Superfluid LDA (SLDA): Local Density Approximation for Systems with Superfluid Correlations
Bulgac, A; Bulgac, Aurel; Yu, Yongle
2004-01-01
We present a concise account of our development of the first genuine Local Density Approximation (LDA) to the Energy Density Functional (EDF) for fermionic systems with superfluid correlations, with a particular emphasis to nuclear systems.
Institute of Scientific and Technical Information of China (English)
Sun Bo; Zhang Ping
2008-01-01
The electronic structures and properties of PuO2 and Pu2O3 have been studied according to the first principles by using the all-electron projector-augmented-wave (PAW) method. The local density approximation (LDA)+U and the generalized gradient approximation (GGA)+U formalisms have been used to account for the strong on-site Coulomb repulsion among the localized Pu 5f electrons. We discuss how the properties of PuO2 and Pu2O3 are affected by choosing the values of U and exchange-correlation potential. Also, the oxidation reaction of Pu2O3, leading to the formation of PuO2, and its dependence on U and exchange-correlation potential have been studied. Our results show that by choosing an appropriate U it is possible to consistently describe structural, electronic, and thermodynamic properties of PuO2 and Pu2O3, which enable the modelling of the redox process involving Pu-based materials.
Electronic structure of ScN and YN:density-functional theory LDA and GW approximation calculations
Institute of Scientific and Technical Information of China (English)
Lü Tie-Yu; Huang Mei-Chun
2007-01-01
The desirable physical properties of hardness, high temperature stability, and conductivity make the early transition metal nitrides important materials for various technological applications. To learn more about the nature of these materials, the local-density approximation(LDA) and GW approximation i.e. combination of the Green function G and the screened Coulomb interaction W, have been performed. This paper investigates the bulk electronic and physical properties of early transition metal mononitrides, ScN and YN in the rocksalt structure. In this paper, the semicore electrons are regarded as valance electrons. ScN appears to be a semimetal, and YN is semiconductor with band gap of0.142 eV within the LDA, but are in fact semiconductors with indirect band gaps of 1.244 and 0.544 eV respectively, as revealed by calculations performed using GW approximation.
Giese, Timothy J; York, Darrin M
2010-12-28
We extend the Kohn-Sham potential energy expansion (VE) to include variations of the kinetic energy density and use the VE formulation with a 6-31G* basis to perform a "Jacob's ladder" comparison of small molecule properties using density functionals classified as being either LDA, GGA, or meta-GGA. We show that the VE reproduces standard Kohn-Sham DFT results well if all integrals are performed without further approximation, and there is no substantial improvement in using meta-GGA functionals relative to GGA functionals. The advantages of using GGA versus LDA functionals becomes apparent when modeling hydrogen bonds. We furthermore examine the effect of using integral approximations to compute the zeroth-order energy and first-order matrix elements, and the results suggest that the origin of the short-range repulsive potential within self-consistent charge density-functional tight-binding methods mainly arises from the approximations made to the first-order matrix elements.
Gritsenko, O V; Mentel, Ł M; Baerends, E J
2016-05-28
In spite of the high quality of exchange-correlation energies Exc obtained with the generalized gradient approximations (GGAs) of density functional theory, their xc potentials vxc are strongly deficient, yielding upshifts of ca. 5 eV in the orbital energy spectrum (in the order of 50% of high-lying valence orbital energies). The GGAs share this deficiency with the local density approximation (LDA). We argue that this error is not caused by the incorrect long-range asymptotics of vxc or by self-interaction error. It arises from incorrect density dependencies of LDA and GGA exchange functionals leading to incorrect (too repulsive) functional derivatives (i.e., response parts of the potentials). The vxc potential is partitioned into the potential of the xc hole vxchole (twice the xc energy density ϵxc), which determines Exc, and the response potential vresp, which does not contribute to Exc explicitly. The substantial upshift of LDA/GGA orbital energies is due to a too repulsive LDA exchange response potential vxresp (LDA) in the bulk region. Retaining the LDA exchange hole potential plus the B88 gradient correction to it but replacing the response parts of these potentials by the model orbital-dependent response potential vxresp (GLLB) of Gritsenko et al. [Phys. Rev. A 51, 1944 (1995)], which has the proper step-wise form, improves the orbital energies by more than an order of magnitude. Examples are given for the prototype molecules: dihydrogen, dinitrogen, carbon monoxide, ethylene, formaldehyde, and formic acid.
Gritsenko, O. V.; Mentel, Ł. M.; Baerends, E. J.
2016-05-01
In spite of the high quality of exchange-correlation energies Exc obtained with the generalized gradient approximations (GGAs) of density functional theory, their xc potentials vxc are strongly deficient, yielding upshifts of ca. 5 eV in the orbital energy spectrum (in the order of 50% of high-lying valence orbital energies). The GGAs share this deficiency with the local density approximation (LDA). We argue that this error is not caused by the incorrect long-range asymptotics of vxc or by self-interaction error. It arises from incorrect density dependencies of LDA and GGA exchange functionals leading to incorrect (too repulsive) functional derivatives (i.e., response parts of the potentials). The vxc potential is partitioned into the potential of the xc hole vxchole (twice the xc energy density ɛxc), which determines Exc, and the response potential vresp, which does not contribute to Exc explicitly. The substantial upshift of LDA/GGA orbital energies is due to a too repulsive LDA exchange response potential vxresp L D A in the bulk region. Retaining the LDA exchange hole potential plus the B88 gradient correction to it but replacing the response parts of these potentials by the model orbital-dependent response potential vxresp G L L B of Gritsenko et al. [Phys. Rev. A 51, 1944 (1995)], which has the proper step-wise form, improves the orbital energies by more than an order of magnitude. Examples are given for the prototype molecules: dihydrogen, dinitrogen, carbon monoxide, ethylene, formaldehyde, and formic acid.
Exact and LDA entanglement of tailored densities in an interacting one-dimensional electron system
Energy Technology Data Exchange (ETDEWEB)
Coe, J P; D' Amico, I, E-mail: jpc503@york.ac.u, E-mail: ida500@york.ac.u [Department of Physics, University of York, York YO10 5DD (United Kingdom)
2010-01-01
We calculate the 'exact' potential corresponding to a one-dimensional interacting system of two electrons with a specific, tailored density. We use one-dimensional density-functional theory with a local-density approximation (LDA) on the same system and calculate densities and energies, which are compared with the 'exact' ones. The 'interacting-LDA system'[4] corresponding to the LDA density is then found and its potential compared with the original one. Finally we calculate and compare the spatial entanglement of the electronic systems corresponding to the interacting-LDA and original interacting system.
Double-counting corrections to the LDA+DMFT method in the exact density limit
Plamada, Andrei Valentin; Staar, Peter; Kozhevnikov, Anton; Ydens, Bart; Schulthess, Thomas C.
2014-03-01
The LDA+U method is commonly used for ab-initio studies of strongly correlated electron materials, and it has been successful in predicting spectral properties of prototypical systems such as NiO when used in conjunction with Dynamical Mean Field Theory (DMFT). Presently the method still includes an empirical term to correct doubly counted correlations. Assuming the double-counting correction is a constant μDC multiplied by the identity operator in the correlated subspace and that the electron density is well approximated with the Local Density Approximation (LDA) to Density Functional Theory, we devise a method to determine μDC directly from LDA and DMFT calculations. The method has been validated for prototypical transition metal oxides and shows promising results that agree with commonly used values for the double counting correction in the respective systems.
Local density approximations from finite systems
Entwistle, Mike; Wetherell, Jack; Longstaff, Bradley; Ramsden, James; Godby, Rex
2016-01-01
The local density approximation (LDA) constructed through quantum Monte Carlo calculations of the homogeneous electron gas (HEG) is the most common approximation to the exchange-correlation functional in density functional theory. We introduce an alternative set of LDAs constructed from slab-like systems of one, two and three electrons that resemble the HEG within a finite region, and illustrate the concept in one dimension. Comparing with the exact densities and Kohn-Sham potentials for various test systems, we find that the LDAs give a good account of the self-interaction correction, but are less reliable when correlation is stronger or currents flow.
DYNAMICAL SPIN SUSCEPTIBILITY IN THE TD-LDA AND QSGW APPROXIMATIONS
Energy Technology Data Exchange (ETDEWEB)
SCHILFGAARDE, MARK VAN; KOTANI, TAKAO
2012-10-15
Abstract. This project was aimed at building the transverse dynamical spin susceptibility with the TD-LDA and the recently-developed Quasparticle Self-Consisent Approximations, which determines an optimum quasiparticle picture in a self-consistent manner within the GW approximation. Our main results were published into two papers, (J. Phys. Cond. Matt. 20, 95214 (2008), and Phys. Rev. B83, 060404(R) (2011). In the first paper we present spin wave dispersions for MnO, NiO, and -MnAs based on quasiparticle self-consistent GW approximation (QSGW). For MnO and NiO, QSGW results are in rather good agreement with experiments, in contrast to the LDA and LDA+U descriptions. For -MnAs, we find a collinear ferromagnetic ground state in QSGW, while this phase is unstable in the LDA. In the second, we apply TD-LDA to the CaFeAs2 the first attempt the first ab initio calculation of dynamical susceptibililty in a system with complex electronic structure Magnetic excitations in the striped phase of CaFe2As2 are studied as a function of local moment amplitude. We find a new kind of excitation: sharp resonances of Stoner-like (itinerant) excitations at energies comparable to the ´eel temperature, originating largely from a narrow band of Fe d states near the Fermi level, and coexisting with more conventional (localized) spin waves. Both kinds of excitations can show multiple branches, highlighting the inadequacy of a description based on a localized spin model.
Symmetry-broken local-density approximation for one-dimensional systems
Rogers, Fergus J M; Loos, Pierre-François
2016-01-01
Within density-functional theory, the local-density approximation (LDA) correlation functional is typically built by fitting the difference between the near-exact and Hartree-Fock (HF) energies of the uniform electron gas (UEG), together with analytic perturbative results from the high- and low-density regimes. Near-exact energies are obtained by performing accurate diffusion Monte Carlo calculations, while HF energies are usually assumed to be the Fermi fluid HF energy. However, it has been known since the seminal work of Overhauser that one can obtain lower, symmetry-broken (SB) HF energies at any density. Here, we have computed the SBHF energies of the one-dimensional UEG and constructed a SB version of the LDA (SBLDA) from the results. We compare the performance of the LDA and SBLDA functionals when applied to one-dimensional systems, including atoms and molecules. Generalization to higher dimensions is also discussed.
Energy Technology Data Exchange (ETDEWEB)
Salmani, E. [LMPHE, associe au CNRST (URAC 12), Faculte des Sciences, Universite Mohammed V-Agdal, Rabat (Morocco); Mounkachi, O. [Institute of Nanomaterials and Nanotechnology, MAScIR, Rabat (Morocco); Ez-Zahraouy, H., E-mail: ezahamid@fsr.ac.ma [LMPHE, associe au CNRST (URAC 12), Faculte des Sciences, Universite Mohammed V-Agdal, Rabat (Morocco); El Kenz, A. [LMPHE, associe au CNRST (URAC 12), Faculte des Sciences, Universite Mohammed V-Agdal, Rabat (Morocco); Hamedoun, M. [Institute of Nanomaterials and Nanotechnology, MAScIR, Rabat (Morocco); Benyoussef, A. [LMPHE, associe au CNRST (URAC 12), Faculte des Sciences, Universite Mohammed V-Agdal, Rabat (Morocco); Institute of Nanomaterials and Nanotechnology, MAScIR, Rabat (Morocco); Hassan II Academy of Science and Technology, Rabat (Morocco)
2013-03-15
Based on first-principles spin-density functional calculations, using the Korringa-Kohn-Rostoker method combined with the coherent potential approximation, we investigated the half-metallic ferromagnetic behavior of (Ga, Fe)N co-doped with carbon within the self-interaction-corrected local density approximation. Mechanism of hybridization and interaction between magnetic ions in p-type (Ga, Fe)N is investigated. Stability energy of ferromagnetic and disorder local moment states was calculated for different carbon concentration. The local density and the self-interaction-corrected approximations have been used to explain the strong ferromagnetic interaction observed and the mechanism that stabilizes this state. The transition temperature to the ferromagnetic state has been calculated within the effective field theory, with a Honmura-Kaneyoshi differential operator technique. - Highlights: Black-Right-Pointing-Pointer The paper focus on the study the magnetic properties and electronic structure of p-type (Ga, Fe)N within LDA and SIC approximation. Black-Right-Pointing-Pointer These methods allow us to explain the strong ferromagnetic interaction observed and the mechanism for its stability and the mechanism of hybridization and interaction between magnetic ions in p-type (Ga, Fe). Black-Right-Pointing-Pointer The results obtained are interesting and can be serve as a reference in the field of dilute magnetic semi conductor.
Kabita, Kh; Maibam, Jameson; Indrajit Sharma, B.; Brojen Singh, R. K.; Thapa, R. K.
2016-01-01
We report first principles phase transition, elastic properties and electronic structure for cadmium telluride (CdTe) under induced pressure in the light of density functional theory using the local density approximation (LDA), generalised gradient approximation (GGA) and modified Becke-Johnson (mBJ) potential. The structural phase transition of CdTe from a zinc blende (ZB) to a rock salt (RS) structure within the LDA calculation is 2.2 GPa while that within GGA is found to be at 4 GPa pressure with a volume collapse of 20.9%. The elastic constants and parameters (Zener anisotropy factor, Shear modulus, Poisson’s ratio, Young’s modulus, Kleinmann parameter and Debye’s temperature) of CdTe at different pressures of both the phases have been calculated. The band diagram of the CdTe ZB structure shows a direct band gap of 1.46 eV as predicted by mBJ calculation which gives better results in close agreement with experimental results as compared to LDA and GGA. An increase in the band gap of the CdTe ZB phase is predicted under induced pressure while the metallic nature is retained in the CdTe RS phase.
Energy Technology Data Exchange (ETDEWEB)
Kizaki, H., E-mail: hkizaki@aquarius.mp.es.osaka-u.ac.j [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 567-8531 (Japan); Toyoda, M.; Sato, K. [The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Katayama-Yoshida, H. [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 567-8531 (Japan); The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)
2009-12-15
Electronic structure of TiO{sub 2} (rutile) based dilute magnetic semiconductors (DMS) are investigated within self-interaction-corrected local density approximation (SIC-LDA) from first-principles calculation. These results are compared with those calculated within standard LDA. It is found that the calculated band-gap energy in the host TiO{sub 2} is different within the LDA and the SIC-LDA. We find that high-spin state is predicted within the SIC-LDA with oxygen vacancy. The calculated density of states within SIC-LDA is in good agreement with photoemission results.
Energy Technology Data Exchange (ETDEWEB)
Kraisler, Eli; Kronik, Leeor [Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100 (Israel)
2014-05-14
The fundamental gap is a central quantity in the electronic structure of matter. Unfortunately, the fundamental gap is not generally equal to the Kohn-Sham gap of density functional theory (DFT), even in principle. The two gaps differ precisely by the derivative discontinuity, namely, an abrupt change in slope of the exchange-correlation energy as a function of electron number, expected across an integer-electron point. Popular approximate functionals are thought to be devoid of a derivative discontinuity, strongly compromising their performance for prediction of spectroscopic properties. Here we show that, in fact, all exchange-correlation functionals possess a derivative discontinuity, which arises naturally from the application of ensemble considerations within DFT, without any empiricism. This derivative discontinuity can be expressed in closed form using only quantities obtained in the course of a standard DFT calculation of the neutral system. For small, finite systems, addition of this derivative discontinuity indeed results in a greatly improved prediction for the fundamental gap, even when based on the most simple approximate exchange-correlation density functional – the local density approximation (LDA). For solids, the same scheme is exact in principle, but when applied to LDA it results in a vanishing derivative discontinuity correction. This failure is shown to be directly related to the failure of LDA in predicting fundamental gaps from total energy differences in extended systems.
Curie temperatures of dilute magnetic semiconductors from LDA+U electronic structure calculations
Energy Technology Data Exchange (ETDEWEB)
Sato, K. [ISIR, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)]. E-mail: ksato@cmp.sanken.osaka-u.ac.jp; Dederichs, P.H. [IFF, Forschungszentrum Juelich, D-52425 Juelich (Germany); Katayama-Yoshida, H. [ISIR, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)
2006-04-01
The magnetic properties of dilute magnetic semiconductors (DMS) are calculated by using the local density approximation +U(LDA+U) method. In the LDA+U, occupied d-states in (Ga, Mn)As are predicted at lower energy than in the LDA and p-d exchange interaction explains calculated concentration dependence of Curie temperature very well. In (Ga, Mn)N, unoccupied d states are predicted at higher energy by LDA+U, resulting in higher Curie temperatures than in LDA at high concentrations due to the suppression of the anti-ferromagnetic super-exchange interaction.
Development of New Density Functional Approximations
Su, Neil Qiang; Xu, Xin
2017-05-01
Kohn-Sham density functional theory has become the leading electronic structure method for atoms, molecules, and extended systems. It is in principle exact, but any practical application must rely on density functional approximations (DFAs) for the exchange-correlation energy. Here we emphasize four aspects of the subject: (a) philosophies and strategies for developing DFAs; (b) classification of DFAs; (c) major sources of error in existing DFAs; and (d) some recent developments and future directions.
Gritsenko, O. V.; Rubio, A.; Balbás, L. C.; Alonso, J. A.
1993-03-01
The model Coulomb pair-correlation functions proposed several years ago by Gritsenko, Bagaturyants, Kazansky, and Zhidomirov are incorporated into the self-consistent local-density approximation (LDA) scheme for electronic systems. Different correlation functions satisfying well-established local boundary conditions and integral conditions have been tested by performing LDA calculations for closed-shell atoms. Those correlation functions contain a single parameter which can be optimized by fitting the atomic correlation energies to empirical data. In this way, a single (universal) value of the parameter is found to give a very good fit for all the atoms studied. The results provide a substantial improvement of calculated correlation energies as compared to the usual LDA functionals and the scheme should be useful for molecular and cluster calculations.
Dielectric constant of NiO and LDA+U
Ye, Lin-Hui; Luo, Ning; Peng, Lian-Mao; Weinert, M.; Freeman, A. J.
2013-02-01
The local density approximation (LDA) and generalized gradient approximations (GGA) of density functional theory systematically overestimate the electronic polarizability of materials. We calculate the dielectric constant of NiO by the direct method and find, contrary to previous suggestions, that the LDA+U method reduces the polarization such that ɛ∞ decreases monotonically with increasing U. We illustrate the existence of a linear term in the effective exchange-correlation potential that counteracts the external electric field, thus demonstrating that the decrease of ɛ∞ is intrinsic to the LDA+U correction. The reduction of the polarization is due mostly to reduced orbital mixing between the unoccupied eg states and the occupied 2p states. Our work establishes LDA+U as a viable method for calculating the dielectric constants of correlated materials.
Fermi surface of CeIn{sub 3} under pressure studied by the LDA+U method
Energy Technology Data Exchange (ETDEWEB)
Suzuki, M.-T. [Department of Condensed Matter Physics, Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501 (Japan)], E-mail: michi@kobe-u.ac.jp; Harima, H. [Department of Condensed Matter Physics, Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501 (Japan)
2008-04-01
We have carried out the electronic structure calculation by a local density approximation (LDA) and an LDA+U method to study the electronic structure of CeIn{sub 3} under pressure. The LDA+U calculation reproduces the f state with mainly occupied |j=5/2 ,{gamma}{sub 7}> orbitals. Then, the calculated Fermi surface drastically changes the character from the LDA result. We have found that the dHvA frequencies observed in the nonmagnetic state are well explained by the LDA+U method with upward shifted f level.
Energy Technology Data Exchange (ETDEWEB)
Kolorenc, Jindrich [Institute of Physics ASCR, Prague (Czech Republic); University of Hamburg, Hamburg (Germany); Shick, Alexander B. [Institute of Physics ASCR, Prague (Czech Republic); Havela, Ladislav [Charles University, Prague (Czech Republic); Lichtenstein, Alexander I. [University of Hamburg, Hamburg (Germany)
2010-07-01
We provide a numerically efficient procedure to perform LDA+Hubbard I calculations including self-consistency over the charge density in the FP-LAPW basis. The method is applied to Pu, Am, and PuAm and PuCe alloys. Our results for valence photoemission spectra (PES) agree with experimental data and with previous LDA+DMFT calculations. Analysis of the J=5/2 and J=7/2 contributions to the f-occupation supports the intermediate-coupling picture of f-states in heavy actinides. The electronic specific heat coefficient is calculated for PuAm and PuCe alloys in reasonable agreement with recent experiments. We show that Pu atoms keep their mixed-valence character in these alloys. Next, we study electronic and spectral properties of Pu-based superconductor PuCoGa{sub 5} and obtain good agreement with experimental PES. Finally, we analyze surface effects. In Pu monolayer, we find substantial modification of PES due to 5f-electron localization consistent with experimental observations.
Exponential Polynomial Approximation with Unrestricted Upper Density
Institute of Scientific and Technical Information of China (English)
Xiang Dong YANG
2011-01-01
We take a new approach to obtaining necessary and sufficient conditions for the incompleteness of exponential polynomials in Lp/α, where Lp/α is the weighted Banach space of complex continuous functions f defined on the real axis (R)satisfying (∫+∞/-∞|f(t)|pe-α(t)dt)1/p, 1 < p < ∞, and α(t) is a nonnegative continuous function defined on the real axis (R). In this paper, the upper density of the sequence which forms the exponential polynomials is not required to be finite. In the study of weighted polynomial approximation, consideration of the case is new.
Energetic, electronic and optical properties of lanthanide doped TiO2: An ab initio LDA+U study
CSIR Research Space (South Africa)
Mulwa, WM
2016-05-01
Full Text Available Substitutional energies, thermodynamic charge transition levels and optical properties of lanthanide doped anatase TiO(sub2) has been investigated using local density approximation with the Hubbard U correction (LDA+U) within the density functional...
Ab initio thermodynamics and phase diagram of solid magnesium: a comparison of the LDA and GGA.
Mehta, S; Price, G D; Alfè, D
2006-11-21
The finite temperature density functional theory and quasiharmonic lattice dynamics have been used to compute numerous thermodynamic properties of hexagonal close packed magnesium using both the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation potential. Generally, it is found that there exist only minor differences between the LDA and GGA computed properties, with both giving good agreement with experiment. The hcp-bcc phase boundary has also been computed and is found to be in agreement with experimental observation. Again, only slight differences are found between the LDA and GGA.
Shi, Li-Bin; Wang, Yong Ping
2016-05-01
The native defects and magnetic properties in undoped rutile TiO2 are studied using local density approximation (LDA) and LDA adding Hubbard parameters (U) schemes. The band gap is adjusted to experimental value of 3.0 eV by combination of UTi d=4.2 eV and UO p=4.8 eV. This LDA+U methodology overcomes the band-gap problem and renders the approach more predictive. The formation energies of oxygen vacancy (VO), oxygen interstitial (Oi), titanium vacancy (VTi), titanium interstitial (Tii), oxygen anti-sites (OTi), and titanium anti-sites (TiO) are investigated by the LDA and LDA+U methods. In addition, some ground state configurations can be obtained by optimization of total spin. It is found that native defects can induce spin polarization and produce magnetic moment.
Skornyakov, S. L.; Anisimov, V. I.
2015-04-01
In this review, we describe general ideas of the LDA+DMFT method which merges dynamical mean-field theory (DMFT) and density functional theory (in particular the local density approximation (LDA)). Nowadays, the LDA+DMFT computational scheme is the most powerful numerical tool for studying physical properties of real materials and chemical compounds. It incorporates the advantage of DMFT to treat the full range of local dynamical Coulomb correlations and the ability of band methods to describe material-specific band dispersion caused by the lattice periodicity. We briefly discuss underlying physical ideas of LDA+DMFT and its mathematical implementation. Then different algorithms applied to solution of the DMFT impurity problem are briefly described. We then give examples of successful applications of the LDA+DMFT method to study spectral and magnetic properties of recently synthesized compounds like pnictide superconductors as well as classic charge-transfer systems NiO and MnO.
Institute of Scientific and Technical Information of China (English)
Zhou Shi-Qi
2007-01-01
A universal theoretical approach is proposed which enables all hard sphere density functional approximations(DFAs) applicable to van der Waals fluids. The resultant DFA obtained by combining the universal theoretical approach with any hard sphere DFAs only needs as input a second-order direct correlation function (DCF) of a coexistence bulk fluid, and is applicable in both supercritical and subcritical temperature regions. The associated effective hard sphere density can be specified by a hard wall sum rule. It is indicated that the value of the effective hard sphere density so determined can be universal, i.e. can be applied to any external potentials different from the single hard wall. As an illustrating example, the universal theoretical approach is combined with a hard sphere bridge DFA to predict the density profile of a hard core attractive Yukawa model fluid influenced by diverse external fields; agreement between the present formalism's predictions and the corresponding simulation data is good or at least comparable to several previous DFT approaches. The primary advantage of the present theoretical approach combined with other hard sphere DFAs is discussed.
Curie temperature of GaMnN and GaMnAs from LDA-SIC electronic structure calculations
Energy Technology Data Exchange (ETDEWEB)
Toyoda, Masayuki; Sato, Kazunori; Katayama-Yoshida, Hiroshi [Department of Computational Nanomaterials Design, Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Akai, Hisazumi [Department of Physics, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan)
2006-07-01
We present the electronic structures, magnetic exchange interactions and Curie temperature (T{sub C}) of GaMnN and GaMnAs calculated by self-interaction-corrected local-density approximation (LDA-SIC). In GaMnAs, the LDA-SIC results of T{sub C} do not differ so much from the LDA results. Both the LDA and LDA-SIC values are in a good agreement with the experimental data. In GaMnN, on the other hand, the ferromagnetic exchange interactions are enhanced due to the suppression of antiferromagnetic super-exchange interaction, resulting in T{sub C} higher than the LDA results. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Conditional Density Approximations with Mixtures of Polynomials
DEFF Research Database (Denmark)
Varando, Gherardo; López-Cruz, Pedro L.; Nielsen, Thomas Dyhre
2015-01-01
Mixtures of polynomials (MoPs) are a non-parametric density estimation technique especially designed for hybrid Bayesian networks with continuous and discrete variables. Algorithms to learn one- and multi-dimensional (marginal) MoPs from data have recently been proposed. In this paper we introduce...... is found. We illustrate and study the methods using data sampled from known parametric distributions, and we demonstrate their applicability by learning models based on real neuroscience data. Finally, we compare the performance of the proposed methods with an approach for learning mixtures of truncated...
Energy Technology Data Exchange (ETDEWEB)
Pandey, S K [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452 017 (India); Kumar, Ashwani [School of Physics, Devi Ahilya University, Khandwa Road, Indore 452 017 (India); Chaudhari, S M [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452 017 (India); Pimpale, A V [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452 017 (India)
2006-02-01
Electronic states of PrCoO{sub 3} are studied using x-ray photoemission spectroscopy. The Pr 3d{sub 5/2} core level and valence band (VB) were recorded using an Mg K {alpha} source. The core level spectrum shows that the 3d{sub 5/2} level is split into two components of multiplicity four and two, respectively, due to coupling of the spin states of the hole in 3d{sub 5/2} with the Pr 4f hole spin state. The observed splitting is 4.5 eV. The VB spectrum is interpreted using density of states (DOS) calculations under LDA and LDA +U. It is noted that LDA is not sufficient to explain the observed VB spectrum. Inclusion of on-site Coulomb correlation for Co 3d electrons in LDA +U calculations gives DOS which is useful in qualitative explanation of the ground state. However, it is necessary to include interactions between Pr 4f electrons to get better agreement with the experimental VB spectrum. It is seen that the VB consists of Pr 4f, Co 3d and O 2p states. Pr 4f, Co 3d and O 2p bands are highly mixed, indicating strong hybridization of these three states. The band near the Fermi level has about equal contributions from Pr 4f and O 2p states with somewhat smaller contribution from Co 3d states. Thus in the Zaanen, Sawatzky and Allen scheme PrCoO{sub 3} can be considered as a charge transfer insulator. The charge transfer energy {delta} can be obtained using LDA DOS calculations and the Coulomb-exchange energy U{sup '} from LDA +U. The explicit values for PrCoO{sub 3} are {delta} = 3.9 eV and U{sup '} = 5.5 eV; the crystal field splitting and 3d bandwidth of Co ions are also found to be 2.8 and 1.8 eV, respectively.
Salmani, E.; Mounkachi, O.; Ez-Zahraouy, H.; El Kenz, A.; Hamedoun, M.; Benyoussef, A.
2013-03-01
Based on first-principles spin-density functional calculations, using the Korringa-Kohn-Rostoker method combined with the coherent potential approximation, we investigated the half-metallic ferromagnetic behavior of (Ga, Fe)N co-doped with carbon within the self-interaction-corrected local density approximation. Mechanism of hybridization and interaction between magnetic ions in p-type (Ga, Fe)N is investigated. Stability energy of ferromagnetic and disorder local moment states was calculated for different carbon concentration. The local density and the self-interaction-corrected approximations have been used to explain the strong ferromagnetic interaction observed and the mechanism that stabilizes this state. The transition temperature to the ferromagnetic state has been calculated within the effective field theory, with a Honmura-Kaneyoshi differential operator technique.
LDA + U and hybrid functional calculations for defects in ZnO, SnO{sub 2}, and TiO{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Janotti, Anderson; Van de Walle, Chris G. [Materials Department, University of California, Santa Barbara, CA 93106-5050 (United States)
2011-04-15
We describe and compare defect calculations based on density functional theory within the local density approximation (LDA), the orbital-dependent LDA + U, and using hybrid functionals. Limitations of the LDA in describing defect formation energies and transition levels are discussed, followed by corrections based on the LDA + U, and the use of the hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE). The band-gap error in LDA leads to large uncertainties not only in defect transition levels but also in formation energies. LDA + U provides a partial correction to the band gap and, when combined with LDA, provides an accurate method for predicting transition levels. Formation energies obtained from the LDA + U/LDA approach depend on the ability of LDA + U to correctly describe the position of the band edges on an absolute energy scale. Although computationally demanding, HSE is demonstrated to be a reliable method for predicting structure and electronic properties of semiconductors, including transition levels and formation energies of defects. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Casida, Mark E.; Salahub, Dennis R.
2000-11-01
The time-dependent density functional theory (TD-DFT) calculation of excitation spectra places certain demands on the DFT exchange-correlation potential, vxc, that are not met by the functionals normally used in molecular calculations. In particular, for high-lying excitations, it is crucial that the asymptotic behavior of vxc be correct. In a previous paper, we introduced a novel asymptotic-correction approach which we used with the local density approximation (LDA) to yield an asymptotically corrected LDA (AC-LDA) potential [Casida, Casida, and Salahub, Int. J. Quantum Chem. 70, 933 (1998)]. The present paper details the theory underlying this asymptotic correction approach, which involves a constant shift to incorporate the effect of the derivative discontinuity (DD) in the bulk region of finite systems, and a spliced asymptotic correction in the large r region. This is done without introducing any adjustable parameters. We emphasize that correcting the asymptotic behavior of vxc is not by itself sufficient to improve the overall form of the potential unless the effect of the derivative discontinuity is taken into account. The approach could be used to correct vxc from any of the commonly used gradient-corrected functionals. It is here applied to the LDA, using the asymptotically correct potential of van Leeuwen and Baerends (LB94) in the large r region. The performance of our AC-LDA vxc is assessed for the calculation of TD-DFT excitation energies for a large number of excitations, including both valence and Rydberg states, for each of four small molecules: N2, CO, CH2O, and C2H4. The results show a significant improvement over those from either the LB94 or the LDA functionals. This confirms that the DD is indeed an important element in the design of functionals. The quality of TDLDA/LB94 and TDLDA/AC-LDA oscillator strengths were also assessed in what we believe to be the first rigorous assessment of TD-DFT molecular oscillator strengths in comparison with
Spectral analysis of individual realization LDA data
Tummers, M.J.; Passchier, D.M.
1998-01-01
The estimation of the autocorrelation function (act) or the spectral density function (sdt) from LDA data poses unique data-processing problems. The random sampling times in LDA preclude the use of the spectral methods for equi-spaced samples. As a consequence, special data-processing algorithms are
Energy Technology Data Exchange (ETDEWEB)
Li Jia, E-mail: jiali@hebut.edu.cn; Zhang Zhidong; Ji Qing; Zhang Hui; Luo Hongzhi
2012-10-05
Highlights: Black-Right-Pointing-Pointer Reproduce of band gap for XSi(X = Fe,Ru,Os) with gap of {approx}10{sup -1} eV. Black-Right-Pointing-Pointer Using the mBJ + LDA first principles in comparison with GGA and LDA. Black-Right-Pointing-Pointer Theoretical optical conductivity is in agreement with the measurement. - Abstract: The electronic structure, optical reflectivity spectra and optical conductivity of semiconducting transition-metal silicides FeSi, RuSi and OsSi have been investigated by using first principles calculation within the recent developed modified Becke-Johnson exchange potential plus local-density approximation (mBJ + LDA). The electronic structures produced by mBJ + LDA, generalized gradient approximation (GGA) and LDA are rather similar although the band gap has been enlarged more or less by the mBJ + LDA compared to the GGA and LDA for the three compounds. The mBJ + LDA, GGA and LDA all have overestimated the band gap for FeSi and OsSi compared to the experiment. For RuSi, the theoretical gap values are basically close to the experimental values and the improvement of gap by mBJ + LDA is only 0.04 eV in comparison with the GGA. The mBJ + LDA and GGA also produce similar results with respect to their optical properties including the reflectivity spectra and optical conductivity except that for the reflectivity spectra of FeSi, the GGA result is little better consistent with the experimental measurement than the mBJ + LDA result. The optical conductivity calculated by mBJ + LDA and GGA both exhibits the absorption edge, in well correspondence to the optical measurement.
Lee, Juho; Haule, Kristjan
2015-03-01
Dynamical Mean Field Theory (DMFT) in combination with Local Density Approximation (LDA) is widely used in solids to predict properties of correlated systems. Here one of the simplest strongly correlated systems, the hydrogen molecule H2, is used as a testbed to develop a parameter-free LDA+DMFT framework. We propose a method to calculate the exact intersection of LDA and DMFT that leads to highly accurate subtraction of the doubly counted correlation in both methods. The total energy accuracy of LDA+DMFT in its single site version is around 0.3%, provided that a good projector to the correlated subspace and the exact double-counting treatment are used. In addition to LDA+DMFT, we also implement combined GW and DMFT for diatomic molecules. The total energy accuracy of GW+DMFT is as remarkable as that of LDA+DMFT is, while the excitation spectrum is predicted in even better agreement with the exact theory.
On exact and approximate exchange-energy densities
DEFF Research Database (Denmark)
Springborg, Michael; Dahl, Jens Peder
1999-01-01
Based on correspondence rules between quantum-mechanical operators and classical functions in phase space we construct exchange-energy densities in position space. Whereas these are not unique but depend on the chosen correspondence rule, the exchange potential is unique. We calculate this exchange......-energy density for 15 closed-shell atoms, and compare it with kinetic- and Coulomb-energy densities. It is found that it has a dominating local-density character, but electron-shell effects are recognizable. The approximate exchange-energy functionals that have been proposed so far are found to account only...
Theory of the insulator ground state of the plutonium monochalcogenides: An LDA+DMFT investigation
Energy Technology Data Exchange (ETDEWEB)
Suzuki, Michi-To; Oppeneer, Peter M, E-mail: michi-to.suzuki@fysik.uu.se [Department of Physics and Materials Science, Box 530, Uppsala University, S-751 21 Uppsala (Sweden)
2010-03-15
The electronic structures and Kondo insulator state of the Pu monochalcogenides are computationally investigated, using the local density approximation (LDA), the LDA+U and dynamical mean field theory (LDA+DMFT) methods. We show that an enhanced hybridization of the Pu-5f state with the conduction bands occurs through the dynamical effect in the DMFT, which leads to the effective formation of a small energy gap around the Fermi level. Our LDA+DMFT calculations explain quantitatively the anomalous energy gap enhancement under pressure, observed for PuTe. The peculiar change of the energy gap of PuTe with pressure is found to result from a subtle crossover in the k-dispersion of the lowest excited states.
LDA+DMFT Approach to Materials with Strong Electronic Correlations
Energy Technology Data Exchange (ETDEWEB)
Held, K; Nekrasov, I A; Keller, G; Eyert, V; Blumer, N; McMahan, A K; Scalettar, R T; Pruschke, T; Anisimov, V I; Volhardt, D
2001-12-02
LDA+DMFT is a novel computational technique for ab initio investigations of real materials with strongly correlated electrons, such as transition metals and their oxides. It combines the strength of conventional band structure theory in the local density approximation (LDA) with a modern many-body approach, the dynamical mean-field theory (DMFT). In the last few years LDA+DMFT has proved to be a powerful tool for the realistic modeling of strongly correlated electronic systems. In this paper the basic ideas and the set-up of the LDA+DMFT(X) approach, where X is the method used to solve the DMFT equations, are discussed. Results obtained with X=QMC (quantum Monte Carlo) and X=NCA (non-crossing approximation) are presented and compared. By means of the model system La{sub 1-x}Sr{sub x}TiO{sub 3} we show that the method X matters qualitatively and quantitatively. Furthermore, they discuss recent results on the Mott-Hubbard metal-insulator transition in the transition metal oxide V{sub 2}O{sub 3} and the {alpha}-{gamma} transition in the 4f-electron system Ce.
Electronic Flux Density beyond the Born-Oppenheimer Approximation.
Schild, Axel; Agostini, Federica; Gross, E K U
2016-05-19
In the Born-Oppenheimer approximation, the electronic wave function is typically real-valued and hence the electronic flux density (current density) seems to vanish. This is unfortunate for chemistry, because it precludes the possibility to monitor the electronic motion associated with the nuclear motion during chemical rearrangements from a Born-Oppenheimer simulation of the process. We study an electronic flux density obtained from a correction to the electronic wave function. This correction is derived via nuclear velocity perturbation theory applied in the framework of the exact factorization of electrons and nuclei. To compute the correction, only the ground state potential energy surface and the electronic wave function are needed. For a model system, we demonstrate that this electronic flux density approximates the true one very well, for coherent tunneling dynamics as well as for over-the-barrier scattering, and already for mass ratios between electrons and nuclei that are much larger than the true mass ratios.
Casida, Mark E.; Jamorski, Christine; Casida, Kim C.; Salahub, Dennis R.
1998-03-01
This paper presents an evaluation of the performance of time-dependent density-functional response theory (TD-DFRT) for the calculation of high-lying bound electronic excitation energies of molecules. TD-DFRT excitation energies are reported for a large number of states for each of four molecules: N2, CO, CH2O, and C2H4. In contrast to the good results obtained for low-lying states within the time-dependent local density approximation (TDLDA), there is a marked deterioration of the results for high-lying bound states. This is manifested as a collapse of the states above the TDLDA ionization threshold, which is at -ɛHOMOLDA (the negative of the highest occupied molecular orbital energy in the LDA). The -ɛHOMOLDA is much lower than the true ionization potential because the LDA exchange-correlation potential has the wrong asymptotic behavior. For this reason, the excitation energies were also calculated using the asymptotically correct potential of van Leeuwen and Baerends (LB94) in the self-consistent field step. This was found to correct the collapse of the high-lying states that was observed with the LDA. Nevertheless, further improvement of the functional is desirable. For low-lying states the asymptotic behavior of the exchange-correlation potential is not critical and the LDA potential does remarkably well. We propose criteria delineating for which states the TDLDA can be expected to be used without serious impact from the incorrect asymptotic behavior of the LDA potential.
Approximation of conditional densities by smooth mixtures of regressions
Norets, Andriy
2010-01-01
This paper shows that large nonparametric classes of conditional multivariate densities can be approximated in the Kullback--Leibler distance by different specifications of finite mixtures of normal regressions in which normal means and variances and mixing probabilities can depend on variables in the conditioning set (covariates). These models are a special case of models known as "mixtures of experts" in statistics and computer science literature. Flexible specifications include models in which only mixing probabilities, modeled by multinomial logit, depend on the covariates and, in the univariate case, models in which only means of the mixed normals depend flexibly on the covariates. Modeling the variance of the mixed normals by flexible functions of the covariates can weaken restrictions on the class of the approximable densities. Obtained results can be generalized to mixtures of general location scale densities. Rates of convergence and easy to interpret bounds are also obtained for different model spec...
Energy Technology Data Exchange (ETDEWEB)
Vildosola, V.L.; Llois, A.M. E-mail: llois@cnea.gov.ar; Weissmann, M.; Sereni, J.G
2001-10-01
Ce intermetallic compounds have been intensively studied in the last few decades due to the large variety of behaviours they exhibit. In particular, two ways of demagnetizing Ce have been experimentally tried within the ferromagnetic systems Ce(Pd{sub 1-x}M{sub x}), namely through electronic concentration variations (M=Rh) and volume reductions (M=Ni). On the other hand, when Pd is substituted by Ag, a transformation from a ferromagnetic to an antiferromagnetic ground state has been observed. In this work, we analyse the evolution of the magnetism of Ce in the above-mentioned family of compounds by calculating the spin contribution to magnetism that results from spin polarised LDA calculations.
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.
Approximate particle number projection for finite range density dependent forces
Valor, A; Robledo, L M
1996-01-01
The Lipkin-Nogami method is generalized to deal with finite range density dependent forces. New expressions are derived and realistic calculations with the Gogny force are performed for the nuclei ^{164}Er and ^{168}Er. The sharp phase transition predicted by the mean field approximation is washed out by the Lipkin-Nogami approach; a much better agreement with the experimental data is reached with the new approach than with the Hartree-Fock_Bogoliubov one, specially at high spins.
Mapping of an Approximate Neutral Density Surface with Ungridded Data
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
A neutral density surface is a logical study frame for water-mass mixing since water parcels spread along such a surface without doing work against buoyancy restoring force. Mesoscale eddies are believed to stir and subsequently mix predominantly along such surfaces. Because of the nonlinear nature of the equation of state of seawater, the process of accurately mapping a neutral density surface necessarily involves lateral computation from one conductivity, temperature and depth (CTD) cast to the next in a logical sequence. By contrast, the depth of a potential density surface on any CTD cast is found solely from the data on this cast. The lateral calculation procedure causes a significant inconvenience. In a previous paper by present author published in this journal (You,2006), the mapping of neutral density surfaces with regularly gridded data such as Levitus data has been introduced. In this note, I present a new method to find the depth of a neutral density surface from a cast without having to specify an integration path in space.An appropriate reference point is required that is on the neutral density surface and thereafter the neutral density surface can be determined by using the CTD casts in any order. This method is only approximate and the likely errors can be estimated by plotting a scatter diagram of all the pressures and potential temperatures on the neutral density surfaces. The method assumes that the variations of potential temperature and pressure (with respect to the values at the reference point) on the neutral density surface are proportional.It is important to select the most appropriate reference point in order to approximately satisfy this assumption, and in practice this is found by inspecting the θ-p plot of data on the surface. This may require that the algorithm be used twice. When the straight lines on the θ-p plot, drawn from the reference point to other points on the neutral density surface, enclose an area that is external to the
Machine-learned approximations to Density Functional Theory Hamiltonians
Hegde, Ganesh; Bowen, R. Chris
2017-01-01
Large scale Density Functional Theory (DFT) based electronic structure calculations are highly time consuming and scale poorly with system size. While semi-empirical approximations to DFT result in a reduction in computational time versus ab initio DFT, creating such approximations involves significant manual intervention and is highly inefficient for high-throughput electronic structure screening calculations. In this letter, we propose the use of machine-learning for prediction of DFT Hamiltonians. Using suitable representations of atomic neighborhoods and Kernel Ridge Regression, we show that an accurate and transferable prediction of DFT Hamiltonians for a variety of material environments can be achieved. Electronic structure properties such as ballistic transmission and band structure computed using predicted Hamiltonians compare accurately with their DFT counterparts. The method is independent of the specifics of the DFT basis or material system used and can easily be automated and scaled for predicting Hamiltonians of any material system of interest. PMID:28198471
Machine-learned approximations to Density Functional Theory Hamiltonians
Hegde, Ganesh; Bowen, R. Chris
2017-02-01
Large scale Density Functional Theory (DFT) based electronic structure calculations are highly time consuming and scale poorly with system size. While semi-empirical approximations to DFT result in a reduction in computational time versus ab initio DFT, creating such approximations involves significant manual intervention and is highly inefficient for high-throughput electronic structure screening calculations. In this letter, we propose the use of machine-learning for prediction of DFT Hamiltonians. Using suitable representations of atomic neighborhoods and Kernel Ridge Regression, we show that an accurate and transferable prediction of DFT Hamiltonians for a variety of material environments can be achieved. Electronic structure properties such as ballistic transmission and band structure computed using predicted Hamiltonians compare accurately with their DFT counterparts. The method is independent of the specifics of the DFT basis or material system used and can easily be automated and scaled for predicting Hamiltonians of any material system of interest.
Implementation of LDA+DMFT with the pseudo-potential-plane-wave method
Institute of Scientific and Technical Information of China (English)
Zhao Jian-Zhou; Zhuang Jia-Ning; Deng Xiao-Yu; Bi Yan; Cai Ling-Cang; Fang Zhong; Dai Xi
2012-01-01
We propose an efficient implementation of combining dynamical mean field theory(DMFT)with electronic structural calculation based on the local density approximation(LDA).The pseudo-potential-plane-wave method is used in the LDA part,which enables it to be applied to large systems.The full loop self consistency of the charge density has been reached in our implementation,which allows us to compute the total energy related properties.The procedure of LDA+DMFT is introduced in detail with a complete flow chart.We have also applied our code to study the electronic structure of several typical strong correlated materials,including cerium,americium and NiO.Our results fit quite well with both the experimental data and previous studies.
Localized and itinerant states in lanthanide oxides united by GW @ LDA+U.
Jiang, Hong; Gomez-Abal, Ricardo I; Rinke, Patrick; Scheffler, Matthias
2009-03-27
Many-body perturbation theory in the GW approach is applied to lanthanide oxides, using the local-density approximation plus a Hubbard U correction (LDA+U) as the starting point. Good agreement between the G0W0 density of states and experimental spectra is observed for CeO2 and Ce2O3. Unlike the LDA+U method G0W0 exhibits only a weak dependence on U in a physically meaningful range of U values. For the whole lanthanide sesquioxide (Ln2O3) series G0W0 @ LDA+U reproduces the main features found for the optical experimental band gaps. The relative positions of the occupied and unoccupied f states predicted by G0W0 confirm the experimental conjecture derived from phenomenological arguments.
A Concept of Approximated Densities for Efficient Nonlinear Estimation
Directory of Open Access Journals (Sweden)
Virginie F. Ruiz
2002-10-01
Full Text Available This paper presents the theoretical development of a nonlinear adaptive filter based on a concept of filtering by approximated densities (FAD. The most common procedures for nonlinear estimation apply the extended Kalman filter. As opposed to conventional techniques, the proposed recursive algorithm does not require any linearisation. The prediction uses a maximum entropy principle subject to constraints. Thus, the densities created are of an exponential type and depend on a finite number of parameters. The filtering yields recursive equations involving these parameters. The update applies the Bayes theorem. Through simulation on a generic exponential model, the proposed nonlinear filter is implemented and the results prove to be superior to that of the extended Kalman filter and a class of nonlinear filters based on partitioning algorithms.
Energy Technology Data Exchange (ETDEWEB)
Nisikawa, Yunori [Department of Material Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585 (Japan)]. E-mail: nisikawa@sci.osaka-cu.ac.jp; Usuda, Manabu [Masago 1-4-8, Ibaraki, Osaka, 567-0851 (Japan); Oguri, Akira [Department of Material Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585 (Japan)
2007-03-15
The electronic structure of CuGeO{sub 3} in the spin-Peierls (SP) phase with the space group of Bbcm is calculated for the first time within the local-density approximation (LDA) and the LDA+U scheme where the local 3d-3d Coulomb interaction U is introduced on the Cu sites. Although the insulating antiferromagnetic solution is obtained in the LDA, the obtained bandgap of 0.19eV and a magnetic moment of 0.39{mu}{sub B}/Cu are much smaller than the experimental bandgap of 3.7eV and the magnetic moment of 0.7{mu}{sub B}/Cu, respectively. With the value of U=6.7eV determined using an electron spectroscopy, the LDA+U calculation yields a charge-transfer bandgap of 1.63eV and gives a magnetic moment of 0.72{mu}{sub B}/Cu. The essential electronic and magnetic properties of CuGeO{sub 3} in the SP phase can be described by means of the LDA+U scheme.
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.
Mean Spherical Approximation-Based Partitioned Density Functional Theory
Institute of Scientific and Technical Information of China (English)
ZHOU Shi-Qi
2003-01-01
Previous literature claims that the density functional theory for non-uniform non-hard sphere interaction potential fluid can be improved on by treating the tail part by the third order functional perturbation expansion approximation (FPEA) with the symmetrical and intuitive consideration-based simple function C0(3)(r1, r2, r3) =ζ∫ dr4a(r4 - r1)a(r4 - r2)a(r4 - r3) as the uniform third order direct correlation function (DCF) for the tail part,here kernel function a(r) = (6/πσ3)Heaviside(σ/2 - r). The present contribution concludes that for the mean spherical approximation-based second order DCF, the terms higher than second order in the FPEA of the tail part of the non-uniform first order DCF are exactly zero. The reason for the partial success of the previous a kernel function-based third order FPEA for the tail part is due to the adjustable parameter ζ and the short range of the a kernel function.Improvement over the previous theories is proposed and tested.
Mean Spherical Approximation-Based Partitioned Density Functional Theory
Institute of Scientific and Technical Information of China (English)
ZHOUShi-Qi
2003-01-01
Previous literature claims that the density functional theory for non-uniform non-hard sphere interaction potential fluid can be improved on by treating the tail part by the third order functional perturbation expansion approximation (FPEA) with the symmetrical and intuitive consideration-based simple function C0(3)(r1, r2, r3) =(∫dr4a(r4-r1)a(r4-r2)a(r4-r3) as the uniform third order direct correlation function (DCF) for the tail part,here kernel function a(r) = (6/πσ3)Heaviside(σ/2 - r). The present contribution concludes that for the mean spherical approximation-based second order DCF, the terms higher than second order in the FPEA of the tail part of the non-uniform first order DCF are exactly zero. The reason for the partial success of the previous a kernel function-based third order FPEA for the tail part is due to the adjustable parameter ξ and the short range of the a kernel function.Improvement over the previous theories is proposed and tested.
Benchmarking mean-field approximations to level densities
Alhassid, Y; Gilbreth, C N; Nakada, H
2015-01-01
We assess the accuracy of finite-temperature mean-field theory using as a standard the Hamiltonian and model space of the shell model Monte Carlo calculations. Two examples are considered: the nucleus $^{162}$Dy, representing a heavy deformed nucleus, and $^{148}$Sm, representing a nearby heavy spherical nucleus with strong pairing correlations. The errors inherent in the finite-temperature Hartree-Fock and Hartree-Fock-Bogoliubov approximations are analyzed by comparing the entropies of the grand canonical and canonical ensembles, as well as the level density at the neutron resonance threshold, with shell model Monte Carlo (SMMC) calculations, which are accurate up to well-controlled statistical errors. The main weak points in the mean-field treatments are seen to be: (i) the extraction of number-projected densities from the grand canonical ensembles, and (ii) the symmetry breaking by deformation or by the pairing condensate. In the absence of a pairing condensate, we confirm that the usual saddle-point appr...
Sato, Shunsuke A.; Taniguchi, Yasutaka; Shinohara, Yasushi; Yabana, Kazuhiro
2015-12-01
We develop methods to calculate electron dynamics in crystalline solids in real-time time-dependent density functional theory employing exchange-correlation potentials which reproduce band gap energies of dielectrics; a meta-generalized gradient approximation was proposed by Tran and Blaha [Phys. Rev. Lett. 102, 226401 (2009)] (TBm-BJ) and a hybrid functional was proposed by Heyd, Scuseria, and Ernzerhof [J. Chem. Phys. 118, 8207 (2003)] (HSE). In time evolution calculations employing the TB-mBJ potential, we have found it necessary to adopt the predictor-corrector step for a stable time evolution. We have developed a method to evaluate electronic excitation energy without referring to the energy functional which is unknown for the TB-mBJ potential. For the HSE functional, we have developed a method for the operation of the Fock-like term in Fourier space to facilitate efficient use of massive parallel computers equipped with graphic processing units. We compare electronic excitations in silicon and germanium induced by femtosecond laser pulses using the TB-mBJ, HSE, and a simple local density approximation (LDA). At low laser intensities, electronic excitations are found to be sensitive to the band gap energy: they are close to each other using TB-mBJ and HSE and are much smaller in LDA. At high laser intensities close to the damage threshold, electronic excitation energies do not differ much among the three cases.
Energy Technology Data Exchange (ETDEWEB)
Sato, Shunsuke A. [Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8571 (Japan); Taniguchi, Yasutaka [Center for Computational Science, University of Tsukuba, Tsukuba 305-8571 (Japan); Department of Medical and General Sciences, Nihon Institute of Medical Science, 1276 Shimogawara, Moroyama-Machi, Iruma-Gun, Saitama 350-0435 (Japan); Shinohara, Yasushi [Max Planck Institute of Microstructure Physics, 06120 Halle (Germany); Yabana, Kazuhiro [Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8571 (Japan); Center for Computational Science, University of Tsukuba, Tsukuba 305-8571 (Japan)
2015-12-14
We develop methods to calculate electron dynamics in crystalline solids in real-time time-dependent density functional theory employing exchange-correlation potentials which reproduce band gap energies of dielectrics; a meta-generalized gradient approximation was proposed by Tran and Blaha [Phys. Rev. Lett. 102, 226401 (2009)] (TBm-BJ) and a hybrid functional was proposed by Heyd, Scuseria, and Ernzerhof [J. Chem. Phys. 118, 8207 (2003)] (HSE). In time evolution calculations employing the TB-mBJ potential, we have found it necessary to adopt the predictor-corrector step for a stable time evolution. We have developed a method to evaluate electronic excitation energy without referring to the energy functional which is unknown for the TB-mBJ potential. For the HSE functional, we have developed a method for the operation of the Fock-like term in Fourier space to facilitate efficient use of massive parallel computers equipped with graphic processing units. We compare electronic excitations in silicon and germanium induced by femtosecond laser pulses using the TB-mBJ, HSE, and a simple local density approximation (LDA). At low laser intensities, electronic excitations are found to be sensitive to the band gap energy: they are close to each other using TB-mBJ and HSE and are much smaller in LDA. At high laser intensities close to the damage threshold, electronic excitation energies do not differ much among the three cases.
Efficient Density Functional Approximation for Electronic Properties of Conjugated Systems
Caldas, Marília J.; Pinheiro, José Maximiano, Jr.; Blum, Volker; Rinke, Patrick
2014-03-01
There is on-going discussion about reliable prediction of electronic properties of conjugated oligomers and polymers, such as ionization potential IP and energy gap. Several exchange-correlation (XC) functionals are being used by the density functional theory community, with different success for different properties. In this work we follow a recent proposal: a fraction α of exact exchange is added to the semi-local PBE XC aiming consistency, for a given property, with the results obtained by many-body perturbation theory within the G0W0 approximation. We focus the IP, taken as the negative of the highest occupied molecular orbital energy. We choose α from a study of the prototype family trans-acetylene, and apply this same α to a set of oligomers for which there is experimental data available (acenes, phenylenes and others). Our results indicate we can have excellent estimates, within 0,2eV mean ave. dev. from the experimental values, better than through complete EN - 1 -EN calculations from the starting PBE functional. We also obtain good estimates for the electrical gap and orbital energies close to the band edge. Work supported by FAPESP, CNPq, and CAPES, Brazil, and DAAD, Germany.
Energy Technology Data Exchange (ETDEWEB)
Mattsson, Ann Elisabet; Modine, Normand Arthur; Desjarlais, Michael Paul; Muller, Richard Partain; Sears, Mark P.; Wright, Alan Francis
2006-11-01
A finite temperature version of 'exact-exchange' density functional theory (EXX) has been implemented in Sandia's Socorro code. The method uses the optimized effective potential (OEP) formalism and an efficient gradient-based iterative minimization of the energy. The derivation of the gradient is based on the density matrix, simplifying the extension to finite temperatures. A stand-alone all-electron exact-exchange capability has been developed for testing exact exchange and compatible correlation functionals on small systems. Calculations of eigenvalues for the helium atom, beryllium atom, and the hydrogen molecule are reported, showing excellent agreement with highly converged quantumMonte Carlo calculations. Several approaches to the generation of pseudopotentials for use in EXX calculations have been examined and are discussed. The difficult problem of finding a correlation functional compatible with EXX has been studied and some initial findings are reported.
Medeiros, Subenia; Araujo, Maeva
2015-03-01
The structural, electronic, vibrational, and optical properties of perovskite CaTiO3 in the cubic, orthorhombic, and tetragonal phase are calculated in the framework of density functional theory (DFT) with different exchange-correlation potentials by CASTEP package. The calculated band structure shows an indirect band gap of 1.88 eV at the Γ-R points in the Brillouin zone to the cubic structure, a direct band gap of 2.41 eV at the Γ- Γ points to the orthorhombic structure, and an indirect band gap of 2.31 eV at theM - Γ points to the tetragonal phase. It is still known that the CaTiO3 has a static dielectric constant that extrapolates to a value greater than 300 at zero temperature, and the dielectric response is dominated by low frequency (ν ~ 90cm-1) polar optical modes in which cation motion opposes oxygen motion. Our calculated lattice parameters, elastic constants, optical properties, and vibrational frequencies are found to be in good agreement with the available theoretical and experimental values. The results for the effective mass in the electron and hole carriers are also presented in this work.
LDA+DCA calculations of cuprate superconductors
Kent, Paul; Macridin, Alexandru; Schulthess, Thomas; Krogh Andersen, Ole
2005-03-01
We present calculations of the properties of realistic models of single-layer cuprate superconductors. A multi-band Hubbard model is obtained from downfolded material specific local density approximation (LDA) density functional theory (DFT) calculations. The on-site U is obtained from constrained DFT calculations. The resulting model is solved using the dynamic cluster approximation (DCA) and quantum Monte Carlo, for small clusters. Some of us have previously shown that DCA calculations of the single band Hubbard model, with empirical parameters, reproduce key features of the experimental phase diagram, including the d-wave superconducting region and pseudogap. In the multi-band model, we find a superconducting region, and discuss how the computed transition temperature depends on the downfolded band structure. In model calculations, we test the sensitivity of the transition temperature to changes in the individual hopping terms, including the copper-oxygen and oxygen-oxygen hybridization. Work supported by the Division of Materials Science and Engineering, U.S. Department of Energy, under Contract DE-AC05-00OR22725 with UT-Battelle LLC.
Energy Technology Data Exchange (ETDEWEB)
Diez, Reinaldo Pis [CEQUINOR, Centro de Quimica Inorganica (CONICET, UNLP), Departamento de Quimica, Facultad de Ciencias Exactas, UNLP CC 962, B1900AVV La Plata (Argentina); Karasiev, Valentin V [Centro de Qimica, Instituto Venezolano de Investigaciones Cientificas, IVIC, Apartado 21827, Caracas 1020-A (Venezuela)
2003-07-14
A relationship between the auxiliary density, {rho}(r), defined within the framework of the weighted density approximation and the kinetic energy modulating factor, A{sub N}([{rho}(r)]; r), which appears in the local-scaling transformation version of density functional theory is presented. This relationship imposes the condition of positiveness on the kinetic energy modulating factor and this, in turn, leads to an important mathematical condition on any approximate kinetic energy density functional. It is shown that two well-known approximate kinetic energy density functionals do not satisfy the above relationship at distances very close to the nucleus. By forcing a given approximate kinetic energy density functional to obey the above condition, both the kinetic and exchange energies can be obtained within a framework similar to that of the weighted density approximation. Results on some closed-shell atomic systems provide support for those ideas.
Energy Technology Data Exchange (ETDEWEB)
Benam, M.R., E-mail: m_benam@pnu.ac.ir [Department of Physics, Payame Noor University, P.O. BOX 19395-3697 (Iran, Islamic Republic of); Abdoshahi, N.; Majidiyan Sarmazdeh, M. [Department of Physics, Payame Noor University, P.O. BOX 19395-3697 (Iran, Islamic Republic of)
2014-08-01
In this paper the effect of pressure on the structural and electronic properties of cubic-LaAlO{sub 3} including the equilibrium lattice constant, bulk modulus, derivative of bulk modulus and band structure have been calculated by density functional theory (DFT) using GGA, LDA, and PBEsol exchange correlation potentials. It is found that the change of the lattice constant with pressure has an exponential behavior: with increasing pressure, the lattice constant decreases first sharply at low pressures, and then more slowly at high pressures. Furthermore, the lattice constant calculated by the PBEsol method and the bulk modulus calculated by LDA and PBEsol methods are closer to the available experimental values than those obtained using other exchange correlation potentials. Regarding the electronic properties, it is shown that an increase in pressure increases the band gap, the change being 0.26 eV at 34.00 GPa. The total density of state (t-DOS) calculations demonstrate that increasing pressure has a significant effect on the core and conduction band, but little effect on the valence band. The band structure calculations indicate that, in this material, the band gap changes from indirect to direct at a pressure of about 25 GPa. Also, increasing pressure produces a clear curvature in the band structure near the bottom of the conduction band, a behavior consistent with the strong pressure dependence of the transport properties.
Benam, M. R.; Abdoshahi, N.; Majidiyan Sarmazdeh, M.
2014-08-01
In this paper the effect of pressure on the structural and electronic properties of cubic-LaAlO3 including the equilibrium lattice constant, bulk modulus, derivative of bulk modulus and band structure have been calculated by density functional theory (DFT) using GGA, LDA, and PBEsol exchange correlation potentials. It is found that the change of the lattice constant with pressure has an exponential behavior: with increasing pressure, the lattice constant decreases first sharply at low pressures, and then more slowly at high pressures. Furthermore, the lattice constant calculated by the PBEsol method and the bulk modulus calculated by LDA and PBEsol methods are closer to the available experimental values than those obtained using other exchange correlation potentials. Regarding the electronic properties, it is shown that an increase in pressure increases the band gap, the change being 0.26 eV at 34.00 GPa. The total density of state (t-DOS) calculations demonstrate that increasing pressure has a significant effect on the core and conduction band, but little effect on the valence band. The band structure calculations indicate that, in this material, the band gap changes from indirect to direct at a pressure of about 25 GPa. Also, increasing pressure produces a clear curvature in the band structure near the bottom of the conduction band, a behavior consistent with the strong pressure dependence of the transport properties.
