Calculation of the vibrational dependence of the electric field gradient in HD

We calculate the deuterium electric field gradient in the HD and D2 molecules at various internuclear separations by making use of a previously proposed variation--perturbation method. We calculate DEFG values at internuclear separations R = 1.2, 1.3, 1.4, 1.5, and 1.6. We also calculate the average values for the vibrational ground state v = 0 and for the vibrational states J = 0, J = 1, and J = 2 of the HD and D2 molecules. The vibrational averaged DEFG value is very close to the equilibrium value at R = 1.4 due to accidental cancellation of different contributions. The difference between our result and other theoretical values is about 2.5%