Nuclear quadrupole coupling constants in alkali halide molecules: an ab initio quantum chemical study

Abstract

The electric field gradients, and hence nuclear quadrupole coupling constants, plus the dipole moments of the alkali halide molecules LiF, LiCl, LiBr, NaF, NaCl, NaBr, KF, KCl and KBr have been calculated using ab initio quantum chemical methods that range from SCF to coupled cluster techniques with perturbative corrections for triple excitations [CCSD(T)], employing basis sets of quadruple zeta quality with multiple sets of polarization functions. Zero-level vibrational corrections to these quantities and spectroscopic constants also were computed. The level of agreement with experimental data is generally good, especially in the case of the light molecules. The field gradients at the Na and Cl nuclei in NaCl were analysed using the constrained spatial orbital variation technique in order to quantify the importance of polarization, charge transfer and Pauli repulsion contributions, and to understand why a simple electrostatic interpretation of the field gradients fails in the case of alkali halides. The dipole polarizabilities, Sternheimer antishielding constants γ∞ and electric field gradient–electric field hyperpolarizabilities ϵ of the alkali and halide ions also were calculated at a correlated level of theory (ACPF).