DEFF Research Database (Denmark)
Olsen, Thomas; Thygesen, Kristian S.
2012-01-01
while chemical bond strengths and absolute correlation energies are systematically underestimated. In this work we extend the RPA by including a parameter-free renormalized version of the adiabatic local-density (ALDA) exchange-correlation kernel. The renormalization consists of a (local) truncation...... of the ALDA kernel for wave vectors q > 2kF, which is found to yield excellent results for the homogeneous electron gas. In addition, the kernel significantly improves both the absolute correlation energies and atomization energies of small molecules over RPA and ALDA. The renormalization can...
The Actinide Transition Revisited by Gutzwiller Approximation
Xu, Wenhu; Lanata, Nicola; Yao, Yongxin; Kotliar, Gabriel
2015-03-01
We revisit the problem of the actinide transition using the Gutzwiller approximation (GA) in combination with the local density approximation (LDA). In particular, we compute the equilibrium volumes of the actinide series and reproduce the abrupt change of density found experimentally near plutonium as a function of the atomic number. We discuss how this behavior relates with the electron correlations in the 5 f states, the lattice structure, and the spin-orbit interaction. Our results are in good agreement with the experiments.
Constrained Parmeterization of Reduced Density Approximation of Kinetic Energy Functionals
Chakraborty, Debajit; Trickey, Samuel; Karasiev, Valentin
2014-03-01
Evaluation of forces in ab initio MD is greatly accelerated by orbital-free DFT, especially at finite temperature. The recent achievement of a fully non-empirical constraint-based generalized gradient (GGA) functional for the Kohn-Sham KE Ts [ n ] brings to light the inherent limitations of GGAs. This motivates inclusion of higher-order derivatives in the form of reduced derivative approximation (RDA) functionals. That, in turn, requires new functional forms and design criteria. RDA functionals are constrained further to produce a positive-definite, non-singular Pauli potential. We focus on designing a non-empirical constraint-based meta-GGA functional with certain combinations of higher-order derivatives which avoid nuclear-site singularities to a specified order of gradient expansion. Here we report progress on this agenda. Work supported by U.S. Dept. of Energy, grant DE-SC0002139.
Obodo, K. O.; Chetty, N.
2013-04-01
The electronic structure and properties of protactinium and its oxides (PaO and PaO2) have been studied within the framework of the local density approximation (LDA), the Perdew-Burke-Ernzerhof generalized gradient approximation [GGA(PBE)], LDA + U and GGA(PBE) + U implementations of density functional theory. The dependence of selected observables of these materials on the effective U parameter has been investigated in detail. The examined properties include lattice constants, bulk moduli, the effect of charge density distributions, the hybridization of the 5f orbital and the energy of formation for PaO and PaO2. The LDA gives better agreement with experiment for the bulk modulus than the GGA for Pa but the GGA gives better structural properties. We found that PaO is metallic and PaO2 is a Mott-Hubbard insulator. This is consistent with observations for the other actinide oxides. We discover that GGA and LDA incorrectly give metallic behavior for PaO2. The GGA(PBE) + U calculated indirect band gap of 3.48 eV reported for PaO2 is a prediction and should stimulate further studies of this material.
Bandstructure meets many-body theory: the LDA+DMFT method
Energy Technology Data Exchange (ETDEWEB)
Held, K [Max-Planck Institut fuer Festkoerperforschung, D-70569 Stuttgart (Germany); Andersen, O K [Max-Planck Institut fuer Festkoerperforschung, D-70569 Stuttgart (Germany); Feldbacher, M [Max-Planck Institut fuer Festkoerperforschung, D-70569 Stuttgart (Germany); Yamasaki, A [Max-Planck Institut fuer Festkoerperforschung, D-70569 Stuttgart (Germany); Yang, Y-F [Max-Planck Institut fuer Festkoerperforschung, D-70569 Stuttgart (Germany)
2008-02-13
Ab initio calculation of the electronic properties of materials is a major challenge for solid-state theory. Whereas 40 years' experience has proven density-functional theory (DFT) in a suitable form, e.g. local approximation (LDA), to give a satisfactory description when electronic correlations are weak, materials with strongly correlated electrons, say d- or f-electrons, remain a challenge. Such materials often exhibit 'colossal' responses to small changes of external parameters such as pressure, temperature, and magnetic field, and are therefore most interesting for technical applications. Encouraged by the success of dynamical mean-field theory (DMFT) in dealing with model Hamiltonians for strongly correlated electron systems, physicists from the bandstructure and many-body communities have joined forces and developed a combined LDA+DMFT method for treating materials with strongly correlated electrons ab initio. As a function of increasing Coulomb correlations, this new approach yields a weakly correlated metal, a strongly correlated metal, or a Mott insulator. In this paper, we introduce the LDA+DMFT method by means of an example, LaMnO{sub 3}. Results for this material, including the 'colossal' magnetoresistance of doped manganites, are presented. We also discuss the advantages and disadvantages of the LDA+DMFT approach.
Bandstructure meets many-body theory: the LDA+DMFT method.
Held, K; Andersen, O K; Feldbacher, M; Yamasaki, A; Yang, Y-F
2008-02-13
Ab initio calculation of the electronic properties of materials is a major challenge for solid-state theory. Whereas 40 years' experience has proven density-functional theory (DFT) in a suitable form, e.g. local approximation (LDA), to give a satisfactory description when electronic correlations are weak, materials with strongly correlated electrons, say d- or f-electrons, remain a challenge. Such materials often exhibit 'colossal' responses to small changes of external parameters such as pressure, temperature, and magnetic field, and are therefore most interesting for technical applications. Encouraged by the success of dynamical mean-field theory (DMFT) in dealing with model Hamiltonians for strongly correlated electron systems, physicists from the bandstructure and many-body communities have joined forces and developed a combined LDA+DMFT method for treating materials with strongly correlated electrons ab initio. As a function of increasing Coulomb correlations, this new approach yields a weakly correlated metal, a strongly correlated metal, or a Mott insulator. In this paper, we introduce the LDA+DMFT method by means of an example, LaMnO(3). Results for this material, including the 'colossal' magnetoresistance of doped manganites, are presented. We also discuss the advantages and disadvantages of the LDA+DMFT approach.
Investigation of real materials with strong electronic correlations by the LDA+DMFT method.
Anisimov, V I; Lukoyanov, A V
2014-02-01
Materials with strong electronic correlations are at the cutting edge of experimental and theoretical studies, capturing the attention of researchers for a great variety of interesting phenomena: metal-insulator, phase and magnetic spin transitions, `heavy fermion' systems, interplay between magnetic order and superconductivity, appearance and disappearance of local magnetic moments, and transport property anomalies. It is clear that the richness of physical phenomena for these compounds is a result of partially filled 3d, 4f or 5f electron shells with local magnetic moments preserved in the solid state. Strong interactions of d and f electrons with each other and with itinerant electronic states of the material are responsible for its anomalous properties. Electronic structure calculations for strongly correlated materials should explicitly take into account Coulombic interactions between d or f electrons. Recent advances in this field are related to the development of the LDA+DMFT method, which combines local density approximation (LDA) with dynamical mean-field theory (DMFT) to account for electronic correlation effects. In recent years, LDA+DMFT has allowed the successful treatment not only of simple systems but also of complicated real compounds. Nowadays, the LDA+DMFT method is the state-of-the-art tool for investigating correlated metals and insulators, spin and metal-insulator transitions (MIT) in transition-metal compounds in paramagnetic and magnetically ordered phases.
Comparing LDA-1/2, HSE03, HSE06 and G₀W₀ approaches for band gap calculations of alloys.
Pela, R R; Marques, M; Teles, L K
2015-12-23
It has long been known that the local density approximation and the generalized gradient approximation do not furnish reliable band gaps, and one needs to go beyond these approximations to reliably describe these properties. Among alternatives are the use of hybrid functionals (HSE03 and HSE06 being popular), the GW approximation or the recently proposed LDA-1/2 method. In this work, we compare rigorously the performance of these four methods in describing the band gaps of alloys, employing the generalized quasi-chemical approach to treat the disorder of the alloy and to obtain judiciously the band gap for the entire compositional range. Zincblende InGaAs and InGaN were chosen as prototypes due to their importance in optoelectronic applications. The comparison between these four approaches was guided both by the agreement between the predicted band gap and the experimental one, and by the demanded computational effort (time and memory). We observed that the HSE06 method provided the most accurate results (in comparison with experiments), whereas, surprisingly, the LDA-1/2 method gave the best compromise between accuracy and computational resources. Due to its low computational cost and good accuracy, we decided to double the supercell used to describe the alloys, and employing LDA-1/2 we observed that the bowing parameter changed remarkably, only agreeing with the measured one for the larger supercell, where LDA-1/2 plays an important role.
Moskvin, A. S.
2016-10-01
I present a critical overview of so-called "ab initio" DFT (density fuctional theory) based calculation schemes for the description of the electronic structure, energy spectrum, and optical response for strongly correlated 3 d oxides, in particular, crystal-field and charge transfer transitions as compared with an "old" cluster model that does generalize crystal-field and ligand-field theory. As a most instructive illustration of validity of numerous calculation techniques I address the prototypical 3 d insulator NiO predicted to be a metal in frames of a standard LDA (local density approximation) band theory.
Energy Technology Data Exchange (ETDEWEB)
Gazhulina, A.P., E-mail: asyagazhulina@yandex.ru; Marychev, M.O.
2015-02-25
Highlights: • We consider 111 compounds of B3 and B20 types by FP-LAPW method using LDA, GGA, mBJ. • Structural, electronic and nonlinear optical properties were investigated. • Some data calculated for the first time for a large part of considered compounds. • NLO properties considered in relation with pseudoinversion for all 111 crystals. - Abstract: The structural, electronic, and nonlinear optical properties of 111 crystals belonging to structural types B3 (84 crystals) and B20 (27 crystals) have been investigated by first-principles calculations using the full-potential linearized augmented plane wave (FP-LAPW) method in the framework of density functional theory. Calculations of the electronic band structure and nonlinear optical properties were performed using local-density approximation (LDA), generalized gradient approximation (GGA), and a combination of modified Becke—Johnson exchange potential plus LDA (mBJ + LDA) for exchange–correlation potential. Equilibrium lattice constant a{sub 0}, bulk modulus B{sub 0}, first pressure derivative B′ of the bulk modulus, band gaps E{sub g}, and second-order nonlinear susceptibility tensor components |χ{sub 123}| at 0 eV and at 1.064 and 10.6 μm wavelengths are presented. The obtained results are compared to available experimental and theoretical (computational) data. A correlation between the |χ{sub 123}| tensor component data arrays and the distributions of crystal structures with respect to their degree of pseudoinversion is analyzed.
Zheng, Zhong; Hämäläinen, Jyri; Tirkkonen, Olav
2012-01-01
We derive a closed-form expression for the orthogonal polynomials associated with the general lognormal density. The result can be utilized to construct easily computable approximations for probability density function of a product of random variables. As an example, we have calculated the approximative distribution for the product of correlated Nakagami-m variables. Simulations indicate that accuracy of the proposed approximation is good.
Thermodynamics of the α -γ transition in cerium studied by an LDA + Gutzwiller method
Tian, Ming-Feng; Song, Hai-Feng; Liu, Hai-Feng; Wang, Cong; Fang, Zhong; Dai, Xi
2015-03-01
Utilizing the local-density approximation (LDA) + Gutzwiller method, we have studied the α -γ transition in cerium. Our results indicate that the volume collapse transition between α and γ phases is present at zero temperature with negative pressure. By further providing a newly finite temperature generalization of the LDA + Gutzwiller method (using the mean-field potential approach), the entropy contributed by both electronic quasiparticles and lattice vibration included, we obtain the Gibbs free energy at a given volume and temperature, from which we get the α -γ transition at finite temperature and pressure. Our results indicate that the electronic entropy and lattice vibrational entropy both play important roles in the α -γ transition. We also calculated the equation of state and phase diagram of cerium, finding good agreement with the experiments.
DFT calculations of electronic and optical properties of SrS with LDA, GGA and mGGA functionals
Sharma, Shatendra; Sharma, Jyotsna; Sharma, Yogita
2016-05-01
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.
The LDA+U calculation of electronic band structure of GaAs
Bahuguna, B. P.; Sharma, R. O.; Saini, L. K.
2016-05-01
We present the electronic band structure of bulk gallium arsenide (GaAs) using first principle approach. A series of calculations has been performed by applying norm-conserving pseudopotentials and ultrasoft non-norm-conserving pseudopotentials within the density functional theory. These calculations yield too small band gap as compare to experiment. Thus, we use semiemperical approach called local density approximation plus the multi-orbital mean-field Hubbard model (LDA+U), which is quite effective in order to describe the band gap of GaAs.
High-Pressure Behaviour of β-HMX Crystal Studied by DFT-LDA
Institute of Scientific and Technical Information of China (English)
LIAN Dan; LU Lai-Yu; WEI Dong-Qing; ZHANG Qing-Ming; GONG Zi-Zheng; GUO Yong-Xin
2008-01-01
@@ Density functional theory (DFT) with local density approximation (LDA) is employed to study the structural and electronic properties of the high explosive octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) under high pressure compression up to 40 GPa.Pressure dependences of the cell volume,lattice constants,and molecular geometry of solid β-HMX are presented and discussed.It is found that N-N and N-C bonds are subject to significant change.
Reshak, Ali H; Auluck, S; Kityk, I V
2009-02-26
We have performed ab inito theoretical calculations of the electronic structure and the linear and nonlinear optical susceptibilities for calcium neodymium oxyborate Ca4NdO(BO3)3 using two approximations for the exchange correlation (XC) potentials, the local density approximation (LDA) and the generalized gradient approximation (GGA). Our calculations show that this compound is metallic-like, with density of states at the Fermi energy E(F), N(E(F)), of 5.95 and 10.33 states/Ry-cell or bare electronic specific heat coefficients of 1.03 and 1.79 mJ/mol-K2 for LDA and GGA, respectively. The overlap between the valence and conduction bands is strong, resulting in metallic behavior. We found that Nd-s/p/d, Ca-s/p, B-p, and O-s/p states controlled the overlapping around E(F). The effect of LDA and GGA on the band structure, density of states, and linear optical properties is very small, while for the nonlinear optical properties, it is very pronounced. Our calculations show that χ(111)(2)(ω) is the dominant component for both LDA and GGA. We find opposite signs of the contributions of the 2ω and 1ω inter/intraband to the real and imaginary parts for the dominant component throughout the wide optical frequency range.
Yang, Weitao; Mori-Sánchez, Paula; Cohen, Aron J
2013-09-14
The exact conditions for density functionals and density matrix functionals in terms of fractional charges and fractional spins are known, and their violation in commonly used functionals has been shown to be the root of many major failures in practical applications. However, approximate functionals are designed for physical systems with integer charges and spins, not in terms of the fractional variables. Here we develop a general framework for extending approximate density functionals and many-electron theory to fractional-charge and fractional-spin systems. Our development allows for the fractional extension of any approximate theory that is a functional of G(0), the one-electron Green's function of the non-interacting reference system. The extension to fractional charge and fractional spin systems is based on the ensemble average of the basic variable, G(0). We demonstrate the fractional extension for the following theories: (1) any explicit functional of the one-electron density, such as the local density approximation and generalized gradient approximations; (2) any explicit functional of the one-electron density matrix of the non-interacting reference system, such as the exact exchange functional (or Hartree-Fock theory) and hybrid functionals; (3) many-body perturbation theory; and (4) random-phase approximations. A general rule for such an extension has also been derived through scaling the orbitals and should be useful for functionals where the link to the Green's function is not obvious. The development thus enables the examination of approximate theories against known exact conditions on the fractional variables and the analysis of their failures in chemical and physical applications in terms of violations of exact conditions of the energy functionals. The present work should facilitate the calculation of chemical potentials and fundamental bandgaps with approximate functionals and many-electron theories through the energy derivatives with respect to the
Directory of Open Access Journals (Sweden)
Yan-Xia Lin
2015-12-01
Full Text Available Lin (2014 developed a framework of the method of the sample-moment-based density approximant, for estimating the probability density function of microdata based on noise multiplied data. Theoretically, it provides a promising method for data users in generating the synthetic data of the original data without accessing the original data; however, technical issues can cause problems implementing the method. In this paper, we describe a software package called MaskDensity14, written in the R language, that uses a computational approach to solve the technical issues and makes the method of the sample-moment-based density approximant feasible. MaskDensity14 has applications in many areas, such as sharing clinical trial data and survey data without releasing the original data.
Directory of Open Access Journals (Sweden)
Slavica Jonić
2016-01-01
Full Text Available Three-dimensional Gaussian functions have been shown useful in representing electron microscopy (EM density maps for studying macromolecular structure and dynamics. Methods that require setting a desired number of Gaussian functions or a maximum number of iterations may result in suboptimal representations of the structure. An alternative is to set a desired error of approximation of the given EM map and then optimize the number of Gaussian functions to achieve this approximation error. In this article, we review different applications of such an approach that uses spherical Gaussian functions of fixed standard deviation, referred to as pseudoatoms. Some of these applications use EM-map normal mode analysis (NMA with elastic network model (ENM (applications such as predicting conformational changes of macromolecular complexes or exploring actual conformational changes by normal-mode-based analysis of experimental data while some other do not use NMA (denoising of EM density maps. In applications based on NMA and ENM, the advantage of using pseudoatoms in EM-map coarse-grain models is that the ENM springs are easily assigned among neighboring grains thanks to their spherical shape and uniformed size. EM-map denoising based on the map coarse-graining was so far only shown using pseudoatoms as grains.
Specification of Density Functional Approximation by Radial Distribution Function of Bulk Fluid
Institute of Scientific and Technical Information of China (English)
ZHOUShi－Qi
2002-01-01
A systematic methodology is proposed to deal with the weighted density approximation version of classical density functional theory by employing the knowledge of radial distribution function of bulk fluid.The present methodology results from the concept of universality of the free energy density functional combined with the test particle method.It is shown that the new method is very accurate for the predictions of density distribution of a hard sphere fluid at different confining geometries.The physical foundation of the present methodology is also applied to the quantum density functional theory.
Velders, G.J.M.; Feil, D.
1989-01-01
Quantum-chemical density-functional theory (DFT) calculations, using the local-density approximation (LDA), have been performed for hydrogen-bounded silicon clusters to determine the electron density distribution of the Si-Si bond. The density distribution in the bonding region is compared with calc
Tuning LDA+U for electron localization and structure at oxygen vacancies in ceria.
Castleton, C W M; Kullgren, J; Hermansson, K
2007-12-28
We examine the real space structure and the electronic structure (particularly Ce4f electron localization) of oxygen vacancies in CeO(2) (ceria) as a function of U in density functional theory studies with the rotationally invariant forms of the LDA+U and GGA+U functionals. The four nearest neighbor Ce ions always relax outwards, with those not carrying localized Ce4f charge moving furthest. Several quantification schemes show that the charge starts to become localized at U approximately 3 eV and that the degree of localization reaches a maximum at approximately 6 eV for LDA+U or at approximately 5.5 eV for GGA+U. For higher U it decreases rapidly as charge is transferred onto second neighbor O ions and beyond. The localization is never into atomic corelike states; at maximum localization about 80-90% of the Ce4f charge is located on the two nearest neighboring Ce ions. However, if we look at the total atomic charge we find that the two ions only make a net gain of (0.2-0.4)e each, so localization is actually very incomplete, with localization of Ce4f electrons coming at the expense of moving other electrons off the Ce ions. We have also revisited some properties of defect-free ceria and find that with LDA+U the crystal structure is actually best described with U=3-4 eV, while the experimental band structure is obtained with U=7-8 eV. (For GGA+U the lattice parameters worsen for U>0 eV, but the band structure is similar to LDA+U.) The best overall choice is U approximately 6 eV with LDA+U and approximately 5.5 eV for GGA+U, since the localization is most important, but a consistent choice for both CeO(2) and Ce(2)O(3), with and without vacancies, is hard to find.
U(1 )×SU (2 ) gauge invariance made simple for density functional approximations
Pittalis, S.; Vignale, G.; Eich, F. G.
2017-07-01
A semirelativistic density-functional theory that includes spin-orbit couplings and Zeeman fields on equal footing with the electromagnetic potentials, is an appealing framework to develop a unified first-principles computational approach for noncollinear magnetism, spintronics, orbitronics, and topological states. The basic variables of this theory include the paramagnetic current and the spin-current density, besides the particle and the spin density, and the corresponding exchange-correlation (xc) energy functional is invariant under local U (1 )×SU (2 ) gauge transformations. The xc-energy functional must be approximated to enable practical applications, but, contrary to the case of the standard density functional theory, finding simple approximations suited to deal with realistic atomistic inhomogeneities has been a long-standing challenge. Here we propose a way out of this impasse by showing that approximate gauge-invariant functionals can be easily generated from existing approximate functionals of ordinary density-functional theory by applying a simple minimal substitution on the kinetic energy density, which controls the short-range behavior of the exchange hole. Our proposal opens the way to the construction of approximate, yet nonempirical functionals, which do not assume weak inhomogeneity and therefore may have a wide range of applicability in atomic, molecular, and condensed matter physics.
Energy Technology Data Exchange (ETDEWEB)
Perez-Navarro, A.; Costa-Quintana, J.; Lopez-Aguilar, F. [Groupe d' Electromagnetisme, Departament de Fisica, Edifici Cn, Facultat de Ciencies, Universitat Autonoma de Barcelona, 08193 Bellaterra (Barcelona) (Spain)
2002-09-08
In this paper we present a method for obtaining the quasiband structure and the renormalized density of quasistates of strongly correlated systems with antiferromagnetic ordering. We calculate the electronic structure of La{sub 2}CuO{sub 4} in order to test this method. The first step required is to calculate the electronic structure from the local density approximation (LDA) in order to obtain the initial non-interacting ground state. The LDA density of states in strongly correlated systems usually presents serious discrepancies with experimental results. As is well known, these discrepancies, fundamentally concerning photoemission, are due to the fact that the dynamic correlation effects are not taken into account within the LDA. In order to include these effects, we obtain a self-energy potential which allows the initial LDA electronic structure to connect with that of the antiferromagnetic ground state arising from a Bogolyubov-like transformation. Within this new ground state, we determine an antiferromagnetic self-energy by means of a spin density wave procedure, and the interacting Green function yields a density of states which is in reasonable agreement with the experimental photoemission result. (Abstract Copyright [2002], Wiley Periodicals, Inc.)
Structural and electronic properties of cerium from LDA+U calculations
Directory of Open Access Journals (Sweden)
F. Kheradmand
2008-12-01
Full Text Available In this work structural, electronic and magnetic properties of alpha and gamma phases of cerium crystal have been calculated by means of the LDA and LDA+U methods. The equilibrium volume and magnetic moment obtained from the GGA approximation in agreement with the experiment are equal to 27.64 Å3 and 0.00018 µB, respectively. This agreement shows that the 4f electrons in alpha phase are itinerant due to the use of the GGA, where no strong correlations have been yet thaken into account. We have observed that even after applying the GGA+U method with U = 6.1 eV, the density of states of f orbital remains still at Fermi surface. Therefore, in complete accord with the experiment, our results show that the 4f electrons in the alpha phase are not localized. This is the case where the LDA and the GGA approximations could not describe the gamma phase properly. Indeed, physical properties of the gamma phase is consistent with the experiment and could only be reproduced after applying LDA+U method with U = 4.4 eV. In this way, the value of equilibrium volume and magnetic moment calculated for the gamma phase were found to be 34.33 Å3 and 1.15 µB, respectively. After including correlations among 4f electrons the γ-Ce DOS is positioned at its more reasonable place lower than Fermi level compared with the DOS obtained from GGA calculations. Our results, then, show that the 4f electrons in the gamma phase, as opposed to the alpha phase, are localized which is indicative of the fact that gamma cerium is a strongly correlated system. The volume of 11 kbar has been obtained for the pressure of the alpha-gamma phase transition .
Adiabatic approximation of time-dependent density matrix functional response theory.
Pernal, Katarzyna; Giesbertz, Klaas; Gritsenko, Oleg; Baerends, Evert Jan
2007-12-07
Time-dependent density matrix functional theory can be formulated in terms of coupled-perturbed response equations, in which a coupling matrix K(omega) features, analogous to the well-known time-dependent density functional theory (TDDFT) case. An adiabatic approximation is needed to solve these equations, but the adiabatic approximation is much more critical since there is not a good "zero order" as in TDDFT, in which the virtual-occupied Kohn-Sham orbital energy differences serve this purpose. We discuss a simple approximation proposed earlier which uses only results from static calculations, called the static approximation (SA), and show that it is deficient, since it leads to zero response of the natural orbital occupation numbers. This leads to wrong behavior in the omega-->0 limit. An improved adiabatic approximation (AA) is formulated. The two-electron system affords a derivation of exact coupled-perturbed equations for the density matrix response, permitting analytical comparison of the adiabatic approximation with the exact equations. For the two-electron system also, the exact density matrix functional (2-matrix in terms of 1-matrix) is known, enabling testing of the static and adiabatic approximations unobscured by approximations in the functional. The two-electron HeH(+) molecule shows that at the equilibrium distance, SA consistently underestimates the frequency-dependent polarizability alpha(omega), the adiabatic TDDFT overestimates alpha(omega), while AA improves upon SA and, indeed, AA produces the correct alpha(0). For stretched HeH(+), adiabatic density matrix functional theory corrects the too low first excitation energy and overpolarization of adiabatic TDDFT methods and exhibits excellent agreement with high-quality CCSD ("exact") results over a large omega range.
Comparing LDA-1/2, HSE03, HSE06 and G 0 W 0 approaches for band gap calculations of alloys
Pela, R. R.; Marques, M.; Teles, L. K.
2015-12-01
It has long been known that the local density approximation and the generalized gradient approximation do not furnish reliable band gaps, and one needs to go beyond these approximations to reliably describe these properties. Among alternatives are the use of hybrid functionals (HSE03 and HSE06 being popular), the GW approximation or the recently proposed LDA-1/2 method. In this work, we compare rigorously the performance of these four methods in describing the band gaps of alloys, employing the generalized quasi-chemical approach to treat the disorder of the alloy and to obtain judiciously the band gap for the entire compositional range. Zincblende InGaAs and InGaN were chosen as prototypes due to their importance in optoelectronic applications. The comparison between these four approaches was guided both by the agreement between the predicted band gap and the experimental one, and by the demanded computational effort (time and memory). We observed that the HSE06 method provided the most accurate results (in comparison with experiments), whereas, surprisingly, the LDA-1/2 method gave the best compromise between accuracy and computational resources. Due to its low computational cost and good accuracy, we decided to double the supercell used to describe the alloys, and employing LDA-1/2 we observed that the bowing parameter changed remarkably, only agreeing with the measured one for the larger supercell, where LDA-1/2 plays an important role.
Specification of Density Functional Approximation by Radial Distribution Function of Bulk Fluid
Institute of Scientific and Technical Information of China (English)
ZHOU Shi-Qi
2002-01-01
A systematic methodology is proposed to deal with the weighted density approximation version of clas-sical density functional theory by employing the knowledge of radial distribution function of bulk fluid. The presentmethodology results from the concept of universality of the free energy density functional combined with the test particlemethod. It is shown that the new method is very accurate for the predictions of density distribution ofa hard sphere fluidat different confining geometries. The physical foundation of the present methodology is also applied to the quantumdensity functional theory.
Intermolecular interaction potentials of methane-argon complex calculated using LDA approaches
Institute of Scientific and Technical Information of China (English)
Bai Yu-Lin; Chen Xiang-Rong; Zhou Xiao-Lin; Yang Xiang-Dong; Wang Hai-Yan
2004-01-01
The intermolecular interaction potential for methane-argon complex is calculated by local density approximation (LDA) approaches. The calculated potential has a minimum when the intermolecular distance of methane-argon complex is 6.75 a.u.; the corresponding depth of the potential is 0.0163eV which has good agreement with experimental data. We also have made a nonlinear fitting of our results for the Lennard-Jones (12-6) potential function and obtain that V(R) = 143794365.332/R12 - 3032.093/R6 (R in a.u. and V(R) in eV).
Toulouse, Julien; Angyan, Janos G; Savin, Andreas
2010-01-01
Using Green-function many-body theory, we present the details of a formally exact adiabatic-connection fluctuation-dissipation density-functional theory based on range separation, which was sketched in Toulouse, Gerber, Jansen, Savin and Angyan, Phys. Rev. Lett. 102, 096404 (2009). Range-separated density-functional theory approaches combining short-range density functional approximations with long-range random phase approximations (RPA) are then obtained as well-identified approximations on the long-range Green-function self-energy. Range-separated RPA-type schemes with or without long-range Hartree-Fock exchange response kernel are assessed on rare-gas and alkaline-earth dimers, and compared to range-separated second-order perturbation theory and range-separated coupled-cluster theory.
Second Approximation Model for Optical Head in Super High Density Storage Technology
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The paper presents second approximation model for optical head in super high-density storage technology firstly and it is an important part for three grades approximate model of ultra-small-size quantum well corn-shaped laser and simulative calculations. It supplies the important and useful results for the NFOD optical head design with ultra thin active layer and ultra small spot laser.
GGA and LDA + U calculations of Pu phases
Energy Technology Data Exchange (ETDEWEB)
Bouchet, J. [CEA-DAM, Departement de Physique Theorique et Appliquee, Bruyeres-le-Chatel (France)], E-mail: johann.bouchet@cea.fr; Albers, R.C. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Jomard, G. [CEA-DAM, Departement de Physique Theorique et Appliquee, Bruyeres-le-Chatel (France)
2007-10-11
The effect of correlations in Pu are studied using GGA and LDA + U. We have used the simplicity of an approximate {alpha} phase structure, which we call a pseudo structure, to understand the main differences between low and high temperatures phases of Pu. Our results show the importance of the local atomic environment.
Graphene on metals: A van der Waals density functional study
DEFF Research Database (Denmark)
Vanin, Marco; Mortensen, Jens Jørgen; Kelkkanen, Kari André;
2010-01-01
We use density functional theory (DFT) with a recently developed van der Waals density functional (vdW-DF) to study the adsorption of graphene on Co, Ni, Pd, Ag, Au, Cu, Pt, and Al(111) surfaces. In contrast to the local-density approximation (LDA) which predicts relatively strong binding for Ni...
Directory of Open Access Journals (Sweden)
D. K. Narvilkar
1979-07-01
Full Text Available In the present paper, the equations of internal ballistics of composite charge consisting of N component charge with quadratic form are solved. Largange density approximation and hydrodynamic flow behaviour, have been assumed and the solutions are obtained for the composite charge for these assumptions.
Bridge density functional approximation for non-uniform hard core repulsive Yukawa fluid
Institute of Scientific and Technical Information of China (English)
Zhou Shi-Qi
2008-01-01
In this work,a bridge density functional approximation(BDFA)(J.Chem.Phys.112,8079(2000))for a non-uniform hard-sphere fluid is extended to a non-uniform hard-core repulsive Yukawa(HCRY)fluid.It is found that the choice of a bulk bridge functional approximation is crucial for both a uniform HCRY fluid and a non-uniform HCRY fluid.A new bridge functional approximation is proposed,which can accurately predict the radial distribution function of the bulk HCRY fluid.With the new bridge functional approximation and its associated bulk second order direct correlation function as input,the BDFA can be used to well calculate the density profile of the HCRY fluid subjected to the influence of varying external fields,and the theoretical predictions are in good agreement with the corresponding simulation data.The calculated results indicate that the present BDFA captures quantitatively the phenomena such as the coexistence of solid-like high density phase and low density gas phase,and the adsorption properties of the HCRY fluid,which qualitatively differ from those of the fluids combining both hard-core repulsion and an attractive tail.
Two-component hybrid time-dependent density functional theory within the Tamm-Dancoff approximation
Energy Technology Data Exchange (ETDEWEB)
Kühn, Michael [Institut für Physikalische Chemie, Karlsruher Institut für Technologie, Kaiserstraße 12, 76131 Karlsruhe (Germany); Weigend, Florian, E-mail: florian.weigend@kit.edu [Institut für Physikalische Chemie, Karlsruher Institut für Technologie, Kaiserstraße 12, 76131 Karlsruhe (Germany); Institut für Nanotechnologie, Karlsruher Institut für Technologie, Postfach 3640, 76021 Karlsruhe (Germany)
2015-01-21
We report the implementation of a two-component variant of time-dependent density functional theory (TDDFT) for hybrid functionals that accounts for spin-orbit effects within the Tamm-Dancoff approximation (TDA) for closed-shell systems. The influence of the admixture of Hartree-Fock exchange on excitation energies is investigated for several atoms and diatomic molecules by comparison to numbers for pure density functionals obtained previously [M. Kühn and F. Weigend, J. Chem. Theory Comput. 9, 5341 (2013)]. It is further related to changes upon switching to the local density approximation or using the full TDDFT formalism instead of TDA. Efficiency is demonstrated for a comparably large system, Ir(ppy){sub 3} (61 atoms, 1501 basis functions, lowest 10 excited states), which is a prototype molecule for organic light-emitting diodes, due to its “spin-forbidden” triplet-singlet transition.
LDA +U calculation of electronic and thermoelectric properties of doped CuCoO 2
Knížek, K.
2015-02-01
Doped CuCoO2 is a candidate oxide material for thermoelectric power generation. The evolution of the band structure and thermoelectric properties of CuCoO2 upon hole and electron doping in the CoO2 layer and hole doping at the Cu site were calculated by the local-density approximation (LDA) and LDA +U methods and using standard Boltzmann theory. The doping was simulated by the virtual atom approximation and the supercell approach and the results were compared with previous calculations using the rigid band approximation. The calculated thermopowers are comparable for the virtual atom and rigid band approximations, but the thermopower obtained from the supercell calculation is significantly lower. The reason is the similar energy of Co and Cu d orbitals and the hybridization of symmetrically related Co a1 g and Cu dz2 orbitals. As a consequence, both cations contribute to the bands around the Fermi level and hence a substitution at any of the cation sites alters the band structure at EF and affects the thermoelectric properties. Our results show that in the case of hole doping, higher thermopower is obtained for substitution at the Cu site than in the CoO2 layer.
Yaakob, M. K.; Taib, M. F. M.; Lu, L.; Hassan, O. H.; Yahya, M. Z. A.
2015-11-01
The structural, electronic, elastic, and optical properties of BiFeO3 were investigated using the first-principles calculation based on the local density approximation plus U (LDA + U) method in the frame of plane-wave pseudopotential density functional theory. The application of self-interaction corrected LDA + U method improved the accuracy of the calculated properties. Results of structural, electronic, elastic, and optical properties of BiFeO3, calculated using the LDA + U method were in good agreement with other calculation and experimental data; the optimized choice of on-site Coulomb repulsion U was 3 eV for the treatment of strong electronic localized Fe 3d electrons. Based on the calculated band structure and density of states, the on-site Coulomb repulsion U had a significant effect on the hybridized O 2p and Fe 3d states at the valence and the conduction band. Moreover, the elastic stiffness tensor, the longitudinal and shear wave velocities, bulk modulus, Poisson’s ratio, and the Debye temperature were calculated for U = 0, 3, and 6 eV. The elastic stiffness tensor, bulk modulus, sound velocities, and Debye temperature of BiFeO3 consistently decreased with the increase of the U value.
A charge self-consistent LDA+DMFT study of the spectral properties of hexagonal NiS
Panda, S. K.; Thunström, P.; Di Marco, I.; Schött, J.; Delin, A.; Dasgupta, I.; Eriksson, O.; Sarma, D. D.
2014-09-01
The electronic structure and spectral properties of hexagonal NiS have been studied in the high temperature paramagnetic phase and low temperature antiferromagnetic phase. The calculations have been performed using charge self-consistent density-functional theory in local density approximation combined with dynamical mean-field theory (LDA+DMFT). The photoemission spectra (PES) and optical properties have been computed and compared with the experimental data. Our results show that the dynamical correlation effects are important to understand the spectral and optical properties of NiS. These effects have been analyzed in detail by means of the computed real and imaginary part of the self-energy.
Belief-Propagation-Approximated Decoding of Low-Density Parity-Check Codes
Institute of Scientific and Technical Information of China (English)
SONG Hui-shi; ZHANG Ping
2004-01-01
In this paper, we propose a new reduced-complexity decoding algorithm of Low-Density Parity-Check (LDPC) codes, called Belief-Propagation-Approximated (BPA) algorithm, which utilizes the idea of normalization and translates approximately the intricate nonlinear operation in the check nodes of the original BP algorithm to only one operation of looking up the table. The normalization factors can be obtained by simulation, or theoretically. Simulation results demonstrate that BPA algorithm exhibits fairly satisfactory bit error performance on the Additive White Gaussian Noise (AWGN) channel.
Band theoretical investigation of substituted CrO2 within the local density approximation
1994-01-01
The effects of substitutions at différent concentrations within the lattice of CrO2 are investigated assuming ordered configurations. For this purpose we use self-consistent band structure calculations based on the local spin density approximation. All results show an antiparallel spin alignment between host Cr and the substitutional M = Ir, Os, Pt. Depending on the nature of M and its concentration, CrO2 transforms from a half metallic ferromagnet to a halfmetallic or metallic ferrimagnet.
Relativistic equation of state at subnuclear densities in the Thomas-Fermi approximation
Zhang, Z W
2014-01-01
We study the non-uniform nuclear matter using the self-consistent Thomas--Fermi approximation with a relativistic mean-field model. The non-uniform matter is assumed to be composed of a lattice of heavy nuclei surrounded by dripped nucleons. At each temperature $T$, proton fraction $Y_p$, and baryon mass density $\\rho_B$, we determine the thermodynamically favored state by minimizing the free energy with respect to the radius of the Wigner--Seitz cell, while the nucleon distribution in the cell can be determined self-consistently in the Thomas--Fermi approximation. A detailed comparison is made between the present results and previous calculations in the Thomas--Fermi approximation with a parameterized nucleon distribution that has been adopted in the widely used Shen EOS.
Morishita, Tetsuya
2009-05-21
We report a first-principles study of the structural, electronic, and dynamical properties of high-density amorphous (HDA) silicon, which was found to be formed by pressurizing low-density amorphous (LDA) silicon (a normal amorphous Si) [T. Morishita, Phys. Rev. Lett. 93, 055503 (2004); P. F. McMillan, M. Wilson, D. Daisenberger, and D. Machon, Nature Mater. 4, 680 (2005)]. Striking structural differences between HDA and LDA are revealed. The LDA structure holds a tetrahedral network, while the HDA structure contains a highly distorted tetrahedral network. The fifth neighboring atom in HDA tends to be located at an interstitial position of a distorted tetrahedron composed of the first four neighboring atoms. Consequently, the coordination number of HDA is calculated to be approximately 5 unlike that of LDA. The electronic density of state (EDOS) shows that HDA is metallic, which is consistent with a recent experimental measurement of the electronic resistance of HDA Si. We find from local EDOS that highly distorted tetrahedral configurations enhance the metallic nature of HDA. The vibrational density of state (VDOS) also reflects the structural differences between HDA and LDA. Some of the characteristic vibrational modes of LDA are dematerialized in HDA, indicating the degradation of covalent bonds. The overall profile of the VDOS for HDA is found to be an intermediate between that for LDA and liquid Si under pressure (high-density liquid Si).
Charge and spin fluctuations in the density functional theory
Energy Technology Data Exchange (ETDEWEB)
Gyoerffy, B.L.; Barbieri, A. (Bristol Univ. (UK). H.H. Wills Physics Lab.); Staunton, J.B. (Warwick Univ., Coventry (UK). Dept. of Physics); Shelton, W.A.; Stocks, G.M. (Oak Ridge National Lab., TN (USA))
1990-01-01
We introduce a conceptual framework which allow us to treat charge and spin fluctuations about the Local density Approximation (LDA) to the Density Functional Theory (DFT). We illustrate the approach by explicit study of the Disordered Local Moment (DLM) state in Fe above the Curie Temperature {Tc} and the Mott insulating state in MnO. 27 refs., 6 figs.
A new method combining LDA and PLS for dimension reduction.
Tang, Liang; Peng, Silong; Bi, Yiming; Shan, Peng; Hu, Xiyuan
2014-01-01
Linear discriminant analysis (LDA) is a classical statistical approach for dimensionality reduction and classification. In many cases, the projection direction of the classical and extended LDA methods is not considered optimal for special applications. Herein we combine the Partial Least Squares (PLS) method with LDA algorithm, and then propose two improved methods, named LDA-PLS and ex-LDA-PLS, respectively. The LDA-PLS amends the projection direction of LDA by using the information of PLS, while ex-LDA-PLS is an extension of LDA-PLS by combining the result of LDA-PLS and LDA, making the result closer to the optimal direction by an adjusting parameter. Comparative studies are provided between the proposed methods and other traditional dimension reduction methods such as Principal component analysis (PCA), LDA and PLS-LDA on two data sets. Experimental results show that the proposed method can achieve better classification performance.
A new method combining LDA and PLS for dimension reduction.
Directory of Open Access Journals (Sweden)
Liang Tang
Full Text Available Linear discriminant analysis (LDA is a classical statistical approach for dimensionality reduction and classification. In many cases, the projection direction of the classical and extended LDA methods is not considered optimal for special applications. Herein we combine the Partial Least Squares (PLS method with LDA algorithm, and then propose two improved methods, named LDA-PLS and ex-LDA-PLS, respectively. The LDA-PLS amends the projection direction of LDA by using the information of PLS, while ex-LDA-PLS is an extension of LDA-PLS by combining the result of LDA-PLS and LDA, making the result closer to the optimal direction by an adjusting parameter. Comparative studies are provided between the proposed methods and other traditional dimension reduction methods such as Principal component analysis (PCA, LDA and PLS-LDA on two data sets. Experimental results show that the proposed method can achieve better classification performance.
Ferrante, Augusto; Ticozzi, Francesco
2009-01-01
This paper deals with a method for the approximation of a spectral density function among the solutions of a generalized moment problem a` la Byrnes/Georgiou/Lindquist. The approximation is pursued with respect to the Kullback-Leibler pseudo-distance, which gives rise to a convex optimization problem. After developing the variational analysis, we discuss the properties of an efficient algorithm for the solution of the corresponding dual problem, based on the iteration of a nonlinear map in a bounded subset of the dual space. Our main result is the proof of local convergence of the latter, established as a consequence of the Central Manifold Theorem. Supported by numerical evidence, we conjecture that, in the mentioned bounded set, the convergence is actually global.
Casida, Mark E; Huix-Rotllant, Miquel
2016-01-01
In their famous paper, Kohn and Sham formulated a formally exact density-functional theory (DFT) for the ground-state energy and density of a system of N interacting electrons, albeit limited at the time by certain troubling representability questions. As no practical exact form of the exchange-correlation (xc) energy functional was known, the xc-functional had to be approximated, ideally by a local or semilocal functional. Nowadays, however, the realization that Nature is not always so nearsighted has driven us up Perdew's Jacob's ladder to find increasingly nonlocal density/wavefunction hybrid functionals. Time-dependent (TD-) DFT is a younger development which allows DFT concepts to be used to describe the temporal evolution of the density in the presence of a perturbing field. Linear response (LR) theory then allows spectra and other information about excited states to be extracted from TD-DFT. Once again the exact TD-DFT xc-functional must be approximated in practical calculations and this has historically been done using the TD-DFT adiabatic approximation (AA) which is to TD-DFT very similar to what the local density approximation (LDA) is to conventional ground-state DFT. Although some of the recent advances in TD-DFT focus on what can be done within the AA, others explore ways around the AA. After giving an overview of DFT, TD-DFT, and LR-TD-DFT, this chapter focuses on many-body corrections to LR-TD-DFT as one way to build hybrid density-functional/wavefunction methodology for incorporating aspects of nonlocality in time not present in the AA.
First-principles LDA+U calculations and luminescence study of YNbO4
Leng Lim, Thong; Nazarov, Mihail; Yoon, Tiem Leong; Low, Lay Chen; Fauzi, M. N. Ahmad
2014-09-01
Yttrium niobate (YNb{{O}_{4}}) phosphor is studied experimentally and through first-principles calculations, in which the structural and electronic properties of YNb{{O}_{4}} are investigated using the local-density approximation LDA+U method. The absorption and luminescence experiments that were conducted on the host lattice show the band gap to be \\approx 4.1 eV. The LDA+U calculations allow us to obtain a band gap of 4.28 eV. The density of states obtained from the calculation shows that O 2p states contribute to the valence band. The lower conduction band is mainly composed of Nb 4d states, while the upper conduction bands involve contribution mainly from Y 4d states. The partial DOS of each atom in the niobate system is then compared to the ultraviolet (UV) and vacuum ultraviolet (VUV) spectra from A photoluminescence excitation (PLE) experiment to explain the nature of the bands observed.
Versatile van der Waals Density Functional Based on a Meta-Generalized Gradient Approximation
Directory of Open Access Journals (Sweden)
Haowei Peng
2016-10-01
Full Text Available A “best-of-both-worlds” van der Waals (vdW density functional is constructed, seamlessly supplementing the strongly constrained and appropriately normed (SCAN meta-generalized gradient approximation for short- and intermediate-range interactions with the long-range vdW interaction from rVV10, the revised Vydrov–van Voorhis nonlocal correlation functional. The resultant SCAN+rVV10 is the only vdW density functional to date that yields excellent interlayer binding energies and spacings, as well as intralayer lattice constants in 28 layered materials. Its versatility for various kinds of bonding is further demonstrated by its good performance for 22 interactions between molecules; the cohesive energies and lattice constants of 50 solids; the adsorption energy and distance of a benzene molecule on coinage-metal surfaces; the binding energy curves for graphene on Cu(111, Ni(111, and Co(0001 surfaces; and the rare-gas solids. We argue that a good semilocal approximation should (as SCAN does capture the intermediate-range vdW through its exchange term. We have found an effective range of the vdW interaction between 8 and 16 Å for systems considered here, suggesting that this interaction is negligibly small at the larger distances where it reaches its asymptotic power-law decay.
Versatile van der Waals Density Functional Based on a Meta-Generalized Gradient Approximation
Peng, Haowei; Yang, Zeng-Hui; Perdew, John P.; Sun, Jianwei
2016-10-01
A "best-of-both-worlds" van der Waals (vdW) density functional is constructed, seamlessly supplementing the strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation for short- and intermediate-range interactions with the long-range vdW interaction from r VV 10 , the revised Vydrov-van Voorhis nonlocal correlation functional. The resultant SCAN +r VV 10 is the only vdW density functional to date that yields excellent interlayer binding energies and spacings, as well as intralayer lattice constants in 28 layered materials. Its versatility for various kinds of bonding is further demonstrated by its good performance for 22 interactions between molecules; the cohesive energies and lattice constants of 50 solids; the adsorption energy and distance of a benzene molecule on coinage-metal surfaces; the binding energy curves for graphene on Cu(111), Ni(111), and Co(0001) surfaces; and the rare-gas solids. We argue that a good semilocal approximation should (as SCAN does) capture the intermediate-range vdW through its exchange term. We have found an effective range of the vdW interaction between 8 and 16 Å for systems considered here, suggesting that this interaction is negligibly small at the larger distances where it reaches its asymptotic power-law decay.
A revised electronic Hessian for approximate time-dependent density functional theory.
Ziegler, Tom; Seth, Michael; Krykunov, Mykhaylo; Autschbach, Jochen
2008-11-14
Time-dependent density functional theory (TD-DFT) at the generalized gradient level of approximation (GGA) has shown systematic errors in the calculated excitation energies. This is especially the case for energies representing electron transitions between two separated regions of space or between orbitals of different spatial extents. It will be shown that these limitations can be attributed to the electronic ground state Hessian G(GGA). Specifically, we shall demonstrate that the Hessian G(GGA) can be used to describe changes in energy due to small perturbations of the electron density (Deltarho), but it should not be applied to one-electron excitations involving the density rearrangement (Deltarho) of a full electron charge. This is in contrast to Hartree-Fock theory where G(HF) has a trust region that is accurate for both small perturbations and one-electron excitations. The large trust radius of G(HF) can be traced back to the complete cancellation of Coulomb and exchange terms in Hartree-Fock (HF) theory representing self-interaction (complete self-interaction cancellation, CSIC). On the other hand, it is shown that the small trust radius for G(GGA) can be attributed to the fact that CSIC is assumed for GGA in the derivation of G(GGA) although GGA (and many other approximate DFT schemes) exhibits incomplete self-interaction cancellation (ISIC). It is further shown that one can derive a new matrix G(R-DFT) with the same trust region as G(HF) by taking terms due to ISIC properly into account. Further, with TD-DFT based on G(R-DFT), energies for state-to-state transitions represented by a one-electron excitation (psi(i)-->psi(a)) are approximately calculated as DeltaE(ai). Here DeltaE(ai) is the energy difference between the ground state Kohn-Sham Slater determinant and the energy of a Kohn-Sham Slater determinant where psi(i) has been replaced by psi(a). We make use of the new Hessian in two numerical applications involving charge-transfer excitations. It is
Energy Technology Data Exchange (ETDEWEB)
Nekrasov, I. A., E-mail: nekrasov@iep.uran.ru; Pavlov, N. S.; Sadovskii, M. V. [Russian Academy of Sciences, Institute for Electrophysics, Ural Branch (Russian Federation)
2013-04-15
We discuss the recently proposed LDA' + DMFT approach providing a consistent parameter-free treatment of the so-called double counting problem arising within the LDA + DMFT hybrid computational method for realistic strongly correlated materials. In this approach, the local exchange-correlation portion of the electron-electron interaction is excluded from self-consistent LDA calculations for strongly correlated electronic shells, e.g., d-states of transition metal compounds. Then, the corresponding double-counting term in the LDA' + DMFT Hamiltonian is consistently set in the local Hartree (fully localized limit, FLL) form of the Hubbard model interaction term. We present the results of extensive LDA' + DMFT calculations of densities of states, spectral densities, and optical conductivity for most typical representatives of two wide classes of strongly correlated systems in the paramagnetic phase: charge transfer insulators (MnO, CoO, and NiO) and strongly correlated metals (SrVO{sub 3} and Sr{sub 2}RuO{sub 4}). It is shown that for NiO and CoO systems, the LDA' + DMFT approach qualitatively improves the conventional LDA + DMFT results with the FLL type of double counting, where CoO and NiO were obtained to be metals. Our calculations also include transition-metal 4s-states located near the Fermi level, missed in previous LDA + DMFT studies of these monoxides. General agreement with optical and the X-ray experiments is obtained. For strongly correlated metals, the LDA' + DMFT results agree well with the earlier LDA + DMFT calculations and existing experiments. However, in general, LDA' + DMFT results give better quantitative agreement with experimental data for band gap sizes and oxygen-state positions compared to the conventional LDA + DMFT method.
Nekrasov, I. A.; Pavlov, N. S.; Sadovskii, M. V.
2013-04-01
We discuss the recently proposed LDA' + DMFT approach providing a consistent parameter-free treatment of the so-called double counting problem arising within the LDA + DMFT hybrid computational method for realistic strongly correlated materials. In this approach, the local exchange-correlation portion of the electron-electron interaction is excluded from self-consistent LDA calculations for strongly correlated electronic shells, e.g., d-states of transition metal compounds. Then, the corresponding double-counting term in the LDA' + DMFT Hamiltonian is consistently set in the local Hartree (fully localized limit, FLL) form of the Hubbard model interaction term. We present the results of extensive LDA' + DMFT calculations of densities of states, spectral densities, and optical conductivity for most typical representatives of two wide classes of strongly correlated systems in the paramagnetic phase: charge transfer insulators (MnO, CoO, and NiO) and strongly correlated metals (SrVO3 and Sr2RuO4). It is shown that for NiO and CoO systems, the LDA' + DMFT approach qualitatively improves the conventional LDA + DMFT results with the FLL type of double counting, where CoO and NiO were obtained to be metals. Our calculations also include transition-metal 4 s-states located near the Fermi level, missed in previous LDA + DMFT studies of these monoxides. General agreement with optical and the X-ray experiments is obtained. For strongly correlated metals, the LDA' + DMFT results agree well with the earlier LDA + DMFT calculations and existing experiments. However, in general, LDA' + DMFT results give better quantitative agreement with experimental data for band gap sizes and oxygen-state positions compared to the conventional LDA + DMFT method.
Pastore, A; Broglia, R A; Vigezzi, E
2008-01-01
The bare nucleon-nucleon interaction is essential for the production of pair correlations in nuclei, but an important contribution also arises from the induced interaction resulting from the exchange of collective vibrations between nucleons moving in time reversal states close to the Fermi energy. The pairing field resulting from the summed interaction is strongly peaked at the nuclear surface. It is possible to reproduce the detailed spatial dependence of this field using a Local Density Approximation (LDA) and a contact interaction, with parameters which are quite different from those commonly used in more phenomenological approaches.
Investigation of correlation effects in FeSe and FeTe by LDA + U method
Lohani, H.; Mishra, P.; Sekhar, B. R.
2015-05-01
We present a comparative study of the influence of Coulomb interaction and Hund's coupling on the electronic structure of FeSe and FeTe. Our calculations are based on density functional theory (DFT) with local density approximation (LDA + U) framework employed in TB-LMTO ASA code. We found the correlation effects are orbital selective due to the strength of interorbital hybridization among the different Fe-3d orbitals mediated via the chalcogen (Se/Te-p) orbitals and are different in both the compounds. The Coulomb interaction is screened significantly by Te-p bands in FeTe. Similarly the orbital selection is different in both the compounds because of the difference in the chalcogen height.
Accelerating selected columns of the density matrix computations via approximate column selection
Damle, Anil; Ying, Lexing
2016-01-01
Localized representation of the Kohn-Sham subspace plays an important role in quantum chemistry and materials science. The recently developed selected columns of the density matrix (SCDM) method [J. Chem. Theory Comput. 11, 1463, 2015] is a simple and robust procedure for finding a localized representation of a set of Kohn-Sham orbitals from an insulating system. The SCDM method allows the direct construction of a well conditioned (or even orthonormal) and localized basis for the Kohn-Sham subspace. The SCDM procedure avoids the use of an optimization procedure and does not depend on any adjustable parameters. The most computationally expensive step of the SCDM method is a column pivoted QR factorization that identifies the important columns for constructing the localized basis set. In this paper, we develop a two stage approximate column selection strategy to find the important columns at much lower computational cost. We demonstrate the effectiveness of this process using a dissociation process of a BH$_{3}...
Car-Parrinello treatment for an approximate density-functional theory method.
Rapacioli, Mathias; Barthel, Robert; Heine, Thomas; Seifert, Gotthard
2007-03-28
The authors formulate a Car-Parrinello treatment for the density-functional-based tight-binding method with and without self-consistent charge corrections. This method avoids the numerical solution of the secular equations, the principal drawback for large systems if the linear combination of atomic orbital ansatz is used. The formalism is applicable to finite systems and for supercells using periodic boundary conditions within the Gamma-point approximation. They show that the methodology allows the application of modern computational techniques such as sparse matrix storage and massive parallelization in a straightforward way. All present bottlenecks concerning computer time and consumption of memory and memory bandwidth can be removed. They illustrate the performance of the method by direct comparison with Born-Oppenheimer molecular dynamics calculations. Water molecules, benzene, the C(60) fullerene, and liquid water have been selected as benchmark systems.
Computation of the electronic flux density in the Born-Oppenheimer approximation.
Diestler, D J; Kenfack, A; Manz, J; Paulus, B; Pérez-Torres, J F; Pohl, V
2013-09-12
A molecule in the electronic ground state described in the Born–Oppenheimer approximation (BOA) by the wave function ΨBO = Φ0χ0 (where Φ0 is the time-independent electronic energy eigenfunction and χ0 is a time-dependent nuclear wave packet) exhibits a nonzero nuclear flux density, whereas it always displays zero electronic flux density (EFD), because the electrons are in a stationary state. A hierarchical approach to the computation of the EFD within the context of the BOA, which utilizes only standard techniques of quantum chemistry (to obtain Φ0) and quantum dynamics (to describe the evolution of χ0 on the ground-state potential energy surface), provides a resolution of this puzzling, nonintuitive result. The procedure is applied to H2(+) oriented parallel with the z-axis and vibrating in the ground state (2)Σg(+). First, Φ0 and χ0 are combined by the coupled-channels technique to give the normally dominant z-component of the EFD. Imposition of the constraints of electronic continuity, cylindrical symmetry of Φ0 and two boundary conditions on the EFD through a scaling procedure yields an improved z-component, which is then used to compute the complementary orthogonal ρ-component. The resulting EFD agrees with its highly accurate counterpart furnished by a non-BOA treatment of the system.
Institute of Scientific and Technical Information of China (English)
BAI Yu-Lin; CHENG Xiao-Hong; CHEN Xiang-Rong; YANG Xiang-Dong; ZHU Jun
2004-01-01
@@ The intermolecular interactions potentials for two configurations of CH4-Ne complex are calculated with local density approximation methods in the frame of density functional theory. It is found that the calculated potentials have two minima when the distance between the carbon atom of CH4 and the Ne atom takes R = 5.80 a.u.and 6.20a. u. for both the two configurations. For the edge configuration, the corresponding depth of the potential is 0.0669536 eV and 0.0671416 eV. For the face configuration, the corresponding depth of the potential is 0.0737956 eV and 0.0645506 eV. The global minimum occurs at R = 5.80 a.u. for the face configuration with a depth of the potential 0.0737956 eV. The depths of our calculation are in better agreement with the experimental data than the quantum chemical calculation approach, while the position of minimum potential for our calculation is underestimated.
Pairing in the BCS and LN approximations using continuum single particle level density
Id Betan, R. M.; Repetto, C. E.
2017-04-01
Understanding the properties of drip line nuclei requires to take into account the correlations with the continuum spectrum of energy of the system. This paper has the purpose to show that the continuum single particle level density is a convenient way to consider the pairing correlation in the continuum. Isospin mean-field and isospin pairing strength are used to find the Bardeen-Cooper-Schrieffer (BCS) and Lipkin-Nogami (LN) approximate solutions of the pairing Hamiltonian. Several physical properties of the whole chain of the Tin isotope, as gap parameter, Fermi level, binding energy, and one- and two-neutron separation energies, were calculated and compared with other methods and with experimental data when they exist. It is shown that the use of the continuum single particle level density is an economical way to include explicitly the correlations with the continuum spectrum of energy in large scale mass calculation. It is also shown that the computed properties are in good agreement with experimental data and with more sophisticated treatment of the pairing interaction.
Pairing in the BCS and LN approximations using continuum single particle level density
Energy Technology Data Exchange (ETDEWEB)
Id Betan, R.M., E-mail: idbetan@ifir-conicet.gov.ar [Instituto de Física Rosario (CONICET-UNR), Bv. 27 de Febrero 210 bis, S2000EZP Rosario (Argentina); Facultad de Ciencias Exactas, Ingeniería y Agrimensura (UNR), Av. Pellegrini 250, S2000BTP Rosario (Argentina); Instituto de Estudios Nucleares y Radiaciones Ionizantes (UNR), Riobamba y Berutti, S2000EKA Rosario (Argentina); Repetto, C.E. [Instituto de Física Rosario (CONICET-UNR), Bv. 27 de Febrero 210 bis, S2000EZP Rosario (Argentina); Facultad de Ciencias Exactas, Ingeniería y Agrimensura (UNR), Av. Pellegrini 250, S2000BTP Rosario (Argentina)
2017-04-15
Understanding the properties of drip line nuclei requires to take into account the correlations with the continuum spectrum of energy of the system. This paper has the purpose to show that the continuum single particle level density is a convenient way to consider the pairing correlation in the continuum. Isospin mean-field and isospin pairing strength are used to find the Bardeen–Cooper–Schrieffer (BCS) and Lipkin–Nogami (LN) approximate solutions of the pairing Hamiltonian. Several physical properties of the whole chain of the Tin isotope, as gap parameter, Fermi level, binding energy, and one- and two-neutron separation energies, were calculated and compared with other methods and with experimental data when they exist. It is shown that the use of the continuum single particle level density is an economical way to include explicitly the correlations with the continuum spectrum of energy in large scale mass calculation. It is also shown that the computed properties are in good agreement with experimental data and with more sophisticated treatment of the pairing interaction.
LDA+DMFT approach to excitations spectrum in half-metallic ferromagnets
Energy Technology Data Exchange (ETDEWEB)
Lichtenstein, Alexander [Institute of Theoretical Physics, University of Hamburg (Germany)
2009-07-01
We present a realistic many-body approach to excitation spectrum in the itinerant magnetic systems. The Half-Metallic Ferromagnets are an important class of itinerant electron materials because of their potential for spin-electronics. The Heusler alloy NiMnSb was the first material predicted to be a Half-Metallic Ferromagnet(HFM)in the framework of the Local Density Approximation (LDA) with the Fermi level in the gap for one of the spin directions. We study the effects of strong correlation between spin and charge degrees of freedom in NiMnSb within the Dynamical Mean Field Theory (DMFT). Based on LDA+DMFT electronic structure calculations we present the first ab-initio evidence for the existence of non-quasiparticle states lying in the gap of the minority spin channel just above the Fermi level. We discuss a general and exact scheme to spin-excitation spectrum in the magnetic nanosystems and investigate the temperature dependence of demagnetization in Half-Metallic Ferromagnets.
Optical response of metallic and insulating VO{sub 2} calculated with the LDA approach
Energy Technology Data Exchange (ETDEWEB)
Mossanek, R J O; Abbate, M [Departamento de Fisica, Universidade Federal do Parana, Caixa Postal 19081, 81531-990 Curitiba PR (Brazil)
2007-08-29
We calculated the optical response of metallic and insulating VO{sub 2} using the local density approximation (LDA) approach. The band structure calculation was based on the full-potential linear-muffin-tin method. The imaginary part of the dielectric function {epsilon}{sub 2}({omega}) is related to the different optical transitions. The Drude tail in the calculation of the metallic phase corresponds to intraband d-d transitions. The calculation in the insulating phase is characterized by the transitions to the d{sub parallel}* band. The low-frequency features, 0.0-5.0 eV, correspond to V 3d-V 3d transitions, whereas the high-frequency structures, 5.0-12 eV, are related to O 2p-V 3d transitions. The calculation helps to explain the imaginary part of the dielectric function {epsilon}{sub 2}({omega}), as well as the electron-energy-loss and reflectance spectra. The results reproduce not only the energy position and relative intensity of the features in the spectra, but also the main changes across the metal-insulator transition and the polarization dependence. The main difference is a shift of about 0.6 eV in the calculation of the insulating phase. This discrepancy arises because the LDA calculation underestimates the value of the band gap.
