Relativistic core–valence correlation effects on molecular properties of the hydrogen halide molecules

Relativistic 4-component Dirac–Fock, MP2 and CCSD calculations have been performed to study relativistic and correlation effects on bond lengths, harmonic frequencies and dissociation energies of the hydrogen halide molecules (HF, HCl, HBr and HI). The core–valence correlation effects are studied by including the first and second highest core shells of spinors in MP2 and CCSD methods. The inclusion of core spinors results in a shortening of the bond and in an increase of the harmonic frequencies and dissociation energies of the hydrogen halides. For an estimation of the relativistic effects corresponding nonrelativistic calculations have been performed. The nonrelativistic SCF results for the systems studied are compared with the accurate, numerical HF values.