non-interacting solution starting from the standard density functional theory ground state. We focus on diffusion quantum Monte Carlo applications that require trial wave functions with optimal Fermion nodes. The theory is extensible and can be used to understand current practices in several electronic structure methods within a generalized density functional framework. The theory justifies and stimulates the search of optimal empirical density functionals and effective potentials for accurate calculations of the properties of real materials, but also cautions on the limits of their applicability. The concepts are tested and validated with a near-analytic model.

Ab Initio Calculations of the Electronic Structures and Biological Functions of Protein Molecules

Science.gov (United States)

Zheng, Haoping

2003-04-01

The self-consistent cluster-embedding (SCCE) calculation method reduces the computational effort from M3 to about M1 (M is the number of atoms in the system) with unchanged calculation precision. So the ab initio, all-electron calculation of the electronic structure and biological function of protein molecule becomes a reality, which will promote new proteomics considerably. The calculated results of two real protein molecules, the trypsin inhibitor from the seeds of squash Cucurbita maxima (CMTI-I, 436 atoms) and the Ascaris trypsin inhibitor (912 atoms, two three-dimensional structures), are presented. The reactive sites of the inhibitors are determined and explained. The precision of structure determination of inhibitors are tested theoretically.

Hybrid functional band gap calculation of SnO{sub 6} containing perovskites and their derived structures

Energy Technology Data Exchange (ETDEWEB)

Lee, Hyewon [Department of Physics, Pusan National University, Pusan 609-735, Republic of South Korea (Korea, Republic of); Cheong, S.W. [Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854 (United States); Kim, Bog G., E-mail: boggikim@pusan.ac.kr [Department of Physics, Pusan National University, Pusan 609-735, Republic of South Korea (Korea, Republic of)

2015-08-15

We have studied the properties of SnO{sub 6} octahedra-containing perovskites and their derived structures using ab initio calculations with different density functionals. In order to predict the correct band gap of the materials, we have used B3LYP hybrid density functional, and the results of B3LYP were compared with those obtained using the local density approximation and generalized gradient approximation data. The calculations have been conducted for the orthorhombic ground state of the SnO{sub 6} containing perovskites. We also have expended the hybrid density functional calculation to the ASnO{sub 3}/A'SnO{sub 3} system with different cation orderings. We propose an empirical relationship between the tolerance factor and the band gap of SnO{sub 6} containing oxide materials based on first principles calculation. - Graphical abstract: (a) Structure of ASnO{sub 3} for orthorhombic ground state. The green ball is A (Ba, Sr, Ca) cation and the small (red) ball on edge is oxygen. SnO{sub 6} octahedrons are plotted as polyhedron. (b) Band gap of ASnO{sub 3} as a function of the tolerance factor for different density functionals. The experimental values of the band gap are marked as green pentagons. (c) ASnO{sub 3}/A'SnO{sub 3} superlattices with two types cation arrangement: [001] layered structure and [111] rocksalt structure, respectively. (d) B3LYP hybrid functional band gaps of ASnO{sub 3}, [001] ordered superlattices, and [111] ordered superlattices of ASnO{sub 3}/A'SnO{sub 3} as a function of the effective tolerance factor. Note the empirical linear relationship between the band gap and effective tolerance factor. - Highlights: • We report the hybrid functional band gap calculation of ASnO{sub 3} and ASnO{sub 3}/A'SnO{sub 3}. • The band gap of ASnO{sub 3} using B3LYP functional reproduces the experimental value. • We propose the linear relationship between the tolerance factor and the band gap.

Application of wavelet scaling function expansion continuous-energy resonance calculation method to MOX fuel problem

International Nuclear Information System (INIS)

Yang, W.; Wu, H.; Cao, L.

2012-01-01

More and more MOX fuels are used in all over the world in the past several decades. Compared with UO 2 fuel, it contains some new features. For example, the neutron spectrum is harder and more resonance interference effects within the resonance energy range are introduced because of more resonant nuclides contained in the MOX fuel. In this paper, the wavelets scaling function expansion method is applied to study the resonance behavior of plutonium isotopes within MOX fuel. Wavelets scaling function expansion continuous-energy self-shielding method is developed recently. It has been validated and verified by comparison to Monte Carlo calculations. In this method, the continuous-energy cross-sections are utilized within resonance energy, which means that it's capable to solve problems with serious resonance interference effects without iteration calculations. Therefore, this method adapts to treat the MOX fuel resonance calculation problem natively. Furthermore, plutonium isotopes have fierce oscillations of total cross-section within thermal energy range, especially for 240 Pu and 242 Pu. To take thermal resonance effect of plutonium isotopes into consideration the wavelet scaling function expansion continuous-energy resonance calculation code WAVERESON is enhanced by applying the free gas scattering kernel to obtain the continuous-energy scattering source within thermal energy range (2.1 eV to 4.0 eV) contrasting against the resonance energy range in which the elastic scattering kernel is utilized. Finally, all of the calculation results of WAVERESON are compared with MCNP calculation. (authors)

Calculation of the structure and IR spectrum of methyl-b-D-glucopyranoside by density functional theory

International Nuclear Information System (INIS)

Babkov, L.M.; Korolevich, M.V.; Moisejkina, E.A.

2010-01-01

Structural-dynamic models of methyl-b-D-glucopyranoside have been constructed by a density functional method using a B3LYP functional in bases 6-31G(d) and 6-31+G(d,p). Energies have been minimized. Structures, dipole moments, polarizabilities, frequencies of normal modes in the harmonic approximation, and the intensity distribution in the molecular IR spectrum have been calculated. The calculation results have been compared with both the experimental spectra of methyl-b-D-glucopyranoside in the region 400-3700 cm -1 and data obtained within the framework of an approach that uses the classical valence-force method to calculate normal mode frequencies and the quantum-chemical CNDO/2 technique to calculate the electronic structure. (authors)

Ninth degree polynomial fit function for calculation of efficiency calibrations for Ge(Li) and HPGe detectors

International Nuclear Information System (INIS)

Uosif, M.A.M.

2006-01-01

A new 9 th degree polynomial fit function has been constructed to calculate the absolute γ-ray detection efficiencies (ηth) of Ge(Li) and HPGe Detectors, for calculating the absolute efficiency at any interesting γ-energy in the energy range between 25 and 2000 keV and distance between 6 and 148 cm. The total absolute γ -ray detection efficiencies have been calculated for six detectors, three of them are Ge(Li) and three HPGe at different distances. The absolute efficiency of the different detectors was calculated at the specific energy of the standard sources for each measuring distances. In this calculation, experimental (η e xp) and fitting (η f it) efficiency have been calculated. Seven calibrated point sources Am-241, Ba-133, Co-57, Co-60, Cs-137, Eu-152 and Ra-226 were used. The uncertainties of efficiency calibration have been calculated also for quality control. The measured (η e xp) and (η f it) calculated efficiency values were compared with efficiency, which calculated, by Gray fit function (time)- The results obtained on the basis of (η e xp)and (η f it) seem to be in very good agreement

The one loop calculation of the strong coupling β function in the Toy Model

International Nuclear Information System (INIS)

Bai Zhiming; Jiang Yuanfang

1991-01-01

The background field quantization is used to calculate the one-loop β function in the Toy Model which has the strong coupling and the SU(3) symmetry. The function obtained is consistent with the Appalquist-Carrazone theorem in the low energy condition

Strict calculation of electron energy distribution functions in inhomogeneous plasmas

International Nuclear Information System (INIS)

Winkler, R.

1996-01-01

It is objective of the paper to report on strict calculations of the velocity or energy distribution function function and related macroscopic properties of the electrons from appropriate electron kinetic equations under various plasma conditions and to contribute to a better understanding of the electron behaviour in inhomogeneous plasma regions. In particular, the spatial relaxation of plasma electrons acted upon by uniform electric fields, the response of plasma electrons on spatial disturbances of the electric field, the electron kinetics under the impact of space charge field confinement in the dc column plasma and the electron velocity distribution is stronger field as occurring in the electrode regions of a dc glow discharge is considered. (author)

Calculation of Multisphere Neutron Spectrometer Response Functions in Energy Range up to 20 MeV

CERN Document Server

Martinkovic, J

2005-01-01

Multisphere neutron spectrometer is a basic instrument of neutron measurements in the scattered radiation field at charged-particles accelerators for radiation protection and dosimetry purposes. The precise calculation of the spectrometer response functions is a necessary condition of the propriety of neutron spectra unfolding. The results of the response functions calculation for the JINR spectrometer with LiI(Eu) detector (a set of 6 homogeneous and 1 heterogeneous moderators, "bare" detector within cadmium cover and without it) at two geometries of the spectrometer irradiation - in uniform monodirectional and uniform isotropic neutron fields - are given. The calculation was carried out by the code MCNP in the neutron energy range 10$^{-8}$-20 MeV.

Density functional calculations for atoms, molecules and clusters

International Nuclear Information System (INIS)

Gunnarsson, O.; Jones, R.O.

1980-01-01

The density functional formalism provides a framework for including exchange and correlation effects in the calculation of ground state properties of many-electron systems. The reduction of the problem to the solution of single-particle equations leads to important numerical advantages over other ab initio methods of incorporating correlation effects. The essential features of the scheme are outlined and results obtained for atomic and molecular systems are surveyed. The local spin density (LSD) approximation gives generally good results for systems where the bonding involves s and p electrons, but results are less satisfactory for d-bonded systems. Non-local modifications to the LSD approximation have been tested on atomic systems yielding much improved total energies. (Auth.)

On calculating double logarithmical asymptotics of vertex functions defined on the mass shell

International Nuclear Information System (INIS)

Belokurov, V.V.; Usyukina, N.I.

1981-01-01

The essence of the calculation method of double logarithmical asymptotics of vertex functions defined on the mass shell is presented. Using the method the asymptotics of the form-factor of electron is calculated. The ladder and cross-ladder diagrams are asymptotically considerable in every order of the perturbation theory. The way in which the asymptotics of the 4-order diagrams is calculated has been shown. The diagrams of this order and reduction procedures for them are given in a graphic form. The photon mass μ 2 not equal to 0 plays the role of a regulator, removing infrared divergencies. The double logarithmical asymptotics of the form-factor of electron on the mass shell is calculated rigorously in an arbitrary order of the perturbation theory [ru

Standard hydrogen electrode and potential of zero charge in density functional calculations

DEFF Research Database (Denmark)

Tripkovic, Vladimir; Björketun, Mårten; Skúlason, Egill

2011-01-01

standard hydrogen electrode potential (ASHEP) from the calculated work function. Although conceptually correct, this procedure introduces two sources of errors: (i) the experimental estimate of the ASHEP varies from 4.28 to 4.85 V and, as has been previously shown and is reconfirmed here, (ii...... possess in order for its computed ASHEP to closely match the experimental benchmark. We capture and quantify these three effects by calculating trends in the ASHEP and PZC on eight close-packed transition metals, considering the four most simple and representative water models. Finally, it is also...

A lattice calculation of the nucleon's spin-dependent structure function g2 revisited

International Nuclear Information System (INIS)

Goeckeler, M.; Rakow, P.E.L.; Schaefer, A.; Schierholz, G.

2000-11-01

Our previous calculation of the spin-dependent structure function g 2 is revisited. The interest in this structure function is to a great extent motivated by the fact that it receives contributions from twist-two as well as from twist-three operators already in leading order of 1/Q 2 thus offering the unique possibility of directly assessing higher-twist effects. In our former calculation the lattice operators were renormalized perturbatively and mixing with lower-dimensional operators was ignored. However, the twist-three operator which gives rise to the matrix element d 2 mixes non-perturbatively with an operator of lower dimension. Taking this effect into account leads to a considerably smaller value of d 2 , which is consistent with the experimental data. (orig.)

Comparison of different eigensolvers for calculating vibrational spectra using low-rank, sum-of-product basis functions

Science.gov (United States)

Leclerc, Arnaud; Thomas, Phillip S.; Carrington, Tucker

2017-08-01

Vibrational spectra and wavefunctions of polyatomic molecules can be calculated at low memory cost using low-rank sum-of-product (SOP) decompositions to represent basis functions generated using an iterative eigensolver. Using a SOP tensor format does not determine the iterative eigensolver. The choice of the interative eigensolver is limited by the need to restrict the rank of the SOP basis functions at every stage of the calculation. We have adapted, implemented and compared different reduced-rank algorithms based on standard iterative methods (block-Davidson algorithm, Chebyshev iteration) to calculate vibrational energy levels and wavefunctions of the 12-dimensional acetonitrile molecule. The effect of using low-rank SOP basis functions on the different methods is analysed and the numerical results are compared with those obtained with the reduced rank block power method. Relative merits of the different algorithms are presented, showing that the advantage of using a more sophisticated method, although mitigated by the use of reduced-rank SOP functions, is noticeable in terms of CPU time.

Efficacy of surface error corrections to density functional theory calculations of vacancy formation energy in transition metals.

Science.gov (United States)

Nandi, Prithwish Kumar; Valsakumar, M C; Chandra, Sharat; Sahu, H K; Sundar, C S

2010-09-01

We calculate properties like equilibrium lattice parameter, bulk modulus and monovacancy formation energy for nickel (Ni), iron (Fe) and chromium (Cr) using Kohn-Sham density functional theory (DFT). We compare the relative performance of local density approximation (LDA) and generalized gradient approximation (GGA) for predicting such physical properties for these metals. We also make a relative study between two different flavors of GGA exchange correlation functional, namely PW91 and PBE. These calculations show that there is a discrepancy between DFT calculations and experimental data. In order to understand this discrepancy in the calculation of vacancy formation energy, we introduce a correction for the surface intrinsic error corresponding to an exchange correlation functional using the scheme implemented by Mattsson et al (2006 Phys. Rev. B 73 195123) and compare the effectiveness of the correction scheme for Al and the 3d transition metals.

Statistical mechanical calculations of molecular pair correlation functions and scattering intensities

International Nuclear Information System (INIS)

Bertagnolli, H.

1978-01-01

For the case of special molecular models representing the acetonitrile molecule the expansion coefficients of the molecular par distribution function are calculated by use of pertubation theory. These results are used to get theoretical access to scattering intensities in the frame of several approximations. The first model describes the molecule by three hard spheres and uses a hard sphere liquid as reference. In the second cast the calculations are based on an anisotropic Lennard-Jones potential by application of a model of overlapping ellipsoids and by use of a Lennard-Jones liquid as a reference system. In the third model dipolar attractive forces are taken into account with an anisotropic hard-sphere liquid as a reference. In the third model dipolar attractive forces are taken into account with an anisotropic hard-sphere liquid as a reference. Finally all the calculations with different intermolecular potentials are compared with neutron scattering experiments. (orig.) 891 HK [de

Calculation of spin-densities within the context of density functional theory. The crucial role of the correlation functional

NARCIS (Netherlands)

Filatov, M; Cremer, D

2005-01-01

It is demonstrated that the LYP correlation functional is not suited to be used for the calculation of electron spin resonance hyperfine structure (HFS) constants, nuclear magnetic resonance spin-spin coupling constants, magnetic, shieldings and other properties that require a balanced account of

First principles calculations for liquids and solids using maximally localized Wannier functions

Science.gov (United States)

Swartz, Charles W., VI

The field of condensed matter computational physics has seen an explosion of applicability over the last 50+ years. Since the very first calculations with ENIAC and MANIAC the field has continued to pushed the boundaries of what is possible; from the first large-scale molecular dynamics simulation, to the implementation of Density Functional Theory and large scale Car-Parrinello molecular dynamics, to million-core turbulence calculations by Standford. These milestones represent not only technological advances but theoretical breakthroughs and algorithmic improvements as well. The work in this thesis was completed in the hopes of furthering such advancement, even by a small fraction. Here we will focus mainly on the calculation of electronic and structural properties of solids and liquids, where we shall implement a wide range of novel approaches that are both computational efficient and physically enlightening. To this end we routinely will work with maximally localized Wannier functions (MLWFs) which have recently seen a revival in mainstream scientific literature. MLWFs present us with interesting opportunity to calculate a localized orbital within the planewave formalism of atomistic simulations. Such a localization will prove to be invaluable in the construction of layer-based superlattice models, linear scaling hybrid functional schemes and model quasiparticle calculations. In the first application of MLWF we will look at modeling functional piezoelectricity in superlattices. Based on the locality principle of insulating superlattices, we apply the method of Wu et al to the piezoelectric strains of individual layers under iifixed displacement field. For a superlattice of arbitrary stacking sequence an accurate model is acquired for predicting piezoelectricity. By applying the model in the superlattices where ferroelectric and antiferrodistortive modes are in competition, functional piezoelectricity can be achieved. A strong nonlinear effect is observed and can

Infrared spectroscopy and density functional calculations on titanium-dinitrogen complexes

Science.gov (United States)

Yoo, Hae-Wook; Choi, Changhyeok; Cho, Soo Gyeong; Jung, Yousung; Choi, Myong Yong

2018-04-01

Titanium-nitrogen complexes were generated by laser ablated titanium (Ti) atoms and N2 gas molecules in this study. These complexes were isolated on the pre-deposited solid Ar matrix on the pre-cooled KBr window (T ∼ 5.4 K), allowing infrared spectra to be measured. Laser ablation experiments with 15N2 isotope provided distinct isotopic shifts in the infrared spectra that strongly implicated the formation of titanium-nitrogen complexes, Ti(NN)x. Density functional theory (DFT) calculations were employed to investigate the molecular structures, electronic ground state, relative energies, and IR frequencies of the anticipated Ti(NN)x complexes. Based on laser ablation experiments and DFT calculations, we were able to assign multiple Ti(NN)x (x = 1-6) species. Particularly, Ti(NN)5 and Ti(NN)6, which have high nitrogen content, may serve as good precursors in preparing polynitrogens.

Improved response function calculations for scintillation detectors using an extended version of the MCNP code

CERN Document Server

Schweda, K

2002-01-01

The analysis of (e,e'n) experiments at the Darmstadt superconducting electron linear accelerator S-DALINAC required the calculation of neutron response functions for the NE213 liquid scintillation detectors used. In an open geometry, these response functions can be obtained using the Monte Carlo codes NRESP7 and NEFF7. However, for more complex geometries, an extended version of the Monte Carlo code MCNP exists. This extended version of the MCNP code was improved upon by adding individual light-output functions for charged particles. In addition, more than one volume can be defined as a scintillator, thus allowing the simultaneous calculation of the response for multiple detector setups. With the implementation of sup 1 sup 2 C(n,n'3 alpha) reactions, all relevant reactions for neutron energies E sub n <20 MeV are now taken into consideration. The results of these calculations were compared to experimental data using monoenergetic neutrons in an open geometry and a sup 2 sup 5 sup 2 Cf neutron source in th...

A Monte Carlo method for calculating strength functions in many-fermion systems

International Nuclear Information System (INIS)

Bloom, S.D.; Grimes, S.M.

1980-01-01

The calculation of moments is an essential first step in the calculation of strength functions for operators. A method for calculating approximate moments of a variety of operators in large vector spaces (dimension Nsub(e)) based on the use of sets of random multiparticle vectors (dimension Nsub(d) in two nuclear cases: 21 Ne(n = 1 to 10) and 28 Si(n = 1 to 3). The random vectors, which we call RRV's (random representative vectors), are constructed by statistically sampling a fraction f = Nsub(d)/Nsub(e) of the full space. Useful results are obtained with f -6 (case of 28 Si, Nsub(e) = 5.5 x 10 7 ). For Nsub(d) = Nsub(e) (case of 21 Ne, Nsub(e) = 1935) our results for the dispersions of the sets of the moments closely approximate the predictions of Porter. (orig.)

New approximations for the Doppler broadening function applied to the calculation of resonance self-shielding factors

International Nuclear Information System (INIS)

Palma, Daniel A.; Goncalves, Alessandro C.; Martinez, Aquilino S.; Silva, Fernando C.

2008-01-01

The activation technique allows much more precise measurements of neutron intensity, relative or absolute. The technique requires the knowledge of the Doppler broadening function ψ(x,ξ) to determine the resonance self-shielding factors in the epithermal range G epi (τ,ξ). Two new analytical approximations for the Doppler broadening function ψ(x,ξ) are proposed. The approximations proposed are compared with other methods found in literature for the calculation of the ψ(x,ξ) function, that is, the 4-pole Pade method and the Frobenius method, when applied to the calculation of G epi (τ,ξ). The results obtained provided satisfactory accuracy. (authors)

New approximations for the Doppler broadening function applied to the calculation of resonance self-shielding factors

Energy Technology Data Exchange (ETDEWEB)

Palma, Daniel A. [CEFET QUIMICA de Nilopolis/RJ, Rio de Janeiro (Brazil); Goncalves, Alessandro C.; Martinez, Aquilino S.; Silva, Fernando C. [COPPE/UFRJ - Programa de Engenharia Nuclear, Rio de Janeiro (Brazil)

2008-07-01

The activation technique allows much more precise measurements of neutron intensity, relative or absolute. The technique requires the knowledge of the Doppler broadening function psi(x,xi) to determine the resonance self-shielding factors in the epithermal range G{sub epi} (tau,xi). Two new analytical approximations for the Doppler broadening function psi(x,xi) are proposed. The approximations proposed are compared with other methods found in literature for the calculation of the psi(x,xi) function, that is, the 4-pole Pade method and the Frobenius method, when applied to the calculation of G{sub epi} (tau,xi). The results obtained provided satisfactory accuracy. (authors)

Does Early Algebraic Reasoning Differ as a Function of Students' Difficulty with Calculations versus Word Problems?

Science.gov (United States)

Powell, Sarah R; Fuchs, Lynn S

2014-08-01

According to national mathematics standards, algebra instruction should begin at kindergarten and continue through elementary school. Most often, teachers address algebra in the elementary grades with problems related to solving equations or understanding functions. With 789 2 nd - grade students, we administered (a) measures of calculations and word problems in the fall and (b) an assessment of pre-algebraic reasoning, with items that assessed solving equations and functions, in the spring. Based on the calculation and word-problem measures, we placed 148 students into 1 of 4 difficulty status categories: typically performing, calculation difficulty, word-problem difficulty, or difficulty with calculations and word problems. Analyses of variance were conducted on the 148 students; path analytic mediation analyses were conducted on the larger sample of 789 students. Across analyses, results corroborated the finding that word-problem difficulty is more strongly associated with difficulty with pre-algebraic reasoning. As an indicator of later algebra difficulty, word-problem difficulty may be a more useful predictor than calculation difficulty, and students with word-problem difficulty may require a different level of algebraic reasoning intervention than students with calculation difficulty.

Does Early Algebraic Reasoning Differ as a Function of Students’ Difficulty with Calculations versus Word Problems?

Science.gov (United States)

Powell, Sarah R.; Fuchs, Lynn S.

2014-01-01

According to national mathematics standards, algebra instruction should begin at kindergarten and continue through elementary school. Most often, teachers address algebra in the elementary grades with problems related to solving equations or understanding functions. With 789 2nd- grade students, we administered (a) measures of calculations and word problems in the fall and (b) an assessment of pre-algebraic reasoning, with items that assessed solving equations and functions, in the spring. Based on the calculation and word-problem measures, we placed 148 students into 1 of 4 difficulty status categories: typically performing, calculation difficulty, word-problem difficulty, or difficulty with calculations and word problems. Analyses of variance were conducted on the 148 students; path analytic mediation analyses were conducted on the larger sample of 789 students. Across analyses, results corroborated the finding that word-problem difficulty is more strongly associated with difficulty with pre-algebraic reasoning. As an indicator of later algebra difficulty, word-problem difficulty may be a more useful predictor than calculation difficulty, and students with word-problem difficulty may require a different level of algebraic reasoning intervention than students with calculation difficulty. PMID:25309044

Complex-scaling of screened Coulomb potentials for resonance calculations utilizing the modified Bessel functions

Science.gov (United States)

Jiao, Li-Guang; Ho, Yew Kam

2014-05-01

The screened Coulomb potential (SCP) has been extensively used in atomic physics, nuclear physics, quantum chemistry and plasma physics. However, an accurate calculation for atomic resonances under SCP is still a challenging task for various methods. Within the complex-scaling computational scheme, we have developed a method utilizing the modified Bessel functions to calculate doubly-excited resonances in two-electron atomic systems with configuration interaction-type basis. To test the validity of our method, we have calculated S- and P-wave resonance states of the helium atom with various screening strengths, and have found good agreement with earlier calculations using different methods. Our present method can be applied to calculate high-lying resonances associated with high excitation thresholds of the He+ ion, and with high-angular-momentum states. The derivation and calculation details of our present investigation together with new results of high-angular-momentum states will be presented at the meeting. Supported by NSC of Taiwan.

Statistical model calculation of fission isomer excitation functions in (n,n') and (n,γ) reactions

International Nuclear Information System (INIS)

Chatterjee, A.; Athougies, A.L.; Mehta, M.K.

1977-01-01

A statistical model developed by Britt and others (1971, 1973) to analyze isomer excitation functions in spallation type reactions like (α,2n) has been adopted in fission isomer calculations for (n,n') and (n,γ) reactions. Calculations done for 235 U(n,n')sup(238m)U and 235 U(n,γ)sup(236m)U reactions have been compared with experimental measurements. A listing of the computer program ISOMER using FORTRAN IV to calculate the isomer to prompt ratios is given. (M.G.B.)

Density functional theory and evolution algorithm calculations of elastic properties of AlON

Energy Technology Data Exchange (ETDEWEB)

Batyrev, I. G.; Taylor, D. E.; Gazonas, G. A.; McCauley, J. W. [U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005 (United States)

2014-01-14

Different models for aluminum oxynitride (AlON) were calculated using density functional theory and optimized using an evolutionary algorithm. Evolutionary algorithm and density functional theory (DFT) calculations starting from several models of AlON with different Al or O vacancy locations and different positions for the N atoms relative to the vacancy were carried out. The results show that the constant anion model [McCauley et al., J. Eur. Ceram. Soc. 29(2), 223 (2009)] with a random distribution of N atoms not adjacent to the Al vacancy has the lowest energy configuration. The lowest energy structure is in a reasonable agreement with experimental X-ray diffraction spectra. The optimized structure of a 55 atom unit cell was used to construct 220 and 440 atom models for simulation cells using DFT with a Gaussian basis set. Cubic elastic constant predictions were found to approach the experimentally determined AlON single crystal elastic constants as the model size increased from 55 to 440 atoms. The pressure dependence of the elastic constants found from simulated stress-strain relations were in overall agreement with experimental measurements of polycrystalline and single crystal AlON. Calculated IR intensity and Raman spectra are compared with available experimental data.

Self-consistent DFT +U method for real-space time-dependent density functional theory calculations

Science.gov (United States)

Tancogne-Dejean, Nicolas; Oliveira, Micael J. T.; Rubio, Angel

2017-12-01

We implemented various DFT+U schemes, including the Agapito, Curtarolo, and Buongiorno Nardelli functional (ACBN0) self-consistent density-functional version of the DFT +U method [Phys. Rev. X 5, 011006 (2015), 10.1103/PhysRevX.5.011006] within the massively parallel real-space time-dependent density functional theory (TDDFT) code octopus. We further extended the method to the case of the calculation of response functions with real-time TDDFT+U and to the description of noncollinear spin systems. The implementation is tested by investigating the ground-state and optical properties of various transition-metal oxides, bulk topological insulators, and molecules. Our results are found to be in good agreement with previously published results for both the electronic band structure and structural properties. The self-consistent calculated values of U and J are also in good agreement with the values commonly used in the literature. We found that the time-dependent extension of the self-consistent DFT+U method yields improved optical properties when compared to the empirical TDDFT+U scheme. This work thus opens a different theoretical framework to address the nonequilibrium properties of correlated systems.

Zeta Function Regularization in Casimir Effect Calculations and J. S. Dowker's Contribution

Science.gov (United States)

Elizalde, Emilio

2012-07-01

A summary of relevant contributions, ordered in time, to the subject of operator zeta functions and their application to physical issues is provided. The description ends with the seminal contributions of Stephen Hawking and Stuart Dowker and collaborators, considered by many authors as the actual starting point of the introduction of zeta function regularization methods in theoretical physics, in particular, for quantum vacuum fluctuation and Casimir effect calculations. After recalling a number of the strengths of this powerful and elegant method, some of its limitations are discussed. Finally, recent results of the so called operator regularization procedure are presented.

A calculation of the three-loop helicity-dependent splitting functions in QCD

International Nuclear Information System (INIS)

Vogt, A.

2014-05-01

We have calculated the complete matrix of three-loop helicity-difference ('polarized') splitting functions ΔP ik (2) (x), i,k=q,g, in massless perturbative QCD. In this note we briefly discuss some properties of the polarized splitting functions and our non-standard determination of the hitherto missing lower-row quantities ΔP gq (2) and ΔP gg (2) . The resulting next-to-next-to-leading order (NNLO) corrections to the evolution of polarized parton distributions are illustrated and found to be small even at rather large values of the strong coupling constant α s .

Lattice dynamics calculations based on density-functional perturbation theory in real space

Science.gov (United States)

Shang, Honghui; Carbogno, Christian; Rinke, Patrick; Scheffler, Matthias

2017-06-01

A real-space formalism for density-functional perturbation theory (DFPT) is derived and applied for the computation of harmonic vibrational properties in molecules and solids. The practical implementation using numeric atom-centered orbitals as basis functions is demonstrated exemplarily for the all-electron Fritz Haber Institute ab initio molecular simulations (FHI-aims) package. The convergence of the calculations with respect to numerical parameters is carefully investigated and a systematic comparison with finite-difference approaches is performed both for finite (molecules) and extended (periodic) systems. Finally, the scaling tests and scalability tests on massively parallel computer systems demonstrate the computational efficiency.

ORBITALES. A program for the calculation of wave functions with an analytical central potential

International Nuclear Information System (INIS)

Yunta Carretero; Rodriguez Mayquez, E.

1974-01-01

In this paper is described the objective, basis, carrying out in FORTRAN language and use of the program ORBITALES. This program calculate atomic wave function in the case of ths analytical central potential (Author) 8 refs

The oxygen reduction reaction mechanism on Pt(111) from density functional theory calculations

DEFF Research Database (Denmark)

Tripkovic, Vladimir; Skulason, Egill; Siahrostami, Samira

2010-01-01

We study the oxygen reduction reaction (ORR) mechanism on a Pt(1 1 1) surface using density functional theory calculations We find that at low overpotentials the surface is covered with a half dissociated water layer We estimate the barrier for proton transfer to this surface and the barrier...

MACK-IV, a new version of MACK: a program to calculate nuclear response functions from data in ENDF/B format

International Nuclear Information System (INIS)

Abdou, M.A.; Gohar, Y.; Wright, R.Q.

1978-07-01

MACK-IV calculates nuclear response functions important to the neutronics analysis of nuclear and fusion systems. A central part of the code deals with the calculation of the nuclear response function for nuclear heating more commonly known as the kerma factor. Pointwise and multigroup neutron kerma factors, individual reactions, helium, hydrogen, and tritium production response functions are calculated from any basic nuclear data library in ENDF/B format. The program processes all reactions in the energy range of 0 to 20 MeV for fissionable and nonfissionable materials. The program also calculates the gamma production cross sections and the gamma production energy matrix. A built-in computational capability permits the code to calculate the cross sections in the resolved and unresolved resonance regions from resonance parameters in ENDF/B with an option for Doppler broadening. All energy pointwise and multigroup data calculated by the code can be punched, printed and/or written on tape files. Multigroup response functions (e.g., kerma factors, reaction cross sections, gas production, atomic displacements, etc.) can be outputted in the format of MACK-ACTIVITY-Table suitable for direct use with current neutron (and photon) transport codes

CALCULATION OF FRAGMENTATION FUNCTIONS IN TWO-HADRON SEMI-INCLUSIVE PROCESSES

International Nuclear Information System (INIS)

BIANCONI, A.; BOFFI, S.; BOER, D.; JAKOB, R.; RADICI, M.

2001-01-01

We investigate the properties of interference fragmentation functions arising from the emission of two leading hadrons inside the same jet for inclusive lepton-nucleon deep inelastic scattering. Using an extended spectator model for the mechanism of the hadronization, we give a complete calculation and numerical estimates for the examples of a proton-pion pair produced with invariant mass on the Roper resonance, and of two pions produced with invariant mass close to the ρ mass. We discuss azimuthal angular dependence of the leading order cross section to point up favourable conditions for extracting transversity from experimental data

Improving the influence function method to take topography into the calculation of mining subsidence

OpenAIRE

Cai , Yinfei; Verdel , Thierry; Deck , Olivier; LI , Xiao-Jong

2016-01-01

International audience; The classic influence function method is often used in the calculation of mining subsidence caused by stratiform underground excavations. Theoretically,its use is limited to the subsidence predictions under the condition of horizontal ground surface. In order to improve the original influence function method to take topographic variations into account. Due to real-world mining conditions that are usually complicated, it is difficult to separate topography influences fr...

Power and Sample Size Calculations for Logistic Regression Tests for Differential Item Functioning

Science.gov (United States)

Li, Zhushan

2014-01-01

Logistic regression is a popular method for detecting uniform and nonuniform differential item functioning (DIF) effects. Theoretical formulas for the power and sample size calculations are derived for likelihood ratio tests and Wald tests based on the asymptotic distribution of the maximum likelihood estimators for the logistic regression model.…

Calculation of scalar products of wave functions and form factors in the framework of the algebraic Bethe ansatz

International Nuclear Information System (INIS)

Slavnov, N.A.

1989-01-01

The Bethe ansatz method is widely used to investigate two-dimensional completely integrable models. In the framework of the quantum inverse scattering method it has proved to be possible to construct an algebraic scheme of the Bethe ansatz, and this has been successfully applied to calculation of correlation functions. One of the important questions of the method is that of the scalar products of the wave functions. In particular, knowledge of the properties of the scalar products is necessary for investigating the form factors and correlation function. In the present paper the author considers a generalized model with R matrix of the model of the nonlinear Schroedinger equation. The main formulas and notation are given in Sec. 2. In Sec. 3 he calculates the scalar product of an arbitrary function and an eigenfunction of the Hamiltonian. The generalized two-site model is introduced in Sec. 4. In Sec. 5 he calculates the form factor of the particle number operator

Monte Carlo calculations of ligth-ion sputtering as a function of the incident angle

International Nuclear Information System (INIS)

Haggmark, L.G.; Biersack, J.P.

1980-01-01

The sputtering of metal surfaces by light ions has been studied as a function of the incident angle using an extension of the TRIM Monte Carlo computer program. Sputtering yields were calculated at both normal and oblique angles of incidence for H, D, T, and 4 He impinging on Ni, Mo, and Au targets with energies <= 10 keV. Direct comparisons are made with the most recent experimental and theoretical results. There is generally good agreement with the experimental data although our calculated maximum in the yield usually occurs at a smaller incident angle, measured from the surface normal. The enhancement of the yield at large incident angles over that at normal incidence is observed to be a complex function of the incident ion's energy and mass and the target's atomic weight and surface binding energy. (orig.)

Calculational model based on influence function method for power distribution and control rod worth in fast reactors

International Nuclear Information System (INIS)

Sanda, T.; Azekura, K.

1983-01-01

A model for calculating the power distribution and the control rod worth in fast reactors has been developed. This model is based on the influence function method. The characteristics of the model are as follows: Influence functions for any changes in the control rod insertion ratio are expressed by using an influence function for an appropriate control rod insertion in order to reduce the computer memory size required for the method. A control rod worth is calculated on the basis of a one-group approximation in which cross sections are generated by bilinear (flux-adjoint) weighting, not the usual flux weighting, in order to reduce the collapse error. An effective neutron multiplication factor is calculated by adjoint weighting in order to reduce the effect of the error in the one-group flux distribution. The results obtained in numerical examinations of a prototype fast reactor indicate that this method is suitable for on-line core performance evaluation because of a short computing time and a small memory size

Right parietal cortex and calculation processing: intraoperative functional mapping of multiplication and addition in patients affected by a brain tumor.

Science.gov (United States)

Della Puppa, Alessandro; De Pellegrin, Serena; d'Avella, Elena; Gioffrè, Giorgio; Munari, Marina; Saladini, Marina; Salillas, Elena; Scienza, Renato; Semenza, Carlo

2013-11-01

The role of parietal areas in number processing is well known. The significance of intraoperative functional mapping of these areas has been only partially explored, however, and only a few discordant data are available in the surgical literature with regard to the right parietal lobe. The purpose of this study was to evaluate the clinical impact of simple calculation in cortical electrostimulation of right-handed patients affected by a right parietal brain tumor. Calculation mapping in awake surgery was performed in 3 right-handed patients affected by high-grade gliomas located in the right parietal lobe. Preoperatively, none of the patients presented with calculation deficits. In all 3 cases, after sensorimotor and language mapping, cortical and intraparietal sulcus areas involved in single-digit multiplication and addition calculations were mapped using bipolar electrostimulation. In all patients, different sites of the right parietal cortex, mainly in the inferior lobule, were detected as being specifically related to calculation (multiplication or addition). In 2 patients the intraparietal sulcus was functionally specific for multiplication. No functional sites for language were detected. All sites functional for calculation were spared during tumor resection, which was complete in all cases without postoperative neurological deficits. These findings provide intraoperative data in support of an anatomofunctional organization for multiplication and addition within the right parietal area. Furthermore, the study shows the potential clinical relevance of intraoperative mapping of calculation in patients undergoing surgery in the right parietal area. Further and larger studies are needed to confirm these data and assess whether mapped areas are effectively essential for function.

Calculation of excitation functions of the 54, 56, 57, 58 Fe (p, n ...

Indian Academy of Sciences (India)

Home; Journals; Pramana – Journal of Physics; Volume 83; Issue 4. Calculation of excitation functions of the 54,56,57 ... Proton-induced reaction cross-sections provide clues to understand the nuclear structure and offers a good testing ground for ideas about nuclear forces. In addition, complete information in this field is ...

Performance of Density Functional Theory Procedures for the Calculation of Proton-Exchange Barriers: Unusual Behavior of M06-Type Functionals.

Science.gov (United States)

Chan, Bun; Gilbert, Andrew T B; Gill, Peter M W; Radom, Leo

2014-09-09

We have examined the performance of a variety of density functional theory procedures for the calculation of complexation energies and proton-exchange barriers, with a focus on the Minnesota-class of functionals that are generally highly robust and generally show good accuracy. A curious observation is that M05-type and M06-type methods show an atypical decrease in calculated barriers with increasing proportion of Hartree-Fock exchange. To obtain a clearer picture of the performance of the underlying components of M05-type and M06-type functionals, we have investigated the combination of MPW-type and PBE-type exchange and B95-type and PBE-type correlation procedures. We find that, for the extensive E3 test set, the general performance of the various hybrid-DFT procedures improves in the following order: PBE1-B95 → PBE1-PBE → MPW1-PBE → PW6-B95. As M05-type and M06-type procedures are related to PBE1-B95, it would be of interest to formulate and examine the general performance of an alternative Minnesota DFT method related to PW6-B95.

DMSA-scintigraphy in paediatrics: is the evaluation of the geometric mean necessary for the calculation of the differential renal function?

International Nuclear Information System (INIS)

Porn, U.; Alalp, S.; Fischer, S.; Dresel, S.; Rossmueller, B.; Hahn, K.

2001-01-01

For assessment of differential renal function (PF) by means of static renal scintigraphy with Tc-99m-dimercaptosuccinic acid (DMSA) the calculation of the geometric mean of counts from the anterior and posterior view is recommended. Aim of this retrospective study was to find out, if the anterior view is necessary to receive an accurate differential renal function by calculating the geometric mean compared to calculating PF using the counts of the posterior view only. Methods: 164 DMSA-scans of 151 children (86 f, 65 m) aged 16 d to 16 a (4.7 ± 3.9 a) were reviewed. The scans were performed using a dual head gamma camera (Picker Prism 2000 XP, low energy ultra high resolution collimator, matrix 256 x 256, 300 kcts/view, Zoom: 1.6-2.0). Background corrected values from both kidneys anterior and posterior were obtained. Using region of interest technique PF was calculated using the counts of the dorsal view and compared with the calculated geometric mean [SQR(Cts dors x Cts ventr )]. Results: The differential function of the right kidney was significantly less when compared to the calculation of the geometric mean (p geom and the PF dors was 1.5 ± 1.4%. A difference ≥5% (5.0-9.5%) was obtained in only 6/164 scans (3.7%). Three of 6 patients presented with an underestimated PF dors due to dystopic kidneys on the left side in 2 patients and on the right side in one patient. The other 3 patients with a difference >5% did not show any renal abnormality. Conclusion: The calculation of the PF from the posterior view only will give an underestimated value of the right kidney compared to the calculation of the geometric mean. This effect is not relevant for the calculation of the differential renal function in orthotopic kidneys, so that in these cases the anterior view is not necessary. However, geometric mean calculation to obtain reliable values for differential renal function should be applied in cases with an obvious anatomical abnormality. (orig.) [de

[Calculation of the partial function of the kidney with DMSA in pediatrics: is the evaluation of the geometric mean necessary?].

Science.gov (United States)

Porn, U; Rossmüller, B; Alalp, S; Fischer, S; Dresel, S; Hahn, K

2001-08-01

For assessment of differential renal function (PF) by means of static renal scintigraphy with Tc-99m-dimercaptosuccinic acid (DMSA) the calculation of the geometric mean of counts from the anterior and posterior view is recommended. Of this retrospective study was to find out, if the anterior view is necessary to receive an accurate differential renal function by calculating the geometric mean compared to calculating PF using the counts of the posterior view only. 164 DMSA-scans of 151 children (86 f, 65 m) aged 16 d to 16 a (4.7 +/- 3.9 a) were reviewed. The scans were performed using a dual head gamma camera (Picker Prism 2000 XP, low energy ultra high resolution collimator, matrix 256 x 256, 300 kcts/view, Zoom: 1.6-2.0). Background corrected values from both kidneys anterior and posterior were obtained. Using region of interest technique PF was calculated using the counts of the dorsal view and compared with the calculated geometric mean [SQR(Ctsdors x Ctsventr)]. The differential function of the right kidney was significantly less when compared to the calculation of the geometric mean (p or = 5% (5.0-9.5%) was obtained in only 6/164 scans (3.7%). Three of 6 patients presented with an underestimated PFdors due to dystopic kidneys on the left side in 2 patients and on the right side in one patient. The other 3 patients with a difference > 5% did not show any renal abnormality. The calculation of the PF from the posterior view only will give an underestimated value of the right kidney compared to the calculation of the geometric mean. This effect is not relevant for the calculation of the differential renal function in orthotopic kidneys, so that in these cases the anterior view is not necessary. However, geometric mean calculation to obtain reliable values for differential renal function should be applied in cases with an obvious anatomical abnormality.