Energy Technology Data Exchange (ETDEWEB)
Camargo-Martínez, J.A., E-mail: jcamargo@unitropico.edu.co [Grupo de Investigación en Ciencias Básicas, Aplicación e Innovación - CIBAIN, Fundación Universitaria Internacional del Trópico Americano– Unitrópico, Yopal, Casanare (Colombia); Martínez-Pieschacón, D.J. [Departamento de Ciencias Básicas, Universidad Santo Tomás, Tunja, Boyaca (Colombia); Baquero, R. [Departamento de Física, CINVESTAV-IPN, Av. IPN 2508, 07360, México (Mexico)
2017-04-15
Highlights: • We present for the first time the effects of Pb doping on structural and electronic properties of Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} (Bi2223) using GGA, compared with LDA results. • We found the Pb concentration for which the Bi–O pockets disappear from the Fermi Surface in the Bi2223 compound using GGA and LDA, respectively. - Abstract: We use Density Functional Theory to study the effects on the crystal structure and the electronic band structure of substituting Pb for Bi in Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}. We further use the Local Density Approximation (LDA) and the Generalized Gradient Approximation (GGA). The Virtual Crystal Approximation (VCA) was used to account for the substitution. We found that GGA reproduces better the lattice parameters although in both cases the internal coordinates were reproduced with some uncertainties. We further looked at the behavior of the so called Bi–O pockets, some electronic states that originate on the Bi–O planes and that appear on the Fermi surface (FS) in contradiction to the experimental evidence. We found that LDA and GGA differ on that subject. With 26% Pb and using LDA, the Bi–O pockets run away from the FS. But when GGA is used, it is needed up to 35% Pb to make the Bi–O pockets disappear from the FS. In the last case, once the Bi–O pockets are removed from the FS, we get a very good agreement with angular resolved photo-emission (ARPES) and nuclear magnetic resonance (NMR) experiments.
Miura, Shinichi; Okazaki, Susumu
2001-09-01
In this paper, the path integral molecular dynamics (PIMD) method has been extended to employ an efficient approximation of the path action referred to as the pair density matrix approximation. Configurations of the isomorphic classical systems were dynamically sampled by introducing fictitious momenta as in the PIMD based on the standard primitive approximation. The indistinguishability of the particles was handled by a pseudopotential of particle permutation that is an extension of our previous one [J. Chem. Phys. 112, 10 116 (2000)]. As a test of our methodology for Boltzmann statistics, calculations have been performed for liquid helium-4 at 4 K. We found that the PIMD with the pair density matrix approximation dramatically reduced the computational cost to obtain the structural as well as dynamical (using the centroid molecular dynamics approximation) properties at the same level of accuracy as that with the primitive approximation. With respect to the identical particles, we performed the calculation of a bosonic triatomic cluster. Unlike the primitive approximation, the pseudopotential scheme based on the pair density matrix approximation described well the bosonic correlation among the interacting atoms. Convergence with a small number of discretization of the path achieved by this approximation enables us to construct a method of avoiding the problem of the vanishing pseudopotential encountered in the calculations by the primitive approximation.
Supersonic beams at high particle densities: model description beyond the ideal gas approximation.
Christen, Wolfgang; Rademann, Klaus; Even, Uzi
2010-10-28
Supersonic molecular beams constitute a very powerful technique in modern chemical physics. They offer several unique features such as a directed, collision-free flow of particles, very high luminosity, and an unsurpassed strong adiabatic cooling during the jet expansion. While it is generally recognized that their maximum flow velocity depends on the molecular weight and the temperature of the working fluid in the stagnation reservoir, not a lot is known on the effects of elevated particle densities. Frequently, the characteristics of supersonic beams are treated in diverse approximations of an ideal gas expansion. In these simplified model descriptions, the real gas character of fluid systems is ignored, although particle associations are responsible for fundamental processes such as the formation of clusters, both in the reservoir at increased densities and during the jet expansion. In this contribution, the various assumptions of ideal gas treatments of supersonic beams and their shortcomings are reviewed. It is shown in detail that a straightforward thermodynamic approach considering the initial and final enthalpy is capable of characterizing the terminal mean beam velocity, even at the liquid-vapor phase boundary and the critical point. Fluid properties are obtained using the most accurate equations of state available at present. This procedure provides the opportunity to naturally include the dramatic effects of nonideal gas behavior for a large variety of fluid systems. Besides the prediction of the terminal flow velocity, thermodynamic models of isentropic jet expansions permit an estimate of the upper limit of the beam temperature and the amount of condensation in the beam. These descriptions can even be extended to include spinodal decomposition processes, thus providing a generally applicable tool for investigating the two-phase region of high supersaturations not easily accessible otherwise.
Lattice dynamics calculations for ferropericlase with internally consistent LDA+U method
Fukui, Hiroshi; Tsuchiya, Taku; Baron, Alfred Q. R.
2012-12-01
Vibrational densities of states and phonon dispersion relations for Mg0.875Fe0.125O ferropericlase in the high- and low-spin (HS and LS) states were calculated from first principles lattice dynamics using the internally consistent LDA+Utechnique. Finite-temperature thermodynamic properties were determined based on the quasi-harmonic approximation including the HS and LS mixing entropy and the magnetic entropy effects, which gave pressure and temperature variations of the low-spin fraction. Our results suggest that for thermodynamic modeling of the earth's interior, the effect of the mixed spin state cannot be ignored in the lower mantle, especially the lowermost part. The anomaly in the seismic wave velocity due to the spin crossover transition of ferropericlase, if it exists, is difficult to detect because of the wide pressure range of the transition, which is broadened by the temperature effect and the damping of the amplitude of the slow seismic wave.
Wang, Guangtao; Qian, Yumin; Xu, Gang; Dai, Xi; Fang, Zhong
2010-01-29
The electronic structures of FeAs compounds are sensitive to FeAs bonding, which is described unsuccessfully by the local density approximation (LDA). Treating the multiorbital fluctuations from ab inito LDA+Gutzwiller method, we can now predict the correct FeAs bond length and bonding strength, which will explain the observed "soft phonon." The bands are narrowed by a factor of 2 from their LDA widths. The d{3z{2}-r{2}} orbital is pushed up to cross the Fermi level, forming a three-dimensional Fermi surface, which reduces the anisotropy. The interorbital Hund's coupling J rather than U plays a crucial role in obtaining these results.
Local density approximation results for bond length alternation in the infinite polyyne chain
Bylaska, Eric; Weare, John
1998-03-01
Calculations for large even numbered carbon ring molecules and band structure calculations for the infinite polyyne chain within the local density approximation are reported. We studied the alternation of bond lengths in this system as a function of size. Particular focus is on alternation in the infinite system. For intermediate and large sized Cn rings with n satisfying n=4N (doubly-antiaromatic rings) there is a substantial first order Jahn-Teller distortion which decreases for large N. On the other hand, for Cn rings satisfying n=4N+2 (doubly-aromatic rings) the second order Jahn-Teller distortion does not produce bond length alternation even by the large C_42 ring. The persistance of aromatic behavior in the very large carbon rings manifests itself in the band structure calculations by making the amount of bond length alternation predicted for the infinite polyyne chain extremely sensitive to the numerical treatment of the Brillouin zone. We have shown that the infinite polyyne has a finite amount of bond length alternation but the condensation energy is very small.
Energy Technology Data Exchange (ETDEWEB)
Barrera, G.D. [ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX (United Kingdom); Departamento de Quimica, Universidad Nacional de la Patagonia SJB, Ciudad Universitaria, 9005 Comodoro Rivadavia (Argentina); Colognesi, D. [Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi, via Madonna del Piano s.n.c., 50019 Sesto Fiorentino (Finland) (Italy); Mitchell, P.C.H. [School of Chemistry, University of Reading, RG6 6AD (United Kingdom); Ramirez-Cuesta, A.J. [ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX (United Kingdom); School of Chemistry, University of Reading, RG6 6AD (United Kingdom)], E-mail: a.j.ramirez-cuesta@rl.ac.uk
2005-10-31
In a previous work, we carried out inelastic neutron scattering (INS) spectroscopy experiments and preliminary first principles calculations on alkali metal hydrides. The complete series of alkali metal hydrides, LiH, NaH, KH, RbH and CsH was measured in the high-resolution TOSCA INS spectrometer at ISIS. Here, we present the results of ab initio electronic structure calculations of the properties of the alkali metal hydrides using both the local density approximation (LDA) and the generalized gradient approximation (GGA), using the Perdew-Burke-Ernzerhof (PBE) parameterization. Properties calculated were lattice parameters, bulk moduli, dielectric constants, effective charges, electronic densities and inelastic neutron scattering (INS) spectra. We took advantage of the currently available computer power to use full lattice dynamics theory to calculate thermodynamic properties for these materials. For the alkali metal hydrides (LiH, NaH, KH, RbH and CsH) using lattice dynamics, we found that the INS spectra calculated using LDA agreed better with the experimental data than the spectra calculated using GGA. Both zero-point effects and thermal contributions to free energies had an important effect on INS and several thermodynamic properties.
Efficient estimation of burst-mode LDA power spectra
DEFF Research Database (Denmark)
Velte, Clara Marika; George, William K
2010-01-01
The estimation of power spectra from LDA data provides signal processing challenges for fluid dynamicists for several reasons. Acquisition is dictated by randomly arriving particles which cause the signal to be highly intermittent. This both creates self-noise and causes the measured velocities......), which was not covered in the previous theory. An efficient algorithm for computing the residence time weighted power spectra using Matlab is proposed and implemented. The algorithm is applied to two experiments, one with high data density (cylinder wake) and one with relatively low data density...
Semiclassical approximation to neutron star superfluidity corrected for proximity effects.
Energy Technology Data Exchange (ETDEWEB)
Barranco, F.; Broglia, R. A.; Esbensen, H.; Vigezzi, E.; Physics; Univ. of Seville; Univ. of Milan and INFN; Univ. of Copenhagen
1998-08-01
The inner crust of a neutron star is a superfluid and inhomogeneous system, consisting of a lattice of nuclei immersed in a sea of neutrons. We perform a quantum calculation of the associated pairing gap and compare it to the results one obtains in the local density approximation (LDA). It is found that the LDA overestimates the spatial dependence of the gap, and leads to a specific heat of the system which is too large at low temperatures, as compared with the quantal result. This is caused by the neglect of proximity effects and the delocalized character of the single-particle wave functions close to the Fermi energy. It is possible to introduce an alternative, simple semiclassical approximation of the pairing gap which leads to a specific heat that is in good agreement with the quantum calculation.
LDA measurements and turbulence spectral analysis in an agitated vessel
Directory of Open Access Journals (Sweden)
Chára Zdeněk
2013-04-01
Full Text Available During the last years considerable improvement of the derivation of turbulence power spectrum from Laser Doppler Anemometry (LDA has been achieved. The irregularly sampled LDA data is proposed to approximate by several methods e.g. Lomb-Scargle method, which estimates amplitude and phase of spectral lines from missing data, methods based on the reconstruction of the auto-correlation function (referred to as correlation slotting technique, methods based on the reconstruction of the time series using interpolation between the uneven sampling and subsequent resampling etc. These different methods were used on the LDA data measured in an agitated vessel and the results of the power spectrum calculations were compared. The measurements were performed in the mixing vessel with flat bottom. The vessel was equipped with four baffles and agitated with a six-blade pitched blade impeller. Three values of the impeller speed (Reynolds number were tested. Long time series of the axial velocity component were measured in selected points. In each point the time series were analyzed and evaluated in a form of power spectrum.
LDA measurements and turbulence spectral analysis in an agitated vessel
Kysela, Bohuš; Konfršt, Jiří; Chára, Zdeněk
2013-04-01
During the last years considerable improvement of the derivation of turbulence power spectrum from Laser Doppler Anemometry (LDA) has been achieved. The irregularly sampled LDA data is proposed to approximate by several methods e.g. Lomb-Scargle method, which estimates amplitude and phase of spectral lines from missing data, methods based on the reconstruction of the auto-correlation function (referred to as correlation slotting technique), methods based on the reconstruction of the time series using interpolation between the uneven sampling and subsequent resampling etc. These different methods were used on the LDA data measured in an agitated vessel and the results of the power spectrum calculations were compared. The measurements were performed in the mixing vessel with flat bottom. The vessel was equipped with four baffles and agitated with a six-blade pitched blade impeller. Three values of the impeller speed (Reynolds number) were tested. Long time series of the axial velocity component were measured in selected points. In each point the time series were analyzed and evaluated in a form of power spectrum.
Electronic structure and magnetism of Eu-doped GaN: first-principles study based on LDA+U
Energy Technology Data Exchange (ETDEWEB)
Goumri-Said, S [Laboratoire de Physique de l' Etat Condense, UMR CNRS 6087, Institut de Recherche en Ingenierie Moleculaire et Materiaux Fonctionnels, FR CNRS 2575 Universite du Maine, Avenue Olivier Messiaen-72085, Le Mans Cedex 9 (France); Kanoun, M B [Laboratoire de Metallurgie Physique, UMR 6630 du CNRS, Universite de Poitiers, Bt. SP2MI, Bd Pierre et Marie Curie, BP 30179, 86962 Futuroscope, Chasseneuil Cedex (France)
2008-02-07
Electronic and magnetic properties of the rare-earth-doped III-nitride semiconductor Ga{sub 1-x}Eu{sub x}N (x = 0.0625) is studied with the full potential (linearized) augmented plane wave method plus the local orbitals method, where we have explored the electronic and magnetic properties of the ferromagnetic Ga{sub 1-x}Eu{sub x}N in the zinc-blende phase. The existence of Eu 4f orbitals has demonstrated that the common local density approximation leads to quantitatively and qualitatively wrong results, while the LDA + U method performs much better. In this paper we present only the results related to the LDA + U method. It is found from the calculation of density of states that the Eu f orbitals spin-polarize the host system and they are predominant in this diluted magnetic semiconductor. The magnetic description is achieved by the calculation of spin densities difference contours and the magnetic moment.
Improved PCA + LDA Applies to Gastric Cancer Image Classification Process
Gan, Lan; Lv, Wenya; Zhang, Xu; Meng, Xiuming
Principal component analysis (PCA) and linear discriminant analysis (LDA) are two most widely used pattern recognition methods in the field of feature extraction,while PCA + LDA is often used in image recognition.Here,we apply PCA + LDA to gastric cancer image feature classification, but the traditional PCA + LDA dimension reduction method has good effect on the training sample dimensionality and clustering, the effect on test samples dimension reduction and clustering is very poor, that is, the traditional PCA + LDA exists Generalization problem on the test samples. To solve this problem, this paper proposes an improved PCA + LDA method, which mainly considers from the LDA transform; improves the traditional PCA + LDA;increase the generalization performance of LDA on test samples and increases the classification accuracy on test samples. The experiment proves that the method can achieve good clustering.
Yan, Zidan; Perdew, John P.; Kurth, Stefan
2000-03-01
Within a density functional context, the random phase approximation (RPA) for the correlation emergy makes a short-range error which is well-suited for correction by a local spin density or generalized gradient approximation (GGA). Here we construct a GGA for the short-range correction, following the same reliable procedure used earlier to construct the GGA for the whole exchange-correlation energy: real-space cutoff of the spurious long-range contribution to the gradient expansion of the hole around an electron. The resulting density functional is nearly local, and predicts a substantial correction to the RPA correlation energy of an atom but \\underlinevery small corrections to the RPA atomization energy of a molecule, which may by itself come close to "chemical accuracy", and to the RPA surface energy of a metal. A by-product of this work is a density functional for the system-averaged correlation hole within RPA.
Energy Technology Data Exchange (ETDEWEB)
Ahn, Hyo Shin [Korea Institute of Science and Technology, Seoul (Korea, Republic of); Seoul National University, Seoul (Korea, Republic of); Cuong, Do Duc; Lee, Jai Chan [Sungkyunkwan University, Suwon (Korea, Republic of); Han, Seung Wu [Ewha Womans University, Seoul (Korea, Republic of)
2006-10-15
Using LDA+U (where LDA stands for local-density-approximation and U for on-site coulomb energy) method, we study the structural and electronic properties of LaTiO{sub 3} and (SrTiO{sub 3}){sub m}(LaTiO{sub 3}){sub n} superlattice structures. Lattice vectors, as well as ionic positions, are relaxed to minimize the LDA+U energy functional. We find that the inclusion of the U term increases the lattice parameters and leads to larger distortions of oxygen octahedra in LaTiO{sub 3} and that the overall agreement with experiment is improved compared to LDA results. In the superlattice, we find that octahedral distortions around the La layer lower the total energy. The ionic relaxations, especially those of Ti atoms near the La layer, affect the spatial distribution of doped electrons, leading to a broader charge profile than the case without ionic relaxation. The corresponding Ti{sup 3+} profile is in good agreement with the electron-energy-loss spectroscopy data.
Properties of hot liquid cerium by LDA + U molecular dynamics.
Siberchicot, Bruno; Clérouin, Jean
2012-11-14
We present ab initio simulations of liquid cerium in the framework of the LDA + U formulation. The liquid density has been determined self-consistently by searching for the zero pressure equilibrium state at 1320 K with the same set of parameters (U and J) and occupation matrices as those optimized for the γ phase. We have computed static and transport properties. The liquid produced by the simulations appears more structured than the available measurements. This raises questions regarding the ability of the theory to describe such a complex liquid. Conductivity calculations and temperature dependences are nevertheless in reasonable agreement with data.
Performance Evaluation of LDA, CCA and AAM
Directory of Open Access Journals (Sweden)
M. Jasmine Pemeena Priyadarsini
2015-03-01
Full Text Available Wouldn't we love to replace passwords access control to avoid theft, forgotten passwords? Wouldn't we like to enter the security areas just in seconds? Yes the answer is face recognition. In this study we explore and compare the performance of three algorithms namely LDA, CCA, AAM. LDA (an evolution of PCA is a dimensionality reduction technique where it solves the problem of illumination to some extent, maximizing the inter class separation and minimizing the intra class variations. CCA, a measure of linear relationship between two multidimensional variables where it takes the advantage of PCA and LDA for maximizing the correlation and better performance. AAM is a model based approach where it just picks the landmarks of the images for recognition therefore reducing the error rate and producing good performance rate.
Energy Technology Data Exchange (ETDEWEB)
Shi Hongliang [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China)] [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Zhang Ping, E-mail: zhang_ping@iapcm.ac.c [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China)] [Center for Applied Physics and Technology, Peking University, Beijing 100871 (China); Li Shushen [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Sun Bo [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Wang Baotian [Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan 030006 (China)
2009-09-21
The electronic structure, elastic constants, Poisson's ratio, and phonon dispersion curves of UC have been systematically investigated from the first-principles calculations by the projector-augmented-wave (PAW) method. In order to describe precisely the strong on-site Coulomb repulsion among the localized U 5f electrons, we adopt the local density approximation (LDA)+U and generalized gradient approximation (GGA)+U formalisms for the exchange correlation term. We systematically study how the electronic properties and elastic constants of UC are affected by the different choice of U as well as the exchange-correlation potential. We show that by choosing an appropriate Hubbard U parameter within the GGA+U approach, most of our calculated results are in good agreement with the experimental data. Therefore, the results obtained by the GGA+U with effective Hubbard parameter U chosen around 3 eV for UC are considered to be reasonable.
Comparing quasiparticle GW+DMFT and LDA+DMFT for the test bed material SrVO3
Taranto, C.; Kaltak, M.; Parragh, N.; Sangiovanni, G.; Kresse, G.; Toschi, A.; Held, K.
2013-10-01
We have implemented the quasiparticle GW+dynamical mean field theory (DMFT) approach in the Vienna ab initio simulation package. To this end, a quasiparticle Hermitization of the G0W0 self-energy a lá Kotani-Schilfgaarde is employed, and the interaction values are obtained from the locally unscreened random phase approximation (RPA) using a projection onto Wannier orbitals. We compare quasiparticle GW+DMFT and local density approximation (LDA)+DMFT against each other and against experiment for SrVO3. We observe a partial compensation of stronger electronic correlations due to the reduced GW bandwidth and weaker correlations due to a larger screening of the RPA interaction, so that the obtained spectra are quite similar and agree well with experiment. Noteworthy, the quasiparticle GW+DMFT better reproduces the position of the lower Hubbard side band.
Energetic, electronic and optical properties of lanthanide doped TiO2: An ab initio LDA+U study
Mulwa, Winfred M.; Ouma, Cecil N. M.; Onani, Martin O.; Dejene, Francis B.
2016-05-01
Substitutional energies, thermodynamic charge transition levels and optical properties of lanthanide doped anatase TiO2 has been investigated using local density approximation with the Hubbard U correction (LDA+U) within the density functional theory formalism. All the lanthanides apart from La introduced impurity states in the host band gap on doping. The calculated substitutional energies indicate that it is possible to dope TiO2 with lanthanide ions. The optimal doping percentage was predicted to be ~3% and dopant levels resulting from Ce, Nd, Sm, Gd and Tm doping were found to possess negative U characteristics. In addition the calculated thermodynamic transition levels predicted Lu as not having any possible charge transitions within the host band gap. The calculated optical absorption coefficients indicate that lanthanide doping led to optical absorption in the visible regime.
LDA optical setup using holographic imaging configuration
Ghosh, Abhijit; Nirala, A. K.
2015-11-01
This paper describes one of the possible ways for improving fringe quality at LDA measuring volume using a holographic imaging configuration consisting of a single hololens. For its comparative study with a conventional imaging configuration, a complete characterization of fringes formed at the measurement volume by both the configuration is presented. Results indicate the qualitative as well as quantitative improvement of the fringes formed at measurement volume by the holographic imaging configuration. Hence it is concluded that use of holographic imaging configuration for making LDA optical setup is a better choice than the conventional one.
Rusanov, Anatoly I
2004-07-22
A novel theory of an equation of state based on excluded volume and formulated in two preceding papers for gases and gaseous mixtures is extended to the entire density range by considering higher (beginning from the third) approximations of the theory. The algorithm of constructing higher approximations is elaborated. Equations of state are deduced using the requirement of maximum simplicity and contain a single free parameter to be chosen by reason of convenience or simplicity or to be used as a fitting parameter with respect to the computer simulation database. In this way, precise equations of state are derived for the hard-sphere fluid in the entire density range. On the side, the theory reproduces most known earlier equations of state for hard spheres and determines their place in the hierarchy of approximations. Equations of state for van der Waals fluids are also presented, and their critical parameters are estimated.
Relativistic hadronic models in LDA
Energy Technology Data Exchange (ETDEWEB)
Silva, J.B.; Delfino, A.; Malheiro, M. [Universidade Federal Fluminense, Niteroi, RJ (Brazil). Inst. de Fisica
2001-07-01
In the framework of the Walecka model we perform a model approximation ({rho}{sub s} = {rho}), in which some nuclear matter observable are calculated analytically. The results are very close to those obtained by the original Walecka model. (author)
Senjean, Bruno; Jensen, Hans Jørgen Aa; Fromager, Emmanuel
2015-01-01
The computation of excitation energies in range-separated ensemble density-functional theory (DFT) is discussed. The latter approach is appealing as it enables the rigorous formulation of a multi-determinant state-averaged DFT method. In the exact theory, the short-range density functional, that complements the long-range wavefunction-based ensemble energy contribution, should vary with the ensemble weights even when the density is held fixed. This weight dependence ensures that the range-separated ensemble energy varies linearly with the ensemble weights. When the (weight-independent) ground-state short-range exchange-correlation functional is used in this context, curvature appears thus leading to an approximate weight-dependent excitation energy. In order to obtain unambiguous approximate excitation energies, we simply propose to interpolate linearly the ensemble energy between equiensembles. It is shown that such a linear interpolation method (LIM) effectively introduces weight dependence effects. LIM has...
Krykunov, Mykhaylo; Autschbach, Jochen
2007-01-14
We report implementations and results of time-dependent density functional calculations (i) of the frequency-dependent magnetic dipole-magnetic dipole polarizability, (ii) of the (observable) translationally invariant linear magnetic response, and (iii) of a linear intensity differential (LID) which includes the dynamic dipole magnetizability. The density functional calculations utilized density fitting. For achieving gauge-origin independence we have employed time-periodic magnetic-field-dependent basis functions as well as the dipole velocity gauge, and have included explicit density-fit related derivatives of the Coulomb potential. We present the results of calculations of static and dynamic magnetic dipole-magnetic dipole polarizabilities for a set of small molecules, the LID for the SF6 molecule, and dispersion curves for M-hexahelicene of the origin invariant linear magnetic response as well as of three dynamic polarizabilities: magnetic dipole-magnetic dipole, electric dipole-electric dipole, and electric dipole-magnetic dipole. We have also performed comparison of the linear magnetic response and magnetic dipole-magnetic dipole polarizability over a wide range of frequencies for H2O and SF6.
Approximate evaluation of the density of single-crystal heat-resistant nickel alloys
Energy Technology Data Exchange (ETDEWEB)
Petrushin, N.V.; Ignatova, I.A.; D`yachkova, L.A.
1992-03-01
On the basis of the generalization and analysis of the author`s and of published experimental data an analytical dependence is obtained of the density of single-crystal heat-resistant nickel alloys on their chemical composition which was characterized by the mean atomic mass of the alloy. 9 refs., 2 tabs.
Heuser, Johannes; Höfener, Sebastian
2017-10-15
We report the derivation and implementation of analytical nuclear gradients for excited states using time-dependent density functional theory using the Tamm-Dancoff approximation combined with uncoupled frozen-density embedding using density fitting. Explicit equations are presented and discussed. The implementation is able to treat singlet as well as triplet states and functionals using the local density approximation, the generalized gradient approximation, combinations with Hartree-Fock exchange (hybrids), and range-separated functionals such as CAM-B3LYP. The new method is benchmarked against supermolecule calculations in two case studies: The solvatochromic shift of the (vertical) fluorescence energy of 4-aminophthalimide on solvation, and the first local excitation of the benzonitrile dimer. Whereas for the 4-aminophthalimide-water complex deviations of about 0.2 eV are obtained to supermolecular calculations, for the benzonitrile dimer the maximum error for adiabatic excitation energies is below 0.01 eV due to a weak coupling of the subsystems. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.
Energy Technology Data Exchange (ETDEWEB)
Pan, Y.; Liu, T. [College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Wei, X.Y. [State Key Laboratory of Surface Physics and Key Laboratory for Computational Physical Sciences (MOE) & Department of Physics, Fudan University, Shanghai 200433 (China); Zhu, Y., E-mail: yzhu@nuaa.edu.cn [College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Shi, D.N., E-mail: shi@nuaa.edu.cn [College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Ma, C.L. [School of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou 215009 (China); Zhang, K.C. [College of Mathematics and Physics, Bohai University, Jinzhou 121013 (China); Yang, Z.Q. [State Key Laboratory of Surface Physics and Key Laboratory for Computational Physical Sciences (MOE) & Department of Physics, Fudan University, Shanghai 200433 (China)
2015-11-06
By local-density approximation plus U (LDA + U) calculations, diluted magnetic semiconductors (DMS) δ-(Zn, Mn, Li)Se are dominated by Zener's p–d exchange, which is different from Zener's double exchange mechanism by PBE calculations. The main peak of Mn d states is shifted to lower energy −3.9 eV versus Fermi energy. All configurations under shape deformation are strong ferromagnetic (FM) ones due to the large splitting of Mn d states. Because of the two-dimensional (2D) ordered Mn atoms with hole and long ranged effect of p–d exchange coupling, exchange energy of the supercell with crystal constant is much larger with p–d exchange than that with double exchange. The largest exchange energy is around the crystal constant. Fermi level across the valley of FM Mn d states makes the FM state much stable. Comparing with pure ZnSe, p-type co-doping of Li in δ-(Zn, Mn, Li)Se has a significant effect on the atomic structure. These results are useful in the research of DMS with shape deformation and p-type co-doping for spintronic applications. - Highlights: • Systematic research on competition between double, p–d and super exchange in DMS. • Double exchange and p–d exchange plays a major role in PBE and LDA + U respectively. • The main peak of Mn d states is compatible with experimental results with LDA + U. • All configurations under shape deformation are strong FM ones in LDA + U.
Energy Technology Data Exchange (ETDEWEB)
Hamdi, Ilyes, E-mail: ilyeshamdi@yahoo.f [Department of Electronics, Electro-technics and Automatics, Institute of Applied Sciences and Technology, 2100 Gafsa (Tunisia); UPMI units of research, Faculty of Sciences at Gafsa, 2100 Gafsa (Tunisia); Meskini, Noureddine [Physics Department, Faculty of Sciences at Tunis, 2092 Tunis (Tunisia)
2010-07-01
A first principles quantum mechanical approach is used to investigate the structural, elastic, vibrational and thermodynamic properties of the hexagonal boron nitride (h-BN) in the framework of the pseudopotential plane wave density-functional perturbation theory for the two popular exchange-correlation functionals: local density approximation and the revised Perdew-Burke-Ernzerhof generalized gradient approximation [Y. Zhang, W. Yang, Phys. Rev. Lett, 80 (1998), 890]. The LDA calculations of the structural parameters are in good agreement with experimental results, whereas GGA largely overestimated them. The computed elastic constants are improved by performing the calculations at room temperature and using the experimental lattice parameters. A good agreement with the experimental data is obtained for the phonon frequencies using both functionals. The thermodynamic properties such as the thermal equation of state, the in-plane and out-of-plane thermal expansion coefficients (LTEC), the bulk modulus and the heat capacity are calculated at the experimental lattice parameters using the quasiharmonic approximation (+ an empirical anharmonic term) for the Helmholtz free energy. Anharmonic corrections are important at high temperature. A good agreement with the experimental data for the LTEC has been obtained with the GGA functional, especially for the out-of-plane LTEC. In contrast with recent experimental findings, our calculated bulk modulus decreases with temperature for both functionals. This (decreasing) behavior is in a good agreement with other experimental data. The constant pressure heat capacity calculated with LDA and GGA is in very good agreement with experimental results.
LOCAL-DENSITY FUNCTIONAL AND ON-SITE CORRELATIONS - THE ELECTRONIC-STRUCTURE OF LA2CUO4 AND LACUO3
CZYZYK, MT; SAWATZKY, GA
1994-01-01
State-of-the-art electronic-structure calculations based on the local-density approximation (LDA) to the density functional fail to reproduce the insulating antiferromagnetic ground state in the parent compounds of the high-temperature oxide superconductors. Similar problems have been observed earli
Corrections to the density-functional theory electronic spectrum: Copper phthalocyanine
DEFF Research Database (Denmark)
Vazquez, Hector; Jelinek, P.; Brandbyge, Mads;
2009-01-01
A method for improving the electronic spectrum of standard Density-Functional Theory (DFT) calculations (i.e., LDA or GGA approximations) is presented, and its application is discussed for the case of the copper phthalocyanine (CuPc) molecule. The method is based on a treatment of exchange and co...
Energy Technology Data Exchange (ETDEWEB)
Reichert, E.; Strehle, M. [ebm Werke GmbH und Co. KG, Mulfingen (Germany); Bohl, K. [Heilbronn Fachhochschule (Germany)
2003-06-01
The contribution describes the application of LDA techniques for flow measurements and optimization of blowers. Three examples are presented to show how LDA measurements can be used for optimization and design of industrial blowers. [German] Der Beitrag beschreibt die Anwendung der LDA-Messtechnik fuer die stroemungstechnische Entwicklung und Optimierung von Ventilatoren. An drei Beispielen wird gezeigt, wie im industriellen Einsatz mit LDA-Messungen wesentliche Informationen ermittelt werden koennen, die dann zur Verbesserung oder zur Auslegung von Ventilatoren eingesetzt werden. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Nakano, Masayoshi, E-mail: mnaka@cheng.es.osaka-u.ac.jp; Minami, Takuya, E-mail: mnaka@cheng.es.osaka-u.ac.jp; Fukui, Hitoshi, E-mail: mnaka@cheng.es.osaka-u.ac.jp; Yoneda, Kyohei, E-mail: mnaka@cheng.es.osaka-u.ac.jp; Shigeta, Yasuteru, E-mail: mnaka@cheng.es.osaka-u.ac.jp; Kishi, Ryohei, E-mail: mnaka@cheng.es.osaka-u.ac.jp [Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); Champagne, Benoît; Botek, Edith [Laboratoire de Chimie Théorique, Facultés Universitaires Notre-Dame de la Paix (FUNDP), rue de Bruxelles, 61, 5000 Namur (Belgium)
2015-01-22
We develop a novel method for the calculation and the analysis of the one-electron reduced densities in open-shell molecular systems using the natural orbitals and approximate spin projected occupation numbers obtained from broken symmetry (BS), i.e., spin-unrestricted (U), density functional theory (DFT) calculations. The performance of this approximate spin projection (ASP) scheme is examined for the diradical character dependence of the second hyperpolarizability (γ) using several exchange-correlation functionals, i.e., hybrid and long-range corrected UDFT schemes. It is found that the ASP-LC-UBLYP method with a range separating parameter μ = 0.47 reproduces semi-quantitatively the strongly-correlated [UCCSD(T)] result for p-quinodimethane, i.e., the γ variation as a function of the diradical character.
Valor, A; Robledo, L M
2000-01-01
We derive the equations for approximate particle number projection based on mean field wave functions with finite range density dependent forces. As an application ground bands of even-A superdeformed nuclei in the A=150 and A=190 regions are calculated with the Gogny force. We discuss nuclear properties such as quadrupole moments, moments of inertia and quasiparticle spectra, among others, as a function of the angular momentum. We obtain a good overall description.
Fast Solution in Sparse LDA for Binary Classification
Moghaddam, Baback
2010-01-01
An algorithm that performs sparse linear discriminant analysis (Sparse-LDA) finds near-optimal solutions in far less time than the prior art when specialized to binary classification (of 2 classes). Sparse-LDA is a type of feature- or variable- selection problem with numerous applications in statistics, machine learning, computer vision, computational finance, operations research, and bio-informatics. Because of its combinatorial nature, feature- or variable-selection problems are NP-hard or computationally intractable in cases involving more than 30 variables or features. Therefore, one typically seeks approximate solutions by means of greedy search algorithms. The prior Sparse-LDA algorithm was a greedy algorithm that considered the best variable or feature to add/ delete to/ from its subsets in order to maximally discriminate between multiple classes of data. The present algorithm is designed for the special but prevalent case of 2-class or binary classification (e.g. 1 vs. 0, functioning vs. malfunctioning, or change versus no change). The present algorithm provides near-optimal solutions on large real-world datasets having hundreds or even thousands of variables or features (e.g. selecting the fewest wavelength bands in a hyperspectral sensor to do terrain classification) and does so in typical computation times of minutes as compared to days or weeks as taken by the prior art. Sparse LDA requires solving generalized eigenvalue problems for a large number of variable subsets (represented by the submatrices of the input within-class and between-class covariance matrices). In the general (fullrank) case, the amount of computation scales at least cubically with the number of variables and thus the size of the problems that can be solved is limited accordingly. However, in binary classification, the principal eigenvalues can be found using a special analytic formula, without resorting to costly iterative techniques. The present algorithm exploits this analytic
Approximation of charge-deposition density in thin slabs irradiated by electrons
Alouani-Bibi, F; Rogov, Y V; Tabata, T
2000-01-01
Charge-deposition distributions in thin slabs irradiated by plane-parallel electron beams are studied. The slabs considered are made of elements with atomic numbers ranging from 4 to 79. The slab thicknesses are from 0.5 to 50 mg/cm sup 2 , and the electron beam energies are from 1 to 10 MeV. Using a new Monte Carlo method (called the trajectory translation method), data on the charge-deposition density have been obtained. Theoretical analysis of these data has been performed. Based on this analysis, a semiempirical model that describes charge-deposition distributions in thin slabs has been developed. The results obtained by the semiempirical model have been compared with those obtained by the PENELOPE Monte Carlo code and show moderate agreement.
Energy Technology Data Exchange (ETDEWEB)
Korshunov, M M [L V Kirensky Institute of Physics, Siberian Branch of Russian Academy of Sciences, 660036 Krasnoyarsk (Russian Federation); Gavrichkov, V A [L V Kirensky Institute of Physics, Siberian Branch of Russian Academy of Sciences, 660036 Krasnoyarsk (Russian Federation); Ovchinnikov, S G [L V Kirensky Institute of Physics, Siberian Branch of Russian Academy of Sciences, 660036 Krasnoyarsk (Russian Federation); Nekrasov, I A [Institute of Electrophysics, Russian Academy of Sciences-Ural Division, 620016 Yekaterinburg, Amundsena 106 (Russian Federation); Kokorina, E E [Institute of Electrophysics, Russian Academy of Sciences-Ural Division, 620016 Yekaterinburg, Amundsena 106 (Russian Federation); Pchelkina, Z V [Institute of Metal Physics, Russian Academy of Sciences-Ural Division, 620041 Yekaterinburg, GSP-170 (Russian Federation)
2007-12-05
In the present work we report band structure calculations for the high-temperature superconductor Nd{sub 2-x}Ce{sub x}CuO{sub 4} in the regime of strong electronic correlations within an LDA+GTB method, which combines the local density approximation (LDA) and the generalized tight-binding method (GTB). The two mechanisms of band structure doping dependence were taken into account. Namely, the one-electron mechanism provided by the doping dependence of the crystal structure, and the many-body mechanism provided by the strong renormalization of the fermionic quasiparticles due to the large on-site Coulomb repulsion. We have shown that, in the antiferromagnetic and in the strongly correlated paramagnetic phases of the underdoped cuprates, the main contribution to the doping evolution of the band structure and Fermi surface comes from the many-body mechanism.
Energy Technology Data Exchange (ETDEWEB)
Toschi, A; Hansmann, P; Sangiovanni, G; Held, K [Institut fuer Festkoerperphysik, Technische Universitaet Wien, Vienna (Austria); Saha-Dasgupta, T [S.N.Bose National Centre for Basic Sciences, Salt Lake, Kolkata (India); Andersen, O K, E-mail: toschi@ifp.tuwien.ac.a [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany)
2010-01-15
Significant progress in the theoretical description of Mott-Hubbard metal-to-insulator transitions has been made in the last years, especially thanks to the LDA+DMFT approach (local density approximation + dynamical mean field theory). Obviously the main attention has been focused on the transition itself, as, for example, in the textbook case of the Cr-doped V{sub 2}O{sub 3}. As we discuss here, however, also the study of the insulating phase, characterized by the opening of a visible Mott-Hubbard gap in the spectral functions is far from being trivial: Strong-correlation effects make this phase strongly sensitive to small changes of external parameters, much more than one would expect for an insulator. In this situation, requiring a full consistency of the theoretical calculations with data from different spectroscopies may provide the most precise estimate for the local Coulomb interaction U in the LDA+DMFT approach.
Interpreting scratch assays using pair density dynamics and approximate Bayesian computation.
Johnston, Stuart T; Simpson, Matthew J; McElwain, D L Sean; Binder, Benjamin J; Ross, Joshua V
2014-09-01
Quantifying the impact of biochemical compounds on collective cell spreading is an essential element of drug design, with various applications including developing treatments for chronic wounds and cancer. Scratch assays are a technically simple and inexpensive method used to study collective cell spreading; however, most previous interpretations of scratch assays are qualitative and do not provide estimates of the cell diffusivity, D, or the cell proliferation rate, λ. Estimating D and λ is important for investigating the efficacy of a potential treatment and provides insight into the mechanism through which the potential treatment acts. While a few methods for estimating D and λ have been proposed, these previous methods lead to point estimates of D and λ, and provide no insight into the uncertainty in these estimates. Here, we compare various types of information that can be extracted from images of a scratch assay, and quantify D and λ using discrete computational simulations and approximate Bayesian computation. We show that it is possible to robustly recover estimates of D and λ from synthetic data, as well as a new set of experimental data. For the first time, our approach also provides a method to estimate the uncertainty in our estimates of D and λ. We anticipate that our approach can be generalized to deal with more realistic experimental scenarios in which we are interested in estimating D and λ, as well as additional relevant parameters such as the strength of cell-to-cell adhesion or the strength of cell-to-substrate adhesion.
A small shoulder of optical absorption in polycrystalline HfO2 by LDA+U approach
Qin, Liyuan; Li, Jinping; Meng, Songhe; Lu, Hantao; Tohyama, Takami
2016-10-01
The dielectric function of the wide-gap optical material HfO2 is investigated by the local density approximation (LDA)+U approach. We focus on the origin of the shoulder-like structure near the edge of the band gap in the imaginary part of the dielectric function, which has been observed on the thin films of monoclinic HfO2. A comparison study on the three polymorphs of hafnia shows that regardless of the underlying crystal structure, the existence of the shoulder is mainly controlled by the value of the shortest length of Hf-O bonds. The proposition is further supported by the numerical simulations of isostatic pressing. A possible implication in high-pressure measurements is suggested accordingly.
Derzsi, Mariana; Stasiewicz, Juliusz; Grochala, Wojciech
2011-09-01
We demonstrate that DFT calculations performed with the local density approximation (LDA) allow for significantly better reproduction of lattice constants, the unit cell volume and the density of Ag(II)SO(4) than those done with generalized gradient approximation (GGA). The LDA+U scheme, which accounts for electronic correlation effects, enables the accurate prediction of the magnetic superexchange constant of this strongly correlated material and its band gap at the Fermi level. The character of the band gap places the compound on the borderline between a Mott insulator and a charge transfer insulator. The size of the band gap (0.82 eV) indicates that AgSO(4) is a ferrimagnetic semiconductor, and possibly an attractive material for spintronics. A bulk modulus of 27.0 GPa and a compressibility of 0.037 GPa(-1) were determined for AgSO(4) from the third-order Birch-Murnaghan isothermal equation of state up to 20 GPa. Several polymorphic types compete with the ambient pressure P-1 phase as the external pressure is increased. The P-1 phase is predicted to resist pressure-induced metallization up to at least 20 GPa.
Superfluid Thomas—Fermi approximation for trapped fermi gases
Hernández, E. S.; Capuzzi, P.; Szybisz, L.
2009-02-01
We present a generalization of fermionic fluiddynamics to the case of two trapped fermion species with a contact interaction. Within a mean field approximation, we derive coupled equations of motion for the particle densities, particle currents, and anomalous pair density. For an inhomogeneous system, the equilibrium situation with vanishing currents is described by a generalized Thomas-Fermi relation that includes the superfluid gap, together with a new nonlocal gap equation that replaces the usual BCS one. These equations are numericaly solved resorting to a local density approximation (LDA). Density and gap profiles are analyzed in terms of the scattering length, revealing that the current frame can exhibit microscopic details of quantum origin that are frequently absent in more macroscopic scenarios.
Superfluid Thomas-Fermi approximation for trapped fermi gases
Energy Technology Data Exchange (ETDEWEB)
Hernandez, E S; Capuzzi, P; Szybisz, L [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, 1428 Buenos Aires (Argentina)], E-mail: shernand@df.uba.ar, E-mail: capuzzi@df.uba.ar, E-mail: szybisz@tandar.cnea.gov.ar
2009-02-01
We present a generalization of fermionic fluiddynamics to the case of two trapped fermion species with a contact interaction. Within a mean field approximation, we derive coupled equations of motion for the particle densities, particle currents, and anomalous pair density. For an inhomogeneous system, the equilibrium situation with vanishing currents is described by a generalized Thomas-Fermi relation that includes the superfluid gap, together with a new nonlocal gap equation that replaces the usual BCS one. These equations are numericaly solved resorting to a local density approximation (LDA). Density and gap profiles are analyzed in terms of the scattering length, revealing that the current frame can exhibit microscopic details of quantum origin that are frequently absent in more macroscopic scenarios.
Institute of Scientific and Technical Information of China (English)
Ken K. Chin
2011-01-01
We present a generic approximate graphical method for determining the equilibrium Fermi level and majority carrier density of a semiconductor with multiple donors and multiple acceptors compensating each other Simple and easy-to-follow procedures of the graphical method are described. By graphically plotting two wrapping step functions facing each other, one for the positive hole-ionized donor and one for the negative electron-ionized acceptor, we have the crossing point that renders the Fermi level and majority carrier density. Using the graphica method, new equations are derived, such as the carrier compensation proportional to NA/ND, not the widely quoted NA - ND. Visual insight is offered to view not only the result of graphic determination of Fermi level and majoriy carrier density but also the dominant and critical pair of donors and acceptors in compensation. The graphica method presented in this work will help to guide the design, adjustment, and improvement of the multiply doped semiconductors. Comparison of this approximate graphical method with previous work on compensation, and with some experimental results, is made. Future work in the field is proposed.
LDA+DMFT study of LaCoO{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Gorelov, Evgeny; Pavarini, Eva [IFF, IAS, Forschungszentrum Juelich, 52425 Juelich (Germany)
2010-07-01
LaCoO{sub 3} has attracted a lot of attention because of its spin-state transitions, the nature of which has been debated since decades. In this work we study LaCoO{sub 3} by means of the LDA+DMFT (local-density approximation+dynamical mean-field theory) method. Using the downfolding procedure based on the N-th Order Muffin-Tin Orbital approach, we calculate ab-initio 3d Wannier functions and construct the corresponding 5-band Hubbard model. We solve this model within dynamical mean-field approximation. We use the weak-coupling CT-quantum Monte Carlo method as impurity solver; this allows us to take into account the full rotationally-invariant Coulomb interaction, including the pair-hopping and spin-flip terms. We also retain the full self-energy matrix in orbital space. We analyze the competition between crystal-field splitting and Hund's rule coupling.
Investigation of correlation effects in FeSe and FeTe by LDA + U method
Energy Technology Data Exchange (ETDEWEB)
Lohani, H.; Mishra, P.; Sekhar, B.R., E-mail: sekhar@iopb.res.in
2015-05-15
Highlights: • Comparative study of the influence of U and J in FeSe and FeTe. • We found correlation effects are strong in Fe-3d orbitals in FeSe and FeTe. • Correlation effects are orbital selective in nature. - Abstract: We present a comparative study of the influence of Coulomb interaction and Hund’s coupling on the electronic structure of FeSe and FeTe. Our calculations are based on density functional theory (DFT) with local density approximation (LDA + U) framework employed in TB-LMTO ASA code. We found the correlation effects are orbital selective due to the strength of interorbital hybridization among the different Fe-3d orbitals mediated via the chalcogen (Se/Te-p) orbitals and are different in both the compounds. The Coulomb interaction is screened significantly by Te-p bands in FeTe. Similarly the orbital selection is different in both the compounds because of the difference in the chalcogen height.
Energy Technology Data Exchange (ETDEWEB)
Mardirossian, Narbe [Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720 (United States); Head-Gordon, Martin, E-mail: mhg@cchem.berkeley.edu [Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720 (United States); Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)
2015-02-21
A meta-generalized gradient approximation density functional paired with the VV10 nonlocal correlation functional is presented. The functional form is selected from more than 10{sup 10} choices carved out of a functional space of almost 10{sup 40} possibilities. Raw data come from training a vast number of candidate functional forms on a comprehensive training set of 1095 data points and testing the resulting fits on a comprehensive primary test set of 1153 data points. Functional forms are ranked based on their ability to reproduce the data in both the training and primary test sets with minimum empiricism, and filtered based on a set of physical constraints and an often-overlooked condition of satisfactory numerical precision with medium-sized integration grids. The resulting optimal functional form has 4 linear exchange parameters, 4 linear same-spin correlation parameters, and 4 linear opposite-spin correlation parameters, for a total of 12 fitted parameters. The final density functional, B97M-V, is further assessed on a secondary test set of 212 data points, applied to several large systems including the coronene dimer and water clusters, tested for the accurate prediction of intramolecular and intermolecular geometries, verified to have a readily attainable basis set limit, and checked for grid sensitivity. Compared to existing density functionals, B97M-V is remarkably accurate for non-bonded interactions and very satisfactory for thermochemical quantities such as atomization energies, but inherits the demonstrable limitations of existing local density functionals for barrier heights.
Pseudogap in normal underdoped phase of Bi2212: LDA + DMFT + ÃÂ£k
Nekrasov, I. A.; Kuchinskii, E. Z.; Pchelkina, Z. V.; Sadovskii, M. V.
2007-09-01
Pseudogap phenomena are observed for normal underdoped phase of different high- Tc cuprates. Among others Bi 2Sr 2CaCu 2O 8- δ (Bi2212) compound is one of the most studied experimentally [A. Damascelli, Z. Hussain, Z.-X. Shen, Rev. Mod. Phys. 75 (2003) 473; J.C. Campuzano, M.R. Norman, M. Randeria, in: K.H. Bennemann, J.B. Ketterson (Eds.), Physics of Superconductors, vol. 2, Springer, Berlin, 2004, p. 167; J. Fink et al., cond-mat/0512307; X.J. Zhou et al., cond-mat/0604284]. To describe pseudogap regime in Bi2212, we employ novel generalized DMFT + Σk approach [E.Z. Kuchinskii, I.A. Nekrasov, M.V. Sadovskii, JETP Lett. 82 (2005) 198; M.V. Sadovskii et al., Phys. Rev. B 72 (2005) 155105, and these proceedings, doi:10.1016/j.physc.2007.03.367]. This approach gives possibility to preserve conventional dynamical mean-field theory (DMFT) equations [A. Georges et al., Rev. Mod. Phys. 68 (1996) 13] and include an additional (momentum dependent) self-energy Σk. In the present case, Σk describes non-local dynamical correlations induced by short-ranged collective Heisenberg-like antiferromagnetic spin fluctuations [M.V. Sadovskii, Physics-Uspekhi 44 (2001) 515, cond-mat/0408489]. The effective single impurity problem in the DMFT + Σk is solved by numerical renormalization group (NRG) [R. Bulla, A.C. Hewson, Th. Pruschke, J. Phys. Cond. Mat. 10 (1998) 8365; R. Bulla, Phys. Rev. Lett. 83 (1999) 136]. To take into account material specific properties of two neighboring CuO 2 layers of Bi2212 we employ local density approximation (LDA) to calculate necessary model parameters, e.g. the values of intra- and interlayer hopping integrals between Cu-sites. Onsite Coulomb interaction U for x2- y2 orbital was calculated in constrained LDA method [O. Gunnarsson et al., Phys. Rev. B 39 (1989) 1708]. The value of pseudogap potential Δ was obtained within DMFT(NRG) [E.Z. Kuchinskii, I.A. Nekrasov, M.V. Sadovskii, JETP Lett. 82 (2005) 198; M.V. Sadovskii et al., Phys. Rev. B 72
Pseudogap in normal underdoped phase of Bi2212: LDA + DMFT + {sigma}{sub k}
Energy Technology Data Exchange (ETDEWEB)
Nekrasov, I.A. [Institute for Electrophysics, Russian Academy of Sciences, Ural Branch, Amundsen Str. 106, Ekaterinburg 620016 (Russian Federation)], E-mail: nekrasov@iep.uran.ru; Kuchinskii, E.Z. [Institute for Electrophysics, Russian Academy of Sciences, Ural Branch, Amundsen Str. 106, Ekaterinburg 620016 (Russian Federation); Pchelkina, Z.V. [Institute for Metal Physics, Russian Academy of Sciences, Ural Branch, S. Kovalevskoj 18, Ekaterinburg 620041 (Russian Federation); Sadovskii, M.V. [Institute for Electrophysics, Russian Academy of Sciences, Ural Branch, Amundsen Str. 106, Ekaterinburg 620016 (Russian Federation)
2007-09-01
Pseudogap phenomena are observed for normal underdoped phase of different high-T{sub c} cuprates. Among others Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8-{delta}} (Bi2212) compound is one of the most studied experimentally [A. Damascelli, Z. Hussain, Z.-X. Shen, Rev. Mod. Phys. 75 (2003) 473; J.C. Campuzano, M.R. Norman, M. Randeria, in: K.H. Bennemann, J.B. Ketterson (Eds.), Physics of Superconductors, vol. 2, Springer, Berlin, 2004, p. 167; J. Fink et al., (cond-mat/0512307); X.J. Zhou et al., (cond-mat/0604284)]. To describe pseudogap regime in Bi2212, we employ novel generalized DMFT + {sigma}{sub k} approach [E.Z. Kuchinskii, I.A. Nekrasov, M.V. Sadovskii, JETP Lett. 82 (2005) 198; M.V. Sadovskii et al., Phys. Rev. B 72 (2005) 155105, and these proceedings, (doi:10.1016/j.physc.2007.03.367)]. This approach gives possibility to preserve conventional dynamical mean-field theory (DMFT) equations [A. Georges et al., Rev. Mod. Phys. 68 (1996) 13] and include an additional (momentum dependent) self-energy {sigma}{sub k}. In the present case, {sigma}{sub k} describes non-local dynamical correlations induced by short-ranged collective Heisenberg-like antiferromagnetic spin fluctuations [M.V. Sadovskii, Physics-Uspekhi 44 (2001) 515, (cond-mat/0408489)]. The effective single impurity problem in the DMFT + {sigma}{sub k} is solved by numerical renormalization group (NRG) [R. Bulla, A.C. Hewson, Th. Pruschke, J. Phys. Cond. Mat. 10 (1998) 8365; R. Bulla, Phys. Rev. Lett. 83 (1999) 136]. To take into account material specific properties of two neighboring CuO{sub 2} layers of Bi2212 we employ local density approximation (LDA) to calculate necessary model parameters, e.g. the values of intra- and interlayer hopping integrals between Cu-sites. Onsite Coulomb interaction U for x{sup 2}-y{sup 2} orbital was calculated in constrained LDA method [O. Gunnarsson et al., Phys. Rev. B 39 (1989) 1708]. The value of pseudogap potential {delta} was obtained within DMFT(NRG) [E.Z. Kuchinskii
Kowalczyk, Piotr; Brualla, Lorenzo; Gauden, Piotr A; Terzyk, Artur P
2009-10-28
We study the applicability of the semiclassical Feynman and Hibbs (FH) (second-order or fourth-order) effective potentials to the description of the thermodynamic properties of quantum fluids at finite temperatures. First, we use path integral Monte Carlo (PIMC) simulations to estimate the thermodynamic/static properties of our model quantum fluid, i.e. low-density 4He at 10 K. With PIMC we obtain the experimental equation of state, the single-particle mean kinetic energy, the single-particle density matrix and the single-particle momentum distribution of this system at low densities. We show that our PIMC results are in full agreement with experimental data obtained with deep inelastic neutron scattering at high momentum transfers (D. Colognesi, C. Andreani, R. Senesi, Europhys. Lett., 2000, 50, 202). As expected, in this region of the 4He phase diagram, quantum effects modify the width of the single-particle momentum distribution but do not alter its Gaussian shape. Knowing the exact values of density, pressure and single-particle mean kinetic energy for our model quantum fluid, we investigate the limitations of the semiclassical FH effective potentials. We show that commonly used 'short-time' approximations to the high-temperature density matrix due to Feynman and Hibbs can only be applied in a very limited range of the 4He phase diagram. We found that FH effective potentials reproduce the experimental densities of 4He at 10 K for Lambda/a < 0.45 (Lambda = 2.73 A denotes the thermal de Broglie wavelength, a = rho(-1/3) is the mean nearest-neighbor distance in the fluid and rho denotes fluid density). Moreover, semiclassical FH effective potentials are able to correctly predict the single-particle mean kinetic energy of 4He at 10 K in a very limited range of fluid densities, i.e.Lambda/a < 0.17. We show that the ad hoc application of the semiclassical FH effective potentials for the calculation of the thermodynamic properties of dense liquid-like para
An efficient LDA+U based tight binding approach.
Sanna, Simone; Hourahine, B; Gallauner, Th; Frauenheim, Th
2007-07-01
The functionals usually applied in DFT calculations have deficiencies in describing systems with strongly localized electrons such as transition metals or rare earth (RE) compounds. In this work, we present the self-consistent charge density based functional tight binding (SCC-DFTB) calculation scheme including LDA+U like potentials and apply it for the simulation of RE-doped GaN. DFTB parameters for the simulation of GaN and a selection of rare earth ions, where the f electrons were explicitly included in the valence, have been created. The results of the simulations were tested against experimental data (where present) and against various more sophisticated but computationally more costly DFT calculations. Our approach is found to correctly reproduce the geometry and the energetic of the studied systems.
Dendritic spine detection using curvilinear structure detector and LDA classifier.
Zhang, Yong; Zhou, Xiaobo; Witt, Rochelle M; Sabatini, Bernardo L; Adjeroh, Donald; Wong, Stephen T C
2007-06-01
Dendritic spines are small, bulbous cellular compartments that carry synapses. Biologists have been studying the biochemical pathways by examining the morphological and statistical changes of the dendritic spines at the intracellular level. In this paper a novel approach is presented for automated detection of dendritic spines in neuron images. The dendritic spines are recognized as small objects of variable shape attached or detached to multiple dendritic backbones in the 2D projection of the image stack along the optical direction. We extend the curvilinear structure detector to extract the boundaries as well as the centerlines for the dendritic backbones and spines. We further build a classifier using Linear Discriminate Analysis (LDA) to classify the attached spines into valid and invalid types to improve the accuracy of the spine detection. We evaluate the proposed approach by comparing with the manual results in terms of backbone length, spine number, spine length, and spine density.
Diestler, D J
2013-06-01
Intuition suggests that a molecular system in the electronic ground state Φ0 should exhibit an electronic flux density (EFD) in response to the motion of its nuclei. If that state is described by the Born-Oppenheimer approximation (BOA), however, a straightforward calculation of the EFD yields zero, since the electrons are in a stationary state, regardless of the state of the nuclear motion. Here an alternative pathway to a nonzero EFD from a knowledge of only the BOA ground-state wave function is proposed. Via perturbation theory a complete set of approximate vibronic eigenfunctions of the whole Hamiltonian is generated. If the complete non-BOA wave function is expressed in the basis of these vibronic eigenfunctions, the ground-state contribution to the EFD is found to involve a summation over excited states. Evaluation of this sum through the so-called "average excitation energy approximation" produces a nonzero EFD. An explicit formula for the EFD for the prototypical system, namely, oriented H2+ vibrating in the electronic ground state, is derived.
March, N. H.; Nagy, Á.
A fonnally exact integral equation theory for the exchange-only potential Vx(r) in density functional theory was recently set up by Howard and March [I.A. Howard, N.H. March, J. Chem. Phys. 119 (2003) 5789]. It involved a `closure' function P(r) satisfying the exact sum rule ∫ P(r) dr = 0. The simplest choice P(r) = 0 recovers then the approximation proposed by Della Sala and Görling [F. Della Sala, A. Görling, J. Chem. Phys. 115 (2001) 5718] and by Gritsenko and Baerends [O.V. Gritsenko, E.J. Baerends, Phys. Rev. A 64 (2001) 042506]. Here, refined choices of P(r) are proposed, the most direct being based on the KLI (Krieger-Li-Iafrate) approximation. A further choice given some attention is where P(r) involves frontier orbital properties. In particular, the introduction of the LUMO (lowest unoccupied molecular) orbital, along with the energy separation between HOMO (highest occupied molecular orbital) and LUMO levels, should prove a significant step beyond current approximations to the optimized potential method, all of which involve only single-particle occupied orbitals.
Bozkaya, Uğur; Sherrill, C David
2016-05-07
An efficient implementation is presented for analytic gradients of the coupled-cluster singles and doubles (CCSD) method with the density-fitting approximation, denoted DF-CCSD. Frozen core terms are also included. When applied to a set of alkanes, the DF-CCSD analytic gradients are significantly accelerated compared to conventional CCSD for larger molecules. The efficiency of our DF-CCSD algorithm arises from the acceleration of several different terms, which are designated as the "gradient terms": computation of particle density matrices (PDMs), generalized Fock-matrix (GFM), solution of the Z-vector equation, formation of the relaxed PDMs and GFM, back-transformation of PDMs and GFM to the atomic orbital (AO) basis, and evaluation of gradients in the AO basis. For the largest member of the alkane set (C10H22), the computational times for the gradient terms (with the cc-pVTZ basis set) are 2582.6 (CCSD) and 310.7 (DF-CCSD) min, respectively, a speed up of more than 8-folds. For gradient related terms, the DF approach avoids the usage of four-index electron repulsion integrals. Based on our previous study [U. Bozkaya, J. Chem. Phys. 141, 124108 (2014)], our formalism completely avoids construction or storage of the 4-index two-particle density matrix (TPDM), using instead 2- and 3-index TPDMs. The DF approach introduces negligible errors for equilibrium bond lengths and harmonic vibrational frequencies.
Tracking topic birth and death in LDA.
Energy Technology Data Exchange (ETDEWEB)
Wilson, Andrew T.; Robinson, David Gerald
2011-09-01
Most topic modeling algorithms that address the evolution of documents over time use the same number of topics at all times. This obscures the common occurrence in the data where new subjects arise and old ones diminish or disappear entirely. We propose an algorithm to model the birth and death of topics within an LDA-like framework. The user selects an initial number of topics, after which new topics are created and retired without further supervision. Our approach also accommodates many of the acceleration and parallelization schemes developed in recent years for standard LDA. In recent years, topic modeling algorithms such as latent semantic analysis (LSA)[17], latent Dirichlet allocation (LDA)[10] and their descendants have offered a powerful way to explore and interrogate corpora far too large for any human to grasp without assistance. Using such algorithms we are able to search for similar documents, model and track the volume of topics over time, search for correlated topics or model them with a hierarchy. Most of these algorithms are intended for use with static corpora where the number of documents and the size of the vocabulary are known in advance. Moreover, almost all current topic modeling algorithms fix the number of topics as one of the input parameters and keep it fixed across the entire corpus. While this is appropriate for static corpora, it becomes a serious handicap when analyzing time-varying data sets where topics come and go as a matter of course. This is doubly true for online algorithms that may not have the option of revising earlier results in light of new data. To be sure, these algorithms will account for changing data one way or another, but without the ability to adapt to structural changes such as entirely new topics they may do so in counterintuitive ways.
Śmiga, Szymon; Fabiano, Eduardo; Constantin, Lucian A; Della Sala, Fabio
2017-02-14
The development of semilocal models for the kinetic energy density (KED) is an important topic in density functional theory (DFT). This is especially true for subsystem DFT, where these models are necessary to construct the required non-additive embedding contributions. In particular, these models can also be efficiently employed to replace the exact KED in meta-Generalized Gradient Approximation (meta-GGA) exchange-correlation functionals allowing to extend the subsystem DFT applicability to the meta-GGA level of theory. Here, we present a two-dimensional scan of semilocal KED models as linear functionals of the reduced gradient and of the reduced Laplacian, for atoms and weakly bound molecular systems. We find that several models can perform well but in any case the Laplacian contribution is extremely important to model the local features of the KED. Indeed a simple model constructed as the sum of Thomas-Fermi KED and 1/6 of the Laplacian of the density yields the best accuracy for atoms and weakly bound molecular systems. These KED models are tested within subsystem DFT with various meta-GGA exchange-correlation functionals for non-bonded systems, showing a good accuracy of the method.
