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1.
Adaptive Finite Element Approximations for a Class of Nonlinear Eigenvalue Problems in Quantum Physics
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Huajie Chen Xingao Gong Lianhua He & Aihui Zhou 《advances in applied mathematics and mechanics.》2011,3(4):493-518
In this paper, we study an adaptive finite element method for a
class of nonlinear eigenvalue problems resulting from quantum
physics that may have a nonconvex energy functional. We prove the
convergence of adaptive finite element approximations and present
several numerical examples of micro-structure of matter calculations
that support our theory. 相似文献
2.
Several methods for effective interaction and operator calculations based on the Rayleigh-Schrödinger and Brillouin-Wigner perturbation expansions are studied. Special emphasis is given to the use of Padé approximants for effective operator calculations. The convergence properties of the methods are studied numerically in a Lipkin many-body model. Among the various methods using Padé-approximants, the method based on a variational approach in the BW scheme is found to give most encouraging results for the present model. 相似文献
3.
We present a new computational method with associated computer program TROVE (Theoretical ROVibrational Energies) to perform variational calculations of rovibrational energies for general polyatomic molecules of arbitrary structure in isolated electronic states. The (approximate) nuclear kinetic energy operator is represented as an expansion in terms of internal coordinates. The main feature of the computational scheme is a numerical construction of the kinetic energy operator, which is an integral part of the computation process. Thus the scheme is self-contained, i.e., it requires no analytical pre-derivation of the kinetic energy operator. It is also general, since it can be used in connection with any internal coordinates. The method represents an extension of our model for pyramidal XY3 molecules reported previously [S.N. Yurchenko, M. Carvajal, P. Jensen, H. Lin, J.J. Zheng, W. Thiel, Mol. Phys. 103 (2005) 359]. Non-rigid molecules are treated in the Hougen-Bunker-Johns approach [J.T. Hougen, P.R. Bunker, J.W.C. Johns, J. Mol. Spectrosc. 34 (1970) 136]. In this case, the variational calculations employ a numerical finite basis representation for the large-amplitude motion using basis functions that are generated by Numerov-Cooley integration of the appropriate one-dimensional Schrödinger equation. 相似文献
4.
K. Salzer 《Annalen der Physik》1980,492(4):271-284
Determination of the NMR-Shielding and of Magnetic Susceptibility by Calculation of the Current Density of Diamagnetic Molecules by the Finite Element Method In paper [20] the finite element method was initiated for calculations of diamagnetic properties of molecules on the basis of a semiclassical approach [18, 19]. In the present work this method is used in the frame of the uncoupled Hartree-Fock-perturbation theory. It is shown that the proposed approach is applicable to localized orbitals, the susceptibility and the shielding being divided into incrementary contributions. Furthermore the relationship to the semiclassical approach and to the approach of Rebane [7] is shown. The H2-molecule, the threedimensional anisotropic harmonic oscillator and the CH4-molecule serve as examples to present the possibilities of this method. 相似文献
5.
M. G. Brik 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(3):269-274
Systematic first-principles analysis of the energy level schemes and ground
state absorption spectra of trivalent chromium in ZnAl2S4 and
ZnGa2O4 crystals has been performed in the present paper. The
recently developed first-principles approach to the analysis of the
absorption spectra of impurity ions in crystals based on the discrete
variational multi-electron (DV-ME) method [K. Ogasawara et al., Phys. Rev. B
64, 115413 (2001)] was used in the calculations. The method is based on the
numerical solution of the Dirac equation; no phenomenological parameters are
used in the calculations. As a result, complete energy level schemes of the
Cr3+ ion and its absorption spectra in both crystals were calculated,
assigned and compared with experimental data. By performing analysis of the
molecular orbital (MO) population, it was shown that the covalency of the
chemical bonds between the Cr3+ and S2- ions is more significant
than that one between the Cr3+ and O2- ions. 相似文献
6.
7.
A. H. Reshak Z. Charifi H. Baaziz 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(4):463-468
We present the results of the ab initio theoretical study of the optical properties for PbFX (X = Cl, Br, I) compounds in its matlockite-type structure using the
full potential linearized augmented plane wave (FP-LAPW) method as
implemented in the WIEN2K code. We employed generalized gradient
approximation (GGA), which is based on exchange-correlation energy
optimization to calculate the total energy. Also we have used the
Engel-Vosko GGA formalism, which optimizes the corresponding potential for
band structure calculations. Our calculations show that the valence band
maximum (VBM) and conduction band minimum (CBM) are located at Z resulting
in a direct energy gap. We present calculations of the frequency-dependent
complex dielectric function ε( ω) and its
zero-frequency limit ε1 ( 0 ). We find that the
values of ε1 ( 0 ) increases with decreasing the
energy gap. The reflectivity spectra and absorption coefficient has been
calculated and compared with the available experimental data. The optical
properties are analyzed and the origin of some of the peaks in the spectra
is discussed in terms of the calculated electronic structure. 相似文献
8.
