The electrostatic model of field gradients at nuclei: an application to hydrogen-bonded complexes of HCl

An SCF wavefunction has been used to calculate the dependence of the electric field gradient at the Cl nucleus in HCl on external non-uniform fields. Analytic coupled Hartree–Fock and numerical methods have been used to find the series of response properties (generalised Sternheimer shieldings) for perturbation by a field and its first three gradients. These parameters have been used in an electrostatic model of the 35Cl quadrupole coupling constant in weakly bound complexes BHCl, where B is a base such as H3N, HCN, CH3CN, H3P and OC. Slow convergence of the series explains the discrepancy between previously published values for the linear dependence of the Cl field gradient on an external uniform field.