Wechselwirkungspotenziale mehratomiger Systeme

The goal of this thesis is the calculation of the interaction potentials of polyatomic systems by generalized Heitler-London (GHL) theory. In GHL theory the potential energies are expressed by Coulomb and exchange energies which are generalizations of the Coulomb and exchange integrals originally introduced by Heitler and London for the calculation of the potentials of the H_2-molecule. In contrast to other methods, GHL theory makes use of non-symmetrized, so-called localized wave functions and Rayleigh Schroedinger perturbation theory. The latter provides the possibility of systematically improving the results by successively including higher orders. In the first part of the thesis, the GHL theory is applied to polyatomic systems. The methods used to calculate the Coulomb and exchange energies are described. Generally, there are two approaches to this problem: surface integral method for the exchange energies and polarization approximation for the Coulomb energy, perturbation series for all Coulomb and exchange energies. Both methods are explained. The leading non-additive contribution to the Coulomb energy at long range is the triple dipole dispersion energy. The Axilrod-Teller-Muto formula describes the long range behavior of this interaction but diverges at small internuclear distances. A damping function for this formula is developed for general three-body systems, explicitly taking into account the united atom limits. (orig.)SIGLEAvailable from TIB Hannover: RA 1396(2000,7) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman