Spin-orbit density functional and ab initio study of HgX(n) (X=F, Cl, Br, and I; n=1, 2, and 4).

Quantum chemical calculations of HgX(n) (X=F, Cl, Br, and I; n=1, 2, and 4) in the gas phase are performed using the density functional theory (DFT), two-component spin-orbit (SO) DFT, and high-level ab initio method with relativistic effective core potentials (RECPs). Molecular geometries, vibrational frequencies, and various thermochemical energies are calculated and compared with available experimental results. We assess the performances of DFT functionals for calculating various molecular properties. The PBE0 functional is generally reasonable for the molecular geometries and the vibrational frequencies, but the M06 functional is more appropriate for estimating thermochemical energies. Both shape-consistent and energy-consistent RECPs correctly describe the SO effect.