Calculation of the Doppler broadening function using Fourier analysis;Calculo da funcao de alargamento Doppler utilizando analise de Fourier

Energy Technology Data Exchange (ETDEWEB)

Goncalves, Alessandro da Cruz

2010-07-01

An efficient and precise method for calculation of Doppler broadening function is very important to obtain average group microscopic cross sections, self shielding factors, resonance integrals and others reactor physics parameter. In this thesis two different methods for calculation of Doppler broadening function and interference term will be presented. The main method is based on a new integral form for Doppler broadening function {psi}(x,{zeta}) which gives a mathematical interpretation of the approximation proposed by Bethe and Placzek, as the convolution of the Lorentzian function with a Gaussian function. This interpretation besides leading to a new integral form for {psi}(x,{zeta}), enables to obtain a simple analytic solution for the Doppler broadening function. (author)

Importance sampling and histogrammic representations of reactivity functions and product distributions in Monte Carlo quasiclassical trajectory calculations

International Nuclear Information System (INIS)

Faist, M.B.; Muckerman, J.T.; Schubert, F.E.

1978-01-01

The application of importance sampling as a variance reduction technique in Monte Carlo quasiclassical trajectory calculations is discussed. Two measures are proposed which quantify the quality of the importance sampling used, and indicate whether further improvements may be obtained by some other choice of importance sampling function. A general procedure for constructing standardized histogrammic representations of differential functions which integrate to the appropriate integral value obtained from a trajectory calculation is presented. Two criteria for ''optimum'' binning of these histogrammic representations of differential functions are suggested. These are (1) that each bin makes an equal contribution to the integral value, and (2) each bin has the same relative error. Numerical examples illustrating these sampling and binning concepts are provided

Performance of exchange-correlation functionals in density functional theory calculations for liquid metal: A benchmark test for sodium

Science.gov (United States)

Han, Jeong-Hwan; Oda, Takuji

2018-04-01

The performance of exchange-correlation functionals in density-functional theory (DFT) calculations for liquid metal has not been sufficiently examined. In the present study, benchmark tests of Perdew-Burke-Ernzerhof (PBE), Armiento-Mattsson 2005 (AM05), PBE re-parameterized for solids, and local density approximation (LDA) functionals are conducted for liquid sodium. The pair correlation function, equilibrium atomic volume, bulk modulus, and relative enthalpy are evaluated at 600 K and 1000 K. Compared with the available experimental data, the errors range from -11.2% to 0.0% for the atomic volume, from -5.2% to 22.0% for the bulk modulus, and from -3.5% to 2.5% for the relative enthalpy depending on the DFT functional. The generalized gradient approximation functionals are superior to the LDA functional, and the PBE and AM05 functionals exhibit the best performance. In addition, we assess whether the error tendency in liquid simulations is comparable to that in solid simulations, which would suggest that the atomic volume and relative enthalpy performances are comparable between solid and liquid states but that the bulk modulus performance is not. These benchmark test results indicate that the results of liquid simulations are significantly dependent on the exchange-correlation functional and that the DFT functional performance in solid simulations can be used to roughly estimate the performance in liquid simulations.

The algorithms for calculating synthetic seismograms from a dipole source using the derivatives of Green's function

Science.gov (United States)

Pavlov, V. M.

2017-07-01

The problem of calculating complete synthetic seismograms from a point dipole with an arbitrary seismic moment tensor in a plane parallel medium composed of homogeneous elastic isotropic layers is considered. It is established that the solutions of the system of ordinary differential equations for the motion-stress vector have a reciprocity property, which allows obtaining a compact formula for the derivative of the motion vector with respect to the source depth. The reciprocity theorem for Green's functions with respect to the interchange of the source and receiver is obtained for a medium with cylindrical boundary. The differentiation of Green's functions with respect to the coordinates of the source leads to the same calculation formulas as the algorithm developed in the previous work (Pavlov, 2013). A new algorithm appears when the derivatives with respect to the horizontal coordinates of the source is replaced by the derivatives with respect to the horizontal coordinates of the receiver (with the minus sign). This algorithm is more transparent, compact, and economic than the previous one. It requires calculating the wavenumbers associated with Bessel function's roots of order 0 and order 1, whereas the previous algorithm additionally requires the second order roots.

Accurate density-functional calculations on large systems: Fullerenes and magnetic clusters

International Nuclear Information System (INIS)

Dunlap, B.I.

1996-01-01

Efforts to accurately compute all-electron density-functional energies for large molecules and clusters using Gaussian basis sets will be reviewed. The foundation of this effort, variational fitting, will be described and followed by three applications of the method. The first application concerns fullerenes. When first discovered, C 60 is quite unstable relative to the higher fullerenes. In addition, to raising questions about the relative abundance of the various fullerenes, this work conflicted with the then state-of-the art density-funcitonal calculations on crystalline graphite. Now high accuracy molecular and band structure calculations are in fairly good agreement. Second, we have used these methods to design transition metal clusters having the highest magnetic moment by maximizing the symmetry-required degeneracy of the one-electron orbitals. Most recently, we have developed accurate, variational generalized-gradient approximation (GGA) forces for use in geometry optimization of clusters and in molecular-dynamics simulations of friction. The GGA optimized geometries of a number of large clusters will be given

Calculation of hadronic part of photon structure function in QCD

International Nuclear Information System (INIS)

Gorskij, A.S.; Ioffe, B.L.; Oganesyan, A.G.; Khodzhamiryan, A.Yu.

1989-01-01

The photon structure function in QCD in the intermediate region of the Bjorken variable 0.2 2 /2pq, where q 2 is the hard photon virtuality, p is the soft photon momentum) is calculated. It is shown that without introduction of fitting parameters the experimental data can be described in the range 3GeV 2 ≤Q 2 2 /Q 2 =-q 2 /not taking account for the leading logarithmic corrections. It is demonstrated that the corrections proportional to μ ν 2 > to the hard photon scattering amplitude on the longitudinal soft photon and to the Callan-Gross relation vanish. 16 refs.; 6 figs

Development of SCINFUL-CG code to calculate response functions of scintillators in various shapes used for neutron measurement

Energy Technology Data Exchange (ETDEWEB)

Endo, Akira; Kim, Eunjoo; Yamaguchi, Yasuhiro [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

2001-10-01

A Monte Carlo code SCINFUL has been utilized for calculating response functions of organic scintillators for high-energy neutron spectroscopy. However, the applicability of SCINFUL is limited to the calculations for cylindrical NE213 and NE110 scintillators. In the present study, SCINFUL-CG was developed by introducing a geometry specifying function and high-energy neutron cross section data into SCINFUL. The geometry package MARS-CG, the extended version of the CG (Combinatorial Geometry), was programmed into SCINFUL-CG to express various geometries of detectors. Neutron spectra in the regions specified by the CG can be evaluated by the track length estimator. The cross section data of silicon, oxygen and aluminum for neutron transport calculation were incorporated up to 100 MeV using the data of LA150 library. Validity of SCINFUL-CG was examined by comparing calculated results with those by SCINFUL and MCNP and experimental data measured using high-energy neutron fields. SCINFUL-CG can be used for the calculations of the response functions and neutron spectra in the organic scintillators in various shapes. The computer code will be applicable to the designs of high-energy neutron spectrometers and neutron monitors using the organic scintillators. The present report describes the new features of SCINFUL-CG and explains how to use the code. (author)

The use of Wannier function in the calculations of band structure of covalent crystals

International Nuclear Information System (INIS)

Lu Dong; Yang Guang

1985-10-01

A variational procedure has been used to build up Wannier functions to study the energy bands of diamond, silicon and α-tin. For the case of silicon the Wannier function, density of charge and band structure are calculated self-consistently and a simple method in a non-self-consistent way has been used to compute the band structure of diamond, silicon and α-tin. The method seems to be effective to describe the electronic properties of covalent crystals. (author)

Causal Correlation Functions and Fourier Transforms: Application in Calculating Pressure Induced Shifts

Science.gov (United States)

Ma, Q.; Tipping, R. H.; Lavrentieva, N. N.

2012-01-01

By adopting a concept from signal processing, instead of starting from the correlation functions which are even, one considers the causal correlation functions whose Fourier transforms become complex. Their real and imaginary parts multiplied by 2 are the Fourier transforms of the original correlations and the subsequent Hilbert transforms, respectively. Thus, by taking this step one can complete the two previously needed transforms. However, to obviate performing the Cauchy principal integrations required in the Hilbert transforms is the greatest advantage. Meanwhile, because the causal correlations are well-bounded within the time domain and band limited in the frequency domain, one can replace their Fourier transforms by the discrete Fourier transforms and the latter can be carried out with the FFT algorithm. This replacement is justified by sampling theory because the Fourier transforms can be derived from the discrete Fourier transforms with the Nyquis rate without any distortions. We apply this method in calculating pressure induced shifts of H2O lines and obtain more reliable values. By comparing the calculated shifts with those in HITRAN 2008 and by screening both of them with the pair identity and the smooth variation rules, one can conclude many of shift values in HITRAN are not correct.

Tight-binding approximations to time-dependent density functional theory — A fast approach for the calculation of electronically excited states

Energy Technology Data Exchange (ETDEWEB)

Rüger, Robert, E-mail: rueger@scm.com [Scientific Computing & Modelling NV, De Boelelaan 1083, 1081 HV Amsterdam (Netherlands); Department of Theoretical Chemistry, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam (Netherlands); Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Linnéstr. 2, 04103 Leipzig (Germany); Lenthe, Erik van [Scientific Computing & Modelling NV, De Boelelaan 1083, 1081 HV Amsterdam (Netherlands); Heine, Thomas [Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Linnéstr. 2, 04103 Leipzig (Germany); Visscher, Lucas [Department of Theoretical Chemistry, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam (Netherlands)

2016-05-14

We propose a new method of calculating electronically excited states that combines a density functional theory based ground state calculation with a linear response treatment that employs approximations used in the time-dependent density functional based tight binding (TD-DFTB) approach. The new method termed time-dependent density functional theory TD-DFT+TB does not rely on the DFTB parametrization and is therefore applicable to systems involving all combinations of elements. We show that the new method yields UV/Vis absorption spectra that are in excellent agreement with computationally much more expensive TD-DFT calculations. Errors in vertical excitation energies are reduced by a factor of two compared to TD-DFTB.

Practical considerations in the calculation of orientation distribution functions from electron back-scattered diffraction patterns

International Nuclear Information System (INIS)

Bowen, A.W.

1994-01-01

Using model data sets for the Brass orientation, the importance of scatter width, angular accuracy and grain size and volume fraction on the sensitivity of the calculated Orientation Distribution Functions have been determined in order to highlight some of the practical considerations needed in the processing of experimental data from individual grain orientation measurements determined by the Electron Back-Scattered Diffraction technique. It is suggested that the most appropriate scatter width can be calculated from the maximum function height versus scatter width curve in order to accommodate variations in texture sharpness. The sensitivity of the ODF to careful sample preparation, mounting and pattern analysis, in order to keep errors in angular accuracy to 1 or less is demonstrated, as is the imperative need to correct for the size of grains, and their volume fractions. (orig.)

Radial basis function networks applied to DNBR calculation in digital core protection systems

International Nuclear Information System (INIS)

Lee, Gyu-Cheon; Heung Chang, Soon

2003-01-01

The nuclear power plant has to be operated with sufficient margin from the specified DNBR limit for assuring its safety. The digital core protection system calculates on-line real-time DNBR by using a complex subchannel analysis program, and triggers a reliable reactor shutdown if the calculated DNBR approaches the specified limit. However, it takes a relatively long calculation time even for a steady state condition, which may have an adverse effect on the operation flexibility. To overcome the drawback, a new method using a radial basis function network is presented in this paper. Nonparametric training approach is utilized, which shows dramatic reduction of the training time, no tedious heuristic process for optimizing parameters, and no local minima problem during the training. The test results show that the predicted DNBR is within about ±2% deviation from the target DNBR for the fixed axial flux shape case. For the variable axial flux case including severely skewed shapes that appeared during accidents, the deviation is within about ±10%. The suggested method could be the alternative that can calculate DNBR very quickly while guaranteeing the plant safety

Calculational model based on influence function method for power distribution and control rod worth in fast reactors

International Nuclear Information System (INIS)

Toshio, S.; Kazuo, A.

1983-01-01

A model for calculating the power distribution and the control rod worth in fast reactors has been developed. This model is based on the influence function method. The characteristics of the model are as follows: 1. Influence functions for any changes in the control rod insertion ratio are expressed by using an influence function for an appropriate control rod insertion in order to reduce the computer memory size required for the method. 2. A control rod worth is calculated on the basis of a one-group approximation in which cross sections are generated by bilinear (flux-adjoint) weighting, not the usual flux weighting, in order to reduce the collapse error. 3. An effective neutron multiplication factor is calculated by adjoint weighting in order to reduce the effect of the error in the one-group flux distribution. The results obtained in numerical examinations of a prototype fast reactor indicate that this method is suitable for on-line core performance evaluation because of a short computing time and a small memory size

Do calendrical savants use calculation to answer date questions? A functional magnetic resonance imaging study

Science.gov (United States)

Cowan, Richard; Frith, Chris

2009-01-01

Calendrical savants can name the weekdays for dates from different years with remarkable speed and accuracy. Whether calculation rather than just memory is involved is disputed. Grounds for doubting whether they can calculate are reviewed and criteria for attributing date calculation skills to them are discussed. At least some calendrical savants possess date calculation skills. A behavioural characteristic observed in many calendrical savants is increased response time for questions about more remote years. This may be because more remote years require more calculation or because closer years are more practised. An experiment is reported that used functional magnetic resonance imaging to attempt to discriminate between these explanations. Only two savants could be scanned and excessive head movement corrupted one savant's mental arithmetic data. Nevertheless, there was increased parietal activation during both mental arithmetic and date questions and this region showed increased activity with more remote dates. These results suggest that the calendrical skills observed in savants result from intensive practice with calculations used in solving mental arithmetic problems. The mystery is not how they solve these problems, but why. PMID:19528025

Calculations with the quasirelativistic local-spin-density-functional theory for high-Z atoms

International Nuclear Information System (INIS)

Guo, Y.; Whitehead, M.A.

1988-01-01

The generalized-exchange local-spin-density-functional theory (LSD-GX) with relativistic corrections of the mass velocity and Darwin terms has been used to calculate statistical total energies for the neutral atoms, the positive ions, and the negative ions for high-Z elements. The effect of the correlation and relaxation correction on the statistical total energy is discussed. Comparing the calculated results for the ionization potentials and electron affinities for the atoms (atomic number Z from 37 to 56 and 72 to 80) with experiment, shows that for the atoms rubidium to barium both the LSD-GX and the quasirelativistic LSD-GX, with self-interaction correction, Gopinathan, Whitehead, and Bogdanovic's Fermi-hole parameters [Phys. Rev. A 14, 1 (1976)], and Vosko, Wilk, and Nusair's correlation correction [Can. J. Phys. 58, 1200 (1980)], are very good methods for calculating ionization potentials and electron affinities. For the atoms hafnium to mercury the relativistic effect has to be considered

Calculating the Ionization Constant of Functional Groups of Carboxyl Ion Exchangers

Science.gov (United States)

Meychik, N. R.; Stepanov, S. I.; Nikolaeva, Yu. I.

2018-02-01

The potentiometric titration of a weakly basic carboxyl cation exchanger, obtained via alkaline hydrolysis of an acrylonitrile copolymer with divinyl benzene (degree of crosslinking, 12%) in a wide range of variation in a solution of pH (2-12) and NaCl (concentration 0.01, 0.1, 0.5, 1 M), is considered. The maximum ion-exchange capacity of the ion exchanger for Na+ is determined (10.10 ± 0.088 mmol/g of the dry mass) and found to be independent of the solution's ionic strength. It is established that in the investigated range of NaCl concentrations and pH, the acid-base balance is adequately described by Gregor's equation. The parameters of this equation are calculated as a function of the NaCl concentration: p K a = 8.13 ± 0.04, n = 1.50 ± 0.02 for 0.01 M; p K a = 6.56 ± 0.04, n = 2.60 ± 0.07 for 0.1 M; and p K a = 5.66 ± 0.6, n = 2.62 ± 0.06 for 0.5 and 1 M. It is shown that to describe the acid-base balance correctly within the proposed model we must estimate the adequacy of the experimental and calculated values of the ion exchanger's capacity at each pH value according to the calculated parameters of Gregor's equation.

Study on calculation of influence function with fracture mechanics analysis method for circumferential through-crack pipe

International Nuclear Information System (INIS)

Zheng Bin; Lu Yuechuan; Zang Fenggang; Sun Yingxue

2009-01-01

In order to widen the application of the engineering method of EPRI, with a series of analysis on the 3D elastic and elastic-plastic fracture mechanics finite element, the crack open displacements (COD) of cracked pipe were calculated and a key influence function h 2 in EPRI engineering method was studied against the COD results of FEM. A calculation method of h2 under the condition of tension and bending combined load was introduced in detail. In order to validate this method, the calculated h 2 results were compared with that of EPRI, and the calculated COD results based on the h 2 results were compared with that of PICEP. The compared results indicated that the calculated h 2 results as well as the COD results and the corresponding reference values were respectively accordant, and the calculation method in this paper was validated accordingly. (authors)

Calculating vibrational spectra with sum of product basis functions without storing full-dimensional vectors or matrices.

Science.gov (United States)

Leclerc, Arnaud; Carrington, Tucker

2014-05-07

We propose an iterative method for computing vibrational spectra that significantly reduces the memory cost of calculations. It uses a direct product primitive basis, but does not require storing vectors with as many components as there are product basis functions. Wavefunctions are represented in a basis each of whose functions is a sum of products (SOP) and the factorizable structure of the Hamiltonian is exploited. If the factors of the SOP basis functions are properly chosen, wavefunctions are linear combinations of a small number of SOP basis functions. The SOP basis functions are generated using a shifted block power method. The factors are refined with a rank reduction algorithm to cap the number of terms in a SOP basis function. The ideas are tested on a 20-D model Hamiltonian and a realistic CH3CN (12 dimensional) potential. For the 20-D problem, to use a standard direct product iterative approach one would need to store vectors with about 10(20) components and would hence require about 8 × 10(11) GB. With the approach of this paper only 1 GB of memory is necessary. Results for CH3CN agree well with those of a previous calculation on the same potential.

Electronic and thermoelectric properties of InN studied using ab initio density functional theory and Boltzmann transport calculations

Energy Technology Data Exchange (ETDEWEB)

Borges, P. D., E-mail: pdborges@gmail.com, E-mail: lscolfaro@txstate.edu; Scolfaro, L., E-mail: pdborges@gmail.com, E-mail: lscolfaro@txstate.edu [Department of Physics, Texas State University, San Marcos, Texas 78666 (United States)

2014-12-14

The thermoelectric properties of indium nitride in the most stable wurtzite phase (w-InN) as a function of electron and hole concentrations and temperature were studied by solving the semiclassical Boltzmann transport equations in conjunction with ab initio electronic structure calculations, within Density Functional Theory. Based on maximally localized Wannier function basis set and the ab initio band energies, results for the Seebeck coefficient are presented and compared with available experimental data for n-type as well as p-type systems. Also, theoretical results for electric conductivity and power factor are presented. Most cases showed good agreement between the calculated properties and experimental data for w-InN unintentionally and p-type doped with magnesium. Our predictions for temperature and concentration dependences of electrical conductivity and power factor revealed a promising use of InN for intermediate and high temperature thermoelectric applications. The rigid band approach and constant scattering time approximation were utilized in the calculations.

Density functional theory calculations of the water interactions with ZrO2 nanoparticles Y2O3 doped

Science.gov (United States)

Subhoni, Mekhrdod; Kholmurodov, Kholmirzo; Doroshkevich, Aleksandr; Asgerov, Elmar; Yamamoto, Tomoyuki; Lyubchyk, Andrei; Almasan, Valer; Madadzada, Afag

2018-03-01

Development of a new electricity generation techniques is one of the most relevant tasks, especially nowadays under conditions of extreme growth in energy consumption. The exothermic heterogeneous electrochemical energy conversion to the electric energy through interaction of the ZrO2 based nanopowder system with atmospheric moisture is one of the ways of electric energy obtaining. The questions of conversion into the electric form of the energy of water molecules adsorption in 3 mol% Y2O3 doped ZrO2 nanopowder systems were investigated using the density functional theory calculations. The density functional theory calculations has been realized as in the Kohn-Sham formulation, where the exchange-correlation potential is approximated by a functional of the electronic density. The electronic density, total energy and band structure calculations are carried out using the all-electron, full potential, linear augmented plane wave method of the electronic density and related approximations, i.e. the local density, the generalized gradient and their hybrid approximations.

Density-functional calculations of the surface tension of liquid Al and Na

Science.gov (United States)

Stroud, D.; Grimson, M. J.

1984-01-01

Calculations of the surface tensions of liquid Al and Na are described using the full ionic density functional formalism of Wood and Stroud (1983). Surface tensions are in good agreement with experiment in both cases, with results substantially better for Al than those found previously in the gradient approximation. Preliminary minimization with respect to surface profile leads to an oscillatory profile superimposed on a nearly steplike ionic density disribution; the oscillations have a wavellength of about a hardsphere diameter.

Molecular Structure And Vibrational Frequencies of Tetrafluoro isophthalonitrile By Hartree-Fock And Density Functional Theory Calculations

International Nuclear Information System (INIS)

Ayikoglu, A.

2008-01-01

The molecular structure, vibrational frequencies and corresponding vibrational assignments of tetrafluoro isophthalonitrile (TFPN) in the ground state have been calculated using the Hartree-Fock (HF) and density functional methods (B3LYP) with 6-311++G (d, p) basis set. The calculations were utilized in the CS symmetry of TFPN. The obtained vibrational frequencies and optimized geometric parameters (bond lengths and bond angles) were seen to be in good agreement with the experimental data. The comparison of the observed and calculated results showed that the B3LYP method is superior to the HF method for both the vibrational frequencies and geometric parameters

Improved Accuracy of Density Functional Theory Calculations for CO2 Reduction and Metal-Air Batteries

DEFF Research Database (Denmark)

Christensen, Rune; Hansen, Heine Anton; Vegge, Tejs

2015-01-01

Density functional theory (DFT) calculations have greatly contributed to the atomic level understanding of electrochemical reactions. However, in some cases, the accuracy can be prohibitively low for a detailed understanding of, e.g. reaction mechanisms. Two cases are examined here, i.e. the elec......Density functional theory (DFT) calculations have greatly contributed to the atomic level understanding of electrochemical reactions. However, in some cases, the accuracy can be prohibitively low for a detailed understanding of, e.g. reaction mechanisms. Two cases are examined here, i.......47 eV and 0.17 eV using metals as reference. The presented approach for error identification is expected to be applicable to a very broad range of systems. References: [1] A. A. Peterson, F. Abild-Pedersen, F. Studt, J. Rossmeisl, and J. K. Nørskov, Energy Environ. Sci., 3,1311 (2010) [2] F. Studt, F...

Four-component relativistic density functional theory calculations of NMR shielding tensors for paramagnetic systems.

Science.gov (United States)

Komorovsky, Stanislav; Repisky, Michal; Ruud, Kenneth; Malkina, Olga L; Malkin, Vladimir G

2013-12-27

A four-component relativistic method for the calculation of NMR shielding constants of paramagnetic doublet systems has been developed and implemented in the ReSpect program package. The method uses a Kramer unrestricted noncollinear formulation of density functional theory (DFT), providing the best DFT framework for property calculations of open-shell species. The evaluation of paramagnetic nuclear magnetic resonance (pNMR) tensors reduces to the calculation of electronic g tensors, hyperfine coupling tensors, and NMR shielding tensors. For all properties, modern four-component formulations were adopted. The use of both restricted kinetically and magnetically balanced basis sets along with gauge-including atomic orbitals ensures rapid basis-set convergence. These approaches are exact in the framework of the Dirac-Coulomb Hamiltonian, thus providing useful reference data for more approximate methods. Benchmark calculations on Ru(III) complexes demonstrate good performance of the method in reproducing experimental data and also its applicability to chemically relevant medium-sized systems. Decomposition of the temperature-dependent part of the pNMR tensor into the traditional contact and pseudocontact terms is proposed.

Relativistic many-body perturbation-theory calculations based on Dirac-Fock-Breit wave functions

International Nuclear Information System (INIS)

Ishikawa, Y.; Quiney, H.M.

1993-01-01

A relativistic many-body perturbation theory based on the Dirac-Fock-Breit wave functions has been developed and implemented by employing analytic basis sets of Gaussian-type functions. The instantaneous Coulomb and low-frequency Breit interactions are treated using a unified formalism in both the construction of the Dirac-Fock-Breit self-consistent-field atomic potential and in the evaluation of many-body perturbation-theory diagrams. The relativistic many-body perturbation-theory calculations have been performed on the helium atom and ions of the helium isoelectronic sequence up to Z=50. The contribution of the low-frequency Breit interaction to the relativistic correlation energy is examined for the helium isoelectronic sequence

Impaired neural networks for approximate calculation in dyscalculic children: a functional MRI study

Directory of Open Access Journals (Sweden)

Dosch Mengia

2006-09-01

Full Text Available Abstract Background Developmental dyscalculia (DD is a specific learning disability affecting the acquisition of mathematical skills in children with otherwise normal general intelligence. The goal of the present study was to examine cerebral mechanisms underlying DD. Methods Eighteen children with DD aged 11.2 ± 1.3 years and twenty age-matched typically achieving schoolchildren were investigated using functional magnetic resonance imaging (fMRI during trials testing approximate and exact mathematical calculation, as well as magnitude comparison. Results Children with DD showed greater inter-individual variability and had weaker activation in almost the entire neuronal network for approximate calculation including the intraparietal sulcus, and the middle and inferior frontal gyrus of both hemispheres. In particular, the left intraparietal sulcus, the left inferior frontal gyrus and the right middle frontal gyrus seem to play crucial roles in correct approximate calculation, since brain activation correlated with accuracy rate in these regions. In contrast, no differences between groups could be found for exact calculation and magnitude comparison. In general, fMRI revealed similar parietal and prefrontal activation patterns in DD children compared to controls for all conditions. Conclusion In conclusion, there is evidence for a deficient recruitment of neural resources in children with DD when processing analog magnitudes of numbers.

One-loop calculations of photon splitting in relativistic quantum plasma by Green's function technique

International Nuclear Information System (INIS)

De la Incera, V.; Ferrer, E.; Shalad, A.Y.

1987-01-01

A homogeneous and isotropic plasma made up of electrons and positrons is examined. The coefficients of the covariant expansion of the three-photon vertex are calculated in the one-loop approximation of the Green's function technique, together with the probability amplitudes of various processes involving three photons that produce information on the probability of the polarization states of the incoming and outgoing photons in the splitting process. The calculation results are used to verify the consequences of all exact symmetries which must be done for the vertex tensor. The case of a charge-symmetric plasma is considered together with the special case of photon collinearity

One-nucleon removal reactions as a test of overlap functions from the one-body density matrix calculations

International Nuclear Information System (INIS)

Dimitrova, S.S.; Gaidarov, M.K.; Antonov, A.N.; Stoitsov, M.V.; Hodgson, P.E; Lukyanov, V.K.; Zemlyanaya, E.V.; Krumova, G.Z.

1997-01-01

Overlap functions and spectroscopic factors extracted from a model one-body density matrix (OBDM) accounting for short-range nucleon-nucleon correlations are used to calculate differential cross sections of (p, d) reactions and the momentum distributions of transitions to single-particle states in 16 O and 40 Ca. A comparison between the experimental (p, d) and (e, e'p) data, their DWBA and CDWIA analyses and the OBDM calculations is made. Our theoretical predictions for the spectroscopic factors are compared with the empirically extracted ones. It is shown that the overlap functions obtained within the Jastrow correlation method are applicable to the description of the quantities considered. (author)

The inclusion of long-range polarisation functions in calculations of low-energy e+-H2 scattering using the Kohn method

International Nuclear Information System (INIS)

Armour, E.A.G.; Plummer, M.

1989-01-01

An explanation is given of why it is necessary to include long-range polarisation functions in the trial function when carrying out Kohn calculations of low-energy positron (and electron) scattering by atoms and simple molecules. The asymptotic form of these functions in low-energy e + -H 2 scattering is deduced. Appropriate functions with this asymptotic form are used to represent the closed-channel part of the wavefunction in a Kohn calculation of the lowest partial wave of Σ u + symmetry in e + -H 2 scattering at very low energies. For k≤0.03a 0 -1 , the results obtained are in good agreement with those obtained using the Born approximation and the asymptotic forms of the static and polarisation potentials. The relationship is pointed out between this method of taking into account long-range polarisation and the polarised pseudostate method used in R-matrix calculations. (author)

Sr_2SmNbO_6 perovskite: Synthesis, characterization and density functional theory calculations

International Nuclear Information System (INIS)

Dutta, Alo; Mukhopadhyay, P.K.; Sinha, T.P.; Shannigrahi, Santiranjan; Himanshu, A.K.; Sen, Pintu; Bandyopadhyay, S.K.

2016-01-01

The density functional theory (DFT) under the generalized gradient approximation (GGA) has been used to investigate the electronic structure of double perovskite oxide Sr_2SmNbO_6 synthesized by the solid-state reaction technique. The Rietveld refinement of the X-ray diffraction pattern of the sample shows the monoclinic P2_1/n phase at room temperature. The X-ray photoemission spectrum (XPS) of the material is collected in the energy window of 0–1200 eV. The chemical shift of the constituent elements calculated from the core level XPS spectra is used to analyze the covalency between the O anion and Sm/Nb cations. The valence band (VB) XPS spectrum is compared with the calculated VB spectrum using partial density of states in a standard way. The Raman spectrum is employed to investigate the phonon modes of the material in the monoclinic phase. Lorentzian lines are used to fit the experimental Raman spectrum, which present 24 phonon modes corresponding to the stretching and banding of NbO_6/SmO_6 octahedra and translational motion of Sr along the Sr−O bond. The discrepancy between the measured and calculated band gap values has been removed by applying modified Becke-Johnson (mBJ) potential in the DFT calculations. The experimental optical band gap obtained from the UV–visible reflectance spectrum is found to be 3.42 eV, which is well matched with the DFT calculated value of 3.2 eV, and suggests the semiconducting nature of the material. The real (ε′) and imaginary (ε″) parts of the optical dielectric constant as a function of energy along the x-, y- and z-polarization directions using mBJ potential are calculated. The collective vibrational modes of the atoms, the Born effective charge of the ions and their effect on the static dielectric constant of the material are studied using DFT. The calculated value of static dielectric constant for SSN is found to be 41.3. - Highlights: • Electronic structure and dynamical properties of Sr_2SmNbO_6 (SSN

Calculation of the RPA response function of nuclei to quasi-elastic electron scattering with a density-dependent NN interaction

International Nuclear Information System (INIS)

Caillon, J-C.; Labarsouque, J.

1997-01-01

So far, the non-relativistic longitudinal and transverse functions in electron quasi-elastic scattering on the nuclei failed in reproducing satisfactorily the existent experimental data. The calculations including relativistic RPA correlations utilize until now the relativistic Hartree approximation to describe the nuclear matter. But, this provides an incompressibility module two times higher than its experimental value what is an important drawback for the calculation of realistic relativistic RPA correlations. Hence, we have determined the RPA response functions of nuclei by utilising a description of the relativistic nuclear matter leading to an incompressibility module in agreement with the empirical value. To do that we have utilized an interaction in the relativistic Hartree approximation in which we have determined the coupling constants σ-N and ω-N as a function of the density in order to reproduce the saturation curve obtained by a Dirac-Brueckner calculation. The results which we have obtained show that the longitudinal response function and the Coulomb sum generally overestimated when one utilizes the pure relativistic Hartree approximation, are here in good agreement with the experimental data for several nuclei

Calculation of uncertainties associated to environmental radioactivity measurements and their functions. Practical Procedure II

International Nuclear Information System (INIS)

Gascon, C.; Anton, M.P.

1997-01-01

Environmental radioactivity measurements are mainly affected by counting uncertainties. In this report the uncertainties associated to certain functions related to activity concentration calculations are determined. Some practical exercise are presented to calculate the uncertainties associated to: a) Chemical recovery of a radiochemical separation when employing tracers (i.e. Pu and Am purification from a sediment sample). b) Indirect determination of a mother radionuclide through one of its daughters (i. e. ''210 Pb quantification following its daughter ''210 Po building-up activity). c) Time span from last separation date of one of the components of a disintegration chain (i.e. Am last purification date from a nuclear weapons following ''241 Am and ''241 Pu measurements). Calculations concerning example b) and c) are based on Baterman equations, regulating radioactive equilibria. Although the exercises here presented are performed with certain radionuclides, they could be applied as generic procedures for other alpha-emitting radioelements

Calculation of Resonance Interaction Effects Using a Rational Approximation to the Symmetric Resonance Line Shape Function

International Nuclear Information System (INIS)

Haeggblom, H.

1968-08-01

The method of calculating the resonance interaction effect by series expansions has been studied. Starting from the assumption that the neutron flux in a homogeneous mixture is inversely proportional to the total cross section, the expression for the flux can be simplified by series expansions. Two types of expansions are investigated and it is shown that only one of them is generally applicable. It is also shown that this expansion gives sufficient accuracy if the approximate resonance line shape function is reasonably representative. An investigation is made of the approximation of the resonance shape function with a Gaussian function which in some cases has been used to calculate the interaction effect. It is shown that this approximation is not sufficiently accurate in all cases which can occur in practice. Then, a rational approximation is introduced which in the first order approximation gives the same order of accuracy as a practically exact shape function. The integrations can be made analytically in the complex plane and the method is therefore very fast compared to purely numerical integrations. The method can be applied both to statistically correlated and uncorrelated resonances

Calculation of Resonance Interaction Effects Using a Rational Approximation to the Symmetric Resonance Line Shape Function

Energy Technology Data Exchange (ETDEWEB)

Haeggblom, H

1968-08-15

The method of calculating the resonance interaction effect by series expansions has been studied. Starting from the assumption that the neutron flux in a homogeneous mixture is inversely proportional to the total cross section, the expression for the flux can be simplified by series expansions. Two types of expansions are investigated and it is shown that only one of them is generally applicable. It is also shown that this expansion gives sufficient accuracy if the approximate resonance line shape function is reasonably representative. An investigation is made of the approximation of the resonance shape function with a Gaussian function which in some cases has been used to calculate the interaction effect. It is shown that this approximation is not sufficiently accurate in all cases which can occur in practice. Then, a rational approximation is introduced which in the first order approximation gives the same order of accuracy as a practically exact shape function. The integrations can be made analytically in the complex plane and the method is therefore very fast compared to purely numerical integrations. The method can be applied both to statistically correlated and uncorrelated resonances.

A third-generation density-functional-theory-based method for calculating canonical molecular orbitals of large molecules.

Science.gov (United States)

Hirano, Toshiyuki; Sato, Fumitoshi

2014-07-28

We used grid-free modified Cholesky decomposition (CD) to develop a density-functional-theory (DFT)-based method for calculating the canonical molecular orbitals (CMOs) of large molecules. Our method can be used to calculate standard CMOs, analytically compute exchange-correlation terms, and maximise the capacity of next-generation supercomputers. Cholesky vectors were first analytically downscaled using low-rank pivoted CD and CD with adaptive metric (CDAM). The obtained Cholesky vectors were distributed and stored on each computer node in a parallel computer, and the Coulomb, Fock exchange, and pure exchange-correlation terms were calculated by multiplying the Cholesky vectors without evaluating molecular integrals in self-consistent field iterations. Our method enables DFT and massively distributed memory parallel computers to be used in order to very efficiently calculate the CMOs of large molecules.

Explicit calculation of multi-fold contour integrals of certain ratios of Euler gamma functions. Pt. 1

Energy Technology Data Exchange (ETDEWEB)

Gonzalez, Ivan [Valparaiso Univ. (Chile). Inst. de Fisica y Astronomia; Kniehl, Bernd A. [Hamburg Univ. (Germany). II. Inst. fuer Theoretische Physik; Kondrashuk, Igor [Univ. del Bio-Bio, Chillan (Chile). Dept. de Ciencias Basicas; Notte-Cuello, Eduardo A. [La Serena Univ. (Chile). Dept. de Matematicas; Parra-Ferrada, Ivan [Talca Univ. (Chile). Inst. de Matematica y Fisica; Rojas-Medar, Marko A. [Univ. de Tarapaca, Arica (Chile). Inst. de Alta Investigacion

2016-12-15

In this paper we proceed to study properties of Mellin-Barnes (MB) transforms of Usyukina-Davydychev (UD) functions. In our previous papers [Nuclear Physics B 870 (2013) 243], [Nuclear Physics B 876 (2013) 322] we showed that multi-fold Mellin-Barnes (MB) transforms of Usyukina-Davydychev (UD) functions may be reduced to two-fold MB transforms and that the higher-order UD functions were obtained in terms of a differential operator by applying it to a slightly modified first UD function. The result is valid in d=4 dimensions and its analog in d=4-2ε dimensions exits too [Theoretical and Mathematical Physics 177 (2013) 1515]. In [Nuclear Physics B 870 (2013) 243] the chain of recurrent relations for analytically regularized UD functions was obtained implicitly by comparing the left hand side and the right hand side of the diagrammatic relations between the diagrams with different loop orders. In turn, these diagrammatic relations were obtained due to the method of loop reductions for the triangle ladder diagrams proposed in 1983 by Belokurov and Usyukina. Here we reproduce these recurrent relations by calculating explicitly via Barnes lemmas the contour integrals produced by the left hand sides of the diagrammatic relations. In such a way we explicitly calculate a family of multi-fold contour integrals of certain ratios of Euler gamma functions. We make a conjecture that similar results for the contour integrals are valid for a wider family of smooth functions which includes the MB transforms of UD functions.

Calculation of momentum distribution function of a non-thermal fermionic dark matter

Energy Technology Data Exchange (ETDEWEB)

Biswas, Anirban; Gupta, Aritra, E-mail: anirbanbiswas@hri.res.in, E-mail: aritra@hri.res.in [Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211 019 (India)

2017-03-01

The most widely studied scenario in dark matter phenomenology is the thermal WIMP scenario. Inspite of numerous efforts to detect WIMP, till now we have no direct evidence for it. A possible explanation for this non-observation of dark matter could be because of its very feeble interaction strength and hence, failing to thermalise with the rest of the cosmic soup. In other words, the dark matter might be of non-thermal origin where the relic density is obtained by the so-called freeze-in mechanism. Furthermore, if this non-thermal dark matter is itself produced substantially from the decay of another non-thermal mother particle, then their distribution functions may differ in both size and shape from the usual equilibrium distribution function. In this work, we have studied such a non-thermal (fermionic) dark matter scenario in the light of a new type of U(1){sub B−L} model. The U(1){sub B−L} model is interesting, since, besides being anomaly free, it can give rise to neutrino mass by Type II see-saw mechanism. Moreover, as we will show, it can accommodate a non-thermal fermionic dark matter as well. Starting from the collision terms, we have calculated the momentum distribution function for the dark matter by solving a coupled system of Boltzmann equations. We then used it to calculate the final relic abundance, as well as other relevant physical quantities. We have also compared our result with that obtained from solving the usual Boltzmann (or rate) equations directly in terms of comoving number density, Y . Our findings suggest that the latter approximation is valid only in cases where the system under study is close to equilibrium, and hence should be used with caution.

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

A massively-parallel electronic-structure calculations based on real-space density functional theory

International Nuclear Information System (INIS)

Iwata, Jun-Ichi; Takahashi, Daisuke; Oshiyama, Atsushi; Boku, Taisuke; Shiraishi, Kenji; Okada, Susumu; Yabana, Kazuhiro

2010-01-01

Based on the real-space finite-difference method, we have developed a first-principles density functional program that efficiently performs large-scale calculations on massively-parallel computers. In addition to efficient parallel implementation, we also implemented several computational improvements, substantially reducing the computational costs of O(N 3 ) operations such as the Gram-Schmidt procedure and subspace diagonalization. Using the program on a massively-parallel computer cluster with a theoretical peak performance of several TFLOPS, we perform electronic-structure calculations for a system consisting of over 10,000 Si atoms, and obtain a self-consistent electronic-structure in a few hundred hours. We analyze in detail the costs of the program in terms of computation and of inter-node communications to clarify the efficiency, the applicability, and the possibility for further improvements.

Structure function of off-mass-shell pions and the calculation of the Sullivan process

International Nuclear Information System (INIS)

Shakin, C.M.; Sun, W.

1994-01-01

We construct a model for the pion (valence) structure function that fits the experimental data obtained in the study of the Drell-Yan process. The model may also be used to calculate the structure function of off-mass-shell pions. We apply our model in the study of deep-inelastic scattering from off-mass-shell pions found in the nucleon and are thus able to resolve a problem encountered in the standard analysis of such processes. The usual analysis is made using the structure function of on-mass-shell pions and requires the use of a soft πNN form factor that is inconsistent with standard nuclear physics phenomenology. The use of our off-mass-shell structure functions allows for a fit to the data for nonperturbative aspects of the nucleon ''sea'' with a pion-nucleon form factor of the standard form

Ab initio density-functional calculations in materials science: from quasicrystals over microporous catalysts to spintronics.

