Electric and Magnetic Properties for the Ground and Excited States of Molecular Hydrogen

Abstract

The study of the electronic structure of atoms and molecules, except for the simplest one-electron systems, is a many-body problem and therefore involves electron correlation, which is one of the most long-standing problems in quantum chemistry. In spite of the general success of the orbital concept of the Hartree—Fock theory, it fails to predict some atomic and molecular properties sufficiently accurately because of its independent particle character. There is still a need to create and apply general and useful approaches which go beyond the independent particle model. In particular there exists a need to understand a variety of spectroscopic phenomena and chemical processes which involve electronically excited states. A number of methods taking into account correlation effects have been developed. One of them, perhaps the most efficient, is the method in which the wavefunction depends explicitly on the interelectronic distance. However, the area of practical application of this method is limited to the two-electron systems, among which the hydrogen molecule is the best known example. The hydrogen molecule is a particularly important molecule, which has been used both for testing new methods in quantum chemistry and also for investigating the importance of small terms in the molecular Hamiltonian. Because of the high accuracy of the theoretical results for this molecule, the theoretical values can be used for the interpretation and verification of experimental data (see for example [1, 2]).