Molecular-orbital calculations on the ground states and optical excitation states corresponding to low energy valence UV spectra of MX~4(M=Ti,Zr,Hf;X=Cl,Br) have been carried out using both self-consistent one-electron nonrelativistic Hartree-Fock-Slater and fully relativistic Dirac-Fock-Slater discrete variational local-density functional methods within the self-consistent multipolar (SCM) charge density framework. The present results are in closer agreement with experiments than other theoretical calculations. The covalent bonding characters of the molecules are also investigated by means of Mulliken population analysis methods. The overlaps between metal and ligands for the molecules are insensitive to the relativistic effects except HfBr~4.

Key words: ELECTRONIC STRUCTURE, TITANIUM COMPOUNDS, ZIRCONIUM COMPOUNDS, COVALENT BONDS, HAFNIUM COMPOUNDS