Malheiro, Carine; Mendiboure, Bruno; Plantier, Frédéric; Blas, Felipe J; Miqueu, Christelle
2014-04-07
As a first step of an ongoing study of thermodynamic properties and adsorption of complex fluids in confined media, we present a new theoretical description for spherical monomers using the Statistical Associating Fluid Theory for potential of Variable Range (SAFT-VR) and a Non-Local Density Functional Theory (NLDFT) with Weighted Density Approximations (WDA). The well-known Modified Fundamental Measure Theory is used to describe the inhomogeneous hard-sphere contribution as a reference for the monomer and two WDA approaches are developed for the dispersive terms from the high-temperature Barker and Henderson perturbation expansion. The first approach extends the dispersive contributions using the scalar and vector weighted densities introduced in the Fundamental Measure Theory (FMT) and the second one uses a coarse-grained (CG) approach with a unique weighted density. To test the accuracy of this new NLDFT/SAFT-VR coupling, the two versions of the theoretical model are compared with Grand Canonical Monte Carlo (GCMC) molecular simulations using the same molecular model. Only the version with the "CG" approach for the dispersive terms provides results in excellent agreement with GCMC calculations in a wide range of conditions while the "FMT" extension version gives a good representation solely at low pressures. Hence, the "CG" version of the theoretical model is used to reproduce methane adsorption isotherms in a Carbon Molecular Sieve and compared with experimental data after a characterization of the material. The whole results show an excellent agreement between modeling and experiments. Thus, through a complete and consistent comparison both with molecular simulations and with experimental data, the NLDFT/SAFT-VR theory has been validated for the description of monomers.
Malheiro, Carine; Mendiboure, Bruno; Plantier, Frédéric; Blas, Felipe J.; Miqueu, Christelle
2014-04-01
As a first step of an ongoing study of thermodynamic properties and adsorption of complex fluids in confined media, we present a new theoretical description for spherical monomers using the Statistical Associating Fluid Theory for potential of Variable Range (SAFT-VR) and a Non-Local Density Functional Theory (NLDFT) with Weighted Density Approximations (WDA). The well-known Modified Fundamental Measure Theory is used to describe the inhomogeneous hard-sphere contribution as a reference for the monomer and two WDA approaches are developed for the dispersive terms from the high-temperature Barker and Henderson perturbation expansion. The first approach extends the dispersive contributions using the scalar and vector weighted densities introduced in the Fundamental Measure Theory (FMT) and the second one uses a coarse-grained (CG) approach with a unique weighted density. To test the accuracy of this new NLDFT/SAFT-VR coupling, the two versions of the theoretical model are compared with Grand Canonical Monte Carlo (GCMC) molecular simulations using the same molecular model. Only the version with the "CG" approach for the dispersive terms provides results in excellent agreement with GCMC calculations in a wide range of conditions while the "FMT" extension version gives a good representation solely at low pressures. Hence, the "CG" version of the theoretical model is used to reproduce methane adsorption isotherms in a Carbon Molecular Sieve and compared with experimental data after a characterization of the material. The whole results show an excellent agreement between modeling and experiments. Thus, through a complete and consistent comparison both with molecular simulations and with experimental data, the NLDFT/SAFT-VR theory has been validated for the description of monomers.
Hartley, Madeline K; Vine, Seanna; Walsh, Elizabeth; Avrantinis, Sara; Daub, G William; Cave, Robert J
2016-03-03
We investigate several representative density functional theory approaches for the calculation of relative activation energies and free energies of a set of model pericyclic reactions, some of which have been studied experimentally. In particular, we use a standard hybrid functional (B3LYP), the same hybrid functional augmented with a basis set superposition error and dispersion correction, a meta-hybrid functional developed to treat transition states and weak interactions (M06-2X), and the recently implemented random phase approximation (RPA) based on Kohn-Sham orbitals from conventional density functional theory by Furche and co-workers. We apply these methods to calculate relative activation energies and estimated free energies for the amide acetal Claisen rearrangement. We focus on relative activation energies to assess the effects of steric and weak interactions in the various methods and compare with experiment where possible. We also discuss the advantages of using this set of reactions as a test bed for the comparison of treatments of weak interactions. We conclude that all methods yield similar trends in relative reactivity, but the RPA yields results in best agreement with the experimental values.
First-principle study on bonding mechanism of ZnO by LDA+U method
Energy Technology Data Exchange (ETDEWEB)
Zhou, G.C. [Key Laboratory of Low Dimensional Materials and Application Technology (Xiangtan University), Ministry of Education, Institute of Modern Physics, Xiangtan University, Xiangtan 411105 (China); Sun, L.Z. [Key Laboratory of Low Dimensional Materials and Application Technology (Xiangtan University), Ministry of Education, Institute of Modern Physics, Xiangtan University, Xiangtan 411105 (China) and National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science, 200083 Shanghai (China)]. E-mail: lzsun@xtu.edu.cn; Zhong, X.L. [Key Laboratory of Low Dimensional Materials and Application Technology (Xiangtan University), Ministry of Education, Institute of Modern Physics, Xiangtan University, Xiangtan 411105 (China); Chen Xiaoshuang [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science, 200083 Shanghai (China)]. E-mail: xschen@mail.sitp.ac.cn; Wei Lu [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science, 200083 Shanghai (China); Wang, J.B. [Key Laboratory of Low Dimensional Materials and Application Technology (Xiangtan University), Ministry of Education, Institute of Modern Physics, Xiangtan University, Xiangtan 411105 (China)]. E-mail: jbwang@xtu.edu.cn
2007-08-13
The electronic structure and the bonding mechanism of ZnO have been studied by using the Full-Potential Linear Augmented Plane Wave (FP-LAPW) method within the density-functional theory (DFT) based on LDA+U exchange correlation potential. The valence and the bonding charge density are calculated and compared with those derived from LDA and GGA to describe the bonding mechanism. The charge transfer along with the bonding process is analyzed by using the theory of Atoms in Molecules (AIM). The bonding, the topological characteristics and the p-d coupling effects on the bonding mechanism of ZnO are shown quantitatively with the critical points (CPs) along the bonding trajectory and the charge in the atomic basins. Meanwhile, the bonding characteristics for wurtzite, zinc blende and rocksalt phase of ZnO are discussed systematically in the present paper.
Stoffel, Ralf P.; Deringer, Volker L.; Simon, Ronnie E.; Hermann, Raphaël P.; Dronskowski, Richard
2015-03-01
We present a comprehensive survey of electronic and lattice-dynamical properties of crystalline antimony telluride (Sb2Te3). In a first step, the electronic structure and chemical bonding have been investigated, followed by calculations of the atomic force constants, phonon dispersion relationships and densities of states. Then, (macroscopic) physical properties of Sb2Te3 have been computed, namely, the atomic thermal displacement parameters, the Grüneisen parameter γ, the volume expansion of the lattice, and finally the bulk modulus B. We compare theoretical results from three popular and economic density-functional theory (DFT) approaches: the local density approximation (LDA), the generalized gradient approximation (GGA), and a posteriori dispersion corrections to the latter. Despite its simplicity, the LDA shows excellent performance for all properties investigated—including the Grüneisen parameter, which only the LDA is able to recover with confidence. In the absence of computationally more demanding hybrid DFT methods, the LDA seems to be a good choice for further lattice dynamical studies of Sb2Te3 and related layered telluride materials.
Comparison of LDA and SPRT on Clinical Dataset Classifications.
Lee, Chih; Nkounkou, Brittany; Huang, Chun-Hsi
2011-04-19
In this work, we investigate the well-known classification algorithm LDA as well as its close relative SPRT. SPRT affords many theoretical advantages over LDA. It allows specification of desired classification error rates α and β and is expected to be faster in predicting the class label of a new instance. However, SPRT is not as widely used as LDA in the pattern recognition and machine learning community. For this reason, we investigate LDA, SPRT and a modified SPRT (MSPRT) empirically using clinical datasets from Parkinson's disease, colon cancer, and breast cancer. We assume the same normality assumption as LDA and propose variants of the two SPRT algorithms based on the order in which the components of an instance are sampled. Leave-one-out cross-validation is used to assess and compare the performance of the methods. The results indicate that two variants, SPRT-ordered and MSPRT-ordered, are superior to LDA in terms of prediction accuracy. Moreover, on average SPRT-ordered and MSPRT-ordered examine less components than LDA before arriving at a decision. These advantages imply that SPRT-ordered and MSPRT-ordered are the preferred algorithms over LDA when the normality assumption can be justified for a dataset.
Efficient face recognition method based on DCT and LDA
Institute of Scientific and Technical Information of China (English)
张燕昆; 刘重庆
2004-01-01
It has been demonstrated that the linear discriminant analysis (LDA) is an effective approach in face recognition tasks. However, due to the high dimensionality of an image space, many LDA based approaches first use the principal component analysis (PCA) to project an image into a lower dimensional space, then perform the LDA transform to extract discriminant feature. But some useful discriminant information to the following LDA transform will be lost in the PCA step. To overcome these defects, a face recognition method based on the discrete cosine transform (DCT) and the LDA is proposed. First the DCT is used to achieve dimension reduction, then LDA transform is performed on the lower space to extract features. Two face databases are used to test our method and the correct recognition rates of 97.5 % and 96.0 % are obtained respectively. The performance of the proposed method is compared with that of the PCA + LDA method and the results show that the method proposed outperforms the PCA + LDA method.
Uncertain LDA: Including Observation Uncertainties in Discriminative Transforms.
Saeidi, Rahim; Astudillo, Ramon Fernandez; Kolossa, Dorothea
2016-07-01
Linear discriminant analysis (LDA) is a powerful technique in pattern recognition to reduce the dimensionality of data vectors. It maximizes discriminability by retaining only those directions that minimize the ratio of within-class and between-class variance. In this paper, using the same principles as for conventional LDA, we propose to employ uncertainties of the noisy or distorted input data in order to estimate maximally discriminant directions. We demonstrate the efficiency of the proposed uncertain LDA on two applications using state-of-the-art techniques. First, we experiment with an automatic speech recognition task, in which the uncertainty of observations is imposed by real-world additive noise. Next, we examine a full-scale speaker recognition system, considering the utterance duration as the source of uncertainty in authenticating a speaker. The experimental results show that when employing an appropriate uncertainty estimation algorithm, uncertain LDA outperforms its conventional LDA counterpart.
Magnetism of UPtAl and UIrAl; LDA+U calculations
Energy Technology Data Exchange (ETDEWEB)
Rusz, Jan [Department of Electronic Structures, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague 2 (Czech Republic)]. E-mail: rusz@mag.mff.cuni.cz; Divis, Martin [Department of Electronic Structures, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague 2 (Czech Republic)
2005-04-15
We report on electronic structure calculations of UPtAl and UIrAl ternary uranium based intermetallic compounds. Calculations were performed in the framework of density functional theory using LDA+U exchange correlation potential. Full relaxation of U and J parameters was performed with the aim of obtaining correct total magnetic moments on uranium site. These parameters are then used in subsequent analysis of magnetic moments (including spin and orbital components) and hybridization effects.
Effects of d-electrons in pseudopotential screened-exchange density functional calculations
Lee, Byounghak; Wang, Lin-Wang; Canning, Andrew
2008-06-01
We report a theoretical study on the role of shallow d states in the screened-exchange local density approximation (sX-LDA) band structure of binary semiconductor systems. We found that inaccurate pseudo-wave functions can lead to (1) an overestimation of the screened-exchange interaction between the localized d states and the delocalized higher energy s and p states, and (2) an underestimation of the screened-exchange interaction between the d states. The resulting sX-LDA band structures have substantially smaller band gaps compared with experiments. We correct the pseudo-wave functions of d states by including the semicore s and p states of the same shell in the valence states. The correction of pseudo-wave functions yields band gaps and d-state binding energies in good agreement with experiments and the full potential linearized augmented plane wave sX-LDA calculations. Compared with the quasiparticle GW method, our sX-LDA results shows not only similar quality on the band gaps but also much better d-state binding energies. Combined with its capability of ground-state structure calculation, the sX-LDA is expected to be a valuable theoretical tool for the II-VI and III-V (especially the III-N) bulk semiconductors and nanostructure studies.
Buda, I. G.; Lane, C.; Barbiellini, B.; Ruzsinszky, A.; Sun, J.; Bansil, A.
2017-03-01
We discuss self-consistently obtained ground-state electronic properties of monolayers of graphene and a number of ’beyond graphene’ compounds, including films of transition-metal dichalcogenides (TMDs), using the recently proposed strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation (meta-GGA) to the density functional theory. The SCAN meta-GGA results are compared with those based on the local density approximation (LDA) as well as the generalized gradient approximation (GGA). As expected, the GGA yields expanded lattices and softened bonds in relation to the LDA, but the SCAN meta-GGA systematically improves the agreement with experiment. Our study suggests the efficacy of the SCAN functional for accurate modeling of electronic structures of layered materials in high-throughput calculations more generally.
Energy Technology Data Exchange (ETDEWEB)
Kuwahara, Riichi [Department of Physics, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501 (Japan); Accelrys K. K., Kasumigaseki Tokyu Building 17F, 3-7-1 Kasumigaseki, Chiyoda-ku, Tokyo 100-0013 (Japan); Tadokoro, Yoichi; Ohno, Kaoru, E-mail: ohno@ynu.ac.jp [Department of Physics, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501 (Japan)
2014-08-28
In this paper, we calculate kinetic and potential energy contributions to the electronic ground-state total energy of several isolated atoms (He, Be, Ne, Mg, Ar, and Ca) by using the local density approximation (LDA) in density functional theory, the Hartree–Fock approximation (HFA), and the self-consistent GW approximation (GWA). To this end, we have implemented self-consistent HFA and GWA routines in our all-electron mixed basis code, TOMBO. We confirm that virial theorem is fairly well satisfied in all of these approximations, although the resulting eigenvalue of the highest occupied molecular orbital level, i.e., the negative of the ionization potential, is in excellent agreement only in the case of the GWA. We find that the wave function of the lowest unoccupied molecular orbital level of noble gas atoms is a resonating virtual bound state, and that of the GWA spreads wider than that of the LDA and thinner than that of the HFA.
Kuwahara, Riichi; Tadokoro, Yoichi; Ohno, Kaoru
2014-08-28
In this paper, we calculate kinetic and potential energy contributions to the electronic ground-state total energy of several isolated atoms (He, Be, Ne, Mg, Ar, and Ca) by using the local density approximation (LDA) in density functional theory, the Hartree-Fock approximation (HFA), and the self-consistent GW approximation (GWA). To this end, we have implemented self-consistent HFA and GWA routines in our all-electron mixed basis code, TOMBO. We confirm that virial theorem is fairly well satisfied in all of these approximations, although the resulting eigenvalue of the highest occupied molecular orbital level, i.e., the negative of the ionization potential, is in excellent agreement only in the case of the GWA. We find that the wave function of the lowest unoccupied molecular orbital level of noble gas atoms is a resonating virtual bound state, and that of the GWA spreads wider than that of the LDA and thinner than that of the HFA.
König, Carolin; Schlüter, Nicolas; Neugebauer, Johannes
2013-01-01
In subsystem time-dependent density functional theory (TDDFT) [J. Neugebauer, J. Chem. Phys. 126, 134116 (2007), 10.1063/1.2713754] localized excitations are used to calculate delocalized excitations in large chromophore aggregates. We have extended this formalism to allow for the Tamm-Dancoff approximation (TDA). The resulting response equations have a form similar to a perturbative configuration interaction singles (CIS) approach. Thus, the inter-subsystem matrix elements in subsystem TDA can, in contrast to the full subsystem-TDDFT case, directly be interpreted as exciton coupling matrix elements. Here, we present the underlying theory of subsystem TDDFT within the TDA as well as first applications. Since for some classes of pigments, such as linear polyenes and carotenoids, TDA has been reported to perform better than full TDDFT, we also report applications of this formalism to exciton couplings in dimers of such pigments and in mixed bacteriochlorophyll-carotenoid systems. The improved description of the exciton couplings can be traced back to a more balanced description of the involved local excitations.
Liu, Jie; Herbert, John M.
2015-07-01
A novel formulation of time-dependent density functional theory (TDDFT) is derived, based on non-orthogonal, absolutely-localized molecular orbitals (ALMOs). We call this approach TDDFT(MI), in reference to ALMO-based methods for describing molecular interactions (MI) that have been developed for ground-state applications. TDDFT(MI) is intended for efficient excited-state calculations in systems composed of multiple, weakly interacting chromophores. The efficiency is based upon (1) a local excitation approximation; (2) monomer-based, singly-excited basis states; (3) an efficient localization procedure; and (4) a one-step Davidson method to solve the TDDFT(MI) working equation. We apply this methodology to study molecular dimers, water clusters, solvated chromophores, and aggregates of naphthalene diimide that form the building blocks of self-assembling organic nanotubes. Absolute errors of 0.1-0.3 eV with respect to supersystem methods are achievable for these systems, especially for cases involving an excited chromophore that is weakly coupled to several explicit solvent molecules. Excited-state calculations in an aggregate of nine naphthalene diimide monomers are ˜40 times faster than traditional TDDFT calculations.
Correlation effects and spin-orbit interaction in Sr{sub 3}Ru{sub 2}O{sub 7}: LDA+DMFT study
Energy Technology Data Exchange (ETDEWEB)
Gorelov, Evgeny; Zhang, Guoren; Pavarini, Eva [IAS-3, Forschungszentrum Juelich, 52425 Juelich (Germany)
2013-07-01
The layered ruthenates of the Ruddlesden-Popper family Sr{sub n+1}Ru{sub n}O{sub 3n+1} are interesting examples of strongly correlated transition metal compounds. Due to competing kinetic and Coulomb energies, that are of the same order for Ru 4d electrons, these compounds have very rich phase diagram, including Mott-insulator, ferro- and meta-magnetic phases. Among layered ruthenates the bilayered compound Sr{sub 3}Ru{sub 2}O{sub 7} is particularly interesting. It is known to be a paramagnetic metal close to ferro-magnetism and exhibits a metamagnetic behavior in external magnetic field. By using the LDA+DMFT (local-density approximation + dynamical mean-field theory) approach, we study magnetic properties and electron mass renormalization due to correlation effects. In our LDA+DMFT scheme we use maximally-localized Wannier orbitals obtained from Linearized Augmented Plane Wave (LAPW) calculations to build a low-energy Hubbard model for the Ru d bands; we use the weak-coupling CT-quantum Monte Carlo method to solve the quantum impurity problem. We take into account the full rotationally-invariant Coulomb interaction, as well as full on-site self-energy matrix in orbital space with spin-orbit coupling.
DEFF Research Database (Denmark)
Marchukov, O. V.; Eriksen, E. H.; Midtgaard, J. M.
2016-01-01
-trivial geometric factors that depend solely on the geometry of the confinement through the single-particle eigenstates of the external potential. To obtain accurate effective Hamiltonians to describe such systems one needs to be able to compute these geometric factors with high precision which is difficult due...... to the computational complexity of the high-dimensional integrals involved. An approach using the local density approximation would therefore be a most welcome approximation due to its simplicity. Here we assess the accuracy of the local density approximation by going beyond the simple harmonic oscillator that has...
Reshak, Ali Hussain; Khenata, R; Kityk, I V; Plucinski, K J; Auluck, S
2009-04-30
An all electron full potential linearized augmented plane wave method has been applied for a theoretical study of the band structure, density of states, and electron charge density of a noncentrosymmetric chalcopyrite compound HgGa(2)S(4) using three different approximations for the exchange correlation potential. Our calculations show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at Gamma resulting in a direct energy gap of about 2.0, 2.2, and 2.8 eV for local density approximation (LDA), generalized gradient approximation (GGA), and Engel-Vosko (EVGGA) compared to the experimental value of 2.84 eV. We notice that EVGGA shows excellent agreement with the experimental data. This agreement is attributed to the fact that the Engel-Vosko GGA formalism optimizes the corresponding potential for band structure calculations. We make a detailed comparison of the density of states deduced from the X-ray photoelectron spectra with our calculations. We find that there is a strong covalent bond between the Hg and S atoms and Ga and S atoms. The Hg-Hg, Ga-Ga, and S-S bonds are found to be weaker than the Hg-S and Ga-S bonds showing that a covalent bond exists between Hg and S atoms and Ga and S atoms.
Efficient estimation of burst-mode LDA power spectra
DEFF Research Database (Denmark)
Velte, Clara Marika; George, William K
2010-01-01
requirements for good statistical convergence due to the random sampling of the data. In the present work, the theory for estimating burst-mode LDA spectra using residence time weighting is discussed and a practical estimator is derived and applied. A brief discussion on the self-noise in spectra...... (axisymmetric turbulent jet). The burst-mode LDA spectra are compared to corresponding spectra from hot-wire data obtained in the same experiments, and to LDA spectra produced by the sample-and-hold methodology. The spectra computed from the residence-time weighted burst-mode algorithm proposed herein compare...
The LDA-1/2 technique: Recent developments
Ferreira, Luiz G.; Pelá, Ronaldo R.; Teles, Lara K.; Marques, Marcelo; Ribeiro, Mauro, Jr.; Furthmüller, Jürgen
2013-12-01
This paper is a review of the LDA(GGA)-1/2 method for band calculation. We review the many applications of the method: band gaps, semiconductor interfaces, semiconductor alloys. The number of applications where the method fails is minimal. Leading to results with a precision comparable to Hedin's GW method, LDA-1/2 has the advantage of being orders of magnitude faster. The paper begins by a short theoretical review in which we try not repeat what is already published. Then we present some results that are scattered in the literature. We find that LDA(GGA)-1/2 is the recommended method for excited state energy calculations.
Zhang, Wei-Bing; Li, Jie; Tang, Bi-Yu
2013-06-28
The structural, electronic, magnetic, and elastic properties of hexagonal nickel sulfide (NiS) have been investigated comparatively by Density Functional theory (DFT) and DFT plus correction for on-site Coulomb interaction (DFT+U), in which two different exchange correlation functionals local density approximations (LDA) and general gradient approximations (GGA) in the form of Perdew-Burke-Ernzerhof (PBE) are used. Our results indicate LDA and PBE methods predict hexagonal NiS to be a paramagnetic metal whereas LDA(PBE)+U calculations with reasonable on-site Coulomb interaction energy give the antiferromagnetic insulating state of low temperature hexagonal NiS successfully. Meanwhile, compared with LDA(PBE) results, LDA(PBE)+U methods give larger lattice parameters, crystal volume, and shear constant c44, consistent with the experimental picture during high-low temperature phase transition of hexagonal NiS, in which an increase of the shear constant c44 and lattice parameters were found in the low-temperature antiferromagnetic phase. The present DFT and DFT+U calculations provide a reasonable description for the properties of high temperature and low temperature hexagonal NiS respectively, which indicates that electronic correlation is responsible for this high-low temperature phase transition.
LDA boost classification: boosting by topics
Lei, La; Qiao, Guo; Qimin, Cao; Qitao, Li
2012-12-01
AdaBoost is an efficacious classification algorithm especially in text categorization (TC) tasks. The methodology of setting up a classifier committee and voting on the documents for classification can achieve high categorization precision. However, traditional Vector Space Model can easily lead to the curse of dimensionality and feature sparsity problems; so it affects classification performance seriously. This article proposed a novel classification algorithm called LDABoost based on boosting ideology which uses Latent Dirichlet Allocation (LDA) to modeling the feature space. Instead of using words or phrase, LDABoost use latent topics as the features. In this way, the feature dimension is significantly reduced. Improved Naïve Bayes (NB) is designed as the weaker classifier which keeps the efficiency advantage of classic NB algorithm and has higher precision. Moreover, a two-stage iterative weighted method called Cute Integration in this article is proposed for improving the accuracy by integrating weak classifiers into strong classifier in a more rational way. Mutual Information is used as metrics of weights allocation. The voting information and the categorization decision made by basis classifiers are fully utilized for generating the strong classifier. Experimental results reveals LDABoost making categorization in a low-dimensional space, it has higher accuracy than traditional AdaBoost algorithms and many other classic classification algorithms. Moreover, its runtime consumption is lower than different versions of AdaBoost, TC algorithms based on support vector machine and Neural Networks.
Estimation of burst-mode LDA power spectra
DEFF Research Database (Denmark)
Velte, Clara Marika; George, William K.; Buchhave, Preben
2014-01-01
The estimation of power spectra from LDA data provides signal processing challenges for fluid dynamicists for several reasons: acquisition is dictated by randomly arriving particles, the registered particle velocities tend to be biased toward higher values, and the signal is highly intermittent...... turbulent jet. These are compared with corresponding hot-wire spectra as well as to alternative algorithms for LDA signals such as the time-slot correlation method, sample-and-hold and common weighting schemes....
Local time estimation for the slotted correlation function of randomly sampled LDA data
Energy Technology Data Exchange (ETDEWEB)
Nobach, H. [Fachgebiet Stroemungslehre und Aerodynamik, Technische Universitaet Darmstadt (Germany)
2002-03-01
The task of autocorrelation and power spectral density estimation from velocity data sampled irregularly in time by a laser-Doppler anemometer (LDA) is addressed in this article. A new method based on the slotting technique was found to be a very reliable estimator. This article describes specific improvements of the slotting technique, the model-based variance estimation and the spectral transform leading to more accurate estimates of the autocorrelation function and the power spectral density. Furthermore, the new method yields more information especially at short time lags of the autocorrelation function, which can be used to derive improved estimates of the Taylor time scale. (orig.)
Boosting training for myoelectric pattern recognition using Mixed-LDA.
Liu, Jianwei; Sheng, Xinjun; Zhang, Dingguo; Zhu, Xiangyang
2014-01-01
Pattern recognition based myoelectric prostheses (MP) need a training procedure for calibrating the classifier. Due to the non-stationarity inhered in surface electromyography (sEMG) signals, the system should be retrained day by day in long-term use of MP. To boost the training procedure in later periods, we propose a method, namely Mixed-LDA, which computes the parameters of LDA through combining the model estimated on the incoming training samples of the current day with the prior models available from earlier days. An experiment ranged for 10 days on 5 subjects was carried out to simulate the long-term use of MP. Results show that the Mixed-LDA is significantly better than the baseline method (LDA) when few samples are used as training set in the new (current) day. For instance, in the task including 13 hand and wrist motions, the average classification rate of the Mixed-LDA is 88.74% when the number of training samples is 104 (LDA: 79.32%). This implies that the approach has the potential to improve the usability of MP based on pattern recognition by reducing the training time.
Institute of Scientific and Technical Information of China (English)
谭明秋; 陶向明
2001-01-01
We report on a self-consistent full-potential linear muffin tin orbital band-structure calculation for the heavy fermion (HF) compound LiV2O4. It is found that a stable local spin density approximation solution for LiV2O4 is lower in total energy than the local density approximation calculation. We speculate that the mechanism responsible for HF properties in LiV2O4 might be of spin fluctuation type and is different from the Kondo mechanism in conventional 4f and 5f HF compounds.
Institute of Scientific and Technical Information of China (English)
喻典; 陈志达; 王繁; 李述周
2001-01-01
Ionization Potentials and electron affinities of 103 elements arecalculated by density functional theory at local density approximation (LDA) level and the LDA/AN level with further non-local corrections for exchange and correlation included self-consistently.The finite difference method is used in calculations on electronegativity and hardness of 103 elements.The calculated results for the various quantities represent an improvement over previous calculations by Robles and Bartolotti under a spin polarized density function theory with the ΧGL and Χα approximations to the exchange-correlation function.The present calculation is to examine both the LDA and LDA/NL approximations in calculations for the ionization potential and electron affinity of the elements with an improved slater transition-state method,and relativistic effects have also been taken into account in the present paper for 103 elements as compared with 86 in the previous work.It is shown that the results calculated by LDA/NL and the improved slater transition-state method in general agree well with experimental values presented by Pearson,and are better than the reported values in the literatures[11,12].%应用密度泛函理论的DFT-LDA、DFT-LDA/NL和改进的Slater过渡态方法,把元素的电离能和电子亲合能的计算扩展到周期表的103种元素.并用有限差分方法计算了这103种元素的电负性和硬度.计算中考虑了相对论效应.计算结果比以前Robles等用密度泛函理论的XGL和Xα近似的交换相关泛函的计算结果有所改进,更接近实验值.
Banerjee, Arup; Harbola, Manoj K.
1999-11-01
van Leeuwen and Baerends proposed a Becke-like nonlocal correction to the local-density-approximation (LDA) exchange-correlation potential so that its asymptotic structure becomes exact i.e., -1/r [Phys. Rev. A 49, 2421 (1994)]. They showed that it significantly improves the value of the highest occupied orbital eigenvalue of atoms and molecules. However, the correction is exchangelike in nature. With this in mind, in this paper we investigate how this correction affects the total energies and highest eigenvalues within the exchange-only approximation. We show that the potential also corrects the LDA errors substantially within this approximation, and leads to total energies and high eigenvalues which compare well with their Hartree-Fock counterparts. Improvement in the asymptotic behavior of the potential should also result in better values of the response properties of these systems. We show that with this correction one obtains better estimates, both within the exchange-only approximation and with correlation included, of the linear and nonlinear polarizabilities of inert gas atoms. This is quite significant, since the LDA is known to overestimate the nonlinear polarizabilities of these atoms by roughly 100%. On the other hand, for alkaline-earth atoms the values of polarizabilities obtained with this correction are not satisfactory. Nonetheless, hyperpolarizabilities show a marked improvement over the LDA results.
The Effect of Dead Time in Random Sampling of the LDA
Velte, Clara; Buchhave, Preben; George, William
2012-11-01
The random sampling emanating from the acquisition of velocities of randomly arriving particles in LDA measurements has since Gaster and Roberts commonly been believed to eliminate aliasing. For a perfect signal, in the sense that acquisition is truly instant and random, this is in principle correct. For real signals however, the acquisition is always afflicted with some finite time/space averaging. This hinders the capture of all realizations, and re-introduces aliasing. Contrary to common practice, using the time slot approximation autocorrelation to obtain the power spectrum also re-introduces aliasing (as noted even by Blackman and Tukey). We will demonstrate techniques for minimizing adverse effects.
Institute of Scientific and Technical Information of China (English)
陈祥磊; 孔伟; 杜淮江; 叶邦角
2009-01-01
On the basis of local density approximation, superposed-neutral-atom model and the finite-difference method (SNA-FD) are used to calculate the positron bulk lifetime and positron monovacancy lifetime in crystals of elements of the periodic table. The distribution of positron wavefunction and positron annihilation rate are analyzed. The calculated results of positron bulk lifetime in elementary substance agree well with the experiment results in literatures, which shows that the method of SNA-FD is an effective method in the study of positron annihilation in elementary substance.%在局域密度近似理论(LDA)的基础上用中性原子叠加模型和有限插分方法(SNA-FD)计算了元素周期表中各种元素单晶的正电子体寿命和单空位寿命.分析了不同结构的单晶中自由正电子的分布信息和湮没信息.元素单晶的正电子寿命计算值与文献中的实验测量值相符合,表明LDA基础上的SNA-FD方法可以作为单晶中正电子湮没理论计算的有效研究手段.
First-principles LDA+U study of magnetism in CuxIn1-xN
González-García, Alvaro; López-Pérez, William; González-Hernández, Rafael
2013-03-01
We have carried out First-principles spin-polarized calculations in order to study the electronic structure and magnetism in Cu-doped InN using the LDA+U and LDA formalisms within density functional theory (DFT) with a plane-wave ultrasoft pseudopotential scheme. We found a stable ferromagnetic state in Cu0.0625In0.9375N with a total magnetization of 1.98μB per supercell, indicating Cu orders ferromagnetically in InN. The results indicate that the ferromagnetic ground state originates from the hybridized Cu(3d)-N(2p)-In(5p)-N(2p) chain formed through p-d coupling. Formation energy and ground state calculations have been performed for ferromagnetic and antiferromagnetic states of CuxIn1-xN (x=0,0625 and 0,125) by LDA+U and LDA formalisms. A weak ferromagnetic behavior for CuxIn1-xN (x=0,125) was found. The results predicted an AFM ground state for cases where the Cu atoms are closer. For longer Cu-Cu distances a stable FM ground state was found. This ferromagnetic behavior in CuxIn1-xN (x=0,125) could be tuned with In or N vacancies.
DEFF Research Database (Denmark)
Senjean, Bruno; Knecht, Stefan; Jensen, Hans Jørgen Aa
2015-01-01
Gross-Oliveira-Kohn density-functional theory (GOK-DFT) for ensembles is, in principle, very attractive but has been hard to use in practice. A practical model based on GOK-DFT for the calculation of electronic excitation energies is discussed. The model relies on two modifications of GOK-DFT: us...
Recent advances in density functional methods, pt. 1-2
Chong, Delano P
1995-01-01
Of all the different areas in computational chemistry, density functional theory (DFT) enjoys the most rapid development. Even at the level of the local density approximation (LDA), which is computationally less demanding, DFT can usually provide better answers than Hartree-Fock formalism for large systems such as clusters and solids. For atoms and molecules, the results from DFT often rival those obtained by ab initio quantum chemistry, partly because larger basis sets can be used. Such encouraging results have in turn stimulated workers to further investigate the formal theory as well as the
Micro analysis of fringe field formed inside LDA measuring volume
Ghosh, Abhijit; Nirala, A. K.
2016-05-01
In the present study we propose a technique for micro analysis of fringe field formed inside laser Doppler anemometry (LDA) measuring volume. Detailed knowledge of the fringe field obtained by this technique allows beam quality, alignment and fringe uniformity to be evaluated with greater precision and may be helpful for selection of an appropriate optical element for LDA system operation. A complete characterization of fringes formed at the measurement volume using conventional, as well as holographic optical elements, is presented. Results indicate the qualitative, as well as quantitative, improvement of fringes formed at the measurement volume by holographic optical elements. Hence, use of holographic optical elements in LDA systems may be advantageous for improving accuracy in the measurement.
Smith, J. C.; Pribram-Jones, A.; Burke, K.
2016-06-01
Thermal density functional theory calculations often use the Mermin-Kohn-Sham scheme, but employ ground-state approximations to the exchange-correlation (XC) free energy. In the simplest solvable nontrivial model, an asymmetric Hubbard dimer, we calculate the exact many-body energies and the exact Mermin-Kohn-Sham functionals for this system and extract the exact XC free energy. For moderate temperatures and weak correlation, we find this approximation to be excellent. We extract various exact free-energy correlation components and the exact adiabatic connection formula.
LDA+DMFT calculations of the Knight shift and relaxation rate in VOMoO{sub 4}
Energy Technology Data Exchange (ETDEWEB)
Kiani, Amin; Pavarini, Eva [Institute for Advanced Simulation and JARA, Forschungszentrum Juelich, 52425 Juelich (Germany)
2013-07-01
By using the LDA+DMFT approach and the local vertex approximation, we calculate the magnetic linear response function of strongly correlated transition-metal oxides. From the susceptibility we obtain Knight shift and relaxation rate. We present results for the frustrated system VOMoO{sub 4}. In particular we investigate how the Knight shift and the relaxation time behave in different temperature and correlation regimes.
van Gisbergen, S. J. A.; Snijders, J. G.; Baerends, E. J.
1998-12-01
In this paper we present time-dependent density functional calculations on frequency-dependent first (β) and second (γ) hyperpolarizabilities for the set of small molecules, N2, CO2, CS2, C2H4, NH3, CO, HF, H2O, and CH4, and compare them to Hartree-Fock and correlated ab initio calculations, as well as to experimental results. Both the static hyperpolarizabilities and the frequency dispersion are studied. Three approximations to the exchange-correlation (xc) potential are used: the widely used Local Density Approximation (LDA), the Becke-Lee-Yang-Parr (BLYP) Generalized Gradient Approximation (GGA), as well as the asymptotically correct Van Leeuwen-Baerends (LB94) potential. For the functional derivatives of the xc potential the Adiabatic Local Density Approximation (ALDA) is used. We have attempted to estimate the intrinsic quality of these methods by using large basis sets, augmented with several diffuse functions, yielding good agreement with recent numerical static LDA results. Contrary to claims which have appeared in the literature on the basis of smaller studies involving basis sets of lesser quality, we find that the static LDA results for β and γ are severely overestimated, and do not improve upon the (underestimated) Hartree-Fock results. No improvement is provided by the BLYP potential which suffers from the same incorrect asymptotic behavior as the LDA potential. The results are however clearly improved upon by the LB94 potential, which leads to underestimated results, slightly improving the Hartree-Fock results. The LDA and BLYP potentials overestimate the frequency dependence as well, which is once again improved by the LB94 potential. Future improvements are expected to come from improved models for asymptotically correct exchange-correlation potentials. Apart from the LB94 potential used in this work, several other asymptotically correct potentials have recently been suggested in the literature and can also be expected to improve considerably
Stainback, P. C.
1986-01-01
There is a renewed interest in hot wire anemometry at transonic speeds. Recent results were published which indicate that at transonic speeds a heated wire is sensitive only to mass flow and total temperature, results similar to those obtained for supersonic flows. Other results were obtained to show that the sensitivity is a function of velocity, density, and total temperature, results in agreement with many of those obtained in the 1950s. An analysis of anemometry results was made to evaluate possible errors when various assumptions were made concerning the sensitivity of a heated wire to fluid flow variables.
Peng, Degao; van Aggelen, Helen; Steinmann, Stephan; Yang, Yang; Yang, Weitao; Duke University Team
2014-03-01
The particle-particle random-phase approximation (pp-RPA) recently attracts extensive interests in quantum chemistry recently. Pp-RPA is a versatile model to calculate ground-state correlation energies, and double ionization potential/double electron affinity. We inspect particle-particle random-phase approximation in different perspectives to further understand its theoretical fundamentals. Viewed as summation of all ladder diagrams, the pp-RPA correlation energy is proved to be analytically equivalent to the ladder coupled-cluster doubles (ladder-CCD) theory. With this equivalence, we can make use of various well-established coupled-cluster techniques to study pp-RPA. Furthermore, we establish linear-response time-dependent density-functional theory with pairing fields (TDDFT-PF), where pp-RPA can be interpreted as the mean-field approximation to a general theory. TDDFT-PF is closely related to the density-functional theory of superconductors, but is applied to normal systems to capture exact N plus/minus 2 excitations. In the linear-response regime, both the adiabatic and non-adiabatic TDDFT-PF equations are established. This sets the fundamentals for further density-functional developments aiming for pp-RPA. These theoretical perspectives will be very helpful for future study.
Kraisler, Eli; Kelson, Itzhak
2010-01-01
The total energies and the spin states for atoms and their first ions with Z = 1-86 are calculated within the the local spin-density approximation (LSDA) and the generalized-gradient approximation (GGA) to the exchange-correlation (xc) energy in density-functional theory. Atoms and ions for which the ground-state density is not pure-state v-representable, are treated as ensemble v- representable with fractional occupations of the Kohn-Sham system. A newly developed algorithm which searches over ensemble v-representable densities [E. Kraisler et al., Phys. Rev. A 80, 032115 (2009)] is employed in calculations. It is found that for many atoms the ionization energies obtained with the GGA are only modestly improved with respect to experimental data, as compared to the LSDA. However, even in those groups of atoms where the improvement is systematic, there remains a non-negligible difference with respect to the experiment. The ab-initio electronic configuration in the Kohn-Sham reference system does not always equ...
Rüger, Robert; Heine, Thomas; Visscher, Lucas
2016-01-01
We propose a new method of calculating electronically excited states that combines a density functional theory (DFT) 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 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 time-dependent density functional theory (TD-DFT) calculations. Errors in vertical excitation energies are reduced by a factor of two compared to TD-DFTB.
Novel C/T technique in LDA System
Li, Chongxiang; Zhang, Yan F.; Liu, Chang W.; Wang, Shikang; Liu, Jie
2002-06-01
Laser Doppler Anemometry (LDA) is a most advanced velocity measurement technique in the field of fluid mechanics, combustion, hydraulics, chemical engineering, meteorology, biomedicine engineering and industrial manufactory for its non-contact, high response, and real-time velocity measurement. In LDA technique, optical signal processing is very important and very complex due to complicated flowing properties of fluid. LDA system includes optical section and signal processing section. In conventional LDA system, these two sections are separated and perform their own functions individually. Because optical section has no active control to measured signal, only mechanically indicates the variation of measured signal, the signal processing section was designed complex and costly. The existed signal-processing methods have different problems which limited the application and in turn increasing the difficulty of signal processing to detect the complex fluid. This paper describes and analyzes a new technique, C/T technique which combined optical section and signal processing section together, made the output signal simpler and solved the problems occurred in tradition methods. On the basis of analysis of C/T method, system construction is described.
High Power Fiber Bundle Array Coupled LDA Module
Institute of Scientific and Technical Information of China (English)
QU Zhou; LIU Yang; ZHAO Chong-guang; WANG Ji; YIN Hong-he; WANG Li-jun
2006-01-01
An optical fiber bundle array coupling module with high output power is presented in this paper. The device integrated the coupling technique of the high power laser diode array (LDA) and the micro-ball lenses fiber array. This module can efficiently couple the output laser of the LDA into 19 fibers array with micro-ball lens endsurface. The difference of the couple efficiency between the flat-end fiber and micro-ball-end fiber is discussed.The micro-ball lenses fiber array made of 19 fibers have the same fiber core diameter of 200 μm, and then the endsurfaces of 19 fibers are fused to 19 micro-ball lenses. The micro-ball lenses fiber array are fixed precisely in the neighborhood on the V-grooves, and the fiber array has the same arrange period with the semiconductor laser units of LDA. This configuration of micro-ball lens fiber array can greatly reduce the divergence of the laser beam from all directions, and a very efficient laser beam homogenizer and shaper are obtained. Finally, high output power of 30.1 W of the fiber coupled LDA is achieved, and the maximal coupling efficiency is ＞83% with the numeral aperture (NA) of 0.16.
Using color histograms and SPA-LDA to classify bacteria.
de Almeida, Valber Elias; da Costa, Gean Bezerra; de Sousa Fernandes, David Douglas; Gonçalves Dias Diniz, Paulo Henrique; Brandão, Deysiane; de Medeiros, Ana Claudia Dantas; Véras, Germano
2014-09-01
In this work, a new approach is proposed to verify the differentiating characteristics of five bacteria (Escherichia coli, Enterococcus faecalis, Streptococcus salivarius, Streptococcus oralis, and Staphylococcus aureus) by using digital images obtained with a simple webcam and variable selection by the Successive Projections Algorithm associated with Linear Discriminant Analysis (SPA-LDA). In this sense, color histograms in the red-green-blue (RGB), hue-saturation-value (HSV), and grayscale channels and their combinations were used as input data, and statistically evaluated by using different multivariate classifiers (Soft Independent Modeling by Class Analogy (SIMCA), Principal Component Analysis-Linear Discriminant Analysis (PCA-LDA), Partial Least Squares Discriminant Analysis (PLS-DA) and Successive Projections Algorithm-Linear Discriminant Analysis (SPA-LDA)). The bacteria strains were cultivated in a nutritive blood agar base layer for 24 h by following the Brazilian Pharmacopoeia, maintaining the status of cell growth and the nature of nutrient solutions under the same conditions. The best result in classification was obtained by using RGB and SPA-LDA, which reached 94 and 100 % of classification accuracy in the training and test sets, respectively. This result is extremely positive from the viewpoint of routine clinical analyses, because it avoids bacterial identification based on phenotypic identification of the causative organism using Gram staining, culture, and biochemical proofs. Therefore, the proposed method presents inherent advantages, promoting a simpler, faster, and low-cost alternative for bacterial identification.
LDA Assessments. Learning Times. Volume 7, Number 1
LDA Minnesota, 2008
2008-01-01
This issue of "Learning Times" discusses how LDA assessments for children and adults provide self-understanding, renewed hope, and improved achievement. It also includes: (1) Where do Your Candidates Stand on Controlling Toxic Chemicals?; (2) ADHD (Attention Deficit Hyperactivity Disorder) Tips: Back-to-School (Ty Sassaman); (3) Healthy Legacy:…
Institute of Scientific and Technical Information of China (English)
高阳; 严建峰; 刘晓升
2015-01-01
并行潜在狄利克雷分配(LDA)主题模型在计算与通信两方面的时间消耗较大,导致训练模型的时间过长,因而无法被广泛应用.提出朴素并行LDA算法,针对计算和通信分别提出改进方法.一方面通过加入单词影响因子以及设置阈值的方法来降低文本训练的粒度,另一方面通过降低通信频率来减少通信时间.实验结果表明,优化后的并行LDA在保证精度损失为1％的前提下,将训练速度提高了36％,有效提高了并行的加速比.
Luenser, Arne; Kussmann, Jörg; Ochsenfeld, Christian
2016-09-01
We present a (sub)linear-scaling algorithm to determine indirect nuclear spin-spin coupling constants at the Hartree-Fock and Kohn-Sham density functional levels of theory. Employing efficient integral algorithms and sparse algebra routines, an overall (sub)linear scaling behavior can be obtained for systems with a non-vanishing HOMO-LUMO gap. Calculations on systems with over 1000 atoms and 20 000 basis functions illustrate the performance and accuracy of our reference implementation. Specifically, we demonstrate that linear algebra dominates the runtime of conventional algorithms for 10 000 basis functions and above. Attainable speedups of our method exceed 6 × in total runtime and 10 × in the linear algebra steps for the tested systems. Furthermore, a convergence study of spin-spin couplings of an aminopyrazole peptide upon inclusion of the water environment is presented: using the new method it is shown that large solvent spheres are necessary to converge spin-spin coupling values.
Luenser, Arne; Kussmann, Jörg; Ochsenfeld, Christian
2016-09-28
We present a (sub)linear-scaling algorithm to determine indirect nuclear spin-spin coupling constants at the Hartree-Fock and Kohn-Sham density functional levels of theory. Employing efficient integral algorithms and sparse algebra routines, an overall (sub)linear scaling behavior can be obtained for systems with a non-vanishing HOMO-LUMO gap. Calculations on systems with over 1000 atoms and 20 000 basis functions illustrate the performance and accuracy of our reference implementation. Specifically, we demonstrate that linear algebra dominates the runtime of conventional algorithms for 10 000 basis functions and above. Attainable speedups of our method exceed 6 × in total runtime and 10 × in the linear algebra steps for the tested systems. Furthermore, a convergence study of spin-spin couplings of an aminopyrazole peptide upon inclusion of the water environment is presented: using the new method it is shown that large solvent spheres are necessary to converge spin-spin coupling values.
Armstrong, Robert A.
2008-10-01
Pasciak and Gavis were first to propose a model of nutrient uptake that includes both physical transport by diffusion and active biological transport across the cell membrane. While the Pasciak-Gavis model is not complicated mathematically (it can be expressed in closed form as a quadratic equation), its parameters are not so easily interpretable biologically as are the parameters of the Michaelis-Menten uptake model; this lack of transparency is probably the main reason the Pasciak-Gavis model has not been adopted by ecologically oriented modelers. Here I derive a Michaelis-like approximation to the Pasciak-Gavis model, and show how the parameters of the latter map to those of the Michaelis-like model. The derived approximation differs from a pure Michaelis-Menten model in a subtle but potentially critical way: in a pure Michaelis-Menten model, the half-saturation constant for nutrient uptake is independent of the density of transporter (or "porter") proteins on the cell surface, while in the Pasciak-Gavis model and its Michaelis-like approximation, the half-saturation constant does depend on the density of porter proteins. The Pasciak-Gavis model predicts a unique relationship between cell size, nutrient concentration in the medium, the half-saturation constant of porter-limited nutrient uptake, and the resulting rate of uptake; the Michaelis-like approximation preserves the most important feature of that relationship, the size at which porter limitation gives way to diffusion limitation. Finally I discuss the implications for community structure that are implied by the Pasciak-Gavis model and its Michaelis-like approximation.
Rivero, Pablo; Loschen, Christoph; Moreira, Ibério De P R; Illas, Francesc
2009-11-15
This work explores the performance of periodic plane wave density functional theory calculations with an on-site Coulomb correction to the standard LDA and GGA exchange-correlation potential--commonly used to describe strongly correlated solids--in describing the magnetic coupling constant of a series of molecular compounds representative of dinuclear Cu complexes and of organic diradicals. The resulting LDA+U or GGA+U formalisms, lead to results comparable to experiment and to those obtained by means of standard hybrid functionals provided that the value of the U parameter is adequately chosen. Hence, these methods offer an alternative efficient computational scheme to correct LDA and GGA approaches to adequately describe the electronic structure and magnetic coupling in large molecular magnetic systems, although at the expenses of introducing an empirical (U) parameter. For all investigated copper dinuclear systems, the LDA+U and GGA+U approaches lead to an improvement in the description of magnetic properties over the original LDA and GGA schemes with an accuracy similar to that arising from the hybrid B3LYP functional, by increasing the on-site Coulomb repulsion with a moderate U value. Nevertheless, the introduction of an arbitrary U value in the 0-10 eV range most often provides the correct ground-state spin distribution and the correct sign of the magnetic coupling constant.
Energy Technology Data Exchange (ETDEWEB)
Zhang Yujuan [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Wang Baotian [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan 030006 (China); Lu Yong; Yang Yu [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Zhang Ping, E-mail: zhang_ping@iapcm.ac.cn [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Center for Applied Physics and Technology, Peking University, Beijing 100871 (China)
2012-11-15
The electronic, mechanical, and thermodynamic properties of {alpha}-UH{sub 3} are comparatively investigated within the LDA and LDA+U formalisms. After choosing a reasonable U parameter, the LDA+U method can produce a more precise lattice constant. For the ground-state electronic structures of {alpha}-UH{sub 3}, the uranium 5f electronic states are divided into multiple peaks in the LDA+U results, resulting in weakening of the material's metallicity, and enhancement of the ionic character of the uranium-hydrogen bonds. However, inclusion of the U parameter induces negligible changes on the mechanical properties of {alpha}-UH{sub 3}. Lastly for thermodynamic properties, systematic phonon dispersion curve calculations reveal that the LDA and LDA+U methods give quite different frequencies for the optical branches of phonons of {alpha}-UH{sub 3}. Our systematical studies can serve as comparisons for further experimental investigations on UH{sub 3}.
Avgin, I.; Boukahil, A.; Huber, D. L.
2015-11-01
Using the coherent potential approximation, we investigate the optical absorption and the density of states of Frenkel exciton systems on simple, body centered, and face centered cubic lattices with nearest-neighbor interactions and a Gaussian distribution of transition frequencies (i.e. Gaussian diagonal disorder). The analysis is based on an elliptic integral approach with a variety of variances. The results for the simple cubic lattice are in good agreement with the finite array calculations of Schreiber and Toyozawa. Our findings suggest that the coherent potential approximation can be useful in interpreting the optical properties of cubic crystals where the optically excited states are Frenkel excitons with the dominant interactions limited to nearest-neighbors.
Energy Technology Data Exchange (ETDEWEB)
Avgin, I. [Department of Electrical and Electronics Engineering, Ege University, Bornova 35100, Izmir (Turkey); Boukahil, A. [Physics Department, University of Wisconsin-Whitewater, Whitewater, WI 53190 (United States); Huber, D.L., E-mail: dhuber@src.wisc.edu [Physics Department, University of Wisconsin-Madison, Madison, WI 53706 (United States)
2015-11-15
Using the coherent potential approximation, we investigate the optical absorption and the density of states of Frenkel exciton systems on simple, body centered, and face centered cubic lattices with nearest-neighbor interactions and a Gaussian distribution of transition frequencies (i.e. Gaussian diagonal disorder). The analysis is based on an elliptic integral approach with a variety of variances. The results for the simple cubic lattice are in good agreement with the finite array calculations of Schreiber and Toyozawa. Our findings suggest that the coherent potential approximation can be useful in interpreting the optical properties of cubic crystals where the optically excited states are Frenkel excitons with the dominant interactions limited to nearest-neighbors.
Error estimates for density-functional theory predictions of surface energy and work function
De Waele, Sam; Lejaeghere, Kurt; Sluydts, Michael; Cottenier, Stefaan
2016-12-01
Density-functional theory (DFT) predictions of materials properties are becoming ever more widespread. With increased use comes the demand for estimates of the accuracy of DFT results. In view of the importance of reliable surface properties, this work calculates surface energies and work functions for a large and diverse test set of crystalline solids. They are compared to experimental values by performing a linear regression, which results in a measure of the predictable and material-specific error of the theoretical result. Two of the most prevalent functionals, the local density approximation (LDA) and the Perdew-Burke-Ernzerhof parametrization of the generalized gradient approximation (PBE-GGA), are evaluated and compared. Both LDA and GGA-PBE are found to yield accurate work functions with error bars below 0.3 eV, rivaling the experimental precision. LDA also provides satisfactory estimates for the surface energy with error bars smaller than 10%, but GGA-PBE significantly underestimates the surface energy for materials with a large correlation energy.
Structural and elastic properties of Ce2O3 under pressure from LDA+ U method
Qi, Yuan-Yuan; Niu, Zhen-Wei; Cheng, Cai; Cheng, Yan
2013-08-01
We investigate the structural and elastic properties of hexagonal Ce2O3 under pressure using LDA+ U scheme in the frame of density functional theory (DFT). The obtained lattice constants and bulk modulus agree well with the available experimental and other theoretical data. The pressure dependences of normalized lattice parameters a/a 0 and c/c 0, ratio c/a, and normalized primitive volume V/V 0 of Ce2O3 are obtained. Moreover, the pressure dependences of elastic properties and three anisotropies of elastic waves of Ce2O3 are investigated for the first time. We find that the negative value of C 44 is indicative of the structural instability of the hexagonal structure Ce2O3 at zero temperature and 30 GPa. Finally, the density of states (DOS) of Ce2O3 under pressure is investigated.
First-principles diffusion barrier of O at Pd (100): A benchmark beyond LDA/GGA
Energy Technology Data Exchange (ETDEWEB)
Zhang, Wei-Bing; Meyer, Joerg; Reuter, Karsten [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany); Technische Universitaet, Muenchen (Germany); Zhang, Yongsheng [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany)
2011-07-01
The diffusion of adsorbates at a solid surface is a core elementary process of critical relevance for many functionalities. The accurate determination of diffusion barriers is correspondingly an important aspect in first-principles kinetic modeling. At extended metal surfaces the state-of-the-art for this is still local (LDA) and semi-local (GGA) density-functional theory. Critically scrutinizing the reliability of such description for the diffusion of O atoms at Pd(100) we first use a cluster expansion approach to separate the overall diffusion barrier into the isolated-adatom limit and contributions arising from lateral interactions with other O adsorbates. Comparing LDA and GGA data suggests that the latter component is surprisingly well described already at this level of theory. However, comparison against experiment reveals a significant error for the barrier in the isolated O adatom limit. We therefore use an exchange-correlation correction approach based on finite cluster calculations to assess the performance of higher level theory, including hybrid and RPA functionals.
Estimation of burst-mode LDA power spectra
Velte, Clara Marika; George, William K.; Buchhave, Preben
2014-03-01
The estimation of power spectra from LDA data provides signal processing challenges for fluid dynamicists for several reasons: acquisition is dictated by randomly arriving particles, the registered particle velocities tend to be biased toward higher values, and the signal is highly intermittent. The signal can be interpreted correctly by applying residence time weighting to all statistics and using the residence time-weighted discrete Fourier transform to compute the Fourier transform. A new spectral algorithm using the latter is applied to two experiments: a cylinder wake and an axisymmetric turbulent jet. These are compared with corresponding hot-wire spectra as well as to alternative algorithms for LDA signals such as the time-slot correlation method, sample-and-hold and common weighting schemes.
Heid, Rolf; Bohnen, Klaus-Peter; Zeyher, Roland; Manske, Dirk
2008-04-04
Using the local density approximation and a realistic phonon spectrum we determine the momentum and frequency dependence of alpha(2)F(k,omega) in YBa(2)Cu(3)O(7) for the bonding, antibonding, and chain band. The resulting self-energy Sigma is rather small near the Fermi surface. For instance, for the antibonding band the maximum of ReSigma as a function of frequency is about 7 meV at the nodal point in the normal state and the ratio of bare and renormalized Fermi velocities is 1.18. These values are a factor of 3-5 too small compared to the experiment showing that only a small part of Sigma can be attributed to phonons. Furthermore, the frequency dependence of the renormalization factor Z(k,omega) is smooth and has no anomalies at the observed kink frequencies which means that phonons cannot produce well-pronounced kinks in stoichiometric YBa(2)Cu()3)O(7), at least, within the local density approximation.
Face recognition using improved-LDA with facial combined feature
Institute of Scientific and Technical Information of China (English)
Dake Zhou; Xin Yang; Ningsong Peng
2005-01-01
@@ Face recognition subjected to various conditions is a challenging task. This paper presents a combined feature improved Fisher classifier method for face recognition. Both of the facial holistic information and local information are used for face representation. In addition, the improved linear discriminant analysis (I-LDA) is employed for good generalization capability. Experiments show that the method is not only robust to moderate changes of illumination, pose and facial expression but also superior to the traditional methods, such as eigenfaces and Fisherfaces.
Towards a natural gesture interface: LDA-based gesture separability
Romaszewski, Michał; Głomb, Przemysław
2011-01-01
The goal of this paper is to analyse a method of validating a subset of gestures to be used as elements of a HCI interface. We investigate the applicability of LDA for gesture data dimensionality reduction. An Gesture mutual separability analysis of a diverse dataset of 22 natural gestures captured with two motion-capture devices is provided. Fisher criterion is used to produce measures of class separability and class overlap.
Institute of Scientific and Technical Information of China (English)
Shao Qing-Yi; Zhang Juan
2011-01-01
In vapour deposition,single atoms(adatoms)on the substrate surface are the main source of growth.The change in its density plays a decisive role in the growth of thin films and quantum size islands.In the nucleation and cluster coalescence stages of vapour deposition,the growth of stable clusters occurs on the substrate surface covered by stable clusters.Nucleation occurs in the non-covered part,while the total area covered by stable clusters on the substrate surface will gradually increase.Carefully taking into account the coverage effect,a revised single atom density rate equation is given for the famous and widely used thin-film rate equation theory,but the work of solving the revised equation has not been done.In this paper,we solve the equation and obtain the single-atom density and capture number by using a uniform depletion approximation.We determine that the single atom density is much lower than that evaluated from the single atom density rate equation in the traditional rate equation theory when the stable cluster coverage fraction is large,and it goes down very fast with an increase in the coverage fraction.The revised equation gives a higher value for the 'average' capture number than the present equation. It also increases with increasing coverage.That makes the preparation of single crystalline thin film materials difficult and the size control of quantum size islands complicated.We also discuss the effect of the revision on coalescence and the number of stable clusters in vapour deposition.
Mohammadpour, Mozhdeh; Jamshidi, Zahra
2016-05-01
The prospect of challenges in reproducing and interpretation of resonance Raman properties of molecules interacting with metal clusters has prompted the present research initiative. Resonance Raman spectra based on the time-dependent gradient approximation are examined in the framework of density functional theory using different methods for representing the exchange-correlation functional. In this work the performance of different XC functionals in the prediction of ground state properties, excitation state energies, and gradients are compared and discussed. Resonance Raman properties based on time-dependent gradient approximation for the strongly low-lying charge transfer states are calculated and compared for different methods. We draw the following conclusions: (1) for calculating the binding energy and ground state geometry, dispersion-corrected functionals give the best performance in comparison to ab initio calculations, (2) GGA and meta GGA functionals give good accuracy in calculating vibrational frequencies, (3) excited state energies determined by hybrid and range-separated hybrid functionals are in good agreement with EOM-CCSD calculations, and (4) in calculating resonance Raman properties GGA functionals give good and reasonable performance in comparison to the experiment; however, calculating the excited state gradient by using the hybrid functional on the hessian of GGA improves the results of the hybrid functional significantly. Finally, we conclude that the agreement of charge-transfer surface enhanced resonance Raman spectra with experiment is improved significantly by using the excited state gradient approximation.
Salmani, El Mehdi; Laghrissi, Ayoub; Lamouri, Rachida; Ez-Zahraouy, Hamid; Benyoussef, Abdelilah
2017-01-01
Electronic structure, magnetic and optical properties of ZnO doped with single and double impurities Zn1-xCrxO, Zn1-xFexO, and Zn1-2xCrxFexO (x=0.03 and 0.06) are investigated using first-principles calculations. Based on the Korringa-Kohn-Rostoker method combined with the coherent potential approximation, we investigated the half-metallic ferromagnetic behavior of doubles impurities (Cr, Fe) doped ZnO. To support our results, we apply the self-interaction-corrected local density approximation (SIC-LDA) to study the electronic structure, optical and magnetic properties of Co-doped ZnO with doubles impurities (Cr, Fe) showing that the half-metallic ferromagnetic state still persists. The stability of the ferromagnetic state compared with the spin-glass state is investigated by comparing their total energies. The exchange interactions obtained from first principle calculations and used in a classical Ising model by a Monte Carlo approach resulted in ferromagnetic states with high Neel temperature.
Laricchia, S; Fabiano, E; Della Sala, F
2014-01-01
We test Laplacian-level meta-generalized gradient approximation (meta-GGA) non-interacting kinetic energy functionals based on the fourth-order gradient expansion (GE4). We consider several well known Laplacian-level meta-GGAs from literature (bare GE4, modified GE4, and the MGGA functional of Perdew and Constantin [Phys. Rev. B \\textbf{75},155109 (2007)]), as well as two newly designed Laplacian-level kinetic energy functionals (named L0.4 and L0.6). First, a general assessment of the different functionals is performed, testing them for model systems (one-electron densities, Hooke's atom and different jellium systems), atomic and molecular kinetic energies as well as for their behavior with respect to density-scaling transformations. Finally, we assess, for the first time, the performance of the different functionals for Subsystem Density Functional Theory (DFT) calculations on non-covalently interacting systems. We find that the different Laplacian-level meta-GGA kinetic functionals may improve the descript...