Abstract We present a numerical simulation of scattering by one-dimensional randomly rough surfaces. It is based on the use of plane-wave expansions to describe the Melds on the surface (i.e. Rayleigh hypothesis). Accuracy and convergence properties of two different numerical implementations are studied. Some examples of results for a dielectric and a metallic Gaussian rough surface are shown to be in good agreement with calculations by a rigorous numerical method. The Rayleigh method appears to be a fast computation tool for dielectric surfaces with slopes of less than 0.2. 相似文献
9.
Samet Y. Kadioglu Dana A. Knoll Robert B. Lowrie Rick M. Rauenzahn 《Journal of computational physics》2010,229(22):8313-8332
We present a second order self-consistent implicit/explicit (methods that use the combination of implicit and explicit discretizations are often referred to as IMEX (implicit/explicit) methods , and ) time integration technique for solving radiation hydrodynamics problems. The operators of the radiation hydrodynamics are splitted as such that the hydrodynamics equations are solved explicitly making use of the capability of well-understood explicit schemes. On the other hand, the radiation diffusion part is solved implicitly. The idea of the self-consistent IMEX method is to hybridize the implicit and explicit time discretizations in a nonlinearly consistent way to achieve second order time convergent calculations. In our self-consistent IMEX method, we solve the hydrodynamics equations inside the implicit block as part of the nonlinear function evaluation making use of the Jacobian-free Newton Krylov (JFNK) method , and . This is done to avoid order reductions in time convergence due to the operator splitting. We present results from several test calculations in order to validate the numerical order of our scheme. For each test, we have established second order time convergence. 相似文献
10.
K. Tatsumi M. Tsutsui G.W. Beall D.F. Mullica W.O. Milligan 《Journal of Electron Spectroscopy and Related Phenomena》1979,16(1):113-118
Using the direct CI method perturbation corrections to the Koopmans ionization energies have been obtained up to order 10 for the molecules CN? and H2O. The results are compared with those from the fully converged CI and Bk-type calculations. The convergence of the perturbation series is found to be quite slow although substantial improvement is possible using a variation-perturbation method. 相似文献
11.
W. Luo J. Souza de Almeida R. Ahuja 《Journal of Physics and Chemistry of Solids》2008,69(9):2274-2276
We have calculated the electronic structure of CsBi4Te6 by means of first-principles self-consistent total-energy calculations within the local-density approximation using the full-potential linear-muffin-tin-orbital method. From our calculated electronic structure we have calculated the frequency dependent dielectric function. Our calculations shows that CsBi4Te6 a semiconductor with a band gap of 0.3 eV. The calculated dielectric function is very anisotropic. Our calculated density of state support the recent experiment of Chung et al. [Science 287 (2000) 1024] that CsBi4Te6 is a high performance thermoelectric material for low temperature applications. 相似文献
12.
S. Saib N. Bouarissa P. Rodríguez-Hernández A. Muñoz 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(4):435-438
We present a theoretical study of the structural properties, namely
lattice constant, bulk modulus and its pressure derivative of zinc-blende
GaxIn1-xN. The calculations are performed using first-principles
calculations in the framework of the density-functional-theory
within the local density approximation under the virtual
crystal approximation. The computed values are in good
agreement with the available experimental data. The composition dependence
of the studied quantities is examined. Besides, the deviation of the alloy
lattice constant from Vegard's law is evaluated. 相似文献
13.
We present theoretical photoluminescence (PL) spectra of undoped and p-doped AlxIn1−x−yGayN/AlXIn1−X−YGaYN double quantum wells (DQWs). The calculations were performed within the k.p method by means of solving a full eight-band Kane Hamiltonian together with the Poisson equation in a plane wave representation, including exchange-correlation effects within the local density approximation. Strain effects due to the lattice mismatch are also taken into account. We show the calculated PL spectra, analyzing the blue and red-shifts in energy as one varies the spike and the well widths, as well as the acceptor doping concentration. We found a transition between a regime of isolated quantum wells and that of interacting DQWs. Since there are few studies of optical properties of quantum wells based on nitride quaternary alloys, the results reported here will provide guidelines for the interpretation of forthcoming experiments. 相似文献
14.
H. Wang X.-Y. Kuang A.-J. Mao X.-F. Huang 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(1):1-5
We perform ab initio calculations using a pseudo-potential plane-wave method
based on density functional theory, within the local density approximation and generalized gradient approximation, in order
to determine and predict the pressure dependence of structural and elastic properties of spinel compounds: MgAl2O4, MgGa2O4 and MgIn2O4. The
results are in agreement with the available experimental data and other theoretical calculations. 相似文献
15.