Science.gov (United States)

Hafner, Jürgen

2010-09-29

During the last 20 years computer simulations based on a quantum-mechanical description of the interactions between electrons and atomic nuclei have developed an increasingly important impact on materials science, not only in promoting a deeper understanding of the fundamental physical phenomena, but also enabling the computer-assisted design of materials for future technologies. The backbone of atomic-scale computational materials science is density-functional theory (DFT) which allows us to cast the intractable complexity of electron-electron interactions into the form of an effective single-particle equation determined by the exchange-correlation functional. Progress in DFT-based calculations of the properties of materials and of simulations of processes in materials depends on: (1) the development of improved exchange-correlation functionals and advanced post-DFT methods and their implementation in highly efficient computer codes, (2) the development of methods allowing us to bridge the gaps in the temperature, pressure, time and length scales between the ab initio calculations and real-world experiments and (3) the extension of the functionality of these codes, permitting us to treat additional properties and new processes. In this paper we discuss the current status of techniques for performing quantum-based simulations on materials and present some illustrative examples of applications to complex quasiperiodic alloys, cluster-support interactions in microporous acid catalysts and magnetic nanostructures.

Hartree-Fock (HF) method and density functional theory calculations of Methanol to Gasoline (MTG) reaction

International Nuclear Information System (INIS)

Seddigi, Z.S.

2004-01-01

We found interesting results regarding some thermodynamical parameters (Delta H, Delta G and Delta S of the MTG Reaction and FTIR Spectra of methanol and dimethylether, using the Hartree-Fock method and Density Functional Theory (DFT) calculations at different computational levels. It is the aim of this paper to highlight these results. The GAUSSIAN 98 program was used to carry out the LCAO-MO-SCF calculations at the following levels: RHF/3-21g, RHF/6-31g and DFT/B3LYP/d95**. Calculations at the restricted Hartree-Fock levels (FHR/3-22 g and RHF/6-31g) were performed since they are expensive as other levels (DFT/B3LYP/d95**. In case of the HF method, working with larger basis set (6-31g) has improved the values slightly, which is as expected. We have noticed that performing calculations at higher levels (DFT/B3LY/D95**) than the Hartree-Fock method does not dramatically improve the situation. Indeed RHF is a reasonable approximation for many single gas phase molecular calculations. HF calculations at relatively small basis sets are adequate. The theoretical vibrational spectra of both methanol and dimethylether were compared with experimental results. (author)

Large scale GW calculations

International Nuclear Information System (INIS)

Govoni, Marco; Argonne National Lab., Argonne, IL; Galli, Giulia; Argonne National Lab., Argonne, IL

2015-01-01

We present GW calculations of molecules, ordered and disordered solids and interfaces, which employ an efficient contour deformation technique for frequency integration and do not require the explicit evaluation of virtual electronic states nor the inversion of dielectric matrices. We also present a parallel implementation of the algorithm, which takes advantage of separable expressions of both the single particle Green's function and the screened Coulomb interaction. The method can be used starting from density functional theory calculations performed with semilocal or hybrid functionals. The newly developed technique was applied to GW calculations of systems of unprecedented size, including water/semiconductor interfaces with thousands of electrons

Identifying Tm-C82 isomers with density functional theory calculations

International Nuclear Information System (INIS)

Zheng Limin; He Hongqing; Yang Minghui; Zeng Qun; Yang Mingli

2010-01-01

Density functional theory calculations have been performed to study the geometrical and electronic properties of endohedral metallofullerene Tm-C 82 isomers. Three energetically favorable isomers (with C s , C 2 and C 2v symmetry, respectively) are identified which are consistent with the nuclear magnetic resonance (NMR) observations. The simulated ultraviolet photoelectron spectra (UPS) based on the three structures agree well with the measurements. Particularly, the parent cage of the experimentally observed Tm-C 82 isomer with C s symmetry is newly assigned, which matches the experiments better than early assignments. In addition, strong interaction between an endohedral Tm atom and the C 82 cage is discussed and is thought to be responsible for the dramatic change in the relative stability of C 82 isomers when Tm is encapsulated.

Automated variance reduction of Monte Carlo shielding calculations using the discrete ordinates adjoint function

International Nuclear Information System (INIS)

Wagner, J.C.; Haghighat, A.

1998-01-01

Although the Monte Carlo method is considered to be the most accurate method available for solving radiation transport problems, its applicability is limited by its computational expense. Thus, biasing techniques, which require intuition, guesswork, and iterations involving manual adjustments, are employed to make reactor shielding calculations feasible. To overcome this difficulty, the authors have developed a method for using the S N adjoint function for automated variance reduction of Monte Carlo calculations through source biasing and consistent transport biasing with the weight window technique. They describe the implementation of this method into the standard production Monte Carlo code MCNP and its application to a realistic calculation, namely, the reactor cavity dosimetry calculation. The computational effectiveness of the method, as demonstrated through the increase in calculational efficiency, is demonstrated and quantified. Important issues associated with this method and its efficient use are addressed and analyzed. Additional benefits in terms of the reduction in time and effort required of the user are difficult to quantify but are possibly as important as the computational efficiency. In general, the automated variance reduction method presented is capable of increases in computational performance on the order of thousands, while at the same time significantly reducing the current requirements for user experience, time, and effort. Therefore, this method can substantially increase the applicability and reliability of Monte Carlo for large, real-world shielding applications

NULLIJN, a program to calculate zero curves of a function of two variables of which one may be complex

International Nuclear Information System (INIS)

Jagher, P.C. de

1978-01-01

When an algorithm for a function f of two variables, for instance a dispersion function f(ω, k) or a potential V(r, z), is known, the program calculates and plots the zero curves, thus giving a graphical representation of an implicitly defined function. One of the variables may be complex. A quadratic extrapolation, followed by a regula falsi algorithm to find a zero is used to calculate a succession of zero-points along a curve. The starting point of a curve is found by detecting a change of sign of the function on the edge of the area G that is examined. Curves that lie entirely inside G are not found. Starting points of curves where the imaginary part of the complex variable is large might be missed. (Auth.)

Atom probe tomography simulations and density functional theory calculations of bonding energies in Cu3Au

KAUST Repository

Boll, Torben; Zhu, Zhiyong; Al-Kassab, Talaat; Schwingenschlö gl, Udo

2012-01-01

In this article the Cu-Au binding energy in Cu3Au is determined by comparing experimental atom probe tomography (APT) results to simulations. The resulting bonding energy is supported by density functional theory calculations. The APT simulations

A comparison of density functional theory and coupled cluster methods for the calculation of electric dipole polarizability gradients of methane

DEFF Research Database (Denmark)

Paidarová, Ivana; Sauer, Stephan P. A.

2012-01-01

We have compared the performance of density functional theory (DFT) using five different exchange-correlation functionals with four coupled cluster theory based wave function methods in the calculation of geometrical derivatives of the polarizability tensor of methane. The polarizability gradient...

Functional renormalization group approach to electronic structure calculations for systems without translational symmetry

Science.gov (United States)

Seiler, Christian; Evers, Ferdinand

2016-10-01

A formalism for electronic-structure calculations is presented that is based on the functional renormalization group (FRG). The traditional FRG has been formulated for systems that exhibit a translational symmetry with an associated Fermi surface, which can provide the organization principle for the renormalization group (RG) procedure. We here advance an alternative formulation, where the RG flow is organized in the energy-domain rather than in k space. This has the advantage that it can also be applied to inhomogeneous matter lacking a band structure, such as disordered metals or molecules. The energy-domain FRG (ɛ FRG) presented here accounts for Fermi-liquid corrections to quasiparticle energies and particle-hole excitations. It goes beyond the state of the art G W -BSE , because in ɛ FRG the Bethe-Salpeter equation (BSE) is solved in a self-consistent manner. An efficient implementation of the approach that has been tested against exact diagonalization calculations and calculations based on the density matrix renormalization group is presented. Similar to the conventional FRG, also the ɛ FRG is able to signalize the vicinity of an instability of the Fermi-liquid fixed point via runaway flow of the corresponding interaction vertex. Embarking upon this fact, in an application of ɛ FRG to the spinless disordered Hubbard model we calculate its phase boundary in the plane spanned by the interaction and disorder strength. Finally, an extension of the approach to finite temperatures and spin S =1 /2 is also given.

The calculation of the viscosity from the autocorrelation function using molecular and atomic stress tensors

Science.gov (United States)

Cui, S. T.

The stress-stress correlation function and the viscosity of a united-atom model of liquid decane are studied by equilibrium molecular dynamics simulation using two different formalisms for the stress tensor: the atomic and the molecular formalisms. The atomic and molecular correlation functions show dramatic difference in short-time behaviour. The integrals of the two correlation functions, however, become identical after a short transient period whichis significantly shorter than the rotational relaxation time of the molecule. Both reach the same plateau value in a time period corresponding to this relaxation time. These results provide a convenient guide for the choice of the upper integral time limit in calculating the viscosity by the Green-Kubo formula.

Structural, elastic, electronic and dynamical properties of OsB and ReB: Density functional calculations

Science.gov (United States)

Li, Yanling; Zeng, Zhi; Lin, Haiqing

2010-06-01

The structural, elastic, electronic and dynamical properties of ReB and OsB are investigated by first-principles calculations based on density functional theory. It turns out that ReB and OsB are metallic ultra-incompressible solids with small elastic anisotropy and high hardness. The change of c/ a ratio in OsB indicates that there is a structural phase transition at about 31 GPa. Phonon spectra calculations show that both OsB and ReB are stable dynamically and there are abnormal phonon dispersions along special directions in Brillouin zone. OsB and ReB do not show superconductivity due to very weak electron-phonon interactions in them.

ERF/ERFC, Calculation of Error Function, Complementary Error Function, Probability Integrals

International Nuclear Information System (INIS)

Vogel, J.E.

1983-01-01

1 - Description of problem or function: ERF and ERFC are used to compute values of the error function and complementary error function for any real number. They may be used to compute other related functions such as the normal probability integrals. 4. Method of solution: The error function and complementary error function are approximated by rational functions. Three such rational approximations are used depending on whether - x .GE.4.0. In the first region the error function is computed directly and the complementary error function is computed via the identity erfc(x)=1.0-erf(x). In the other two regions the complementary error function is computed directly and the error function is computed from the identity erf(x)=1.0-erfc(x). The error function and complementary error function are real-valued functions of any real argument. The range of the error function is (-1,1). The range of the complementary error function is (0,2). 5. Restrictions on the complexity of the problem: The user is cautioned against using ERF to compute the complementary error function by using the identity erfc(x)=1.0-erf(x). This subtraction may cause partial or total loss of significance for certain values of x

High-throughput density functional calculations to optimize properties and interfacial chemistry of piezoelectric materials

Science.gov (United States)

Barr, Jordan A.; Lin, Fang-Yin; Ashton, Michael; Hennig, Richard G.; Sinnott, Susan B.

2018-02-01

High-throughput density functional theory calculations are conducted to search through 1572 A B O3 compounds to find a potential replacement material for lead zirconate titanate (PZT) that exhibits the same excellent piezoelectric properties as PZT and lacks both its use of the toxic element lead (Pb) and the formation of secondary alloy phases with platinum (Pt) electrodes. The first screening criterion employed a search through the Materials Project database to find A -B combinations that do not form ternary compounds with Pt. The second screening criterion aimed to eliminate potential candidates through first-principles calculations of their electronic structure, in which compounds with a band gap of 0.25 eV or higher were retained. Third, thermodynamic stability calculations were used to compare the candidates in a Pt environment to compounds already calculated to be stable within the Materials Project. Formation energies below or equal to 100 meV/atom were considered to be thermodynamically stable. The fourth screening criterion employed lattice misfit to identify those candidate perovskites that have low misfit with the Pt electrode and high misfit of potential secondary phases that can be formed when Pt alloys with the different A and B components. To aid in the final analysis, dynamic stability calculations were used to determine those perovskites that have dynamic instabilities that favor the ferroelectric distortion. Analysis of the data finds three perovskites warranting further investigation: CsNb O3 , RbNb O3 , and CsTa O3 .

Calculation of spatial weight functions for WWER-440 ex-core neutron detectors

International Nuclear Information System (INIS)

Csom, Gy.; Czifrus, Sz.; Feher, S.; Berki, T.

2001-01-01

The objective of the work presented in this paper was determination of a spatial weight function for WWER-440 ex-core detectors to be used for the interpretation of reload startup rod drop measurements. In view of the complexity of the geometry of the core as well as the detector, furthermore the presence of a cavity between the vessel and the concrete shield, Monte Carlo calculations were applied. In spite of the fact that in the corresponding literature the use of adjoint methods dominates, in the present case the forward method was chosen and implemented using MCNP4C (Authors)

Molecular wave function and effective adiabatic potentials calculated by extended multi-configuration time-dependent Hartree-Fock method

Energy Technology Data Exchange (ETDEWEB)

Kato, Tsuyoshi; Ide, Yoshihiro; Yamanouchi, Kaoru [Department of Chemistry, School of Science, The University of Tokyo, 7-3-1, Hongo Bunkyo-ku, Tokyo, 113-0033 (Japan)

2015-12-31

We first calculate the ground-state molecular wave function of 1D model H{sub 2} molecule by solving the coupled equations of motion formulated in the extended multi-configuration time-dependent Hartree-Fock (MCTDHF) method by the imaginary time propagation. From the comparisons with the results obtained by the Born-Huang (BH) expansion method as well as with the exact wave function, we observe that the memory size required in the extended MCTDHF method is about two orders of magnitude smaller than in the BH expansion method to achieve the same accuracy for the total energy. Second, in order to provide a theoretical means to understand dynamical behavior of the wave function, we propose to define effective adiabatic potential functions and compare them with the conventional adiabatic electronic potentials, although the notion of the adiabatic potentials is not used in the extended MCTDHF approach. From the comparison, we conclude that by calculating the effective potentials we may be able to predict the energy differences among electronic states even for a time-dependent system, e.g., time-dependent excitation energies, which would be difficult to be estimated within the BH expansion approach.

General theory for calculating disorder-averaged Green's function correlators within the coherent potential approximation

Science.gov (United States)

Zhou, Chenyi; Guo, Hong

2017-01-01

We report a diagrammatic method to solve the general problem of calculating configurationally averaged Green's function correlators that appear in quantum transport theory for nanostructures containing disorder. The theory treats both equilibrium and nonequilibrium quantum statistics on an equal footing. Since random impurity scattering is a problem that cannot be solved exactly in a perturbative approach, we combine our diagrammatic method with the coherent potential approximation (CPA) so that a reliable closed-form solution can be obtained. Our theory not only ensures the internal consistency of the diagrams derived at different levels of the correlators but also satisfies a set of Ward-like identities that corroborate the conserving consistency of transport calculations within the formalism. The theory is applied to calculate the quantum transport properties such as average ac conductance and transmission moments of a disordered tight-binding model, and results are numerically verified to high precision by comparing to the exact solutions obtained from enumerating all possible disorder configurations. Our formalism can be employed to predict transport properties of a wide variety of physical systems where disorder scattering is important.

Beam brightness calculation for analytical and empirical distribution functions

International Nuclear Information System (INIS)

Myers, T.J.; Boulais, K.A.; O, Y.S.; Rhee, M.J.

1992-01-01

The beam brightness, a figure of merit for a beam quality useful for high-current low-emittance beams, was introduced by van Steenbergen as B = I/V 4 , where I is the beam current and V 4 is the hypervolume in the four-dimensional trace space occupied by the beam particles. Customarily, the brightness is expressed in terms of the product of emittances ε x ε y as B = ηI/(π 2 ε x ε y ), where η is a form factor of order unity which depends on the precise definition of emittance and hypervolume. Recently, a refined definition of the beam brightness based on the arithmetic mean value defined in statistics is proposed. The beam brightness is defined as B triple-bond 4 > = I -1 ∫ ρ 4 2 dxdydx'dy', where I is the beam current given by I ∫ ρ 4 dxdydx'dy'. Note that in this definition, neither the hypervolume V 4 nor the emittance, are explicitly used; the brightness is determined solely by the distribution function. Brightnesses are unambiguously calculated and expressed analytically in terms of the respective beam current and effective emittance for a few commonly used distribution functions, including Maxwellian and water-bag distributions. Other distributions of arbitrary shape frequently encountered in actual experiments are treated numerically. The resulting brightnesses are expressed in the form B = ηI/(π 2 ε x ε y ), and η is found to be weakly dependent on the form of velocity distribution as well as spatial distribution

Conformational and vibrational analysis of 5-hydroxy 2-nitrobenzaldehyde by AB initio hartree-fock, density functional theory calculations

International Nuclear Information System (INIS)

Cinakli, S.; Sert, Y.; Boeyuekata, M.; Ucun, F.

2010-01-01

The vibrational spectra of benzaldehyde and its derivatives have been studied earlier. The substitution of a functional group changes the spectra markedly. Recent spectroscopic studies of the benzaldehyde and their derivatives have been motivated because the vibrational spectra are very useful for understanding of specific biological process and in the analysis of relatively complex systems. The optimized molecular structure, vibrational frequencies and corresponding vibrational assignments, the total energy calculations, relative energies, the mean vibrational deviations of the two planar O-cis and O-trans roomers of 5-Hydroxy 2-nitrobenzaldehydes have been calculated using ab initio Hartree Fock (HF) and Density Functional Theory (B3LYP) with 6-311++G(d,p) basis set. All computations have been performed on personal computer using the Gaussian 03 program package. The calculations were adapted to Cs symmetries of all the molecules. The O-trans rotomers with lower energy of all the molecules have been found as preferential rotomers in the ground state.

Nature of adsorption on TiC(111) investigated with density-functional calculations

Science.gov (United States)

Ruberto, Carlo; Lundqvist, Bengt I.

2007-06-01

Extensive density-functional calculations are performed for chemisorption of atoms in the three first periods (H, B, C, N, O, F, Al, Si, P, S, and Cl) on the polar TiC(111) surface. Calculations are also performed for O on TiC(001), for full O(1×1) monolayer on TiC(111), as well as for bulk TiC and for the clean TiC(111) and (001) surfaces. Detailed results concerning atomic structures, energetics, and electronic structures are presented. For the bulk and the clean surfaces, previous results are confirmed. In addition, detailed results are given on the presence of C-C bonds in the bulk and at the surface, as well as on the presence of a Ti-based surface resonance (TiSR) at the Fermi level and of C-based surface resonances (CSR’s) in the lower part of the surface upper valence band. For the adsorption, adsorption energies Eads and relaxed geometries are presented, showing great variations characterized by pyramid-shaped Eads trends within each period. An extraordinarily strong chemisorption is found for the O atom, 8.8eV /adatom. On the basis of the calculated electronic structures, a concerted-coupling model for the chemisorption is proposed, in which two different types of adatom-substrate interactions work together to provide the obtained strong chemisorption: (i) adatom-TiSR and (ii) adatom-CSR’s. This model is used to successfully describe the essential features of the calculated Eads trends. The fundamental nature of this model, based on the Newns-Anderson model, should make it apt for general application to transition-metal carbides and nitrides and for predictive purposes in technological applications, such as cutting-tool multilayer coatings and MAX phases.

Analysis of the Vignale-Kohn current functional in the calculation of the optical spectra of semiconductors

NARCIS (Netherlands)

Berger, J. A.; de Boeij, P. L.; van Leeuwen, R.

In this work, we investigate the Vignale-Kohn current functional when applied to the calculation of optical spectra of semiconductors. We discuss our results for silicon. We found qualitatively similar results for other semiconductors. These results show that there are serious limitations to the

Calculation of Spectra of Solids:

DEFF Research Database (Denmark)

Lindgård, Per-Anker

1975-01-01

The Gilat-Raubenheimer method simplified to tetrahedron division is used to calculate the real and imaginary part of the dynamical response function for electrons. A frequency expansion for the real part is discussed. The Lindhard function is calculated as a test for numerical accuracy...

Mechanisms for catalytic carbon nanofiber growth studied by ab initio density functional theory calculations

DEFF Research Database (Denmark)

Abild-Pedersen, Frank; Nørskov, Jens Kehlet; Rostrup-Nielsen, Jens

2006-01-01

Mechanisms and energetics of graphene growth catalyzed by nickel nanoclusters were studied using ab initio density functional theory calculations. It is demonstrated that nickel step-edge sites act as the preferential growth centers for graphene layers on the nickel surface. Carbon is transported......, and it is argued how these processes may lead to different nanofiber structures. The proposed growth model is found to be in good agreement with previous findings....

Four-Component Relativistic Density-Functional Theory Calculations of Nuclear Spin-Rotation Constants: Relativistic Effects in p-Block Hydrides.

Science.gov (United States)

Komorovsky, Stanislav; Repisky, Michal; Malkin, Elena; Demissie, Taye B; Ruud, Kenneth

2015-08-11

We present an implementation of the nuclear spin-rotation (SR) constants based on the relativistic four-component Dirac-Coulomb Hamiltonian. This formalism has been implemented in the framework of the Hartree-Fock and Kohn-Sham theory, allowing assessment of both pure and hybrid exchange-correlation functionals. In the density-functional theory (DFT) implementation of the response equations, a noncollinear generalized gradient approximation (GGA) has been used. The present approach enforces a restricted kinetic balance condition for the small-component basis at the integral level, leading to very efficient calculations of the property. We apply the methodology to study relativistic effects on the spin-rotation constants by performing calculations on XHn (n = 1-4) for all elements X in the p-block of the periodic table and comparing the effects of relativity on the nuclear SR tensors to that observed for the nuclear magnetic shielding tensors. Correlation effects as described by the density-functional theory are shown to be significant for the spin-rotation constants, whereas the differences between the use of GGA and hybrid density functionals are much smaller. Our calculated relativistic spin-rotation constants at the DFT level of theory are only in fair agreement with available experimental data. It is shown that the scaling of the relativistic effects for the spin-rotation constants (varying between Z(3.8) and Z(4.5)) is as strong as for the chemical shieldings but with a much smaller prefactor.

CO2 flowrate calculator

International Nuclear Information System (INIS)

Carossi, Jean-Claude

1969-02-01

A CO 2 flowrate calculator has been designed for measuring and recording the gas flow in the loops of Pegase reactor. The analog calculator applies, at every moment, Bernoulli's formula to the values that characterize the carbon dioxide flow through a nozzle. The calculator electronics is described (it includes a sampling calculator and a two-variable function generator), with its amplifiers, triggers, interpolator, multiplier, etc. Calculator operation and setting are presented

Evaluation of neutron thermalization parameters and benchmark reactor calculations using a synthetic scattering function for molecular gases

International Nuclear Information System (INIS)

Gillete, V.H.; Patino, N.E.; Granada, J.E.; Mayer, R.E.

1988-01-01

Using a synthetic scattering function which describes the interaction of neutrons with molecular gases we provide analytical expressions for zero-and first-order scattering kernels, σ 0 (E 0 →E), σ 1 (E 0 →E), and total cross section σ 0 (E 0 ). Based on these quantities, we have performed calculations of thermalization parameters and transport coefficients for H 2 O, D 2 O, C 6 H 6 and (CH 2 ) n at room temperature. Comparasion of such values with available experimental data and other calculations is satisfactory. We also generated nuclear data libraries for H 2 O with 47 thermal groups at 300K and performed some benchmark calculations ( 235 U, 239 Pu, PWR cell and typical APWR cell); the resulting reactivities are compared with experimental data and ENDF/B-IV calculations. (author) [pt

Efficient calculation of nuclear spin-rotation constants from auxiliary density functional theory

International Nuclear Information System (INIS)

Zuniga-Gutierrez, Bernardo; Camacho-Gonzalez, Monica; Bendana-Castillo, Alfonso; Simon-Bastida, Patricia; Calaminici, Patrizia; Köster, Andreas M.

2015-01-01

The computation of the spin-rotation tensor within the framework of auxiliary density functional theory (ADFT) in combination with the gauge including atomic orbital (GIAO) scheme, to treat the gauge origin problem, is presented. For the spin-rotation tensor, the calculation of the magnetic shielding tensor represents the most demanding computational task. Employing the ADFT-GIAO methodology, the central processing unit time for the magnetic shielding tensor calculation can be dramatically reduced. In this work, the quality of spin-rotation constants obtained with the ADFT-GIAO methodology is compared with available experimental data as well as with other theoretical results at the Hartree-Fock and coupled-cluster level of theory. It is found that the agreement between the ADFT-GIAO results and the experiment is good and very similar to the ones obtained by the coupled-cluster single-doubles-perturbative triples-GIAO methodology. With the improved computational performance achieved, the computation of the spin-rotation tensors of large systems or along Born-Oppenheimer molecular dynamics trajectories becomes feasible in reasonable times. Three models of carbon fullerenes containing hundreds of atoms and thousands of basis functions are used for benchmarking the performance. Furthermore, a theoretical study of temperature effects on the structure and spin-rotation tensor of the H 12 C– 12 CH–DF complex is presented. Here, the temperature dependency of the spin-rotation tensor of the fluorine nucleus can be used to identify experimentally the so far unknown bent isomer of this complex. To the best of our knowledge this is the first time that temperature effects on the spin-rotation tensor are investigated

Efficient calculation of nuclear spin-rotation constants from auxiliary density functional theory

Energy Technology Data Exchange (ETDEWEB)

Zuniga-Gutierrez, Bernardo, E-mail: bzuniga.51@gmail.com [Departamento de Ciencias Computacionales, Universidad de Guadalajara, Blvd. Marcelino García Barragán 1421, C.P. 44430 Guadalajara, Jalisco (Mexico); Camacho-Gonzalez, Monica [Universidad Tecnológica de Tecámac, División A2, Procesos Industriales, Carretera Federal México Pachuca Km 37.5, Col. Sierra Hermosa, C.P. 55740 Tecámac, Estado de México (Mexico); Bendana-Castillo, Alfonso [Universidad Tecnológica de Tecámac, División A3, Tecnologías de la Información y Comunicaciones, Carretera Federal México Pachuca Km 37.5, Col. Sierra Hermosa, C.P. 55740 Tecámac, Estado de México (Mexico); Simon-Bastida, Patricia [Universidad Tecnlógica de Tulancingo, División Electromecánica, Camino a Ahuehuetitla No. 301, Col. Las Presas, C.P. 43642 Tulancingo, Hidalgo (Mexico); Calaminici, Patrizia; Köster, Andreas M. [Departamento de Química, CINVESTAV, Avenida Instituto Politécnico Nacional 2508, A.P. 14-740, México D.F. 07000 (Mexico)

2015-09-14

The computation of the spin-rotation tensor within the framework of auxiliary density functional theory (ADFT) in combination with the gauge including atomic orbital (GIAO) scheme, to treat the gauge origin problem, is presented. For the spin-rotation tensor, the calculation of the magnetic shielding tensor represents the most demanding computational task. Employing the ADFT-GIAO methodology, the central processing unit time for the magnetic shielding tensor calculation can be dramatically reduced. In this work, the quality of spin-rotation constants obtained with the ADFT-GIAO methodology is compared with available experimental data as well as with other theoretical results at the Hartree-Fock and coupled-cluster level of theory. It is found that the agreement between the ADFT-GIAO results and the experiment is good and very similar to the ones obtained by the coupled-cluster single-doubles-perturbative triples-GIAO methodology. With the improved computational performance achieved, the computation of the spin-rotation tensors of large systems or along Born-Oppenheimer molecular dynamics trajectories becomes feasible in reasonable times. Three models of carbon fullerenes containing hundreds of atoms and thousands of basis functions are used for benchmarking the performance. Furthermore, a theoretical study of temperature effects on the structure and spin-rotation tensor of the H{sup 12}C–{sup 12}CH–DF complex is presented. Here, the temperature dependency of the spin-rotation tensor of the fluorine nucleus can be used to identify experimentally the so far unknown bent isomer of this complex. To the best of our knowledge this is the first time that temperature effects on the spin-rotation tensor are investigated.

Efficient calculation of nuclear spin-rotation constants from auxiliary density functional theory.

Science.gov (United States)

Zuniga-Gutierrez, Bernardo; Camacho-Gonzalez, Monica; Bendana-Castillo, Alfonso; Simon-Bastida, Patricia; Calaminici, Patrizia; Köster, Andreas M

2015-09-14

The computation of the spin-rotation tensor within the framework of auxiliary density functional theory (ADFT) in combination with the gauge including atomic orbital (GIAO) scheme, to treat the gauge origin problem, is presented. For the spin-rotation tensor, the calculation of the magnetic shielding tensor represents the most demanding computational task. Employing the ADFT-GIAO methodology, the central processing unit time for the magnetic shielding tensor calculation can be dramatically reduced. In this work, the quality of spin-rotation constants obtained with the ADFT-GIAO methodology is compared with available experimental data as well as with other theoretical results at the Hartree-Fock and coupled-cluster level of theory. It is found that the agreement between the ADFT-GIAO results and the experiment is good and very similar to the ones obtained by the coupled-cluster single-doubles-perturbative triples-GIAO methodology. With the improved computational performance achieved, the computation of the spin-rotation tensors of large systems or along Born-Oppenheimer molecular dynamics trajectories becomes feasible in reasonable times. Three models of carbon fullerenes containing hundreds of atoms and thousands of basis functions are used for benchmarking the performance. Furthermore, a theoretical study of temperature effects on the structure and spin-rotation tensor of the H(12)C-(12)CH-DF complex is presented. Here, the temperature dependency of the spin-rotation tensor of the fluorine nucleus can be used to identify experimentally the so far unknown bent isomer of this complex. To the best of our knowledge this is the first time that temperature effects on the spin-rotation tensor are investigated.

One-loop calculations of photon splitting in a relativistic quantum plasma by the Green function method

International Nuclear Information System (INIS)

De Lya Insera, V.; Ferrer, Eh.; Shabad, A.E.

1986-01-01

Homogeneous and isotopic plasma of electrons and positrons is considered. Coefficients of covariant expansion of three-photon vertex in one-loop approximation of a technique of the Green temperature functions have been calculated and as a result amplitudes of different processes probability with the participation of three photons giving the data on the polarization state probability of incoming and outgoing photons in the splitting process. Sequences of all exact symmetries, which must be accomplished for vertex tensor, have been checked from calculational results. A case of charge-symmetrical plasma and a special case of photon collinearity have been considered

Molecular and vibrational structure of diphenylether and its 4,4' -dibromo derivative. Infrared linear dichroism spectroscopy and density functional theory calculations

DEFF Research Database (Denmark)

Eriksen, Troels K; Karlsen, Eva; Spanget-Larsen, Jens

2015-01-01

The title compounds were investigated by means of Linear Dichroism (LD) IR spectroscopy on samples partially aligned in uniaxially stretched low-density polyethylene and by density functional theory calculations. Satisfactory overall agreement between observed and calculated vibrational wavenumbers...

Leading relativistic corrections for atomic P states calculated with a finite-nuclear-mass approach and all-electron explicitly correlated Gaussian functions

Science.gov (United States)

Stanke, Monika; Bralin, Amir; Bubin, Sergiy; Adamowicz, Ludwik

2018-01-01

In this work we report progress in the development and implementation of quantum-mechanical methods for calculating bound ground and excited states of small atomic systems. The work concerns singlet states with the L =1 total orbital angular momentum (P states). The method is based on the finite-nuclear-mass (non-Born-Oppenheimer; non-BO) approach and the use of all-particle explicitly correlated Gaussian functions for expanding the nonrelativistic wave function of the system. The development presented here includes derivation and implementation of algorithms for calculating the leading relativistic corrections for singlet states. The corrections are determined in the framework of the perturbation theory as expectation values of the corresponding effective operators using the non-BO wave functions. The method is tested in the calculations of the ten lowest 1P states of the helium atom and the four lowest 1P states of the beryllium atom.

Adaptive local basis set for Kohn–Sham density functional theory in a discontinuous Galerkin framework II: Force, vibration, and molecular dynamics calculations

Energy Technology Data Exchange (ETDEWEB)

Zhang, Gaigong [Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Lin, Lin, E-mail: linlin@math.berkeley.edu [Department of Mathematics, University of California, Berkeley, Berkeley, CA 94720 (United States); Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Hu, Wei, E-mail: whu@lbl.gov [Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Yang, Chao, E-mail: cyang@lbl.gov [Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Pask, John E., E-mail: pask1@llnl.gov [Physics Division, Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States)

2017-04-15

Recently, we have proposed the adaptive local basis set for electronic structure calculations based on Kohn–Sham density functional theory in a pseudopotential framework. The adaptive local basis set is efficient and systematically improvable for total energy calculations. In this paper, we present the calculation of atomic forces, which can be used for a range of applications such as geometry optimization and molecular dynamics simulation. We demonstrate that, under mild assumptions, the computation of atomic forces can scale nearly linearly with the number of atoms in the system using the adaptive local basis set. We quantify the accuracy of the Hellmann–Feynman forces for a range of physical systems, benchmarked against converged planewave calculations, and find that the adaptive local basis set is efficient for both force and energy calculations, requiring at most a few tens of basis functions per atom to attain accuracies required in practice. Since the adaptive local basis set has implicit dependence on atomic positions, Pulay forces are in general nonzero. However, we find that the Pulay force is numerically small and systematically decreasing with increasing basis completeness, so that the Hellmann–Feynman force is sufficient for basis sizes of a few tens of basis functions per atom. We verify the accuracy of the computed forces in static calculations of quasi-1D and 3D disordered Si systems, vibration calculation of a quasi-1D Si system, and molecular dynamics calculations of H{sub 2} and liquid Al–Si alloy systems, where we show systematic convergence to benchmark planewave results and results from the literature.

The effect of the 238U neutron strength function uncertainty on resonance structure calculations in unresolved regions

International Nuclear Information System (INIS)

Koshcheev, V.N.; Manturov, G.N.; Sinitsa, V.V.

1991-01-01

The effects of the neutron strength function uncertainties on the calculated values of the self-shielding factors and energy dependence of the total and capture 238 U cross-sections in the unresolved resonance region are investigated. (author). 26 refs, 5 figs

Identifying the distinct features of geometric structures for hole trapping to generate radicals on rutile TiO₂(110) in photooxidation using density functional theory calculations with hybrid functional.

Science.gov (United States)

Wang, Dong; Wang, Haifeng; Hu, P

2015-01-21

Using density functional theory calculations with HSE 06 functional, we obtained the structures of spin-polarized radicals on rutile TiO2(110), which is crucial to understand the photooxidation at the atomic level, and further calculate the thermodynamic stabilities of these radicals. By analyzing the results, we identify the structural features for hole trapping in the system, and reveal the mutual effects among the geometric structures, the energy levels of trapped hole states and their hole trapping capacities. Furthermore, the results from HSE 06 functional are compared to those from DFT + U and the stability trend of radicals against the number of slabs is tested. The effect of trapped holes on two important steps of the oxygen evolution reaction, i.e. water dissociation and the oxygen removal, is investigated and discussed.

Use of the Green function method for calculation of cross section of x-ray photoabsorption for solids

International Nuclear Information System (INIS)

Kozhakhmetov, S.K.

1996-01-01

Possibility of Green formalism use for calculation of photoabsorption of high-energy x-ray radiation is shown. Analytical expression for photoabsorption cross section is carried out. It does not contains wave functions in explicit form responding to finite states of photoelectron. 5 refs

All-loops calculation of the structure function x→0 in perturbative QCD

International Nuclear Information System (INIS)

Catani, S.

1991-01-01

We study in perturbative QCD the initial-state radiation associated to hadron processes in the semi-hard region of small x (x is the Bjorken variable). A recent analysis of the exclusive multi-gluon distributions to double (infrared and collinear) logarithmic accuracy is extended to the case of inclusive distributions, which we evaluate to single (infrared) logarithmic accuracy. Thus the resulting x→0 structure function or N→1 gluon anomalous dimension is computed to all-loops accuracy. For the inclusive distributions we are able to perform a calculation to such an accuracy by extensively using cancellations which originate from coherence of QCD radiation and the infrared regularity of real-virtual singularities. We find that the x→0 structure function satisfies the Lipatov equation. With the present study we therefore provide a new derivation of the Lipatov result in the context of hard collisions together with a fully exclusive description. We discuss the structure of the Lipatov equation in relation with the x→0 exclusive distributions previously obtained and with the Altarelli-Parisi equation valid for finite values of x. (orig.)

Density functional theory calculations on alkali and the alkaline Ca atoms adsorbed on graphene monolayers

International Nuclear Information System (INIS)

Dimakis, Nicholas; Valdez, Danielle; Flor, Fernando Antonio; Salgado, Andres; Adjibi, Kolade; Vargas, Sarah; Saenz, Justin

2017-01-01

Highlights: • Li, K, Na, and Ca graphene interaction is primarily ionic, whereas small covalent interactions also co-exist in these cases. • Van der Waals interactions are revealed by comparing adatom-graphene geometries between 1.4% and 3% adatom coverages and using Grimme corrections. • The Li, K, Na graphene interactions are accurately described by both PBE0 and PBE functionals. For Ca/graphene, the PBE0 functional should not be used. • For Li, K, and Na adsorbed on graphene, adatom-graphene interaction weakens as the adatom coverages increases. • The Ca-graphene interaction strength, which is stronger at high coverages, is opposite to increases in the Ca–4s orbital population. - Abstract: The adsorption of the alkali Li, K, and Na and the alkaline Ca on graphene is studied using periodic density functional theory (DFT) under various adatom coverages. The charge transfers between the adatom and the graphene sheet and the almost unchanged densities-of-states spectra in the energy region near and below the Fermi level support an ionic bond pattern between the adatom and the graphene atoms. However, the presence of small orbital overlap between the metal and the nearest graphene atom is indicative of small covalent bonding. Van der Waals interactions are examined through a semiempirical correction in the DFT functional and by comparing adatom-graphene calculations between 3% and 1.4% adatom coverages. Optimized adatom-graphene geometries identify the preferred adatom sites, whereas the adatom-graphene strength is correlated with the adsorption energy and the adatom distance from the graphene plane. Calculated electronic properties and structural parameters are obtained using hybrid functionals and a generalized gradient approximation functional paired with basis sets of various sizes. We found that due to long range electrostatic forces between the alkali/alkaline adatoms and the graphene monolayer, the adatom-graphene structural and electronic

Density functional theory calculations on alkali and the alkaline Ca atoms adsorbed on graphene monolayers

Energy Technology Data Exchange (ETDEWEB)

Dimakis, Nicholas, E-mail: nicholas.dimakis@utrgv.edu [Department of Physics, University of Texas Rio Grande Valley, Edinburg, TX (United States); Valdez, Danielle; Flor, Fernando Antonio; Salgado, Andres; Adjibi, Kolade [Department of Physics, University of Texas Rio Grande Valley, Edinburg, TX (United States); Vargas, Sarah; Saenz, Justin [Robert Vela High School, Edinburg, TX (United States)

2017-08-15

Highlights: • Li, K, Na, and Ca graphene interaction is primarily ionic, whereas small covalent interactions also co-exist in these cases. • Van der Waals interactions are revealed by comparing adatom-graphene geometries between 1.4% and 3% adatom coverages and using Grimme corrections. • The Li, K, Na graphene interactions are accurately described by both PBE0 and PBE functionals. For Ca/graphene, the PBE0 functional should not be used. • For Li, K, and Na adsorbed on graphene, adatom-graphene interaction weakens as the adatom coverages increases. • The Ca-graphene interaction strength, which is stronger at high coverages, is opposite to increases in the Ca–4s orbital population. - Abstract: The adsorption of the alkali Li, K, and Na and the alkaline Ca on graphene is studied using periodic density functional theory (DFT) under various adatom coverages. The charge transfers between the adatom and the graphene sheet and the almost unchanged densities-of-states spectra in the energy region near and below the Fermi level support an ionic bond pattern between the adatom and the graphene atoms. However, the presence of small orbital overlap between the metal and the nearest graphene atom is indicative of small covalent bonding. Van der Waals interactions are examined through a semiempirical correction in the DFT functional and by comparing adatom-graphene calculations between 3% and 1.4% adatom coverages. Optimized adatom-graphene geometries identify the preferred adatom sites, whereas the adatom-graphene strength is correlated with the adsorption energy and the adatom distance from the graphene plane. Calculated electronic properties and structural parameters are obtained using hybrid functionals and a generalized gradient approximation functional paired with basis sets of various sizes. We found that due to long range electrostatic forces between the alkali/alkaline adatoms and the graphene monolayer, the adatom-graphene structural and electronic

Sr{sub 2}SmNbO{sub 6} perovskite: Synthesis, characterization and density functional theory calculations

Energy Technology Data Exchange (ETDEWEB)

Dutta, Alo, E-mail: alo_dutta@yahoo.com [Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector III, Salt Lake, Kolkata, 700106 (India); Mukhopadhyay, P.K. [Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector III, Salt Lake, Kolkata, 700106 (India); Sinha, T.P. [Department of Physics, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Kolkata, 700 009 (India); Shannigrahi, Santiranjan [Institute of Materials Research and Engineering, Agency for Science Technology and Research, 3 Research Link, Singapore, 117602 (Singapore); Himanshu, A.K.; Sen, Pintu; Bandyopadhyay, S.K. [Variable Energy Cyclotron Centre, 1/AF Bidhannagar, Kolkata, 700064 (India)

2016-08-15

The density functional theory (DFT) under the generalized gradient approximation (GGA) has been used to investigate the electronic structure of double perovskite oxide Sr{sub 2}SmNbO{sub 6} synthesized by the solid-state reaction technique. The Rietveld refinement of the X-ray diffraction pattern of the sample shows the monoclinic P2{sub 1}/n phase at room temperature. The X-ray photoemission spectrum (XPS) of the material is collected in the energy window of 0–1200 eV. The chemical shift of the constituent elements calculated from the core level XPS spectra is used to analyze the covalency between the O anion and Sm/Nb cations. The valence band (VB) XPS spectrum is compared with the calculated VB spectrum using partial density of states in a standard way. The Raman spectrum is employed to investigate the phonon modes of the material in the monoclinic phase. Lorentzian lines are used to fit the experimental Raman spectrum, which present 24 phonon modes corresponding to the stretching and banding of NbO{sub 6}/SmO{sub 6} octahedra and translational motion of Sr along the Sr−O bond. The discrepancy between the measured and calculated band gap values has been removed by applying modified Becke-Johnson (mBJ) potential in the DFT calculations. The experimental optical band gap obtained from the UV–visible reflectance spectrum is found to be 3.42 eV, which is well matched with the DFT calculated value of 3.2 eV, and suggests the semiconducting nature of the material. The real (ε′) and imaginary (ε″) parts of the optical dielectric constant as a function of energy along the x-, y- and z-polarization directions using mBJ potential are calculated. The collective vibrational modes of the atoms, the Born effective charge of the ions and their effect on the static dielectric constant of the material are studied using DFT. The calculated value of static dielectric constant for SSN is found to be 41.3. - Highlights: • Electronic structure and dynamical

Calculation of exchange coupling constants in triply-bridged dinuclear Cu(II) compounds based on spin-flip constricted variational density functional theory.

