Collect. Czech. Chem. Commun. 2003, 68, 374-386

Similarity-Transformed Hamiltonians by Means of Gaussian-Damped Interelectronic Distances

Henk J. A. Zweistra, Claire C. M. Samson and Wim Klopper*

Theoretical Chemistry Group, Debye Institute, Utrecht University, P.O. Box 80052, NL-3508 TB Utrecht, Netherlands


A method is presented to improve the description of electron correlation in configuration interaction (CI) calculations. In this method, the standard CI expansion ψ is multiplied by a correlation function ϕ = exp (F) with F = Σ(from m = 1 to M) cm Σ(for i < j) rij exp(-γmrij2). With this correlation function, the total wavefunction Ψ = ϕψ exhibits the right behavior when two electron coalesce while F vanishes for large interelectronic distances. The correlation function is implemented using the methodology of similarity-transformed Hamiltonians and is applied to two-electron systems. A generalization to many-electron systems is indicated. The new method yields more accurate results than standard CI calculations of the energy and interelectronic distance of the He atom. The H2 molecule was chosen to study the long-range behavior of the correlation function.

Keywords: Hamiltonian; Gaussian; Wavefunctions; Configuration interaction; Correlation functions; Ab initio calculations.

References: 28 live references.