Spin―orbit effects on species containing halogen elements

Abstract

The spin―orbit effects on the spectroscopic constants (bond lengths, dissociation energies and harmonic vibrational frequencies) for IX (X=F, Cl, Br and I) molecules have been studied using shape-consistent relativistic effective core potentials (RECPs) with effective one-electron spin―orbit operator at HF, MP2, CCSD and CCSD(T) levels. The spectroscopic constants calculated by our effective core potential (ECP) method are in good agreement with those from all-electron Dirac―Coulomb calculations at every level of calculation considered. The spin―orbit effects elongate the bond lengths, while reduce the harmonic vibrational frequencies and dissociation energies. From the spin―orbit effects on the dissociation energies, it is confirmed that the extent of spin―orbit effects increases in F < Cl < Br < I order. For the dissociation energies, the spin―orbit effects and electron correlation effects may not be additive, and may better be treated simultaneously. Two-component spin―orbit density functional theory (SODFT) calculations for spectroscopic constants of IX (X=F, Cl, Br and I) molecules have also been performed using several functionals. Our SODFT results obtained with the B3LYP functional are in very good accord with the results of two-component CCSD(T) calculations. BLYP and BP86 functionals overestimate the bond lengths and dissociation energies, while underestimate harmonic vibrational frequencies, when the results are compared with those of two-component CCSD(T) calculations. The two-component SODFT calculations imitate reported all-electron four-component relativistic DFT calculations and ZORA results well. In addition, the spectroscopic constants from three hybrid functionals, B3LYP, ACM and PBE0, give the best agreement with the experimental values. The spin―orbit effects from the SODFT calculations result in an increase of bond length, and decrease of harmonic vibrational frequency and dissociation energy. The spin―orbit effects from the SODFT calcula...