Shedge, Sapana V; Carmona-Espíndola, Javier; Pal, Sourav; Köster, Andreas M
2010-02-18
We present a theoretical study of the polarizabilities of free and disubstituted azoarenes employing auxiliary density perturbation theory (ADPT) and the noniterative approximation to the coupled perturbed Kohn-Sham (NIA-CPKS) method. Both methods are noniterative but use different approaches to obtain the perturbed density matrix. NIA-CPKS is different from the conventional CPKS approach in that the perturbed Kohn-Sham matrix is obtained numerically, thereby yielding a single-step solution to CPKS. ADPT is an alternative approach to the analytical CPKS method in the framework of the auxiliary density functional theory. It is shown that the polarizabilities obtained using these two methods are in good agreement with each other. Comparisons are made for disubstituted azoarenes, which give support to the push-pull mechanism. Both methods reproduce the same trend for polarizabilities because of the substitution pattern of the azoarene moiety. Our results are consistent with the standard organic chemistry "activating/deactivating" sequence. We present the polarizabilities of the above molecules calculated with three different exchange-correlation functionals and two different auxiliary function sets. The computational advantages of both methods are also discussed.
LDA'+DMFT investigation of electronic structure of K1 - x Fe2 - y Se2 superconductor
Nekrasov, I. A.; Pavlov, N. S.; Sadovskii, M. V.
2013-03-01
We investigate electronic structure of the new iron chalcogenide high temperature superconductor K1- x Fe2- y Se2 (hole doped case with x = 0.24, y = 0.28) in the normal phase using the novel LDA'+DMFT computational approach. We show that this iron chalcogenide is more correlated in a sense of bandwidth renormalization (energy scale compression by factor about 5 in the interval ±1.5 eV), than typical iron pnictides (compression factor about 2), though the Coulomb interaction strength is almost the same in both families. Our results for spectral densities are in general agreement with recent ARPES data on this system. It is found that all Fe-3 d( t 2 g ) bands crossing the Fermi level have equal renormalization, in contrast to some previous interpretations. Electronic states at the Fermi level are of predominantly xy symmetry. Also we show that LDA'+DMFT results are in better agreement with experimental spectral function maps, than the results of conventional LDA+DMFT. Finally we make predictions for photoemission spectra lineshape for K0.76Fe1.72Se2.
Enhanced Z-LDA for Small Sample Size Training in Brain-Computer Interface Systems
Directory of Open Access Journals (Sweden)
Dongrui Gao
2015-01-01
Full Text Available Background. Usually the training set of online brain-computer interface (BCI experiment is small. For the small training set, it lacks enough information to deeply train the classifier, resulting in the poor classification performance during online testing. Methods. In this paper, on the basis of Z-LDA, we further calculate the classification probability of Z-LDA and then use it to select the reliable samples from the testing set to enlarge the training set, aiming to mine the additional information from testing set to adjust the biased classification boundary obtained from the small training set. The proposed approach is an extension of previous Z-LDA and is named enhanced Z-LDA (EZ-LDA. Results. We evaluated the classification performance of LDA, Z-LDA, and EZ-LDA on simulation and real BCI datasets with different sizes of training samples, and classification results showed EZ-LDA achieved the best classification performance. Conclusions. EZ-LDA is promising to deal with the small sample size training problem usually existing in online BCI system.
Laricchia, Savio; Constantin, Lucian A; Fabiano, Eduardo; Della Sala, Fabio
2014-01-14
We tested Laplacian-level meta-generalized gradient approximation (meta-GGA) noninteracting kinetic energy functionals based on the fourth-order gradient expansion (GE4). We considered several well-known Laplacian-level meta-GGAs from the literature (bare GE4, modified GE4, and the MGGA functional of Perdew and Constantin (Phys. Rev. B 2007,75, 155109)), as well as two newly designed Laplacian-level kinetic energy functionals (L0.4 and L0.6). First, a general assessment of the different functionals is performed to test them for model systems (one-electron densities, Hooke's atom, and different jellium systems) and atomic and molecular kinetic energies as well as for their behavior with respect to density-scaling transformations. Finally, we assessed, for the first time, the performance of the different functionals for subsystem density functional theory (DFT) calculations on noncovalently interacting systems. We found that the different Laplacian-level meta-GGA kinetic functionals may improve the description of different properties of electronic systems, but no clear overall advantage is found over the best GGA functionals. Concerning the subsystem DFT calculations, the here-proposed L0.4 and L0.6 kinetic energy functionals are competitive with state-of-the-art GGAs, whereas all other Laplacian-level functionals fail badly. The performance of the Laplacian-level functionals is rationalized thanks to a two-dimensional reduced-gradient and reduced-Laplacian decomposition of the nonadditive kinetic energy density.
Zuehlsdorff, Tim J; Payne, Mike C; Haynes, Peter D
2015-01-01
We present a solution of the full TDDFT eigenvalue equation in the linear response formalism exhibiting a linear-scaling computational complexity with system size, without relying on the simplifying Tamm-Dancoff approximation (TDA). The implementation relies on representing the occupied and unoccupied subspace with two different sets of in situ optimised localised functions, yielding a very compact and efficient representation of the transition density matrix of the excitation with the accuracy associated with a systematic basis set. The TDDFT eigenvalue equation is solved using a preconditioned conjugate-gradients algorithm that is very memory-efficient. The algorithm is validated on a test molecule and a good agreement with results obtained from standard quantum chemistry packages is found, with the preconditioner yielding a significant improvement in convergence rates. The method developed in this work is then used to reproduce experimental results of the absorption spectrum of bacteriochlorophyll (BChl) i...
Energy Technology Data Exchange (ETDEWEB)
Zuehlsdorff, T. J., E-mail: tjz21@cam.ac.uk; Payne, M. C. [Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Hine, N. D. M. [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Haynes, P. D. [Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom); Department of Physics, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom); Thomas Young Centre for Theory and Simulation of Materials, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom)
2015-11-28
We present a solution of the full time-dependent density-functional theory (TDDFT) eigenvalue equation in the linear response formalism exhibiting a linear-scaling computational complexity with system size, without relying on the simplifying Tamm-Dancoff approximation (TDA). The implementation relies on representing the occupied and unoccupied subspaces with two different sets of in situ optimised localised functions, yielding a very compact and efficient representation of the transition density matrix of the excitation with the accuracy associated with a systematic basis set. The TDDFT eigenvalue equation is solved using a preconditioned conjugate gradient algorithm that is very memory-efficient. The algorithm is validated on a small test molecule and a good agreement with results obtained from standard quantum chemistry packages is found, with the preconditioner yielding a significant improvement in convergence rates. The method developed in this work is then used to reproduce experimental results of the absorption spectrum of bacteriochlorophyll in an organic solvent, where it is demonstrated that the TDA fails to reproduce the main features of the low energy spectrum, while the full TDDFT equation yields results in good qualitative agreement with experimental data. Furthermore, the need for explicitly including parts of the solvent into the TDDFT calculations is highlighted, making the treatment of large system sizes necessary that are well within reach of the capabilities of the algorithm introduced here. Finally, the linear-scaling properties of the algorithm are demonstrated by computing the lowest excitation energy of bacteriochlorophyll in solution. The largest systems considered in this work are of the same order of magnitude as a variety of widely studied pigment-protein complexes, opening up the possibility of studying their properties without having to resort to any semiclassical approximations to parts of the protein environment.
Zuehlsdorff, T. J.; Hine, N. D. M.; Payne, M. C.; Haynes, P. D.
2015-11-01
We present a solution of the full time-dependent density-functional theory (TDDFT) eigenvalue equation in the linear response formalism exhibiting a linear-scaling computational complexity with system size, without relying on the simplifying Tamm-Dancoff approximation (TDA). The implementation relies on representing the occupied and unoccupied subspaces with two different sets of in situ optimised localised functions, yielding a very compact and efficient representation of the transition density matrix of the excitation with the accuracy associated with a systematic basis set. The TDDFT eigenvalue equation is solved using a preconditioned conjugate gradient algorithm that is very memory-efficient. The algorithm is validated on a small test molecule and a good agreement with results obtained from standard quantum chemistry packages is found, with the preconditioner yielding a significant improvement in convergence rates. The method developed in this work is then used to reproduce experimental results of the absorption spectrum of bacteriochlorophyll in an organic solvent, where it is demonstrated that the TDA fails to reproduce the main features of the low energy spectrum, while the full TDDFT equation yields results in good qualitative agreement with experimental data. Furthermore, the need for explicitly including parts of the solvent into the TDDFT calculations is highlighted, making the treatment of large system sizes necessary that are well within reach of the capabilities of the algorithm introduced here. Finally, the linear-scaling properties of the algorithm are demonstrated by computing the lowest excitation energy of bacteriochlorophyll in solution. The largest systems considered in this work are of the same order of magnitude as a variety of widely studied pigment-protein complexes, opening up the possibility of studying their properties without having to resort to any semiclassical approximations to parts of the protein environment.
MaLDA:medication analysis based on LDA%MaLDA：基于LDA的用药分析
Institute of Scientific and Technical Information of China (English)
周靖; 佘玉轩; 熊赟
2016-01-01
为了给医生及病人安全、合理、高效用药提供决策支持，提出了一种基于LDA（Latent Dirichlet Allocation）的用药分析方法MaLDA（Medication Analysis based on LDA）。该方法结合了用药记录和就诊记录，将药物看作文档、药物功能看作主题、疾病看作词语，通过主题模型LDA发现隐含的药物功能，通过药物功能，将相关药物、相关疾病和药物与疾病联系起来。根据药物对药物功能的分布对药物进行聚类，每一类药物被相关的疾病所描述，进而对临床用药进行分析。MaLDA不仅能发现临床用药中针对某一类疾病效用较好的药物，而且能发现隐含的联合用药。实验数据来源于上海市某医院137510位病人的用药记录和就诊记录。实验结果证实了MaLDA相对于其他方法在对电子就医记录进行用药分析的有效性。%To provide support for doctors and patients to use drugs in a safer, more rational and efficient way, this paper proposes a framework for medication analysis based on LDA(Latent Dirichlet Allocation), MaLDA(Medication Analysis based on the LDA). MaLDA combines the usage of medication records and diagnostic records, infers the function of each drug using topic-based inference model LDA, which regards a drug as a document, a function as a topic, and a disease as a word. As a result, related drugs, drug and disease, related diseases are associated by functions. Then clustering all drugs according to its distribution of functions, and each cluster is described by related diseases. Finally, it analyzes the clinical medication based on the results of clustering. The result generated by MaLDA can not only find the drug which is better in treatment, but also find the drug combination which lays the foundation for mining drug side effects and the complications of disease. The method is evaluated by using 137 510 patients’diagnostic records and medication records. The results justify
Energy Technology Data Exchange (ETDEWEB)
Mizutani, U; Inukai, M; Sato, H; Zijlstra, E S; Lin, Q
2014-05-16
There are three key electronic parameters in elucidating the physics behind the Hume–Rothery electron concentration rule: the square of the Fermi diameter (2kF)2, the square of the critical reciprocal lattice vector and the electron concentration parameter or the number of itinerant electrons per atom e/a. We have reliably determined these three parameters for 10 Rhombic Triacontahedron-type 2/1–2/1–2/1 (N = 680) and 1/1–1/1–1/1 (N = 160–162) approximants by making full use of the full-potential linearized augmented plane wave-Fourier band calculations based on all-electron density-functional theory. We revealed that the 2/1–2/1–2/1 approximants Al13Mg27Zn45 and Na27Au27Ga31 belong to two different sub-groups classified in terms of equal to 126 and 109 and could explain why they take different e/a values of 2.13 and 1.76, respectively. Among eight 1/1–1/1–1/1 approximants Al3Mg4Zn3, Al9Mg8Ag3, Al21Li13Cu6, Ga21Li13Cu6, Na26Au24Ga30, Na26Au37Ge18, Na26Au37Sn18 and Na26Cd40Pb6, the first two, the second two and the last four compounds were classified into three sub-groups with = 50, 46 and 42; and were claimed to obey the e/a = 2.30, 2.10–2.15 and 1.70–1.80 rules, respectively.
Mizutani, U.; Inukai, M.; Sato, H.; Zijlstra, E. S.; Lin, Q.
2014-08-01
There are three key electronic parameters in elucidating the physics behind the Hume-Rothery electron concentration rule: the square of the Fermi diameter (2kF)2, the square of the critical reciprocal lattice vector ? and the electron concentration parameter or the number of itinerant electrons per atom e/a. We have reliably determined these three parameters for 10 Rhombic Triacontahedron-type 2/1-2/1-2/1 (N = 680) and 1/1-1/1-1/1 (N = 160-162) approximants by making full use of the full-potential linearized augmented plane wave-Fourier band calculations based on all-electron density-functional theory. We revealed that the 2/1-2/1-2/1 approximants Al13Mg27Zn45 and Na27Au27Ga31 belong to two different sub-groups classified in terms of ? equal to 126 and 109 and could explain why they take different e/a values of 2.13 and 1.76, respectively. Among eight 1/1-1/1-1/1 approximants Al3Mg4Zn3, Al9Mg8Ag3, Al21Li13Cu6, Ga21Li13Cu6, Na26Au24Ga30, Na26Au37Ge18, Na26Au37Sn18 and Na26Cd40Pb6, the first two, the second two and the last four compounds were classified into three sub-groups with ? = 50, 46 and 42; and were claimed to obey the e/a = 2.30, 2.10-2.15 and 1.70-1.80 rules, respectively.
LDA+ U calculation of structural and thermodynamic properties of Ce2O3
Zhu, Bo; Cheng, Yan; Niu, Zhen-Wei; Zhou, Meng; Gong, Min
2014-08-01
We investigated the structure and thermodynamic properties of the hexagonal Ce2O3 by using LDA+ U scheme in the frame of density functional theory (DFT), together with the quasi-harmonic Debye model. The obtained lattice constants, bulk modulus, and the insulating gap agree well with the available experimental data. We successfully yielded the temperature dependence of bulk modulus, volume, thermal expansion coefficient, Debye temperature, specific heat as well as the entropy at different U values. It is found that the introduction of the U value cannot only correct the calculation of the structure but also improve the accurate description of the thermodynamic properties of Ce2O3. When U = 6 eV the calculated volume (538 Bohr3) at 300 K agrees well with the experimental value (536 Bohr3). The calculated entropy curve becomes more and more close to the experimental curve with the increasing U value.
Class Dependent LDA Optimization Using Genetic Algorithm for Robust MFCC Extraction
Abbasian, Houman; Nasersharif, Babak; Akbari, Ahmad
Linear Discrimination analysis (LDA) finds transformations that maximizes the between-class scatter and minimizes within-class scatter. In this paper, we propose a method to use class-dependent LDA for speech recognition and MFCC extraction. To this end, we first use logarithm of clean speech Mel filter bank energies (LMFE) of each class then we obtain class-dependent LDA transformation matrix using multidimensional genetic algorithm (MGA) and use this matrix in place of DCT in MFCC feature extraction. The experimental results show that proposed speech recognition and optimization methods using class-dependent LDA, achieves to a significant isolated word recognition rate on Aurora2 database.
Comparing GW+DMFT and LDA+DMFT for the testbed material SrVO{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Taranto, Ciro; Toschi, Alessandro; Held, Karsten [Institute for Solid State Physics, Vienna University of Technology (Austria); Kaltak, Merzuk; Kresse, Georg [University of Vienna, Faculty of Physics and Center for Computational Materials Science (Austria); Parragh, Nicolaus; Sangiovanni, Giorgio [Institut fuer Theoretische Physik und Astrophysik, Universitaet Wuerzburg (Germany)
2013-07-01
We have implemented the GW+dynamical mean field theory (DMFT) approach in the Vienna ab initio simulation package. Employing the interaction values obtained from the locally unscreened random phase approximation (RPA), we compare GW+DMFT and LDA+DMFT against each other and against experiment for SrVO{sub 3}. We observed a partial compensation of stronger electronic correlations due to the reduced GW bandwidth and weaker correlations due to a larger screening of the RPA interaction, so that the obtained spectra are quite similar and well agree with experiment. Noteworthily, the GW+DMFT better reproduces the position of the lower Hubbard side band.
Hari Sutrisno
2016-01-01
This article is a theoritical approach to calculate the electronic structure of undoped- and non-metal anions doped-TiO2-anatase. The objective of the research is to calculate abinitio the band structure and the density of states (DOS) of undoped-, C-, N-, and S-doped TiO2-anatase. Kohn-Sham equations are performed with the density functional theory (DFT) using the local density approximation (LDA) for exchange-correlation functional. The first-principle calculations were done using supercell...
First-principles calculations of electronic and magnetic properties of CeN: The LDA + U method
Hao, Ai-Min; Bai, Jing
2013-10-01
Electronic and magnetic properties of CeN are investigated using first-principles calculations based on density functional theory (DFT) with the LDA + U method. Our results show that CeN is a half-metal. The majority-spin electron band structure has metallic intersections, whereas the minority-spin electron band structure has a semiconducting gap straddling the Fermi level. A small indirect energy gap occurs between X and W. The calculated magnetic moment is 0.99 μB per unit cell.
Directory of Open Access Journals (Sweden)
Luiz G. Ferreira
2011-09-01
Full Text Available The very old and successful density-functional technique of half-occupation is revisited [J. C. Slater, Adv. Quant. Chem. 6, 1 (1972]. We use it together with the modern exchange-correlation approximations to calculate atomic ionization energies and band gaps in semiconductors [L. G. Ferreira et al., Phys. Rev. B 78, 125116 (2008]. Here we enlarge the results of the previous paper, add to its understandability, and show when the technique might fail. Even in this latter circumstance, the calculated band gaps are far better than those of simple LDA or GGA. As before, the difference between the Kohn-Sham ground state one-particle eigenvalues and the half-occupation eigenvalues is simply interpreted as the self-energy (not self-interaction of the particle excitation. In both cases, that of atomic ionization energies and semiconductor band gaps, the technique is proven to be very worthy, because not only the results can be very precise but the calculations are fast and very simple.
Pan, Y.; Liu, T.; Wei, X. Y.; Zhu, Y.; Shi, D. N.; Ma, C. L.; Zhang, K. C.; Yang, Z. Q.
2015-11-01
By local-density approximation plus U (LDA + U) calculations, diluted magnetic semiconductors (DMS) δ-(Zn, Mn, Li)Se are dominated by Zener's p-d exchange, which is different from Zener's double exchange mechanism by PBE calculations. The main peak of Mn d states is shifted to lower energy -3.9 eV versus Fermi energy. All configurations under shape deformation are strong ferromagnetic (FM) ones due to the large splitting of Mn d states. Because of the two-dimensional (2D) ordered Mn atoms with hole and long ranged effect of p-d exchange coupling, exchange energy of the supercell with crystal constant is much larger with p-d exchange than that with double exchange. The largest exchange energy is around the crystal constant. Fermi level across the valley of FM Mn d states makes the FM state much stable. Comparing with pure ZnSe, p-type co-doping of Li in δ-(Zn, Mn, Li)Se has a significant effect on the atomic structure. These results are useful in the research of DMS with shape deformation and p-type co-doping for spintronic applications.
Energy Technology Data Exchange (ETDEWEB)
Heid, Rolf; Bohnen, Klaus-Peter [Forschungszentrum Karlsruhe, Institut fuer Festkoerperphysik (Germany); Zeyher, Roland; Manske, Dirk [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany)
2008-07-01
The observation of kinks in the electronic dispersion of high-T{sub c} cuprates by angle resolved photoemission experiments has revived the discussion about the importance of electron-phonon interaction in the cuprates. Here we determine the effect of the electron-phonon coupling on the electronic self-energy in the normal state within the local-density approximation. Using a realistic phonon spectrum we determine the momentum and frequency dependence of {alpha}{sup 2}F(k,{omega}) in YBa{sub 2}Cu{sub 3}O{sub 7} for the bonding, antibonding, and chain band. We find that the maximum in the real part of the self-energy at low frequencies is about a factor 5 too small compared to the experiment. The renormalization factor Z(k,{omega}), which determines the change in the slope of the electronic dispersion due to the interaction, varies smoothly as a function of frequency and momentum. These findings show that, at least within the LDA, phonons cannot produce well-pronounced kinks in YBa{sub 2}Cu{sub 3}O{sub 7}.
Energy Technology Data Exchange (ETDEWEB)
Piefke, Christoph; Lechermann, Frank [Institut fuer Theoretische Physik, Universitaet Hamburg, 20355 Hamburg (Germany)
2011-10-15
The combination of the local-density approximation (LDA) with the rotationally invariant slave-boson theory (RISB) is used to investigate the realistic correlated electronic structure of Sr{sub 3}Ru{sub 2}O{sub 7}. From Wannier-downfolding the low-energy band structure to a three-band model for the Ru(t{sub 2g}) states, the interacting problem is solved including intra- and inter-orbital Hubbard terms as well as spin-flip and pair-hopping interactions. Therewith it is possible to obtain valuable insight into the orbital occupations, relevant local spin multiplets, and the fermiology with increasing correlation strength. Besides generic correlation-induced band-narrowing and -shifting, an intriguing quasiparticle structure close to the Fermi level is found in the neighborhood of the notorious {gamma}{sub 2} pocket in the Brillouin zone. Along the {gamma}-X direction in k-space, that structure appears very sensitive to electronic self-energy effects. The subtle sensitivity, connected also to its manifest multi-orbital character, may put this very low-energy structure in context with the puzzling metamagnetic properties of the compound. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Correlation effects in ruthenates: LDA+DMFT study
Energy Technology Data Exchange (ETDEWEB)
Gorelov, Evgeny; Pavarini, Eva [IAS-3, Forschungszentrum Juelich, 52425 Juelich (Germany)
2012-07-01
The ruthenates of the Ruddlesden-Popper family A{sub n+1}Ru{sub n} O{sub 3n+1} where A=(Sr,Ca) are unique among transition-metal oxides, because the change of cation A and/or in the number n of RuO{sub 2} layers leads to a variety of collective phenomena, ranging from multi-band Mott transitions to ferro- and meta-magnetism. To understand these systems, it is necessary to disentangle the effects of Coulomb repulsion in the 4d{sup 4}Ru shell from those of lattice distortions and chemistry. By using the LDA+DMFT approach, we show how such disentanglement explains the nature of the metal-insulator transition in single-layered Ca ruthenates and the evolution of electronic structure in n-layered Sr ruthenates. We use LDA+DMFT scheme based on the N-th Order Muffin-Tin Orbital approach and the weak-coupling CT-quantum Monte Carlo method as impurity solver. This method allows us to take into account the full rotationally-invariant Coulomb interaction, as well as full on-site self-energy matrix in orbital space with spin-orbit coupling. We discuss changes in effective mass and orbital polarization as a result of spin-flip processes and spin-orbit interaction.
LDA measurements in the Francis-99 draft tube cone
Sundstrom, L. R. J.; Amiri, K.; Bergan, C.; Cervantes, M. J.; Dahlhaug, O. G.
2014-03-01
Velocity measurements were performed in the draft tube cone of a 1:5.1 scaled model of the Tokke hydropower plant, Norway; also known as the Francis-99 model. Results from the laser Doppler anemometry measurements undertaken at three operating points will be used as validation data for an upcoming workshop on the state of the art of Francis turbine numerical simulation. With the turbine operating at the best efficiency point, a sensitivity analysis of the flow parameters head, flow rate and runner rotational speed shows that the effects on the dimensionless velocity profiles are small as long as nED and QED are held constant. The results indicate a well-functioning turbine at the best efficiency point and high load. At the part load operating point, a vortex breakdown occurs which distorts the velocity profiles and significantly lowers the turbine's hydraulic efficiency. Frequency spectrums of each LDA signal at part load reveals a peak which is asynchronous to that of the runner angular speed. The peaks might be related to the precession of a rotating vortex rope but the characteristics of the LDA signals are different compared to previous studies involving rotating vortex ropes.
Garza, Alejandro J; Alencar, Ana G Sousa; Sun, Jianwei; Perdew, John P; Scuseria, Gustavo E
2015-01-01
Contrary to standard coupled cluster doubles (CCD) and Brueckner doubles (BD), singlet-paired analogues of CCD and BD (denoted here as CCD0 and BD0) do not break down when static correlation is present, but neglect substantial amounts of dynamic correlation. In fact, CCD0 and BD0 do not account for any contributions from multielectron excitations involving only same-spin electrons at all. We exploit this feature to add---without introducing double counting, self-interaction, or increase in cost---the missing correlation to these methods via meta-GGA density functionals (TPSS and SCAN). Furthermore, we improve upon these CCD0+DFT blends by invoking range separation: the short- and long-range correlations absent in CCD0/BD0 are evaluated with DFT and the direct random phase approximation (dRPA), respectively. This corrects the description of long-range van der Waals forces. Comprehensive benchmarking shows that the combinations presented here are very accurate for weakly correlated systems, while also providing...
Score-moment combined linear discrimination analysis (SMC-LDA) as an improved discrimination method.
Han, Jintae; Chung, Hoeil; Han, Sung-Hwan; Yoon, Moon-Young
2007-01-01
A new discrimination method called the score-moment combined linear discrimination analysis (SMC-LDA) has been developed and its performance has been evaluated using three practical spectroscopic datasets. The key concept of SMC-LDA was to use not only the score from principal component analysis (PCA), but also the moment of the spectrum, as inputs for LDA to improve discrimination. Along with conventional score, moment is used in spectroscopic fields as an effective alternative for spectral feature representation. Three different approaches were considered. Initially, the score generated from PCA was projected onto a two-dimensional feature space by maximizing Fisher's criterion function (conventional PCA-LDA). Next, the same procedure was performed using only moment. Finally, both score and moment were utilized simultaneously for LDA. To evaluate discrimination performances, three different spectroscopic datasets were employed: (1) infrared (IR) spectra of normal and malignant stomach tissue, (2) near-infrared (NIR) spectra of diesel and light gas oil (LGO) and (3) Raman spectra of Chinese and Korean ginseng. For each case, the best discrimination results were achieved when both score and moment were used for LDA (SMC-LDA). Since the spectral representation character of moment was different from that of score, inclusion of both score and moment for LDA provided more diversified and descriptive information.
[Application of DPLS-based LDA in corn qualitative near infrared spectroscopy analysis].
Qin, Hong; Wang, Hui-rong; Li, Wei-jun; Jin, Xiao-xian
2011-07-01
NIR technology is a rapid, nondestructive and user-friendly method ideally suited for Qualitative analysis. In this paper the authors present the use of discriminant partial least Squares (DPLS)-based linear discriminant analysis (LDA) in corn qualitative near infrared spectroscopy analysis. Firstly, a training set including 30 corn varieties (each variety has 20 samples) was used to build the DPLS regression model, and 28 principal components (DPLS-PCs) were obtained from original spectrum. Secondly, the DPLS-PCs scores of the training set were extracted as DPLS features. Thirdly, LDA was applied to the DPLS features, determining 26 principal components (LDA-PCs). A test sample was first projected onto the DPLS-PCs and then onto the LDA-PCs, and finally 26 DPLS+LDA features were obtained. The recognition results were obtained by minimum distance classifier. DPLS+LDA method achieved 96.18% recognition rate, while traditional DPLS regression method and DPLS feature extraction method only achieved 85.38% and 95.76% recognition rate respectively. The experiment results indicated that DPLS +LDA method is with better generalization ability compared with traditional DPLS regression method and NIRS analysis by DPLS+LDA method is an efficient way to discriminate corn species.
Pernal, Katarzyna
2012-05-14
Time-dependent density functional theory (TD-DFT) in the adiabatic formulation exhibits known failures when applied to predicting excitation energies. One of them is the lack of the doubly excited configurations. On the other hand, the time-dependent theory based on a one-electron reduced density matrix functional (time-dependent density matrix functional theory, TD-DMFT) has proven accurate in determining single and double excitations of H(2) molecule if the exact functional is employed in the adiabatic approximation. We propose a new approach for computing excited state energies that relies on functionals of electron density and one-electron reduced density matrix, where the latter is applied in the long-range region of electron-electron interactions. A similar approach has been recently successfully employed in predicting ground state potential energy curves of diatomic molecules even in the dissociation limit, where static correlation effects are dominating. In the paper, a time-dependent functional theory based on the range-separation of electronic interaction operator is rigorously formulated. To turn the approach into a practical scheme the adiabatic approximation is proposed for the short- and long-range components of the coupling matrix present in the linear response equations. In the end, the problem of finding excitation energies is turned into an eigenproblem for a symmetric matrix. Assignment of obtained excitations is discussed and it is shown how to identify double excitations from the analysis of approximate transition density matrix elements. The proposed method used with the short-range local density approximation (srLDA) and the long-range Buijse-Baerends density matrix functional (lrBB) is applied to H(2) molecule (at equilibrium geometry and in the dissociation limit) and to Be atom. The method accounts for double excitations in the investigated systems but, unfortunately, the accuracy of some of them is poor. The quality of the other
Torres, Alfredo G; Tutt, Christopher B; Duval, Lisabeth; Popov, Vsevolod; Nasr, Abdelhakim Ben; Michalski, Jane; Scaletsky, Isabel C A
2007-04-01
Atypical enteropathogenic Escherichia coli (aEPEC) strains are frequently implicated in infant diarrhoea in developing countries. Not much is known about the adherence properties of aEPEC; however, it has been shown that these strains can adhere to tissue-cultured cells. A chromosomal region designated the locus for diffuse adherence (LDA) confers aEPEC strain 22 the ability to adhere to culture cells. LDA is an afimbrial adhesin that contains a major subunit, LdaG, whose expression is induced on MacConkey agar at 37 degrees C. We hypothesized that the bile salts found in this culture media induce the expression of LdaG. Strain 22 and the LdaG mutant were grown in Luria-Bertani (LB) media in the presence or absence of bile salts and heat-extracted surface-expressed proteins were separated by SDS-PAGE to determine whether expression of the 25 kDa LdaG protein was induced. Western blot analysis with anti-LdaG confirmed that bile salts enhance LdaG expression at 37 degrees C. Adhesion assays on HeLa cells revealed that adhesion in a diffuse pattern of strain 22 increased in the presence of bile salts. We also confirmed that expression of the localized adherence pattern observed in the ldaG mutant required the presence of a large cryptic plasmid found in strain 22 and that this phenotype was not induced by bile salts. At the transcriptional level, the ldaG-lacZ promoter fusion displayed maximum beta-galactosidase activity when the parent strain was grown in LB supplemented with bile salts. Fluorescence Activated Cell Sorting analysis, immunogold labelling electron microscopy and immunofluorescence using anti-LdaG sera confirmed that LDA is a bile salts-inducible surface-expressed afimbrial adhesin. Finally, LdaG expression was induced in presence of individual bile salts but not by other detergents. We concluded that bile salts increase expression of LDA, conferring a diffuse adherence pattern and having an impact on the adhesion properties of this aEPEC strain.
Evaluation of LDA Ensembles Classifiers for Brain Computer Interface
Arjona, Cristian; Pentácolo, José; Gareis, Iván; Atum, Yanina; Gentiletti, Gerardo; Acevedo, Rubén; Rufiner, Leonardo
2011-12-01
The Brain Computer Interface (BCI) translates brain activity into computer commands. To increase the performance of the BCI, to decode the user intentions it is necessary to get better the feature extraction and classification techniques. In this article the performance of a three linear discriminant analysis (LDA) classifiers ensemble is studied. The system based on ensemble can theoretically achieved better classification results than the individual counterpart, regarding individual classifier generation algorithm and the procedures for combine their outputs. Classic algorithms based on ensembles such as bagging and boosting are discussed here. For the application on BCI, it was concluded that the generated results using ER and AUC as performance index do not give enough information to establish which configuration is better.
MANOVA, LDA, and FA criteria in clusters parameter estimation
Directory of Open Access Journals (Sweden)
Stan Lipovetsky
2015-12-01
Full Text Available Multivariate analysis of variance (MANOVA and linear discriminant analysis (LDA apply such well-known criteria as the Wilks’ lambda, Lawley–Hotelling trace, and Pillai’s trace test for checking quality of the solutions. The current paper suggests using these criteria for building objectives for finding clusters parameters because optimizing such objectives corresponds to the best distinguishing between the clusters. Relation to Joreskog’s classification for factor analysis (FA techniques is also considered. The problem can be reduced to the multinomial parameterization, and solution can be found in a nonlinear optimization procedure which yields the estimates for the cluster centers and sizes. This approach for clustering works with data compressed into covariance matrix so can be especially useful for big data.
Face recognition based on LDA in manifold subspace
Directory of Open Access Journals (Sweden)
Hung Phuoc Truong
2016-05-01
Full Text Available Although LDA has many successes in dimensionality reduction and data separation, it also has disadvantages, especially the small sample size problem in training data because the "within-class scatter" matrix may not be accurately estimated. Moreover, this algorithm can only operate correctly with labeled data in supervised learning. In practice, data collection is very huge and labeling data requires high-cost, thus the combination of a part of labeled data and unlabeled data for this algorithm in Manifold subspace is a novelty research. This paper reports a study that propose a semi-supervised method called DSLM, which aims at overcoming all these limitations. The proposed method ensures that the discriminative information of labeled data and the intrinsic geometric structure of data are mapped to new optimal subspace. Results are obtained from the experiments and compared to several related methods showing the effectiveness of our proposed method.
Hu, Chunping; Sugino, Osamu; Tateyama, Yoshitaka
2009-02-11
Time-dependent density functional theory (TDDFT) has become a standard tool for investigation of electronic excited states. However, for certain types of electronic excitations, TDDFT is known to give systematically inaccurate results, which has been attributed to the insufficiency of conventional exchange-correlation functionals, such as the local density approximation (LDA). To improve TDDFT performance within LDA, a modified linear response (MLR) scheme was recently proposed, in which the responses from not only the ground state, but also the intermediate excited states are taken into account. This scheme was shown to greatly improve TDDFT performance on the prediction of Rydberg and charge-transfer excitation energies of molecules. Yet, for a validation of this TDDFT-MLR scheme for excitation energies, there remain issues to be resolved regarding Rydberg transitions of single atoms before going to larger systems. In the present work, we show an adapted algorithm to construct the intermediate excited states for rare-gas atoms. With the technique, Rydberg transition energies can be well decoded from LDA, as will also be shown in the application of the TDDFT-MLR scheme to other types of atoms.
Hoffmann, Mark R; Helgaker, Trygve
2015-03-01
A new variation of the second-order generalized van Vleck perturbation theory (GVVPT2) for molecular electronic structure is suggested. In contrast to the established procedure, in which CASSCF or MCSCF orbitals are first obtained and subsequently used to define a many-electron model (or reference) space, the use of an orbital space obtained from the local density approximation (LDA) variant of density functional theory is considered. Through a final, noniterative diagonalization of an average Fock matrix within orbital subspaces, quasicanonical orbitals that are otherwise indistinguishable from quasicanonical orbitals obtained from a CASSCF or MCSCF calculation are obtained. Consequently, all advantages of the GVVPT2 method are retained, including use of macroconfigurations to define incomplete active spaces and rigorous avoidance of intruder states. The suggested variant is vetted on three well-known model problems: the symmetric stretching of the O-H bonds in water, the dissociation of N2, and the stretching of ground and excited states C2 to more than twice the equilibrium bond length of the ground state. It is observed that the LDA-based GVVPT2 calculations yield good results, of comparable quality to conventional CASSCF-based calculations. This is true even for the C2 model problem, in which the orbital space for each state was defined by the LDA orbitals. These results suggest that GVVPT2 can be applied to much larger problems than previously accessible.
e-IQ and IQ knowledge mining for generalized LDA
Jenkins, Jeffrey; van Bergem, Rutger; Sweet, Charles; Vietsch, Eveline; Szu, Harold
2015-05-01
How can the human brain uncover patterns, associations and features in real-time, real-world data? There must be a general strategy used to transform raw signals into useful features, but representing this generalization in the context of our information extraction tool set is lacking. In contrast to Big Data (BD), Large Data Analysis (LDA) has become a reachable multi-disciplinary goal in recent years due in part to high performance computers and algorithm development, as well as the availability of large data sets. However, the experience of Machine Learning (ML) and information communities has not been generalized into an intuitive framework that is useful to researchers across disciplines. The data exploration phase of data mining is a prime example of this unspoken, ad-hoc nature of ML - the Computer Scientist works with a Subject Matter Expert (SME) to understand the data, and then build tools (i.e. classifiers, etc.) which can benefit the SME and the rest of the researchers in that field. We ask, why is there not a tool to represent information in a meaningful way to the researcher asking the question? Meaning is subjective and contextual across disciplines, so to ensure robustness, we draw examples from several disciplines and propose a generalized LDA framework for independent data understanding of heterogeneous sources which contribute to Knowledge Discovery in Databases (KDD). Then, we explore the concept of adaptive Information resolution through a 6W unsupervised learning methodology feedback system. In this paper, we will describe the general process of man-machine interaction in terms of an asymmetric directed graph theory (digging for embedded knowledge), and model the inverse machine-man feedback (digging for tacit knowledge) as an ANN unsupervised learning methodology. Finally, we propose a collective learning framework which utilizes a 6W semantic topology to organize heterogeneous knowledge and diffuse information to entities within a society in
Alam, Md. Mehboob; Knecht, Stefan; Fromager, Emmanuel
2016-07-01
Ensemble density-functional theory (eDFT) suffers from the so-called "ghost-interaction" error when approximate exchange-correlation functionals are used. In this work, we present a rigorous ghost-interaction correction (GIC) scheme in the context of range-separated eDFT. The method relies on an exact decomposition of the ensemble short-range exchange-correlation energy into a multideterminantal exact exchange term, which involves the long-range interacting ensemble density matrix, instead of the Kohn-Sham (KS) one, and a complementary density-functional correlation energy. A generalized adiabatic connection formula is derived for the latter. In order to perform practical calculations, the complementary correlation functional is simply modeled by its ground-state local density approximation (LDA), while long-range interacting ground- and excited-state wave functions are obtained self-consistently by combining a long-range configuration-interaction calculation with a short-range LDA potential. We show that the GIC reduces the curvature of approximate range-separated ensemble energies drastically while providing considerably more accurate excitation energies, even for charge-transfer and double excitations. Interestingly, the method performs well also in the context of standard KS-eDFT, which is recovered when the range-separation parameter is set to 0.
Density functional calculation of equilibrium geometry and electronic structure of pyrite
Institute of Scientific and Technical Information of China (English)
邱冠周; 肖奇; 胡岳华; 徐竞
2001-01-01
The equilibrium geometry and electronic structure of pyrite has been studied using self-consistent density-functional theory within the local density approximation (LDA). The optimum bulk geometry is in good agreement with crystallographic data. The calculated band structure and density of states in the region around the Fermi energy show that valence-band maximum (VBM) is at X (100), and the conduction-band minimum (CBM) is at G (000). The indirect and direct band gaps are 0.6eV and 0.74eV, respectively. The calculated contour map of difference of charge density shows excess charge in nonbonding d electron states on the Fe sites. The density increases between sulfur nuclei and between iron and sulfur nuclei qualitatively reveal that S-S bond and Fe-S bond are covalent binding.
Dimensionality-driven phonon softening and incipient charge density wave instability in TiS2
Dolui, Kapildeb; Sanvito, Stefano
2016-08-01
Density functional theory and density functional perturbation theory are used to investigate the electronic and vibrational properties of TiS2. Within the local density approximation the material is a semimetal both in the bulk and in the monolayer form. Most interestingly we observe a Kohn anomaly in the bulk phonon dispersion, which turns into a charge density wave instability when TiS2 is thinned to less than four monolayers. Such instability, however, disappears when one calculates the electronic structure with a functional, such as the LDA+U, which returns an insulating ground state. In this situation charge-doping or strain does not bring back the charge density wave instability, whereas the formation of the TiSSe alloy does.
Combined LDA and LDA-1/2 method to obtain defect formation energies in large silicon supercells
Matusalem, Filipe; Ribeiro, Mauro, Jr.; Marques, Marcelo; Pelá, Ronaldo R.; Ferreira, Luiz G.; Teles, Lara K.
2013-12-01
A source of uncertainty in the state of the art calculations of defect levels is the inaccurate prediction of band-gap energies. Several approaches were developed to surpass this problem. However, another source of uncertainty remains: the small number of clustered atoms imposed by the computational restrictions. In this work, the LDA-1/2 method is explored in an attempt to overcome both problems with a small computational cost. We considered the self-interstitial defects in silicon as a benchmark for calculating defect states and charge-transition levels of point defects in semiconductors. We found neutral formation energies, including reaction barriers, of 4.65, 4.49, and 4.87 eV, for hexagonal, split and C3v configurations, respectively, in good agreement with most experimental results.
Density functional study of AgScO_2: Electronic and optical properties
Bhamu, K. C.; Sahariya, Jagrati; Vyas, Rishi; Priolkar, K. R.
2017-07-01
This paper focusses on the electronic and optical properties of scandium-based silver delafossite (AgScO_2) semiconductor. The density functional theory (DFT) in the framework of full potential linearized augmented plane wave (FP-LAPW) scheme has been used for the present calculations with local density approximation (LDA) and generalized gradient approximation (GGA). Electronic properties deal with energy bands and density of states (DOSs), while optical properties describe refractive index and absorption coefficient. The energy bands are interpreted in terms of DOSs. The computed value of band gap is in agreement with that reported in the literature. Our results predict AgScO_2 as indirect band-gap semiconductor. Our calculated value of the refractive index in zero frequency limits is 2.42. The absorption coefficient predicts the applicability of AgScO_2 in solar cells and flat panel liquid crystal display as a transparent top window layer.
Bennett, M. J.; Mawlood, S. N.; Al-Daini, A. J.; Girgis, N. S.
Three flow-velocity measurement systems, an on-axis LDA, an LTA, and a constant temperature hot-wire anemometer (CTA), are described and compared by applying them to the measurement of velocity in a high-pressure closed-circuit wind tunnel and to the velocity profiles of a free jet. A system operating on the LTA principle, the Polytec L2F, was used to produce the probability density functions for the two flow situations and to calibrate the hot-wire CTA system, and the hot-wire calibration curve at normal pressure and temperature was used to develop a semiempirical model for the evaluation of velocity at elevated pressures and temperatures. An experimental arrangement in which LTA and LDA measuring systems may be used simultaneously with no separation of the respective measuring volumes in any axis is described, and the methods which may be used to counteract the inaccuracies of such an arrangement are discussed.
An MPCA/LDA Based Dimensionality Reduction Algorithm for Face Recognition
Directory of Open Access Journals (Sweden)
Jun Huang
2014-01-01
Full Text Available We proposed a face recognition algorithm based on both the multilinear principal component analysis (MPCA and linear discriminant analysis (LDA. Compared with current traditional existing face recognition methods, our approach treats face images as multidimensional tensor in order to find the optimal tensor subspace for accomplishing dimension reduction. The LDA is used to project samples to a new discriminant feature space, while the K nearest neighbor (KNN is adopted for sample set classification. The results of our study and the developed algorithm are validated with face databases ORL, FERET, and YALE and compared with PCA, MPCA, and PCA + LDA methods, which demonstrates an improvement in face recognition accuracy.
AB INITIO STUDY OF OPTOELECTRONIC PROPERTIES OF SPINEL ZnAl2O4 BEYOND GGA AND LDA
Yousaf, Masood; Saeed, M. A.; Isa, Ahmad Radzi Mat; Rahnamaye Aliabad, H. A.; Noor, N. A.
2012-12-01
Electronic band structure and optical parameters of ZnAl2O4 are investigated by first-principles technique based on a new potential approximation, known as modified Becke-Johnson (mBJ). This method describes the excited states of insulators and semiconductors more accurately The recent direct band gap result by EV-GGA is underestimated by about 15% compared to our band gap value using mBJ-GGA. The value of the band gap of ZnAl2O4 decreases as follows: Eg(mBJ-GGA/LDA) > Eg(GGA) > Eg(LDA). The band structure base optical parametric quantities (dielectric constant, index of refraction, reflectivity and optical conductivity) are also calculated, and their variations with energy range are discussed. The first critical point (optical absorption's edge) in ZnAl2O4 occurs at about 5.26 eV in case of mBJ. This study about the optoelectronic properties indicates that ZnAl2O4 can be used in optical devices.
The role of exchange and correlation in time-dependent density-functional theory for photoionization
Stener, M.; Decleva, P.; Görling, A.
2001-05-01
Atomic photoionization cross sections are calculated by time-dependent density-functional (TDDF) methods using different exchange-correlation potentials including the exact one. The exchange-correlation kernel is treated in the adiabatic local density approximation (ALDA). Results for the exact full and the exact exchange-only Kohn-Sham (KS) potential are very similar, the calculated photo cross section agree very well with experimental data. Thus the exact correlation potential seems to have no influence on photoionization and the ALDA for the exchange-correlation kernel seems to be sufficient for most features of the cross sections. The TDDF method employing the exact exchange-only KS potential in combination with the ALDA exchange-correlation kernel therefore is a promising approach to describe photoionization. Deviations from experiment are observed for the widths and shape of the autoionization resonances and have to be attributed to deficiencies of the ALDA exchange-correlation kernel. The calculation of widths and shapes of autoionization resonances therefore may serve as a severe test for new approximate exchange-correlation density-functionals. The asymptotically exact exchange-correlation potential of van Leeuwen and Baerends also leads to quite good photo cross section, which, however, shows deficiencies close to the ionization threshold and in the energetic position of the autoionization resonances. Supplementation of the exact exchange potential with the LDA correlation potential leads to a worsening of the photo cross section because the LDA correlation potential is too attractive.
Carlson, Rebecca K; Truhlar, Donald G; Gagliardi, Laura
2015-09-08
We extend the on-top density functional of multiconfiguration pair-density functional theory (MC-PDFT) to include the gradient of the on-top density as well as the gradient of the density. We find that the theory is reasonably stable to this extension; furthermore, it provides improved accuracy for molecules containing transition metals. We illustrate the extended on-top density functionals by applying them to Cr2, Cu2, Ag2, Os2, and Re2Cl8(2-) as well as to our previous database of 56 data for bond dissociation energies, barrier heights, reaction energies, proton affinities, and the water dimer. The performance of MC-PDFT is comparable to or better than that of CASPT2.
Directory of Open Access Journals (Sweden)
Shereena V. B
2015-04-01
Full Text Available The aim of this paper is to present a comparative study of two linear dimension reduction methods namely PCA (Principal Component Analysis and LDA (Linear Discriminant Analysis. The main idea of PCA is to transform the high dimensional input space onto the feature space where the maximal variance is displayed. The feature selection in traditional LDA is obtained by maximizing the difference between classes and minimizing the distance within classes. PCA finds the axes with maximum variance for the whole data set where LDA tries to find the axes for best class seperability. The proposed method is experimented over a general image database using Matlab. The performance of these systems has been evaluated by Precision and Recall measures. Experimental results show that PCA based dimension reduction method gives the better performance in terms of higher precision and recall values with lesser computational complexity than the LDA based method.
Feature Dimension Reduction of NaXi Pictographs Characters Recognition based on LDA
Directory of Open Access Journals (Sweden)
Hai Guo
2012-11-01
Full Text Available As a kind of pictographic character, Naxi pictographs character has received little academic attention. Proposing dimension reduction method of Naxi pictographs characters on the basis of LDA (Linear Discriminant Analysis, this paper thus makes an in-depth study of feature dimension reduction, an important issue in the recognition of Naxi pictographs characters. By constructing a recognition sample library involving four features of grid feature, permeability number feature, moment invariant feature, and directional element feature (DEF, 50% of data are selected from sample library as training set and testing set respectively. Two dimension reduction methods of LDA and FA (Factor Analysis are applied to dimension reduction experiment of features of Naxi pictographs characters. The experiment result proves LDA method to be significantly superior to FA method, as LDA method could still maintain a 99% recognition precision when the dimension is reduced to 10% of the original dimension.
LDA算法在Mahout下的高效实现%Efficient implementation for LDA in Mahout
Institute of Scientific and Technical Information of China (English)
许伯熹; 胡宁; 陈文斌; 高卫国; 程晋
2013-01-01
通过对运用Gibbs采样的Latent Dirichlet Allocation (LDA)算法和MapReduce计算框架的细致研究,实现了LDA算法在Mahout下的分布式并行计算.详细地考察了该分布式并行计算程序的计算性能,并深入地探讨了一些影响计算性能的关键问题.%In a careful study of Latent Dirichlet Allocation (LDA) using Gibbs sampling and the MapReduce framework,an efficient implementation for LDA in Mahout was achieved.The experiments showed the high performance of this distributed parallel LDA program,and several issues about enhancing performance were discussed.
LDA - Measurements of Transitional Flows Induced by a Square Rib
Energy Technology Data Exchange (ETDEWEB)
Becker, S.; Durst, F.; Stoots, Carl Marcel; Condie, Keith Glenn; McEligot, Donald Marinus
2002-03-01
New fundamental measurements are presented for the transition process in flat plate boundary layers downstream of two-dimensional square ribs. By use of laser Doppler anemometry (LDA) and a large Matched-Index-of-Refraction (MIR) flow system, data for wall-normal fluctuations and Reynolds stresses were obtained in the near wall region to y+<0.1 in addition to the usual mean streamwise velocity component and its fluctuation. By varying velocity and rib height, the experiment investigated the following range of conditions: k+ = 5.5 to 21, 0.3
Toward unsupervised adaptation of LDA for brain-computer interfaces.
Vidaurre, C; Kawanabe, M; von Bünau, P; Blankertz, B; Müller, K R
2011-03-01
There is a step of significant difficulty experienced by brain-computer interface (BCI) users when going from the calibration recording to the feedback application. This effect has been previously studied and a supervised adaptation solution has been proposed. In this paper, we suggest a simple unsupervised adaptation method of the linear discriminant analysis (LDA) classifier that effectively solves this problem by counteracting the harmful effect of nonclass-related nonstationarities in electroencephalography (EEG) during BCI sessions performed with motor imagery tasks. For this, we first introduce three types of adaptation procedures and investigate them in an offline study with 19 datasets. Then, we select one of the proposed methods and analyze it further. The chosen classifier is offline tested in data from 80 healthy users and four high spinal cord injury patients. Finally, for the first time in BCI literature, we apply this unsupervised classifier in online experiments. Additionally, we show that its performance is significantly better than the state-of-the-art supervised approach.
Institute of Scientific and Technical Information of China (English)
黄正鹏
2008-01-01
本文对流量控制算法LDA+进行了深入研究,针对其在带宽竞争中有可能出现的不公平现象,提出了一种改进算法.当某一个媒体流的RTCP报告丢失或延迟到达,或者由于最小丢包率单位的限制而导致其中的丢包率为零时,该算法可以有效的阻止该流强占额外带宽,提高了带宽竞争的公平性.同时.该算法采用合理的估算方法决定发送速率,即提高了网络带宽利用率,又避免了在发送初期就发生网络拥塞的危险性.
Ye, Jieping; Chen, Jianhui; Janardan, Ravi; Kumar, Sudhir
2008-03-01
Gene expression in a developing embryo occurs in particular cells (spatial patterns) in a time-specific manner (temporal patterns), which leads to the differentiation of cell fates. Images of a Drosophila melanogaster embryo at a given developmental stage, showing a particular gene expression pattern revealed by a gene-specific probe, can be compared for spatial overlaps. The comparison is fundamentally important to formulating and testing gene interaction hypotheses. Expression pattern comparison is most biologically meaningful when images from a similar time point (developmental stage) are compared. In this paper, we present LdaPath, a novel formulation of Linear Discriminant Analysis (LDA) for automatic developmental stage range classification. It employs multivariate linear regression with the L(1)-norm penalty controlled by a regularization parameter for feature extraction and visualization. LdaPath computes an entire solution path for all values of regularization parameter with essentially the same computational cost as fitting one LDA model. Thus, it facilitates efficient model selection. It is based on the equivalence relationship between LDA and the least squares method for multi-class classifications. This equivalence relationship is established under a mild condition, which we show empirically to hold for many high-dimensional datasets, such as expression pattern images. Our experiments on a collection of 2705 expression pattern images show the effectiveness of the proposed algorithm. Results also show that the LDA model resulting from LdaPath is sparse, and irrelevant features may be removed. Thus, LdaPath provides a general framework for simultaneous feature selection and feature extraction.
The LDA beamformer: Optimal estimation of ERP source time series using linear discriminant analysis.
Treder, Matthias S; Porbadnigk, Anne K; Shahbazi Avarvand, Forooz; Müller, Klaus-Robert; Blankertz, Benjamin
2016-04-01
We introduce a novel beamforming approach for estimating event-related potential (ERP) source time series based on regularized linear discriminant analysis (LDA). The optimization problems in LDA and linearly-constrained minimum-variance (LCMV) beamformers are formally equivalent. The approaches differ in that, in LCMV beamformers, the spatial patterns are derived from a source model, whereas in an LDA beamformer the spatial patterns are derived directly from the data (i.e., the ERP peak). Using a formal proof and MEG simulations, we show that the LDA beamformer is robust to correlated sources and offers a higher signal-to-noise ratio than the LCMV beamformer and PCA. As an application, we use EEG data from an oddball experiment to show how the LDA beamformer can be harnessed to detect single-trial ERP latencies and estimate connectivity between ERP sources. Concluding, the LDA beamformer optimally reconstructs ERP sources by maximizing the ERP signal-to-noise ratio. Hence, it is a highly suited tool for analyzing ERP source time series, particularly in EEG/MEG studies wherein a source model is not available.
Kuchinskii, E. Z.; Nekrasov, I. A.; Pavlov, N. S.
2013-08-01
We propose a generalization of the LDA + DMFT + Σ k approach to the multiband case, in which correlated and uncorrelated states are present in the model simultaneously. Using the multiband version of the LDA + DMFT + Σ k approach, we calculate the density of states and spectral functions for the Emery model in a wide energy interval around the Fermi level. We also obtain the Fermi surfaces for the electron-doped high-temperature superconductor Nd2 - x Ce x CuO4 in the pseudogap phase. The self-energy part Σ k introduced additionally to take into account pseudogap fluctuations describes the nonlocal interaction of correlated electrons with collective Heisenberg short-range spin fluctuations. To solve the effective impurity model, the numerical renorm-group (NRG) method is used for the DMFT equations. Good qualitative agreement of the Fermi surfaces calculated using the LDA + DMFT + Σ k approach and experimental angle-resolved photoemission spectroscopic data is attained. The stability of the dielectric solution with charge transfer in the Emery model with correction for double counting is analyzed in the Appendix.
Energy Technology Data Exchange (ETDEWEB)
Petzold, Vivien; Rosner, Helge [Max-Planck-Institut fuer Chemische Physik fester Stoffe, Dresden (Germany)
2011-07-01
Electronic band structure calculations are routinely applied to many problems in chemistry and physics. The methods rely on a number of approximations, where the treatment of exchange and correlation is a very prominent issue, probably the most prominent in the development of new density functionals in the framework of density functional theory (DFT). The present work highlights effects that arise from the more fundamental Born-Oppenheimer approximation. Based on this approximation, the original problem - the quantum-mechanical description of matter consisting of nuclei and electrons - is decomposed into a nuclear and an electronic problem, the latter of which is treated by electronic band structure methods. Utilizing the most common density functionals, the local density approximation (LDA) and the generalized gradient approximation (GGA), we observe deviations between experimental and theoretical de Haas van Alphen (dHvA) frequencies for MgB{sub 2} and ZrB{sub 2} that can be consistently understood by electron-phonon coupling effects, which the theory is lacking. The explanation is based on a highly accurate computation of dHvA frequencies indicating an electron-phonon coupling-induced shift of the electronic bands.
Rafal Podlaski; Francis A. Roesch
2014-01-01
Two-component mixtures of either the Weibull distribution or the gamma distribution and the kernel density estimator were used for describing the diameter at breast height (dbh) empirical distributions of two-cohort stands. The data consisted of study plots from the Å wietokrzyski National Park (central Poland) and areas close to and including the North Carolina section...
Bruning, J.; Dobrokhotov, S.Y.; Katsnelson, M.I.; Minenkov, D.S.
2016-01-01
We consider the two-dimensional stationary Schrodinger and Dirac equations in the case of radial symmetry. A radially symmetric potential simulates the tip of a scanning tunneling microscope. We construct semiclassical asymptotic forms for generalized eigenfunctions and study the local density of st
Ataide, C. A.; Pelá, R. R.; Marques, M.; Teles, L. K.; Furthmüller, J.; Bechstedt, F.
2017-01-01
We investigate ZnO, CdO, and MgO oxides crystallizing in rocksalt, wurtzite, and zincblende structures. Whereas in MgO calculations, the conventional LDA-1/2 method is employed through a self-energy potential (VS), the shallow d bands in ZnO and CdO are treated through an increased amplitude (A ) of VS to modulate the self-energy of the d states to place them in the quasiparticle position. The LDA+A -1/2 scheme is applied to calculate band structures and electronic density of states of ZnO and CdO. We compare the results with those of more sophisticated quasiparticle calculations and experiments. We demonstrate that this new LDA+A -1/2 method reaches accuracy comparable to state-of-the-art methods, opening a door to study more complex systems containing shallow core electrons to the prize of LDA studies.
Nagai, Yuki; Hayashi, Nobuhiko
2008-08-01
By measuring the angular-oscillations behavior of the heat capacity with respect to the applied field direction, one can detect the details of the gap structure. We introduce the Kramer-Pesch approximation as a new method to analyze the field-angle-dependent experiments, which improves the previous Doppler-shift technique. We show that the Fermi-surface anisotropy is an indispensable factor for identifying the superconducting gap symmetry.
DoD Planewave: A General Scalable Density Functional Code For Solids And Clusters
Kim, Seong-Gon; Singh, D. J.; Kajihara, S. A.; Woodward, C.
2000-03-01
We will present our latest version of the DoD Planewave code, a general purpose scalable planewave basis density functional code. DoD Planewave is written in highly portable Fortran 90 and runs on many high-performance parallel machines including IBM SP2, SGI Orgin 2000 clusters and Pentium machines running Linux. The package including the complete source code and example runs is freely available. The code is capable of treating clusters or bulk structures of insulators, semiconductors, metals and magnetic materials, with general symmetry. The present version performs self-consistent electronic structure, total energy and force calculations within the Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA). It also does automatic structure optimization and ab initio molecular dynamics. Calculations demonstrating the capabilities of the code are presented. Further information may be found on our web-site (http://cst- www.nrl.navy.mil/people/singh/planewave/).
Global hybrids from the semiclassical atom theory satisfying the local density linear response
Fabiano, E; Cortona, P; Della Sala, F
2015-01-01
We propose global hybrid approximations of the exchange-correlation (XC) energy functional which reproduce well the modified fourth-order gradient expansion of the exchange energy in the semiclassical limit of many-electron neutral atoms and recover the full local density approximation (LDA) linear response. These XC functionals represent the hybrid versions of the APBE functional [Phys. Rev. Lett. 106, 186406, (2011)] yet employing an additional correlation functional which uses the localization concept of the correlation energy density to improve the compatibility with the Hartree-Fock exchange as well as the coupling-constant-resolved XC potential energy. Broad energetical and structural testings, including thermochemistry and geometry, transition metal complexes, non-covalent interactions, gold clusters and small gold-molecule interfaces, as well as an analysis of the hybrid parameters, show that our construction is quite robust. In particular, our testing shows that the resulting hybrid, including 20\\% o...
Institute of Scientific and Technical Information of China (English)
周世琦
2005-01-01
A universal theoretical way is proposed which enables all of hard sphere density functional approximations (DFAs) applicable to non-hard sphere fluids.The resultant DFA by combining the universal theoretical way with any hard sphere DFAs only needs as input a second order direct correlation function (DCF) of a coexistence bulk fluid,and can be applicable to both supercitical and subcritical temperature regions.The associated effective hard sphere density can be specified by a hard wall sum rule. It is indicated that so determined value of the effective hard sphere density can be universal,i.e. can be applied for any external potentials different from the single hard wall. As an illustrating example,the universal theoretical way is combined with a hard sphere BDFA to predict density profile of a hard core attractive Yukawa model fluid influenced by diverse external fields,agreement between the present formalism predictions and the corresponding simulation data is very good or at least comparable with several previous DFT approaches. The most advantage of the present theoretical way combined with other hard sphere DFAs is discused.%提出了一个普适性的理论方案,该方案使一切硬球密度泛函近似能被扩展到非硬球流体的情形.将该普适性理论方案与任意硬球密度泛函近似结合所形成的非硬球密度泛函近似,仅仅需要共存体相流体的二阶直接相关函数作为输入,因而能用于超临界与亚临界区域的情形.其中的有效硬球密度可由硬墙Sum规则确定.结果表明,如此确定的有效硬球密度可用于任意外势情形.作为代表性的例子,我们将该普适性理论方案与一个最近提出的桥密度泛函近似结合,用以预言硬核吸引汤川势流体在几个不同的外场影响下的密度分布.此理论与相应的计算机模拟数据符合很好,或至少与以前的几个密度泛函近似相当.并讨论了该方法相比于以前的几个方法所具有的优点.
Labeled LDA Model Based on Shared Background Topics%基于共享背景主题的 Labeled LDA 模型
Institute of Scientific and Technical Information of China (English)
江雨燕; 李平; 王清
2013-01-01
LDA (Latent Dirichlet Allocation) is widely used in text analysis and images processing .However ,LDA and most of its modifications are unsupervised learning models ,which are not appropriate for classification especially multi-label classification problem .Through the study on the multi-label documents and LDA models ,this paper proposes a new Labeled LDA model ,namely Shared Background Topics Labeled LDA (SBTL-LDA ) .In this new model ,each label has not only a set of local topics ,but also has several background (global ) topics .Experienmental results show that SBTL-LDA can decrease the affect of similarities and de-pendence between different topics and because the label of document is mapped as a combination of local topics and shared topics , so it has a high accuracy when learning from multi-Labeled documents .In addition ,this model can be viewed as a semi-supervised clustering model which can utilize the information of labels and outperfom other models .%隐藏狄利克雷分配（Latent Dirichlet Allocation ，LDA ）模型被广泛应用于文本分析、图像识别等领域。但由于LDA及其扩展模型多为无监督学习模型，无法将其应用于分类任务中。本文通过研究文档标记与LDA模型中主题的映射关系，提出一种新的Labeled LDA模型（Shared Background Topics Labeled LDA ，SBTL-LDA ）。在SBTL-LDA模型中每个标记除了存在若干个独享的局部主题外，还存在若干个共享的背景（Background ）主题，这样可以有效分析不同标记所含主题之间的依赖关系，而文档标记被映射为局部主题和共享主题的组合，因此SBTL-LDA模型可以有效提升文档标记判别的准确性。同时SBTL-LDA模型还可以看成是一种半监督聚类模型，在对文档进行聚类分析的过程中模型可以有效的利用文档的标记信息提升文档聚类效果。实验证明SBTL-LDA模型能够有效解决PLDA模型中主题之间的相
Approximate Representations and Approximate Homomorphisms
Moore, Cristopher
2010-01-01
Approximate algebraic structures play a defining role in arithmetic combinatorics and have found remarkable applications to basic questions in number theory and pseudorandomness. Here we study approximate representations of finite groups: functions f:G -> U_d such that Pr[f(xy) = f(x) f(y)] is large, or more generally Exp_{x,y} ||f(xy) - f(x)f(y)||^2$ is small, where x and y are uniformly random elements of the group G and U_d denotes the unitary group of degree d. We bound these quantities in terms of the ratio d / d_min where d_min is the dimension of the smallest nontrivial representation of G. As an application, we bound the extent to which a function f : G -> H can be an approximate homomorphism where H is another finite group. We show that if H's representations are significantly smaller than G's, no such f can be much more homomorphic than a random function. We interpret these results as showing that if G is quasirandom, that is, if d_min is large, then G cannot be embedded in a small number of dimensi...
