arXiv subjects

I. Koltracht

Publications and source records attributed to I. Koltracht.

4 recordsLinked to original sources

arXiv2006

An economical method to calculate eigenvalues of the Schroedinger Equation

The method is an extension to negative energies of a spectral integral equation method to solve the Schroedinger equation, developed previously for scattering applications. One important innovation is a re-scaling procedure in order to compensate for the exponential behaviour of the negative energy Green's function. Another is the need to find approximate energy eigenvalues, to serve as starting values for a subsequent iteration procedure. In order to illustrate the new method, the binding energy of the He-He dimer is calculated, using the He-He TTY potential. In view of the small value of the binding energy, the wave function has to be calculated out to a distance of 3000 a.u. Two hundred mesh points were sufficient to obtain an accuracy of three significant figures for the binding energy, and with 320 mesh points the accuracy increased to six significant figures. An application to a potential with two wells separated by a barrier, is also made.

physics.comp-ph↗

arXiv2004

An accurate spectral method for solving the Schroedinger equation

The solution of the Lippman-Schwinger (L-S) integral equation is equivalent to the the solution of the Schroedinger equation. A new numerical algorithm for solving the L-S equation is described in simple terms, and its high accuracy is confirmed for several physical situations. They are: the scattering of an electron from a static hydrogen atom in the presence of exchange, the scattering of two atoms at ultra low temperatures, and barrier penetration in the presence of a resonance for a Morse potential. A key ingredient of the method is to divide the radial range into partitions, and in each partition expand the solution of the L-S equation into a set of Chebyshev polynomials. The expansion is called "spectral" because it converges rapidly to high accuracy. Properties of the Chebyshev expansion, such as rapid convergence, are illustrated by means of a simple example.

physics.comp-ph↗

arXiv2002

A Novel Method for the Solution of the Schroedinger Eq. in the Presence of Exchange Terms

In the Hartree-Fock approximation the Pauli exclusion principle leads to a Schroedinger Eq. of an integro-differential form. We describe a new spectral noniterative method (S-IEM), previously developed for solving the Lippman-Schwinger integral equation with local potentials, which has now been extended so as to include the exchange nonlocality. We apply it to the restricted case of electron-Hydrogen scattering in which the bound electron remains in the ground state and the incident electron has zero angular momentum, and we compare the acuracy and economy of the new method to three other methods. One is a non-iterative solution (NIEM) of the integral equation as described by Sams and Kouri in 1969. Another is an iterative method introduced by Kim and Udagawa in 1990 for nuclear physics applications, which makes an expansion of the solution into an especially favorable basis obtained by a method of moments. The third one is based on the Singular Value Decomposition of the exchange term followed by iterations over the remainder. The S-IEM method turns out to be more accurate by many orders of magnitude than any of the other three methods described above for the same number of mesh points.

physics.atom-ph↗

arXiv1998

Solution of Integral Equations by a Chebyshev Expansion Method

A new spectral type method for solving the one dimensional quantum-mechanical Lippmann-Schwinger integral equation in configuration space is described. The radial interval is divided into partitions, not necessarily of equal length. Two independent local solutions of the integral equation are obtained in each interval via Clenshaw-Curtis quadrature in terms of Chebyshev Polynomials. The local solutions are then combined into a global solution by solving a matrix equation for the coefficients. This matrix is sparse and the equation is easily soluble. The method shows excellent numerical stability, as is demonstrated by several numerical examples.

nucl-th↗