Science.gov (United States)

Seidu, Issaka; Zhekova, Hristina R; Seth, Michael; Ziegler, Tom

2012-03-08

The performance of the second-order spin-flip constricted variational density functional theory (SF-CV(2)-DFT) for the calculation of the exchange coupling constant (J) is assessed by application to a series of triply bridged Cu(II) dinuclear complexes. A comparison of the J values based on SF-CV(2)-DFT with those obtained by the broken symmetry (BS) DFT method and experiment is provided. It is demonstrated that our methodology constitutes a viable alternative to the BS-DFT method. The strong dependence of the calculated exchange coupling constants on the applied functionals is demonstrated. Both SF-CV(2)-DFT and BS-DFT affords the best agreement with experiment for hybrid functionals.

DGDFT: A massively parallel method for large scale density functional theory calculations.

Science.gov (United States)

Hu, Wei; Lin, Lin; Yang, Chao

2015-09-28

We describe a massively parallel implementation of the recently developed discontinuous Galerkin density functional theory (DGDFT) method, for efficient large-scale Kohn-Sham DFT based electronic structure calculations. The DGDFT method uses adaptive local basis (ALB) functions generated on-the-fly during the self-consistent field iteration to represent the solution to the Kohn-Sham equations. The use of the ALB set provides a systematic way to improve the accuracy of the approximation. By using the pole expansion and selected inversion technique to compute electron density, energy, and atomic forces, we can make the computational complexity of DGDFT scale at most quadratically with respect to the number of electrons for both insulating and metallic systems. We show that for the two-dimensional (2D) phosphorene systems studied here, using 37 basis functions per atom allows us to reach an accuracy level of 1.3 × 10(-4) Hartree/atom in terms of the error of energy and 6.2 × 10(-4) Hartree/bohr in terms of the error of atomic force, respectively. DGDFT can achieve 80% parallel efficiency on 128,000 high performance computing cores when it is used to study the electronic structure of 2D phosphorene systems with 3500-14 000 atoms. This high parallel efficiency results from a two-level parallelization scheme that we will describe in detail.

DGDFT: A massively parallel method for large scale density functional theory calculations

International Nuclear Information System (INIS)

Hu, Wei; Yang, Chao; Lin, Lin

2015-01-01

We describe a massively parallel implementation of the recently developed discontinuous Galerkin density functional theory (DGDFT) method, for efficient large-scale Kohn-Sham DFT based electronic structure calculations. The DGDFT method uses adaptive local basis (ALB) functions generated on-the-fly during the self-consistent field iteration to represent the solution to the Kohn-Sham equations. The use of the ALB set provides a systematic way to improve the accuracy of the approximation. By using the pole expansion and selected inversion technique to compute electron density, energy, and atomic forces, we can make the computational complexity of DGDFT scale at most quadratically with respect to the number of electrons for both insulating and metallic systems. We show that for the two-dimensional (2D) phosphorene systems studied here, using 37 basis functions per atom allows us to reach an accuracy level of 1.3 × 10 −4 Hartree/atom in terms of the error of energy and 6.2 × 10 −4 Hartree/bohr in terms of the error of atomic force, respectively. DGDFT can achieve 80% parallel efficiency on 128,000 high performance computing cores when it is used to study the electronic structure of 2D phosphorene systems with 3500-14 000 atoms. This high parallel efficiency results from a two-level parallelization scheme that we will describe in detail

DGDFT: A massively parallel method for large scale density functional theory calculations

Energy Technology Data Exchange (ETDEWEB)

Hu, Wei, E-mail: whu@lbl.gov; Yang, Chao, E-mail: cyang@lbl.gov [Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Lin, Lin, E-mail: linlin@math.berkeley.edu [Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Mathematics, University of California, Berkeley, California 94720 (United States)

2015-09-28

We describe a massively parallel implementation of the recently developed discontinuous Galerkin density functional theory (DGDFT) method, for efficient large-scale Kohn-Sham DFT based electronic structure calculations. The DGDFT method uses adaptive local basis (ALB) functions generated on-the-fly during the self-consistent field iteration to represent the solution to the Kohn-Sham equations. The use of the ALB set provides a systematic way to improve the accuracy of the approximation. By using the pole expansion and selected inversion technique to compute electron density, energy, and atomic forces, we can make the computational complexity of DGDFT scale at most quadratically with respect to the number of electrons for both insulating and metallic systems. We show that for the two-dimensional (2D) phosphorene systems studied here, using 37 basis functions per atom allows us to reach an accuracy level of 1.3 × 10{sup −4} Hartree/atom in terms of the error of energy and 6.2 × 10{sup −4} Hartree/bohr in terms of the error of atomic force, respectively. DGDFT can achieve 80% parallel efficiency on 128,000 high performance computing cores when it is used to study the electronic structure of 2D phosphorene systems with 3500-14 000 atoms. This high parallel efficiency results from a two-level parallelization scheme that we will describe in detail.

Does Early Algebraic Reasoning Differ as a Function of Students' Difficulty with Calculations versus Word Problems?

Science.gov (United States)

Powell, Sarah R.; Fuchs, Lynn S.

2014-01-01

According to national mathematics standards, algebra instruction should begin at kindergarten and continue through elementary school. Most often, teachers address algebra in the elementary grades with problems related to solving equations or understanding functions. With 789 second-grade students, we administered: (1) measures of calculations and…

Thermal transport across metal silicide-silicon interfaces: First-principles calculations and Green's function transport simulations

Science.gov (United States)

Sadasivam, Sridhar; Ye, Ning; Feser, Joseph P.; Charles, James; Miao, Kai; Kubis, Tillmann; Fisher, Timothy S.

2017-02-01

Heat transfer across metal-semiconductor interfaces involves multiple fundamental transport mechanisms such as elastic and inelastic phonon scattering, and electron-phonon coupling within the metal and across the interface. The relative contributions of these different transport mechanisms to the interface conductance remains unclear in the current literature. In this work, we use a combination of first-principles calculations under the density functional theory framework and heat transport simulations using the atomistic Green's function (AGF) method to quantitatively predict the contribution of the different scattering mechanisms to the thermal interface conductance of epitaxial CoSi2-Si interfaces. An important development in the present work is the direct computation of interfacial bonding from density functional perturbation theory (DFPT) and hence the avoidance of commonly used "mixing rules" to obtain the cross-interface force constants from bulk material force constants. Another important algorithmic development is the integration of the recursive Green's function (RGF) method with Büttiker probe scattering that enables computationally efficient simulations of inelastic phonon scattering and its contribution to the thermal interface conductance. First-principles calculations of electron-phonon coupling reveal that cross-interface energy transfer between metal electrons and atomic vibrations in the semiconductor is mediated by delocalized acoustic phonon modes that extend on both sides of the interface, and phonon modes that are localized inside the semiconductor region of the interface exhibit negligible coupling with electrons in the metal. We also provide a direct comparison between simulation predictions and experimental measurements of thermal interface conductance of epitaxial CoSi2-Si interfaces using the time-domain thermoreflectance technique. Importantly, the experimental results, performed across a wide temperature range, only agree well with

MORSEC-SP, Step Function Angular Distribution for Cross-Sections Calculation by Program MORSE

International Nuclear Information System (INIS)

1980-01-01

1 - Description of problem or function: MORSEC-SP allows one to utilize a step distribution to describe the angular dependence of the multi- group function in the MORSEC cross section module of the MORSE Monte Carlo code. The step distribution is always non-negative and may be used in the random walk and for making point detector estimators. 2 - Method of solution: MORSEC-SP utilizes a table look up procedure to provide the probability of scattering when making point detector estimates for a given incident energy group and scattering angle. In the random walk, the step distributions are converted to cumulative distributions and an angle of scatter is selected from the cumulative distributions. Step distributions are obtained from calculation using the converted moments from the given Legendre coefficients of the scattering distributions. 3 - Restrictions on the complexity of the problem: Additional coding to the MORSEC module is variable dimensional and fully incorporated into blank common

POLYANA-A tool for the calculation of molecular radial distribution functions based on Molecular Dynamics trajectories

Science.gov (United States)

Dimitroulis, Christos; Raptis, Theophanes; Raptis, Vasilios

2015-12-01

We present an application for the calculation of radial distribution functions for molecular centres of mass, based on trajectories generated by molecular simulation methods (Molecular Dynamics, Monte Carlo). When designing this application, the emphasis was placed on ease of use as well as ease of further development. In its current version, the program can read trajectories generated by the well-known DL_POLY package, but it can be easily extended to handle other formats. It is also very easy to 'hack' the program so it can compute intermolecular radial distribution functions for groups of interaction sites rather than whole molecules.

Modeling of oxygen incorporation in Th, ThC, and ThN by density functional theory calculations

Science.gov (United States)

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

2017-12-01

Oxygen incorporation in nuclear fuel materials is an important issue deserving investigation due to its influence on thermophysical and structural properties. Even if there has been a renewed interest in thorium and thorium compounds in the last years, there is still not much research done on this topic. In this work, we study, by means of density functional theory calculations, the incorporation of oxygen in Th, ThC, and ThN. We analyze the electronic structure finding a characteristic peak to be attributed to oxygen incorporation. We also calculate incorporation and solution energies and obtain migration energies of oxygen through different paths finding that migration through vacancy sites is more energetically favorable than through interstitial ones.

Combining Kohn-Sham and orbital-free density-functional theory for Hugoniot calculations to extreme pressures.

Science.gov (United States)

Sheppard, Daniel; Kress, Joel D; Crockett, Scott; Collins, Lee A; Desjarlais, Michael P

2014-12-01

The shock Hugoniot for lithium 6 deuteride ((6)LiD) was calculated via first principles using Kohn-Sham density-functional theory molecular dynamics (KSMD) for temperatures of 0.5-25 eV. The upper limit of 25 eV represents a practical limit where KSMD is no longer computationally feasible due to the number of electronic bands which are required to be populated. To push the Hugoniot calculations to higher temperatures we make use of orbital-free density-functional theory molecular dynamics (OFMD). Thomas-Fermi-Dirac-based OFMD gives a poor description of the electronic structure at low temperatures so the initial state is not well defined. We propose a method of bootstrapping the Hugoniot from OFMD to the Hugoniot from KSMD between 10 and 20 eV, where the two methods are in agreement. The combination of KSMD and OFMD allows construction of a first-principles Hugoniot from the initial state to 1000 eV. Theoretical shock-compression results are in good agreement with available experimental data and exhibit the appropriate high-temperature limits. We show that a unified KSMD-OFMD Hugoniot can be used to assess the quality of the existing equation-of-state (EOS) models and inform better EOS models based on justifiable physics.

Representation and calculation of economic uncertainties

DEFF Research Database (Denmark)

Schjær-Jacobsen, Hans

2002-01-01

Management and decision making when certain information is available may be a matter of rationally choosing the optimal alternative by calculation of the utility function. When only uncertain information is available (which is most often the case) decision-making calls for more complex methods...... of representation and calculation and the basis for choosing the optimal alternative may become obscured by uncertainties of the utility function. In practice, several sources of uncertainties of the required information impede optimal decision making in the classical sense. In order to be able to better handle...... to uncertain economic numbers are discussed. When solving economic models for decision-making purposes calculation of uncertain functions will have to be carried out in addition to the basic arithmetical operations. This is a challenging numerical problem since improper methods of calculation may introduce...

Calculation of wave resistance by using Kochin function in the Rankine source method; Rankinsosuho ni okeru kochin kansu wo mochiita zoha teiko keisan

Energy Technology Data Exchange (ETDEWEB)

Yasukawa, H [Mitsubishi Heavy Industries, Ltd., Tokyo (Japan)

1997-10-01

In order to avoid negative wave resistance (which is physically incomprehensible) generated in calculating wave resistance by using the Rankine source method, a proposal was made on a wave resistance calculation method using the Kochin function which describes behavior of speed potential in regions far apart from a hull. The Baba`s condition was used as a free surface condition for the speed potential which expresses wave motions around a hull. This has allowed a new Kochin function which uses as unknown the speed potential on the hull surface and the free surface near the hull to be defined and combined with the Rankine source method. A comparison was made between the calculated values for wave resistance, hull subsidence and trim change of an ore transporting vessel (SR107 type of ship) in a fully loaded condition and the result of water tank tests. The wave resistance values derived from pressure integration have all become negative when the Froude number is from 0.1 to 0.2, while no negative resistance has appeared in the calculations by using the Kochin function, but the result has agreed with that of the water tank tests. Accuracy of the calculations at low speeds was improved. The trim change in the calculations was slightly smaller than that in the water tank tests. The subsidence showed a good agreement. 7 refs., 1 fig.

Nonperturbative non-Markovian quantum master equation: Validity and limitation to calculate nonlinear response functions

Science.gov (United States)

Ishizaki, Akihito; Tanimura, Yoshitaka

2008-05-01

Based on the influence functional formalism, we have derived a nonperturbative equation of motion for a reduced system coupled to a harmonic bath with colored noise in which the system-bath coupling operator does not necessarily commute with the system Hamiltonian. The resultant expression coincides with the time-convolutionless quantum master equation derived from the second-order perturbative approximation, which is also equivalent to a generalized Redfield equation. This agreement occurs because, in the nonperturbative case, the relaxation operators arise from the higher-order system-bath interaction that can be incorporated into the reduced density matrix as the influence operator; while the second-order interaction remains as a relaxation operator in the equation of motion. While the equation describes the exact dynamics of the density matrix beyond weak system-bath interactions, it does not have the capability to calculate nonlinear response functions appropriately. This is because the equation cannot describe memory effects which straddle the external system interactions due to the reduced description of the bath. To illustrate this point, we have calculated the third-order two-dimensional (2D) spectra for a two-level system from the present approach and the hierarchically coupled equations approach that can handle quantal system-bath coherence thanks to its hierarchical formalism. The numerical demonstration clearly indicates the lack of the system-bath correlation in the present formalism as fast dephasing profiles of the 2D spectra.

Calculations of Excitation Functions of Some Structural Fusion Materials for ( n, t) Reactions up to 50 MeV Energy

Science.gov (United States)

Tel, E.; Durgu, C.; Aktı, N. N.; Okuducu, Ş.

2010-06-01

Fusion serves an inexhaustible energy for humankind. Although there have been significant research and development studies on the inertial and magnetic fusion reactor technology, there is still a long way to go to penetrate commercial fusion reactors to the energy market. Tritium self-sufficiency must be maintained for a commercial power plant. For self-sustaining (D-T) fusion driver tritium breeding ratio should be greater than 1.05. So, the working out the systematics of ( n, t) reaction cross sections is of great importance for the definition of the excitation function character for the given reaction taking place on various nuclei at different energies. In this study, ( n, t) reactions for some structural fusion materials such as 27Al, 51V, 52Cr, 55Mn, and 56Fe have been investigated. The new calculations on the excitation functions of 27Al( n, t)25Mg, 51V( n, t)49Ti, 52Cr( n, t)50V, 55Mn( n, t)53Cr and 56Fe( n, t)54Mn reactions have been carried out up to 50 MeV incident neutron energy. In these calculations, the pre-equilibrium and equilibrium effects have been investigated. The pre-equilibrium calculations involve the new evaluated the geometry dependent hybrid model, hybrid model and the cascade exciton model. Equilibrium effects are calculated according to the Weisskopf-Ewing model. Also in the present work, we have calculated ( n, t) reaction cross-sections by using new evaluated semi-empirical formulas developed by Tel et al. at 14-15 MeV energy. The calculated results are discussed and compared with the experimental data taken from the literature.

Molecular Structure And Vibrational Frequencies of 2,3,4 Nitro anilines By Hartree-Fock And Density Functional Theory Calculations

International Nuclear Information System (INIS)

Sert, Y.

2008-01-01

The optimised molecular structure, vibrational frequencies and corresponding vibrational assignments of 2-, 3- and 4- nitro anilines have been calculated using the Hartree-Fock (HF) and density functional methods (B3LYP) with 6-311++G (d, p) basis set. The calculations were adapted to the C S symmetries of all the molecules. The calculated vibrational frequencies and geometric parameters (bond lengths and bond angles) were seen to be in good agreement with the experimental data. The comparison of the experimental and theoretical results showed that the HF method is superior to the B3LYP method for both the vibrational frequencies and geometric parameters

Model representations of kerogen structures: An insight from density functional theory calculations and spectroscopic measurements.

Science.gov (United States)

Weck, Philippe F; Kim, Eunja; Wang, Yifeng; Kruichak, Jessica N; Mills, Melissa M; Matteo, Edward N; Pellenq, Roland J-M

2017-08-01

Molecular structures of kerogen control hydrocarbon production in unconventional reservoirs. Significant progress has been made in developing model representations of various kerogen structures. These models have been widely used for the prediction of gas adsorption and migration in shale matrix. However, using density functional perturbation theory (DFPT) calculations and vibrational spectroscopic measurements, we here show that a large gap may still remain between the existing model representations and actual kerogen structures, therefore calling for new model development. Using DFPT, we calculated Fourier transform infrared (FTIR) spectra for six most widely used kerogen structure models. The computed spectra were then systematically compared to the FTIR absorption spectra collected for kerogen samples isolated from Mancos, Woodford and Marcellus formations representing a wide range of kerogen origin and maturation conditions. Limited agreement between the model predictions and the measurements highlights that the existing kerogen models may still miss some key features in structural representation. A combination of DFPT calculations with spectroscopic measurements may provide a useful diagnostic tool for assessing the adequacy of a proposed structural model as well as for future model development. This approach may eventually help develop comprehensive infrared (IR)-fingerprints for tracing kerogen evolution.

Density functional studies: First principles and semiempirical calculations of clusters and surfaces

International Nuclear Information System (INIS)

Sinnott, S.B.

1993-01-01

In the research presented here, various theoretical electronic structure techniques are utilized to analyze widely different systems from silicon clusters to transition metal solids and surfaces. For the silicon clusters, first principles density functional methods are used to investigate Si N for N = 2-8. The goal is to understand the different types of bonding that can occur in such small clusters where the coordination of the atoms differs substantially from that of the stable bulk tetrahedral bonding. Such uncoordinated structures can provide a good test of more approximate theories that can be used eventually to model silicon surfaces, of obvious technological importance. For the transition metal systems, non-self-consistent electronic structure methods are used to provide an understanding of the driving force for surface relaxations. An in-depth analysis of the results is presented and the physical basis of surface relaxation within the theory is discussed. In addition, the limitations inherent in calculations of metal surface relaxation are addressed. Finally, in an effort to increase understanding of approximate methods, a novel non-self-consistent density functional electronic structure method is developed that is ∼1000 times faster computationally than more sophisticated methods. This new method is tested for a variety of systems including diatomics, mixed clusters, surfaces and bulk lattices. The strengths and weaknesses of the new theory are discussed in detail, leading to greater understanding of non-self-consistent density functional theories as a whole

Efficient pseudospectral methods for density functional calculations

International Nuclear Information System (INIS)

Murphy, R. B.; Cao, Y.; Beachy, M. D.; Ringnalda, M. N.; Friesner, R. A.

2000-01-01

Novel improvements of the pseudospectral method for assembling the Coulomb operator are discussed. These improvements consist of a fast atom centered multipole method and a variation of the Head-Gordan J-engine analytic integral evaluation. The details of the methodology are discussed and performance evaluations presented for larger molecules within the context of DFT energy and gradient calculations. (c) 2000 American Institute of Physics

Density functional theory calculations of magnetocrystalline anisotropy energies for (Fe(1-x)Co(x))(2)B.

Science.gov (United States)

Däne, Markus; Kim, Soo Kyung; Surh, Michael P; Åberg, Daniel; Benedict, Lorin X

2015-07-08

We present and discuss density functional theory calculations of magnetic properties of the family of ferromagnetic compounds, (Fe(1-x)Co(x))(2)B, focusing specifically on the magnetocrystalline anisotropy energy (MAE). Using periodic supercells of various sizes (up to 96 atoms), it is shown that the general qualitative features of the composition dependence of the MAE is in agreement with experimental findings, while our predicted magnitudes are larger than those of experiment. We find that the use of small supercells (6 and 12-atom) favors larger MAE values relative to a statistical sample of configurations constructed with 96-atom supercells. The effect of lattice relaxations is shown to be small. Calculations of the Curie temperature for this alloy are also presented.

Volume Transport Stream Function Calculated from World Ocean Atlas 2013 (WOA13-VTSF) and Climatological Wind (NCEI Accession 0138646)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The dataset consists of calculated annual and monthly mean ocean volume transport stream function on 1 degree resolution using the WOA13 (T, S) and corresponding...

PWR core design calculations

International Nuclear Information System (INIS)

Trkov, A.; Ravnik, M.; Zeleznik, N.

1992-01-01

Functional description of the programme package Cord-2 for PWR core design calculations is presented. Programme package is briefly described. Use of the package and calculational procedures for typical core design problems are treated. Comparison of main results with experimental values is presented as part of the verification process. (author) [sl

Two-dimensional sensitivity calculation code: SENSETWO

International Nuclear Information System (INIS)

Yamauchi, Michinori; Nakayama, Mitsuo; Minami, Kazuyoshi; Seki, Yasushi; Iida, Hiromasa.

1979-05-01

A SENSETWO code for the calculation of cross section sensitivities with a two-dimensional model has been developed, on the basis of first order perturbation theory. It uses forward neutron and/or gamma-ray fluxes and adjoint fluxes obtained by two-dimensional discrete ordinates code TWOTRAN-II. The data and informations of cross sections, geometry, nuclide density, response functions, etc. are transmitted to SENSETWO by the dump magnetic tape made in TWOTRAN calculations. The required input for SENSETWO calculations is thus very simple. The SENSETWO yields as printed output the cross section sensitivities for each coarse mesh zone and for each energy group, as well as the plotted output of sensitivity profiles specified by the input. A special feature of the code is that it also calculates the reaction rate with the response function used as the adjoint source in TWOTRAN adjoint calculation and the calculated forward flux from the TWOTRAN forward calculation. (author)

Nuclear structure calculations for astrophysical applications

International Nuclear Information System (INIS)

Moeller, P.; Kratz, K.L.

1992-01-01

Here we present calculated results on such diverse properties as nuclear energy levels, ground-state masses and shapes, β-decay properties and fission-barrier heights. Our approach to these calculations is to use a unified theoretical framework within which the above properties can all be studied. The results are obtained in the macroscopic-microscopic approach in which a microscopic nuclear-structure single-particle model with extensions is combined with a macroscopic model, such as the liquid drop model. In this model the total potential energy of the nucleus may be calculated as a function of shape. The maxima and minima in this function correspond to such features as the ground state, fission saddle points and shape-isomeric states. Various transition rate matrix elements are determined from wave-functions calculated in the single-particle model with pairing and other relevant residual interactions taken into account

Density functional theory calculations of the lowest energy quintet and triplet states of model hemes: role of functional, basis set, and zero-point energy corrections.

Science.gov (United States)

Khvostichenko, Daria; Choi, Andrew; Boulatov, Roman

2008-04-24

We investigated the effect of several computational variables, including the choice of the basis set, application of symmetry constraints, and zero-point energy (ZPE) corrections, on the structural parameters and predicted ground electronic state of model 5-coordinate hemes (iron(II) porphines axially coordinated by a single imidazole or 2-methylimidazole). We studied the performance of B3LYP and B3PW91 with eight Pople-style basis sets (up to 6-311+G*) and B97-1, OLYP, and TPSS functionals with 6-31G and 6-31G* basis sets. Only hybrid functionals B3LYP, B3PW91, and B97-1 reproduced the quintet ground state of the model hemes. With a given functional, the choice of the basis set caused up to 2.7 kcal/mol variation of the quintet-triplet electronic energy gap (DeltaEel), in several cases, resulting in the inversion of the sign of DeltaEel. Single-point energy calculations with triple-zeta basis sets of the Pople (up to 6-311G++(2d,2p)), Ahlrichs (TZVP and TZVPP), and Dunning (cc-pVTZ) families showed the same trend. The zero-point energy of the quintet state was approximately 1 kcal/mol lower than that of the triplet, and accounting for ZPE corrections was crucial for establishing the ground state if the electronic energy of the triplet state was approximately 1 kcal/mol less than that of the quintet. Within a given model chemistry, effects of symmetry constraints and of a "tense" structure of the iron porphine fragment coordinated to 2-methylimidazole on DeltaEel were limited to 0.3 kcal/mol. For both model hemes the best agreement with crystallographic structural data was achieved with small 6-31G and 6-31G* basis sets. Deviation of the computed frequency of the Fe-Im stretching mode from the experimental value with the basis set decreased in the order: nonaugmented basis sets, basis sets with polarization functions, and basis sets with polarization and diffuse functions. Contraction of Pople-style basis sets (double-zeta or triple-zeta) affected the results

The geometrically averaged density of states calculated from the local Green's function as a measure of localization

International Nuclear Information System (INIS)

Wortis, R.; Song Yun; Atkinson, W.A.

2008-01-01

With the goal of measuring localization in disordered interacting systems, we examine the finite-size scaling of the geometrically averaged density of states calculated from the local Green's function with finite energy resolution. Our results show that, unlike in a simple energy binning procedure, there is no limit in which the finite energy resolution is irrelevant

Structural studies of crystals of organic and organoelement compounds using modern quantum chemical calculations within the framework of the density functional theory

International Nuclear Information System (INIS)

Korlyukov, Alexander A; Antipin, Mikhail Yu

2012-01-01

The review generalizes the results of structural studies of crystals of organic and organometallic compounds by modern quantum chemical calculations within the framework of the density functional theory reported in the last decade. Features of the software for such calculations are discussed. Examples of the use of quantum chemical calculations for the studies of the electronic structure, spectroscopic and other physicochemical properties of molecular crystals are presented. The bibliography includes 223 references.

Use of sap flow measurements to validate stomatal functions for mature beech (Fagus sylvatica) in view of ozone uptake calculations

International Nuclear Information System (INIS)

Braun, Sabine; Schindler, Christian; Leuzinger, Sebastian

2010-01-01

For a quantitative estimate of the ozone effect on vegetation reliable models for ozone uptake through the stomata are needed. Because of the analogy of ozone uptake and transpiration it is possible to utilize measurements of water loss such as sap flow for quantification of ozone uptake. This technique was applied in three beech (Fagus sylvatica) stands in Switzerland. A canopy conductance was calculated from sap flow velocity and normalized to values between 0 and 1. It represents mainly stomatal conductance as the boundary layer resistance in forests is usually small. Based on this relative conductance, stomatal functions to describe the dependence on light, temperature, vapour pressure deficit and soil moisture were derived using multivariate nonlinear regression. These functions were validated by comparison with conductance values directly estimated from sap flow. The results corroborate the current flux parameterization for beech used in the DO 3 SE model. - A method was developed to derive stomatal functions and ozone uptake calculation from sap flow.

Optimal catalyst curves: Connecting density functional theory calculations with industrial reactor design and catalyst selection

DEFF Research Database (Denmark)

Jacobsen, C.J.H.; Dahl, Søren; Boisen, A.

2002-01-01

For ammonia synthesis catalysts a volcano-type relationship has been found experimentally. We demonstrate that by combining density functional theory calculations with a microkinetic model the position of the maximum of the volcano curve is sensitive to the reaction conditions. The catalytic...... ammonia synthesis activity, to a first approximation, is a function only of the binding energy of nitrogen to the catalyst. Therefore, it is possible to evaluate which nitrogen binding energy is optimal under given reaction conditions. This leads to the concept of optimal catalyst curves, which illustrate...... the nitrogen binding energies of the optimal catalysts at different temperatures, pressures, and synthesis gas compositions. Using this concept together with the ability to prepare catalysts with desired binding energies it is possible to optimize the ammonia process. In this way a link between first...

Vanillin and isovanillin: Comparative vibrational spectroscopic studies, conformational stability and NLO properties by density functional theory calculations

Science.gov (United States)

Balachandran, V.; Parimala, K.

This study is a comparative analysis of FT-IR and FT-Raman spectra of vanillin (3-methoxy-4-hydroxybenzaldehyde) and isovanillin (3-hydroxy-4-methoxybenzaldehyde). The molecular structure, vibrational wavenumbers, infrared intensities, Raman scattering activities were calculated for both molecules using the B3LYP density functional theory (DFT) with the standard 6-311++G∗∗ basis set. The computed values of frequencies are scaled using multiple scaling factors to yield good coherence with the observed values. The calculated harmonic vibrational frequencies are compared with experimental FT-IR and FT-Raman spectra. The geometrical parameters and total energies of vanillin and isovanillin were obtained for all the eight conformers (a-h) from DFT/B3LYP method with 6-311++G∗∗ basis set. The computational results identified the most stable conformer of vanillin and isovanillin as in the "a" form. Non-linear properties such as electric dipole moment (μ), polarizability (α), and hyperpolarizability (β) values of the investigated molecules have been computed using B3LYP quantum chemical calculation. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecules.

Ab initio quasi-particle approximation bandgaps of silicon nanowires calculated at density functional theory/local density approximation computational effort

Energy Technology Data Exchange (ETDEWEB)

Ribeiro, M., E-mail: ribeiro.jr@oorbit.com.br [Office of Operational Research for Business Intelligence and Technology, Principal Office, Buffalo, Wyoming 82834 (United States)

2015-06-21

Ab initio calculations of hydrogen-passivated Si nanowires were performed using density functional theory within LDA-1/2, to account for the excited states properties. A range of diameters was calculated to draw conclusions about the ability of the method to correctly describe the main trends of bandgap, quantum confinement, and self-energy corrections versus the diameter of the nanowire. Bandgaps are predicted with excellent accuracy if compared with other theoretical results like GW, and with the experiment as well, but with a low computational cost.

Ab initio quasi-particle approximation bandgaps of silicon nanowires calculated at density functional theory/local density approximation computational effort

International Nuclear Information System (INIS)

Ribeiro, M.

2015-01-01

Ab initio calculations of hydrogen-passivated Si nanowires were performed using density functional theory within LDA-1/2, to account for the excited states properties. A range of diameters was calculated to draw conclusions about the ability of the method to correctly describe the main trends of bandgap, quantum confinement, and self-energy corrections versus the diameter of the nanowire. Bandgaps are predicted with excellent accuracy if compared with other theoretical results like GW, and with the experiment as well, but with a low computational cost

Calculation of the nucleon structure function from the nucleon wave function

Science.gov (United States)

Hussar, Paul E.

1993-01-01

Harmonic oscillator wave functions have played an historically important role in our understanding of the structure of the nucleon, most notably by providing insight into the mass spectra of the low-lying states. High energy scattering experiments are known to give us a picture of the nucleon wave function at high-momentum transfer and in a frame in which the nucleon is traveling fast. A simple model that crosses the twin bridges of momentum scale and Lorentz frame that separate the pictures of the nucleon wave function provided by the deep inelastic scattering data and by the oscillator model is presented.

Combining functional CT and FDG PET allows the calculation of FDG extraction fraction and hepatic glucose phosphorylation

Energy Technology Data Exchange (ETDEWEB)

Griffiths, M R [Centre for Medical and Health Physics, Queensland University of Technology (Australia); Wesley Research Institute, QLD (Australia); Miles, K A [Centre for Medical and Health Physics, Queensland University of Technology (Australia); Wesley Research Institute, QLD (Australia); Southern X-ray Clinics, Brisbane [Australia; Keith, C J [Wesley Research Institute, QLD (Australia)

2002-09-01

Perfusion data from Functional CT and FDG-PET data may be combined to provide additional information about the uptake of FDG. We have developed methods to calculate FDG extraction fraction in tissues and to quantify hepatic glucose phosphorylation in the liver. Extraction fraction: Functional CT and FDG-PET studies were used to obtain measurements of perfusion and glucose uptake respectively within ten pulmonary nodules. The net influx constant (Ki) was determined from SUV measurements for each lung mass Extraction fraction (E) for each mass lesion was determined from: E=Ki/(Px[1-Hct]). A pixel by pixel calculation allowed generation of extraction fraction maps. The extraction fraction measurements ranged (median) from 0.6% to 4.81% (2.7%). The values for a benign nodule and an organising pneumonia were 0.6% and 0.71% respectively. Extraction fraction measurements for the malignant nodules ranged from 2.01% to 4.81%. A clearer separation of benign and malignant lesions is seen with E values rather than with SUV. Hepatic Glucose Phosphorylation: Functional CT and FDG-PET were utilised to obtain measurements of perfusion and glucose uptake respectively within the livers of a series of 35 patients with colorectal cancer. Hepatic perfusion and the net influx constant were incorporated into FDG kinetic analysis to determine hepatic glucose phosphorylation fraction. SUV and Ki were significantly lower in the 12 patients with advanced disease (p=0.015 and p=0.013 respectively) whereas portal and total hepatic perfusion were increased (p=0.013 and p=0.008 respectively). Combining the PET and CT data yielded phosphorylation fractions of 1.14% and 0.74% for early and advanced disease respectively (p=0.002). By combining functional CT measurements of blood flow with PET measurements of FDG uptake, it is possible to calculate the extraction fraction of FDG and Hepatic glucose phosphorylation. The use of the extraction fraction has improved the distinction between malignant and

Combining functional CT and FDG PET allows the calculation of FDG extraction fraction and hepatic glucose phosphorylation

International Nuclear Information System (INIS)

Griffiths, M.R.; Miles, K.A.; Keith, C.J.

2002-01-01

Perfusion data from Functional CT and FDG-PET data may be combined to provide additional information about the uptake of FDG. We have developed methods to calculate FDG extraction fraction in tissues and to quantify hepatic glucose phosphorylation in the liver. Extraction fraction: Functional CT and FDG-PET studies were used to obtain measurements of perfusion and glucose uptake respectively within ten pulmonary nodules. The net influx constant (Ki) was determined from SUV measurements for each lung mass Extraction fraction (E) for each mass lesion was determined from: E=Ki/(Px[1-Hct]). A pixel by pixel calculation allowed generation of extraction fraction maps. The extraction fraction measurements ranged (median) from 0.6% to 4.81% (2.7%). The values for a benign nodule and an organising pneumonia were 0.6% and 0.71% respectively. Extraction fraction measurements for the malignant nodules ranged from 2.01% to 4.81%. A clearer separation of benign and malignant lesions is seen with E values rather than with SUV. Hepatic Glucose Phosphorylation: Functional CT and FDG-PET were utilised to obtain measurements of perfusion and glucose uptake respectively within the livers of a series of 35 patients with colorectal cancer. Hepatic perfusion and the net influx constant were incorporated into FDG kinetic analysis to determine hepatic glucose phosphorylation fraction. SUV and Ki were significantly lower in the 12 patients with advanced disease (p=0.015 and p=0.013 respectively) whereas portal and total hepatic perfusion were increased (p=0.013 and p=0.008 respectively). Combining the PET and CT data yielded phosphorylation fractions of 1.14% and 0.74% for early and advanced disease respectively (p=0.002). By combining functional CT measurements of blood flow with PET measurements of FDG uptake, it is possible to calculate the extraction fraction of FDG and Hepatic glucose phosphorylation. The use of the extraction fraction has improved the distinction between malignant and

A CALCULATION OF SEMI-EMPIRICAL ONE-ELECTRON WAVE FUNCTIONS FOR MULTI-ELECTRON ATOMS USED FOR ELEMENTARY PROCESS SIMULATION IN NONLOCAL PLASMA

Directory of Open Access Journals (Sweden)

M. V. Tchernycheva

2017-01-01

Full Text Available Subject of Research. The paper deals with development outcomes for creation method of one-electron wave functions of complex atoms, relatively simple, symmetrical for all atom electrons and free from hard computations. The accuracy and resource intensity of the approach are focused on systematic calculations of cross sections and rate constants of elementary processes of inelastic collisions of atoms or molecules with electrons (ionization, excitation, excitation transfer, and others. Method. The method is based on a set of two iterative processes. At the first iteration step the Schrödinger equation was solved numerically for the radial parts of the electron wave functions in the potential of the atomic core self-consistent field. At the second iteration step the new approximationfor the atomic core field is created that uses found solutions for all one-electron wave functions. The solution optimization for described multiparameter problem is achieved by the use of genetic algorithm. The suitability of the developed method was verified by comparing the calculation results with numerous data on the energies of atoms in the ground and excited states. Main Results. We have created the run-time version of the program for creation of sets of one-electron wave functions and calculation of the cross sections and constants of collisional transition rates in the first Born approximation. The priori available information about binding energies of the electrons for any many-particle system for creation of semi-empirical refined solutions for the one-electron wave functions can be considered at any step of this procedure. Practical Relevance. The proposed solution enables a simple and rapid preparation of input data for the numerical simulation of nonlocal gas discharge plasma. The approach is focused on the calculation of discharges in complex gas mixtures requiring inclusion in the model of a large number of elementary collisional and radiation

Comparison of the projector augmented-wave, pseudopotential, and linearized augmented-plane-wave formalisms for density-functional calculations of solids

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

Electronic structure, magnetism, and exchange integrals in transition-metal oxides: Role of the spin polarization of the functional in DFT+U calculations

Science.gov (United States)

Keshavarz, Samara; Schött, Johan; Millis, Andrew J.; Kvashnin, Yaroslav O.

2018-05-01

Density functional theory augmented with Hubbard-U corrections (DFT+U ) is currently one of the most widely used methods for first-principles electronic structure modeling of insulating transition-metal oxides (TMOs). Since U is relatively large compared to bandwidths, the magnetic excitations in TMOs are expected to be well described by a Heisenberg model. However, in practice the calculated exchange parameters Ji j depend on the magnetic configuration from which they are extracted and on the functional used to compute them. In this work we investigate how the spin polarization dependence of the underlying exchange-correlation functional influences the calculated magnetic exchange constants of TMOs. We perform a systematic study of the predictions of calculations based on the local density approximation plus U (LDA+U ) and the local spin density approximation plus U (LSDA+U ) for the electronic structures, total energies, and magnetic exchange interactions Ji j extracted from ferromagnetic (FM) and antiferromagnetic (AFM) configurations of several transition-metal oxide materials. We report that for realistic choices of Hubbard U and Hund's J parameters, LSDA+U and LDA+U calculations result in different values of the magnetic exchange constants and band gap. The dependence of the band gap on the magnetic configuration is stronger in LDA+U than in LSDA+U and we argue that this is the main reason why the configuration dependence of Ji j is found to be systematically more pronounced in LDA+U than in LSDA+U calculations. We report a very good correspondence between the computed total energies and the parametrized Heisenberg model for LDA+U calculations, but not for LSDA+U , suggesting that LDA+U is a more appropriate method for estimating exchange interactions.

Electronic and optical properties of nanocrystalline WO3 thin films studied by optical spectroscopy and density functional calculations

International Nuclear Information System (INIS)

Johansson, Malin B; Niklasson, Gunnar A; Österlund, Lars; Baldissera, Gustavo; Persson, Clas; Valyukh, Iryna; Arwin, Hans

2013-01-01

The optical and electronic properties of nanocrystalline WO 3 thin films prepared by reactive dc magnetron sputtering at different total pressures (P tot ) were studied by optical spectroscopy and density functional theory (DFT) calculations. Monoclinic films prepared at low P tot show absorption in the near infrared due to polarons, which is attributed to a strained film structure. Analysis of the optical data yields band-gap energies E g ≈ 3.1 eV, which increase with increasing P tot by 0.1 eV, and correlate with the structural modifications of the films. The electronic structures of triclinic δ-WO 3 , and monoclinic γ- and ε-WO 3 were calculated using the Green function with screened Coulomb interaction (GW approach), and the local density approximation. The δ-WO 3 and γ-WO 3 phases are found to have very similar electronic properties, with weak dispersion of the valence and conduction bands, consistent with a direct band-gap. Analysis of the joint density of states shows that the optical absorption around the band edge is composed of contributions from forbidden transitions (>3 eV) and allowed transitions (>3.8 eV). The calculations show that E g in ε-WO 3 is higher than in the δ-WO 3 and γ-WO 3 phases, which provides an explanation for the P tot dependence of the optical data. (paper)

Electronic and optical properties of nanocrystalline WO3 thin films studied by optical spectroscopy and density functional calculations

Science.gov (United States)

Johansson, Malin B.; Baldissera, Gustavo; Valyukh, Iryna; Persson, Clas; Arwin, Hans; Niklasson, Gunnar A.; Österlund, Lars

2013-05-01

The optical and electronic properties of nanocrystalline WO3 thin films prepared by reactive dc magnetron sputtering at different total pressures (Ptot) were studied by optical spectroscopy and density functional theory (DFT) calculations. Monoclinic films prepared at low Ptot show absorption in the near infrared due to polarons, which is attributed to a strained film structure. Analysis of the optical data yields band-gap energies Eg ≈ 3.1 eV, which increase with increasing Ptot by 0.1 eV, and correlate with the structural modifications of the films. The electronic structures of triclinic δ-WO3, and monoclinic γ- and ε-WO3 were calculated using the Green function with screened Coulomb interaction (GW approach), and the local density approximation. The δ-WO3 and γ-WO3 phases are found to have very similar electronic properties, with weak dispersion of the valence and conduction bands, consistent with a direct band-gap. Analysis of the joint density of states shows that the optical absorption around the band edge is composed of contributions from forbidden transitions (>3 eV) and allowed transitions (>3.8 eV). The calculations show that Eg in ε-WO3 is higher than in the δ-WO3 and γ-WO3 phases, which provides an explanation for the Ptot dependence of the optical data.

