Intramolecular dependence of the frequency dependent polarizabilities of Li2(a 3Σ+ u) and Na2(a 3Σ+ u) and van der Waals dispersion coefficients for atom-diatom and diatom-diatom alkali dimers

Abstract

An ab initio time dependent gauge invariant method (TDGI) has been used to compute the frequency dependent dipole and quadrupole polarizabilities of Li, Na, Li2(a3Σ+ u) and Na2(a3Σ+ u) and their dependence on the internuclear distance of the diatomic species. The dependence of the isotropic and anisotropic components of the static dipole polarizabilities on the diatomic distance was fitted to an analytical form which has an asymptotic form in agreement with the theoretical expression derived by Heijmen, T. G. A., Moszynski, R., Wormer, P. E. S., and van der Avoird, A., Molec. Phys., 89, 81. Long range two-body C6 coefficients have been evaluated for all combinations of atom-atom, atom-homonuclear diatom and homonuclear diatom-homonuclear diatom systems in which the diatomics are in the a 3Σ+ u state. Furthermore, the C8 coefficients for the atom-atom and atom-diatom interactions and the three-body C9 coefficients for the four atom-diatom systems have been obtained. For the atom-diatom case, the dipole-induced dipole C6 coefficients have been calculated for various diatomic distances up to 15 Å. The distance dependence of their isotropic C000 6 and anisotropic C202 6 components has been fitted to an analytical form similar to that used for the static dipole polarizabilities of the diatomics.