Huang, Jian; Yuen, Pong C; Chen, Wen-Sheng; Lai, Jian Huang
2007-08-01
This paper addresses the problem of automatically tuning multiple kernel parameters for the kernel-based linear discriminant analysis (LDA) method. The kernel approach has been proposed to solve face recognition problems under complex distribution by mapping the input space to a high-dimensional feature space. Some recognition algorithms such as the kernel principal components analysis, kernel Fisher discriminant, generalized discriminant analysis, and kernel direct LDA have been developed in the last five years. The experimental results show that the kernel-based method is a good and feasible approach to tackle the pose and illumination variations. One of the crucial factors in the kernel approach is the selection of kernel parameters, which highly affects the generalization capability and stability of the kernel-based learning methods. In view of this, we propose an eigenvalue-stability-bounded margin maximization (ESBMM) algorithm to automatically tune the multiple parameters of the Gaussian radial basis function kernel for the kernel subspace LDA (KSLDA) method, which is developed based on our previously developed subspace LDA method. The ESBMM algorithm improves the generalization capability of the kernel-based LDA method by maximizing the margin maximization criterion while maintaining the eigenvalue stability of the kernel-based LDA method. An in-depth investigation on the generalization performance on pose and illumination dimensions is performed using the YaleB and CMU PIE databases. The FERET database is also used for benchmark evaluation. Compared with the existing PCA-based and LDA-based methods, our proposed KSLDA method, with the ESBMM kernel parameter estimation algorithm, gives superior performance.
Giovambattista, Nicolas; Sciortino, Francesco; Starr, Francis W; Poole, Peter H
2016-12-14
The potential energy landscape (PEL) formalism is a valuable approach within statistical mechanics to describe supercooled liquids and glasses. Here we use the PEL formalism and computer simulations to study the pressure-induced transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA) at different temperatures. We employ the ST2 water model for which the LDA-HDA transformations are remarkably sharp, similar to what is observed in experiments, and reminiscent of a first-order phase transition. Our results are consistent with the view that LDA and HDA configurations are associated with two distinct regions (megabasins) of the PEL that are separated by a potential energy barrier. At higher temperature, we find that low-density liquid (LDL) configurations are located in the same megabasin as LDA, and that high-density liquid (HDL) configurations are located in the same megabasin as HDA. We show that the pressure-induced LDL-HDL and LDA-HDA transformations occur along paths that interconnect these two megabasins, but that the path followed by the liquid is different from the path followed by the amorphous solid. At higher pressure, we also study the liquid-to-ice-VII first-order phase transition, and find that the behavior of the PEL properties across this transition is qualitatively similar to the changes found during the LDA-HDA transformation. This similarity supports the interpretation that the LDA-HDA transformation is a first-order phase transition between out-of-equilibrium states. Finally, we compare the PEL properties explored during the LDA-HDA transformations in ST2 water with those reported previously for SPC/E water, for which the LDA-HDA transformations are rather smooth. This comparison illuminates the previous work showing that, at accessible computer times scales, a liquid-liquid phase transition occurs in the case of ST2 water, but not for SPC/E water.
Giovambattista, Nicolas; Sciortino, Francesco; Starr, Francis W.; Poole, Peter H.
2016-12-01
The potential energy landscape (PEL) formalism is a valuable approach within statistical mechanics to describe supercooled liquids and glasses. Here we use the PEL formalism and computer simulations to study the pressure-induced transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA) at different temperatures. We employ the ST2 water model for which the LDA-HDA transformations are remarkably sharp, similar to what is observed in experiments, and reminiscent of a first-order phase transition. Our results are consistent with the view that LDA and HDA configurations are associated with two distinct regions (megabasins) of the PEL that are separated by a potential energy barrier. At higher temperature, we find that low-density liquid (LDL) configurations are located in the same megabasin as LDA, and that high-density liquid (HDL) configurations are located in the same megabasin as HDA. We show that the pressure-induced LDL-HDL and LDA-HDA transformations occur along paths that interconnect these two megabasins, but that the path followed by the liquid is different from the path followed by the amorphous solid. At higher pressure, we also study the liquid-to-ice-VII first-order phase transition, and find that the behavior of the PEL properties across this transition is qualitatively similar to the changes found during the LDA-HDA transformation. This similarity supports the interpretation that the LDA-HDA transformation is a first-order phase transition between out-of-equilibrium states. Finally, we compare the PEL properties explored during the LDA-HDA transformations in ST2 water with those reported previously for SPC/E water, for which the LDA-HDA transformations are rather smooth. This comparison illuminates the previous work showing that, at accessible computer times scales, a liquid-liquid phase transition occurs in the case of ST2 water, but not for SPC/E water.
CERN. Geneva
2015-01-01
Most physics results at the LHC end in a likelihood ratio test. This includes discovery and exclusion for searches as well as mass, cross-section, and coupling measurements. The use of Machine Learning (multivariate) algorithms in HEP is mainly restricted to searches, which can be reduced to classification between two fixed distributions: signal vs. background. I will show how we can extend the use of ML classifiers to distributions parameterized by physical quantities like masses and couplings as well as nuisance parameters associated to systematic uncertainties. This allows for one to approximate the likelihood ratio while still using a high dimensional feature vector for the data. Both the MEM and ABC approaches mentioned above aim to provide inference on model parameters (like cross-sections, masses, couplings, etc.). ABC is fundamentally tied Bayesian inference and focuses on the “likelihood free” setting where only a simulator is available and one cannot directly compute the likelihood for the dat...
Osinga, V. P.; van Gisbergen, S. J. A.; Snijders, J. G.; Baerends, E. J.
1997-03-01
The generalized gradient-approximated (GGA) energy functionals used in density functional theory (DFT) provide accurate results for many different properties. However, one of their weaknesses lies in the fact that Van der Waals forces are not described. In spite of this, it is possible to obtain reliable long-range potential energy surfaces within DFT. In this paper, we use time-dependent density functional response theory to obtain the Van der Waals dispersion coefficients C6, C7, and C8 (both isotropic and anisotropic). They are calculated from the multipole polarizabilities at imaginary frequencies of the two interacting molecules. Alternatively, one might use one of the recently-proposed Van der Waals energy functionals for well-separated systems, which provide fairly good approximations to our isotropic results. Results with the local density approximation (LDA), Becke-Perdew (BP) GGA and the Van Leeuwen-Baerends (LB94) exchange-correlation potentials are presented for the multipole polarizabilities and the dispersion coefficients of several rare gases, diatomics and the water molecule. The LB94 potential clearly performs best, due to its correct Coulombic asymptotic behavior, yielding results which are close to those obtained with many-body perturbation theory (MBPT). The LDA and BP results are systematically too high for the isotropic properties. This becomes progressively worse for the higher dispersion coefficients. The results for the relative anisotropies are quite satisfactory for all three potentials, however.
Wavelet-Based Linear-Response Time-Dependent Density-Functional Theory
Natarajan, Bhaarathi; Casida, Mark E; Deutsch, Thierry; Burchak, Olga N; Philouze, Christian; Balakirev, Maxim Y
2011-01-01
Linear-response time-dependent (TD) density-functional theory (DFT) has been implemented in the pseudopotential wavelet-based electronic structure program BigDFT and results are compared against those obtained with the all-electron Gaussian-type orbital program deMon2k for the calculation of electronic absorption spectra of N2 using the TD local density approximation (LDA). The two programs give comparable excitation energies and absorption spectra once suitably extensive basis sets are used. Convergence of LDA density orbitals and orbital energies to the basis-set limit is significantly faster for BigDFT than for deMon2k. However the number of virtual orbitals used in TD-DFT calculations is a parameter in BigDFT, while all virtual orbitals are included in TD-DFT calculations in deMon2k. As a reality check, we report the x-ray crystal structure and the measured and calculated absorption spectrum (excitation energies and oscillator strengths) of the small organic molecule N-cyclohexyl-2-(4-methoxyphenyl)imidaz...
Beyond the random phase approximation
DEFF Research Database (Denmark)
Olsen, Thomas; Thygesen, Kristian S.
2013-01-01
We assess the performance of a recently proposed renormalized adiabatic local density approximation (rALDA) for ab initio calculations of electronic correlation energies in solids and molecules. The method is an extension of the random phase approximation (RPA) derived from time-dependent density...
Pang, Shaoning; Ban, Tao; Kadobayashi, Youki; Kasabov, Nikola K
2012-04-01
To adapt linear discriminant analysis (LDA) to real-world applications, there is a pressing need to equip it with an incremental learning ability to integrate knowledge presented by one-pass data streams, a functionality to join multiple LDA models to make the knowledge sharing between independent learning agents more efficient, and a forgetting functionality to avoid reconstruction of the overall discriminant eigenspace caused by some irregular changes. To this end, we introduce two adaptive LDA learning methods: LDA merging and LDA splitting. These provide the benefits of ability of online learning with one-pass data streams, retained class separability identical to the batch learning method, high efficiency for knowledge sharing due to condensed knowledge representation by the eigenspace model, and more preferable time and storage costs than traditional approaches under common application conditions. These properties are validated by experiments on a benchmark face image data set. By a case study on the application of the proposed method to multiagent cooperative learning and system alternation of a face recognition system, we further clarified the adaptability of the proposed methods to complex dynamic learning tasks.
Institute of Scientific and Technical Information of China (English)
杨端端; 金连文; 尹俊勋
2006-01-01
线性判决分析(linear discriminate analysis,LDA) 作为一种经典线性工具已经被广泛地运用在各种模式识别问题中,为了降低参数估计误差对于LDA性能的影响,我们提出了一种改进的线性判决分析(modified linear discriminate analysis,MLDA)算法,并运用到手写汉字识别中,使得识别率有所提高.在此基础上,针对大类别的汉字识别问题,提出了两级LDA的手写汉字识别方法,即MLDA+LDA.在对GB 2312-80的1 034个汉字类别的350套手写样本的实验表明,这个两级LDA识别策略针识别率较最小距离分类器有着3.77%的提高,较LDA+最小距离分类方法有1.71%的提高,表明方法的有效性.
LDA based community discovery model jointly considering structure and content%基于 LDA 的结构-内容联合社团发现模型
Institute of Scientific and Technical Information of China (English)
叶娟; 陈启买
2016-01-01
In social networks,discovering communities according to the structure and content of networks can not only group users in communities,but also predict latent relationship between users.In order to improve the performance of community discovery,this paper proposed a LDA based community discovery model jointly considering structure and content.Firstly,it transformed the graph of a social network into a LDA based model.Secondly,it extended the transformed LDA model by incor-porating contents of actions between users.Finally,it estimated the parameters of the proposed model based on Gibbs sam-pling.The experiments show that,compared with the related works,the proposed model is more efficient in discovering com-munities which users are tightly connected and having similar interests.Moreover,based on the communities discovery,it can better predict the latent friendships in a social network.%在社会网络中，根据已有的连接关系和文本信息发掘社会网络中的社团不但可以将相似的用户划分在一个社团，还可以用来预测网络中潜在的连接关系。为了提高社会网络中社团发现的性能，提出了一种基于LDA 的结构—内容联合社团发现模型。首先，对社会网络的图论描述进行转换，使其适用于 LDA 模型；其次，对LDA 模型描述进行扩充，使其包含了用户间交互的文本信息；最后，通过 Gibbs 采样方法对模型的参数进行估计。实验表明，提出的社团发现模型与其他相关方法相比较，社团发现得到的社团不仅用户间连接的紧密度和用户共享兴趣爱好的强度高，而且可以更好地用于社会网络中潜在连接的预测。
Agrawal, Divya
Dual-beam ELF/VLF wave generation experiments performed at the High-frequency Active Auroral Research Program (HAARP) HF transmitter in Gakona, Alaska are critically compared with the predictions of a newly developed ionospheric high frequency (HF) heating model that accounts for the simultaneous propagation and absorption of multiple HF beams. The dual-beam HF heating experiments presented herein consist of two HF beams transmitting simultaneously: one amplitude modulated (AM) HF beam modulates the conductivity of the lower ionosphere in the extremely low frequency (ELF, 30 Hz to 3 kHz) and/or very low frequency (VLF, 3 kHz to 30 kHz) band while a second HF beam broadcasts a continuous waveform (CW) signal, modifying the efficiency of ELF/VLF conductivity modulation and thereby the efficiency of ELF/VLF wave generation. Ground-based experimental observations are used together with the predictions of the theoretical model to identify the property of the received ELF/VLF wave that is most sensitive to the effects of multi-beam HF heating, and that property is determined to be the ELF/VLF signal magnitude. The dependence of the generated ELF/VLF wave magnitude on several HF transmission parameters (HF power, HF frequency, and modulation waveform) is then experimentally measured and analyzed within the context of the multi-beam HF heating model. For all cases studied, the received ELF/VLF wave magnitude as a function of transmission parameter is analyzed to identify the dependence on the ambient D-region electron density (Ne) and/or electron temperature ( Te), in turn identifying the HF transmission parameters that provide significant independent information regarding the ambient conditions of the D-region ionosphere. A theoretical analysis is performed to determine the conditions under which the effects of Ne and Te can be decoupled, and the results of this analysis are applied to identify an electron density profile that can reproduce the unusually high level of ELF
LDA measurements in a Mach 2 flow over a rearward facing step with staged transverse injection
Wang, J.-A.; Dancey, C. L.
1992-01-01
Measurements of the mean velocity field and selected turbulence statistics have been obtained via 2D LDA in a Mach 2 flow over a rearward facing step with downstream transverse injection. Axial mean velocity profiles, profiles of the axial and normal RMS levels, and the correlation coefficient between the axial and normal fluctuating components are presented for locations upstream of the step. These data, through comparison with other reported measurements in zero pressure gradient compressible boundary layers indicate that the boundary layers upstream of the step are consistent with 'quasi-equilibrium' turbulent boundary layers with the adiabatic wall boundary condition. Mean velocity field measurements on the symmetry plane of the tunnel are compared to laser induced iodine fluorescence measurements reported in the literature and obtained in the same facility. This comparison demonstrates the quality of the present LDA data set and shows that particle lag is not significant in the LDA measurements despite the complex nature of the downstream flow.
A DOCUMENT EXPLORING SYSTEM ON LDA TOPIC MODEL FOR WIKIPEDIA ARTICLES
Directory of Open Access Journals (Sweden)
Zhou Tong1
2016-08-01
Full Text Available A Large number of digital text information is generated every day. Effectively searching, managing and exploring the text data has become a main task. In this paper, we first present an introduction to text mining and LDA topic model. Then we deeply explained how to apply LDA topic model to text corpus by doing experiments on Simple Wikipedia documents. The experiments include all necessary steps of data retrieving, pre-processing, fitting the model and an application of document exploring system. The result of the experiments shows LDA topic model working effectively on documents clustering and finding the similar documents. Furthermore, the document exploring system could be a useful research tool for students and researchers
LDA measurements in a Mach 2 flow over a rearward facing step with staged transverse injection
Wang, J.-A.; Dancey, C. L.
1992-01-01
Measurements of the mean velocity field and selected turbulence statistics have been obtained via 2D LDA in a Mach 2 flow over a rearward facing step with downstream transverse injection. Axial mean velocity profiles, profiles of the axial and normal RMS levels, and the correlation coefficient between the axial and normal fluctuating components are presented for locations upstream of the step. These data, through comparison with other reported measurements in zero pressure gradient compressible boundary layers indicate that the boundary layers upstream of the step are consistent with 'quasi-equilibrium' turbulent boundary layers with the adiabatic wall boundary condition. Mean velocity field measurements on the symmetry plane of the tunnel are compared to laser induced iodine fluorescence measurements reported in the literature and obtained in the same facility. This comparison demonstrates the quality of the present LDA data set and shows that particle lag is not significant in the LDA measurements despite the complex nature of the downstream flow.
Hyperspectral remote sensing image classification based on combined SVM and LDA
Zhang, Chunsen; Zheng, Yiwei
2014-11-01
This paper presents a novel method for hyperspectral image classification based on the minimum noise fraction (MNF) and an approach combining support vector machine (SVM) and linear discriminant analysis (LDA). A new SVM/LDA algorithm is used for the classification. First, we use MNF method to reduce the dimension and extract features of the image, and then use the SVM/LDA algorithm to transform the extracted features. Next, we train the result of transformation, optimize the parameters through cross-validation and grid search method, then get a optimal hyperspectral image classifier. Finally, we use this classifier to complete classification. In order to verify the proposed method, the AVIRIS Indian Pines image was used. The experimental results show that the proposed method can solve the contradiction between the small amount of samples and high dimension, improve classification accuracy compared to the classical SVM method.
LDA and molecular dynamics determination of Ag deposition onto (1 0 0) surfaces in silicon
Energy Technology Data Exchange (ETDEWEB)
Mazzone, A.M
2003-03-20
This study analyzes the effects of the surface morphology on the deposition of Ag onto Si using LDA and isothermal molecular dynamics. The (1 0 0) silicon surface has either a bulk termination or the dimerization pattern experimentally observed. Small clusters representing a section of these surfaces have been used in LDA calculations to find preferred adsorption sites. Isothermal molecular dynamics describe the motions of the diffusing adatoms in a temperature range from T=10 to 1000 K. Both calculations indicate that Ag and Si do not mix and the deposited structure is formed by linear chains located in the trench between surface atoms. However, MD calculations show that, due to the relaxation of the surface and to thermal lattice vibrations, the stable state of the deposited atoms may considerably differ from the one calculated from LDA. This result has both a practical and a methodological significance.
Ii, Barry Moore; Autschbach, Jochen
2013-11-12
The lowest-energy/longest-wavelength electronic singlet excitation energies of linear cyanine dyes are examined, using time-dependent density functional theory (TDDFT) and selected wave function methods in comparison with literature data. Variations of the bond-length alternation obtained with different optimized structures produce small differences of the excitation energy in the limit of an infinite chain. Hybrid functionals with range-separated exchange are optimally 'tuned', which is shown to minimize the delocalization error (DE) in the cyanine π systems. Much unlike the case of charge-transfer excitations, small DEs are not strongly correlated with better performance. A representative cyanine is analyzed in detail. Compared with accurate benchmark data, TDDFT with 'pure' local functionals gives too high singlet excitation energies for all systems, but DFT-based ΔSCF calculations with a local functional severely underestimates the energies. TDDFT strongly overestimates the difference between singlet and triplet excitation energies. An analysis points to systematically much too small magnitudes of integrals from the DFT components of the exchange-correlation response kernel as the likely culprit. The findings support previous suggestions that the differential correlation energy between the ground and excited state is not correctly produced by TDDFT with most functionals.
LDA-measurements of jets in crossflow for effusion cooling applications
Energy Technology Data Exchange (ETDEWEB)
Gustafsson, K.M.B. [Chalmers Univ. of Technology, Goeteborg (Sweden). Dept. of Thermo and Fluid Dynamics
2002-07-01
There is a need for better cooling of hot parts in gas turbines. Film cooling and effusion cooling are often used in parts where there is a great heat load. However, modern numerical methods cannot predict heat transfer on film-cooled walls, where there are many rows of holes. There is thus a great need for better understanding of the topology of the flow field, the way in which different vortices interact in multiple row film cooling (effusion cooling) and how fluid packages with different densities affect the flow. Laser-Doppler anemometry was used here to examine the flow field of an oblique jet in a crossflow. The jet was located in the third row of holes. The operational parameters used in this investigation were Re{sub d} = 6000, U{sub jet}/U{sub 0} = 0.8, T{sub jet}/T{sub 0} = 1 and {rho}{sub jet}/{rho}{sub 0} = 1, and the injection hole was slanted at an angle of 30 . One major finding in LDA measurements in the wake was the two counter-rotating foci close to the wall. In the foci shown here, the mean velocity field changed dramatically from 0 m/s to 10 m/s in only 0.4 mm. This is of the same magnitude as the wall gradient in a flat-plate boundary layer with the same free stream velocity. All Reynolds stresses are presented in several planes for the global flow field of the jet. (orig.)
Improvement of fringe quality at LDA measuring volume using compact two hololens imaging system
Ghosh, Abhijit; Nirala, A. K.
2015-03-01
Design, analysis and construction of an LDA optical setup using conventional as well as compact two hololens imaging system have been performed. Fringes formed at measurement volume by both the imaging systems have been recorded. After experimentally analyzing these fringes, it is found that fringes obtained using compact two hololens imaging system get improved both qualitatively and quantitatively compared to that obtained using conventional imaging system. Hence it is concluded that use of the compact two hololens imaging system for making LDA optical setup is a better choice over the conventional one.
On the peculiarities of LDA method in two-phase flows with high concentrations of particles
Poplavski, S. V.; Boiko, V. M.; Nesterov, A. U.
2016-10-01
Popular applications of laser Doppler anemometry (LDA) in gas dynamics are reviewed. It is shown that the most popular method cannot be used in supersonic flows and two-phase flows with high concentrations of particles. A new approach to implementation of the known LDA method based on direct spectral analysis, which offers better prospects for such problems, is presented. It is demonstrated that the method is suitable for gas-liquid jets. Owing to the progress in laser engineering, digital recording of spectra, and computer processing of data, the method is implemented at a higher technical level and provides new prospects of diagnostics of high-velocity dense two-phase flows.
Classification of Arrhythmias with LDA and ANN using Orthogonal Rotations for Feature Reduction
Directory of Open Access Journals (Sweden)
Manpreet Kaur
2012-07-01
Full Text Available This paper presents a new approach for feature reduction by using orthogonal rotations. Wavelet coefficients for beat segments are taken as features which are reduced by factor analysis method using orthogonal rotations. LDA (Linear Discriminant Analysis and ANN (Artificial Neural Network classifiers are used for classification. The signals are taken from MIT-BIH arrhythmia database to classify into Normal, PVC, Paced, LBBB and RBBB. The performance of classification output has been compared by the performance parameters. Both the classifiers have given best overall accuracy for equimax rotation. 96% accuracy is achieved with LDA classifier,99.2% accuracy is achieved using ANN.
Facial expression recognition based on fuzzy-LDA/CCA%基于模糊LDA/CCA的面部表情识别
Institute of Scientific and Technical Information of China (English)
周晓彦; 郑文明; 邹采荣; 赵力
2008-01-01
提出了一种新颖的基于典型相关分析(CCA)的模糊判别分析方法(fuzzy-LDA/CCA),并应用于面部表情识别问题.首先为每幅表情图像建立一个相关联的类模糊隶属度矢量,用于表示表情图像与基本表情类别的隶属关系,在此基础上应用CCA方法建立表情图像同表情类别的关系表达式,最后通过对表情图像的类隶属度矢量的估计来实现表情的分类.此外,还将fuzzy-LDA/CCA方法在核空间中进行了非线性推广,从而来解决非线性判别分析的问题.实验证明提出的方法获得了更好的识别效果.%A novel fuzzy linear discriminant analysis method by the canonical correlation analysis (fuzzy-LDA/CCA)is presented and applied to the facial expression recognition. The fuzzy method is used to evaluate the degree of the class membership to which each training sample belongs. CCA is then used to establish the relationship between each facial image and the corresponding class membership vector, and the class membership vector of a test image is estimated using this relationship. Moreover, the fuzzy-LDA/CCA method is also generalized to deal with nonlinear discriminant analysis problems via kernel method. The performance of the proposed method is demonstrated using real data.
AllahTavakoli, Yahya; Safari, Abdolreza; Vaníček, Petr
2016-12-01
This paper resurrects a version of Poisson's Partial Differential Equation (PDE) associated with the gravitational field at the Earth's surface and illustrates how the PDE possesses a capability to extract the mass density of Earth's topography from land-based gravity data. Herein, first we propound a theorem which mathematically introduces this version of Poisson's PDE adapted for the Earth's surface and then we use this PDE to develop a method of approximating the terrain mass density. Also, we carry out a real case study showing how the proposed approach is able to be applied to a set of land-based gravity data. In the case study, the method is summarized by an algorithm and applied to a set of gravity stations located along a part of the north coast of the Persian Gulf in the south of Iran. The results were numerically validated via rock-samplings as well as a geological map. Also, the method was compared with two conventional methods of mass density reduction. The numerical experiments indicate that the Poisson PDE at the Earth's surface has the capability to extract the mass density from land-based gravity data and is able to provide an alternative and somewhat more precise method of estimating the terrain mass density.
Effect of LDA/Kevlar on Low Signal Insulation Based RTV Silicone Rubber%LDA/Kevlar对RTV硅橡胶绝热层材料性能影响
Institute of Scientific and Technical Information of China (English)
邹德荣; 王宏; 刘桂生; 孙美
2001-01-01
在以室温硫化(RTV)硅橡胶为基的低特征信号绝热层材料研制过程中，选用了高含氮物质联二脲(LDA)和有机纤维Kevlar作为阻燃消烟剂。试验结果表明，无论是单独使用，还是复配使用，随着配方中联二脲和Kevlar含量的增加，绝热层材料对激光、可见光、红外信号的透过率得到提高，材料的力学性能(拉伸强度和伸长率)则下降。%The flame retardant of LDA and organic fiber-Kevelar are selected during the development of low signal insulation. The basic material of insulation is RTV silicone rubber. The results show that with the increasing of LDA and/or Kevelar in the insulation,the insulation′s signature penetrating rate of laser,visible light,infrared ray can be increased,but it′s mechanical properties decrease.
LDA-CF: A Mixture Model for Collaborative Filtering%LDA-CF:一种混合协同过滤方法
Institute of Scientific and Technical Information of China (English)
廉涛; 马军; 王帅强; 崔超然
2014-01-01
推荐系统是一种克服信息过载的重要工具,其中最流行的方法是协同过滤.该文提出一种结合潜在因素模型和邻域方法的混合协同过滤方法LDA-CF.我们首先将评分矩阵转换成伪文档集合,使用LDA(LatentDirichlet Allocation)主题模型发现用户和物品潜在因素向量;然后在低维潜在因素空间计算用户和物品相似度;最后采用邻域方法预测未知评分.在MovieLens 100k数据集上的实验表明:在评分预测任务中,LDA-CF取得的MAE性能指标优于传统的邻域方法.因此,LDA可以有效地从评分矩阵中发现对计算相似度十分有用的用户和物品低维特征表示,在一定程度上缓解了数据稀疏问题.
Choi, Jinwoo; Chang, Eonho; Anstine, Dylan M.; Chakraborty, Himadri
2016-05-01
We study the ground state properties of C60 and C240 molecules in a spherical frame of local density approximation (LDA). Within this mean-field theory, two different approximations to the exchange-correlation (xc) functional are used: (i) The Gunnerson-Lundqvist parametrization augmented by a treatment to correct for the electron self-interaction and (ii) the van Leeuwen and Baerends (LB94) model potential that inclusively restores electron's asymptotic properties. Results show differences in the ground-state potential, level energies and electron densities between the two xc choices. We then use the ground structure to find the excited and ionized states of the systems and calculate dipole single-photoionization cross sections in a time-dependent LDA method that incorporates linear-response dynamical correlations. Comparative effects of the choices of xc on collective plasmon and single-excitation Auger resonances as well as on geometry driven cavity oscillations are found significant. The work is supported by the NSF, USA.
Energy Technology Data Exchange (ETDEWEB)
Reshak, A.H., E-mail: maalidph@yahoo.co.uk [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Kamarudin, H. [Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Alahmed, Z.A. [Department of Physics and Astronomy, King Saud University, Riyadh 11451 (Saudi Arabia); Auluck, S. [CSIR-National Physical Laboratory, Dr. K S Krishnan Marg, New Delhi 110012 (India); Chyský, Jan [Department of Instrumentation and Control Engineering, Faculty of Mechanical Engineering, CTU in Prague, Technicka 4, 166 07 Prague 6 (Czech Republic)
2014-06-01
A comprehensive theoretical density functional investigation of the electronic crystal structure, chemical bonding, and the electron charge densities of 9-Methyl-3-Thiophen-2-YI-Thieno [3, 2-e] [1, 2, 4] Thriazolo [4,3-c] Pyrimidine-8-Carboxylic Acid Ethyl Ester (C{sub 15}H{sub 12}N{sub 4}O{sub 2}S{sub 2}) is performed. The density of states at Fermi level equal to 5.50 (3.45) states/Ry cell, and the calculated bare electronic specific heat coefficient is found to be 0.95 (0.59) mJ/mole-K{sup 2} for the local density approximation (Engel–Vosko generalized gradient approximation). The electronic charge density space distribution contours in (1 0 0) and (1 1 0) planes were calculated. We find that there are two independent molecules (A and B) in the asymmetric unit exhibit intramolecular C–H…O, C–H…N interactions. This intramolecular interaction is different in molecules A and B, where A molecule show C–H…O interaction while B molecule exhibit C–H…N interaction. We should emphasis that there is π–π interaction between the pyrimidine rings of the two neighbors B molecules gives extra strengths and stabilizations to the superamolecular structure. The calculated distance between the two neighbors pyrimidine rings found to be 3.345 Å, in good agreement with the measured one (3.424(1) Å). - Highlights: • Electronic structure, chemical bonding, and electron charge density were studied. • Density of states at Fermi level is 5.50 (3.45) states/Ry cell, for LDA (EVGGA). • Bare electronic specific heat coefficient is 0.95 (0.59) mJ/mole-K{sup 2} for LDA(EVGGA). • There are two independent molecules (A and B) in the asymmetric unit.
Sugano, Kentaro
2011-06-01
Low-dose aspirin (LDA) and nonsteroidal anti-inflammatory drugs (NSAIDs) are frequently prescribed in Japan mostly due to increasing elderly population. Since LDA/NSAIDs cause gastrointestinal injury, serious side effects such as bleeding accompanied with their usage have been frequently reported. Awareness of such problems prompted clinical trials to facilitate a more effective approach to prevent LDA/NSAIDs-induced gastrointestinal ulcer. Two drugs recently approved for health insurance reimbursement, celecoxib, a cyclooxygenase (COX)-2 specific inhibitor and low-dose lansoprazole for prevention of recurrent peptic ulcer due to LDA/NSAIDs will be instrumental in mitigating the gastrointestinal injuries. However, continuous, intensive educational programs will be required to the change in the prescription behaviors of the general physicians. Furthermore, we need to search for effective measures to detect and prevent mid and lower gastrointestinal injury caused by LDA/NSAIDs which account for about 30% of all GI bleedings.
Xu, Xiu-Hua; Wang, Xin; Liu, Guo-kai; Tokunaga, Etsuko; Shibata, Norio
2012-05-18
Novel heteroaryl triflones including oxindole, pyrazolone, pyridine, and quinoline derivatives have been regioselectively synthesized by LDA-mediated thia-Fries rearrangement for the first time. These reactions are also the first examples of the application of anionic thia-Fries rearrangement in heteroaromatic compounds.
Fusion of PCA-Based and LDA-Based Similarity Measures for Face Verification
Directory of Open Access Journals (Sweden)
Kittler Josef
2010-01-01
Full Text Available The problem of fusing similarity measure-based classifiers is considered in the context of face verification. The performance of face verification systems using different similarity measures in two well-known appearance-based representation spaces, namely Principle Component Analysis (PCA and Linear Discriminant Analysis (LDA is experimentally studied. The study is performed for both manually and automatically registered face images. The experimental results confirm that our optimised Gradient Direction (GD metric within the LDA feature space outperforms the other adopted metrics. Different methods of selection and fusion of the similarity measure-based classifiers are then examined. The experimental results demonstrate that the combined classifiers outperform any individual verification algorithm. In our studies, the Support Vector Machines (SVMs and Weighted Averaging of similarity measures appear to be the best fusion rules. Another interesting achievement of the work is that although features derived from the LDA approach lead to better results than those of the PCA algorithm for all the adopted scoring functions, fusing the PCA- and LDA-based scores improves the performance of the system.
LDA-Promoted Synthesis of 3-Amino Furans by Selective Lithiation of Enaminones.
Kong, Lingkai; Shao, Yushang; Li, Yanli; Liu, Yuanyuan; Li, Yanzhong
2015-12-18
An efficient cascade β-metalation/addition/cyclization reaction promoted by LDA is described in which 3-amino furans were constructed from enaminones and aldehydes. A broad range of substituents on the starting compounds was tolerated, and the polysubstituted furans were gained with moderate to excellent yields within 2 h.
Ji, Xinfei; Huang, Tao; Wu, Wei; Liang, Fang; Cao, Song
2015-10-16
A practical and convenient approach for the secondary C(sp(3))-H arylation of diarylmethanes with various fluoroarenes is described. The reaction proceeds smoothly in the presence of LDA (lithium diisopropylamide) at room temperature and affords triarylmethanes in moderate to high yields.
Density functional study of $\\rm{AgScO_2}$: Electronic and optical properties
Indian Academy of Sciences (India)
K C BHAMU; JAGRATI SAHARIYA; RISHI VYAS; K R PRIOLKAR
2017-07-01
This paper focusses on the electronic and optical properties of scandium-based silver delafossite $\\rm{(AgScO_2)}$ semiconductor. The density functional theory (DFT) in the framework of full potential linearized augmented plane wave (FP-LAPW) scheme has been used for the present calculations with local densityapproximation (LDA) and generalized gradient approximation (GGA). Electronic properties deal with energy bands and density of states (DOSs), while optical properties describe refractive index and absorption coefficient.The energy bands are interpreted in terms of DOSs. The computed value of band gap is in agreement with that reported in the literature. Our results predict $\\rm{AgScO_2}$ as indirect band-gap semiconductor. Our calculated value of the refractive index in zero frequency limits is 2.42. The absorption coefficient predicts the applicability of $\\rm{AgScO_2}$ in solar cells and flat panel liquid crystal display as a transparent top window layer.
Energy Technology Data Exchange (ETDEWEB)
Reshak, A.H. [New Technologies—Research Center, University of West Bohemia, Univerzitni 8, 30614 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Azam, Sikander, E-mail: sikander.physicst@gmail.com [New Technologies—Research Center, University of West Bohemia, Univerzitni 8, 30614 Pilsen (Czech Republic)
2014-05-01
The electronic structure, charge density and Fermi surface of Na{sub 3}VF{sub 6} compound have been examined with the support of density functional theory (DFT). Using the full potential linear augmented plane wave method, we employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel–Vosko GGA (EVGGA) to treat the exchange correlation potential to solve Kohn–Sham equations. The calculation show that Na{sub 3}VF{sub 6} compound has metallic nature and the Fermi energy (E{sub F}) is assessed by overlapping of V-d state. The calculated density of states at the E{sub F} are about 18.655, 51.932 and 13.235 states/eV, and the bare linear low-temperature electronic specific heat coefficient (γ) is found to be 3.236 mJ/mol-K{sup 2}, 9.008 mJ/mol-K{sup 2} and 2.295 mJ/mol-K{sup 2} for LDA, GGA and EVGGA, respectively. The Fermi surface is composed of two sheets. The chemical bonding of Na{sub 3}VF{sub 6} compound is analyzed through the electronic charge density in the (1 1 0) crystallographic plane. The optical constants and thermal properties were also calculated and discussed. - Highlights: • DFT-FPLAPW method used for calculating the properties of investigated compounds. • For predicting the chemical bonding the charge density behavior is studied in 2D. • The optical properties were also calculated and analyzed. • The Fermi surface is composed of two bands crossing along the EF level. • The thermoelectric properties have also calculated.
Gritsenko, Oleg V; Baerends, Evert Jan
2009-06-14
Time-dependent density functional (response) theory (TDDF(R)T) is applied almost exclusively in its adiabatic approximation (ATDDFT), which is restricted to predominantly single electronic excitations and neglects additional roots of the TDDFT eigenvalue problem stemming from the interaction between single and double excitations. We incorporate the effect of the latter interaction into a non-adiabatic frequency-dependent and spatially non-local Hartree-exchange-correlation (Hxc) kernel fCEDAHxc (r1, r2, omega), the explicit analytical expression of which is derived for interacting single and double excitations well separated from the other excitations, within the common energy denominator approximation (CEDA) for the Kohn-Sham (KS) and interacting density response functions, chis and chi, respectively. The kernel fCEDAHxc (r1, r2, omega) obtained from the direct analytical inverse of chiCEDAs and chiCEDA is a sum of the delta-function and non-local orbital-dependent spatial terms with frequency-dependent factors, with which fCEDAHxc acquires a modulated quadratic dependence on omega. The effective incorporation in fCEDAHxc of the complete manifold of excited states (through the delta function term) represents an extension of the kernel reported by Maitra, Zhang, Cave, and Burke [J. Chem. Phys., 2004, 120, 5932]. In the TDDFT eigenvalue equations considered in the diagonal approximation, fCEDAHxc generates two excitation energies omegaq and omegaq+1, which both correspond to the same single KS excitation omegasq, thus producing the effect of the single-double excitation interaction.
Isegawa, Miho; Truhlar, Donald G.
2013-04-01
Time-dependent density functional theory (TDDFT) holds great promise for studying photochemistry because of its affordable cost for large systems and for repeated calculations as required for direct dynamics. The chief obstacle is uncertain accuracy. There have been many validation studies, but there are also many formulations, and there have been few studies where several formulations were applied systematically to the same problems. Another issue, when TDDFT is applied with only a single exchange-correlation functional, is that errors in the functional may mask successes or failures of the formulation. Here, to try to sort out some of the issues, we apply eight formulations of adiabatic TDDFT to the first valence excitations of ten molecules with 18 density functionals of diverse types. The formulations examined are linear response from the ground state (LR-TDDFT), linear response from the ground state with the Tamm-Dancoff approximation (TDDFT-TDA), the original collinear spin-flip approximation with the Tamm-Dancoff (TD) approximation (SF1-TDDFT-TDA), the original noncollinear spin-flip approximation with the TDA approximation (SF1-NC-TDDFT-TDA), combined self-consistent-field (SCF) and collinear spin-flip calculations in the original spin-projected form (SF2-TDDFT-TDA) or non-spin-projected (NSF2-TDDFT-TDA), and combined SCF and noncollinear spin-flip calculations (SF2-NC-TDDFT-TDA and NSF2-NC-TDDFT-TDA). Comparing LR-TDDFT to TDDFT-TDA, we observed that the excitation energy is raised by the TDA; this brings the excitation energies underestimated by full linear response closer to experiment, but sometimes it makes the results worse. For ethylene and butadiene, the excitation energies are underestimated by LR-TDDFT, and the error becomes smaller making the TDA. Neither SF1-TDDFT-TDA nor SF2-TDDFT-TDA provides a lower mean unsigned error than LR-TDDFT or TDDFT-TDA. The comparison between collinear and noncollinear kernels shows that the noncollinear kernel
Energy Technology Data Exchange (ETDEWEB)
Reshak, A.H. [Institute of Complex Systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Khan, Saleem Ayaz, E-mail: sayaz_usb@yahoo.com [Institute of Complex Systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic)
2013-11-15
Graphical abstract: - Highlights: • FPLAPW method is used for calculating the electronic and optical properties of CdGa{sub 2}X{sub 4}. • Electronic and optical properties were calculated using LDA, GGA, EVGGA and mBJ. • Band gap conformed that CdGa{sub 2}X{sub 4} are semiconductors fit for UV and visible light. • The ECD shows that change in the bond length and bond nature affect the band gap. • The dielectric tensor components and its derivatives show considerable anisotropy. - Abstract: A density functional theory (DFT) based on full potential linear augmented plane wave (FPLAPW) was used for calculating the electronic structure, charge density and optical properties of CdGa{sub 2}X{sub 4} (X = S, Se) compounds. Local density approximation (LDA), generalized gradient approximation (GGA), Engle Vasko generalized gradient approximation (EVGGA) and recently modified Becke–Johnson (mBJ) were applied to calculate the band structure, total and partial density of states. The investigation of band structures and density of states of CdGa{sub 2}X{sub 4} (X = S, Se) elucidate that mBJ potential show close agreement to the experimental results. The mBJ potential was selected for further explanation of optical properties of CdGa{sub 2}X{sub 4} (X = S, Se). The study of electronic charge density contours shows that change in the bond lengths and bond nature affect the band gap of the compounds. The two non-zero dielectric tensor components and its derivatives show considerable anisotropy between the perpendicular and parallel components. The present work provide accurate information about the combination (hybridization) of orbital, formation of bands and dispersion of non-zero tensor components of CdGa{sub 2}X{sub 4} (X = S, Se)
Directory of Open Access Journals (Sweden)
Luis Ceferino Franco Arbeláez
2008-07-01
Full Text Available Este artículo es resultado de un proyecto de investigación sobre la gestión integral del riesgo operacional promovido por la Vicerrectoria de Investigaciones de la Universidad de Medellín, y cofinanciado por una firma comisionista. Se presenta una aplicación del modelo LDA, el cual se basa en la recopilación de los datos de pérdidas históricas (frecuencia y severidad, que se registran internamente en las organizaciones. Dichos datos pueden ser complementados con datos externos. Estas pérdidas son clasificadas en una matriz que relaciona las líneas de negocio de la organización y los eventos operacionales de pérdida, a partir de la cual se calcula la carga de capital. La aplicación se desarrolló para una entidad financiera. El artículo está organizado de la siguiente forma: la primera sección es introductoria al tema. En la segunda parte se presenta formalmente el modelo LDA; luego se realiza una aplicación, y en la cuarta sección se presentan algunas conclusiones.This paper is the result of a research project on integrated management of operational risk, promoted by Universidad de Medellin Research Vice-Principal's Office and co-financed by a financial company. It presents an application of the LDA model, which is based on data collection of historical losses (frequency and severity, which are recorded internally in organizations. Such data can be supplemented with external data. These losses are classified in a matrix that relates business lines of the organization and operational loss events, from which capital charge is estimated. The application was developed for a financial institution. The paper is organized as follows: The first section is introductory to the subject. The second part formally presents a LDA model; then an application is made, and in the fourth part some conclusions are presented.
LDA Technology Today and Possibilities in the Future%线阵探测器(LDA)的现状及发展趋势
Institute of Scientific and Technical Information of China (English)
J．柯斯克能; 高冬; 蔺春涛
2002-01-01
本文概述了当前的线阵探测器(LDA)技术及未来发展, 同时详细说明了LDA的重要性能特征,并对不同应用下不同的阵列设计进行了讨论.目前芬兰探测技术公司已将该项技术成功应用于大型集装箱检测系统, 工业CT, 医用CT, L型双能探测器等工业医学应用中.
Chinese Text Similarity Computing Based on LDA%基于 LDA 的中文文本相似度计算
Institute of Scientific and Technical Information of China (English)
孙昌年; 郑诚; 夏青松
2013-01-01
传统基于 TF-IDF 的向量空间模型的文本相似度计算存在高维、数据稀疏、缺乏语义和维度未归一等问题,基于其上的语义扩展的 TF-IDF 向量空间模型中部分解决了语义问题,但是其基于词典的词语相似度计算限制了其应用范围。提出了一种基于潜在狄利克雷分配(Latent Dirichlet Allocation, LDA)的文本相似度计算方法,LDA 模型可以在没有词典的情况下解决上述所有问题,通过吉比斯抽样方法将文本建模到主题空间,然后使用 JS(Jensen-Shannon)距离来计算文本相似度。通过聚类实验表明该方法取得了较高的 F 值。%Text similarity calculation based on traditional TF-IDF vector space model exists high dimensional sparse data,lack of semantic and dimension normalization,the TF-IDF vector space model based on its semantic extension is to solve the partial problem of semantic, but its word similarity computation based on dictionary limits its application scope. Proposed a text similarity computing method based on potential Dirichlet distribution (Latent Dirichlet Allocation,LDA),LDA model can solve all these problems in no dictionary,through the Gibbs sampling method,the text modeling to subject space,and then use JS (Jensen-Shannon) distance computing text similarity. The clustering experiment results show that this method can achieve high F value.
Energy Technology Data Exchange (ETDEWEB)
Backes, Steffen
2017-04-15
The study of the electronic properties of correlated systems is a very diverse field and has lead to valuable insight into the physics of real materials. In these systems, the decisive factor that governs the physical properties is the ratio between the electronic kinetic energy, which promotes delocalization over the lattice, and the Coulomb interaction, which instead favours localized electronic states. Due to this competition, correlated electronic systems can show unique and interesting properties like the Metal-Insulator transition, diverse phase diagrams, strong temperature dependence and in general a high sensitivity to the environmental conditions. A theoretical description of these systems is not an easy task, since perturbative approaches that do not preserve the competition between the kinetic and interaction terms can only be applied in special limiting cases. One of the most famous approaches to obtain the electronic properties of a real material is the ab initio density functional theory (DFT) method. It allows one to obtain the ground state density of the system under investigation by mapping onto an effective non-interacting system that has to be found self-consistently. While being an exact theory, in practical implementations certain approximations have to be made to the exchange-correlation potential. The local density approximation (LDA), which approximates the exchange-correlation contribution to the total energy by that of a homogeneous electron gas with the corresponding density, has proven quite successful in many cases. Though, this approximation in general leads to an underestimation of electronic correlations and is not able to describe a metal-insulator transition due to electronic localization in the presence of strong Coulomb interaction. A different approach to the interacting electronic problem is the dynamical mean-field theory (DMFT), which is non-perturbative in the kinetic and interaction term but neglects all non
Density-functional approach to the valence change in SmS: Normal and high-pressure phases
Schumann, R.; Richter, M.; Steinbeck, L.; Eschrig, H.
1995-09-01
The electronic structure of SmS in dependence of the lattice constant is calculated by means of density-functional theory. The local-density approximation (LDA) to the exchange and correlation potential is employed. The 4f electrons, however, are treated in three different ways, viz., (i) as localized core states, (ii) as extended band states, and (iii) as self-interaction corrected (SIC) band states. While the experimentally observed Sm valency of normal state SmS (black phase) cannot be described by methods (i) and (ii) the SIC calculations are consistent with the measured value. For pressures above 30 kbar, method (ii) agrees well with the observed Sm valency, whereas methods (i) and (iii) fail. Therefore we conclude that the phase transition in SmS is very similar to the α-γ transition in Ce metal. The SIC band structure shows the splitting between the occupied and empty 4f states due to the large on-site electron correlation. The Fermi level ɛF is situated in the gap between the S 3p states and the Sm band states mainly of 5d character. In the high-pressure phase the 4f states presumably become delocalized, resulting in vanishing self-interaction corrections. Therefore the uncorrected LDA results are appropriate for the high-pressure phase.
用LDA Boosting算法进行客户流失预测%Research on the LDA Boosting in Customer Churn Prediction
Institute of Scientific and Technical Information of China (English)
应维云; 蔺楠; 谢雅雅; 李秀
2010-01-01
本文提出一种LDA boost(Linear Discriminant Analysis boost)分类方法,该算法能有效利用样本的所有特征,并且能够从高维特征空间里提取并组合优化出最具有判别能力的低维特征,使得样本类间离散度和类内离散度的比值最大,从而不会产生过度学习,大大提高算法效率.该算法有效性在某商业银行的客户流失预测过程的真实数据集中得到了验证.与其他同类算法,如人工神经网络、决策树、支持向量机等运算结果相比,该方法可以显著提高运算精度.同时,LDA boosting与其他boosting算法相比,也具有显著的优越性.
Novel Method Fusing (2D) 2 LDA with Multichannel Model for Face Recognition
Institute of Scientific and Technical Information of China (English)
Xia Liu∗; Yang Cao; Yu Cao; Bo Wang
2015-01-01
A fusion method of Gabor features and (2D)2LDA for face feature extraction is proposed in this paper. Gabor filters are utilized to extract multi⁃direction and multi⁃scale features from facial image to employ its robust performance for illumination, expressional variability and other factors. The extracted features have the defect of high dimension and redundancy data. (2D)2LDA is implemented to reduce the dimension of Gabor features and select effective feature data. Finally, the nearest neighbor classifier is used to classify characteristics and complete face recognition. The experiments are implemented by using ORL database and Yale database respectively. The experimental results show that the proposed method significantly reduces the dimension of Gabor features and decrease the influence of other factors. The proposed method acquires excellent recognition accuracy and has light architectures as well.
Double counting in LDA + DMFT-The example of NiO
Energy Technology Data Exchange (ETDEWEB)
Karolak, M., E-mail: mkarolak@physnet.uni-hamburg.d [I. Institut fuer Theoretische Physik, Universitaet Hamburg, Jungiusstrasse 9, D-20355 Hamburg (Germany); Ulm, G.; Wehling, T. [I. Institut fuer Theoretische Physik, Universitaet Hamburg, Jungiusstrasse 9, D-20355 Hamburg (Germany); Mazurenko, V. [Theoretical Physics and Applied Mathematic Department, Urals State Technical University, 620002, Mira street 19, Yekaterinburg (Russian Federation); Poteryaev, A. [Institute of Metal Physics, Russian Academy of Sciences, 620041 Yekaterinburg GSP-170 (Russian Federation); Lichtenstein, A. [I. Institut fuer Theoretische Physik, Universitaet Hamburg, Jungiusstrasse 9, D-20355 Hamburg (Germany)
2010-07-15
An intrinsic issue of the LDA + DMFT approach is the so called double counting of interaction terms. How to choose the double-counting potential in a manner that is both physically sound and consistent is unknown. We have conducted an extensive study of the charge-transfer system NiO in the LDA + DMFT framework using quantum Monte Carlo and exact diagonalization as impurity solvers. By explicitly treating the double-counting correction as an adjustable parameter we systematically investigated the effects of different choices for the double counting on the spectral function. Different methods for fixing the double counting can drive the result from Mott insulating to almost metallic. We propose a reasonable scheme for the determination of double-counting corrections for insulating systems.
Deconvolution as a means of correcting turbulence power spectra measured by LDA
Buchhave, Preben; Velte, Clara
2014-11-01
Measurement of turbulence power spectra by means of laser Doppler anemometry (LDA) has proven to be a difficult task. Among the problems affecting the shape of the spectrum are noise in the signal and changes in the sample rate caused by unintentional effects in the measuring apparatus or even in the mathematical algorithms used to evaluate the spectrum. We analyze the effect of various causes of bias in the sample rate and show that the effect is a convolution of the true spectrum with various spectral functions. We show that these spectral functions can be measured with the available data from a standard LDA processor and we use this knowledge to correct the measured spectrum by deconvolution. We present results supported by realistic computer generated data using two different spectral estimators, the so-called slotted autocovariance method and the so-called direct method.
Wang, Jinjia; Zhou, Lina
2011-12-01
The magnetoencephalography (MEG) can be used as a control signal for brain computer interface (BCI). The BCI also includes the pattern information of the direction of hand movement. In the MEG signal classification, the feature extraction based on signal processing and linear classification is usually used. But the recognition rate has been difficult to improve. In the present paper, a principal component analysis (PCA) and linear discriminant analysis (LDA) method has been proposed for the feature extraction, and the non-linear nearest neighbor classification is introduced for the classifier. The confusion matrix is analyzed based on the results. The experimental results show that the PCA + LDA method is effective in the analysis of multi-channel MEG signals, improves the recognition rate to the extent of the average recognition rate 55.7%, which is better than the recognition rate 46.9% in the BCI competition IV.
A New Face Recognition Framework: Symmetrical Bilateral 2DPLS plus LDA
Directory of Open Access Journals (Sweden)
Jiadong Song
2011-02-01
Full Text Available A novel face recognition framework is proposed in this paper to alleviate "Small Sample Size" (SSS problem of the conventional Linear Discriminant Analysis (LDA. This method is based on the feature extraction of global odd and even face image representation, and a dimension reduction process via Symmetrical Bilateral 2D Partial Least Square Analysis(2DPLS. The low-dimensional features are then used to train a LDA classifier which uses Frobenius-norm classification measure, and uses pseudo inverse to make sure between-class matrix Sw be full rank. Experimental results on Yale Face Database B, ORL, and FERET Face Database demonstrate that our framework is highly efficient and gives the state-of-the-art recognition rate.
Finding complex biological relationships in recent PubMed articles using Bio-LDA.
Directory of Open Access Journals (Sweden)
Huijun Wang
Full Text Available The overwhelming amount of available scholarly literature in the life sciences poses significant challenges to scientists wishing to keep up with important developments related to their research, but also provides a useful resource for the discovery of recent information concerning genes, diseases, compounds and the interactions between them. In this paper, we describe an algorithm called Bio-LDA that uses extracted biological terminology to automatically identify latent topics, and provides a variety of measures to uncover putative relations among topics and bio-terms. Relationships identified using those approaches are combined with existing data in life science datasets to provide additional insight. Three case studies demonstrate the utility of the Bio-LDA model, including association predication, association search and connectivity map generation. This combined approach offers new opportunities for knowledge discovery in many areas of biology including target identification, lead hopping and drug repurposing.
Optical guidelines and signal quality for LDA applications in circular pipes
Energy Technology Data Exchange (ETDEWEB)
Zhang, Z. [Sulzer Innotec, 8401, Winterthur (Switzerland); Faculty of Science and Technology, University of Applied Sciences Aargau, 5210, Windisch (Switzerland)
2004-07-01
The optical performance of laser Doppler anemometer (LDA) technology in applications to circular pipes with an external plane wall has been clarified and quantified. It is shown that optical aberration is a persistent feature in such LDA measurements and measurements from each direction along a full pipe diameter are needed to obtain the flow distribution. For measurements of axial velocities in a circular pipe no special care has to be taken, even if the optical plane deviates from the pipe axis. For measurements of tangential and radial velocities detailed operating guidelines have been presented with respect to the shift of the measurement volume, its optical properties and the beam waist dislocations. The analysis reveals the possible influences on both the signal quality and the measurement accuracy. (orig.)
An improved sample-and-hold reconstruction procedure for estimation of power spectra from LDA data
Energy Technology Data Exchange (ETDEWEB)
Simon, Laurent [Laboratoire d' Acoustique de l' Universite du Maine, UMR-CNRS 6613, Avenue Messiaen, 72085, Le Mans (France); Fitzpatrick, John [Mechanical Engineering Department, Trinity College, Dublin 2 (Ireland)
2004-08-01
Techniques for deriving the auto or power spectrum (PSD) of turbulence from laser Doppler anemometry (LDA) measurements are reviewed briefly. The low pass filter and step noise errors associated with the sample-and-hold process are considered and a discrete version of the low pass filter for the resampled signal is derived. This is then used to develop a procedure by which the PSD estimates obtained from sample and hold measurements can be corrected. The application of the procedures is examined using simulated data and the results show that the frequency range of the analysis can be extended beyond the Nyquist frequency based on the mean sample rate. The results are shown to be comparable to those obtained using the method of Nobach et al. (1998) but the new procedures are more straightforward to implement. The technique is then used to determine the PSD of real LDA data and the results are compared with those from a hot wire anemometer. (orig.)
Finding complex biological relationships in recent PubMed articles using Bio-LDA.
Wang, Huijun; Ding, Ying; Tang, Jie; Dong, Xiao; He, Bing; Qiu, Judy; Wild, David J
2011-03-23
The overwhelming amount of available scholarly literature in the life sciences poses significant challenges to scientists wishing to keep up with important developments related to their research, but also provides a useful resource for the discovery of recent information concerning genes, diseases, compounds and the interactions between them. In this paper, we describe an algorithm called Bio-LDA that uses extracted biological terminology to automatically identify latent topics, and provides a variety of measures to uncover putative relations among topics and bio-terms. Relationships identified using those approaches are combined with existing data in life science datasets to provide additional insight. Three case studies demonstrate the utility of the Bio-LDA model, including association predication, association search and connectivity map generation. This combined approach offers new opportunities for knowledge discovery in many areas of biology including target identification, lead hopping and drug repurposing.
An adaptation strategy of using LDA classifier for EMG pattern recognition.
Zhang, Haoshi; Zhao, Yaonan; Yao, Fuan; Xu, Lisheng; Shang, Peng; Li, Guanglin
2013-01-01
The time-varying character of myoelectric signal usually causes a low classification accuracy in traditional supervised pattern recognition method. In this work, an unsupervised adaptation strategy of linear discriminant analysis (ALDA) based on probability weighting and cycle substitution was suggested in order to improve the performance of electromyography (EMG)-based motion classification in multifunctional myoelectric prostheses control in changing environment. The adaptation procedure was firstly introduced, and then the proposed ALDA classifier was trained and tested with surface EMG recordings related to multiple motion patterns. The accuracies of the ALDA classifier and traditional LDA classifier were compared when the EMG recordings were added with different degrees of noise. The experimental results showed that compared to the LDA method, the suggested ALDA method had a better performance in improving the classification accuracy of sEMG pattern recognition, in both stable situation and noise added situation.
Roper, Ian P E; Besley, Nicholas A
2016-03-21
The simulation of X-ray emission spectra of transition metal complexes with time-dependent density functional theory (TDDFT) is investigated. X-ray emission spectra can be computed within TDDFT in conjunction with the Tamm-Dancoff approximation by using a reference determinant with a vacancy in the relevant core orbital, and these calculations can be performed using the frozen orbital approximation or with the relaxation of the orbitals of the intermediate core-ionised state included. Both standard exchange-correlation functionals and functionals specifically designed for X-ray emission spectroscopy are studied, and it is shown that the computed spectral band profiles are sensitive to the exchange-correlation functional used. The computed intensities of the spectral bands can be rationalised by considering the metal p orbital character of the valence molecular orbitals. To compute X-ray emission spectra with the correct energy scale allowing a direct comparison with experiment requires the relaxation of the core-ionised state to be included and the use of specifically designed functionals with increased amounts of Hartree-Fock exchange in conjunction with high quality basis sets. A range-corrected functional with increased Hartree-Fock exchange in the short range provides transition energies close to experiment and spectral band profiles that have a similar accuracy to those from standard functionals.
2D Face Recognition System Based on Selected Gabor Filters and Linear Discriminant Analysis LDA
Hafez, Samir F.; Selim, Mazen M.; Hala H. Zayed
2015-01-01
We present a new approach for face recognition system. The method is based on 2D face image features using subset of non-correlated and Orthogonal Gabor Filters instead of using the whole Gabor Filter Bank, then compressing the output feature vector using Linear Discriminant Analysis (LDA). The face image has been enhanced using multi stage image processing technique to normalize it and compensate for illumination variation. Experimental results show that the proposed system is effective for ...
A Hybrid LDA+gCCA Model for fMRI Data Classification and Visualization.
Afshin-Pour, Babak; Shams, Seyed-Mohammad; Strother, Stephen
2015-05-01
Linear predictive models are applied to functional MRI (fMRI) data to estimate boundaries that predict experimental task states for scans. These boundaries are visualized as statistical parametric maps (SPMs) and range from low to high spatial reproducibility across subjects (e.g., Strother , 2004; LaConte , 2003). Such inter-subject pattern reproducibility is an essential characteristic of interpretable SPMs that generalize across subjects. Therefore, we introduce a flexible hybrid model that optimizes reproducibility by simultaneously enhancing the prediction power and reproducibility. This hybrid model is formed by a weighted summation of the optimization functions of a linear discriminate analysis (LDA) model and a generalized canonical correlation (gCCA) model (Afshin-Pour , 2012). LDA preserves the model's ability to discriminate the fMRI scans of multiple brain states while gCCA finds a linear combination for each subject's scans such that the estimated boundary map is reproducible. The hybrid model is implemented in a split-half resampling framework (Strother , 2010) which provides reproducibility (r) and prediction (p) quality metrics. Then the model was compared with LDA, and Gaussian Naive Bayes (GNB). For simulated fMRI data, the hybrid model outperforms the other two techniques in terms of receiver operating characteristic (ROC) curves, particularly for detecting less predictable but spatially reproducible networks. These techniques were applied to real fMRI data to estimate the maps for two task contrasts. Our results indicate that compared to LDA and GNB, the hybrid model can provide maps with large increases in reproducibility for small reductions in prediction, which are jointly closer to the ideal performance point of (p=1, r=1).
Final report on EURAMET project No. 827: LDA-based intercomparison of anemometers
Müller, Harald
2013-01-01
A regional air speed comparison between six EURAMET laboratories used an ultrasonic anemometer and a laser Doppler anemometer (LDA) at air speeds between 0.2 m s-1 and 40 m s-1. Based on periodic calibrations at the pilot laboratory (PTB), the uncertainty contributed to the comparison by the LDA was 0.2% and the uncertainty contributed by the ultrasonic anemometer depended on the air speed and varied between 2.95% and 0.11%. The degrees of equivalence between the participants were notably better for the laser Doppler anemometer data than for the ultrasonic anemometer data. For example, using the 95% chi-squared consistency check, 16 of the original 59 participant data points were removed as discrepant from the ultrasonic data set, but only one point was discrepant in the LDA data. A possible explanation is that the LDA is non-intrusive and therefore does not alter the velocity field in the wind tunnel whereas the ultrasonic device does produce blockage effects. The results of this comparison (and prior EURAMET and CIPM comparisons) indicate a need for more attention to blockage effects during air speed calibrations and their effect on air speed uncertainty statements. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
Ciofini, I.; Adamo, C.; Chermette, H.
2005-09-01
The calculation of the bond-length alternation (BLA) in trans-polyacetylene has been chosen as benchmark to emphasize the effect of the self-interaction error within density-functional theory (DFT). In particular, the BLA of increasingly long acetylene oligomers has been computed using the Møller-Plesset wave-function method truncated at the second order and several DFT models. While local-density approximation (LDA) or generalized gradient corrected (GGA) functionals strongly underestimate the BLA, approaches including self-interaction corrections (SIC) provide significant improvements. Indeed, the simple averaged-density SIC scheme (ADSIC), recently proposed by Legrand et al. [J. Phys. B 35, 1115 (2002)], provides better results for the structure of large oligomers than the more complex approach of Krieger et al. [Phys. Rev. A 45, 101 (1992)]. The ADSIC method is particularly promising since both the exchange-correlation energy and potential are improved with respect to standard LDA/GGA using a physically appealing correction, through a different route than the more popular approach through the Hartree-Fock exchange inclusion within the hybrid functionals.