Calculation of ex-core detector weighting functions for a sodium-cooled tru burner mockup using MCNP5

International Nuclear Information System (INIS)

Pham Nhu Viet Ha; Min Jae Lee; Sunghwan Yun; Sang Ji Kim

2015-01-01

Power regulation systems of fast reactors are based on the signals of excore detectors. The excore detector weighting functions, which establish correspondence between the core power distribution and detector signal, are very useful for detector response analyses, e.g., in rod drop experiments. This paper presents the calculation of the weighting functions for a TRU burner mockup of the Korean Prototype Generation-IV Sodium-cooled Fast Reactor (named BFS-76-1A) using the MCNP5 multi-group adjoint capability. For generation of the weighting functions, all fuel assemblies were considered and each of them was divided into ten horizontal layers. Then the weighting functions for individual fuel assembly horizontal layers, the assembly weighting functions, and the shape annealing functions at RCP (Reactor Critical Point) and at conditions under which a control rod group was fully inserted into the core while other control rods at RCP were determined and evaluated. The results indicate that the weighting functions can be considered relatively insensitive to the control rods position during the rod drop experiments and therefore those weighting values at RCP can be applied to the dynamic rod worth simulation for the BFS-76-1A. (author)

On the use of a Hamiltonian with projected potential for the calculation of scattering wave functions : Methods and general properties

International Nuclear Information System (INIS)

Colle, R.; Simonucci, S.

1996-01-01

The theoretical framework of a method that utilizes a projected potential operator to construct scattering wave functions is presented. Theorems and spectral properties of a Hamiltonian with the potential energy operator represented in terms of L'2(R'3)-functions are derived. The computational advantages offered by the method for calculating spectroscopic quantities, like resonance energies, decay probabilities and photoionization cross-sections, are discussed

Antioxidant Properties of Kynurenines: Density Functional Theory Calculations

Science.gov (United States)

2016-01-01

Kynurenines, the main products of tryptophan catabolism, possess both prooxidant and anioxidant effects. Having multiple neuroactive properties, kynurenines are implicated in the development of neurological and cognitive disorders, such as Alzheimer's, Parkinson's, and Huntington's diseases. Autoxidation of 3-hydroxykynurenine (3HOK) and its derivatives, 3-hydroxyanthranilic acid (3HAA) and xanthommatin (XAN), leads to the hyperproduction of reactive oxygen species (ROS) which damage cell structures. At the same time, 3HOK and 3HAA have been shown to be powerful ROS scavengers. Their ability to quench free radicals is believed to result from the presence of the aromatic hydroxyl group which is able to easily abstract an electron and H-atom. In this study, the redox properties for kynurenines and several natural and synthetic antioxidants have been calculated at different levels of density functional theory in the gas phase and water solution. Hydroxyl bond dissociation enthalpy (BDE) and ionization potential (IP) for 3HOK and 3HAA appear to be lower than for xanthurenic acid (XAA), several phenolic antioxidants, and ascorbic acid. BDE and IP for the compounds with aromatic hydroxyl group are lower than for their precursors without hydroxyl group. The reaction rate for H donation to *O-atom of phenoxyl radical (Ph-O*) and methyl peroxy radical (Met-OO*) decreases in the following rankings: 3HOK ~ 3HAA > XAAOXO > XAAENOL. The enthalpy absolute value for Met-OO* addition to the aromatic ring of the antioxidant radical increases in the following rankings: 3HAA* < 3HOK* < XAAOXO* < XAAENOL*. Thus, the high free radical scavenging activity of 3HAA and 3HOK can be explained by the easiness of H-atom abstraction and transfer to O-atom of the free radical, rather than by Met-OO* addition to the kynurenine radical. PMID:27861556

Origin of the 20-electron structure of Mg3 MnH7 : Density functional calculations

Science.gov (United States)

Gupta, M.; Singh, D. J.; Gupta, R.

2005-03-01

The electronic structure and stability of the 20-electron complex hydride, Mg3MnH7 is studied using density functional calculations. The heat of formation is larger in magnitude than that of MgH2 . The deviation from the 18-electron rule is explained by the predominantly ionic character of the band structure and a large crystal-field splitting of the Mn d bands. In particular, each H provides one deep band accomodating two electrons, while the Mn t2g bands hold an additional six electrons per formula unit.

Density Functional Calculation of the 0.5ML-Terminated Allyl Mercaptan/Si(100)-(2 × 1) Surface

International Nuclear Information System (INIS)

Chun-Mei, Tang; Kai-Ming, Deng; Xuan, Chen; Chuan-Yun, Xiao; Yu-Zhen, Liu; Qun-Xiang, Li

2009-01-01

The structural and electronic properties of the 0.5 ML-terminated allyl mercaptan (ALM)/Si(100)-(2 × 1) surface are studied using the density functional method. The calculated absorption energy of the ALM molecule on the 0.5 ML-terminated ALM/Si(100)-(2 × 1) surface is 3.36 eV, implying that adsorption is strongly favorable. The electronic structure calculations show that the ALM/Si(100)-(2 × 1), the clean Si(100)-(2 × 1), and the fully-terminated H/Si(100)-(2 × 1) surfaces have the nature of an indirect band gap semiconductor. The highest occupied molecular orbital is dominated by the ALM, confirming the mechanism proposed by Hossain for its chain reaction. (condensed matter: structure, mechanical and thermal properties)

Computing the full spectrum of large sparse palindromic quadratic eigenvalue problems arising from surface Green's function calculations

Science.gov (United States)

Huang, Tsung-Ming; Lin, Wen-Wei; Tian, Heng; Chen, Guan-Hua

2018-03-01

Full spectrum of a large sparse ⊤-palindromic quadratic eigenvalue problem (⊤-PQEP) is considered arguably for the first time in this article. Such a problem is posed by calculation of surface Green's functions (SGFs) of mesoscopic transistors with a tremendous non-periodic cross-section. For this problem, general purpose eigensolvers are not efficient, nor is advisable to resort to the decimation method etc. to obtain the Wiener-Hopf factorization. After reviewing some rigorous understanding of SGF calculation from the perspective of ⊤-PQEP and nonlinear matrix equation, we present our new approach to this problem. In a nutshell, the unit disk where the spectrum of interest lies is broken down adaptively into pieces small enough that they each can be locally tackled by the generalized ⊤-skew-Hamiltonian implicitly restarted shift-and-invert Arnoldi (G⊤SHIRA) algorithm with suitable shifts and other parameters, and the eigenvalues missed by this divide-and-conquer strategy can be recovered thanks to the accurate estimation provided by our newly developed scheme. Notably the novel non-equivalence deflation is proposed to avoid as much as possible duplication of nearby known eigenvalues when a new shift of G⊤SHIRA is determined. We demonstrate our new approach by calculating the SGF of a realistic nanowire whose unit cell is described by a matrix of size 4000 × 4000 at the density functional tight binding level, corresponding to a 8 × 8nm2 cross-section. We believe that quantum transport simulation of realistic nano-devices in the mesoscopic regime will greatly benefit from this work.

Polarization Dependent Bulk-sensitive Valence Band Photoemission Spectroscopy and Density Functional Theory Calculations: Part I. 3d Transition Metals

Science.gov (United States)

Ueda, Shigenori; Hamada, Ikutaro

2017-12-01

The X-ray polarization dependent valence band HAXPES spectra of 3d transition metals (TMs) of Ti-Zn were measured to investigate the orbital resolved electronic structures by utilizing that the fact the photoionization cross-section of the atomic orbitals strongly depends on the experimental geometry. We have calculated the HAXPES spectra, which correspond to the cross-section weighted densities of states (CSW-DOSs), where the DOSs were obtained by the density functional theory calculations, and we have determined the relative photoionization cross-sections of the 4s and 4p orbitals to the 3d orbital in the 3d TMs. The experimentally obtained bulk-sensitive 3d and 4s DOSs were good agreement with the calculated DOSs in Ti, V, Cr, and Cu. In contrast, the deviations between the experimental and calculated 3d DOSs for Mn, Fe, Co, Ni were found, suggesting that the electron correlation plays an important role in the electronic structures for these materials.

Adducts of nitrogenous ligands with rhodium(II) tetracarboxylates and tetraformamidinate: NMR spectroscopy and density functional theory calculations.

Science.gov (United States)

Cmoch, Piotr; Głaszczka, Rafał; Jaźwiński, Jarosław; Kamieński, Bohdan; Senkara, Elżbieta

2014-03-01

Complexation of tetrakis(μ2-N,N'-diphenylformamidinato-N,N')-di-rhodium(II) with ligands containing nitrile, isonitrile, amine, hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups has been studied in liquid and solid phases using (1)H, (13)C and (15)N NMR, (13)C and (15)N cross polarisation-magic angle spinning NMR, and absorption spectroscopy in the visible range. The complexation was monitored using various NMR physicochemical parameters, such as chemical shifts, longitudinal relaxation times T1 , and NOE enhancements. Rhodium(II) tetraformamidinate selectively bonded only unbranched amine (propan-1-amine), pentanenitrile, and (1-isocyanoethyl)benzene. No complexation occurred in the case of ligands having hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups, and more expanded amine molecules such as butan-2-amine and 1-azabicyclo[2.2.2]octane. Such features were opposite to those observed in rhodium(II) tetracarboxylates, forming adducts with all kind of ligands. Special attention was focused on the analysis of Δδ parameters, defined as a chemical shift difference between signal in adduct and corresponding signal in free ligand. In the case of (1)H NMR, Δδ values were either negative in adducts of rhodium(II) tetraformamidinate or positive in adducts of rhodium(II) tetracarboxylates. Experimental findings were supported by density functional theory molecular modelling and gauge independent atomic orbitals chemical shift calculations. The calculation of chemical shifts combined with scaling procedure allowed to reproduce qualitatively Δδ parameters. Copyright © 2013 John Wiley & Sons, Ltd.

OCOPTR, Minimization of Nonlinear Function, Variable Metric Method, Derivative Calculation. DRVOCR, Minimization of Nonlinear Function, Variable Metric Method, Derivative Calculation

International Nuclear Information System (INIS)

Nazareth, J. L.

1979-01-01

1 - Description of problem or function: OCOPTR and DRVOCR are computer programs designed to find minima of non-linear differentiable functions f: R n →R with n dimensional domains. OCOPTR requires that the user only provide function values (i.e. it is a derivative-free routine). DRVOCR requires the user to supply both function and gradient information. 2 - Method of solution: OCOPTR and DRVOCR use the variable metric (or quasi-Newton) method of Davidon (1975). For OCOPTR, the derivatives are estimated by finite differences along a suitable set of linearly independent directions. For DRVOCR, the derivatives are user- supplied. Some features of the codes are the storage of the approximation to the inverse Hessian matrix in lower trapezoidal factored form and the use of an optimally-conditioned updating method. Linear equality constraints are permitted subject to the initial Hessian factor being chosen correctly. 3 - Restrictions on the complexity of the problem: The functions to which the routine is applied are assumed to be differentiable. The routine also requires (n 2 /2) + 0(n) storage locations where n is the problem dimension

Calculation of damage function of Al{sub 2}O{sub 3} in irradiation facilities for fusion reactor applications

Energy Technology Data Exchange (ETDEWEB)

Mota, F., E-mail: fernando.mota@ciemat.es [Laboratorio Nacional de Fusión por Confinamiento Magnético – CIEMAT, 28040 Madrid (Spain); Ortiz, C.J., E-mail: christophe.ortiz@ciemat.es [Laboratorio Nacional de Fusión por Confinamiento Magnético – CIEMAT, 28040 Madrid (Spain); Vila, R., E-mail: rafael.vila@ciemat.es [Laboratorio Nacional de Fusión por Confinamiento Magnético – CIEMAT, 28040 Madrid (Spain); Casal, N., E-mail: natalia.casal@ciemat.es [Laboratorio Nacional de Fusión por Confinamiento Magnético – CIEMAT, 28040 Madrid (Spain); García, A., E-mail: angela.garcia@ciemat.es [Laboratorio Nacional de Fusión por Confinamiento Magnético – CIEMAT, 28040 Madrid (Spain); Ibarra, A., E-mail: Angel.ibarra@ciemat.es [Laboratorio Nacional de Fusión por Confinamiento Magnético – CIEMAT, 28040 Madrid (Spain)

2013-11-15

A rigorous material testing program is essential for the development of the nuclear fusion world program. In particular, it is very important to predict the generation of the displacement damage in materials, because the irradiation intensity expected in fusion conditions is such that the performance of materials and components under these extreme conditions is unknown. To study the damage produced by neutrons in materials of interest for fusion, a specific computational methodology was developed. Neutron fluxes expected in different irradiation facilities (International Fusion Materials Irradiation Facility [IFMIF] and DEMO-HCLL) and in different irradiation spots were obtained with particles transport codes (McDeLicious, MCNP). The energy differential cross sections of primary knock-on atoms were calculated using the NJOY code. Resulting data were input into the Monte Carlo code MARLOWE to calculate the corresponding displacements (i.e., interstitials (I) and vacancies (V)). However, the number of Frenkel pairs created during irradiation strongly depends on the recombination radius between interstitials and vacancies. This parameter corresponds to the minimum distance below which instantaneous recombination occurs. Mainly, the influence of such parameter on the damage function in Al{sub 2}O{sub 3} was assessed in this report. The displacements per atom values calculated as a function of the recombination radius considered are compared to experimental data to determine the most appropriate capture radius. In addition, the damage function and damage dose generated at different experimental irradiation facilities are compared with those expected in DEMO. The conclusion is that both IFMIF and TechnoFusión (future triple beam ion accelerator to emulate fusion neutron irradiation effects in materials) facilities are suited to perform relevant irradiation experiments for the design of DEMO.

The Effects of the Use of Microsoft Math Tool (Graphical Calculator) Instruction on Students' Performance in Linear Functions

Science.gov (United States)

Kissi, Philip Siaw; Opoku, Gyabaah; Boateng, Sampson Kwadwo

2016-01-01

The aim of the study was to investigate the effect of Microsoft Math Tool (graphical calculator) on students' achievement in the linear function. The study employed Quasi-experimental research design (Pre-test Post-test two group designs). A total of ninety-eight (98) students were selected for the study from two different Senior High Schools…

Redox reaction characteristics of riboflavin: a fluorescence spectroelectrochemical analysis and density functional theory calculation.

Science.gov (United States)

Chen, Wei; Chen, Jie-Jie; Lu, Rui; Qian, Chen; Li, Wen-Wei; Yu, Han-Qing

2014-08-01

Riboflavin (RF), the primary redox active component of flavin, is involved in many redox processes in biogeochemical systems. Despite of its wide distribution and important roles in environmental remediation, its redox behaviors and reaction mechanisms in hydrophobic sites remain unclear yet. In this study, spectroelectrochemical analysis and density functional theory (DFT) calculation were integrated to explore the redox behaviors of RF in dimethyl sulfoxide (DMSO), which was used to create a hydrophobic environment. Specifically, cyclic voltafluorometry (CVF) and derivative cyclic voltafluorometry (DCVF) were employed to track the RF concentration changing profiles. It was found that the reduction contained a series of proton-coupled electron transfers dependent of potential driving force. In addition to the electron transfer-chemical reaction-electron transfer process, a disproportionation (DISP1) process was also identified to be involved in the reduction. The redox potential and free energy of each step obtained from the DFT calculations further confirmed the mechanisms proposed based on the experimental results. The combination of experimental and theoretical approaches yields a deep insight into the characteristics of RF in environmental remediation and better understanding about the proton-coupled electron transfer mechanisms. Copyright © 2014 Elsevier B.V. All rights reserved.

Quantum chemical calculations of using density functional theory ...

Indian Academy of Sciences (India)

K RACKESH JAWAHER

2018-02-15

Feb 15, 2018 ... Quantum chemical calculations have been employed to study the molecular effects produced by. Cr2O3/SnO2 optimised structure. ... are exploited in solar cells [2], high-capacity lithium– storage [3], solid-state chemical ..... bond distance of metal–oxygen is positively (0.5 Е) deviated to oxygen–oxygen ...

Density-functional band-structure calculations for La-, Y-, and Sc-filled CoP3-based skutterudite structures

International Nuclear Information System (INIS)

Loevvik, O.M.; Prytz, O.

2004-01-01

The crystal structure, thermodynamic stability, and electronic structure of La-, Y-, and Sc-filled CoP 3 are predicted from density-functional band-structure calculations. The size of the cubic voids in the skutterudite structure is changed much less than the difference in size between the different filling atoms, and we expect that the larger rattling amplitude of the smaller Sc and Y atoms may decrease the lattice thermal conductivity of Sc- and Y-filled structures significantly compared to La-filled structures. The solubility of La, Y, and Sc in CoP 3 is calculated to be around 5, 3-6 %, and below 1% at 0 K, respectively. Based on similar systems, this is expected to increase considerably if Fe is substituted for Co. Fe substitution is also expected to compensate the increased charge carrier concentration of the filled structures that is seen in the calculated electron density of states. In conclusion, Sc- or Y-filled (FeCo)P 3 skutterudite structures are promising materials for thermoelectric applications

Monte Carlo Simulations of Electron Energy-Loss Spectra with the Addition of Fine Structure from Density Functional Theory Calculations.

Science.gov (United States)

Attarian Shandiz, Mohammad; Guinel, Maxime J-F; Ahmadi, Majid; Gauvin, Raynald

2016-02-01

A new approach is presented to introduce the fine structure of core-loss excitations into the electron energy-loss spectra of ionization edges by Monte Carlo simulations based on an optical oscillator model. The optical oscillator strength is refined using the calculated electron energy-loss near-edge structure by density functional theory calculations. This approach can predict the effects of multiple scattering and thickness on the fine structure of ionization edges. In addition, effects of the fitting range for background removal and the integration range under the ionization edge on signal-to-noise ratio are investigated.

Comparison of approximations in density functional theory calculations: Energetics and structure of binary oxides

Science.gov (United States)

Hinuma, Yoyo; Hayashi, Hiroyuki; Kumagai, Yu; Tanaka, Isao; Oba, Fumiyasu

2017-09-01

High-throughput first-principles calculations based on density functional theory (DFT) are a powerful tool in data-oriented materials research. The choice of approximation to the exchange-correlation functional is crucial as it strongly affects the accuracy of DFT calculations. This study compares performance of seven approximations, six of which are based on Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) with and without Hubbard U and van der Waals corrections (PBE, PBE+U, PBED3, PBED3+U, PBEsol, and PBEsol+U), and the strongly constrained and appropriately normed (SCAN) meta-GGA on the energetics and crystal structure of elementary substances and binary oxides. For the latter, only those with closed-shell electronic structures are considered, examples of which include C u2O , A g2O , MgO, ZnO, CdO, SnO, PbO, A l2O3 , G a2O3 , I n2O3 , L a2O3 , B i2O3 , Si O2 , Sn O2 , Pb O2 , Ti O2 , Zr O2 , Hf O2 , V2O5 , N b2O5 , T a2O5 , Mo O3 , and W O3 . Prototype crystal structures are selected from the Inorganic Crystal Structure Database (ICSD) and cation substitution is used to make a set of existing and hypothetical oxides. Two indices are proposed to quantify the extent of lattice and internal coordinate relaxation during a calculation. The former is based on the second invariant and determinant of the transformation matrix of basis vectors from before relaxation to after relaxation, and the latter is derived from shifts of internal coordinates of atoms in the unit cell. PBED3, PBEsol, and SCAN reproduce experimental lattice parameters of elementary substances and oxides well with few outliers. Notably, PBEsol and SCAN predict the lattice parameters of low dimensional structures comparably well with PBED3, even though these two functionals do not explicitly treat van der Waals interactions. SCAN gives formation enthalpies and Gibbs free energies closest to experimental data, with mean errors (MEs) of 0.01 and -0.04 eV, respectively, and root

On the evaluation of modified Bessel functions of the second kind and fractional order for synchrotron radiation calculations

International Nuclear Information System (INIS)

Rutt, H.N.

2003-01-01

The modified Bessel functions of the second kind and fractional order K 1/3 (x) and K 2/3 (x) are of importance in the calculation of the frequency spectrum of synchrotron radiation. The parameter range of interest is typically 10 -6 x10. Recently, there has been particular interest in the generation of 'terahertz' radiation, which can be coherently enhanced by many orders of magnitude when the electron bunch length is shorter than the terahertz wavelength. This requires evaluation of the Bessel functions for small values of the argument. It is shown that the series commonly used to evaluate these functions has poor convergence properties under these conditions. An alternative series is derived which has much better convergence for x1

Calculation of spherical harmonics and Wigner d functions by FFT. Applications to fast rotational matching in molecular replacement and implementation into AMoRe.

Science.gov (United States)

Trapani, Stefano; Navaza, Jorge

2006-07-01

The FFT calculation of spherical harmonics, Wigner D matrices and rotation function has been extended to all angular variables in the AMoRe molecular replacement software. The resulting code avoids singularity issues arising from recursive formulas, performs faster and produces results with at least the same accuracy as the original code. The new code aims at permitting accurate and more rapid computations at high angular resolution of the rotation function of large particles. Test calculations on the icosahedral IBDV VP2 subviral particle showed that the new code performs on the average 1.5 times faster than the original code.

Are both symmetric and buckled dimers on Si(100) minima? Density functional and multireference perturbation theory calculations

International Nuclear Information System (INIS)

Jung, Yousung; Shao, Yihan; Gordon, Mark S.; Doren, Douglas J.; Head-Gordon, Martin

2003-01-01

We report a spin-unrestricted density functional theory (DFT) solution at the symmetric dimer structure for cluster models of Si(100). With this solution, it is shown that the symmetric structure is a minimum on the DFT potential energy surface, although higher in energy than the buckled structure. In restricted DFT calculations the symmetric structure is a saddle point connecting the two buckled minima. To further assess the effects of electron correlation on the relative energies of symmetric versus buckled dimers on Si(100), multireference second order perturbation theory (MRMP2) calculations are performed on these DFT optimized minima. The symmetric structure is predicted to be lower in energy than the buckled structure via MRMP2, while the reverse order is found by DFT. The implications for recent experimental interpretations are discussed

Calculation of deuteron wave functions with relativistic interactions

International Nuclear Information System (INIS)

Buck, W.W. III.

1976-01-01

Deuteron wave functions with a repulsive core are obtained numerically from a fully relativistic wave equation introduced by Gross. The numerical technique enables analytic solutions for classes of interactions composed of the relativistic exchanges of a single pion and a single phenomenological meson, sigma. The pion is chosen to interact as a mixture of pseudoscalar and pseudovector. The amount of mixture is determined by a free mixing parameter, lambda, ranging between 1 (pure pseudoscalar) and (pure pseudovector). Each value of lambda corresponds, then, to a different interaction. Solutions are found for lambda = 1, .9, .8, .6, and 0. The wave functions for each interaction come in a group of four. Of the four wave functions, two are the usual S and D state wave functions, while the remaining two, arising out of the relativistic prescription, are identified as 3 P 1 and 1 P 1 wave functions (P state wave functions). For the interactions solved for, the D state probabilities ranged between 5.1 percent and 6.3 percent, while the total P state probabilities ranged between 0.7 percent and 2.7 percent. The method of obtaining solutions was to adjust the sigma meson parameters to give the correct binding energy and a good quadrupole moment. All wave functions obtained are applied to relativistic N-d scattering in the backward direction where the effect of the P states is quite measurable

Radar Signature Calculation Facility

Data.gov (United States)

Federal Laboratory Consortium — FUNCTION: The calculation, analysis, and visualization of the spatially extended radar signatures of complex objects such as ships in a sea multipath environment and...

Assessing the reliability of calculated catalytic ammonia synthesis rates

DEFF Research Database (Denmark)

Medford, Andrew James; Wellendorff, Jess; Vojvodic, Aleksandra

2014-01-01

We introduce a general method for estimating the uncertainty in calculated materials properties based on density functional theory calculations. We illustrate the approach for a calculation of the catalytic rate of ammonia synthesis over a range of transition-metal catalysts. The correlation...... between errors in density functional theory calculations is shown to play an important role in reducing the predicted error on calculated rates. Uncertainties depend strongly on reaction conditions and catalyst material, and the relative rates between different catalysts are considerably better described...

HAMMER, 1-D Multigroup Neutron Transport Infinite System Cell Calculation for Few-Group Diffusion Calculation

International Nuclear Information System (INIS)

Honeck, H.C.

1984-01-01

1 - Description of problem or function: HAMMER performs infinite lattice, one-dimensional cell multigroup calculations, followed (optionally) by one-dimensional, few-group, multi-region reactor calculations with neutron balance edits. 2 - Method of solution: Infinite lattice parameters are calculated by means of multigroup transport theory, composite reactor parameters by few-group diffusion theory. 3 - Restrictions on the complexity of the problem: - Cell calculations - maxima of: 30 thermal groups; 54 epithermal groups; 20 space points; 20 regions; 18 isotopes; 10 mixtures; 3 thermal up-scattering mixtures; 200 resonances per group; no overlap or interference; single level only. - Reactor calculations - maxima of : 40 regions; 40 mixtures; 250 space points; 4 groups

Efficient O(N) integration for all-electron electronic structure calculation using numeric basis functions

International Nuclear Information System (INIS)

Havu, V.; Blum, V.; Havu, P.; Scheffler, M.

2009-01-01

We consider the problem of developing O(N) scaling grid-based operations needed in many central operations when performing electronic structure calculations with numeric atom-centered orbitals as basis functions. We outline the overall formulation of localized algorithms, and specifically the creation of localized grid batches. The choice of the grid partitioning scheme plays an important role in the performance and memory consumption of the grid-based operations. Three different top-down partitioning methods are investigated, and compared with formally more rigorous yet much more expensive bottom-up algorithms. We show that a conceptually simple top-down grid partitioning scheme achieves essentially the same efficiency as the more rigorous bottom-up approaches.

Broyden's method in nuclear structure calculations

International Nuclear Information System (INIS)

Baran, Andrzej; Bulgac, Aurel; Forbes, Michael McNeil; Hagen, Gaute; Nazarewicz, Witold; Schunck, Nicolas; Stoitsov, Mario V.

2008-01-01

Broyden's method, widely used in quantum chemistry electronic-structure calculations for the numerical solution of nonlinear equations in many variables, is applied in the context of the nuclear many-body problem. Examples include the unitary gas problem, the nuclear density functional theory with Skyrme functionals, and the nuclear coupled-cluster theory. The stability of the method, its ease of use, and its rapid convergence rates make Broyden's method a tool of choice for large-scale nuclear structure calculations

Density functional calculation of the electronic and magnetic properties of α-CoV2O6

Science.gov (United States)

Saul, Andres; Radtke, Guillaume

2012-02-01

In this work, the magnetic properties of the low dimensional α-CoV2O6 system have been investigated using density-functional calculations. This system is constituted of CoO6 octahedra connected by the edges and forming one dimensional linear chains. The experimental magnetization curves recorded at very low temperature show a surprising magnetization plateau at one-third of the saturation magnetization and a strong anisotropy. The estimated Co magnetic moment is large reaching a value of 4.5 μB suggesting a large orbital contribution. Our calculations show that three different magnetic configurations for the Co are possible, the lowest energy one being a high spin configuration in agreement with the S=3/2 character of the Co+2 ion observed in this compound. Spin-orbit interactions have been included in order to calculate the magnetic anisotropy and the orbital contribution to the magnetic moment. The results are discussed in terms of crystal field splitting of the 3d orbital and a tight-binding Hamiltonian. Using a broken-symmetry formalism we have evaluated the effective exchange interactions of the Heisenberg Hamiltonian. They allow us to propose the magnetic structures corresponding to the ground state and to the observed magnetization plateaus.

Improvement of the MSG code for the MONJU evaporators. Additional function of reverse flow calculation on water/steam model and animation for post processing

International Nuclear Information System (INIS)

Toda, Shin-ichi; Yoshikawa, Shinji; Oketani, Kazuhiro

2003-05-01

The improved version of the MSG code (Multi-dimensional Thermal-hydraulic Analysis Code for Steam Generators) has been released. It has been carried out to improve based on the original version in order to calculate reverse flow on water/steam side, and to animate the post-processing data. To calculate reverse flow locally, modification to set pressure at each divided node point of water/steam region in the helical-coil heat transfer tubes has been carried out. And the matrix solver has been also improved to treat a problem within practical calculation time against increasing the pressure points. In this case pressure and enthalpy have to be calculated simultaneously, however, it was found out that using the block-Jacobean method make a diagonal-dominant matrix, and solve the matrix efficiently with a relaxation method. As the result of calculations of a steady-state condition and a transient of SG blow down with manual trip operation, the improvement on calculation function of the MSG code was confirmed. And an animation function of temperature contour in the sodium shell side as a post processing has been added. Since the animation is very effective to understand thermal-hydraulic behavior on the sodium shell side of the SG, especially in case of transient condition, the analysis and evaluation of the calculation results will be enabled to be more quickly and effectively. (author)

Kinetic-energy functionals studied by surface calculations

DEFF Research Database (Denmark)

Vitos, Levente; Skriver, Hans Lomholt; Kollár, J.

1998-01-01

The self-consistent jellium model of metal surfaces is used to study the accuracy of a number of semilocal kinetic-energy functionals for independent particles. It is shown that the poor accuracy exhibited by the gradient expansion approximation and most of the semiempirical functionals in the lo...... density, high gradient limit may be subtantially improved by including locally a von Weizsacker term. Based on this, we propose a simple one-parameter Pade's approximation, which reproduces the exact Kohn-Sham surface kinetic energy over the entire range of metallic densities....

Locating the rate-limiting step for the interaction of hydrogen with Mg(0001) using density-functional theory calculations and rate theory

DEFF Research Database (Denmark)

Vegge, Tejs

2004-01-01

The dissociation of molecular hydrogen on a Mgs0001d surface and the subsequent diffusion of atomic hydrogen into the magnesium substrate is investigated using Density Functional Theory (DFT) calculations and rate theory. The minimum energy path and corresponding transition states are located usi...... to be rate-limiting for the ab- and desorption of hydrogen, respectively. Zero-point energy contributions are found to be substantial for the diffusion of atomic hydrogen, but classical rates are still found to be within an order of magnitude at room temperature.......The dissociation of molecular hydrogen on a Mgs0001d surface and the subsequent diffusion of atomic hydrogen into the magnesium substrate is investigated using Density Functional Theory (DFT) calculations and rate theory. The minimum energy path and corresponding transition states are located using...

Calculation of strained BaTiO3 with different exchange correlation functionals examined with criterion by Ginzburg-Landau theory, uncovering expressions by crystallographic parameters

Science.gov (United States)

Watanabe, Yukio

2018-05-01

In the calculations of tetragonal BaTiO3, some exchange-correlation (XC) energy functionals such as local density approximation (LDA) have shown good agreement with experiments at room temperature (RT), e.g., spontaneous polarization (PS), and superiority compared with other XC functionals. This is due to the error compensation of the RT effect and, hence, will be ineffective in the heavily strained case such as domain boundaries. Here, ferroelectrics under large strain at RT are approximated as those at 0 K because the strain effect surpasses the RT effects. To find effective XC energy functionals for strained BaTiO3, we propose a new comparison, i.e., a criterion. This criterion is the properties at 0 K given by the Ginzburg-Landau (GL) theory because GL theory is a thermodynamic description of experiments working under the same symmetry-constraints as ab initio calculations. With this criterion, we examine LDA, generalized gradient approximations (GGA), meta-GGA, meta-GGA + local correlation potential (U), and hybrid functionals, which reveals the high accuracy of some XC functionals superior to XC functionals that have been regarded as accurate. This result is examined directly by the calculations of homogenously strained tetragonal BaTiO3, confirming the validity of the new criterion. In addition, the data points of theoretical PS vs. certain crystallographic parameters calculated with different XC functionals are found to lie on a single curve, despite their wide variations. Regarding these theoretical data points as corresponding to the experimental results, analytical expressions of the local PS using crystallographic parameters are uncovered. These expressions show the primary origin of BaTiO3 ferroelectricity as oxygen displacements. Elastic compliance and electrostrictive coefficients are estimated. For the comparison of strained results, we show that the effective critical temperature TC under strain 1000 K from an approximate method combining ab initio

Density-matrix-functional calculations for matter in strong magnetic fields: Ground states of heavy atoms

DEFF Research Database (Denmark)

Johnsen, Kristinn; Yngvason, Jakob

1996-01-01

We report on a numerical study of the density matrix functional introduced by Lieb, Solovej, and Yngvason for the investigation of heavy atoms in high magnetic fields. This functional describes exactly the quantum mechanical ground state of atoms and ions in the limit when the nuclear charge Z...... and the electron number N tend to infinity with N/Z fixed, and the magnetic field B tends to infinity in such a way that B/Z4/3→∞. We have calculated electronic density profiles and ground-state energies for values of the parameters that prevail on neutron star surfaces and compared them with results obtained...... by other methods. For iron at B=1012 G the ground-state energy differs by less than 2% from the Hartree-Fock value. We have also studied the maximal negative ionization of heavy atoms in this model at various field strengths. In contrast to Thomas-Fermi type theories atoms can bind excess negative charge...

Efficient approximation of the Struve functions Hn occurring in the calculation of sound radiation quantities.

Science.gov (United States)

Aarts, Ronald M; Janssen, Augustus J E M

2016-12-01

The Struve functions H n (z), n=0, 1, ...  are approximated in a simple, accurate form that is valid for all z≥0. The authors previously treated the case n = 1 that arises in impedance calculations for the rigid-piston circular radiator mounted in an infinite planar baffle [Aarts and Janssen, J. Acoust. Soc. Am. 113, 2635-2637 (2003)]. The more general Struve functions occur when other acoustical quantities and/or non-rigid pistons are considered. The key step in the paper just cited is to express H 1 (z) as (2/π)-J 0 (z)+(2/π) I(z), where J 0 is the Bessel function of order zero and the first kind and I(z) is the Fourier cosine transform of [(1-t)/(1+t)] 1/2 , 0≤t≤1. The square-root function is optimally approximated by a linear function ĉt+d̂, 0≤t≤1, and the resulting approximated Fourier integral is readily computed explicitly in terms of sin z/z and (1-cos z)/z 2 . The same approach has been used by Maurel, Pagneux, Barra, and Lund [Phys. Rev. B 75, 224112 (2007)] to approximate H 0 (z) for all z≥0. In the present paper, the square-root function is optimally approximated by a piecewise linear function consisting of two linear functions supported by [0,t̂ 0 ] and [t̂ 0 ,1] with t̂ 0 the optimal take-over point. It is shown that the optimal two-piece linear function is actually continuous at the take-over point, causing a reduction of the additional complexity in the resulting approximations of H 0 and H 1 . Furthermore, this allows analytic computation of the optimal two-piece linear function. By using the two-piece instead of the one-piece linear approximation, the root mean square approximation error is reduced by roughly a factor of 3 while the maximum approximation error is reduced by a factor of 4.5 for H 0 and of 2.6 for H 1 . Recursion relations satisfied by Struve functions, initialized with the approximations of H 0 and H 1 , yield approximations for higher order Struve functions.

BSATOM - package of programs for calculating the energy levels and wave functions of helium-like systems taking into account isotope effects

International Nuclear Information System (INIS)

Abrashkevich, A.G.; Abrashkevich, D.G.; Vinitskij, S.I.; Puzynin, I.V.

1989-01-01

Description of package BCATOM for calculating the energy levels and wave functions of helium-like systems in the hyperspherical adiabatic approach taking into account the isotopic effects is given. The corresponding Sturm-Liouville problems are approximated by the difference method and the high order accuracy finite element method. The obtained generalized algebraic eigenvalue problems are solved by subspace iteration method. Possibilities of the package are demonstrated by calculating the ground state characteristics of a negative hydrogen ion. 33 refs.; 1 fig

Quantum chromodynamical calculations of meson wave functions in the light-cone formalism by means of QCD sum rules

International Nuclear Information System (INIS)

Guellenstern, S.

1991-09-01

Using the technique of Cherniak and Zhitnitzky we have calculated the wavefunctions of ρ(770) and Φ(1020) within the framework of QCD sum rules. Whereas the standard approach assumes light-like distances of the quarks (z 2 = 0), we also have taken into account higher order terms in z 2 . Thus, we obtained non-vanishing orbital angular momentum contributions. The first few moments of various invariant functions have been calculated with the help of an especially developed REDUCE program package. In zeroth order (z 2 = 0) our results of the reconstructed wavefunctions agree with those in the literature. However, we got first order contributions in z 2 of an amount of almost 10% of the corresponding zeroth order. (orig.)

Analytical Calculation of D- and Q-axis Inductance for Interior Permanent Magnet Motors Based on Winding Function Theory

Directory of Open Access Journals (Sweden)

Peixin Liang

2016-07-01

Full Text Available Interior permanent magnet (IPM motors are widely used in electric vehicles (EVs, benefiting from the excellent advantages of a more rational use of energy. For further improvement of energy utilization, this paper presents an analytical method of d- and q-axis inductance calculation for IPM motors with V-shaped rotor in no-load condition. A lumped parameter magnetic circuit model (LPMCM is adopted to investigate the saturation and nonlinearity of the bridge. Taking into account the influence of magnetic field distribution on inductance, the winding function theory (WFT is employed to accurately calculate the armature reaction airgap magnetic field and d- and q-axis inductances. The validity of the analytical technique is verified by the finite element method (FEM.

Density functional theory calculations of H/D isotope effects on polymer electrolyte membrane fuel cell operations

Energy Technology Data Exchange (ETDEWEB)

Yanase, Satoshi; Oi, Takao [Sophia Univ., Tokyo (Japan). Faculty of Science and Technology

2015-10-01

To elucidate hydrogen isotope effects observed between fuel and exhaust hydrogen gases during polymer electrolyte membrane fuel cell operations, H-to-D reduced partition function ratios (RPFRs) for the hydrogen species in the Pt catalyst phase of the anode and the electrolyte membrane phase of the fuel cell were evaluated by density functional theory calculations on model species of the two phases. The evaluation yielded 3.2365 as the value of the equilibrium constant of the hydrogen isotope exchange reaction between the two phases at 39 C, which was close to the experimentally estimated value of 3.46-3.99 at the same temperature. It was indicated that H{sup +} ions on the Pt catalyst surface of the anode and H species in the electrolyte membrane phase were isotopically in equilibrium with one another during fuel cell operations.

Importance iteration in MORSE Monte Carlo calculations

International Nuclear Information System (INIS)

Kloosterman, J.L.; Hoogenboom, J.E.

1994-01-01

An expression to calculate point values (the expected detector response of a particle emerging from a collision or the source) is derived and implemented in the MORSE-SGC/S Monte Carlo code. It is outlined how these point values can be smoothed as a function of energy and as a function of the optical thickness between the detector and the source. The smoothed point values are subsequently used to calculate the biasing parameters of the Monte Carlo runs to follow. The method is illustrated by an example that shows that the obtained biasing parameters lead to a more efficient Monte Carlo calculation

Importance iteration in MORSE Monte Carlo calculations

International Nuclear Information System (INIS)

Kloosterman, J.L.; Hoogenboom, J.E.

1994-02-01

An expression to calculate point values (the expected detector response of a particle emerging from a collision or the source) is derived and implemented in the MORSE-SGC/S Monte Carlo code. It is outlined how these point values can be smoothed as a function of energy and as a function of the optical thickness between the detector and the source. The smoothed point values are subsequently used to calculate the biasing parameters of the Monte Carlo runs to follow. The method is illustrated by an example, which shows that the obtained biasing parameters lead to a more efficient Monte Carlo calculation. (orig.)

Fully self-consistent GW calculations for molecules

DEFF Research Database (Denmark)

Rostgaard, Carsten; Jacobsen, Karsten Wedel; Thygesen, Kristian Sommer

2010-01-01

We calculate single-particle excitation energies for a series of 34 molecules using fully self-consistent GW, one-shot G0W0, Hartree-Fock (HF), and hybrid density-functional theory (DFT). All calculations are performed within the projector-augmented wave method using a basis set of Wannier...... functions augmented by numerical atomic orbitals. The GW self-energy is calculated on the real frequency axis including its full frequency dependence and off-diagonal matrix elements. The mean absolute error of the ionization potential (IP) with respect to experiment is found to be 4.4, 2.6, 0.8, 0.4, and 0...

Effective action calculation in lattice QCD

International Nuclear Information System (INIS)

Hoek, J.

1983-01-01

A method (called the effective action method) devised to make analytic calculations in Quantum Chromodynamics in the region of strong coupling is presented. First, the author deals with developing the calculation of a strong coupling expansion of the generating functional for gauge systems on a lattice with arbitrary sources. An accompanying manual describes the implementation of this calculation on a computer. The next step consists of substituting the expressions for the one-link free energies for a specific gauge group in the result of the previous calculation. This process of substitution, together with the replacement of the sources by a bilinear combination of fermion fields, is described for the group SU(3). More details on the implementation of the substitution scheme on a computer can be found in the accompanying manual. From the effective action thus obtained in terms of meson fields and baryon fields the Green functions of the theory can be derived. As an illustrative application the effective potential determining the vacuum expectation value of the meson field is calculated. (Auth.)

