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Variational Calculations (variational + calculation)

Distribution by Scientific Domains

Physics and Astronomy	50%
Chemistry	50%

Selected Abstracts

Vibronic polarons: Self-trapping, local rotation, and band features

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2002
A. G. Andreev
Abstract We revisit basic theoretical concepts of local and itinerant vibronic polarons in crystals. The following results may be regarded as novel: (1) The electron self-trapping rate to a small polaron is calculated via the reaction rate method; subsequently, self-trapped on-center small polarons relax to an off-center vibronic polaron state. (2) The general vibronic Hamiltonian is redefined so as to incorporate both local and itinerant behavior and pairing into bipolarons or Cooper pairs. (3) The planar rotation and diametral tunneling of an off-center polaron around and across its centrosymmetrical site are dealt with to adiabatic approximation. (4) Variational calculations are made for vibronic polarons itinerant along 1-D chains by means of a two-band extension of Merrifield's ansatz. This investigation of vibronic polarons is undertaken in view of their presumed role in high-temperature superconductivity and colossal magnetoresistance. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source]

Spherical quantum dot under an electric field

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2004
Gerardo J. Vázquez
Abstract We investigate the effect of an electric field applied to a spherical quantum dot on the energy groundstate of carriers in the quantum dot using an infinite confining potential well model. We perform a simple variational calculation for low electric fields and we find a quadratic shift of the energy levels with the electric field while for strong fields, the Stark shift of the energy groundstate increases almost linearly with the electric field. There is a transition for quasi-one dimensional to three-dimensional behavior when the dot radius is large. The comparison of our results with previous exact calculations is very good. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

On the applicability of multireference second-order perturbation theory to study weak magnetic coupling in molecular complexes,

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2008
Núria Queralt
Abstract The performance of multiconfigurational second-order perturbation techniques is established for the calculation of small magnetic couplings in heterobinuclear complexes. Whereas CASPT2 gives satisfactory results for relatively strong magnetic couplings, the method shows important deviations from the expected Heisenberg spectrum for couplings smaller than 15,20 cm,1. The standard choice of the zeroth-order CASPT2 Hamiltonian is compared to alternative definitions published in the literature and the stability of the results is tested against increasing level shifts. Furthermore, we compare CASPT2 with an alternative implementation of multiconfigurational perturbation theory, namely NEVPT2 and with variational calculations based on the difference dedicated CI technique. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source]

Effect of dielectric screening on the binding energies and diamagnetic susceptibility of a donor in a quantum well wire

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2006
M. Latha
Abstract The effect of the dielectric screening on donor binding energies in a quantum wire has been estimated. Since the screening function is shown to be significant in a few phenomena like carrier transport, and not so in a few cases like the donor binding energy calculations, five different screening functions have been used in the calculations to see their relative merits. It is observed that the dielectric function obtained by Resta using the Thomas,Fermi approximation not only gives lower estimates of the ionization energies for all well widths (L ), but also is shown to vary very rapidly with L . The other functions used are those of Hermanson and Vinsome & Richardson. Using the results of the variational calculations for the finite barrier problem, the diamagnetic susceptibility of a donor as a function of L has also been estimated. Though experimental results are not available, we have compared our results for Eion with other theoretical estimates available in the literature. The agreement is found to be good. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]