基于PCA和LDA的方言辨识%Dialect Identification Based on PCA and LDA
Institute of Scientific and Technical Information of China (English)
何艳; 于凤芹
2012-01-01
针对PCA没有有效利用样本的类别信息而导致方言识别率低的问题,采用PCA和LDA组合方法进行特征提取.首先用PCA对普通话、上海话、广东话和闽南话四种方言进行降维,然后在降维后的空间中用LDA进一步特征提取,最后将该特征向量送入BP神经网络进行辨识.仿真实验结果表明,基于PCA和LDA的方言识别的平均识别率高达85％.%In order to solve the low dialect identification rate because PCA doesn't effectively use the sample classification information, a method of feature extraction using PCA and LDA is employed. In this paper, PCA is used to effectively reduce the dimensions of Mandarin, Shanghainese, Cantonese, Minnanese, and then LDA is adopted to extract feature vectors from the dimension-reduced space as the input vectors with BP neural network to recognize. The Simulation results demonstrate that the average dialect identification rate based on PCA and LDA can be up to 85%.
De la Pierre, M; Orlando, R; Maschio, L; Doll, K; Ugliengo, P; Dovesi, R
2011-07-15
The performance of six different density functionals (LDA, PBE, PBESOL, B3LYP, PBE0, and WC1LYP) in describing the infrared spectrum of forsterite, a crystalline periodic system with orthorhombic unit cell (28 atoms in the primitive cell, Pbmn space group), is investigated by using the periodic ab initio CRYSTAL09 code and an all-electron Gaussian-type basis set. The transverse optical (TO) branches of the 35 IR active modes are evaluated at the equilibrium geometry together with the oscillator strengths and the high-frequency dielectric tensor ϵ(∞) . These quantities are essential to compute the dielectric function ϵ(ν), and then the reflectance spectrum R(ν), which is compared with experiment. It turns out that hybrid functionals perform better than LDA and GGA, in general; that B3LYP overperforms WC1LYP and, in turn, PBE0; that PBESOL is better than PBE; that LDA is the worst performing functional among the six under study.
Energy Technology Data Exchange (ETDEWEB)
Kuchinskii, E. Z.; Nekrasov, I. A., E-mail: nekrasov@iep.uran.ru; Pavlov, N. S. [Russian Academy of Sciences, Institute of Electrophysics, Ural Branch (Russian Federation)
2013-08-15
We propose a generalization of the LDA + DMFT + {Sigma}{sub k} approach to the multiband case, in which correlated and uncorrelated states are present in the model simultaneously. Using the multiband version of the LDA + DMFT + {Sigma}{sub k} approach, we calculate the density of states and spectral functions for the Emery model in a wide energy interval around the Fermi level. We also obtain the Fermi surfaces for the electron-doped high-temperature superconductor Nd{sub 2-x}Ce{sub x}CuO{sub 4} in the pseudogap phase. The self-energy part {Sigma}{sub k} introduced additionally to take into account pseudogap fluctuations describes the nonlocal interaction of correlated electrons with collective Heisenberg short-range spin fluctuations. To solve the effective impurity model, the numerical renorm-group (NRG) method is used for the DMFT equations. Good qualitative agreement of the Fermi surfaces calculated using the LDA + DMFT + {Sigma}{sub k} approach and experimental angle-resolved photoemission spectroscopic data is attained. The stability of the dielectric solution with charge transfer in the Emery model with correction for double counting is analyzed in the Appendix.
Probabilistic electron density distribution in CdTe at RT and 200K
Energy Technology Data Exchange (ETDEWEB)
Saravanan, R. [Department of Physics, The Madura College, Madurai - 625 011, Tamil Nadu (India); Israel, S. [Department of Physics, American College, Madurai - 625 002, Tamil Nadu (India); Ono, Y.; Kajitani, T. [Department of Applied Physics, Graduate School of Engineering, Tohoku University, Sendai 980-8579 (Japan); Ohno, K. [Institute for Materials Research, Tohoku University, Sendai, 980-8577 (Japan); Isshiki, M. [Institute for Advanced Materials Processing, Tohoku University, Sendai, 980-8577 (Japan); Rajaram, R.K. [School of Physics, Madurai Kamaraj University, Madurai - 625 021, Tamil Nadu (India)
2006-03-15
The bonding between the atoms in the II-VI compound semiconductors has always been a subject of rigorous research because of their tremendous applications in a variety of fields. The bonding and ionic character in CdTe at 300 and 200 K have been determined quantitatively as well as qualitatively using single crystal X-ray data sets and MEM (Maximum Entropy Method) as the tool for the reconstruction of the electron densities distributed within the unit cell. The ab-initio band calculation of the total and valence charge densities have been carried out theoretically by means of the local density approximation (LDA) method in support of the experimentally derived MEM maps. The difference density maps show fewer errors between the theoretical and experimental charge density and thus gives credence to the results accordingly. Along the bonding direction [111], the mid-bond electron densities are found to be 0.233 e/Aa{sup 3} and 0.284 e/Aa{sup 3} at 300 K and 200 K at distances 1.4026 Aa and 1.4036 Aa respectively. The densities along [100] and [110] show an increase in the charge concentration at the bond at lower temperatures. copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim. (orig.)
Performance of density functional theory methods to describe intramolecular hydrogen shifts
Indian Academy of Sciences (India)
Nelly González-Rivas; Andrés Cedillo
2005-09-01
The performance of three exchange and correlation density functionals, LDA, BLYP and B3LYP, with four basis sets is tested in three intramolecular hydrogen shift reactions. The best reaction and activation energies come from the hybrid functional B3LYP with triple- basis sets, when they are compared with high-level post-Hartree-Fock results from the literature. For a fixed molecular geometry, the electrophilic Fukui function is computed from a finite difference approximation. Fukui function shows a small dependence with both the exchange and correlation functional and the basis set. Evolution of the Fukui function along the reaction path describes important changes in the basic sites of the corresponding molecules. These results are in agreement with the chemical behavior of those species.
Energy Technology Data Exchange (ETDEWEB)
Sipr, Ondrej; Simunek, Antonin [Institute of Physics AS CR, Cukrovarnicka 10, Prague (Czech Republic); Minar, Jan; Ebert, Hubert [Universitaet Muenchen (Germany)
2010-07-01
L{sub 2,3}-edge XAS and XMCD spectra of 3d elements are calculated via a self-consistent LDA+DMFT method (including thus valence-band correlations). It is found that the asymmetry of the calculated XAS white lines increases upon inclusion of the correlations for Fe and Co but not for Ni. The change in the height of the L{sub 3} and L{sub 2} peaks in the XMCD spectra is in a good agreement with the change of the orbital magnetic moment caused by adding the valence-band correlations. As a whole, adding valence-band correlations improves the agreement between the theory and experiment but visible differences still remain. Therefore, a core hole is additionally accounted for via the final state approximation and the impact of such a procedure is assessed.
Energy Technology Data Exchange (ETDEWEB)
Korshunov, Maxim M. [L.V. Kirensky Institute of Physics, Siberian Branch of RAS, Akademgorodok, 660036 Krasnoyarsk (Russian Federation); Max-Planck-Institut fuer Physik komplexer Systeme, Noethnitzer Str. 38, D-01187 Dresden (Germany)], E-mail: maxim@mpipks-dresden.mpg.de; Ovchinnikov, Sergey G. [Max-Planck-Institut fuer Physik komplexer Systeme, Noethnitzer Str. 38, D-01187 Dresden (Germany)
2007-09-01
Mean-field theory of the non-superconducting phase of the high-T{sub c} cuprates is formulated within the effective t-t'-t''-J model with three-site correlated hoppings. This model with the ab initio calculated parameters results from the LDA + GTB method. The static spin and kinematical correlation functions beyond Hubbard I approximation are calculated self-consistently taking into account hoppings to the first, the second, and the third neighboring sites, as well as the three-site correlated hoppings. The obtained Fermi surface evolves from hole-pockets at low-doping to large hole-type Fermi surface at higher doping concentrations. Calculated doping dependence of the nodal Fermi velocity, the effective mass and the chemical potential shift are in good agreement with experimental data.
Coulomb interaction parameters in bcc iron: an LDA+DMFT study.
Belozerov, A S; Anisimov, V I
2014-09-17
We study the influence of Coulomb interaction parameters on electronic structure and magnetic properties of paramagnetic bcc Fe by means of the local density approximation plus dynamical mean-field theory approach. We consider the local Coulomb interaction in the density-density form as well as in the form with spin rotational invariance approximated by averaging over all directions of the quantization axis. Our results indicate that the magnetic properties of bcc Fe are mainly affected by the Hund's rule coupling J rather than by the Hubbard U. By employing the constrained density functional theory approach in the basis of Wannier functions of spd character, we obtain U = 4 eV and J = 0.9 eV. In spite of the widespread belief that U = 4 eV is too large for bcc Fe, our calculations with the obtained values of U and J result in a satisfactory agreement with the experiment. The correlation effects caused by U are found to be weak even for large U = 6 eV. The agreement between the calculated and experimental Curie temperatures is further improved if J is reduced to 0.8 eV. However, with the decrease of J, the effective local magnetic moment moves further away from the experimental value.
Coulomb interaction parameters in bcc iron: an LDA+DMFT study
Belozerov, A. S.; Anisimov, V. I.
2014-09-01
We study the influence of Coulomb interaction parameters on electronic structure and magnetic properties of paramagnetic bcc Fe by means of the local density approximation plus dynamical mean-field theory approach. We consider the local Coulomb interaction in the density-density form as well as in the form with spin rotational invariance approximated by averaging over all directions of the quantization axis. Our results indicate that the magnetic properties of bcc Fe are mainly affected by the Hund's rule coupling J rather than by the Hubbard U. By employing the constrained density functional theory approach in the basis of Wannier functions of spd character, we obtain U = 4 eV and J = 0.9 eV. In spite of the widespread belief that U = 4 eV is too large for bcc Fe, our calculations with the obtained values of U and J result in a satisfactory agreement with the experiment. The correlation effects caused by U are found to be weak even for large U = 6 eV. The agreement between the calculated and experimental Curie temperatures is further improved if J is reduced to 0.8 eV. However, with the decrease of J, the effective local magnetic moment moves further away from the experimental value.
García-Aldea, David; Alvarellos, J. E.
2009-03-01
We present several nonlocal exchange energy density functionals that reproduce the linear response function of the free electron gas. These nonlocal functionals are constructed following a similar procedure used previously for nonlocal kinetic energy density functionals by Chac'on-Alvarellos-Tarazona, Garc'ia-Gonz'alez et al., Wang-Govind-Carter and Garc'ia-Aldea-Alvarellos. The exchange response function is not known but we have used the approximate response function developed by Utsumi and Ichimaru, even we must remark that the same ansatz can be used to reproduce any other response function with the same scaling properties. We have developed two families of new nonlocal functionals: one is constructed with a mathematical structure based on the LDA approximation -- the Dirac functional for the exchange - and for the second one the structure of the second order gradient expansion approximation is took as a model. The functionals are constructed is such a way that they can be used in localized systems (using real space calculations) and in extended systems (using the momentum space, and achieving a quasilinear scaling with the system size if a constant reference electron density is defined).
3D Face Recognition based on Radon Transform, PCA, LDA using KNN and SVM
Directory of Open Access Journals (Sweden)
P. S. Hiremath
2014-06-01
Full Text Available Biometrics (or biometric authentication refers to the identification of humans by their characteristics or traits. Bio-metrics is used in computer science as a form of identification and access control. It is also used to identify individuals in groups that are under surveillance. Biometric identifiers are the distinctive, measurable characteristics used to label and describe individuals. Three dimensional (3D human face recognition is emerging as a significant biometric technology. Research interest into 3D face recognition has increased during recent years due to the availability of improved 3D acquisition devices and processing algorithms. Three dimensional face recognition also helps to resolve some of the issues associated with two dimensional (2D face recognition. In the previous research works, there are several methods for face recognition using range images that are limited to the data acquisition and pre-processing stage only. In the present paper, we have proposed a 3D face recognition algorithm which is based on Radon transform, Principal Component Analysis (PCA and Linear Discriminant Analysis (LDA. The Radon transform (RT is a fundamental tool to normalize 3D range data. The PCA is used to reduce the dimensionality of feature space, and the LDA is used to optimize the features, which are finally used to recognize the faces. The experimentation has been done using three publicly available databases, namely, Bhosphorus, Texas and CASIA 3D face databases. The experimental results are shown that the proposed algorithm is efficient in terms of accuracy and detection time, in comparison with other methods based on PCA only and RT+PCA. It is observed that 40 Eigen faces of PCA and 5 LDA components lead to an average recognition rate of 99.20% using SVM classifier.
An efficient method of DFT/LDA band-gap correction
Scharoch, Pawel; Winiarski, Maciej
2013-12-01
It has been shown that the underestimated by DFT/LDA(GGA) band-gap can be efficiently corrected by an averaging procedure of transition energies over a region close to the direct band-gap transition, which we call the Δ(EIG) method (the differences in the Kohn-Sham eigenvalues). For small excitations the averaging appears to be equivalent to the Δ(SCF) approach (differences in the self-consistent energies), which is a consequence of Janak’s theorem and has been confirmed numerically. The Gaussian distribution in k-space for electronic excitation has been used (occupation numbers in the Δ(SCF) or eigenenergy sampling in the Δ(EIG)). A systematic behavior of the k-space localization parameter σk correcting the band-gap has been observed in numerical experiments. On that basis some sampling schemes for band-gap correction have been proposed and tested in the prediction of the band-gap behavior in InxGa(1-x)N semiconducting alloy, and a very good agreement with independent calculations has been obtained. In the context of the work the issue of electron localization in the r-space has been discussed which, as it has been predicted by Mori-Sánchez et al. [P. Mori-Sánchez, A.J. Cohen, W. Yang, Phys. Rev. Lett. 100 (2008) 146401], should reduce the effect of the convex behavior of the LDA/GGA functionals and improve the band-gap prediction within DFT/LDA(GGA). A scheme for electron localization in r-space has been suggested.
Menezla, S.; Kadri, A.; Zitouni, K.; Djelal, A.; Djermouni, M.; Hallouche, A.; Zaoui, A.
2015-12-01
We present an ab-initio theoretical study of structural and elastic properties of GaAs1-xBix alloys in the Zinc-Blende (ZB) phase. We use a recent version of Wien2k package code based on Density Functional Theory (DFT) Full Potential and Linearized Augmented Plane Waves (FP-LAPW) method including recent Tran-Blaha modified Becke-Johnson correction of the exchange potential (TB-mBJ) and the spin-orbit interaction (SO). The calculations are performed within the Local Density Approximation (LDA) as well as the Generalized Gradient Approximation (GGA). We study first the structural properties of GaAs1-xBix alloys by solving Murnaghan equation of state. Our results show that the ZB phase is the lowest equilibrium crystal structure of GaAs1-xBix in the whole alloy composition range, in agreement with previous theoretical predictions. The variations versus Bi contents of the ZB GaAs1-xBix lattice constant a0, bulk modulus B0 and its pressure derivative B0‧ are also found very close to other theoretical and experimental data, but with much smaller bowing effects indicating a better resolution thanks to TB-mBJ correction. The variations of B0 versus the reverse equilibrium volume of the unit cell (1/V0) are found to be described by the simple linear empirical expression B0 = -0.21068 + 0.16695/V0 which is close to the theoretical prediction for III-V semiconductors with, however, somewhat lower linear coefficients values, suggesting a more metallic behavior. In a second part of this work, we use Birch-Murnaghan approach to study the elastic properties of GaAs1-xBix alloys. The elastic stiffness coefficients, C11, C12 and C44, and their variations versus alloy composition were determined for ZB GaAs1-xBix alloy. Their values in GaAs and GaBi binary compounds are found in very good agreement with available experimental and/or theoretical data. Their variations in GaAs1-xBix alloy show a monotonic decrease with increasing Bi contents, indicating a softening behavior as is
PIV and LDA measurements of the wake behind a wind turbine model
DEFF Research Database (Denmark)
Naumov, I. V.; Mikkelsen, Robert Flemming; Okulov, Valery
2014-01-01
diameters downstream from the rotor. The initial flume flow was subject to a very low turbulence level with a uniform velocity profile, limiting the influence of external disturbances on the development of the inherent vortex instability. Using PIV measurements and visualizations, special attention was paid...... to detect and categorize different types of wake instabilities and the development of the flow in the near and the far wake. In parallel to PIV, LDA measurements provided data for various rotor regimes, revealing the existence of three main regular frequencies governing the development of different...
LDA-SVM-based EGFR mutation model for NSCLC brain metastases: an observational study.
Hu, Nan; Wang, Ge; Wu, Yu-Hao; Chen, Shi-Feng; Liu, Guo-Dong; Chen, Chuan; Wang, Dong; He, Zhong-Shi; Yang, Xue-Qin; He, Yong; Xiao, Hua-Liang; Huang, Ding-De; Xiong, Kun-Lin; Wu, Yan; Huang, Ming; Yang, Zhen-Zhou
2015-02-01
Epidermal growth factor receptor (EGFR) activating mutations are a predictor of tyrosine kinase inhibitor effectiveness in the treatment of non-small-cell lung cancer (NSCLC). The objective of this study is to build a model for predicting the EGFR mutation status of brain metastasis in patients with NSCLC. Observation and model set-up. This study was conducted between January 2003 and December 2011 in 6 medical centers in Southwest China. The study included 31 NSCLC patients with brain metastases. Eligibility requirements were histological proof of NSCLC, as well as sufficient quantity of paraffin-embedded lung and brain metastases specimens for EGFR mutation detection. The linear discriminant analysis (LDA) method was used for analyzing the dimensional reduction of clinical features, and a support vector machine (SVM) algorithm was employed to generate an EGFR mutation model for NSCLC brain metastases. Training-testing-validation (3 : 1 : 1) processes were applied to find the best fit in 12 patients (validation test set) with NSCLC and brain metastases treated with a tyrosine kinase inhibitor and whole-brain radiotherapy. Primary and secondary outcome measures: EGFR mutation analysis in patients with NSCLC and brain metastases and the development of a LDA-SVM-based EGFR mutation model for NSCLC brain metastases patients. EGFR mutation discordance between the primary lung tumor and brain metastases was found in 5 patients. Using LDA, 13 clinical features were transformed into 9 characteristics, and 3 were selected as primary vectors. The EGFR mutation model constructed with SVM algorithms had an accuracy, sensitivity, and specificity for determining the mutation status of brain metastases of 0.879, 0.886, and 0.875, respectively. Furthermore, the replicability of our model was confirmed by testing 100 random combinations of input values. The LDA-SVM-based model developed in this study could predict the EGFR status of brain metastases in this small cohort of
Lean na gestão de fluxos logísticos da Dorel Portugal, Lda.
Lourenço, Leonel Alberto Correia
2014-01-01
O presente trabalho debruça-se sobre a análise de fluxos de informação e materiais na empresa Dorel Portugal, Lda.. Mais concretamente, são analisados os fluxos de transmissão de informação e os fluxos de movimentação de materiais nos duais fornecedores/armazém e armazém/setor de montagem. O estudo referido terá como propósito a identificação de elementos, associados ao estado atual, passíveis e/ou carentes de melhoria. Identificados e nomeados os pontos ...
LDA-SVM-Based EGFR Mutation Model for NSCLC Brain Metastases
Hu, Nan; Wang, Ge; Wu, Yu-Hao; Chen, Shi-Feng; Liu, Guo-Dong; Chen, Chuan; Wang, Dong; He, Zhong-Shi; Yang, Xue-Qin; He, Yong; Xiao, Hua-Liang; Huang, Ding-De; Xiong, Kun-Lin; Wu, Yan; Huang, Ming; Yang, Zhen-Zhou
2015-01-01
Abstract Epidermal growth factor receptor (EGFR) activating mutations are a predictor of tyrosine kinase inhibitor effectiveness in the treatment of non–small-cell lung cancer (NSCLC). The objective of this study is to build a model for predicting the EGFR mutation status of brain metastasis in patients with NSCLC. Observation and model set-up. This study was conducted between January 2003 and December 2011 in 6 medical centers in Southwest China. The study included 31 NSCLC patients with brain metastases. Eligibility requirements were histological proof of NSCLC, as well as sufficient quantity of paraffin-embedded lung and brain metastases specimens for EGFR mutation detection. The linear discriminant analysis (LDA) method was used for analyzing the dimensional reduction of clinical features, and a support vector machine (SVM) algorithm was employed to generate an EGFR mutation model for NSCLC brain metastases. Training-testing-validation (3 : 1 : 1) processes were applied to find the best fit in 12 patients (validation test set) with NSCLC and brain metastases treated with a tyrosine kinase inhibitor and whole-brain radiotherapy. Primary and secondary outcome measures: EGFR mutation analysis in patients with NSCLC and brain metastases and the development of a LDA-SVM-based EGFR mutation model for NSCLC brain metastases patients. EGFR mutation discordance between the primary lung tumor and brain metastases was found in 5 patients. Using LDA, 13 clinical features were transformed into 9 characteristics, and 3 were selected as primary vectors. The EGFR mutation model constructed with SVM algorithms had an accuracy, sensitivity, and specificity for determining the mutation status of brain metastases of 0.879, 0.886, and 0.875, respectively. Furthermore, the replicability of our model was confirmed by testing 100 random combinations of input values. The LDA-SVM-based model developed in this study could predict the EGFR status of brain metastases in this
A Bayes optimal matrix-variate LDA for extraction of spatio-spectral features from EEG signals.
Mahanta, Mohammad Shahin; Aghaei, Amirhossein S; Plataniotis, Konstantinos N
2012-01-01
Classification of mental states from electroencephalogram (EEG) signals is used for many applications in areas such as brain-computer interfacing (BCI). When represented in the frequency domain, the multichannel EEG signal can be considered as a two-directional spatio-spectral data of high dimensionality. Extraction of salient features using feature extractors such as the commonly used linear discriminant analysis (LDA) is an essential step for the classification of these signals. However, multichannel EEG is naturally in matrix-variate format, while LDA and other traditional feature extractors are designed for vector-variate input. Consequently, these methods require a prior vectorization of the EEG signals, which ignores the inherent matrix-variate structure in the data and leads to high computational complexity. A matrix-variate formulation of LDA have previously been proposed. However, this heuristic formulation does not provide the Bayes optimality benefits of LDA. The current paper proposes a Bayes optimal matrix-variate formulation of LDA based on a matrix-variate model for the spatio-spectral EEG patterns. The proposed formulation also provides a strategy to select the most significant features among the different rows and columns.
A low density area along the ventricular catheter on CT scan
Energy Technology Data Exchange (ETDEWEB)
Suzuki, Yasuo; Ishii, Ryoji; Watanabe, Akira; Hirano, Kazuhiro; Kamada, Masaki; Okamura, Hironari (Kawasaki Medical School, Kurashiki, Okayama (Japan))
1990-12-01
Ten patients with hydrocephalus due to various causes, such as subarachnoid or intraventricular hemorrhage, had low density area (LDA) along the ventricular catheter on CT scans. This is an analysis of the 10 patients, with a discussion of the etiology. Ventriculoperitoneal (VS) shunt was performed in 8 patients, and 3 underwent ventricular drainage. None of the patients had postoperative hemorrhage. According to CT findings, the patients were divided into three groups. The first group consisted of 3 patients whose CT scans showed progressive ventricular dilatation and a presence of LDA along the ventricular catheter. After surgical resolution of high intraventricular pressure, repeated CT scans showed a remarkably decreased ventricles and LDA. In this group, an increased intraventricular pressure may play an important role in the formation of LDA. In the second group consisting of 3 patients, there was no postoperative CT evidence of progressive ventricular dilatation, but LDA was present. Follow-up CT scans revealed a decreased lesion. A slightly increased intraventricular pressure may result in LDA. In the last group of 4 patients, CT scans showed a small, irregular, marginal LDA along the ventricular catheter, with no evidence of increased ventricle. On repeated CT scans after conservative treatment, the lesion persisted for several years after VP shunt. There was a good correlation between CT findings and patient age. Children seemed to have a large porencephalic cyst. In conclusion, LDA may be an accumulation of CSF within the unresisting white matter along the ventricular catheter due to increased intraventricular pressure. Various CT patterns seem to depend on the increased degree of intraventricular pressure and the compliance of the surrounding white matter. (N.K.).
Maschio, L.; Ferrabone, M.; Meyer, A.; Garza, J.; Dovesi, R.
2011-01-01
The performance of five different density functionals (LDA, PBE, PBESOL, B3LYP and PBE0) in describing the infrared spectrum of a crystalline periodic system with a large unit cell (spessartine, 80 atoms in the primitive cell) is studied by using the periodic ab initio CRYSTAL09 code and an all electron basis set. The transverse (TO) and longitudinal (LO) optical branches of the 17 IR active modes are evaluated together with the oscillator strengths and the high frequency dielectric tensor ɛ∞ . These ingredients permit to compute the dielectric function ɛ (ν) , and then the reflectance spectrum R (ν) , which is compared with experiment.
PARALLEL LDA ALGORITHM BASED ON SHARED MEMORY%基于共享内存的并行 LDA 算法
Institute of Scientific and Technical Information of China (English)
杨希; 刘晓升; 杨璐; 严建峰
2016-01-01
现有的共享内存的并行潜在狄利克雷分配（LDA）主题模型，通常由于数据分布的原因，线程之间一般存在等待导致效率低下。针对线程等待问题进行研究，提出一种基于动态的线程调度方案。该方案能够根据线程的数量进行分块，在此基础上及时为空闲的线程动态地分配任务，从而减少线程间等待时间。实验表明，这种新的调度方案能够有效地解决线程等待问题。该方案不仅在保证收敛精度的同时能够获得加速比25％的提升，还能显著提高向上扩展比。对于大规模分布式集群上单个节点的并行 LDA算法来说，这种调度可以更有效地利用计算资源。%Existing topical model of parallel latent Dirichlet allocation (LDA)with shared memory needs to wait between threads as a rule usually due to the unbalance distribution of data,which leads to low efficiency.In this paper we study the problem of thread waiting and pro-pose a dynamic-based threads scheduling scheme.The scheme can partition the data to blocks according to the number of threads and dynami-cally allocates tasks to idle threads timely on this basis,so as to reduce the waiting time between threads.Experiment shows that such new scheduling scheme can effectively solve threads waiting problem.It can achieve a 25% raise in speedups while ensuring convergence accura-cy,besides,it can also remarkably improve the upward expansion ratio.For parallel LDA algorithm of a single node in large-scale distributed cluster,the scheduling can more effectively utilise the computing resource.
News Schemes for Activity Recognition Systems Using PCA-WSVM, ICA-WSVM, and LDA-WSVM
Directory of Open Access Journals (Sweden)
M’hamed Bilal Abidine
2015-08-01
Full Text Available Feature extraction and classification are two key steps for activity recognition in a smart home environment. In this work, we used three methods for feature extraction: Principal Component Analysis (PCA, Independent Component Analysis (ICA, and Linear Discriminant Analysis (LDA. The new features selected by each method are then used as the inputs for a Weighted Support Vector Machines (WSVM classifier. This classifier is used to handle the problem of imbalanced activity data from the sensor readings. The experiments were implemented on multiple real-world datasets with Conditional Random Fields (CRF, standard Support Vector Machines (SVM, Weighted SVM, and combined methods PCA+WSVM, ICA+WSVM, and LDA+WSVM showed that LDA+WSVM had a higher recognition rate than other methods for activity recognition.
Simplification of QPLDA: A practical method to the correction for the LDA band gap problem
Kikuchi, Akihito
2012-01-01
It is necessary to employ quasi-particle calculations to correct band gap problems in LDA. As an expedient way for the reliable but massive GWA, Quasi-Particle-LDA (QPLDA) is proposed by several authors, where the total computational cost scales with N. Historically, Sham and Kohn introduced the idea of the local mass operator based on local wavenumber similar to WKB, but did not execute actual numerical calculations. They took into account exchange interaction only, from which we could not expect precise treatments anyway. Later, Pickett and Wang had proposed a more qualitative method and had shown its potentiality in examples of semiconductors, such as silicon, diamond and GaP. They used a model analytic formula for the dialectic function and adopted a model energy dispersion, which is free-electron like one, except that, being accompanied with an artificial band-gap discontinuity. The latter method has two shortcomings. First, to execute the calculation, several parameters are needed, such as the macroscop...
Directory of Open Access Journals (Sweden)
Shunfang Wang
2015-12-01
Full Text Available An effective representation of a protein sequence plays a crucial role in protein sub-nuclear localization. The existing representations, such as dipeptide composition (DipC, pseudo-amino acid composition (PseAAC and position specific scoring matrix (PSSM, are insufficient to represent protein sequence due to their single perspectives. Thus, this paper proposes two fusion feature representations of DipPSSM and PseAAPSSM to integrate PSSM with DipC and PseAAC, respectively. When constructing each fusion representation, we introduce the balance factors to value the importance of its components. The optimal values of the balance factors are sought by genetic algorithm. Due to the high dimensionality of the proposed representations, linear discriminant analysis (LDA is used to find its important low dimensional structure, which is essential for classification and location prediction. The numerical experiments on two public datasets with KNN classifier and cross-validation tests showed that in terms of the common indexes of sensitivity, specificity, accuracy and MCC, the proposed fusing representations outperform the traditional representations in protein sub-nuclear localization, and the representation treated by LDA outperforms the untreated one.
Wang, Shunfang; Liu, Shuhui
2015-12-19
An effective representation of a protein sequence plays a crucial role in protein sub-nuclear localization. The existing representations, such as dipeptide composition (DipC), pseudo-amino acid composition (PseAAC) and position specific scoring matrix (PSSM), are insufficient to represent protein sequence due to their single perspectives. Thus, this paper proposes two fusion feature representations of DipPSSM and PseAAPSSM to integrate PSSM with DipC and PseAAC, respectively. When constructing each fusion representation, we introduce the balance factors to value the importance of its components. The optimal values of the balance factors are sought by genetic algorithm. Due to the high dimensionality of the proposed representations, linear discriminant analysis (LDA) is used to find its important low dimensional structure, which is essential for classification and location prediction. The numerical experiments on two public datasets with KNN classifier and cross-validation tests showed that in terms of the common indexes of sensitivity, specificity, accuracy and MCC, the proposed fusing representations outperform the traditional representations in protein sub-nuclear localization, and the representation treated by LDA outperforms the untreated one.
Face Detection and Recognition Using Viola-Jones with PCA-LDA and Square Euclidean Distance
Directory of Open Access Journals (Sweden)
Nawaf Hazim Barnouti
2016-05-01
Full Text Available In this paper, an automatic face recognition system is proposed based on appearance-based features that focus on the entire face image rather than local facial features. The first step in face recognition system is face detection. Viola-Jones face detection method that capable of processing images extremely while achieving high detection rates is used. This method has the most impact in the 2000’s and known as the first object detection framework to provide relevant object detection that can run in real time. Feature extraction and dimension reduction method will be applied after face detection. Principal Component Analysis (PCA method is widely used in pattern recognition. Linear Discriminant Analysis (LDA method that used to overcome drawback the PCA has been successfully applied to face recognition. It is achieved by projecting the image onto the Eigenface space by PCA after that implementing pure LDA over it. Square Euclidean Distance (SED is used. The distance between two images is a major concern in pattern recognition. The distance between the vectors of two images leads to image similarity. The proposed method is tested on three databases (MUCT, Face94, and Grimace. Different number of training and testing images are used to evaluate the system performance and it show that increasing the number of training images will increase the recognition rate.
The PCA and LDA Analysis on the Differential Expression of Proteins in Breast Cancer
Directory of Open Access Journals (Sweden)
Seng Liang
2010-01-01
Full Text Available Breast cancer is a leading cause of mortality in women. In Malaysia, it is the most common cancer to affect women. The most common form of breast cancer is infiltrating ductal carcinoma (IDC. A proteomic approach was undertaken to identify protein profile changes between cancerous and normal breast tissues from 18 patients. Two protein extracts; aqueous soluble and membrane associated protein extracts were studied. Thirty four differentially expressed proteins were identified. The intensities of the proteins were used as variables in PCA and reduced data of six principal components (PC were subjected to LDA in order to evaluate the potential of these proteins as collective biomarkers for breast cancer. The protein intensities of SEC13-like 1 (isoform b and calreticulin contributed the most to the first PC while the protein intensities of fibrinogen beta chain precursor and ATP synthase D chain contributed the most to the second PC. Transthyretin precursor and apolipoprotein A-1 precursor contributed the most to the third PC. The results of LDA indicated good classification of samples into normal and cancerous types when the first 6 PCs were used as the variables. The percentage of correct classification was 91.7% for the originally grouped tissue samples and 88.9% for cross-validated samples.
Electronic and magnetic properties of Gd-based materials: Beyond the LDA
Energy Technology Data Exchange (ETDEWEB)
Abdelouahed, Samir; Henk, Juergen [Max Planck Institute of Microstructure Physics, Halle (Germany); Alouani, Mebarek [Institut de Physique et de Chimie des Materiaux de Strasbourg (IPCMS) (France)
2009-07-01
The FLAPW method has been used to study the electronic structure of gadolinium-based materials. The 4f electron-electron interaction was treated by the LDA+U method to improve the description of electronic and magnetic properties. For gadolinium, X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) spectra calculated including U agree better with experiment, as compared to those of the standard LDA (GGA) treatment. Furthermore, the XMCD spin and orbital moments, obtained from the sum rules, compare favorably to the self-consistent results. The tiny magnetocrystalline anisotropy energies (MAE's) of bulk Gd, GdN, and GdFe{sub 2} have been calculated by means of the magnetic-force theorem. The energy position of the 4f-state affects significantly the MAE's. For example, the magnetic anisotropies in GGA and in GGA-core calculations are factors of about 10 and 3 larger than that of the GGA+U approach, indicating the importance of hybridization in these systems.
The PCA and LDA analysis on the differential expression of proteins in breast cancer.
Liang, Seng; Singh, Manjit; Dharmaraj, Saravanan; Gam, Lay-Harn
2010-01-01
Breast cancer is a leading cause of mortality in women. In Malaysia, it is the most common cancer to affect women. The most common form of breast cancer is infiltrating ductal carcinoma (IDC). A proteomic approach was undertaken to identify protein profile changes between cancerous and normal breast tissues from 18 patients. Two protein extracts; aqueous soluble and membrane associated protein extracts were studied. Thirty four differentially expressed proteins were identified. The intensities of the proteins were used as variables in PCA and reduced data of six principal components (PC) were subjected to LDA in order to evaluate the potential of these proteins as collective biomarkers for breast cancer. The protein intensities of SEC13-like 1 (isoform b) and calreticulin contributed the most to the first PC while the protein intensities of fibrinogen beta chain precursor and ATP synthase D chain contributed the most to the second PC. Transthyretin precursor and apolipoprotein A-1 precursor contributed the most to the third PC. The results of LDA indicated good classification of samples into normal and cancerous types when the first 6 PCs were used as the variables. The percentage of correct classification was 91.7% for the originally grouped tissue samples and 88.9% for cross-validated samples.
LDA measurements on the turbulent flow characteristics of a small-sized axial fan
Energy Technology Data Exchange (ETDEWEB)
Kim, Jang Kweon [Kunsan National Univ., Kunsan (Korea, Republic of)
2001-07-01
The operating point of a small-sized axial fan for refrigerator is strongly dependent upon the system resistance. Therefore, the turbulent flow characteristics around a small-sized axial fan may change significantly according to the operating point. This study represents three-dimensional turbulent flow characteristics around a small-sized axial fan measured at the four operating points such as {phi}=0.1, 0.18, 0.25 and 0.32 by using fiber-optic type LDA system. This LDA system is composed of a 5 W Argon-ion laser, two optics in back-scatter mode, three BSA's, a PC, and a three-dimensional automatic traversing system. A kind of paraffin fluid is utilized for supplying particles by means of fog generator. Mean velocity profiles downstream of a small--sized axial fan along the radial distance show that both the streamwise and the tangential components exist predominantly in downstream except {phi}=0.1 and have a maximum value at the radial distance ratio of about 0.8, but the radial component, which its velocity is relatively small, is acting role that only turns flow direction to the outside or the central part of axial fan. Moreover, all of the velocity components downstream at {phi}=0.1 show much smaller than those upstream due to the static pressure rise at the low-flowrate region.
Dead time effects in turbulence spectra measured by burst-mode LDA
Velte, Clara; Buchhave, Preben; George, William
2014-11-01
Dead time effects in laser Doppler measurements have not so far been considered a major problem. We show how dead time occurs in burst-mode laser Doppler anemometry (LDA) when using a so-called burst-mode LDA processor and describe their effects on the measured power spectra. We show how dead time effects may be caused by more than one seed particle being present in the measurement volume at the same time and explain analytically how dead time causes a reduction in the power in the spectrum at low frequencies and an oscillation in the spectrum at the high frequency end. We also present a realistic model for the data sampled from a processor with dead time and use this model to generate turbulence velocity data in a computer. Finally we compare the spectrum computed from realistic values of dead time and sample rate in the computer generated data and compare this spectrum to a measured spectrum in a free turbulent jet with similar parameters. The excellent agreement between the features of these spectra show that our model and explanation of the dead time effect is a valid one.
LDA/PIV measurements of gas flow in a 4-stroke motored engine
Energy Technology Data Exchange (ETDEWEB)
Obokata, T.; Kato, M.; Ishima, T. [Gunma Univ., Tenjin, Kiryu (Japan). Graduate School of Mechanical Engineering; Kaneko, M. [Fuji Heavy Industries Ltd., Tokyo (Japan)
2009-07-01
The key technology for improving the internal combustion engine involves understanding and controlling the gas flows in the cylinder. However, it is not easy to understand the turbulence characteristics of gas flows because they are intermittent, highly turbulent, and three-dimensional complex flows. Numerical simulations of gas flow and combustion are important and powerful tools to understand the gas flows in the cylinder. It is important to verify the numerical simulation results by the reliable and detailed experimental data obtained at the same engine. This presentation discussed an investigation on the turbulent characteristics of in-cylinder flows at the same engine by laser doppler anemometry (LDA) and particulate image velocimetry for verifying the numerical results. Turbulent characteristics of gas flow in the internal combustion engine were also experimentally analysed under various operating conditions. The experimental setup was illustrated and the specifications of LDA and the test engine were identified. The prototype tumble generation valve was also illustrated and the results of the measurement of flow velocity through an intake valve and measurement of in-cylinder flow velocity were offered. Animations of the flow velocity through a valve were also presented. It was concluded that the effect of the turbulence generating valve (TGV) was clarified by the experimental data. The effect of the TGV was remarkable in the upper side of the cylinder. tabs., figs.
How to get spatial resolution inside probe volumes of commercial 3D LDA systems
Energy Technology Data Exchange (ETDEWEB)
Strunck, V.; Sodomann, T.; Mueller, H.; Dopheide, D. [Section of Fluid Flow Measuring Techniques, Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116, Braunschweig (Germany)
2004-01-01
In laser Doppler anemometry (LDA) it is often the aim to determine the velocity profile for a given fluid flow. The spatial resolution of such velocity profiles is limited in principal by the size of the probe volume. The method of using time of flight data from two probe volumes allows improvements of the spatial resolution by at least one order of magnitude and measurements of small-scale velocity profiles inside the measuring volume along the optical axis of commercial available 3D anemometers without moving the probe. No change of the optical set-up is necessary. An increased spatial resolution helps to acquire more precise data in areas where the flow velocity changes rapidly as shown in the vicinity of the stagnation point of a cuboid. In the overlapping region of three measuring volumes a spatially resolved 3D velocity vector profile is obtained in the direction of the optical axis in near plane flow conditions. In plane laminar flows the probe volume is extended by a few millimetres. The limitation of the method to a plane flow is that it would require a two-component LDA in a very special off-axis arrangement, but this arrangement is available in most commercial 3D systems. (orig.)
Development of bond-length alternation in very large carbon rings: LDA pseudopotential results
Bylaska, Eric J.; Weare, John H.; Kawai, Ryoichi
1998-09-01
Carbon rings Cn and infinite chains C∞ are investigated by molecular-orbital and band-structure calculations within the local-density approximation. Carbon rings C4N (N=20). For the infinite carbon chain uniform Brillouin-zone sampling with an even number of points Ns gives bond alternation. An odd number of sampling points gives no bond alternation for less than Ns=41. In the large Ns limit even and odd sampling lead to an upper and lower bound of 0.070a0 and 0.065a0 for bond alternation and 0.021-0.090 millihartrees/atom for condensation energy.
Topological transitions of the Fermi surface of osmium under pressure: an LDA+DMFT study
Feng, Qingguo; Ekholm, Marcus; Tasnádi, Ferenc; Jönsson, H. Johan M.; Abrikosov, Igor A.
2017-03-01
The influence of pressure on the electronic structure of Os has attracted substantial attention recently due to reports on isostructural electronic transitions in this metal. Here, we theoretically investigate the Fermi surface of Os from ambient to high pressure, using density functional theory combined with dynamical mean field theory. We provide a detailed discussion of the calculated Fermi surface and its dependence on the level of theory used for the treatment of the electron–electron interactions. Although we confirm that Os can be classified as weakly correlated metal, the inclusion of local quantum fluctuations between 5{{d}} electrons beyond the local density approximation explains the most recent experimental reports regarding the occurrence of electronic topological transitions in Os.
LDA + U and GGA + U studies of Al-rich and bulk goethite ({alpha}-FeOOH)
Energy Technology Data Exchange (ETDEWEB)
Fuente, Silvia A. [INQUISUR, Departamento de Quimica, Universidad Nacional del Sur, Av. Alem 1253, Bahia Blanca B8000CP (Argentina); Belelli, Patricia G., E-mail: pbelelli@plapiqui.edu.ar [IFISUR, Grupo de Materiales y Sistemas Cataliticos, Departamento de Fisica, Universidad Nacional del Sur, Av. Alem 1253, Bahia Blanca B8000CP (Argentina); Castellani, Norberto J. [IFISUR, Grupo de Materiales y Sistemas Cataliticos, Departamento de Fisica, Universidad Nacional del Sur, Av. Alem 1253, Bahia Blanca B8000CP (Argentina); Avena, Marcelo [INQUISUR, Departamento de Quimica, Universidad Nacional del Sur, Av. Alem 1253, Bahia Blanca B8000CP (Argentina)
2013-01-15
The electronic and structural properties of bulk goethite and Al-rich goethite were studied on the basis of spin-polarized DFT at the LDA + U and GGA(PW91) + U levels. Firstly, the periodic model of bulk goethite was optimized varying the value of U{sub eff}. Considering all the results obtained we can conclude that the bulk goethite described at the GGA + U level with U{sub eff} = 6 eV gives us the better agreement with different physical properties. The results of magnetic moments of Fe ions, the DOS analysis and the Bader atomic charges identify goethite as an antiferromagnetic Fe(III) compound. For Al-rich goethite the GGA + U (U{sub eff} = 6 eV) approach was used. The isomorphous substitution of one Fe ion with Al ion produces the reduction of the cell parameters with respect to the bulk goethite. Regarding the magnetic ordering, it was observed that Fe atoms surrounding the Al atom must have the same spin projection, i.e., spin-up or -down. The charge density was changed with the addition of Al ion, producing a depletion where the ion is located and some electron redistribution in the zone of the oxygen atoms surrounding the Al ion. This behavior produces some small magnetization in these O ions. -- Highlights: Black-Right-Pointing-Pointer We studied electronic and structural properties of bulk goethite and Al-rich goethite. Black-Right-Pointing-Pointer The goethite is well described with the GGA + U level using the U{sub eff} = 6 eV value. Black-Right-Pointing-Pointer The Al-rich goethite model has different magnetic structures with similar energies. Black-Right-Pointing-Pointer The isomorphic substitution of Fe by Al atom in goethite results in a lattice contraction.
Energy Technology Data Exchange (ETDEWEB)
Buettner, L.; Czarske, J. [Group Laser Metrology, Laser Zentrum Hannover e.V., Hollerithallee 8, 30419, Hannover (Germany)
2004-01-01
A novel LDA system using laser diode arrays and multi-mode fibers in the transmitting optics is presented. The use of high numerical aperture multi-mode step-index fibres results in measurement volumes with, for example, 80 {mu}m length and minimal speckle effects. Because of the high spatial resolution and low relative fringe spacing variation of {delta}d/d{approx}5 x 10{sup -4} the multi-mode fibre LDA is predestined for investigating turbulent flows. Boundary layer measurements carried out show excellent agreement with theoretical velocity profiles. (orig.)
Study of electronic structures of CeRu{sub 2}Si{sub 2} by LDA+U method
Energy Technology Data Exchange (ETDEWEB)
Suzuki, Michi-To [Department of Condensed Matter Physics, Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501 (Japan)]. E-mail: michi@kobe-u.ac.jp; Harima, Hisatomo [Department of Condensed Matter Physics, Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501 (Japan)
2007-03-15
Electronic structures of CeRu{sub 2}Si{sub 2} are calculated by LDA+U method extended for magnetic system with strong spin-orbit interaction. The LDA+U method significantly improves the character of the ground state in the nonmagnetic state. The calculated electronic structures explain change of physical properties associated with metamagnetic transition. The Fermi surfaces after metamagnetic transition were reproduced well in this method, although the continuous change of electronic structure by metamagnetic transition is not described.
Diophantine approximation and badly approximable sets
DEFF Research Database (Denmark)
Kristensen, S.; Thorn, R.; Velani, S.
2006-01-01
Let (X,d) be a metric space and (Omega, d) a compact subspace of X which supports a non-atomic finite measure m. We consider `natural' classes of badly approximable subsets of Omega. Loosely speaking, these consist of points in Omega which `stay clear' of some given set of points in X. The clas......Let (X,d) be a metric space and (Omega, d) a compact subspace of X which supports a non-atomic finite measure m. We consider `natural' classes of badly approximable subsets of Omega. Loosely speaking, these consist of points in Omega which `stay clear' of some given set of points in X....... The classical set Bad of `badly approximable' numbers in the theory of Diophantine approximation falls within our framework as do the sets Bad(i,j) of simultaneously badly approximable numbers. Under various natural conditions we prove that the badly approximable subsets of Omega have full Hausdorff dimension...
Marchois, J; Fressigné, C; Lecachey, B; Maddaluno, J
2015-06-18
The competition between basicity and nucleophilicity of two standard organolithium reagents was studied using DFT. Comparing the reactivity of solvated (MeLi)2 and (LDA)2 toward propanal finally explains why methyllithium adds onto the carbonyl while LDA deprotonates the α-position, in accord with experiment and Ireland's deprotonation TS.
Zhang, Yachao
2014-12-07
A first-principles study of critical temperatures (T(c)) of spin crossover (SCO) materials requires accurate description of the strongly correlated 3d electrons as well as much computational effort. This task is still a challenge for the widely used local density or generalized gradient approximations (LDA/GGA) and hybrid functionals. One remedy, termed density functional theory plus U (DFT+U) approach, introduces a Hubbard U term to deal with the localized electrons at marginal computational cost, while treats the delocalized electrons with LDA/GGA. Here, we employ the DFT+U approach to investigate the T(c) of a pair of iron(II) SCO molecular crystals (α and β phase), where identical constituent molecules are packed in different ways. We first calculate the adiabatic high spin-low spin energy splitting ΔE(HL) and molecular vibrational frequencies in both spin states, then obtain the temperature dependent enthalpy and entropy changes (ΔH and ΔS), and finally extract T(c) by exploiting the ΔH/T - T and ΔS - T relationships. The results are in agreement with experiment. Analysis of geometries and electronic structures shows that the local ligand field in the α phase is slightly weakened by the H-bondings involving the ligand atoms and the specific crystal packing style. We find that this effect is largely responsible for the difference in T(c) of the two phases. This study shows the applicability of the DFT+U approach for predicting T(c) of SCO materials, and provides a clear insight into the subtle influence of the crystal packing effects on SCO behavior.
Leike, Reimar H
2016-01-01
In Bayesian statistics probability distributions express beliefs. However, for many problems the beliefs cannot be computed analytically and approximations of beliefs are needed. We seek a ranking function that quantifies how "embarrassing" it is to communicate a given approximation. We show that there is only one ranking under the requirements that (1) the best ranked approximation is the non-approximated belief and (2) that the ranking judges approximations only by their predictions for actual outcomes. We find that this ranking is equivalent to the Kullback-Leibler divergence that is frequently used in the literature. However, there seems to be confusion about the correct order in which its functional arguments, the approximated and non-approximated beliefs, should be used. We hope that our elementary derivation settles the apparent confusion. We show for example that when approximating beliefs with Gaussian distributions the optimal approximation is given by moment matching. This is in contrast to many su...
Raangs, R.; Schlicke, Ted; Barham, Richard
2005-01-01
In this paper, a new method of calibrating an acoustic particle velocity sensor using laser Doppler anemometry (LDA) is discussed. The results were compared and were in good agreement with the results obtained by conventional methods, where the sensitivity of the microflown is obtained with the use
Nonlocal Coulomb interactions and metal-insulator transition in Ti2O3: a cluster LDA+DMFT approach.
Poteryaev, A.I.; Lichtenstein, A.I.; Kotliar, G.
2004-01-01
We present an ab initio quantum theory of the metal-insulator transition in Ti2O3. The recently developed cluster LDA+DMFT scheme is applied to describe the many-body features of this compound. The conventional single site DMFT cannot reproduce a low temperature insulating phase for any reasonable
LDA-PIV Diagnostics and 3D Simulation of Oscillating Swirl Flow in a Closed Cylindrical Container
DEFF Research Database (Denmark)
Naumov, Igor; Okulov, V. L.; Meyer, Knud Erik
2003-01-01
Results on unsteady vortex breakdown are obained simultaneously using two diagnostics methods: a) determination of velocity fields by particle tracks (Particle Image Velocimeter - PIV), b) determination of velocity fields by Laser Doppler Anemometry (LDA), are presented.The experiments data are i...
Wen, Zhen-cai; Sun, Tong; Geng, Xiang; Liu, Mu-hua
2013-09-01
Camellia oil is a special and high quality edible oil in China, and quality of pressed camellia oils is superior to extracted camellia oils. The objective of the present research was to discriminate pressed and extracted camellia oils by visible/near infrared (Vis/NIR) spectroscopy. The transmission spectra of pressed and extracted camellia oil samples were acquired using a QualitySpec spectrometer in the wavelength range of 350-1800 nm. Uninformative variable elimination (UVE) was used to select informative wavelength variables, and eliminate uninformative wavelength variables, then partial least squares combined with linear discriminant analysis (PLS-LDA) was used to develop classification model. At last, the classification model was used to discriminate 26 samples in the prediction set. The results indicate that UVE-PLS-LDA is an efficient discrimination and classification method, pressed and extracted camellia oils can be discriminated well by the classification model developed by UVE-PLS-LDA, the accurate rate is 100% for both samples in the calibration and prediction sets. So, Vis/NIR spectra combined with UVE-PLS-LDA is an effective method for discriminating pressed and extracted camellia oils.
An investigation of particle behavior in gas-solid horizontal pipe flow by an extended LDA technique
Energy Technology Data Exchange (ETDEWEB)
Yong Lu; Donald H. Glass; William J. Easson [University of Edinburgh, Edinburgh (United Kingdom). Institute for Materials and Processes
2009-12-15
An extended Laser Doppler Anemometry (LDA) technique has been developed to measure the distributions of particle velocities and particle number rates over a whole pipe cross-section in a dilute pneumatic conveying system. The first extension concentrates on the transform matrix for predicting the laser beams' cross point in a pipe according to the shift coordinate of the 3D computer-controlled traverse system on which the probes of the LDA system were mounted. The second focuses on the proper LDA sample rate for the measurement of gas-solid pipe flow with polydisperse particles. A suitable LDA sample rate should ensure that enough data is recorded in the measurement interval to precisely calculate the particle mean velocity or other statistical values at every sample point. The present study explores the methodology as well as the fundamentals of measurements, using a laser facility, of the cross-sectional distributions of solid phase. In the horizontal gas-solid pipe flow (glass beads less than 110 {mu}m), the experimental data show that the cross-sectional flow patterns of the solid phase can be classified by annulus-like flow describing the axial particle velocity contours and stratified flow characterising particle number rate distribution over a cross-section. Thus, the cross-sectional flow pattern of the solid phase in a horizontal pipe may be annular or stratified dependent on whether the axial particle velocity or particle number rate is the phenomenon studied. 13 refs., 16 figs., 1 tab.
Rašin, Andrija
1994-01-01
We discuss the idea of approximate flavor symmetries. Relations between approximate flavor symmetries and natural flavor conservation and democracy models is explored. Implications for neutrino physics are also discussed.
On Element SDD Approximability
Avron, Haim; Toledo, Sivan
2009-01-01
This short communication shows that in some cases scalar elliptic finite element matrices cannot be approximated well by an SDD matrix. We also give a theoretical analysis of a simple heuristic method for approximating an element by an SDD matrix.
Aubert, A. H.; Tavenard, R.; Emonet, R.; De Lavenne, A.; Malinowski, S.; Guyet, T.; Quiniou, R.; Odobez, J.; Merot, P.; Gascuel-odoux, C.
2013-12-01
Studying floods has been a major issue in hydrological research for years, both in quantitative and qualitative hydrology. Stream chemistry is a mix of solutes, often used as tracers, as they originate from various sources in the catchment and reach the stream by various flow pathways. Previous studies (for instance (1)) hypothesized that stream chemistry reaction to a rainfall event is not unique but varies seasonally, and according to the yearly meteorological conditions. Identifying a typology of flood temporal chemical patterns is a way to better understand catchment processes at the flood and seasonal time scale. We applied a probabilistic model (Latent Dirichlet Allocation or LDA (2)) mining recurrent sequential patterns from a dataset of floods. A set of 472 floods was automatically extracted from a daily 12-year long record of nitrate, dissolved organic carbon, sulfate and chloride concentrations. Rainfall, discharge, water table depth and temperature are also considered. Data comes from a long-term hydrological observatory (AgrHys, western France) located at Kervidy-Naizin. From each flood, a document has been generated that is made of a set of "hydrological words". Each hydrological word corresponds to a measurement: it is a triplet made of the considered variable, the time at which the measurement is made (relative to the beginning of the flood), and its magnitude (that can be low, medium or high). The documents and the number of pattern to be mined are used as input data to the LDA algorithm. LDA relies on spotting co-occurrences (as an alternative to the more traditional study of correlation) between words that appear within the flood documents. It has two nice properties that are its ability to easily deal with missing data and its additive property that allows a document to be seen as a mixture of several flood patterns. The output of LDA is a set of patterns easily represented in graphics. These patterns correspond to typical reactions to rainfall
Face recognition combining GLRAM with LDA%GLRAM与LDA相结合的人脸识别
Institute of Scientific and Technical Information of China (English)
徐冬冬; 陈秀宏
2010-01-01
提出了一种GLRAM(矩阵的广义低秩逼近)与LDA(线性判别分析)相结合的人脸识别方法.首先利用GLRAM方法获得人脸图像的有效特征,然后通过LDA对获得的特征进行进一步的降维并获得最佳分类特征.这样使得抽取特征的判断能力得到了显著增强.实验结果表明,该算法在较短的时间内取得了较高的识别率,效果优于单独运用GLRAM方法和LDA方法.
LDA measurement of the passage flow field in an annular airfoil cascade
Stauter, R. C.; Fleeter, S.
1987-01-01
Models to predict the complex three-dimensional flow through turbomachine blade rows are being developed. To verify these models and direct necessary refinements, it is necessary that predictions be correlated with data obtained in experiments which model the fundamental three-dimensional blade row flow phenomena. This paper describes a series of experiments performed in a large scale, subsonic, annular cascade facility specifically designed to provide such data. In particular, the effect of incidence angle on the three-dimensional passage flow field through an annular cascade of cambered airfoils is investigated and quantified, accomplished by obtaining detailed and expensive LDA data. These data demonstrate and quantify the development of the passage vortices through the airfoil passage and their strong interaction with the endwall boundary layers.
An LDA investigation of three-dimensional normal shock-boundary layer interactions in a corner
Chriss, R. M.; Keith, T. G., Jr.; Hingst, W. R.; Strazisar, A. J.; Porro, A. R.
1987-01-01
Nonintrusive, three-dimensional, measurements have been made of a normal shock wave-turbulent boundary layer interaction. The measurements were made in the corner of the test section of a continuous supersonic wind tunnel in which a normal shock wave had been stabilized. LDA, surface pressure measurement and flow visualization techniques were employed for two freestream Mach number test cases: 1.6 and 1.3. The former contained separated flow regions and a system of shock waves. The latter was found to be far less complicated. The reported results are believed to accurately define the flow physics of each case and may be used as benchmark data to verify three-dimensional computer codes.
An LDA investigation of the normal shock wave boundary layer interaction
Chriss, R. M.; Hingst, W. R.; Strazisar, A. J.; Keith, T. G.
1990-01-01
Nonintrusive measurements have been made of two normal shock wave-boundary layer interactions. Two-dimensional measurements were made throughout the interaction region while three-dimensional measurements were made in the vicinity of the shock wave. The measurements were made in the corner of the test section of a continuous flow supersonic wind tunnel in which a normal shock wave had been stabilized. LDA, surface pressure measurement and flow visualization techniques were employed for two freestream Mach number test cases: 1.6 and 1.3. The former contained separated flow regions and a system of shock waves. The latter was found to be far less complicated. The reported results define the flowfield structure in detail for each case.
A hetero-alkali-metal version of the utility amide LDA: lithium-potassium diisopropylamide.
Armstrong, David R; Kennedy, Alan R; Mulvey, Robert E; Robertson, Stuart D
2013-03-14
Designed to extend the synthetically important alkali-metal diisopropylamide [N(i)Pr(2); DA] class of compounds, the first example of a hetero-alkali-metallic complex of DA has been prepared as a partial TMEDA solvate. Revealed by an X-ray crystallographic study, its structure exists as a discrete lithium-rich trinuclear Li(2)KN(3) heterocycle, with TMEDA only solvating the largest of the alkali-metals, with the two-coordinate lithium atoms being close to linearity [161.9(2)°]. A variety of NMR spectroscopic studies, including variable temperature and DOSY NMR experiments, suggests that this new form of LDA maintains its integrity in non-polar hydrocarbon solution. This complex thus represents a rare example of a KDA molecule which is soluble in non-polar medium without the need for excessive amounts of solubilizing Lewis donor being added.
Classification of ECG signals using LDA with factor analysis method as feature reduction technique.
Kaur, Manpreet; Arora, A S
2012-11-01
The analysis of ECG signal, especially the QRS complex as the most characteristic wave in ECG, is a widely accepted approach to study and to classify cardiac dysfunctions. In this paper, first wavelet coefficients calculated for QRS complex are taken as features. Next, factor analysis procedures without rotation and with orthogonal rotation (varimax, equimax and quartimax) are used for feature reduction. The procedure uses the 'Principal Component Method' to estimate component loadings. Further, classification has been done with a LDA classifier. The MIT-BIH arrhythmia database is used and five types of beats (normal, PVC, paced, LBBB and RBBB) are considered for analysis. Accuracy, sensitivity and positive predictivity are performance parameters used for comparing performance of feature reduction techniques. Results demonstrate that the equimax rotation method yields maximum average accuracy of 99.056% for unknown data sets among other used methods.
Shalit, Andrey; Perakis, Fivos; Hamm, Peter
2014-04-01
We apply two-dimensional infrared spectroscopy to differentiate between the two polyamorphous forms of glassy water, low-density (LDA) and high-density (HDA) amorphous ices, that were obtained by slow vapor deposition at 80 and 11 K, respectively. Both the vibrational lifetime and the bandwidth of the 1-2 transition of the isolated OD stretch vibration of HDO in H2O exhibit characteristic differences when comparing hexagonal (Ih), LDA, and HDA ices, which we attribute to the different local structures - in particular the presence of interstitial waters in HDA ice - that cause different delocalization lengths of intermolecular phonon degrees of freedom. Moreover, temperature dependent measurements show that the vibrational lifetime closely follows the structural transition between HDA and LDA phases.
Energy Technology Data Exchange (ETDEWEB)
Lee, C.C.; Ku, W.; Hsueh, H.C.
2010-08-30
Within the framework of time-dependent density-functional theory (TDDFT), we derive the dynamical linear response of local-density approximation plus U functional and benchmark it on NiO, a prototypical Mott insulator. Formulated using real-space Wannier functions, our computationally inexpensive framework gives detailed insights into the formation of tightly bound Frenkel excitons with reasonable accuracy. Specifically, a strong hybridization of multiple excitons is found to significantly modify the exciton properties. Furthermore, our study exposes a significant generic limitation of adiabatic approximation in TDDFT with hybrid functionals and in existing Bethe-Salpeter-equation approaches, advocating the necessity of strongly energy-dependent kernels in future development.
Approximate iterative algorithms
Almudevar, Anthony Louis
2014-01-01
Iterative algorithms often rely on approximate evaluation techniques, which may include statistical estimation, computer simulation or functional approximation. This volume presents methods for the study of approximate iterative algorithms, providing tools for the derivation of error bounds and convergence rates, and for the optimal design of such algorithms. Techniques of functional analysis are used to derive analytical relationships between approximation methods and convergence properties for general classes of algorithms. This work provides the necessary background in functional analysis a
A lake detection algorithm (LDA) using Landsat 8 data: A comparative approach in glacial environment
Bhardwaj, Anshuman; Singh, Mritunjay Kumar; Joshi, P. K.; Snehmani; Singh, Shaktiman; Sam, Lydia; Gupta, R. D.; Kumar, Rajesh
2015-06-01
Glacial lakes show a wide range of turbidity. Owing to this, the normalized difference water indices (NDWIs) as proposed by many researchers, do not give appropriate results in case of glacial lakes. In addition, the sub-pixel proportion of water and use of different optical band combinations are also reported to produce varying results. In the wake of the changing climate and increasing GLOFs (glacial lake outburst floods), there is a need to utilize wide optical and thermal capabilities of Landsat 8 data for the automated detection of glacial lakes. In the present study, the optical and thermal bandwidths of Landsat 8 data were explored along with the terrain slope parameter derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model Version2 (ASTER GDEM V2), for detecting and mapping glacial lakes. The validation of the algorithm was performed using manually digitized and subsequently field corrected lake boundaries. The pre-existing NDWIs were also evaluated to determine the supremacy and the stability of the proposed algorithm for glacial lake detection. Two new parameters, LDI (lake detection index) and LF (lake fraction) were proposed to comment on the performances of the indices. The lake detection algorithm (LDA) performed best in case of both, mixed lake pixels and pure lake pixels with no false detections (LDI = 0.98) and very less areal underestimation (LF = 0.73). The coefficient of determination (R2) between areal extents of lake pixels, extracted using the LDA and the actual lake area, was very high (0.99). With understanding of the terrain conditions and slight threshold adjustments, this work can be replicated for any mountainous region of the world.