Development of a BWR core burn-up calculation code COREBN-BWR

International Nuclear Information System (INIS)

Morimoto, Yuichi; Okumura, Keisuke

1992-05-01

In order to evaluate core performances of BWR type reactors, the three dimensional core burnup calculation code COREBN-BWR and the fuel management code HIST-BWR have been developed. In analyses of BWR type reactors, thermal hydraulics calculations must be coupled with neutronics calculations to evaluate core performances, because steam void distribution changes according to the change of the power distribution. By installing new functions as follows to the three dimensional core burnup code COREBN2 developed in JAERI for PWR type reactor analyses, the code system becomes to be applicable to burnup analyses of BWR type reactors. (1) Macroscopic cross section calculation function taking into account of coolant void distribution. (2) Thermal hydraulics calculation function to evaluate core flow split, coolant void distribution and thermal margin. (3) Burnup calculation function under the Haling strategy. (4) Fuel management function to incorporate the thermal hydraulics information. This report consists of the general description, calculational models, input data requirements and their explanations, detailed information on usage and sample input. (author)

Full charge-density calculation of the surface energy of metals

DEFF Research Database (Denmark)

Vitos, Levente; Kollár, J..; Skriver, Hans Lomholt

1994-01-01

of a spherically symmetrized charge density, while the Coulomb and exchange-correlation contributions are calculated by means of the complete, nonspherically symmetric charge density within nonoverlapping, space-filling Wigner-Seitz cells. The functional is used to assess the convergence and the accuracy......We have calculated the surface energy and the work function of the 4d metals by means of an energy functional based on a self-consistent, spherically symmetric atomic-sphere potential. In this approach the kinetic energy is calculated completely within the atomic-sphere approximation (ASA) by means...... of the linear-muffin-tin-orbitals (LMTO) method and the ASA in surface calculations. We find that the full charge-density functional improves the agreement with recent full-potential LMTO calculations to a level where the average deviation in surface energy over the 4d series is down to 10%....

Anomalies in Ward identities revisited. Explicit calculation of the three point functions

International Nuclear Information System (INIS)

Dalmolin, Fabricio Tronco

2007-01-01

others already performed within the same issue. In particular, in one of such investigation a pioneer and traditional reference has been revisited by using the alternative strategy mentioned above. In such study, a systematic treatment of purely fermionic one, two and three point functions, associated to scalar, pseudo-scalar, vector and axial-vector densities, has done. There, however, only the explicit expressions for one and two point functions were developed. The conclusions pointed out, in a very clear way, that the association between intrinsic ambiguities of the perturbative calculation and violations in symmetry properties is not consistent. At the same time, it was concluded that only in an investigation where the explicit forms for the three point functions involved are considered clean and sound conclusions can be extracted. This is due to the fact that, in the relevant symmetry properties, it is involved three ward identities and a low energy limit. This is precisely the main purpose of the present work: to promote a detailed investigation of the relations among green functions and ward identities, within the context of a model having only one specie of 1/2 spin fermionic field, that consider all the amplitudes having superficial degree of divergence higher than the logarithmic one, in a similar way as that made in the work of Gerstein and Jackiw, taking however the explicit form for the three point functions. This is one to get in the analysis, simultaneously, the ward identities and the low energy limits involved in the anomalous amplitudes as required by the Sutherland-Veltman theorem, in order to get an adequate understanding of the anomaly phenomena. We will show that our final results can be mapped in those found with the use of the Dimensional Regularization, in situation where this technique can be applied, or in those of Gerstein and Jackiw, however with conflicting interpretations. Finally, we will show that in the context of the adopted technique

On calculation of zeta function of integral matrix

Czech Academy of Sciences Publication Activity Database

Janáček, Jiří

2009-01-01

Roč. 134, č. 1 (2009), s. 49-58 ISSN 0862-7959 R&D Projects: GA AV ČR(CZ) IAA100110502 Institutional research plan: CEZ:AV0Z50110509 Keywords : Epstein zeta function * integral lattice * Riemann theta function Subject RIV: BA - General Mathematics

Time-dependent density functional calculation of the energy loss of antiprotons colliding with metallic nanoshells

International Nuclear Information System (INIS)

Quijada, M.; Borisov, A.G.; Muino, R.D.

2008-01-01

Time-dependent density functional theory is used to study the interaction between antiprotons and metallic nanoshells. The ground state electronic properties of the nanoshell are obtained in the jellium approximation. The energy lost by the antiproton during the collision is calculated and compared to that suffered by antiprotons traveling in metal clusters. The resulting energy loss per unit path length of material in thin nanoshells is larger than the corresponding quantity for clusters. It is shown that the collision process can be interpreted as the antiproton crossing of two nearly bi-dimensional independent metallic systems. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Calculation of the exchange coupling constants of copper binuclear systems based on spin-flip constricted variational density functional theory.

Science.gov (United States)

Zhekova, Hristina R; Seth, Michael; Ziegler, Tom

2011-11-14

We have recently developed a methodology for the calculation of exchange coupling constants J in weakly interacting polynuclear metal clusters. The method is based on unrestricted and restricted second order spin-flip constricted variational density functional theory (SF-CV(2)-DFT) and is here applied to eight binuclear copper systems. Comparison of the SF-CV(2)-DFT results with experiment and with results obtained from other DFT and wave function based methods has been made. Restricted SF-CV(2)-DFT with the BH&HLYP functional yields consistently J values in excellent agreement with experiment. The results acquired from this scheme are comparable in quality to those obtained by accurate multi-reference wave function methodologies such as difference dedicated configuration interaction and the complete active space with second-order perturbation theory. © 2011 American Institute of Physics

Density Functional Theory Calculations of Activation Energies for Carrier Capture by Defects in Semiconductors

Science.gov (United States)

Modine, N. A.; Wright, A. F.; Lee, S. R.

The rate of defect-induced carrier recombination is determined by both defect levels and carrier capture cross-sections. Density functional theory (DFT) has been widely and successfully used to predict defect levels, but only recently has work begun to focus on using DFT to determine carrier capture cross-sections. Lang and Henry developed the theory of carrier-capture by multiphonon emission in the 1970s and showed that carrier-capture cross-sections differ between defects primarily due to differences in their carrier capture activation energies. We present an approach to using DFT to calculate carrier capture activation energies that does not depend on an assumed configuration coordinate and that fully accounts for anharmonic effects, which can substantially modify carrier activation energies. We demonstrate our approach for intrinisic defects in GaAs and GaN and discuss how our results depend on the choice of exchange-correlation functional and the treatment of spin polarization. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

Filling- and interaction-driven Mott transition. Quantum cluster calculations within self-energy-functional theory

International Nuclear Information System (INIS)

Balzer, Matthias

2008-01-01

The central goal of this thesis is the examination of strongly correlated electron systems on the basis of the two-dimensional Hubbard model. We analyze how the properties of the Mott insulator change upon doping and with interaction strength. The numerical evaluation is done using quantum cluster approximations, which allow for a thermodynamically consistent description of the ground state properties. The framework of self-energy-functional theory offers great flexibility for the construction of cluster approximations. A detailed analysis sheds light on the quality and the convergence properties of different cluster approximations within the self-energy-functional theory. We use the one-dimensional Hubbard model for these examinations and compare our results with the exact solution. In two dimensions the ground state of the particle-hole symmetric model at half-filling is an antiferromagnetic insulator, independent of the interaction strength. The inclusion of short-range spatial correlations by our cluster approach leads to a considerable improvement of the antiferromagnetic order parameter as compared to dynamical mean-field theory. In the paramagnetic phase we furthermore observe a metal-insulator transition as a function of the interaction strength, which qualitatively differs from the pure mean-field scenario. Starting from the antiferromagnetic Mott insulator a filling-controlled metal-insulator transition in a paramagnetic metallic phase can be observed. Depending on the cluster approximation used an antiferromagnetic metallic phase may occur at first. In addition to long-range antiferromagnetic order, we also considered superconductivity in our calculations. The superconducting order parameter as a function of doping is in good agreement with other numerical methods, as well as with experimental results. (orig.)

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

First-principles calculations of mobility

Science.gov (United States)

Krishnaswamy, Karthik

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

Vibrational and UV spectroscopic studies of 2-coumaranone by experimental and density functional theory calculations

Science.gov (United States)

Priya, Y. Sushma; Rao, K. Ramachandra; Chalapathi, P. V.; Satyavani, M.; Veeraiah, A.

2017-09-01

The vibrational and electronic properties of 2-coumaranone have been reported in the ground state using experimental techniques (FT-IR, FT-Raman, UV spectra and fluorescence microscopic imaging) and density functional theory (DFT) employing B3LYP correlation with the 6-31G(d, p) basis set. The theoretically reported optimized parameters, vibrational frequencies etc., were compared with the experimental values, which yielded good concurrence between the experimental and calculated values. The assignments of the vibrational spectra were done with the help of normal co-ordinate analysis (NCA) following the Scaled Quantum Mechanical Force Field(SQMFF) methodology. The whole assignments of fundamental modes were based on the potential energy distribution (PED) matrix. The electric dipole moment and the first order hyperpolarizability of the 2-coumaranone have been computed using quantum mechanical calculations. NBO and HOMO, LUMO analyses have been carried out. UV spectrum of 2-coumaranone was recorded in the region 100-300 nm and compared with the theoretical UV spectrum using TD-DFT and SAC-CI methods by which a good agreement is observed. Fluorescence microscopic imaging study reflects that the compound fluoresces in the green-yellow region.

Analysis of calculating methods for failure distribution function based on maximal entropy principle

International Nuclear Information System (INIS)

Guo Chunying; Lin Yuangen; Jiang Meng; Wu Changli

2009-01-01

The computation of invalidation distribution functions of electronic devices when exposed in gamma rays is discussed here. First, the possible devices failure distribution models are determined through the tests of statistical hypotheses using the test data. The results show that: the devices' failure distribution can obey multi-distributions when the test data is few. In order to decide the optimum failure distribution model, the maximal entropy principle is used and the elementary failure models are determined. Then, the Bootstrap estimation method is used to simulate the intervals estimation of the mean and the standard deviation. On the basis of this, the maximal entropy principle is used again and the simulated annealing method is applied to find the optimum values of the mean and the standard deviation. Accordingly, the electronic devices' optimum failure distributions are finally determined and the survival probabilities are calculated. (authors)

Calculation of the two-electron Darwin term using explicitly correlated wave functions

International Nuclear Information System (INIS)

Middendorf, Nils; Höfener, Sebastian; Klopper, Wim; Helgaker, Trygve

2012-01-01

Graphical abstract: The two-electron Darwin term is computed analytically at the MP2-F12 level of theory using density fitted integrals. Highlights: ► Two-electron Darwin term computed analytically at the MP2-F12 level. ► Darwin two-electron integrals computed using density fitting techniques. ► Two-electron Darwin term dominated by singlet pair contributions. ► Much improved basis set convergence is achieved with F12 methods. ► Interference correction works well for the two-electron Darwin term. - Abstract: This article is concerned with the calculation of the two-electron Darwin term (D2). At the level of explicitly correlated second-order perturbation theory (MP2-F12), the D2 term is obtained as an analytic energy derivative; at the level of explicitly correlated coupled-cluster theory, it is obtained from finite differences. To avoid the calculation of four-center integrals, a density-fitting approximation is applied to the D2 two-electron integrals without loss of accuracy, even though the absolute value of the D2 term is typically about 0.1 mE h . Explicitly correlated methods provide a qualitatively correct description of the short-range region around the Coulomb hole, even for small orbital basis sets. Therefore, explicitly correlated wave functions remedy the otherwise extremely slow convergence of the D2 contribution with respect to the basis-set size, yielding more accurate results than those obtained by two-point basis-set extrapolation. Moreover, we show that the interference correction of Petersson’s complete-basis-set model chemistry can be used to compute a D2 basis-set correction at the MP2-F12 level to improve standard coupled-cluster singles-and-doubles results.

Density functional theory calculations establish the experimental evidence of the DX center atomic structure in CdTe.

Science.gov (United States)

Lany, Stephan; Wolf, Herbert; Wichert, Thomas

2004-06-04

The In DX center and the DX-like configuration of the Cd host atom in CdTe are investigated using density functional theory. The simultaneous calculation of the atomic structure and the electric field gradient (EFG) allows one to correlate the theoretically predicted structure of the DX center with an experimental observable, namely, the EFG obtained from radioactive 111In/111Cd probe atoms in In doped CdTe. In this way, the experimental identification of the DX center structure is established.

A statistical calculation of the β- strength function

International Nuclear Information System (INIS)

Arvieu, R.; Haq, R.U.; Touchard, J.

1976-01-01

A microscopic calculation of the Gamow-Teller strength between the 0 + ground state of 208 Pb and the 1 + particle-hole states of 208 Bi assuming the particle-hole matrix elements as random numbers with some specified distribution, is described. Under certain conditions for the two-body matrix elements, a G.T. resonance occurs. The stability of this collective state along with the accompanying low energy β - -strength tail is studied for various samples of p-h matrix elements [fr

Quantum mechanical methods for calculation of force constants

International Nuclear Information System (INIS)

Mullally, D.J.

1985-01-01

The focus of this thesis is upon the calculation of force constants; i.e., the second derivatives of the potential energy with respect to nuclear displacements. This information is useful for the calculation of molecular vibrational modes and frequencies. In addition, it may be used for the location and characterization of equilibrium and transition state geometries. The methods presented may also be applied to the calculation of electric polarizabilities and infrared and Raman vibrational intensities. Two approaches to this problem are studied and evaluated: finite difference methods and analytical techniques. The most suitable method depends on the type and level of theory used to calculate the electronic wave function. Double point displacement finite differencing is often required for accurate calculation of the force constant matrix. These calculations require energy and gradient calculations on both sides of the geometry of interest. In order to speed up these calculations, a novel method is presented that uses geometry dependent information about the wavefunction. A detailed derivation for the analytical evaluation of force constants with a complete active space multiconfiguration self consistent field wave function is presented

Role of various Dirac covariants in the BS wave functions in decay constant calculations of pseudoscalar mesons using a power counting scheme

International Nuclear Information System (INIS)

Bhatnagar, S.; Mahecha, J.

2008-09-01

We have employed the framework of Bethe-Salpeter equation under Covariant Instantaneous Ansatz to calculate the leptonic decay constants of unequal mass pseudoscalar mesons. In the Dirac structure of BS wave function, the covariants are incorporated from their complete set in accordance with a recently proposed power counting rule, order-by-order in powers of inverse of meson mass. The decay constants are calculated incorporating both Leading Order (LO) as well as Next-to-leading Order (NLO) Dirac covariants. The contribution of both LO as well as NLO covariants to decay constants are studied in detail in this paper. The results are found to improve dramatically, and hence validating the power counting rule which also provides a practical means of incorporating Dirac covariants in the BS wave function of a hadron. (author)

Hybrid functional pseudopotentials

Science.gov (United States)

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.

Calculation methods for determining dose equivalent

International Nuclear Information System (INIS)

Endres, G.W.R.; Tanner, J.E.; Scherpelz, R.I.; Hadlock, D.E.

1988-01-01

A series of calculations of neutron fluence as a function of energy in an anthropomorphic phantom was performed to develop a system for determining effective dose equivalent for external radiation sources. critical organ dose equivalents are calculated and effective dose equivalents are determined using ICRP-26 methods. Quality factors based on both present definitions and ICRP-40 definitions are used in the analysis. The results of these calculations are presented and discussed

Additive manufacturing of a functionally graded material from Ti-6Al-4V to Invar: Experimental characterization and thermodynamic calculations

International Nuclear Information System (INIS)

Bobbio, Lourdes D.; Otis, Richard A.; Borgonia, John Paul; Dillon, R. Peter; Shapiro, Andrew A.; Liu, Zi-Kui; Beese, Allison M.

2017-01-01

In functionally graded materials (FGMs), the elemental composition, or structure, within a component varies gradually as a function of position, allowing for the gradual transition from one alloy to another, and the local tailoring of properties. One method for fabricating FGMs with varying elemental composition is through layer-by-layer directed energy deposition additive manufacturing. This work combines experimental characterization and computational analysis to investigate a material graded from Ti-6Al-4V to Invar 36 (64 wt% Fe, 36 wt% Ni). The microstructure, composition, phases, and microhardness were determined as a function of position within the FGM. During the fabrication process, detrimental phases associated with the compositional blending of the Ti-6Al-4V and Invar formed, leading to cracking in the final deposited part. Intermetallic phases (FeTi, Fe_2Ti, Ni_3Ti, and NiTi_2) were experimentally identified to occur throughout the gradient region, and were considered as the reason that the FGM cracked during fabrication. CALPHAD (CALculation of PHase Diagrams) thermodynamic calculations were used concurrently to predict phases that would form during the manufacturing process and were compared to the experimental results. The experimental-computational approach described herein for characterizing FGMs can be used to improve the understanding and design of other FGMs.

Calculations of the response functions of Bonner spheres with a spherical 3He proportional counter using a realistic detector model

International Nuclear Information System (INIS)

Wiegel, B.; Alevra, A.V.; Siebert, B.R.L.

1994-11-01

A realistic geometry model of a Bonner sphere system with a spherical 3 He-filled proportional counter and 12 polyethylene moderating spheres with diameters ranging from 7,62 cm (3'') to 45,72 cm (18'') is introduced. The MCNP Monte Carlo computer code is used to calculate the responses of this Bonner sphere system to monoenergetic neutrons in the energy range between 1 meV to 20 MeV. The relative uncertainties of the responses due to the Monte Carlo calculations are less than 1% for spheres up to 30,48 cm (12'') in diameter and less than 2% for the 15'' and 18'' spheres. Resonances in the carbon cross section are seen as significant structures in the response functions. Additional calculations were made to study the influence of the 3 He number density and the polyethylene mass density on the response as well as the angular dependence of the Bonner sphere system. The calculated responses can be adjusted to a large set of calibration measurements with only a single fit factor common to all sphere diameters and energies. (orig.) [de

Alternative definitions of the frozen energy in energy decomposition analysis of density functional theory calculations.

Science.gov (United States)

Horn, Paul R; Head-Gordon, Martin

2016-02-28

In energy decomposition analysis (EDA) of intermolecular interactions calculated via density functional theory, the initial supersystem wavefunction defines the so-called "frozen energy" including contributions such as permanent electrostatics, steric repulsions, and dispersion. This work explores the consequences of the choices that must be made to define the frozen energy. The critical choice is whether the energy should be minimized subject to the constraint of fixed density. Numerical results for Ne2, (H2O)2, BH3-NH3, and ethane dissociation show that there can be a large energy lowering associated with constant density orbital relaxation. By far the most important contribution is constant density inter-fragment relaxation, corresponding to charge transfer (CT). This is unwanted in an EDA that attempts to separate CT effects, but it may be useful in other contexts such as force field development. An algorithm is presented for minimizing single determinant energies at constant density both with and without CT by employing a penalty function that approximately enforces the density constraint.

Examining real-time time-dependent density functional theory nonequilibrium simulations for the calculation of electronic stopping power

Science.gov (United States)

Yost, Dillon C.; Yao, Yi; Kanai, Yosuke

2017-09-01

In ion irradiation processes, electronic stopping power describes the energy transfer rate from the irradiating ion to the target material's electrons. Due to the scarcity and significant uncertainties in experimental electronic stopping power data for materials beyond simple solids, there has been growing interest in the use of first-principles theory for calculating electronic stopping power. In recent years, advances in high-performance computing have opened the door to fully first-principles nonequilibrium simulations based on real-time time-dependent density functional theory (RT-TDDFT). While it has been demonstrated that the RT-TDDFT approach is capable of predicting electronic stopping power for a wide range of condensed matter systems, there has yet to be an exhaustive examination of the physical and numerical approximations involved and their effects on the calculated stopping power. We discuss the results of such a study for crystalline silicon with protons as irradiating ions. We examine the influences of key approximations in RT-TDDFT nonequilibrium simulations on the calculated electronic stopping power, including approximations related to basis sets, finite size effects, exchange-correlation approximation, pseudopotentials, and more. Finally, we propose a simple and efficient correction scheme to account for the contribution from core-electron excitations to the stopping power, as it was found to be significant for large proton velocities.

Total energy calculations from self-energy models

International Nuclear Information System (INIS)

Sanchez-Friera, P.

2001-06-01

Density-functional theory is a powerful method to calculate total energies of large systems of interacting electrons. The usefulness of this method, however, is limited by the fact that an approximation is required for the exchange-correlation energy. Currently used approximations (LDA and GGA) are not sufficiently accurate in many physical problems, as for instance the study of chemical reactions. It has been shown that exchange-correlation effects can be accurately described via the self-energy operator in the context of many-body perturbation theory. This is, however, a computationally very demanding approach. In this thesis a new scheme for calculating total energies is proposed, which combines elements from many-body perturbation theory and density-functional theory. The exchange-correlation energy functional is built from a simplified model of the self-energy, that nevertheless retains the main features of the exact operator. The model is built in such way that the computational effort is not significantly increased with respect to that required in a typical density-functional theory calculation. (author)

An experimental and theoretical study of molecular structure and vibrational spectra of 2-methylphenyl boronic acid by density functional theory calculations

Science.gov (United States)

Hiremath, Sudhir M.; Hiremath, C. S.; Khemalapure, S. S.; Patil, N. R.

2018-05-01

This paper reports the experimental and theoretical study on the structure and vibrations of 2-Methylphenyl boronic acid (2MPBA). The different spectroscopic techniques such as FT-IR (4000-400 cm-1) and FT-Raman (4000-50 cm-1) of the title molecule in the solid phase were recorded. The geometry of the molecule was fully optimized using density functional theory (DFT) (B3LYP) with 6-311++G(d, p) basis set calculations. The vibrational wavenumbers were also corrected with scale factor to take better results for the calculated data. Vibrational spectra were calculated and fundamental vibrations were assigned on the basis of the potential energy distribution (PED) of the vibrational modes obtained from VEDA 4 program. The calculated wavenumbers showed the best agreement with the experimental results. Whereas, it is observed that, the theoretical frequencies are more than the experimental one for O-H stretching vibration modes of the title molecule.

Time-dependent importance sampling in semiclassical initial value representation calculations for time correlation functions. II. A simplified implementation.

Science.gov (United States)

Tao, Guohua; Miller, William H

2012-09-28

An efficient time-dependent (TD) Monte Carlo (MC) importance sampling method has recently been developed [G. Tao and W. H. Miller, J. Chem. Phys. 135, 024104 (2011)] for the evaluation of time correlation functions using the semiclassical (SC) initial value representation (IVR) methodology. In this TD-SC-IVR method, the MC sampling uses information from both time-evolved phase points as well as their initial values, and only the "important" trajectories are sampled frequently. Even though the TD-SC-IVR was shown in some benchmark examples to be much more efficient than the traditional time-independent sampling method (which uses only initial conditions), the calculation of the SC prefactor-which is computationally expensive, especially for large systems-is still required for accepted trajectories. In the present work, we present an approximate implementation of the TD-SC-IVR method that is completely prefactor-free; it gives the time correlation function as a classical-like magnitude function multiplied by a phase function. Application of this approach to flux-flux correlation functions (which yield reaction rate constants) for the benchmark H + H(2) system shows very good agreement with exact quantum results. Limitations of the approximate approach are also discussed.

Calculations for the excitation functions of the 63Cup, n63Zn, 63Cup, 2n62Zn and 65Cup, n65Zn reactions

International Nuclear Information System (INIS)

Gul, K.

2001-01-01

Calculations for the excitation functions of 63 Cup, n 63 Zn, 63 Cup, 2n 62 Zn and 65 Cup, n 65 Zn reactions have been carried out in 3-30 MeV energy range using statistical and pre-equilibrium nuclear reaction models. The calculations have been compared with reported measurements and discussed

Electronic states of thiophene/phenylene co-oligomers: Extreme-ultra violet excited photoelectron spectroscopy observations and density functional theory calculations

International Nuclear Information System (INIS)

Kawaguchi, Yoshizo; Sasaki, Fumio; Mochizuki, Hiroyuki; Ishitsuka, Tomoaki; Tomie, Toshihisa; Ootsuka, Teruhisa; Watanabe, Shuji; Shimoi, Yukihiro; Yamao, Takeshi; Hotta, Shu

2013-01-01

We have investigated electronic states in the valence electron bands for the thin films of three thiophene/phenylene co-oligomer (TPCO) compounds, 2,5-bis(4-biphenylyl)thiophene (BP1T), 1,4-bis(5-phenylthiophen-2-yl)benzene (AC5), and 1,4-bis{5-[4-(trifluoromethyl)phenyl]thiophen-2-yl}benzene (AC5-CF 3 ), by using extreme-UV excited photoelectron spectroscopy (EUPS). By comparing both EUPS spectra and secondary electron spectra between AC5 and AC5-CF 3 , we confirm that CF 3 substitution to AC5 deepens valence states by 2 eV, and increases the ionization energy by 3 eV. From the cut-off positions of secondary electron spectra, the work functions of AC5, AC5-CF 3 , and BP1T are evaluated to be 3.8 eV, 4.8 eV, and 4.0 eV, respectively. We calculate molecular orbital (MO) energy levels by the density functional theory and compare results of calculations with those of experiments. Densities of states obtained by broadening MO levels well explain the overall features of experimental EUPS spectra of three TPCOs.

Effects of Cu intercalation on the graphene/Ni(111) surface: density-functional calculations

International Nuclear Information System (INIS)

Kwon, Se Gab; Kang, Myung Ho

2012-01-01

The Cu-intercalated graphene/Ni(111) surface has been studied by using density-functional theory calculations. We find that (1) the intercalation-induced decoupling between graphene and the Ni(111) substrate begins sharply at a Cu coverage of about 0.75 ML, (2) at the optimal Cu coverage of 1 ML, graphene recovers an almost ideal Dirac-cone band structure with no band gap, and (3) the Dirac point is located at 0.17 eV below the Fermi level, indicating a small charge transfer from the substrate. Cu thus plays essentially the same role as Au in realizing quasi-free-standing graphene by intercalation. Our charge character analysis shows that the Dirac-cone bands near the Fermi level reveal a weakening of their π character when crossing the Ni d bands, suggesting that the resulting low Dirac-cone intensity could possibly be the origin of the recent photoemission report of a relatively large band gap of 0.18 eV.

Nature and strength of bonding in a crystal of semiconducting nanotubes: van der Waals density functional calculations and analytical results

DEFF Research Database (Denmark)

Kleis, Jesper; Schröder, Elsebeth; Hyldgaard, Per

2008-01-01

calculations, the vdW-DF study predicts an intertube vdW bonding with a strength that is consistent with recent observations for the interlayer binding in graphitics. It also produces a nanotube wall-to-wall separation, which is in very good agreement with experiments. Moreover, we find that the vdW-DF result...... for the nanotube-crystal binding energy can be approximated by a sum of nanotube-pair interactions when these are calculated in vdW-DR This observation suggests a framework for an efficient implementation of quantum-physical modeling of the carbon nanotube bundling in more general nanotube bundles, including......The dispersive interaction between nanotubes is investigated through ab initio theory calculations and in an analytical approximation. A van der Waals density functional (vdW-DF) [M. Dion et al., Phys. Rev. Lett. 92, 246401 (2004)] is used to determine and compare the binding of a pair of nanotubes...

Structure and stability of acrolein and allyl alcohol networks on Ag(111) from density functional theory based calculations with dispersion corrections

Science.gov (United States)

Ferullo, Ricardo M.; Branda, Maria Marta; Illas, Francesc

2013-11-01

The interaction of acrolein and allyl alcohol with the Ag(111) surface has been studied by means of periodic density functional theory based calculations including explicitly dispersion terms. Different coverage values have been explored going from isolated adsorbed molecules to isolated dimers, interacting dimers or ordered overlayers. The inclusion of the dispersion terms largely affects the calculated values of the adsorption energy and also the distance between adsorbed molecule and the metallic surface but much less the adsorbate-adsorbate interactions. Owing to the large dipole moment of acrolein, the present calculations predict that at high coverage this molecule forms a stable extensive two-dimensional network on the surface, caused by the alignment of the adsorbate dipoles. For the case of allyl alcohol, dimers and complex networks exhibit similar stability.

Density functional calculations of backbone 15N shielding tensors in beta-sheet and turn residues of protein G

International Nuclear Information System (INIS)

Cai Ling; Kosov, Daniel S.; Fushman, David

2011-01-01

We performed density functional calculations of backbone 15 N shielding tensors in the regions of beta-sheet and turns of protein G. The calculations were carried out for all twenty-four beta-sheet residues and eight beta-turn residues in the protein GB3 and the results were compared with the available experimental data from solid-state and solution NMR measurements. Together with the alpha-helix data, our calculations cover 39 out of the 55 residues (or 71%) in GB3. The applicability of several computational models developed previously (Cai et al. in J Biomol NMR 45:245–253, 2009) to compute 15 N shielding tensors of alpha-helical residues is assessed. We show that the proposed quantum chemical computational model is capable of predicting isotropic 15 N chemical shifts for an entire protein that are in good correlation with experimental data. However, the individual components of the predicted 15 N shielding tensor agree with experiment less well: the computed values show much larger spread than the experimental data, and there is a profound difference in the behavior of the tensor components for alpha-helix/turns and beta-sheet residues. We discuss possible reasons for this.

Li-ion conduction in the LiBH4:LiI system from Density Functional Theory calculations and Quasi-Elastic Neutron Scattering

DEFF Research Database (Denmark)

Myrdal, Jon Steinar Gardarsson; Blanchard, Didier; Sveinbjörnsson, Dadi Þorsteinn

2013-01-01

The hexagonal high-temperature polymorph of LiBH4 is stabilized by solid solution with LiI to exhibit superionic Li+ ionic conductivity at room temperature. Herein, the mechanisms for the Li+ diffusion are investigated for the first time by density functional theory (DFT) calculations coupled...

"Cloud" functions and templates of engineering calculations for nuclear power plants

Science.gov (United States)

Ochkov, V. F.; Orlov, K. A.; Ko, Chzho Ko

2014-10-01

The article deals with an important problem of setting up computer-aided design calculations of various circuit configurations and power equipment carried out using the templates and standard computer programs available in the Internet. Information about the developed Internet-based technology for carrying out such calculations using the templates accessible in the Mathcad Prime software package is given. The technology is considered taking as an example the solution of two problems relating to the field of nuclear power engineering.

Fission neutron multiplicity calculations

International Nuclear Information System (INIS)

Maerten, H.; Ruben, A.; Seeliger, D.

1991-01-01

A model for calculating neutron multiplicities in nuclear fission is presented. It is based on the solution of the energy partition problem as function of mass asymmetry within a phenomenological approach including temperature-dependent microscopic energies. Nuclear structure effects on fragment de-excitation, which influence neutron multiplicities, are discussed. Temperature effects on microscopic energy play an important role in induced fission reactions. Calculated results are presented for various fission reactions induced by neutrons. Data cover the incident energy range 0-20 MeV, i.e. multiple chance fission is considered. (author). 28 refs, 13 figs

Adding glycaemic index and glycaemic load functionality to DietPLUS, a Malaysian food composition database and diet intake calculator.

Science.gov (United States)

Shyam, Sangeetha; Wai, Tony Ng Kock; Arshad, Fatimah

2012-01-01

This paper outlines the methodology to add glycaemic index (GI) and glycaemic load (GL) functionality to food DietPLUS, a Microsoft Excel-based Malaysian food composition database and diet intake calculator. Locally determined GI values and published international GI databases were used as the source of GI values. Previously published methodology for GI value assignment was modified to add GI and GL calculators to the database. Two popular local low GI foods were added to the DietPLUS database, bringing up the total number of foods in the database to 838 foods. Overall, in relation to the 539 major carbohydrate foods in the Malaysian Food Composition Database, 243 (45%) food items had local Malaysian values or were directly matched to International GI database and another 180 (33%) of the foods were linked to closely-related foods in the GI databases used. The mean ± SD dietary GI and GL of the dietary intake of 63 women with previous gestational diabetes mellitus, calculated using DietPLUS version3 were, 62 ± 6 and 142 ± 45, respectively. These values were comparable to those reported from other local studies. DietPLUS version3, a simple Microsoft Excel-based programme aids calculation of diet GI and GL for Malaysian diets based on food records.

A computer program for calculation of parameters necessary for the computation of reliable pair distribution functions of non-crystalline materials from limited diffraction data. II

International Nuclear Information System (INIS)

Hansen, F.Y.

1978-01-01

The pair distribution function of non-crystalline materials may be obtained by a Fourier transform of the structure factor as calculated in part I of this series. The structure factor is often limited in the sense that it shows significant oscillations at the maximal wave vector transfers obtainable. The Fourier transform of such functions, therefore, introduces truncation errors in the transformed function. With this program a parametrization of the small distance part of the pair distribution function is obtained according to a method described which enables one to eliminate truncation error from the final pair distribution function. It is based on a least squares fit calculation of the small distance part of the pair distribution function obtained by a direct transform of the experimental structure factor and a model pair distribution function obtained from a model structure factor truncated at the same wave vector transfers as the experimental factor. The storage requirement depends on the number of structure factor data and the number of peaks used to resolve the small distance part of the pair distribution function. In the present set-up storage requirement is set to 15083 words, which is estimated to be satisfactory for a large number of cases. (Auth.)

Model calculations of excitation functions of neutron-induced reactions on Rh

International Nuclear Information System (INIS)

Strohmaier, Brigitte

1995-01-01

Cross sections of neutron-induced reactions on 103 Rh have been calculated by means of the statistical model and the coupled-channels optical model for incident-neutron energies up to 30 MeV. The incentive for this study was a new measurement of the 103 Rh(n, n') 103m Rh cross section which will - together with the present calculations -enter into a dosimetry-reaction evaluation. The validation of the model parameters relied on nuclear-structure data as far as possible. (author)

Scheme for ab initio calculation of the Green function in large disordered systems with application to transport properties

Science.gov (United States)

Tanaka, Hiroshi

1998-01-01

A real-space scheme is developed to calculate matrix elements of the Green function from first principles for large disordered systems. The scheme is an extension of the particle source method, combined with the tight-binding linear muffin-tin orbitals and has the following advantages: (i) It is possible to evaluate both the diagonal and off-diagonal parts of the Green function and also their products with other quantum operators, (ii) it allows for an explicit control of the numerical accuracy and clear-cut physical interpretations of the results on the basis of the definition of the Green function, and (iii) the scheme is suitable for both vector and parallel processing and requires CPU time and memory size proportional only to the system size. The method is applied to the densities of states of bcc and amorphous Fe. The dc conductivity is also evaluated for the latter from the Kubo-Greenwood formula.

Assessment of Density-Functional Tight-Binding Ionization Potentials and Electron Affinities of Molecules of Interest for Organic Solar Cells Against First-Principles GW Calculations

Directory of Open Access Journals (Sweden)

Ala Aldin M. H. M. Darghouth

2015-12-01

Full Text Available Ionization potentials (IPs and electron affinities (EAs are important quantities input into most models for calculating the open-circuit voltage (Voc of organic solar cells. We assess the semi-empirical density-functional tight-binding (DFTB method with the third-order self-consistent charge (SCC correction and the 3ob parameter set (the third-order DFTB (DFTB3 organic and biochemistry parameter set against experiments (for smaller molecules and against first-principles GW (Green’s function, G, times the screened potential, W calculations (for larger molecules of interest in organic electronics for the calculation of IPs and EAs. Since GW calculations are relatively new for molecules of this size, we have also taken care to validate these calculations against experiments. As expected, DFTB is found to behave very much like density-functional theory (DFT, but with some loss of accuracy in predicting IPs and EAs. For small molecules, the best results were found with ΔSCF (Δ self-consistent field SCC-DFTB calculations for first IPs (good to ± 0.649 eV. When considering several IPs of the same molecule, it is convenient to use the negative of the orbital energies (which we refer to as Koopmans’ theorem (KT IPs as an indication of trends. Linear regression analysis shows that KT SCC-DFTB IPs are nearly as accurate as ΔSCF SCC-DFTB eigenvalues (± 0.852 eV for first IPs, but ± 0.706 eV for all of the IPs considered here for small molecules. For larger molecules, SCC-DFTB was also the ideal choice with IP/EA errors of ± 0.489/0.740 eV from ΔSCF calculations and of ± 0.326/0.458 eV from (KT orbital energies. Interestingly, the linear least squares fit for the KT IPs of the larger molecules also proves to have good predictive value for the lower energy KT IPs of smaller molecules, with significant deviations appearing only for IPs of 15–20 eV or larger. We believe that this quantitative analysis of errors in SCC-DFTB IPs and EAs may be of

Calculation of the vibrational linewidth and line shape of Raman spectra using the relaxation function : I. method and application to nitrogen

NARCIS (Netherlands)

Kooi, M.E.; Smit, F.; Michels, J.P.J.; Schouten, J.A.

2000-01-01

The spectral line shape of the fundamental vibration of nitrogen is calculated from molecular dynamics simulations by determining the Fourier transform of the relaxation function. It has been applied to the fluid phase at various pressures and temperatures, and to solid d-N2. The validity of the

Calculation of the exponential function of linear idempotent operators

International Nuclear Information System (INIS)

Chavoya-Aceves, O.; Luna, H.M.

1989-01-01

We give a method to calculate the exponential EXP[A r ] where A is a linear operator which satisfies the reaction A n =I, n is an integer and I is the identity operator. The method is generalised to operators such that A n +1=A and is applied to obtain some Lorentz transformations which generalise the notion of 'boost'. (Author)

Molecular dynamics calculation of shear viscosity for molten salt

International Nuclear Information System (INIS)

Okamoto, Yoshihiro; Yokokawa, Mitsuo; Ogawa, Toru

1993-12-01

A computer program of molecular dynamics simulation has been made to calculate shear viscosity of molten salt. Correlation function for an off-diagonal component of stress tensor can be obtained as the results of calculation. Shear viscosity is calculated by integration of the correlation function based on the Kubo-type formula. Shear viscosities for a molten KCl ranging in temperature from 1047K to 1273K were calculated using the program. Calculation of 10 5 steps (1 step corresponds to 5 x 10 -15 s) was performed for each temperature in the 216 ions system. The obtained results were in good agreement with the reported experimental values. The program has been vectorized to achieve a faster computation in supercomputer. It makes possible to calculate the viscosity using a large number of statistics amounting to several million MD steps. (author)

Non-perturbative background field calculations

International Nuclear Information System (INIS)

Stephens, C.R.; Department of Physics, University of Utah, Salt Lake City, Utah 84112)

1988-01-01

New methods are developed for calculating one loop functional determinants in quantum field theory. Instead of relying on a calculation of all the eigenvalues of the small fluctuation equation, these techniques exploit the ability of the proper time formalism to reformulate an infinite dimensional field theoretic problem into a finite dimensional covariant quantum mechanical analog, thereby allowing powerful tools such as the method of Jacobi fields to be used advantageously in a field theory setting. More generally the methods developed herein should be extremely valuable when calculating quantum processes in non-constant background fields, offering a utilitarian alternative to the two standard methods of calculation: perturbation theory in the background field or taking the background field into account exactly. The formalism developed also allows for the approximate calculation of covariances of partial differential equations from a knowledge of the solutions of a homogeneous ordinary differential equation. copyright 1988 Academic Press, Inc

High-temperature partition functions, specific heats and spectral radiative properties of diatomic molecules with an improved calculation of energy levels

Science.gov (United States)

Qin, Z.; Zhao, J. M.; Liu, L. H.

2018-05-01

The level energies of diatomic molecules calculated by the frequently used Dunham expansion will become less accurate for high-lying vibrational and rotational levels. In this paper, the potential curves for the lower-lying electronic states with accurate spectroscopic constants are reconstructed using the Rydberg-Klein-Rees (RKR) method, which are extrapolated to the dissociation limits by fitting of the theoretical potentials, and the rest of the potential curves are obtained from the ab-initio results in the literature. Solving the rotational dependence of the radial Schrödinger equation over the obtained potential curves, we determine the rovibrational level energies, which are then used to calculate the equilibrium and non-equilibrium thermodynamic properties of N2, N2+, NO, O2, CN, C2, CO and CO+. The partition functions and the specific heats are systematically validated by available data in the literature. Finally, we calculate the radiative source strengths of diatomic molecules in thermodynamic equilibrium, which agree well with the available values in the literature. The spectral radiative intensities for some diatomic molecules in thermodynamic non-equilibrium are calculated and validated by available experimental data.

Assessment of time-dependent density functional theory with the restricted excitation space approximation for excited state calculations of large systems

Science.gov (United States)

Hanson-Heine, Magnus W. D.; George, Michael W.; Besley, Nicholas A.

2018-06-01

The restricted excitation subspace approximation is explored as a basis to reduce the memory storage required in linear response time-dependent density functional theory (TDDFT) calculations within the Tamm-Dancoff approximation. It is shown that excluding the core orbitals and up to 70% of the virtual orbitals in the construction of the excitation subspace does not result in significant changes in computed UV/vis spectra for large molecules. The reduced size of the excitation subspace greatly reduces the size of the subspace vectors that need to be stored when using the Davidson procedure to determine the eigenvalues of the TDDFT equations. Furthermore, additional screening of the two-electron integrals in combination with a reduction in the size of the numerical integration grid used in the TDDFT calculation leads to significant computational savings. The use of these approximations represents a simple approach to extend TDDFT to the study of large systems and make the calculations increasingly tractable using modest computing resources.

Detailed calculations on low-energy positron-hydrogen-molecule and helium-antihydrogen scattering

Energy Technology Data Exchange (ETDEWEB)

Armour, E A G; Cooper, J N; Gregory, M R; Todd, A C [School of Mathematical Sciences, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Jonsell, S [Department of Physics, University of Swansea, Swansea SA2 8PP (United Kingdom); Plummer, M, E-mail: edward.armour@nottingham.ac.u [Computational Science and Engineering, STFC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom)

2010-01-01

In this paper, we consider two scattering processes: low-energy positron-hydrogen-molecule and helium-antihydrogen scattering. In the positron-hydrogen-molecule scattering calculations, we use the Kohn variational method to calculate Z{sub eff}, the number of target electrons available to the positron for annihilation. In the helium-antihydrogen scattering calculations, we use the Rayleigh-Ritz variational method to calculate a wave function for the leptons as a function of the distance between the helium and the antihydrogen. This is used, together with the associated nuclear wave function and the wave function for {alpha} p-bar + Ps{sup -}, to calculate the cross section for the rearrangement reaction He + H-bar {yields} {alpha} p-bar + Ps{sup -}, using the T-matrix and a form of the distorted wave approximation. For both processes, positron-electron correlation is taken into account accurately using Hylleraas-type functions.

