Calculations of the deuterium electric field gradient from simple wave functions in the HD molecule

We attempt to find a simple procedure for evaluating the electric field gradient at the position of a deuteron in a molecule by performing a set of sample calculations on the HD molecule. Starting from a set of simple molecular orbital or valence bond functions, we calculate the expectation values of the DEFG (deuterium electric field gradient) values with an accuracy of about 10%. By making use of a variation–perturbation procedure we evaluate correction terms which reduce the errors to 1% or 2%. An essential feature in the variation-perturbation method is the use of 3d atomic orbitals with unusually large orbital exponents (q = 7). We feel that our methods are applicable to larger molecules also.