ALL-ELECTRON MOLECULAR DIRAC-HARTREE-FOCK CALCULATIONS - THE GROUP-IV TETRAHYDRIDES CH4, SIH4, GEH4, SNH4, AND PBH4

We describe a basis-set-expansion Dirac-Hartree-Fock program for molecules. Bond lengths and harmonic frequencies are presented for the ground states of the group IV tetrahydrides CH4, SiH4, GeH4, SnH4, and PbH4. The results are compared with relativistic effective core potential (RECP) calculations, first-order perturbation theory (PT) calculations and with experimental data. The bond lengths are well predicted by first-order perturbation theory for all molecules, but none of the sets of RECPs considered provides a consistent prediction. Perturbation theory overestimates the relativistic correction to the harmonic frequencies; the RECP calculations underestimate the correction.