Rain Scattering and Co-ordinate Distance Calculation

Directory of Open Access Journals (Sweden)

M. Hajny

1998-12-01

Full Text Available Calculations of scattered field on the rain objects are based on using of Multiple MultiPole (MMP numerical method. Both bi-static scattering function and bi-static scattering cross section are calculated in the plane parallel to Earth surface. The co-ordination area was determined using the simple model of scattering volume [1]. Calculation for frequency 9.595 GHz and antenna elevation of 25° was done. Obtained results are compared with calculation in accordance to ITU-R recommendation.

Calculation of uncertainties associated to environmental radioactivity measurements and their functions. Practical Procedure

International Nuclear Information System (INIS)

Gasco Leonarte, C.; Anton Mateos, M.P.

1995-12-01

This report summarizes the procedure used to calculate the uncertainties associated to environmental radioactivity measurements. focusing on those obtained by radiochemical separation in which tracers have been added. Uncertainties linked to activity concentration calculations, isotopic ratio, inventories, sequential leaching data, chronology dating by using C.R.S model and duplicate analysis are described in detail. The objective of this article is to serve as a guide to people not familiarized with this kind of calculations, showing clear practical examples. The input of the formulas and all the data needed to achieve these calculations into the Lotus 1,2,3, WIN is outlined as well. (Author)

Calculation of uncertainties associated to environmental radioactivity measurements and their functions. Practical Procedure

International Nuclear Information System (INIS)

Gasco Leonarte, C; Anton Mateos, M. P.

1995-01-01

This report summarizes the procedure used to calculate the uncertainties associated to environmental radioactivity measurements, focusing on those obtained by radiochemical separation in which tracers have been added. Uncertainties linked to activity concentration calculations, isotopic rat iso, inventories, sequential leaching data, chronology dating by using C.R.S. model and duplicate analysis are described in detail. The objective of this article is to serve as a guide to people not familiarized with this kind of calculations, showing clear practical examples. The input of the formulas and all the data needed to achieve these calculations into the Lotus 1, 2, 3 WTN is outlined as well. (Author) 13 refs

Calculation of Si(Li) x-ray detector efficiencies

International Nuclear Information System (INIS)

Zaluzec, N.; Holton, R.

1984-01-01

The calculation of detector efficiency functions is an important step in the quantitative analysis of x-ray spectra when approached by a standardless technique. In this regard, it becomes essential that the analyst not only model the physical aspects of the absorption and transmission of the various windows present, but also use the most accurate data available for the mass absorption coefficients required in these calculations. The topic of modeling the size and shape of the windows present is beyond the scope of this paper and the authors instead concentrate on the mass absorption coefficients used in the calculations and their implications to efficiency calculations. For the purposes of this paper, the authors consider that the relative detector efficiency function of a conventional Si(Li) detector can be modeled by a simple expression

Ab-initio ZORA calculations

NARCIS (Netherlands)

Faas, S.; Snijders, Jaap; van Lenthe, J.H.; HernandezLaguna, A; Maruani, J; McWeeny, R; Wilson, S

2000-01-01

In this paper we present the first application of the ZORA (Zeroth Order Regular Approximation of the Dirac Fock equation) formalism in Ab Initio electronic structure calculations. The ZORA method, which has been tested previously in the context of Density Functional Theory, has been implemented in

DRY TRANSFER FACILITY CRITICALITY SAFETY CALCULATIONS

International Nuclear Information System (INIS)

C.E. Sanders

2005-01-01

This design calculation updates the previous criticality evaluation for the fuel handling, transfer, and staging operations to be performed in the Dry Transfer Facility (DTF) including the remediation area. The purpose of the calculation is to demonstrate that operations performed in the DTF and RF meet the nuclear criticality safety design criteria specified in the ''Project Design Criteria (PDC) Document'' (BSC 2004 [DIRS 171599], Section 4.9.2.2), the nuclear facility safety requirement in ''Project Requirements Document'' (Canori and Leitner 2003 [DIRS 166275], p. 4-206), the functional/operational nuclear safety requirement in the ''Project Functional and Operational Requirements'' document (Curry 2004 [DIRS 170557], p. 75), and the functional nuclear criticality safety requirements described in the ''Dry Transfer Facility Description Document'' (BSC 2005 [DIRS 173737], p. 3-8). A description of the changes is as follows: (1) Update the supporting calculations for the various Category 1 and 2 event sequences as identified in the ''Categorization of Event Sequences for License Application'' (BSC 2005 [DIRS 171429], Section 7). (2) Update the criticality safety calculations for the DTF staging racks and the remediation pool to reflect the current design. This design calculation focuses on commercial spent nuclear fuel (SNF) assemblies, i.e., pressurized water reactor (PWR) and boiling water reactor (BWR) SNF. U.S. Department of Energy (DOE) Environmental Management (EM) owned SNF is evaluated in depth in the ''Canister Handling Facility Criticality Safety Calculations'' (BSC 2005 [DIRS 173284]) and is also applicable to DTF operations. Further, the design and safety analyses of the naval SNF canisters are the responsibility of the U.S. Department of the Navy (Naval Nuclear Propulsion Program) and will not be included in this document. Also, note that the results for the Monitored Geologic Repository (MGR) Site specific Cask (MSC) calculations are limited to the

Calculation of the line shapes of radiators immersed in plasma

International Nuclear Information System (INIS)

Hayrapetian, A.S.

1987-01-01

This work reports the results of theoretical calculations of line shapes of radiators immersed in plasma. The fluctuating electric field of the plasma perturbs the atomic structure of the immersed ions or atoms. The perturbed line shape is an important diagnostic tool for the temperature and density measurements of plasma. The line-shape calculation here is done by first deriving the line-shape expression, then it is shown that the problem is equivalent to calculating the temperature Green's function of the bound electron. The total Hamiltonian of the system includes the atomic, plasma, and atom-plasma parts. The temperature Green's function is calculated perturbatively by expanding in orders of atom-plasma interaction. By solving a Dyson equation, the dressed Green's functions of the bound electrons are obtained. At this point, the line shape is calculated by an analytic continuation from the complex frequency plane to real line. To derive the atomic electron Green's function, the momentum integral in the self-energy is approximated by a Riemann sum. With this approximation, the algebraic form of the line shape is obtained for an undetermined number of terms in the Riemann sum. Numerical calculation of line shape is done by using this result

Conductance calculations with a wavelet basis set

DEFF Research Database (Denmark)

Thygesen, Kristian Sommer; Bollinger, Mikkel; Jacobsen, Karsten Wedel

2003-01-01

We present a method based on density functional theory (DFT) for calculating the conductance of a phase-coherent system. The metallic contacts and the central region where the electron scattering occurs, are treated on the same footing taking their full atomic and electronic structure into account....... The linear-response conductance is calculated from the Green's function which is represented in terms of a system-independent basis set containing wavelets with compact support. This allows us to rigorously separate the central region from the contacts and to test for convergence in a systematic way...

PWR core design calculations

Energy Technology Data Exchange (ETDEWEB)

Trkov, A; Ravnik, M; Zeleznik, N [Inst. Jozef Stefan, Ljubljana (Slovenia)

1992-07-01

Functional description of the programme package Cord-2 for PWR core design calculations is presented. Programme package is briefly described. Use of the package and calculational procedures for typical core design problems are treated. Comparison of main results with experimental values is presented as part of the verification process. (author) [Slovenian] Opisali smo programski paket CORD-2, ki se uporablja pri projektnih izracunih sredice pri upravljanju tlacnovodnega reaktorja. Prikazana je uporaba paketa in racunskih postopkov za tipicne probleme, ki nastopajo pri projektiranju sredice. Primerjava glavnih rezultatov z eksperimentalnimi vrednostmi je predstavljena kot del preveritvenega procesa. (author)

Hualien forced vibration calculation with a finite element model

International Nuclear Information System (INIS)

Wang, F.; Gantenbein, F.; Nedelec, M.; Duretz, Ch.

1995-01-01

The forced vibration tests of the Hualien mock-up were useful to validate finite element models developed for soil-structure interaction. In this paper the two sets of tests with and without backfill were analysed. the methods used are based on finite element modeling for the soil. Two approaches were considered: calculation of soil impedance followed by the calculation of the transfer functions with a model taking into account the superstructure and the impedance; direct calculation of the soil-structure transfer functions, with the soil and the structure being represented in the same model by finite elements. Blind predictions and post-test calculations are presented and compared with the test results. (author). 4 refs., 8 figs., 2 tabs

Magnesium acceptor in gallium nitride. II. Koopmans-tuned Heyd-Scuseria-Ernzerhof hybrid functional calculations of its dual nature and optical properties

Science.gov (United States)

Demchenko, D. O.; Diallo, I. C.; Reshchikov, M. A.

2018-05-01

The problem of magnesium acceptor in gallium nitride is that experimental photoluminescence measurements clearly reveal a shallow defect state, while most theoretical predictions favor a localized polaronic defect state. To resolve this contradiction, we calculate properties of magnesium acceptor using the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, tuned to fulfill the generalized Koopmans condition. We test Koopmans tuning of HSE for defect calculations in GaN using two contrasting test cases: a deep state of gallium vacancy and a shallow state of magnesium acceptor. The obtained parametrization of HSE allows calculations of optical properties of acceptors using neutral defect-state eigenvalues, without relying on corrections due to charged defects in periodic supercells. Optical transitions and vibrational properties of M gGa defect are analyzed to bring the dual (shallow and deep) nature of this defect into accord with experimental photoluminescence measurements of the ultraviolet band in Mg-doped GaN samples.

Molecular simulations and density functional theory calculations of bromine in clathrate hydrate phases

Energy Technology Data Exchange (ETDEWEB)

Dureckova, Hana, E-mail: houci059@uottawa.ca; Woo, Tom K., E-mail: tom.woo@uottawa.ca [Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, Ontario K1N 5N6 (Canada); Alavi, Saman, E-mail: saman.alavi@nrc-cnrc.gc.ca [Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, Ontario K1N 5N6 (Canada); National Research Council of Canada, 100 Sussex Dr., Ottawa, Ontario K1N 6N5 (Canada); Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, British Columbia V6T 1Z3 (Canada)

2016-01-28

Bromine forms a tetragonal clathrate hydrate structure (TS-I) very rarely observed in clathrate hydrates of other guest substances. The detailed structure, energetics, and dynamics of Br{sub 2} and Cl{sub 2} in TS-I and cubic structure I (CS-I) clathrate hydrates are studied in this work using molecular dynamics and quantum chemical calculations. X-ray diffraction studies show that the halogen-water–oxygen distances in the cages of these structures are shorter than the sum of the van der Waals radii of halogen and oxygen atoms. This suggests that the stabilizing effects of halogen bonding or other non-covalent interactions (NCIs) may contribute to the formation of the unique tetragonal bromine hydrate structure. We performed molecular dynamics simulations of Br{sub 2} and Cl{sub 2} clathrate hydrates using our previously developed five-site charge models for the dihalogen molecules [Dureckova et al. Can. J. Chem. 93, 864 (2015)] which reproduce the computed electrostatic potentials of the dihalogens and account for the electropositive σ-hole of the halogen bond donor (the dihalogen). Analysis of the radial distribution functions, enthalpies of encapsulation, velocity and orientation autocorrelation functions, and polar angle distributions are carried out for Br{sub 2} and Cl{sub 2} guests in various cages to contrast the properties of these guests in the TS-I and CS-I phases. Quantum chemical partial geometry optimizations of Br{sub 2} and Cl{sub 2} guests in the hydrate cages using the M06-2X functional give short halogen-water distances compatible with values observed in X-ray diffraction experiments. NCI plots of guest-cage structures are generated to qualitatively show the relative strength of the non-bonding interactions between dihalogens and water molecules. The differences between behaviors of Br{sub 2} and Cl{sub 2} guests in the hydrate cages may explain why bromine forms the unique TS-I phase.

Calculation of probability density functions for temperature and precipitation change under global warming

International Nuclear Information System (INIS)

Watterson, Ian G.

2007-01-01

Full text: he IPCC Fourth Assessment Report (Meehl ef al. 2007) presents multi-model means of the CMIP3 simulations as projections of the global climate change over the 21st century under several SRES emission scenarios. To assess the possible range of change for Australia based on the CMIP3 ensemble, we can follow Whetton etal. (2005) and use the 'pattern scaling' approach, which separates the uncertainty in the global mean warming from that in the local change per degree of warming. This study presents several ways of representing these two factors as probability density functions (PDFs). The beta distribution, a smooth, bounded, function allowing skewness, is found to provide a useful representation of the range of CMIP3 results. A weighting of models based on their skill in simulating seasonal means in the present climate over Australia is included. Dessai ef al. (2005) and others have used Monte-Carlo sampling to recombine such global warming and scaled change factors into values of net change. Here, we use a direct integration of the product across the joint probability space defined by the two PDFs. The result is a cumulative distribution function (CDF) for change, for each variable, location, and season. The median of this distribution provides a best estimate of change, while the 10th and 90th percentiles represent a likely range. The probability of exceeding a specified threshold can also be extracted from the CDF. The presentation focuses on changes in Australian temperature and precipitation at 2070 under the A1B scenario. However, the assumption of linearity behind pattern scaling allows results for different scenarios and times to be simply obtained. In the case of precipitation, which must remain non-negative, a simple modification of the calculations (based on decreases being exponential with warming) is used to avoid unrealistic results. These approaches are currently being used for the new CSIRO/ Bureau of Meteorology climate projections

Communication: importance sampling including path correlation in semiclassical initial value representation calculations for time correlation functions.

Science.gov (United States)

Pan, Feng; Tao, Guohua

2013-03-07

Full semiclassical (SC) initial value representation (IVR) for time correlation functions involves a double phase space average over a set of two phase points, each of which evolves along a classical path. Conventionally, the two initial phase points are sampled independently for all degrees of freedom (DOF) in the Monte Carlo procedure. Here, we present an efficient importance sampling scheme by including the path correlation between the two initial phase points for the bath DOF, which greatly improves the performance of the SC-IVR calculations for large molecular systems. Satisfactory convergence in the study of quantum coherence in vibrational relaxation has been achieved for a benchmark system-bath model with up to 21 DOF.

Density-functional, density-functional tight-binding, and wave-function calculations on biomolecular systems

Czech Academy of Sciences Publication Activity Database

Kubař, Tomáš; Jurečka, Petr; Černý, Jiří; Řezáč, Jan; Otyepka, M.; Valdes, Haydee; Hobza, Pavel

2007-01-01

Roč. 111, č. 26 (2007), s. 5642-5647 ISSN 1089-5639 R&D Projects: GA MŠk LC512; GA AV ČR IAA400550510; GA ČR(CZ) GD203/05/H001; GA ČR GA203/05/0009 Institutional research plan: CEZ:AV0Z40550506 Keywords : density functional theory * empirical dispersion-energy term * non-covalent interactions Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.918, year: 2007

Excited State Charge Transfer reaction with dual emission from 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile: Spectral measurement and theoretical density functional theory calculation

Science.gov (United States)

Jana, Sankar; Dalapati, Sasanka; Ghosh, Shalini; Kar, Samiran; Guchhait, Nikhil

2011-07-01

The excited state intramolecular charge transfer process in donor-chromophore-acceptor system 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile (DMAPPDN) has been investigated by steady state absorption and emission spectroscopy in combination with Density Functional Theory (DFT) calculations. This flexible donor acceptor molecule DMAPPDN shows dual fluorescence corresponding to emission from locally excited and charge transfer state in polar solvent. Large solvatochromic emission shift, effect of variation of pH and HOMO-LUMO molecular orbital pictures support excited state intramolecular charge transfer process. The experimental findings have been correlated with the calculated structure and potential energy surfaces based on the Twisted Intramolecular Charge Transfer (TICT) model obtained at DFT level using B3LYP functional and 6-31+G( d, p) basis set. The theoretical potential energy surfaces for the excited states have been generated in vacuo and acetonitrile solvent using Time Dependent Density Functional Theory (TDDFT) and Time Dependent Density Functional Theory Polarized Continuum Model (TDDFT-PCM) method, respectively. All the theoretical results show well agreement with the experimental observations.

Linear response calculation using the canonical-basis TDHFB with a schematic pairing functional

International Nuclear Information System (INIS)

Ebata, Shuichiro; Nakatsukasa, Takashi; Yabana, Kazuhiro

2011-01-01

A canonical-basis formulation of the time-dependent Hartree-Fock-Bogoliubov (TDHFB) theory is obtained with an approximation that the pair potential is assumed to be diagonal in the time-dependent canonical basis. The canonical-basis formulation significantly reduces the computational cost. We apply the method to linear-response calculations for even-even nuclei. E1 strength distributions for proton-rich Mg isotopes are systematically calculated. The calculation suggests strong Landau damping of giant dipole resonance for drip-line nuclei.

Phase-space path-integral calculation of the Wigner function

International Nuclear Information System (INIS)

Samson, J H

2003-01-01

The Wigner function W(q, p) is formulated as a phase-space path integral, whereby its sign oscillations can be seen to follow from interference between the geometrical phases of the paths. The approach has similarities to the path-centroid method in the configuration-space path integral. Paths can be classified by the midpoint of their ends; short paths where the midpoint is close to (q, p) and which lie in regions of low energy (low P function of the Hamiltonian) will dominate, and the enclosed area will determine the sign of the Wigner function. As a demonstration, the method is applied to a sequence of density matrices interpolating between a Poissonian number distribution and a number state, each member of which can be represented exactly by a discretized path integral with a finite number of vertices. Saddle-point evaluation of these integrals recovers (up to a constant factor) the WKB approximation to the Wigner function of a number state

Density functional theory calculation of monolayer WTe2 transition metal dichalcogenides doped with H, Li and Be

Science.gov (United States)

Igumbor, E.; Mapasha, R. E.; Meyer, W. E.

2018-04-01

Results based on density functional theory modelling of electronic and structural properties of single layer WTe2 dichalcogenides doped with X (X=H, Li and Be) were presented. The generalized gradient approximation functional of Perdew, Burke, and Ernzerhof exchange correlation was used for all calculations. Formation energies of X dopant substituted for W (XW) were obtained to be between 3.59 and 2.61 eV. The LiW defect with energy of formation of 2.14 eV was energetically the most favourable. For all dopants considered, while the HW induced no magnetic moment, the LiW and BeW induced magnetic moments of 3.44 and 0.05 μB, respectively. The band gap of the WTe2 as a result of the dopants was populated with several orbital ground states, and thus reduced within a few eV. While all XW behave as p - type dopant, the LiW defect posses half metallic character.

The Positron-Electron Correlation Energy In ZnO Calculated With The Modified Single Wave Function Of Positron

International Nuclear Information System (INIS)

Chau Van Tao; Trinh Hoa Lang; Le Hoang Chien; Nguyen Huu Loc; Nguyen Anh Tuan

2011-01-01

Positron-electron correlation energy of the ZnO - positron system is studied on assumption that positron binds with the outer shell electrons of Zinc and Oxygen to form the pseudo ZnO - positron molecule before it annihilates with one of these electrons. In this work, the single wave function for positron is form by LCAO approximation and is modified according to the principle of linear superposition, and by using Variational Quantum Monte Carlo method (VQMC) [7] the correlation energy of this system is estimated with the value E c e-p = - 9.3 ± 1.1 eV. In the theoretical aspect it turns out that this result is more reasonable and closer to those of other methods [3] than the one which is done without modifying the wave function of positron [1]. To confirm this legitimate approach, however, the further calculations of positron annihilation rate in ZnO have to be carried out in our next work. (author)

Calculation of pion form factor

International Nuclear Information System (INIS)

Vahedi, N.; Amirarjomand, S.

1975-09-01

The pion form factor is calculated using the structure function Wsub(2), which incorporates kinematical constraints, threshold behaviour and scaling. The Bloom-Gilman sum rule is used and only the two leading Regge trajectories are taken into account

Elementary exact calculations of degree growth and entropy for discrete equations.

Science.gov (United States)

Halburd, R G

2017-05-01

Second-order discrete equations are studied over the field of rational functions [Formula: see text], where z is a variable not appearing in the equation. The exact degree of each iterate as a function of z can be calculated easily using the standard calculations that arise in singularity confinement analysis, even when the singularities are not confined. This produces elementary yet rigorous entropy calculations.

SCRAM reactivity calculations with the KIKO3D code

International Nuclear Information System (INIS)

Hordosy, G.; Kerszturi, A.; Maraczy, Cs.; Temesvari, E.

1999-01-01

Discrepancies between calculated static reactivities and measured reactivities evaluated with reactivity meters led to investigating SCRAM with the KIKO3D dynamic code, The time and space dependent neutron flux in the reactor core during the rod drop measurement was calculated by the KIKO3D nodal diffusion code. For calculating the ionisation chamber signals the Green function technique was applied. The Green functions of ionisation chambers were evaluated via solving the neutron transport equation in the reflector regions with the MCNP Monte Carlo code. The detector signals during asymmetric SCRAM measurements were calculated and compared with measured data using the inverse point kinetics transformation. The sufficient agreement validates the KIKO3D code to determine the reactivities after SCRAM. (Authors)

Direct calculation of wind turbine tip loss

DEFF Research Database (Denmark)

Wood, D.H.; Okulov, Valery; Bhattacharjee, D.

2016-01-01

. We develop three methods for the direct calculation of the tip loss. The first is the computationally expensive calculation of the velocities induced by the helicoidal wake which requires the evaluation of infinite sums of products of Bessel functions. The second uses the asymptotic evaluation......The usual method to account for a finite number of blades in blade element calculations of wind turbine performance is through a tip loss factor. Most analyses use the tip loss approximation due to Prandtl which is easily and cheaply calculated but is known to be inaccurate at low tip speed ratio...

convergent methods for calculating thermodynamic Green functions

OpenAIRE

Bowen, S. P.; Williams, C. D.; Mancini, J. D.

1984-01-01

A convergent method of approximating thermodynamic Green functions is outlined briefly. The method constructs a sequence of approximants which converges independently of the strength of the Hamiltonian's coupling constants. Two new concepts associated with the approximants are introduced: the resolving power of the approximation, and conditional creation (annihilation) operators. These ideas are illustrated on an exactly soluble model and a numerical example. A convergent expression for the s...

Determination of the structures of small gold clusters on stepped magnesia by density functional calculations.

Science.gov (United States)

Damianos, Konstantina; Ferrando, Riccardo

2012-02-21

The structural modifications of small supported gold clusters caused by realistic surface defects (steps) in the MgO(001) support are investigated by computational methods. The most stable gold cluster structures on a stepped MgO(001) surface are searched for in the size range up to 24 Au atoms, and locally optimized by density-functional calculations. Several structural motifs are found within energy differences of 1 eV: inclined leaflets, arched leaflets, pyramidal hollow cages and compact structures. We show that the interaction with the step clearly modifies the structures with respect to adsorption on the flat defect-free surface. We find that leaflet structures clearly dominate for smaller sizes. These leaflets are either inclined and quasi-horizontal, or arched, at variance with the case of the flat surface in which vertical leaflets prevail. With increasing cluster size pyramidal hollow cages begin to compete against leaflet structures. Cage structures become more and more favourable as size increases. The only exception is size 20, at which the tetrahedron is found as the most stable isomer. This tetrahedron is however quite distorted. The comparison of two different exchange-correlation functionals (Perdew-Burke-Ernzerhof and local density approximation) show the same qualitative trends. This journal is © The Royal Society of Chemistry 2012

Evaluation and reffinement of the neutronic calculation methodology

International Nuclear Information System (INIS)

Conti Filho, P.

1984-01-01

A computational code that has the homogenized cross section given by the LEOPARD code as input was developed. The code gives polinomial coefficients that represent the homogenized cross section as a function of the local burnup and the boron concentration for the assembly, for each step in the reactor Burnup. Lately, were developed an interface between the LEOPARD code Polinomiun Generator program and CITATION code to became possible to CITATION code to set the homogenized microscopic cross section as function of the local caracteristics of the assembly on the way to make the calculation of the reactor Burnup. For a choosen reactor (1900MWth) have been done the inicial calculation (super-cells calculation and others Input) and after that were done the calculation with and without the polinomia. The analyses of the results of the CITATION code were done and the principal results were presented here. (Author) [pt

Variational calculation for the ground state of 12C

International Nuclear Information System (INIS)

Consoni, L.H.A.; Coelho, H.T.; Das, T.K.

1983-01-01

A variational calculation is done for the ground state of a 3α-particle system. Two simple trial wavefunctions are used and results are compared with an exact calculation done by the Hyperspherical Harmonic method. A modifed Ali-Bodmer potential for the α-α interaction is considered for all calculations. It is found that these simple wave functions can be very useful for phenomenological calculations. (Author) [pt

Exact-exchange-based quasiparticle calculations

International Nuclear Information System (INIS)

Aulbur, Wilfried G.; Staedele, Martin; Goerling, Andreas

2000-01-01

One-particle wave functions and energies from Kohn-Sham calculations with the exact local Kohn-Sham exchange and the local density approximation (LDA) correlation potential [EXX(c)] are used as input for quasiparticle calculations in the GW approximation (GWA) for eight semiconductors. Quasiparticle corrections to EXX(c) band gaps are small when EXX(c) band gaps are close to experiment. In the case of diamond, quasiparticle calculations are essential to remedy a 0.7 eV underestimate of the experimental band gap within EXX(c). The accuracy of EXX(c)-based GWA calculations for the determination of band gaps is as good as the accuracy of LDA-based GWA calculations. For the lowest valence band width a qualitatively different behavior is observed for medium- and wide-gap materials. The valence band width of medium- (wide-) gap materials is reduced (increased) in EXX(c) compared to the LDA. Quasiparticle corrections lead to a further reduction (increase). As a consequence, EXX(c)-based quasiparticle calculations give valence band widths that are generally 1-2 eV smaller (larger) than experiment for medium- (wide-) gap materials. (c) 2000 The American Physical Society

Non-perturbative background field calculations

Science.gov (United States)

Stephens, C. R.

1988-01-01

New methods are developed for calculating one loop functional determinants in quantum field theory. Instead of relying on a calculation of all the eigenvalues of the small fluctuation equation, these techniques exploit the ability of the proper time formalism to reformulate an infinite dimensional field theoretic problem into a finite dimensional covariant quantum mechanical analog, thereby allowing powerful tools such as the method of Jacobi fields to be used advantageously in a field theory setting. More generally the methods developed herein should be extremely valuable when calculating quantum processes in non-constant background fields, offering a utilitarian alternative to the two standard methods of calculation—perturbation theory in the background field or taking the background field into account exactly. The formalism developed also allows for the approximate calculation of covariances of partial differential equations from a knowledge of the solutions of a homogeneous ordinary differential equation.

Density functional theory calculations of charge transport properties ...

Indian Academy of Sciences (India)

ZIRAN CHEN

2017-08-04

Aug 4, 2017 ... properties of 'plate-like' coronene topological structures ... Keywords. Organic semiconductors; density functional theory; charge carrier mobility; ambipolar transport; ..... nology Department of Sichuan Province (Grant Number.

Dielectric Response at THz Frequencies of Fe Water Complexes and Their Interaction with O3 Calculated by Density Functional Theory

Science.gov (United States)

2012-10-24

geometric arrangement of the atoms in a chemical system , at the maximal peak of the energy surface separating reactants from products . In the...Sonnenberg, M. Hada, M. Ehara, K. Toyota , R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda , O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery... using DFT. The calculation of ground state resonance structure is for the construction of parameterized dielectric response functions for excitation

Calculation code NIRVANA for free boundary MHD equilibrium

International Nuclear Information System (INIS)

Ninomiya, Hiromasa; Suzuki, Yasuo; Kameari, Akihisa

1975-03-01

The calculation method and code of solving the free boundary problem for MHD equilibrium has been developed. Usage of the code ''NIRVANA'' is described. The toroidal plasma current density determined as a function of the flux function PSI is substituted by a group of the ring currents, whereby the equation of MHD equilibrium is transformed into an integral equation. Either of the two iterative methods is chosen to solve the integral equation, depending on the assumptions made of the plasma surface points. Calculation of the magnetic field configurations is possible when the plasma surface coincides self-consistently with the magnetic flux including the separatrix points. The code is usable in calculation of the circular or non-circular shell-less Tokamak equilibrium. (auth.)

Synthesis, Spectroscopic Properties and DFT Calculation of Novel ...

Indian Academy of Sciences (India)

density functional theory (DFT) calculations. Keywords. ... time-dependent density functional theory (TD-DFT) calcu- lations. .... reaction, the pH of the solution was adjusted to 7 .... ORTEP diagram for L1 showing 30% probability ellipsoids.

Ab-initio calculations for dilute magnetic semiconductors

Energy Technology Data Exchange (ETDEWEB)

Belhadji, Brahim

2008-03-03

This thesis focusses on ab-initio calculations for the electronic structure and the magnetic properties of dilute magnetic semiconductors (DMS). In particular we aim at the understanding of the complex exchange interactions in these systems. Our calculations are based on density functional theory, being ideally suited for a description of the material specific properties of the considered DMS. Moreover we use the KKR Green function method in connection with the coherent potential approximation (CPA), which allows to include the random substitutional disorder in a mean field-like approximation for the electronic structure. Finally we calculate the exchange coupling constants J{sub ij} between two impurities in a CPA medium by using the Lichtenstein formula and from this calculate the Curie temperature by a numerically exact Monte Carlo method. Based on this analysis we found and investigated four different exchange mechanisms being of importance in DMS systems: Double exchange, p-d exchange, antiferromagnetic superexchanges, and ferromagnetic superexchange. A second topic we have investigated in this thesis is the pressure dependence of the exchange interactions and the Curie temperatures in (Ga,Mn)As and (In,Mn)As, using the LDA and the LDA+U approximations. Exact calculations of T{sub C} by Monte Carlo simulations show a somehow different behavior. (orig.)

RHEIN, Modular System for Reactor Design Calculation

International Nuclear Information System (INIS)

Reiche, Christian; Barz, Hansulrich; Kunzmann, Bernd; Seifert, Eberhard; Wand, Hartmut

1990-01-01

1 - Description of program or function: RHEIN is a modular reactor code system for neutron physics calculations. It consists of a small number of system codes for execution control, data management, and handling support, as well as of the physical calculation routines. The execution is controlled by input data containing mathematical and physical parameters and simple commands for routine calls and data manipulations. The calculation routines are in tune with one another and the system takes care of the data transfer between them. Cross-section libraries with self shielding parameters are added to the system. 2 - Method of solution: The calculation routines can be used for solving the following physics problems: - Calculation of cross-section sets for infinite mediums, taking into account chord length. - Zero-dimensional spectrum calculation in diffusion, P1, or B1 approximation. - One-dimensional calculation in diffusion, P1, or collision probability approximation. - Two-dimensional diffusion calculation. - Cell calculation by THERMOS. - Zone-wise homogenized group collapsing within zero, one, or two-dimensional models. - Normalization, summarizing, etc. - Output of cross-section sets to off systems Sn and Monte-Carlo calculations

Atom probe tomography simulations and density functional theory calculations of bonding energies in Cu3Au

KAUST Repository

Boll, Torben

2012-10-01

In this article the Cu-Au binding energy in Cu3Au is determined by comparing experimental atom probe tomography (APT) results to simulations. The resulting bonding energy is supported by density functional theory calculations. The APT simulations are based on the Müller-Schottky equation, which is modified to include different atomic neighborhoods and their characteristic bonds. The local environment is considered up to the fifth next nearest neighbors. To compare the experimental with simulated APT data, the AtomVicinity algorithm, which provides statistical information about the positions of the neighboring atoms, is applied. The quality of this information is influenced by the field evaporation behavior of the different species, which is connected to the bonding energies. © Microscopy Society of America 2012.

Electronic, Magnetic, and Transport Properties of Polyacrylonitrile-Based Carbon Nanofibers of Various Widths: Density-Functional Theory Calculations

Science.gov (United States)

Partovi-Azar, P.; Panahian Jand, S.; Kaghazchi, P.

2018-01-01

Edge termination of graphene nanoribbons is a key factor in determination of their physical and chemical properties. Here, we focus on nitrogen-terminated zigzag graphene nanoribbons resembling polyacrylonitrile-based carbon nanofibers (CNFs) which are widely studied in energy research. In particular, we investigate magnetic, electronic, and transport properties of these CNFs as functions of their widths using density-functional theory calculations together with the nonequilibrium Green's function method. We report on metallic behavior of all the CNFs considered in this study and demonstrate that the narrow CNFs show finite magnetic moments. The spin-polarized electronic states in these fibers exhibit similar spin configurations on both edges and result in spin-dependent transport channels in the narrow CNFs. We show that the partially filled nitrogen dangling-bond bands are mainly responsible for the ferromagnetic spin ordering in the narrow samples. However, the magnetic moment becomes vanishingly small in the case of wide CNFs where the dangling-bond bands fall below the Fermi level and graphenelike transport properties arising from the π orbitals are recovered. The magnetic properties of the CNFs as well as their stability have also been discussed in the presence of water molecules and the hexagonal boron nitride substrate.

Program for the calculation of the semiempirical radial wave functions by means of the variable Tomas-Fermi potential and for the determination of the radial integrals of the dipole transitions

International Nuclear Information System (INIS)

Kuzmitskite, L.L.

1980-01-01

The program is meant for the determination of the semiempirical radial wave functions of the positive ions and the calculation of the radial integrals of the dipole transition. The semiempirical wave functions are calculated using Tomas-Fermi potential with the variable parameter, which provides for the coincidence of the energy obtained with the ionization energy of the state under consideration. The program is written in the FORTRAN language for the BESM-6 computer

Assignment of near-edge x-ray absorption fine structure spectra of metalloporphyrins by means of time-dependent density-functional calculations

International Nuclear Information System (INIS)

Schmidt, Norman; Fink, Rainer; Hieringer, Wolfgang

2010-01-01

The C 1s and N 1s near-edge x-ray absorption fine structure (NEXAFS) spectra of three prototype tetraphenyl porphyrin (TPP) molecules are discussed in the framework of a combined experimental and theoretical study. We employ time-dependent density-functional theory (TDDFT) to compute the NEXAFS spectra of the open- and closed-shell metalloporphyrins CoTPP and ZnTPP as well as the free-base 2HTPP in realistic nonplanar conformations. Using Becke's well-known half-and-half hybrid functional, the computed core excitation spectra are mostly in good agreement with the experimental data in the low-energy region below the appropriate ionization threshold. To make these calculations feasible, we apply a new, simple scheme based on TDDFT using a modified single-particle input spectrum. This scheme is very easy to implement in standard codes and allows one to compute core excitation spectra at a similar cost as ordinary UV/vis spectra even for larger molecules. We employ these calculations for a detailed assignment of the NEXAFS spectra including subtle shifts in certain peaks of the N 1s spectra, which depend on the central coordination of the TPP ligand. We furthermore assign the observed NEXAFS resonances to the individual molecular subunits of the investigated TPP molecules.

Calculation of the inter-nuclei separation of HD+

International Nuclear Information System (INIS)

Zhu Zhousen; Shi Miangong; Tang Ayou; Yang Baifang; Miao Jingwei

1993-01-01

With the Ritz variational principle, the authors calculate the inter nuclei separation of the HD + molecular ion, and introduces a method to calculate the inter nuclei separations of other simple non-symmetry two-atom molecular ions. One way to work out the trial wave function is provided

New theoretical development for the calculating of physical properties of D2O

International Nuclear Information System (INIS)

Moreira, Osvaldo

2011-01-01

In this work we have developed a new method for calculating the physical properties of heavy water, D 2 O, using the Helmholtz free energy state function, A = U − T S, exclusively for this molecule. The state function has been calculated as ā = ā 0 +ā 1 (specific dimensionless values), where ā 0 is related to the properties of heavy water in gaseous state and ā 1 describes the liquid state. The canonical variables of the state function are absolute temperature and volume. To calculate the physical properties defining absolute pressure and temperature, here a variable change method was developed, based on the solution of a differential equation (function ζ) using numerical algorithms (scaling and Newton-Raphson). Physical quantities calculated are: density ϱ(specific volume υ), specific enthalpy h and entropy s. The results obtained agree completely with the values calculated by the National Institute of Standards and Technology (NIST). In this report it has also proposed an adjustment function to calculate the saturation absolute temperature of heavy water as a function of the pressure: T s (p) = exp[a·b(p)], where a is a vector of constant coefficients and b a vector function of pressure, using theoretical values and extending the wording proposed by the Oak Ridge National Laboratory. The new setting has an error less than 0.03%. (author)

Calculations on neutron irradiation damage in reactor materials

International Nuclear Information System (INIS)

Sone, Kazuho; Shiraishi, Kensuke

1976-01-01

Neutron irradiation damage calculations were made for Mo, Nb, V, Fe, Ni and Cr. Firstly, damage functions were calculated as a function of neutron energy with neutron cross sections of elastic and inelastic scatterings, and (n,2n) and (n,γ) reactions filed in ENDF/B-III. Secondly, displacement damage expressed in displacements per atom (DPA) was estimated for neutron environments such as fission spectrum, thermal neutron reactor (JMTR), fast breeder reactor (MONJU) and two fusion reactors (The Conceptual Design of Fusion Reactor in JAERI and ORNL-Benchmark). then, damage cross section in units of dpa. barn was defined as a factor to convert a given neutron fluence to the DPA value, and was calculated for the materials in the above neutron environments. Finally, production rates of helium and hydrogen atoms were calculated with (n,α) and (n,p) cross sections in ENDF/B-III for the materials irradiated in the above reactors. (auth.)

QEDMOD: Fortran program for calculating the model Lamb-shift operator

Science.gov (United States)

Shabaev, V. M.; Tupitsyn, I. I.; Yerokhin, V. A.

2018-02-01

We present Fortran package QEDMOD for computing the model QED operator hQED that can be used to account for the Lamb shift in accurate atomic-structure calculations. The package routines calculate the matrix elements of hQED with the user-specified one-electron wave functions. The operator can be used to calculate Lamb shift in many-electron atomic systems with a typical accuracy of few percent, either by evaluating the matrix element of hQED with the many-electron wave function, or by adding hQED to the Dirac-Coulomb-Breit Hamiltonian.

HgTe-CdTe phase diagrams calculation by RAS model

International Nuclear Information System (INIS)

Hady, A.A.A.

1986-11-01

The model of Regular Associated Solutions (RAS) for binary solution, which extended onto the ternary solution was used for Mercury-Cadnium-Tellurim phase diagrams calculations. The function of dissociation parameters is used here as a function of temperature and it is independent of composition. The ratio of mole fractions has a weak dependence on temperature and is not neglected. The calculated liquidus binary temperature and the experimental one are so fitted to give the best values of parameters used to calculate the HgTe-CdTe phase diagrams. (author)

Combining density functional theory calculations, supercomputing, and data-driven methods to design new materials (Conference Presentation)

Science.gov (United States)

Jain, Anubhav

2017-04-01

Density functional theory (DFT) simulations solve for the electronic structure of materials starting from the Schrödinger equation. Many case studies have now demonstrated that researchers can often use DFT to design new compounds in the computer (e.g., for batteries, catalysts, and hydrogen storage) before synthesis and characterization in the lab. In this talk, I will focus on how DFT calculations can be executed on large supercomputing resources in order to generate very large data sets on new materials for functional applications. First, I will briefly describe the Materials Project, an effort at LBNL that has virtually characterized over 60,000 materials using DFT and has shared the results with over 17,000 registered users. Next, I will talk about how such data can help discover new materials, describing how preliminary computational screening led to the identification and confirmation of a new family of bulk AMX2 thermoelectric compounds with measured zT reaching 0.8. I will outline future plans for how such data-driven methods can be used to better understand the factors that control thermoelectric behavior, e.g., for the rational design of electronic band structures, in ways that are different from conventional approaches.

CALCULATIONS OF DOUBLE IMPURITY DIFFUSION IN INTEGRATED CIRCUIT PRODUCTION

Directory of Open Access Journals (Sweden)

V. A. Bondarev

2005-01-01

Full Text Available Analytical formulae for calculating simultaneous diffusion of two impurities in silicon are presented. The formulae are based on analytical solutions of diffusion equations that have been obtained for the first time by the author while using some special mathematical functions. In contrast to usual formal mathematical approaches, new functions are determined in the process of investigation of real physical models. Algorithms involve some important relations from thermodynamics of irreversible processes and also variational thermodynamic functionals that were previously obtained by the author for transfer processes. Calculations considerably reduce the time required for development of new integrated circuits. 

Hydrogen adsorption and storage on Palladium – functionalized graphene with NH-dopant: A first principles calculation

Energy Technology Data Exchange (ETDEWEB)

Faye, Omar, E-mail: omf071@mail.usask.ca [Department of Mechanical Engineering, College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, S7N 5A9 Saskatchewan (Canada); Department of Condensed Matter Physics, Cheikh Anta Diop University, Dakar (Senegal); Szpunar, Jerzy A; Szpunar, Barbara [Department of Mechanical Engineering, College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, S7N 5A9 Saskatchewan (Canada); Beye, Aboubaker Chedikh [Department of Condensed Matter Physics, Cheikh Anta Diop University, Dakar (Senegal)

2017-01-15

Highlights: • H{sub 2} adsorption in single and double-sided Pd-G(3x3) and the effect of NH radical on graphene were studied. • Strong interaction of Pd and graphene in double-sided Pd-G(3x3) than that in the single-sided Pd-G(3x3). • The storage capacity was 3.622 wt% with a binding energy of 0.658 eV/H2. • The increase of NH radicals on Pd-G(3x3) enhanced the binding of Pd atoms on the graphene sheet. • We predicted that 2NH-dopant at the opposite site of Pd atoms prevents the desorption of Pd atom from graphene sheet. - Abstract: We conducted a detailed theoretical investigation of the structural and electronic properties of single and double sided Pd-functionalized graphene and NH-doped Pd-functionalized graphene, which are shown to be efficient materials for hydrogen storage. Nitrene radical dopant was an effective addition required for enhancing the Pd binding on the graphene sheet as well as the storage of hydrogen. We found that up to eight H{sub 2} molecules could be adsorbed by double-sided Pd-functionalized graphene at 0 K with an average binding energy in the range 1.315–0.567 eVA gravimetric hydrogen density of 3.622 wt% was reached in the Pd-functionalized graphene on both sides. The binding mechanism of H{sub 2} molecules came not only the polarization mechanism between Pd and H atoms but also from the binding of the Pd atoms on the graphene sheet and the orbital hybridization. The most crucial part of our work is measuring the effect of nitrene radical on the H{sub 2} adsorption on Pd-functionalized graphene. Our calculations predicted that the addition of NH radicals on Pd-functionalized graphene enhance the binding of H{sub 2} molecules, which helps also to avoid the desorption of Pd(H{sub 2}){sub n} (n = 1–5) complexes from graphene sheet. Our results also predict Pd-functionalized NH-doped graphene is a potential hydrogen storage medium for on-board applications.