We discuss the origin of the intrinsic visible band emission of ABO3 perovskite oxides (so-called ‘green luminescence’) which remains a topic of high interest during the last quarter of the century. We present a theoretical calculation modelling of this emission in the framework of a concept of charge transfer vibronic excitons [Phys. Solid State, 40 (1998) 834], i.e. as a result of radiative recombination of correlated (bound) self-trapped electron and hole polarons in the highly polarizable ABO3-type matrix. The Intermediate Neglect of Differential Overlap method combined with the Large Unit Cell periodic defect model was used for quantum chemical calculations and theoretical simulation of the green emission for a series of model ABO3 perovskites. The ‘green’ luminescence energies for PbTiO3, SrTiO3, BaTiO3, KNbO3 and KTaO3 perovskite-type crystals agree well with those experimentally observed earlier. 相似文献
16.
Antony Lewis Chris Doran Anthony Lasenby 《International Journal of Theoretical Physics》2001,40(1):363-376
Using the spacetime algebra formulation of the Dirac equation, we demonstrate how to perform cross-section calculations following a method suggested by Hestenes (1982). Instead of an S-matrix, we use an operator that rotates the initial states into the scattered states. By allowing the scattering operator to become a function of the initial spin, we can neatly handle spin-dependent calculations. When the operator is independent of spin, we can provide manifestly spin-independent results. We use neither spin basis nor spin sums, instead handling the spin orientation directly. As examples, we perform spin-dependent calculations in Coulomb scattering to second order, and briefly consider more complicated calculations in QED. 相似文献
17.
V. Lensky V. Baru E. Epelbaum C. Hanhart J. Haidenbauer A. Kudryavtsev U. -G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2007,33(4):339-348
We discuss the possibility to extract the neutron-neutron scattering length ann from experimental spectra on the reaction γd → π+
nn . The transition operator is calculated to high accuracy from chiral perturbation theory. We argue that for properly chosen
kinematics, the theoretical uncertainty of the method can be as low as 0.1 fm. 相似文献
18.
H. Deutsch K. Becker T.D. Märk 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(2):283-287
We report calculations of the electron-impact ionization cross-sections of selected dimers (homonuclear diatomic molecules)
and trimers (homonuclear triatomic molecules) using a method which relies only on macroscopic quantities in conjunction with
a “defect concept”. The empirically determined defect describes the deviation of the cluster (dimer, trimer) cross-sections
from a simple linear dependence on the cluster size. We compare the calculated cross-sections to experimental data for the
dimers S2 and F2 and the trimer O3 and we present predictions for the ionization cross-sections of Br2, I2, C2 and C3 for which no experimental data are available. Lastly, we extend the method to the calculation of ionization cross-sections
for the fullerenes C60 and C70.
Received 6 December 1999 and Received in final form 10 April 2000 相似文献
19.
V. Srivastava M. Rajagopalan S. P. Sanyal 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(2):131-139
A first-principles tight-binding linear muffin tin orbital (TB-LMTO) method
within the local-density approximation is used to calculate the total
energy, lattice parameter, bulk modulus, magnetic moment, density of states
and energy band structures of half-metallic CrO2 at ambient as well as
at high pressure. The magnetic and structural stabilities are determined
from the total energy calculations. From the present study we predict a
magnetic transition from ferromagnetic (FM) state to a non-magnetic (NM)
state at 65 GPa, which is of second order in nature. We also observe from
our calculations that CrO2 is more stable in tetragonal phase
(rutile-type) at ambient conditions and undergoes a transition to an
orthorhombic structure (CaCl2-type) at 9.6 GPa, which is in good
agreement with the experimental results. We predict a second structural
phase transition from CaCl2- to fluorite-type structure at 89.6 GPa
with a volume collapse of 7.3%, which is yet to be confirmed
experimentally. Interestingly, CrO2 shows half metallicity under
ambient conditions. After the first structural phase transition from
tetragonal to orthorhombic, half metallicity has been retained in CrO2 and it vanishes at a pressure of 41.6 GPa. Ferromagnetism is quenched at a
pressure of 65 GPa. 相似文献
20.
Algebraic aspects of the Hirzebruch signature operator and applications to transitive Lie algebroids
The index of the classical Hirzebruch signature operator on a manifold M is equal to the signature of the manifold. The examples of Lusztig ([10], 1972) and Gromov ([4], 1985) present the Hirzebruch
signature operator for the cohomology (of a manifold) with coefficients in a flat symmetric or symplectic vector bundle. In
[6], we gave a signature operator for the cohomology of transitive Lie algebroids.
In this paper, firstly, we present a general approach to the signature operator, and the above four examples become special
cases of a single general theorem. 相似文献