Electric field gradients and Sternheimer-type properties of the BrCl molecule: correlated, relativistic, ab initio calculations and modelling of nuclear quadrupole coupling constants in complexes B ⋯ BrCl

The generalised polarisabilities describing the response to an applied field of the electric field gradients at the nuclei of BrCl are calculated ab initio using the correlated CCSD(T) method with relativistic corrections estimated by the Douglas-Kroll ‘no-pair’ model. The magnitudes of 86.9 and 42.3 α0−1 for the electric field derivatives of the gradients at Br and Cl include substantial and opposing correlation and relativistic corrections amounting to −12% and −16% of the respective non-relativistic self-consistent-field values. Relevance of the calculations to the Townes-Dailey model of the measured nuclear quadrupole coupling constants of complexes B ⋯ BrCl of BrCl with a base B is discussed.