Hydrogen adsorption and storage on Palladium – functionalized graphene with NH-dopant: A first principles calculation

International Nuclear Information System (INIS)

Faye, Omar; Szpunar, Jerzy A; Szpunar, Barbara; Beye, Aboubaker Chedikh

2017-01-01

Highlights: • H_2 adsorption in single and double-sided Pd-G(3x3) and the effect of NH radical on graphene were studied. • Strong interaction of Pd and graphene in double-sided Pd-G(3x3) than that in the single-sided Pd-G(3x3). • The storage capacity was 3.622 wt% with a binding energy of 0.658 eV/H2. • The increase of NH radicals on Pd-G(3x3) enhanced the binding of Pd atoms on the graphene sheet. • We predicted that 2NH-dopant at the opposite site of Pd atoms prevents the desorption of Pd atom from graphene sheet. - Abstract: We conducted a detailed theoretical investigation of the structural and electronic properties of single and double sided Pd-functionalized graphene and NH-doped Pd-functionalized graphene, which are shown to be efficient materials for hydrogen storage. Nitrene radical dopant was an effective addition required for enhancing the Pd binding on the graphene sheet as well as the storage of hydrogen. We found that up to eight H_2 molecules could be adsorbed by double-sided Pd-functionalized graphene at 0 K with an average binding energy in the range 1.315–0.567 eVA gravimetric hydrogen density of 3.622 wt% was reached in the Pd-functionalized graphene on both sides. The binding mechanism of H_2 molecules came not only the polarization mechanism between Pd and H atoms but also from the binding of the Pd atoms on the graphene sheet and the orbital hybridization. The most crucial part of our work is measuring the effect of nitrene radical on the H_2 adsorption on Pd-functionalized graphene. Our calculations predicted that the addition of NH radicals on Pd-functionalized graphene enhance the binding of H_2 molecules, which helps also to avoid the desorption of Pd(H_2)_n (n = 1–5) complexes from graphene sheet. Our results also predict Pd-functionalized NH-doped graphene is a potential hydrogen storage medium for on-board applications.

Development of Monte Carlo decay gamma-ray transport calculation system

Energy Technology Data Exchange (ETDEWEB)

Sato, Satoshi [Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment; Kawasaki, Nobuo [Fujitsu Ltd., Tokyo (Japan); Kume, Etsuo [Japan Atomic Energy Research Inst., Center for Promotion of Computational Science and Engineering, Tokai, Ibaraki (Japan)

2001-06-01

In the DT fusion reactor, it is critical concern to evaluate the decay gamma-ray biological dose rates after the reactor shutdown exactly. In order to evaluate the decay gamma-ray biological dose rates exactly, three dimensional Monte Carlo decay gamma-ray transport calculation system have been developed by connecting the three dimensional Monte Carlo particle transport calculation code and the induced activity calculation code. The developed calculation system consists of the following four functions. (1) The operational neutron flux distribution is calculated by the three dimensional Monte Carlo particle transport calculation code. (2) The induced activities are calculated by the induced activity calculation code. (3) The decay gamma-ray source distribution is obtained from the induced activities. (4) The decay gamma-rays are generated by using the decay gamma-ray source distribution, and the decay gamma-ray transport calculation is conducted by the three dimensional Monte Carlo particle transport calculation code. In order to reduce the calculation time drastically, a biasing system for the decay gamma-ray source distribution has been developed, and the function is also included in the present system. In this paper, the outline and the detail of the system, and the execution example are reported. The evaluation for the effect of the biasing system is also reported. (author)

Hybrid functional calculations of potential hydrogen storage material: Complex dimagnesium iron hydride

KAUST Repository

Ul Haq, Bakhtiar

2014-06-01

By employing the state of art first principles approaches, comprehensive investigations of a very promising hydrogen storage material, Mg 2FeH6 hydride, is presented. To expose its hydrogen storage capabilities, detailed structural, elastic, electronic, optical and dielectric aspects have been deeply analysed. The electronic band structure calculations demonstrate that Mg2FeH6 is semiconducting material. The obtained results of the optical bandgap (4.19 eV) also indicate that it is a transparent material for ultraviolet light, thus demonstrating its potential for optoelectronics application. The calculated elastic properties reveal that Mg2FeH6 is highly stiff and stable hydride. Finally, the calculated hydrogen (H2) storage capacity (5.47 wt.%) within a reasonable formation energy of -78 kJ mol-1, at room temperature, can be easily achievable, thus making Mg2FeH6 as potential material for practical H2 storage applications. Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Calculation of the counting efficiency for extended sources

International Nuclear Information System (INIS)

Korun, M.; Vidmar, T.

2002-01-01

A computer program for calculation of efficiency calibration curves for extended samples counted on gamma- and X ray spectrometers is described. The program calculates efficiency calibration curves for homogeneous cylindrical samples placed coaxially with the symmetry axis of the detector. The method of calculation is based on integration over the sample volume of the efficiencies for point sources measured in free space on an equidistant grid of points. The attenuation of photons within the sample is taken into account using the self-attenuation function calculated with a two-dimensional detector model. (author)

Oxygen self-diffusion mechanisms in monoclinic Zr O2 revealed and quantified by density functional theory, random walk analysis, and kinetic Monte Carlo calculations

Science.gov (United States)

Yang, Jing; Youssef, Mostafa; Yildiz, Bilge

2018-01-01

In this work, we quantify oxygen self-diffusion in monoclinic-phase zirconium oxide as a function of temperature and oxygen partial pressure. A migration barrier of each type of oxygen defect was obtained by first-principles calculations. Random walk theory was used to quantify the diffusivities of oxygen interstitials by using the calculated migration barriers. Kinetic Monte Carlo simulations were used to calculate diffusivities of oxygen vacancies by distinguishing the threefold- and fourfold-coordinated lattice oxygen. By combining the equilibrium defect concentrations obtained in our previous work together with the herein calculated diffusivity of each defect species, we present the resulting oxygen self-diffusion coefficients and the corresponding atomistically resolved transport mechanisms. The predicted effective migration barriers and diffusion prefactors are in reasonable agreement with the experimentally reported values. This work provides insights into oxygen diffusion engineering in Zr O2 -related devices and parametrization for continuum transport modeling.

A Mathematical Method to Calculate Tumor Contact Surface Area: An Effective Parameter to Predict Renal Function after Partial Nephrectomy.

Science.gov (United States)

Hsieh, Po-Fan; Wang, Yu-De; Huang, Chi-Ping; Wu, Hsi-Chin; Yang, Che-Rei; Chen, Guang-Heng; Chang, Chao-Hsiang

2016-07-01

We proposed a mathematical formula to calculate contact surface area between a tumor and renal parenchyma. We examined the applicability of using contact surface area to predict renal function after partial nephrectomy. We performed this retrospective study in patients who underwent partial nephrectomy between January 2012 and December 2014. Based on abdominopelvic computerized tomography or magnetic resonance imaging, we calculated the contact surface area using the formula (2*π*radius*depth) developed by integral calculus. We then evaluated the correlation between contact surface area and perioperative parameters, and compared contact surface area and R.E.N.A.L. (Radius/Exophytic/endophytic/Nearness to collecting system/Anterior/Location) score in predicting a reduction in renal function. Overall 35, 26 and 45 patients underwent partial nephrectomy with open, laparoscopic and robotic approaches, respectively. Mean ± SD contact surface area was 30.7±26.1 cm(2) and median (IQR) R.E.N.A.L. score was 7 (2.25). Spearman correlation analysis showed that contact surface area was significantly associated with estimated blood loss (p=0.04), operative time (p=0.04) and percent change in estimated glomerular filtration rate (p contact surface area and R.E.N.A.L. score independently affected percent change in estimated glomerular filtration rate (p contact surface area was a better independent predictor of a greater than 10% change in estimated glomerular filtration rate compared to R.E.N.A.L. score (AUC 0.86 vs 0.69). Using this simple mathematical method, contact surface area was associated with surgical outcomes. Compared to R.E.N.A.L. score, contact surface area was a better predictor of functional change after partial nephrectomy. Copyright © 2016 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

Insertion device calculations with mathematica

Energy Technology Data Exchange (ETDEWEB)

Carr, R. [Stanford Synchrotron Radiation Lab., CA (United States); Lidia, S. [Univ. of California, Davis, CA (United States)

1995-02-01

The design of accelerator insertion devices such as wigglers and undulators has usually been aided by numerical modeling on digital computers, using code in high level languages like Fortran. In the present era, there are higher level programming environments like IDL{reg_sign}, MatLab{reg_sign}, and Mathematica{reg_sign} in which these calculations may be performed by writing much less code, and in which standard mathematical techniques are very easily used. The authors present a suite of standard insertion device modeling routines in Mathematica to illustrate the new techniques. These routines include a simple way to generate magnetic fields using blocks of CSEM materials, trajectory solutions from the Lorentz force equations for given magnetic fields, Bessel function calculations of radiation for wigglers and undulators and general radiation calculations for undulators.

Unconventional application of the two-flux approximation for the calculation of the Ambartsumyan-Chandrasekhar function and the angular spectrum of the backward-scattered radiation for a semi-infinite isotropically scattering medium

Science.gov (United States)

Remizovich, V. S.

2010-06-01

It is commonly accepted that the Schwarzschild-Schuster two-flux approximation (1905, 1914) can be employed only for the calculation of the energy characteristics of the radiation field (energy density and energy flux density) and cannot be used to characterize the angular distribution of radiation field. However, such an inference is not valid. In several cases, one can calculate the radiation intensity inside matter and the reflected radiation with the aid of this simplest approximation in the transport theory. In this work, we use the results of the simplest one-parameter variant of the two-flux approximation to calculate the angular distribution (reflection function) of the radiation reflected by a semi-infinite isotropically scattering dissipative medium when a relatively broad beam is incident on the medium at an arbitrary angle relative to the surface. We do not employ the invariance principle and demonstrate that the reflection function exhibits the multiplicative property. It can be represented as a product of three functions: the reflection function corresponding to the single scattering and two identical h functions, which have the same physical meaning as the Ambartsumyan-Chandrasekhar function ( H) has. This circumstance allows a relatively easy derivation of simple analytical expressions for the H function, total reflectance, and reflection function. We can easily determine the relative contribution of the true single scattering in the photon backscattering at an arbitrary probability of photon survival Λ. We compare all of the parameters of the backscattered radiation with the data resulting from the calculations using the exact theory of Ambartsumyan, Chandrasekhar, et al., which was developed decades after the two-flux approximation. Thus, we avoid the application of fine mathematical methods (the Wiener-Hopf method, the Case method of singular functions, etc.) and obtain simple analytical expressions for the parameters of the scattered radiation

Effects of B site doping on electronic structures of InNbO4 based on hybrid density functional calculations

Science.gov (United States)

Lu, M. F.; Zhou, C. P.; Li, Q. Q.; Zhang, C. L.; Shi, H. F.

2018-01-01

In order to improve the photocatalytic activity under visible-light irradiation, we adopted first principle calculations based on density functional theory (DFT) to calculate the electronic structures of B site transition metal element doped InNbO4. The results indicated that the complete hybridization of Nb 4d states and some Ti 3d states contributed to the new conduction band of Ti doped InNbO4, barely changing the position of band edge. For Cr doping, some localized Cr 3d states were introduced into the band gap. Nonetheless, the potential of localized levels was too positive to cause visible-light reaction. When it came to Cu doping, the band gap was almost same with that of InNbO4 as well as some localized Cu 3d states appeared above the top of VB. The introduction of localized energy levels benefited electrons to migrate from valence band (VB) to conduction band (CB) by absorbing lower energy photons, realizing visible-light response.

Computational Modeling and Theoretical Calculations on the Interactions between Spermidine and Functional Monomer (Methacrylic Acid in a Molecularly Imprinted Polymer

Directory of Open Access Journals (Sweden)

Yujie Huang

2015-01-01

Full Text Available This paper theoretically investigates interactions between a template and functional monomer required for synthesizing an efficient molecularly imprinted polymer (MIP. We employed density functional theory (DFT to compute geometry, single-point energy, and binding energy (ΔE of an MIP system, where spermidine (SPD and methacrylic acid (MAA were selected as template and functional monomer, respectively. The geometry was calculated by using B3LYP method with 6-31+(d basis set. Furthermore, 6-311++(d, p basis set was used to compute the single-point energy of the above geometry. The optimized geometries at different template to functional monomer molar ratios, mode of bonding between template and functional monomer, changes in charge on natural bond orbital (NBO, and binding energy were analyzed. The simulation results show that SPD and MAA form a stable complex via hydrogen bonding. At 1 : 5 SPD to MAA ratio, the binding energy is minimum, while the amount of transferred charge between the molecules is maximum; SPD and MAA form a stable complex at 1 : 5 molar ratio through six hydrogen bonds. Optimizing structure of template-functional monomer complex, through computational modeling prior synthesis, significantly contributes towards choosing a suitable pair of template-functional monomer that yields an efficient MIP with high specificity and selectivity.

Calculation of quantum-mechanical system energy spectra using path integrals

International Nuclear Information System (INIS)

Evseev, A.M.; Dmitriev, V.P.

1977-01-01

A solution of the Feynman quantum-mechanical integral connecting a wave function (psi (x, t)) at a moment t+tau (tau → 0) with the wave function at the moment t is provided by complex variable substitution and subsequent path integration. Time dependence of the wave function is calculated by the Monte Carlo method. The Fourier inverse transformation of the wave function by path integration calculated has been applied to determine the energy spectra. Energy spectra are presented of a hydrogen atom derived from wave function psi (x, t) at different x, as well as boson energy spectra of He, Li, and Be atoms obtained from psi (x, t) at X = O

Geometrical correction for the inter- and intramolecular basis set superposition error in periodic density functional theory calculations.

Science.gov (United States)

Brandenburg, Jan Gerit; Alessio, Maristella; Civalleri, Bartolomeo; Peintinger, Michael F; Bredow, Thomas; Grimme, Stefan

2013-09-26

We extend the previously developed geometrical correction for the inter- and intramolecular basis set superposition error (gCP) to periodic density functional theory (DFT) calculations. We report gCP results compared to those from the standard Boys-Bernardi counterpoise correction scheme and large basis set calculations. The applicability of the method to molecular crystals as the main target is tested for the benchmark set X23. It consists of 23 noncovalently bound crystals as introduced by Johnson et al. (J. Chem. Phys. 2012, 137, 054103) and refined by Tkatchenko et al. (J. Chem. Phys. 2013, 139, 024705). In order to accurately describe long-range electron correlation effects, we use the standard atom-pairwise dispersion correction scheme DFT-D3. We show that a combination of DFT energies with small atom-centered basis sets, the D3 dispersion correction, and the gCP correction can accurately describe van der Waals and hydrogen-bonded crystals. Mean absolute deviations of the X23 sublimation energies can be reduced by more than 70% and 80% for the standard functionals PBE and B3LYP, respectively, to small residual mean absolute deviations of about 2 kcal/mol (corresponding to 13% of the average sublimation energy). As a further test, we compute the interlayer interaction of graphite for varying distances and obtain a good equilibrium distance and interaction energy of 6.75 Å and -43.0 meV/atom at the PBE-D3-gCP/SVP level. We fit the gCP scheme for a recently developed pob-TZVP solid-state basis set and obtain reasonable results for the X23 benchmark set and the potential energy curve for water adsorption on a nickel (110) surface.

Relativistic Band Calculation and the Optical Properties of Gold

DEFF Research Database (Denmark)

Christensen, N Egede; Seraphin, B. O.

1971-01-01

of magnitude as the gaps (approximately 1 eV). Various integrated functions, density of states, joint density of states, and energy distributions of joint density of states are derived from the RAPW calculation. These functions are used in an interpretation of photoemission and static reflectance measurements......The energy band structure of gold is calculated by the relativistic augmented-plane-wave (RAPW) method. A nonrelativistic calculation is also presented, and a comparison between this and the RAPW results demonstrates that the shifts and splittings due to relativistic effects are of the same order...... to trace out the regions in k→ space where the edge and tail transitions occur. It is demonstrated that structure in the static reflection curves are not related to critical points in the band structure. The arguments are supported by calculations of temperature shifts of the critical-point energies...

Molecular structures and vibrational frequencies of xanthine and its methyl derivatives (caffeine and theobromine) by ab initio Hartree-Fock and density functional theory calculations

Science.gov (United States)

Ucun, Fatih; Sağlam, Adnan; Güçlü, Vesile

2007-06-01

The molecular structures, vibrational frequencies and corresponding vibrational assignments of xanthine and its methyl derivatives (caffeine and theobromine) have been calculated using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods with 6-31G(d, p) basis set level. The calculations were utilized to the CS symmetries of the molecules. The obtained vibrational frequencies and optimised geometric parameters (bond lengths and bond angles) were seen to be well agreement with the experimental data. The used scale factors which have been obtained the ratio of the frequency values of the strongest peaks in the calculated and experimental spectra seem to cause the gained vibrations well corresponding to the experimental ones. Theoretical infrared intensities and Raman activities are also reported.

Mixed-linker UiO-66: structure-property relationships revealed by a combination of high-resolution powder X-ray diffraction and density functional theory calculations.

Science.gov (United States)

Taddei, Marco; Tiana, Davide; Casati, Nicola; van Bokhoven, Jeroen A; Smit, Berend; Ranocchiari, Marco

2017-01-04

The use of mixed-linker metal-organic frameworks (MIXMOFs) is one of the most effective strategies to modulate the physical-chemical properties of MOFs without affecting the overall crystal structure. In many instances, MIXMOFs have been recognized as solid solutions, with random distribution of ligands, in agreement with the empirical rule known as Vegard's law. In this work, we have undertaken a study combining high-resolution powder X-ray diffraction (HR-PXRD) and density functional theory (DFT) calculations with the aim of understanding the reasons why UiO-66-based amino- and bromo-functionalized MIXMOFs (MIXUiO-66) undergo cell expansion obeying Vegard's law and how this behaviour is related to their physical-chemical properties. DFT calculations predict that the unit cell in amino-functionalized UiO-66 experiences only minor expansion as a result of steric effects, whereas major modification to the electronic features of the framework leads to weaker metal-linker interaction and consequently to the loss of stability at higher degrees of functionalization. For bromo-functionalized UiO-66, steric repulsion due to the size of bromine yields a large cell expansion, but the electronic features remain very similar to pristine UiO-66, preserving the stability of the framework upon functionalization. MIXUiO-66 obtained by either direct synthesis or by post-synthetic exchange shows Vegard-like behaviour, suggesting that both preparation methods yield solid solutions, but the thermal stability and the textural properties of the post-synthetic exchanged materials do not display a clear dependence on the chemical composition, as observed for the MOFs obtained by direct synthesis.

Calculations of optical rotation: Influence of molecular structure

Directory of Open Access Journals (Sweden)

Yu Jia

2012-01-01

Full Text Available Ab initio Hartree-Fock (HF method and Density Functional Theory (DFT were used to calculate the optical rotation of 26 chiral compounds. The effects of theory and basis sets used for calculation, solvents influence on the geometry and values of calculated optical rotation were all discussed. The polarizable continuum model, included in the calculation, did not improve the accuracy effectively, but it was superior to γs. Optical rotation of five or sixmembered of cyclic compound has been calculated and 17 pyrrolidine or piperidine derivatives which were calculated by HF and DFT methods gave acceptable predictions. The nitrogen atom affects the calculation results dramatically, and it is necessary in the molecular structure in order to get an accurate computation result. Namely, when the nitrogen atom was substituted by oxygen atom in the ring, the calculation result deteriorated.

Dispersion relations in loop calculations

International Nuclear Information System (INIS)

Kniehl, B.A.

1996-01-01

These lecture notes give a pedagogical introduction to the use of dispersion relations in loop calculations. We first derive dispersion relations which allow us to recover the real part of a physical amplitude from the knowledge of its absorptive part along the branch cut. In perturbative calculations, the latter may be constructed by means of Cutkosky's rule, which is briefly discussed. For illustration, we apply this procedure at one loop to the photon vacuum-polarization function induced by leptons as well as to the γf anti-f vertex form factor generated by the exchange of a massive vector boson between the two fermion legs. We also show how the hadronic contribution to the photon vacuum polarization may be extracted from the total cross section of hadron production in e + e - annihilation measured as a function of energy. Finally, we outline the application of dispersive techniques at the two-loop level, considering as an example the bosonic decay width of a high-mass Higgs boson. (author)

Diffusion quantum Monte Carlo and density functional calculations of the structural stability of bilayer arsenene

Science.gov (United States)

Kadioglu, Yelda; Santana, Juan A.; Özaydin, H. Duygu; Ersan, Fatih; Aktürk, O. Üzengi; Aktürk, Ethem; Reboredo, Fernando A.

2018-06-01

We have studied the structural stability of monolayer and bilayer arsenene (As) in the buckled (b) and washboard (w) phases with diffusion quantum Monte Carlo (DMC) and density functional theory (DFT) calculations. DMC yields cohesive energies of 2.826(2) eV/atom for monolayer b-As and 2.792(3) eV/atom for w-As. In the case of bilayer As, DMC and DFT predict that AA-stacking is the more stable form of b-As, while AB is the most stable form of w-As. The DMC layer-layer binding energies for b-As-AA and w-As-AB are 30(1) and 53(1) meV/atom, respectively. The interlayer separations were estimated with DMC at 3.521(1) Å for b-As-AA and 3.145(1) Å for w-As-AB. A comparison of DMC and DFT results shows that the van der Waals density functional method yields energetic properties of arsenene close to DMC, while the DFT + D3 method closely reproduced the geometric properties from DMC. The electronic properties of monolayer and bilayer arsenene were explored with various DFT methods. The bandgap values vary significantly with the DFT method, but the results are generally qualitatively consistent. We expect the present work to be useful for future experiments attempting to prepare multilayer arsenene and for further development of DFT methods for weakly bonded systems.

Cross Talk Analysis on Multiple Coupled Transmission Lines; (The calculation of transfer functions on multiple coupled tansmission lines in an inhomogeneous dielectric medium)

DEFF Research Database (Denmark)

Dalby, Arne Brejning

1994-01-01

A flow graph relating voltages and the forward and reflected propagation modes (¿ TEM) on multiple coupled transmission lines in an inhomogeneous dielectric medium is presented. This flow graph directy gives the different transfer functions, including S-parameters, in matrix form needed to calcul......A flow graph relating voltages and the forward and reflected propagation modes (¿ TEM) on multiple coupled transmission lines in an inhomogeneous dielectric medium is presented. This flow graph directy gives the different transfer functions, including S-parameters, in matrix form needed...

Unit cell structure of the wurtzite phase of GaP nanowires : X-ray diffraction studies and density functional theory calculations

OpenAIRE

Kriegner, D.; Assali, S.; Belabbes, A.; Etzelstorfer, T.; Holy, V.; Schülli, T.U.; Bechstedt, F.; Bakkers, E.P.A.M.; Bauer, G.; Stangl, J.

2013-01-01

We present structural characterization of the wurtzite crystal structure of GaP nanowires, which were recently shown to have a direct electronic band gap. The structural parameters of the wurtzite phase do consist of two lattice parameters and one internal degree of freedom, determining the Ga-P bond length along the c direction. Using density functional theory calculations, we study the influence of the internal degree of freedom on the band structure. By synchrotron x-ray diffraction studie...

Parallel computational in nuclear group constant calculation

International Nuclear Information System (INIS)

Su'ud, Zaki; Rustandi, Yaddi K.; Kurniadi, Rizal

2002-01-01

In this paper parallel computational method in nuclear group constant calculation using collision probability method will be discuss. The main focus is on the calculation of collision matrix which need large amount of computational time. The geometry treated here is concentric cylinder. The calculation of collision probability matrix is carried out using semi analytic method using Beckley Naylor Function. To accelerate computation speed some computer parallel used to solve the problem. We used LINUX based parallelization using PVM software with C or fortran language. While in windows based we used socket programming using DELPHI or C builder. The calculation results shows the important of optimal weight for each processor in case there area many type of processor speed

Composite space charge density functions for the calculation of gamma sensitivity of self-powered neutron detectors, using Warren's model

Science.gov (United States)

Mahant, A. K.; Rao, P. S.; Misra, S. C.

1994-07-01

In the calculational model developed by Warren and Shah for the computation of the gamma sensitivity ( Sγ) it has been observed that the computed Sγ value is quite sensitive to the space charge distribution function assumed for the insulator region and the energy of the gamma photons. The Sγ of SPNDs with Pt, Co and V emitters (manufactured by Thermocoax, France) has been measured at 60Co photon energy and a good correlation between the measured and computed values has been obtained using a composite space charge density function (CSCD), the details of which are presented in this paper. The arguments are extended for evaluating the Sγ values of several SPNDs for which Warren and Shah reported the measured values for a prompt fission gamma spectrum obtained in a swimming pool reactor. These results are also discussed.

Harris functional and related methods for calculating total energies in density-functional theory

International Nuclear Information System (INIS)

Averill, F.W.; Painter, G.S.

1990-01-01

The simplified energy functional of Harris has given results of useful accuracy for systems well outside the limits of weakly interacting fragments for which the method was originally proposed. In the present study, we discuss the source of the frequent good agreement of the Harris energy with full Kohn-Sham self-consistent results. A procedure is described for extending the applicability of the scheme to more strongly interacting systems by going beyond the frozen-atom fragment approximation. A gradient-force expression is derived, based on the Harris functional, which accounts for errors in the fragment charge representation. Results are presented for some diatomic molecules, illustrating the points of this study

Three-dimensional space-charge calculation method

International Nuclear Information System (INIS)

Lysenko, W.P.; Wadlinger, E.A.

1980-09-01

A method is presented for calculating space-charge forces on individual particles in a particle tracing simulation code. Poisson's equation is solved in three dimensions with boundary conditions specified on an arbitrary surface. When the boundary condition is defined by an impressed radio-frequency field, the external electric fields as well as the space-charge fields are determined. A least squares fitting procedure is used to calculate the coefficients of expansion functions, which need not be orthogonal nor individually satisfy the boundary condition

Validation of Calculations in a Digital Thermometer Firmware

Science.gov (United States)

Batagelj, V.; Miklavec, A.; Bojkovski, J.

2014-04-01

State-of-the-art digital thermometers are arguably remarkable measurement instruments, measuring outputs from resistance thermometers and/or thermocouples. Not only that they can readily achieve measuring accuracies in the parts-per-million range, but they also incorporate sophisticated algorithms for the transformation calculation of the measured resistance or voltage to temperature. These algorithms often include high-order polynomials, exponentials and logarithms, and must be performed using both standard coefficients and particular calibration coefficients. The numerical accuracy of these calculations and the associated uncertainty component must be much better than the accuracy of the raw measurement in order to be negligible in the total measurement uncertainty. In order for the end-user to gain confidence in these calculations as well as to conform to formal requirements of ISO/IEC 17025 and other standards, a way of validation of these numerical procedures performed in the firmware of the instrument is required. A software architecture which allows a simple validation of internal measuring instrument calculations is suggested. The digital thermometer should be able to expose all its internal calculation functions to the communication interface, so the end-user can compare the results of the internal measuring instrument calculation with reference results. The method can be regarded as a variation of the black-box software validation. Validation results on a thermometer prototype with implemented validation ability show that the calculation error of basic arithmetic operations is within the expected rounding error. For conversion functions, the calculation error is at least ten times smaller than the thermometer effective resolution for the particular probe type.

CTMC calculation of Si2+ + H impact ionization

International Nuclear Information System (INIS)

Liu Chunlei; He Bin; Ning Ye; Yan Jun; Wang Jianguo

2005-01-01

The Si 2+ + H collision ionization is studied using classical trajectory Monte-Carlo (CTMC) method. The total cross section as functions of the energy of incident projectile, single differential cross section and double differential cross section as a functions of the energy and the angle of the ejected electron are calculated. The ionization mechanisms of soft collision, electron capture to the continuum state, binary encounter collision are demonstrated. The effect of 'saddle point' is also discussed by calculating the ejected electron distribution depending on the ratios of distances between electron and target and between electron and projectile. (author)

Variational Variance Reduction for Monte Carlo Criticality Calculations

International Nuclear Information System (INIS)

Densmore, Jeffery D.; Larsen, Edward W.

2001-01-01

A new variational variance reduction (VVR) method for Monte Carlo criticality calculations was developed. This method employs (a) a variational functional that is more accurate than the standard direct functional, (b) a representation of the deterministically obtained adjoint flux that is especially accurate for optically thick problems with high scattering ratios, and (c) estimates of the forward flux obtained by Monte Carlo. The VVR method requires no nonanalog Monte Carlo biasing, but it may be used in conjunction with Monte Carlo biasing schemes. Some results are presented from a class of criticality calculations involving alternating arrays of fuel and moderator regions

The number processing and calculation system: evidence from cognitive neuropsychology.

Science.gov (United States)

Salguero-Alcañiz, M P; Alameda-Bailén, J R

2015-04-01

Cognitive neuropsychology focuses on the concepts of dissociation and double dissociation. The performance of number processing and calculation tasks by patients with acquired brain injury can be used to characterise the way in which the healthy cognitive system manipulates number symbols and quantities. The objective of this study is to determine the components of the numerical processing and calculation system. Participants consisted of 6 patients with acquired brain injuries in different cerebral localisations. We used Batería de evaluación del procesamiento numérico y el cálculo, a battery assessing number processing and calculation. Data was analysed using the difference in proportions test. Quantitative numerical knowledge is independent from number transcoding, qualitative numerical knowledge, and calculation. Recodification is independent from qualitative numerical knowledge and calculation. Quantitative numerical knowledge and calculation are also independent functions. The number processing and calculation system comprises at least 4 components that operate independently: quantitative numerical knowledge, number transcoding, qualitative numerical knowledge, and calculation. Therefore, each one may be damaged selectively without affecting the functioning of another. According to the main models of number processing and calculation, each component has different characteristics and cerebral localisations. Copyright © 2013 Sociedad Española de Neurología. Published by Elsevier Espana. All rights reserved.

Course on hybrid calculation

International Nuclear Information System (INIS)

Weill, J.; Tellier; Bonnemay; Craigne; Chareton; Di Falco

1969-02-01

After a definition of hybrid calculation (combination of analogue and digital calculation) with a distinction between series and parallel hybrid computing, and a description of a hybrid computer structure and of task sharing between computers, this course proposes a description of hybrid hardware used in Saclay and Cadarache computing centres, and of operations performed by these systems. The next part addresses issues related to programming languages and software. The fourth part describes how a problem is organised for its processing on these computers. Methods of hybrid analysis are then addressed: resolution of optimisation problems, of partial differential equations, and of integral equations by means of different methods (gradient, maximum principle, characteristics, functional approximation, time slicing, Monte Carlo, Neumann iteration, Fischer iteration)

Density Functional Theory Calculations Revealing Metal-like Band Structures for Ultrathin Ge {111} and {211} Surface Layers.

Science.gov (United States)

Tan, Chih-Shan; Huang, Michael Hsuan-Yi

2018-05-21

To find out if germanium should also possess facet-dependent electrical conductivity properties, surface state density functional theory (DFT) calculations were performed on 1-6 layers of Ge (100), (110), (111), and (211) planes. Tunable Ge (100) and (110) planes always present the same semiconducting band structure with a band gap of 0.67 eV expected of bulk germanium. In contrast, 1, 2, 4, and 5 layers of Ge (111) and (211) plane models show metal-like band structures with continuous density of states (DOS) throughout the entire band. For 3 and 6 layers of Ge (111) and (211) plane models, the normal semiconducting band structure was obtained. The plane layers with metal-like band structures also show Ge-Ge bond length deviations and bond distortions, as well as significantly different 4s and 4p frontier orbital electron count and their relative percentages integrated over the valence and conduction bands from those of the semiconducting state. These differences should contribute to strikingly dissimilar band structures. The calculation results suggest observation of facet-dependent electrical conductivity properties of germanium materials, and transistors made of germanium may also need to consider the facet effects with shrinking dimensions approaching 3 nm. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Quantum mechanical calculations to chemical accuracy

Science.gov (United States)

Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

1991-01-01

The accuracy of current molecular-structure calculations is illustrated with examples of quantum mechanical solutions for chemical problems. Two approaches are considered: (1) the coupled-cluster singles and doubles (CCSD) with a perturbational estimate of the contribution of connected triple excitations, or CCDS(T); and (2) the multireference configuration-interaction (MRCI) approach to the correlation problem. The MRCI approach gains greater applicability by means of size-extensive modifications such as the averaged-coupled pair functional approach. The examples of solutions to chemical problems include those for C-H bond energies, the vibrational frequencies of O3, identifying the ground state of Al2 and Si2, and the Lewis-Rayleigh afterglow and the Hermann IR system of N2. Accurate molecular-wave functions can be derived from a combination of basis-set saturation studies and full configuration-interaction calculations.

Low-energy calculations for nuclear photodisintegration

Directory of Open Access Journals (Sweden)

Deflorian S.

2016-01-01

Full Text Available In the Standard Solar Model a central role in the nucleosynthesis is played by reactions of the kind XZ1A11+XZ2A22→YZ1+Z2A1+A2+γ${}_{{Z_1}}^{{A_1}}{X_1} + {}_{{Z_2}}^{{A_2}}{X_2} \\to {}_{{Z_1} + {Z_2}}^{{A_1} + {A_2}}Y + \\gamma $, which enter the proton-proton chains. These reactions can also be studied through the inverse photodisintegration reaction. One option is to use the Lorentz Integral Transform approach, which transforms the continuum problem into a bound state-like one. A way to check the reliability of such methods is a direct calculation, for example using the Kohn Variational Principle to obtain the scattering wave function and then directly calculate the response function of the reaction.

Unambiguity of renormalization group calculations in QCD

International Nuclear Information System (INIS)

Vladimirov, A.A.

1979-01-01

A detailed analysis of the reduction of ambiguities determined by an arbitrary renormalization scheme is presented for the renormalization group calculations of physical quantities in quantum chromodynamics (QCD). Some basic formulas concerning the renormalization-scheme dependence of Green's and renormalization group functions are given. A massless asymptotically free theory with one coupling constant g is considered. In conclusion, several rules for renormalization group calculations in QCD are formulated

Ti-84 Plus graphing calculator for dummies

CERN Document Server

McCalla

2013-01-01

Get up-to-speed on the functionality of your TI-84 Plus calculator Completely revised to cover the latest updates to the TI-84 Plus calculators, this bestselling guide will help you become the most savvy TI-84 Plus user in the classroom! Exploring the standard device, the updated device with USB plug and upgraded memory (the TI-84 Plus Silver Edition), and the upcoming color screen device, this book provides you with clear, understandable coverage of the TI-84's updated operating system. Details the new apps that are available for download to the calculator via the USB cabl

Density Functional Theory Calculations of the Quantum Capacitance of Graphene Oxide as a Supercapacitor Electrode.

Science.gov (United States)

Song, Ce; Wang, Jinyan; Meng, Zhaoliang; Hu, Fangyuan; Jian, Xigao

2018-03-31

Graphene oxide has become an attractive electrode-material candidate for supercapacitors thanks to its higher specific capacitance compared to graphene. The quantum capacitance makes relative contributions to the specific capacitance, which is considered as the major limitation of graphene electrodes, while the quantum capacitance of graphene oxide is rarely concerned. This study explores the quantum capacitance of graphene oxide, which bears epoxy and hydroxyl groups on its basal plane, by employing density functional theory (DFT) calculations. The results demonstrate that the total density of states near the Fermi level is significantly enhanced by introducing oxygen-containing groups, which is beneficial for the improvement of the quantum capacitance. Moreover, the quantum capacitances of the graphene oxide with different concentrations of these two oxygen-containing groups are compared, revealing that more epoxy and hydroxyl groups result in a higher quantum capacitance. Notably, the hydroxyl concentration has a considerable effect on the capacitive behavior. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Packing simulation code to calculate distribution function of hard spheres by Monte Carlo method : MCRDF

International Nuclear Information System (INIS)

Murata, Isao; Mori, Takamasa; Nakagawa, Masayuki; Shirai, Hiroshi.

1996-03-01

High Temperature Gas-cooled Reactors (HTGRs) employ spherical fuels named coated fuel particles (CFPs) consisting of a microsphere of low enriched UO 2 with coating layers in order to prevent FP release. There exist many spherical fuels distributed randomly in the cores. Therefore, the nuclear design of HTGRs is generally performed on the basis of the multigroup approximation using a diffusion code, S N transport code or group-wise Monte Carlo code. This report summarizes a Monte Carlo hard sphere packing simulation code to simulate the packing of equal hard spheres and evaluate the necessary probability distribution of them, which is used for the application of the new Monte Carlo calculation method developed to treat randomly distributed spherical fuels with the continuous energy Monte Carlo method. By using this code, obtained are the various statistical values, namely Radial Distribution Function (RDF), Nearest Neighbor Distribution (NND), 2-dimensional RDF and so on, for random packing as well as ordered close packing of FCC and BCC. (author)

Iodine concentration calculated by dual-energy computed tomography (DECT) as a functional parameter to evaluate thyroid metabolism in patients with hyperthyroidism.

Science.gov (United States)

Binh, Duong Duc; Nakajima, Takahito; Otake, Hidenori; Higuchi, Tetsuya; Tsushima, Yoshito

2017-07-19

Thyroid function in patients with Grave's disease is usually evaluated by thyroid scintigraphy with radioactive iodine. Recently, dual-energy computed tomography (DECT) with two different energy X-rays can calculate iodine concentrations and can be applied for iodine measurements in thyroid glands. This study aimed to assess the potential use of DECT for the functional assessment of the thyroid gland. Thirteen patients with Grave's disease treated at our hospital from May to September 2015 were included in this retrospective study. Before treatments, all subjects had undergone both iodine scintigraphy [three and 24 h after oral administration of 123 I (20 μCi)] and non-enhanced DECT. The region of interests (ROIs) were placed in both lobes of the thyroid glands, and CT values (HU: Hounsfield unit) and iodine concentrations (mg/mL) calculated from DECT images were measured. The correlation between CT values and iodine concentrations from DECT in the thyroid gland was evaluated and then the iodine concentrations were compared with radioactive iodine uptake ratios by thyroid scintigraphy. Mean (±SD) 123 I uptake increased from 46.3 (±22.2) % (range, 11.1-80.1) at 3 h, to 66.5 (±15.2) % (range, 40.0-86.1) at 24 h (p hyperthyroid patients.

Understanding and Calibrating Density-Functional-Theory Calculations Describing the Energy and Spectroscopy of Defect Sites in Hexagonal Boron Nitride.

Science.gov (United States)

Reimers, Jeffrey R; Sajid, A; Kobayashi, Rika; Ford, Michael J

2018-03-13

Defect states in 2-D materials present many possible uses but both experimental and computational characterization of their spectroscopic properties is difficult. We provide and compare results from 13 DFT and ab initio computational methods for up to 25 excited states of a paradigm system, the V N C B defect in hexagonal boron nitride (h-BN). Studied include: (i) potentially catastrophic effects for computational methods arising from the multireference nature of the closed-shell and open-shell states of the defect, which intrinsically involves broken chemical bonds, (ii) differing results from DFT and time-dependent DFT (TDDFT) calculations, (iii) comparison of cluster models to periodic-slab models of the defect, (iv) the starkly differing effects of nuclear relaxation on the various electronic states that control the widths of photoabsorption and photoemission spectra as broken bonds try to heal, (v) the effect of zero-point energy and entropy on free-energy differences, (vi) defect-localized and conduction/valence-band transition natures, and (vii) strategies needed to ensure that the lowest-energy state of a defect can be computationally identified. Averaged state-energy differences of 0.3 eV are found between CCSD(T) and MRCI energies, with thermal effects on free energies sometimes also being of this order. However, DFT-based methods can perform very poorly. Simple generalized-gradient functionals like PBE fail at the most basic level and should never be applied to defect states. Hybrid functionals like HSE06 work very well for excitations within the triplet manifold of the defect, with an accuracy equivalent to or perhaps exceeding the accuracy of the ab initio methods used. However, HSE06 underestimates triplet-state energies by on average of 0.7 eV compared to closed-shell singlet states, while open-shell singlet states are predicted to be too low in energy by 1.0 eV. This leads to misassignment of the ground state of the V N C B defect. Long

Direct calculations of the odderon intercept in perturbative QCD

Energy Technology Data Exchange (ETDEWEB)

Braun, M.A.; Gauron, P.; Nicolescu, B

1999-03-08

The odderon intercept is calculated directly, from its expression via an average energy of the odderon Hamiltonian, using both trial wave functions in the variational approach and the wave function recently constructed by Janik and Wosiek. The results confirm their reported value for the energy. Variational calculations give energies some 30% higher. However, they also predict the odderon intercept to be quite close to unity. In fact, for realistic values of {alpha}{sub s}, the intercept calculated variationally is at most 2% lower than the exact one: 0.94 instead of 0.96. It is also found that the solution for q{sub 3} = 0 does not belong to the odderon spectrum. The diffusion parameter is found to be of the order 0.6.