基于LDA-wSVM模型的文本分类研究%Research on text categorization based on LDA-wSVM model
Institute of Scientific and Technical Information of China (English)
李锋刚; 梁钰; GAO Xiao-zhi; ZENGER Kai
2015-01-01
SVM分类算法处理高维数据具有较大优势,但其未考虑语义的相似性度量问题,而LDA主题模型可以解决传统的文本分类中相似性度量和主题单一性问题.为了充分结合SVM和LDA算法的优势并提高分类精确度,提出了一种新的LDA-wSVM高效分类算法模型.利用LDA主题模型进行建模和特征选择,确定主题数和隐主题—文本矩阵;在经典权重计算方法上作改进,考虑各特征项与类别的关联度,设计了一种新的权重计算方法;在特征词空间上使用这种基于权重计算的wSVM分类器进行分类.实验基于R软件平台对搜狗实验室的新闻文本集进行分类,得到了宏平均值为0.943的高精确度分类结果.实验结果表明,提出的LDA-wSVM模型在文本自动分类中具有很好的优越性能.
Approximation of distributed delays
Lu, Hao; Eberard, Damien; Simon, Jean-Pierre
2010-01-01
We address in this paper the approximation problem of distributed delays. Such elements are convolution operators with kernel having bounded support, and appear in the control of time-delay systems. From the rich literature on this topic, we propose a general methodology to achieve such an approximation. For this, we enclose the approximation problem in the graph topology, and work with the norm defined over the convolution Banach algebra. The class of rational approximates is described, and a constructive approximation is proposed. Analysis in time and frequency domains is provided. This methodology is illustrated on the stabilization control problem, for which simulations results show the effectiveness of the proposed methodology.
Diophantine approximation and badly approximable sets
DEFF Research Database (Denmark)
Kristensen, S.; Thorn, R.; Velani, S.
2006-01-01
Let (X,d) be a metric space and (Omega, d) a compact subspace of X which supports a non-atomic finite measure m. We consider `natural' classes of badly approximable subsets of Omega. Loosely speaking, these consist of points in Omega which `stay clear' of some given set of points in X. The clas......Let (X,d) be a metric space and (Omega, d) a compact subspace of X which supports a non-atomic finite measure m. We consider `natural' classes of badly approximable subsets of Omega. Loosely speaking, these consist of points in Omega which `stay clear' of some given set of points in X...
Sparse approximation with bases
2015-01-01
This book systematically presents recent fundamental results on greedy approximation with respect to bases. Motivated by numerous applications, the last decade has seen great successes in studying nonlinear sparse approximation. Recent findings have established that greedy-type algorithms are suitable methods of nonlinear approximation in both sparse approximation with respect to bases and sparse approximation with respect to redundant systems. These insights, combined with some previous fundamental results, form the basis for constructing the theory of greedy approximation. Taking into account the theoretical and practical demand for this kind of theory, the book systematically elaborates a theoretical framework for greedy approximation and its applications. The book addresses the needs of researchers working in numerical mathematics, harmonic analysis, and functional analysis. It quickly takes the reader from classical results to the latest frontier, but is written at the level of a graduate course and do...
Comparative study of metal cluster fission in Hartree-Fock and LDA
Lyalin, A; Greiner, W; Lyalin, Andrey; Solov'yov, Andrey; Greiner, Walter
2001-01-01
Fission of doubly charged metal clusters is studied using the open-shell two-center deformed jellium Hartree-Fock model and Local Density Approximation. Results of calculations of the electronic structure and fission barriers for the symmetric and asymmetric channels associated with the following processes Na_{10}^{2+} --> Na_{7}^{+} + Na_{3}^{+}, Na_{18}^{2+} --> Na_{15}^{+} + Na_{3}^{+} and Na_{18}^{2+} --> 2 Na_{9}^{+} are presented. The role of the exact exchange and many-body correlation effects in metal clusters fission is analysed. It is demonstrated that the influence of many-electron correlation effects on the height of the fission barrier is more profound if the barrier arises nearby or beyond the scission point. The importance of cluster deformation effects in the fission process is elucidated with the use of the overlapping-spheroids shape parametrization allowing one an independent variation of deformations in the parent and daughter clusters.
ACT-LDA: A Probabilistic Model of Topic, Community and User Influence%ACT-LDA:集成话题、社区和影响力分析的概率模型
Institute of Scientific and Technical Information of China (English)
吴良; 黄威靖; 陈薇; 王腾蛟; 雷凯; 刘月琴
2013-01-01
随着社交网络的发展,社交网络中的用户形成大规模的用户关系图,用户在社交网络中发表内容,这些内容及其链接关系形成大规模的文档图.如何根据用户关系图、文档图,挖掘出用户所形成的社区、社区用户的影响力以及各个社区的话题,是重要的问题,而目前这些工作相对独立.考虑了用户发表内容、用户之间的关系信息,利用话题传播、社区形成和用户影响力之间的关联性,提出了一个基于LDA (latent Dirichlet allocation)的集成话题发现、社区发现和用户影响力分析的统一模型ACT-LDA(author-community-topic LDA).模型采用变分推理的方法解决推理问题.在DBLP数据上进行了实验,取得了非常好的结果,证明了模型的有效性.%With the development of social network,users in all kinds of social networks form a large user graph.The articles published by users and the links between articles form a large document graph.According to the user graph and document graph,how to mine the topics,communities and user influence is an important problem,but now this problem is handled independently.Considering the inter-dependence of the problem and making use of text content and coauthor relationship,this paper proposes a joint model of topic modeling,community discovery and user influence analysis based on LDA (latent Dirichlet allocation),called ACT-LDA (author-community-topic LDA),which uses variation method for inference.The experiments on DBLP data show very good results,which validates the proposed model.
Approximation techniques for engineers
Komzsik, Louis
2006-01-01
Presenting numerous examples, algorithms, and industrial applications, Approximation Techniques for Engineers is your complete guide to the major techniques used in modern engineering practice. Whether you need approximations for discrete data of continuous functions, or you''re looking for approximate solutions to engineering problems, everything you need is nestled between the covers of this book. Now you can benefit from Louis Komzsik''s years of industrial experience to gain a working knowledge of a vast array of approximation techniques through this complete and self-contained resource.
Achieser, N I
2004-01-01
A pioneer of many modern developments in approximation theory, N. I. Achieser designed this graduate-level text from the standpoint of functional analysis. The first two chapters address approximation problems in linear normalized spaces and the ideas of P. L. Tchebysheff. Chapter III examines the elements of harmonic analysis, and Chapter IV, integral transcendental functions of the exponential type. The final two chapters explore the best harmonic approximation of functions and Wiener's theorem on approximation. Professor Achieser concludes this exemplary text with an extensive section of pr
Discovering temporal patterns in water quality time series, focusing on floods with the LDA method
Hélène Aubert, Alice; Tavenard, Romain; Emonet, Rémi; Malinowski, Simon; Guyet, Thomas; Quiniou, René; Odobez, Jean-Marc; Gascuel-Odoux, Chantal
2013-04-01
Studying floods has been a major issue in hydrological research for years. It is often done in terms of water quantity but it is also of interest in terms of water quality. Stream chemistry is a mix of solutes. They originate from various sources in the catchment, reach the stream by various flow pathways and are transformed by biogeochemical reactions at different locations. Therefore, we hypothesized that reaction of the stream chemistry to a rainfall event is not unique but varies according to the season (1), and the global meteorological conditions of the year (2). Identifying a typology of temporal chemical patterns of reaction to a rainfall event is a way to better understand catchment processes at the flood time scale. To answer this issue, we applied a probabilistic model (Latent Dirichlet Allocation or LDA (3)) mining recurrent sequential patterns to a dataset of floods. The dataset is 12 years long and daily recorded. It gathers a broad range of parameters from which we selected rainfall, discharge, water table depth, temperature as well as nitrate, dissolved organic carbon, sulphate and chloride concentrations. It comes from a long-term hydrological observatory (AgrHys, western France) located at Kervidy-Naizin. A set of 472 floods was automatically extracted (4). From each flood, a document has been generated that is made of a set of "hydrological words". Each hydrological word corresponds to a measurement: it is a triplet made of the considered variable, the time at which the measurement is made (relative to the beginning of the flood), and its magnitude (that can be low, medium or high). The documents are used as input data to the LDA algorithm. LDA relies on spotting co-occurrences (as an alternative to the more traditional study of correlation) between words that appear within the flood documents. It has two nice properties that are its ability to easily deal with missing data and its additive property that allows a document to be seen as a mixture
Ansari, Reza; Ajori, Shahram; Malakpour, Sina
2016-04-01
The considerable demand for novel materials with specific properties has motivated the researchers to synthesize supramolecular nanostructures through different methods. Porous graphene is the first two-dimensional hydrocarbon synthesized quite recently. This investigation is aimed at studying the mechanical properties of atom-decorated (functionalized) porous graphene by employing density functional theory (DFT) calculation within both local density approximations (LDA) and generalized gradient approximations (GGA). The atoms are selected from period 3 of periodic table as well as Li and O atom from period 2. The results reveal that metallic atoms and noble gases are adsorbed physically on porous graphene and nonmetallic ones form chemical bonds with carbon atom in porous graphene structure. Also, it is shown that, in general, atom decoration reduces the values of mechanical properties such as Young's, bulk and shear moduli as well as Poisson's ratio, and this reduction is more considerable in the case of nonmetallic atoms (chemical adsorption), especially oxygen atoms, as compared to metallic atoms and noble gases (physical adsorption).
Expectation Consistent Approximate Inference
DEFF Research Database (Denmark)
Opper, Manfred; Winther, Ole
2005-01-01
We propose a novel framework for approximations to intractable probabilistic models which is based on a free energy formulation. The approximation can be understood from replacing an average over the original intractable distribution with a tractable one. It requires two tractable probability dis...
Ordered cones and approximation
Keimel, Klaus
1992-01-01
This book presents a unified approach to Korovkin-type approximation theorems. It includes classical material on the approximation of real-valuedfunctions as well as recent and new results on set-valued functions and stochastic processes, and on weighted approximation. The results are notonly of qualitative nature, but include quantitative bounds on the order of approximation. The book is addressed to researchers in functional analysis and approximation theory as well as to those that want to applythese methods in other fields. It is largely self- contained, but the readershould have a solid background in abstract functional analysis. The unified approach is based on a new notion of locally convex ordered cones that are not embeddable in vector spaces but allow Hahn-Banach type separation and extension theorems. This concept seems to be of independent interest.
Approximate Modified Policy Iteration
Scherrer, Bruno; Ghavamzadeh, Mohammad; Geist, Matthieu
2012-01-01
Modified policy iteration (MPI) is a dynamic programming (DP) algorithm that contains the two celebrated policy and value iteration methods. Despite its generality, MPI has not been thoroughly studied, especially its approximation form which is used when the state and/or action spaces are large or infinite. In this paper, we propose three approximate MPI (AMPI) algorithms that are extensions of the well-known approximate DP algorithms: fitted-value iteration, fitted-Q iteration, and classification-based policy iteration. We provide an error propagation analysis for AMPI that unifies those for approximate policy and value iteration. We also provide a finite-sample analysis for the classification-based implementation of AMPI (CBMPI), which is more general (and somehow contains) than the analysis of the other presented AMPI algorithms. An interesting observation is that the MPI's parameter allows us to control the balance of errors (in value function approximation and in estimating the greedy policy) in the fina...
LDA-Based Unified Topic Modeling for Similar TV User Grouping and TV Program Recommendation.
Pyo, Shinjee; Kim, Eunhui; Kim, Munchurl
2015-08-01
Social TV is a social media service via TV and social networks through which TV users exchange their experiences about TV programs that they are viewing. For social TV service, two technical aspects are envisioned: grouping of similar TV users to create social TV communities and recommending TV programs based on group and personal interests for personalizing TV. In this paper, we propose a unified topic model based on grouping of similar TV users and recommending TV programs as a social TV service. The proposed unified topic model employs two latent Dirichlet allocation (LDA) models. One is a topic model of TV users, and the other is a topic model of the description words for viewed TV programs. The two LDA models are then integrated via a topic proportion parameter for TV programs, which enforces the grouping of similar TV users and associated description words for watched TV programs at the same time in a unified topic modeling framework. The unified model identifies the semantic relation between TV user groups and TV program description word groups so that more meaningful TV program recommendations can be made. The unified topic model also overcomes an item ramp-up problem such that new TV programs can be reliably recommended to TV users. Furthermore, from the topic model of TV users, TV users with similar tastes can be grouped as topics, which can then be recommended as social TV communities. To verify our proposed method of unified topic-modeling-based TV user grouping and TV program recommendation for social TV services, in our experiments, we used real TV viewing history data and electronic program guide data from a seven-month period collected by a TV poll agency. The experimental results show that the proposed unified topic model yields an average 81.4% precision for 50 topics in TV program recommendation and its performance is an average of 6.5% higher than that of the topic model of TV users only. For TV user prediction with new TV programs, the average
Approximate calculation of integrals
Krylov, V I
2006-01-01
A systematic introduction to the principal ideas and results of the contemporary theory of approximate integration, this volume approaches its subject from the viewpoint of functional analysis. In addition, it offers a useful reference for practical computations. Its primary focus lies in the problem of approximate integration of functions of a single variable, rather than the more difficult problem of approximate integration of functions of more than one variable.The three-part treatment begins with concepts and theorems encountered in the theory of quadrature. The second part is devoted to t
Approximate and renormgroup symmetries
Energy Technology Data Exchange (ETDEWEB)
Ibragimov, Nail H. [Blekinge Institute of Technology, Karlskrona (Sweden). Dept. of Mathematics Science; Kovalev, Vladimir F. [Russian Academy of Sciences, Moscow (Russian Federation). Inst. of Mathematical Modeling
2009-07-01
''Approximate and Renormgroup Symmetries'' deals with approximate transformation groups, symmetries of integro-differential equations and renormgroup symmetries. It includes a concise and self-contained introduction to basic concepts and methods of Lie group analysis, and provides an easy-to-follow introduction to the theory of approximate transformation groups and symmetries of integro-differential equations. The book is designed for specialists in nonlinear physics - mathematicians and non-mathematicians - interested in methods of applied group analysis for investigating nonlinear problems in physical science and engineering. (orig.)
Approximating Stationary Statistical Properties
Institute of Scientific and Technical Information of China (English)
Xiaoming WANG
2009-01-01
It is well-known that physical laws for large chaotic dynamical systems are revealed statistically. Many times these statistical properties of the system must be approximated numerically. The main contribution of this manuscript is to provide simple and natural criterions on numerical methods (temporal and spatial discretization) that are able to capture the stationary statistical properties of the underlying dissipative chaotic dynamical systems asymptotically. The result on temporal approximation is a recent finding of the author, and the result on spatial approximation is a new one. Applications to the infinite Prandtl number model for convection and the barotropic quasi-geostrophic model are also discussed.
Gareis, Iván; Atum, Yanina; Gentiletti, Gerardo; Acevedo, Rubén; Medina Bañuelos, Verónica; Rufiner, Leonardo
2011-12-01
Brain computer interfaces (BCIs) translate brain activity into computer commands. To enhance the performance of a BCI, it is necessary to improve the feature extraction techniques being applied to decode the users' intentions. Objective comparison methods are needed to analyze different feature extraction techniques. One possibility is to use the classifier performance as a comparative measure. In this work the effect of several variables that affect the behaviour of linear discriminant analysis (LDA) has been studied when used to distinguish between electroencephalographic signals with and without the presence of event related potentials (ERPs). The error rate (ER) and the area under the receiver operating characteristic curve (AUC) were used as performance estimators of LDA. The results show that the number of characteristics, the degree of balance of the training patterns set and the number of averaged trials affect the classifier's performance and therefore, must be considered in the design of the integrated system.
2014-01-01
Laser Doppler anemometry (LDA) has been employed to quantify the liquid velocity field around a single bubble in its generating and accelerating stage in carboxymethylcellulose (CMC) aqueous solution. The instantanoues velocities were treated by Reynolds time-averaged method, and mean velocities and its contours in both axial and radial directions were investigated. The results show that in vertical direction, the flow field characteristics of the liquids around the bubble are determined by b...
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The Metzner and Otto correlation is the single practical method for incorporating non-Newtonian effects in the mixing process. In this article, the Metzner and Otto' s idea, the role of viscoelasticity on the Metzner and Otto coefficient, ks, effects of flow regime on ks and the determination of ks for Rushton turbine impeller have been studied using the direct method of the laser Doppler anemometry (LDA) velocity meusurement for the case of viscoelastic liquids. The normalized mean tangential velocity profiles are independent of Rushton turbine impeller speeds. Contrary to literature findings, it is shown that the variation of local shear rate against the impeller speed is better correlated by the power equation, i.e. γ = ks＇ * Nb＇, in the transition region, i.e. ～ 30 ＜ Re <～ 2000.Also, a correlation between improved coefficient, ks＇, and the elasticity number of viscoelastic liquids is given which is very helpful in designing of the mixing of both viscoelastic and inelastic non-Newtonian fluids through relating rheological properties to kinematical and dynamical parameters of the mixing process.
Latent Dirichlet Allocation (LDA) for Sentiment Analysis Toward Tourism Review in Indonesia
Putri, IR; Kusumaningrum, R.
2017-01-01
The tourism industry is one of foreign exchange sector, which has considerable potential development in Indonesia. Compared to other Southeast Asia countries such as Malaysia with 18 million tourists and Singapore 20 million tourists, Indonesia which is the largest Southeast Asia’s country have failed to attract higher tourist numbers compared to its regional peers. Indonesia only managed to attract 8,8 million foreign tourists in 2013, with the value of foreign tourists each year which is likely to decrease. Apart from the infrastructure problems, marketing and managing also form of obstacles for tourism growth. An evaluation and self-analysis should be done by the stakeholder to respond toward this problem and capture opportunities that related to tourism satisfaction from tourists review. Recently, one of technology to answer this problem only relying on the subjective of statistical data which collected by voting or grading from user randomly. So the result is still not to be accountable. Thus, we proposed sentiment analysis with probabilistic topic model using Latent Dirichlet Allocation (LDA) method to be applied for reading general tendency from tourist review into certain topics that can be classified toward positive and negative sentiment.
Improving 2D Boosted Classifiers Using Depth LDA Classifier for Robust Face Detection
Directory of Open Access Journals (Sweden)
Mahmood Rahat
2012-05-01
Full Text Available Face detection plays an important role in Human Robot Interaction. Many of services provided by robots depend on face detection. This paper presents a novel face detection algorithm which uses depth data to improve the efficiency of a boosted classifier on 2D data for reduction of false positive alarms. The proposed method uses two levels of cascade classifiers. The classifiers of the first level deal with 2D data and classifiers of the second level use depth data captured by a stereo camera. The first level employs conventional cascade of boosted classifiers which eliminates many of nonface sub windows. The remaining sub windows are used as input to the second level. After calculating the corresponding depth model of the sub windows, a heuristic classifier along with a Linear Discriminant analysis (LDA classifier is applied on the depth data to reject remaining non face sub windows. The experimental results of the proposed method using a Bumblebee-2 stereo vision system on a mobile platform for real time detection of human faces in natural cluttered environments reveal significantly reduction of false positive alarms of 2D face detector.
Investigation of a CO2 round jet using an integrated Raman-LDA system
Ballal, D. R.; Chen, T. H.
1987-01-01
An experimental investigation of a CO2 round jet spreading into a low-turbulence, coflowing airstream has been performed. Velocity and concentration properties in axial (x/D up to 20) and radial (r/D up to + or - 2.5) planes have been measured using an integrated Raman-LDA optical diagnostic system. These properties include mean value, fluctuating intensity, Reynolds shear stress, skewness, kurtosis, turbulent kinetic energy, joint pdfs, turbulent scalar fluxes and turbulent Schmidt number. From these quantitative measurements, and available flow visualization evidence, a three-region description of the jet structure is developed. It is found that: (1) in the instability dominated region, circumferential vortex rings are formed around the jet boundary; (2) in the near-field region, pairing, growth, coalescence and stretching processes are important; and (3) these processes ultimately produce the small-scale turbulence of the far-field region. Furthermore, measured peak values of turbulent fluctuations confirm the coalescence and streching of vortices, skewness and kurtosis data highlight the production of small-scale turbulence, and measurements of joint pdfs suggest that radial flow transports the jet concentration outward. Finally, concentration spreads faster than velocity, resulting in a turbulent Schmidt number below unity. A comparison of these results with those of other workers is made and the outcome is discussed.
Rare-earth defect pairs in GaN: LDA+U calculations
Sanna, Simone; Schmidt, W. G.; Frauenheim, Th.; Gerstmann, U.
2009-09-01
The structural and electronic properties of rare-earth (RE) (Eu, Er, and Tm) related defect pairs in GaN have been investigated theoretically. Based on LDA+U total-energy calculations, their possible role in the luminescence process is discussed. In all charge states, the lanthanides show a strong preference for the Ga-lattice site, either as isolated substitutional or complexed with intrinsic defects. With respect to the electronic valence, a proper description of correlation effects of the strongly localized 4f electrons is shown to be crucial, especially if the REGa is paired with donors like the Ga interstitial or the N vacancy. The pairs formed by REGa substitutionals and vacancies or interstitials lower the symmetry and are found to locally distort the environment. By this, they are quite effective in relaxing the selection rules for the luminescent intra- 4f -shell transitions. While for n -type GaN, the next-nearest-neighbor pair REGaVGa pair is energetically favored, for p -type GaN, the REGaVN pair provides the most stable configuration and introduces shallow levels close to the conduction band, which can act as assistant levels in the luminescence process.
基于LDA和SVM的步态识别%GAIT RECOGNITION BASED ON LDA AND SVM
Institute of Scientific and Technical Information of China (English)
许文芳; 吴清江; 王青力
2008-01-01
提出了一种新的基于人体中线投影的步态特征提取方法,同时将线性判别分析(LDA)和支持向量机(SVM)相结合进行步态的分类和识别.应用背景差方法分割出运动人体轮廓,对外轮廓沿人体中线投影可以得到前后两个向量,合成1D向量作为步态特征.通过线性判别分析对得到的一维向量进行特征提取和压缩,对得到的识别量应用支持向量机进行步态的分类和识别.应用上述方法在中科院自动化所的步态数据库上进行了实验,实验结果表明该步态识别方法具有较好的识别性能.
基于LDA模型的主题分析%Topic Analysis Based on LDA Model
Institute of Scientific and Technical Information of China (English)
石晶; 范猛; 李万龙
2009-01-01
在文本分割的基础上,确定片段主题,进而总结全文的中心主题,使文本的主题脉络呈现出来,主题以词串的形式表示.为了分析准确,利用LDA(Latent dirichlet allocation)为语料库及文奉建模,以Clarity度量块间相似性,并通过局部最小值识别片段边界.依据词汇的香农信息提取片段主题词,采取背景词汇聚类及主题词联想的方式将主题词扩充到待分析文本之外,尝试挖掘隐藏于字词表面之下的文本内涵.实验表明,文本分析的结果明显好于其他方法,可以为下一步文本推理的工作提供有价值的预处理.
LDA Based Face Recognition by Using Hidden Markov Model in Current Trends
Directory of Open Access Journals (Sweden)
S.Sharavanan
2009-10-01
Full Text Available Hidden Markov model (HMM is a promising method that works well for images with variations in lighting, facial expression, and orientation. Face recognition draws attention as a complex task due to noticeable changes produced on appearance by illumination, facial expression, size, orientation and other external factors. To process images using HMM, the temporal or space sequences are to be considered. In simple terms HMM can be defined as set of finite states with associated probability distributions. Only the outcome is visible to the external user not the states and hence the name Hidden Markov Model. The paper deals with various techniques and methodologies used for resolving the problem .We discuss about appearance based, feature based, model based and hybrid methods for face identification. Conventional techniques such as Principal Component Analysis (PCA, Linear Discriminant Analysis (LDA, Independent Component Analysis (ICA, and feature based Elastic Bunch Graph Matching (EBGM and 2D and 3D face models are well-known for face detection and recognition.
Biased Parameter Estimation for LDA%LDA模型参数有偏估计方法
Institute of Scientific and Technical Information of China (English)
袁伯秋; 周一民; 李林
2010-01-01
LDA(Latent Dirichlet Allocation)等基于隐含topic的模型在离散数据处理中的应用逐渐增多.然而LDA使用Dirichlet分布作为隐含topic的分布函数,未能很好表示各topic之间相互关系.目前常见改进方法是通过DAG(Directed Acyclic Graph)图或对数正态分布等其他分布函数表达topic之间的关系.本文通过参数有偏估计的方法,考虑topic混合过程中词项上的重叠关系,改变topic内部词项分布,最终改进LDA模型性能.在回顾一些基础内容后,重点介绍参数有偏估计及简化计算方法.最后通过LDA模型在信息检索中的实验验证这种改进的有效性,并初步分析模型参数选用规律.
Weighted piecewise LDA for solving the small sample size problem in face verification.
Kyperountas, Marios; Tefas, Anastasios; Pitas, Ioannis
2007-03-01
A novel algorithm that can be used to boost the performance of face-verification methods that utilize Fisher's criterion is presented and evaluated. The algorithm is applied to similarity, or matching error, data and provides a general solution for overcoming the "small sample size" (SSS) problem, where the lack of sufficient training samples causes improper estimation of a linear separation hyperplane between the classes. Two independent phases constitute the proposed method. Initially, a set of weighted piecewise discriminant hyperplanes are used in order to provide a more accurate discriminant decision than the one produced by the traditional linear discriminant analysis (LDA) methodology. The expected classification ability of this method is investigated throughout a series of simulations. The second phase defines proper combinations for person-specific similarity scores and describes an outlier removal process that further enhances the classification ability. The proposed technique has been tested on the M2VTS and XM2VTS frontal face databases. Experimental results indicate that the proposed framework greatly improves the face-verification performance.
Study of Semantic Understanding by LDA%LDA语义理解研究
Institute of Scientific and Technical Information of China (English)
高阳; 杨璐; 刘晓升; 严建峰
2015-01-01
潜在狄利克雷分配(LDA)被广泛应用于文本的聚类.有效理解信息检索的查询和文本,被证明能提高信息检索的性能.其中吉布斯采样和置信传播是求解LDA模型的两种热门的近似推理算法.比较了两种近似推理算法在不同主题规模下对信息检索性能的影响,并比较了LDA对文本解释的两种不同方式,即用文档的主题分布来替换原查询和文本,以及用文档的单词重构来替换原查询和文本.实验结果表明,文档的主题解释以及吉布斯采样算法能够有效提高信息检索的性能.
Energy Technology Data Exchange (ETDEWEB)
Lang, M.; Rist, U.; Wagner, S. [Institut fuer Aerodynamik und Gasdynamik, Universitaet Stuttgart, Pfaffenwaldring 21, 70550, Stuttgart (Germany)
2004-01-01
When a laminar boundary layer separates because of an adverse streamwise pressure gradient, the flow is subject to increased instability with respect to small-amplitude disturbances. Laminar-turbulent transition occurs under a rapid three-dimensional (3D) development within the separated shear layer. When the following turbulent boundary layer reattaches, a laminar separation bubble is formed. To allow controlled measurements, a small-amplitude Tollmien-Schlichting wave (TS wave) was introduced into the boundary layer without (case I) and with (case II) spanwise forcing of steady 3D disturbances. Combined application of laser-Doppler anemometry (LDA) and particle image velocimetry (PIV) demonstrates the suitability of both measurement techniques to capture the development of unsteady, periodic phenomena. The transition mechanism occurring in the flow field under consideration is discussed, and results obtained by controlled measurements are compared to direct numerical simulations (DNS) and predictions from linear stability theory (LST). Flow visualizations and stereoscopic PIV measurements give better insight into the 3D breakdown of the separated shear layer. (orig.)
Directory of Open Access Journals (Sweden)
Malvina Baica
1985-01-01
Full Text Available The author uses a new modification of Jacobi-Perron Algorithm which holds for complex fields of any degree (abbr. ACF, and defines it as Generalized Euclidean Algorithm (abbr. GEA to approximate irrationals.
Approximations in Inspection Planning
DEFF Research Database (Denmark)
Engelund, S.; Sørensen, John Dalsgaard; Faber, M. H.
2000-01-01
Planning of inspections of civil engineering structures may be performed within the framework of Bayesian decision analysis. The effort involved in a full Bayesian decision analysis is relatively large. Therefore, the actual inspection planning is usually performed using a number of approximations....... One of the more important of these approximations is the assumption that all inspections will reveal no defects. Using this approximation the optimal inspection plan may be determined on the basis of conditional probabilities, i.e. the probability of failure given no defects have been found...... by the inspection. In this paper the quality of this approximation is investigated. The inspection planning is formulated both as a full Bayesian decision problem and on the basis of the assumption that the inspection will reveal no defects....
The Karlqvist approximation revisited
Tannous, C
2015-01-01
The Karlqvist approximation signaling the historical beginning of magnetic recording head theory is reviewed and compared to various approaches progressing from Green, Fourier, Conformal mapping that obeys the Sommerfeld edge condition at angular points and leads to exact results.
Approximations in Inspection Planning
DEFF Research Database (Denmark)
Engelund, S.; Sørensen, John Dalsgaard; Faber, M. H.
2000-01-01
Planning of inspections of civil engineering structures may be performed within the framework of Bayesian decision analysis. The effort involved in a full Bayesian decision analysis is relatively large. Therefore, the actual inspection planning is usually performed using a number of approximations....... One of the more important of these approximations is the assumption that all inspections will reveal no defects. Using this approximation the optimal inspection plan may be determined on the basis of conditional probabilities, i.e. the probability of failure given no defects have been found...... by the inspection. In this paper the quality of this approximation is investigated. The inspection planning is formulated both as a full Bayesian decision problem and on the basis of the assumption that the inspection will reveal no defects....
Gautschi, Walter; Rassias, Themistocles M
2011-01-01
Approximation theory and numerical analysis are central to the creation of accurate computer simulations and mathematical models. Research in these areas can influence the computational techniques used in a variety of mathematical and computational sciences. This collection of contributed chapters, dedicated to renowned mathematician Gradimir V. Milovanovia, represent the recent work of experts in the fields of approximation theory and numerical analysis. These invited contributions describe new trends in these important areas of research including theoretic developments, new computational alg
Approximation Behooves Calibration
DEFF Research Database (Denmark)
da Silva Ribeiro, André Manuel; Poulsen, Rolf
2013-01-01
Calibration based on an expansion approximation for option prices in the Heston stochastic volatility model gives stable, accurate, and fast results for S&P500-index option data over the period 2005–2009.......Calibration based on an expansion approximation for option prices in the Heston stochastic volatility model gives stable, accurate, and fast results for S&P500-index option data over the period 2005–2009....
Xue, Kan-Hao; Miao, Xiang-Shui
2016-01-01
The LDA-1/2 method expands Slater's half occupation technique to infinite solid state materials by introducing a self-energy potential centered at the anions to cancel the energy associated with electron-hole self-interaction. To avoid an infinite summation of long-ranged self-energy potentials they must be trimmed at a variationally-defined cutoff radius. The method has been successful in predicting accurate band gaps for a large number of elementary and binary semiconductors. Nevertheless, there has been some confusion regarding carbon and silicon, both in the cubic diamond structure, which require different ionizations of the valence charge, 1/2 for carbon and 1/4 for silicon respectively, to yield band gaps in agreement with experimental data. We here analyze the spatial distribution of the valence electrons of these two materials to conclude that in silicon and in carbon LDA-1/4 and LDA-1/2, respectively, must be adopted for the proper cancellation of the self-energies. Such analysis should be applied to...
Kong, Shu
2012-01-01
In practical applications, we often have to deal with high order data, such as a grayscale image and a video sequence are intrinsically 2nd-order tensor and 3rd-order tensor, respectively. For doing clustering or classification of these high order data, it is a conventional way to vectorize these data before hand, as PCA or FDA does, which often induce the curse of dimensionality problem. For this reason, experts have developed many methods to deal with the tensorial data, such as multilinear PCA, multilinear LDA, and so on. In this paper, we still address the problem of high order data representation and recognition, and propose to study the result of merging multilinear PCA and multilinear LDA into one scenario, we name it \\textbf{GDA} for the abbreviation of Generalized Discriminant Analysis. To evaluate GDA, we perform a series of experiments, and the experimental results demonstrate our GDA outperforms a selection of competing methods such (2D)$^2$PCA, (2D)$^2$LDA, and MDA.
LDA+DMFT study of the Sn/Si(111)({radical}(3) x {radical}(3))R30 surface states
Energy Technology Data Exchange (ETDEWEB)
Schuwalow, Sergej; Boehnke, Lewin; Lechermann, Frank [I. Institut fuer Theoretische Physik, Universitaet Hamburg, 20355 Hamburg (Germany)
2009-07-01
Experimental studies and LDA+U calculations for the Sn/Si(111)({radical}(3) x {radical}(3))R30 surface suggest a Mott-insulating surface state originating dominantly from strongly correlated Sn (5p) orbitals below about 70K. Interestingly, the Sn atoms form a 1/3 monolayer on an effective triangular lattice. Hence the issue of spin liquid physics may arise due to possible frustration effects. In the scope of this work, we have first obtained an effective Hamiltonian for the surface states of this system in terms of maximally localized Wannier functions from LDA calculations. From there, we performed DMFT calculations for both a 1-band and a 3-band effective Hamiltonian to map out the temperature-dependent behavior of the spectral function close to the suggested metal-insulator transition and to investigate the importance of the different surface bands. In the case of the 3-band Hamiltonian, the full U matrix was used for the calculations. Finally, we compared the results of our dynamical approach to those obtained within the static LDA+U formalism.
[Study on discrimination of varieties of corn using near-infrared spectroscopy based on GA and LDA].
Wang, Hui-rong; Li, Wei-jun; Liu, Yang-yang; Chen, Xin-liang; Lai, Jiang-liang
2011-03-01
A new method for the fast discrimination of varieties of corn based on near-infrared spectroscopy using genetic algorithm and linear discriminant analysis (LDA) was proposed. First, data of NIS of 37 varieties of corn was collected, second, genetic algorithm used for choosing the feature band of spectrum, then PCA and LDA were used to extract features, and finally corn seeds were classified. The result showed that GA could remove noise band effectively and improve the generalization ability of LDA. A large number of redundant data was removed to simplify the computing, which resulted in the data dimension reduction from 2075 to 233. For the 300 samples of test set one, the average correct recognition rate and average correct rejection rate attained 99.30% for both, and the average correct recognition rate of 73.33% varieties of corn attained for 100%. For the 175 samples of test set 2 (all of whose varieties had not been trained), the average correct recognition rate attained 99.65%. The run time is shorter and the correct rate is higher compared to the common method of PCA.
Approximate kernel competitive learning.
Wu, Jian-Sheng; Zheng, Wei-Shi; Lai, Jian-Huang
2015-03-01
Kernel competitive learning has been successfully used to achieve robust clustering. However, kernel competitive learning (KCL) is not scalable for large scale data processing, because (1) it has to calculate and store the full kernel matrix that is too large to be calculated and kept in the memory and (2) it cannot be computed in parallel. In this paper we develop a framework of approximate kernel competitive learning for processing large scale dataset. The proposed framework consists of two parts. First, it derives an approximate kernel competitive learning (AKCL), which learns kernel competitive learning in a subspace via sampling. We provide solid theoretical analysis on why the proposed approximation modelling would work for kernel competitive learning, and furthermore, we show that the computational complexity of AKCL is largely reduced. Second, we propose a pseudo-parallelled approximate kernel competitive learning (PAKCL) based on a set-based kernel competitive learning strategy, which overcomes the obstacle of using parallel programming in kernel competitive learning and significantly accelerates the approximate kernel competitive learning for large scale clustering. The empirical evaluation on publicly available datasets shows that the proposed AKCL and PAKCL can perform comparably as KCL, with a large reduction on computational cost. Also, the proposed methods achieve more effective clustering performance in terms of clustering precision against related approximate clustering approaches.
Directory of Open Access Journals (Sweden)
Maksim Duškin
2015-11-01
Full Text Available Approximation and supposition This article compares exponents of approximation (expressions like Russian около, примерно, приблизительно, более, свыше and the words expressing supposition (for example Russian скорее всего, наверное, возможно. These words are often confused in research, in particular researchers often mention exponents of supposition in case of exponents of approximation. Such approach arouses some objections. The author intends to demonstrate in this article a notional difference between approximation and supposition, therefore the difference between exponents of these two notions. This difference could be described by specifying different attitude of approximation and supposition to the notion of knowledge. Supposition implies speaker’s ignorance of the exact number, while approximation does not mean such ignorance. The article offers examples proving this point of view.
Rakhmanov, Vitaly V.; Kulikov, Dmitry V.
2014-08-01
Possibility of use of a refractive-index-matching method for flow investigation by LDA method in models of the fire chambers of complex geometry is shown. The technique of flows investigation by LDA method is developed. The given technique can be successfully applied in leading branches of a thermal and hydropower engineering, in case of need of flows diagnostics in models of devices with the complex geometry.
Energy Technology Data Exchange (ETDEWEB)
Simoens, S.; Michelot, C.; Ayrault, M. [Ecole Centrale de Lyon, 69 - Ecully (France). Lab. de Mecanique des Fluides et d`Acoustique; Sabelnikov, V. [Institut Vaktsin i Syvorotok, Moscow (Russian Federation)
1997-12-31
This note presents the results obtained from the theoretical analysis of the continuous stochastic mixing model (CSM model) and its discretized counterpart. The CSM model contains an unspecified coefficient {xi}. When {xi} is a random variable uniformly distributed in the range [0, 1], the CSM model is reduced to the Hsu and Chen (1991) model. Differential approximation of the concentration pdf equation corresponding to the discretized CSM model for homogeneous turbulence is derived. The analysis shows that the pdf shape tends to a Gaussian shape only in the case when {xi} is a deterministic variable. The model is then in agreement with experimental data (Jayesh and Warhaft, 1992). (author)
Pellett, G. L.; Northam, G. B.; Wilson, L. G.; Jarrett, Olin, Jr.; Antcliff, R. R.
1989-01-01
An experimental study of H-air counterflow diffusion flames (CFDFs) is reported. Coaxial tubular opposed jet burners were used to form dish-shaped CFDFs centered by opposing laminar jets of H2/N2 and air in an argon bath at 1 atm. Jet velocities for extinction and flame restoration limits are shown versus input H2 concentration. LDA velocity data and CARS temperature and absolute N2, O2 density data give detailed flame structure on the air side of the stagnation point. The results show that air jet velocity is a more fundamental and appropriate measure of H2-air CFDF extinction than input H2 mass flux or fuel jet velocity. It is proposed that the observed constancy of air jet velocity for fuel mixtures containing 80 to 100 percent H2 measure a maximum, kinetically controlled rate at which the CFDF can consume oxygen in air. Fuel velocity mainly measures the input jet momentum required to center an H2/N2 versus air CFDF.
Low Rank Approximation in $G_0W_0$ Approximation
Shao, Meiyue; Yang, Chao; Liu, Fang; da Jornada, Felipe H; Deslippe, Jack; Louie, Steven G
2016-01-01
The single particle energies obtained in a Kohn--Sham density functional theory (DFT) calculation are generally known to be poor approximations to electron excitation energies that are measured in transport, tunneling and spectroscopic experiments such as photo-emission spectroscopy. The correction to these energies can be obtained from the poles of a single particle Green's function derived from a many-body perturbation theory. From a computational perspective, the accuracy and efficiency of such an approach depends on how a self energy term that properly accounts for dynamic screening of electrons is approximated. The $G_0W_0$ approximation is a widely used technique in which the self energy is expressed as the convolution of a non-interacting Green's function ($G_0$) and a screened Coulomb interaction ($W_0$) in the frequency domain. The computational cost associated with such a convolution is high due to the high complexity of evaluating $W_0$ at multiple frequencies. In this paper, we discuss how the cos...
Oxygen vacancy clustering and electron localization in oxygen-deficient SrTiO(3): LDA + U study.
Cuong, Do Duc; Lee, Bora; Choi, Kyeong Mi; Ahn, Hyo-Shin; Han, Seungwu; Lee, Jaichan
2007-03-16
We find, using a local density approximation +Hubbard U method, that oxygen vacancies tend to cluster in a linear way in SrTiO(3), a prototypical perovskite oxide, accompanied by strong electron localization at the 3d state of the nearby Ti transition metal ion. The vacancy clustering and the associated electron localization lead to a profound impact on materials properties, e.g., the reduction in free-carrier densities, the appearance of characteristic optical spectra, and the decrease in vacancy mobility. The high stability against the vacancy migration also suggests the physical reality of the vacancy cluster.
Nekrasov, I. A.; Pavlov, N. S.; Sadovskii, M. V.
2013-11-01
We present a detailed LDA' + DMFT investigation of the doping dependence of correlation effects in the novel K1 - x Fe2 - y Se2 superconductor. Calculations are performed at four different hole doping levels, starting from a hypothetical stoichiometric composition with the total number of electrons equal to 29 per unit cell through 28 and 27.2 electrons toward the case of 26.52, which corresponds to the chemical composition K0.76Fe1.72Se2 studied in recent ARPES experiments. In the general case, the increase in hole doping leads to quasiparticle bands in a wide energy window ±2 eV around the Fermi level becoming more broadened by lifetime effects, while correlation-induced compression of Fe-3 d LDA' bandwidths stays almost the same, of the order of 1.3 for all hole concentrations. However, close to the Fermi level, the situation is more complicated. In the energy interval from -1.0 eV to 0.4 eV, the bare Fe-3 d LDA' bands are compressed by significantly larger renormalization factors up to 5 with increased hole doping, while the value of Coulomb interaction remains the same. This fact manifests the increase in correlation effects with hole doping in the K1 - x Fe2 - y Se2 system. Moreover, in contrast to typical pnictides, K1 - x Fe2 - y Se2 does not have well-defined quasiparticle bands on the Fermi levels, but has a "pseudogap"-like dark region instead. We also find that with the growth of hole doping, Fe-3 d orbitals of various symmetries are affected by correlations differently in different parts of the Brillouin zone. To illustrate this, we determine the quasiparticle mass renormalization factors and energy shifts that transform the bare Fe-3 d LDA' bands of various symmetries into LDA' + DMFT quasiparticle bands. These renormalization factors effectively mimic more complicated energy-dependent self-energy effects and can be used to analyze the available ARPES data.
基于KPCA和LDA的信号调制识别%Signal modulation recognition based on KPCA and LDA
Institute of Scientific and Technical Information of China (English)
周欣; 吴瑛
2011-01-01
Aiming at the problem of signal feature selection and classification, an algorithm of kernel principle component analysis (KPCA) and linear discriminant analysis (LDA) classifier is brought forward According to the characteristic of communication signals, first the eliminating correlation and dimensionality reduction for these feature parameters are realized using a KPCA approach Then the automatic recognition of modulation signals is designed by the LDA classifier. Simulation result shows that over a wide range of signal-to-noise ratio scenarios, KPCA has a high performance in nonlinear classified feature The classification accuracy based on KPCA+LDA is higher than prinaple component analysis (PCA)+ template matching. Through analysis it can also be seen that the KPCA+LDA algorithm is equal to the method of kemel Fisher discriminant analysis (KFDA).%对信号的特征选择与分类问题进行研究,提出了一种基于核主分量分析(kernel principle component analysis,KPCA)和线性判别(1inear discriminant analysis,LDA)分类器的信号调制识别算法.针对通信信号的特点,首先利用KPCA的方法对特征参数进行主分量组合,以消除信号特征间的相关性和压缩特征向量的维教,然后利用LDA分类器进行信号调制方式的自动识别.仿真表明,在一个较大的信噪比范围内当特征非线性可分时,KPCA在特征选择方面性能更优,且基于KPCA+LDA的识别方法精度高于主分量分析(principle component analysis,PCA)+模板匹配算法.通过分析还可得出,KPCA+LDA等价于基于核的Fisher判别分析(kernel Fisher diseriminant analysis,KFDA)方法.
Covariant approximation averaging
Shintani, Eigo; Blum, Thomas; Izubuchi, Taku; Jung, Chulwoo; Lehner, Christoph
2014-01-01
We present a new class of statistical error reduction techniques for Monte-Carlo simulations. Using covariant symmetries, we show that correlation functions can be constructed from inexpensive approximations without introducing any systematic bias in the final result. We introduce a new class of covariant approximation averaging techniques, known as all-mode averaging (AMA), in which the approximation takes account of contributions of all eigenmodes through the inverse of the Dirac operator computed from the conjugate gradient method with a relaxed stopping condition. In this paper we compare the performance and computational cost of our new method with traditional methods using correlation functions and masses of the pion, nucleon, and vector meson in $N_f=2+1$ lattice QCD using domain-wall fermions. This comparison indicates that AMA significantly reduces statistical errors in Monte-Carlo calculations over conventional methods for the same cost.
Diophantine approximations on fractals
Einsiedler, Manfred; Shapira, Uri
2009-01-01
We exploit dynamical properties of diagonal actions to derive results in Diophantine approximations. In particular, we prove that the continued fraction expansion of almost any point on the middle third Cantor set (with respect to the natural measure) contains all finite patterns (hence is well approximable). Similarly, we show that for a variety of fractals in [0,1]^2, possessing some symmetry, almost any point is not Dirichlet improvable (hence is well approximable) and has property C (after Cassels). We then settle by similar methods a conjecture of M. Boshernitzan saying that there are no irrational numbers x in the unit interval such that the continued fraction expansions of {nx mod1 : n is a natural number} are uniformly eventually bounded.
Monotone Boolean approximation
Energy Technology Data Exchange (ETDEWEB)
Hulme, B.L.
1982-12-01
This report presents a theory of approximation of arbitrary Boolean functions by simpler, monotone functions. Monotone increasing functions can be expressed without the use of complements. Nonconstant monotone increasing functions are important in their own right since they model a special class of systems known as coherent systems. It is shown here that when Boolean expressions for noncoherent systems become too large to treat exactly, then monotone approximations are easily defined. The algorithms proposed here not only provide simpler formulas but also produce best possible upper and lower monotone bounds for any Boolean function. This theory has practical application for the analysis of noncoherent fault trees and event tree sequences.
Salmani, El mehdi; Mounkachi, Omar; Ez-Zahraouy, Hamid; Benyoussef, Abdelilah; Hamedoun, Mohammed; Hlil, El kebir
2013-11-01
Electronic structure, magnetic and optical properties of GaN:TM (TM: V, Cr, Mn, Fe, Co, Ni), based dilute magnetic semiconductors (DMS), are investigated using first-principles calculations. The energy difference between the ferromagnetic and disorder local moment states has been evaluated. Moreover, the optical absorption spectra obtained by ab-initio calculations confirm the ferromagnetic stability based on the charge state of magnetic impurities. Our results show that the ferromagnetic state is stable when TM introduce simultaneously magnetic moment and intrinsic carriers in (Ga, TM)N. Some studied ferromagnetic DMS exhibit half-metallic behavior, which is suitable for spintronics applications.
Many Faces of Boussinesq Approximations
Vladimirov, Vladimir A
2016-01-01
The \\emph{equations of Boussinesq approximation} (EBA) for an incompressible and inhomogeneous in density fluid are analyzed from a viewpoint of the asymptotic theory. A systematic scaling shows that there is an infinite number of related asymptotic models. We have divided them into three classes: `poor', `reasonable' and `good' Boussinesq approximations. Each model can be characterized by two parameters $q$ and $k$, where $q =1, 2, 3, \\dots$ and $k=0, \\pm 1, \\pm 2,\\dots$. Parameter $q$ is related to the `quality' of approximation, while $k$ gives us an infinite set of possible scales of velocity, time, viscosity, \\emph{etc.} Increasing $q$ improves the quality of a model, but narrows the limits of its applicability. Parameter $k$ allows us to vary the scales of time, velocity and viscosity and gives us the possibility to consider any initial and boundary conditions. In general, we discover and classify a rich variety of possibilities and restrictions, which are hidden behind the routine use of the Boussinesq...
Prestack wavefield approximations
Alkhalifah, Tariq
2013-09-01
The double-square-root (DSR) relation offers a platform to perform prestack imaging using an extended single wavefield that honors the geometrical configuration between sources, receivers, and the image point, or in other words, prestack wavefields. Extrapolating such wavefields, nevertheless, suffers from limitations. Chief among them is the singularity associated with horizontally propagating waves. I have devised highly accurate approximations free of such singularities which are highly accurate. Specifically, I use Padé expansions with denominators given by a power series that is an order lower than that of the numerator, and thus, introduce a free variable to balance the series order and normalize the singularity. For the higher-order Padé approximation, the errors are negligible. Additional simplifications, like recasting the DSR formula as a function of scattering angle, allow for a singularity free form that is useful for constant-angle-gather imaging. A dynamic form of this DSR formula can be supported by kinematic evaluations of the scattering angle to provide efficient prestack wavefield construction. Applying a similar approximation to the dip angle yields an efficient 1D wave equation with the scattering and dip angles extracted from, for example, DSR ray tracing. Application to the complex Marmousi data set demonstrates that these approximations, although they may provide less than optimal results, allow for efficient and flexible implementations. © 2013 Society of Exploration Geophysicists.
On Convex Quadratic Approximation
den Hertog, D.; de Klerk, E.; Roos, J.
2000-01-01
In this paper we prove the counterintuitive result that the quadratic least squares approximation of a multivariate convex function in a finite set of points is not necessarily convex, even though it is convex for a univariate convex function. This result has many consequences both for the field of
Norton, Andrew H.
1991-01-01
Local spline approximants offer a means for constructing finite difference formulae for numerical solution of PDEs. These formulae seem particularly well suited to situations in which the use of conventional formulae leads to non-linear computational instability of the time integration. This is explained in terms of frequency responses of the FDF.
On Convex Quadratic Approximation
den Hertog, D.; de Klerk, E.; Roos, J.
2000-01-01
In this paper we prove the counterintuitive result that the quadratic least squares approximation of a multivariate convex function in a finite set of points is not necessarily convex, even though it is convex for a univariate convex function. This result has many consequences both for the field of
Approximation by Cylinder Surfaces
DEFF Research Database (Denmark)
Randrup, Thomas
1997-01-01
We present a new method for approximation of a given surface by a cylinder surface. It is a constructive geometric method, leading to a monorail representation of the cylinder surface. By use of a weighted Gaussian image of the given surface, we determine a projection plane. In the orthogonal...
PIV and LDA measurements of the wake behind a wind turbine model
Naumov, I. V.; Mikkelsen, R. F.; Okulov, V. L.; Sørensen, J. N.
2014-06-01
In the present work we review the results of a series of measurements of the flow behind a model scale of a horizontal axis wind turbine rotor carried out at the water flume at Technical University of Denmark (DTU). The rotor is three-bladed and designed using Glauert theory for tip speed ratio λ =5 with a constant design lift coefficient along the span, CLdesign= 0.8. The measurements include dye visualization, Particle Image Velocimetry and Laser Doppler Anemometry. The wake instability has been studied in the range λ =3 - 9 at different cross-sections from the very near wake up to 10 rotor diameters downstream from the rotor. The initial flume flow was subject to a very low turbulence level with a uniform velocity profile, limiting the influence of external disturbances on the development of the inherent vortex instability. Using PIV measurements and visualizations, special attention was paid to detect and categorize different types of wake instabilities and the development of the flow in the near and the far wake. In parallel to PIV, LDA measurements provided data for various rotor regimes, revealing the existence of three main regular frequencies governing the development of different processes and instabilities in the rotor wake. In the far wake a constant frequency corresponding to the Strouhal number was found for the long-scale instabilities. This Strouhal number is in good agreement with the well-known constant that usually characterizes the oscillation in wakes behind bluff bodies. From associated visualizations and reconstructions of the flow field, it was found that the dynamics of the far wake is associated with the precession (rotation) of a helical vortex core. The data indicate that Strouhal number of this precession is independent of the rotor angular speed.
19. Yüzyılda İngiltere’nin Basra Bölgesindeki Faaliyetleri
Directory of Open Access Journals (Sweden)
Şennur Şenel
2016-06-01
Full Text Available Uzun süre Osmanlı Devleti’nin hakimiyet alanı içinde yer alan Basra bölgesi, sahip olduğu jeostratejik öneminden dolayı her dönemde ciddi gelişmelere sahne olmuştur. Bilhassa devletin askeri ve siyasi yönden zaafa düştüğü 19.yüzyılda Osmanlı Orta Doğusu’ndaki gelişmeler İngiltere başta olmak üzere, İran’ı, Rusya’yı, Fransa’yı ve hatta Almanya’yı yakından ilgilendirmiştir. İngiltere açısından bölgenin önemi, özellikle Hindistan’daki sömürgeleri sebebiyle hayati derecededir. Önce, Çarlık Rusya’nın sıcak denizlere inme ideali, ardından ve eş zamanlı Almanya’nın bölge üzerindeki birtakım politikalarının ortaya çıkması karşısında İngiltere, ekonomik çıkarlar ve Hindistan sömürgelerine ilişkin stratejisi sebebiyle Osmanlı toprak bütünlüğünü koruma politikasını 19.yüzyılın ilk üç çeyreğinde benimsemiş ancak denge unsurları ve mevcut durumun değişmesi üzerine 1878 Berlin Antlaşması’ndan sonra bu politikasından vazgeçmiştir. Her iki politik tutum döneminde de İngiltere en kazançlı taraf olmayı sürdürmüştür. Araştırmamızda bugüne kadar birçok araştırmaya ve esere konu olan Osmanlı-İngiliz ilişkileri, Basra bölgesi özelinde farklı bir bakış açısı ile kısaca değerlendirilmekte ve Osmanlı arşiv belgelerine dayalı olarak İngiltere’nin gerek Osmanlı toprak bütünlüğünü koruma politikasını benimsediği dönemde gerekse bu politikadan vazgeçtiği dönemdeki faaliyetleri açıklanmaya çalışılmaktadır. İki devlet arasında 19.yüzyılda gelişen ilişkilerin, siyasi, iktisadi, diplomatik ve ticari boyutları vardır. Makalede Osmanlı-İngiliz ilişkilerinin Basra bölgesi özelinde 19.yüzyıl öncesi döneme kısa bir bakıştan sonra 19.yüzyılda yaşanan ve bilhassa karşılıklı uzlaşıyı ihtiva eden antlaşmaların dışında kalan, ancak İngiltere’nin bölgede nüfuz tesis etmek i
Institute of Scientific and Technical Information of China (English)
王路; 徐江荣
2015-01-01
统一色噪声近似方法对简单一维色噪声问题研究较为充分，本文将统一色噪声法应用到高度复杂的多维气固两相湍流系统之中。首先从颗粒运动Langevin方程出发，利用统一色噪声法获得两相湍流Fokker-Planck方程，然后以此为基础建立颗粒轨道两阶矩模型。文中建立的新模型成功应用于后台阶两相湍流流场的数值模拟，预报合理正确。研究表明，对于多维两相湍流系统，统一色噪声法仍然行之有效。%A unified colored-noise approximation (UCNA) method has been widely used to solve the simple one-dimensional problem, and this paper attempts to extend this method to multi-dimensional systems. Firstly, a Fokker-Planck equation is obtained by UCNA method based on the Langevin equation for particle motion, then a two-order moment trajectory model is established on this basis. The new model can be successfully used to predict the backward-facing step two-phase flow, and the simulation results agree well with the measurements. This study shows that the UCNA method is still effective in dealing with multi-dimensional two-phase turbulent systems.
Energy Technology Data Exchange (ETDEWEB)
Karolak, Michael; Wehling, Tim; Lechermann, Frank; Lichtenstein, Alexander [I. Institut fuer Theoretische Physik, Universitaet Hamburg, Jungiusstrasse 9, 20355 Hamburg (Germany)
2009-07-01
Ca{sub x}Sr{sub 2-x}RuO{sub 4} is an interesting model system to study the interplay of structural distortions and the electronic metal to insulator transition. We present an ab-initio study within the LDA+DMFT framework of this system. In this way we account for changes in the one particle Hamiltonian due to the structural distortions in a first principles manner. We obtain the electronic density of states and the self energy. The mechanism of the metal to insulator transition in the bulk and at the surface of this system is discussed. A strong enhancement of electron correlation effects is found for the low temperature structures.
Topology, calculus and approximation
Komornik, Vilmos
2017-01-01
Presenting basic results of topology, calculus of several variables, and approximation theory which are rarely treated in a single volume, this textbook includes several beautiful, but almost forgotten, classical theorems of Descartes, Erdős, Fejér, Stieltjes, and Turán. The exposition style of Topology, Calculus and Approximation follows the Hungarian mathematical tradition of Paul Erdős and others. In the first part, the classical results of Alexandroff, Cantor, Hausdorff, Helly, Peano, Radon, Tietze and Urysohn illustrate the theories of metric, topological and normed spaces. Following this, the general framework of normed spaces and Carathéodory's definition of the derivative are shown to simplify the statement and proof of various theorems in calculus and ordinary differential equations. The third and final part is devoted to interpolation, orthogonal polynomials, numerical integration, asymptotic expansions and the numerical solution of algebraic and differential equations. Students of both pure an...
Prestack traveltime approximations
Alkhalifah, Tariq Ali
2011-01-01
Most prestack traveltime relations we tend work with are based on homogeneous (or semi-homogenous, possibly effective) media approximations. This includes the multi-focusing or double square-root (DSR) and the common reflection stack (CRS) equations. Using the DSR equation, I analyze the associated eikonal form in the general source-receiver domain. Like its wave-equation counterpart, it suffers from a critical singularity for horizontally traveling waves. As a result, I derive expansion based solutions of this eikonal based on polynomial expansions in terms of the reflection and dip angles in a generally inhomogenous background medium. These approximate solutions are free of singularities and can be used to estimate travetimes for small to moderate offsets (or reflection angles) in a generally inhomogeneous medium. A Marmousi example demonstrates the usefulness of the approach. © 2011 Society of Exploration Geophysicists.
Optimization and approximation
Pedregal, Pablo
2017-01-01
This book provides a basic, initial resource, introducing science and engineering students to the field of optimization. It covers three main areas: mathematical programming, calculus of variations and optimal control, highlighting the ideas and concepts and offering insights into the importance of optimality conditions in each area. It also systematically presents affordable approximation methods. Exercises at various levels have been included to support the learning process.
Topics in Metric Approximation
Leeb, William Edward
This thesis develops effective approximations of certain metrics that occur frequently in pure and applied mathematics. We show that distances that often arise in applications, such as the Earth Mover's Distance between two probability measures, can be approximated by easily computed formulas for a wide variety of ground distances. We develop simple and easily computed characterizations both of norms measuring a function's regularity -- such as the Lipschitz norm -- and of their duals. We are particularly concerned with the tensor product of metric spaces, where the natural notion of regularity is not the Lipschitz condition but the mixed Lipschitz condition. A theme that runs throughout this thesis is that snowflake metrics (metrics raised to a power less than 1) are often better-behaved than ordinary metrics. For example, we show that snowflake metrics on finite spaces can be approximated by the average of tree metrics with a distortion bounded by intrinsic geometric characteristics of the space and not the number of points. Many of the metrics for which we characterize the Lipschitz space and its dual are snowflake metrics. We also present applications of the characterization of certain regularity norms to the problem of recovering a matrix that has been corrupted by noise. We are able to achieve an optimal rate of recovery for certain families of matrices by exploiting the relationship between mixed-variable regularity conditions and the decay of a function's coefficients in a certain orthonormal basis.
Magnetic properties of f-electron systems in spin-polarized relativistic density functional theory
Yamagami, H.; Mavromaras, A.; Kübler, J.
1997-12-01
The magnetic ground state of the series of lanthanide and actinide trivalent ions is investigated by means of spin-polarized relativistic spin-density functional theory. In the local density functional approximation (LDA) an internal effective magnetic field due to exchange and correlation couples to the spin degrees of freedom. The resulting set of coupled Dirac equations yields ground-state multiplets that obey the well-known Hund's rules. This remarkable result comes about by the coupling of the j = l + 1/2 with the j = l - 1/2 states due to the exchange - correlation potential that is, as usual, the functional derivative of the exchange - correlation energy with respect to the spin magnetic moment. The effect of the coupling is shown to depend on the varying relative strengths of spin - orbit coupling and exchange splitting within the f series. Since in the f levels the internal exchange splitting dominates rather than the spin - orbit splitting, the energy level scheme is that of the Paschen - Back effect, and thus features of the Russell - Saunders coupling persist in spite of relativistic effects.
Energy Technology Data Exchange (ETDEWEB)
McMahan, A K
2005-03-30
This paper reports calculations for compressed Ce (4f{sup 1}), Pr (4f{sup 2}), and Nd (4f{sup 3}) using a combination of the local-density approximation (LDA) and dynamical mean field theory (DMFT), or LDA+DMFT. The 4f moment, spectra, and the total energy among other properties are examined as functions of volume and atomic number for an assumed face-centered cubic (fcc) structure. These materials are seen to be strongly localized at ambient pressure and for compressions up through the experimentally observed fcc phases ({gamma} phase for Ce), in the sense of having fully formed Hund's rules moments and little 4f spectral weight at the Fermi level. Subsequent compression for all three lanthanides brings about significant deviation of the moments from their Hund's rules values, a growing Kondo resonance at the fermi level, an associated softening in the total energy, and quenching of the spin orbit since the Kondo resonance is of mixed spin-orbit character while the lower Hubbard band is predominantly j = 5/2. while the most dramatic changes for Ce occur within the two-phase region of the {gamma}-{alpha} volume collapse transition, as found in earlier work, those for Pr and Nd occur within the volume range of the experimentally observed distorted fcc (dfcc) phase, which is therefore seen here as transitional and not part of the localized trivalent lanthanide sequence. The experimentally observed collapse to the {alpha}-U structure in Pr occurs only on further compression, and no such collapse is found in Nd. These lanthanides start closer to the localized limit for increasing atomic number, and so the theoretical signatures noted above are also offset to smaller volume as well, which is possibly related to the measured systematics of the size of the volume collapse being 15%, 9%, and none for Ce, Pr, and Nd, respectively.
Staying Thermal with Hartree Ensemble Approximations
Salle, M; Vink, Jeroen C
2000-01-01
Using Hartree ensemble approximations to compute the real time dynamics of scalar fields in 1+1 dimension, we find that with suitable initial conditions, approximate thermalization is achieved much faster than found in our previous work. At large times, depending on the interaction strength and temperature, the particle distribution slowly changes: the Bose-Einstein distribution of the particle densities develops classical features. We also discuss variations of our method which are numerically more efficient.