Molecular relativistic calculations of the electric field gradients at the nuclei in the hydrogen halides

Electric field gradients at the position of the nuclei in the hydrogen halides are calculated using four-component relativistic methods. Benchmark values at the Dirac-Hartree-Fock level of theory are obtained by using large uncontracted basis sets. Electron correlation corrections are obtained by means of finite field MP2, CCSD, and CCSD(T) calculations in smaller basis sets. The importance of spin-orbit coupling and the so-called picture change effect are discussed. (C) 1998 American Institute of physics. [S0021-9606(98)30446-8].