A distributed electrostatic model for field gradients at nuclei in van der Waals molecules: application to complexes of HCl

A distributed model for the response of the electric field gradient at a nucleus to perturbation by external fields is proposed, and an implementation using perturbation of distributed multipole moments by a test nuclear quadrupole is described. Calculations on the HCl and Cl2 molecules show the response of the electric field gradient at Cl to be dominated by induced σ charge flow. Application to hydrogen-bonded complexes of HCl gives a qualitative explanation of 35Cl quadrupole coupling constants in B…HCl where B is a base such as H3N, HCN, CH3CN, H3P and OC.