Generalization of the valence bond method for calculation of the electronic structure of diatomic molecules

A new variant of the nonempirical valence bond method, which uses a set of numerical Hartree-Fock atomlike orbitals as its basis, is proposed for calc ulating the electronic structure of diatomic molecules. The method is based on using the procedure of configuration interaction for various covalent a nd ionic configurations of the molecule. As a many-electron basis, a set of Slater determinants constructed from nonorthogonal orbitals of the atomic type localized at different centers is employed. This approach is designed for calculations of molecules containing heavy atoms and is an all-electron method, which does not require the introduction of a pseudopotential or an effective core potential to eliminate core states. The use of the numerica l Haltree-Fock basis is especially efficient in calculations of such physic al characteristics as densities at a nucleus, hyperfine splitting parameter s, energies of X-ray transitions, and chemical shifts. The results of calcu lations of spectral characteristics for the AgH molecule and AgH+ ion are p resented.