Quantum Chemical Calculations of Infrared and Raman Intensities for Diatomics on the Basis of the Virial Theorem

An ab initio method of calculations of the analytic dipole moment and polarizability geometric derivatives for diatomics by means of differentiation of expression for the quantum mechanical virial theorem in the presence of an external field is suggested. Within the framework of the Hartree−Fock perturbation theory, a dependence of both the density matrix and basis functions on the external field strength is taken into account. The results of our test calculations for some diatomics are in satisfactory agreement with the prior theoretical calculations as well as experimental data.