No abstract

In this paper we present results of four-component relativistic density-functional calculations for diatomic molecules with heavy constituents. The fully relativistic treatment of the electron kinematics is used for a consistent examination of the importance of gradient and relativistic corrections to the exchange-correlation energy functional. In agreement with recent scalar relativistic calculations, we find that relativistic corrections to exchange-correlation functionals give no significant contribution to the binding properties of the investigated diatomic molecules. On the other hand, the effect of gradient terms is sizable, leading to a clear improvement of dissociation energies over the standard local-density approximation. The usefulness of gradient contributions in the high-Z regime is nevertheless somewhat questioned by the fact that they overcorrect the small errors in bond lengths found with the local-density approximation. ͓S1050-2947͑99͒04506-0͔

Relativistic self-consistent charge Dirac–Slater discrete variational method calculations have been done for the series of molecules MBr5, where M=Nb, Ta, Pa, and element 105, Ha. The electronic structure data show that the trends within the group 5 pentabromides resemble those for the corresponding pentaclorides with the latter being more ionic. Estimation of the volatility of group 5 bromides has been done on the basis of the molecular orbital calculations. According to the results of the theoretical interpretation HaBr5 seems to be more volatile than NbBr5 and TaBr5.

Electronic structures of MOCl3 and MOBr3 molecules, where M=V, Nb, Ta, Pa, and element 105, hahnium, have been calculated using the relativistic Dirac–Slater discrete-variational method. The character of bonding has been analyzed using the Mulliken population analysis of the molecular orbitals. It was shown that hahnium oxytrihalides have similar properties to oxytrihalides of Nb and Ta and that hahnium has the highest tendency to form double bond with oxygen. Some peculiarities in the electronic structure of HaOCl3 and HaOBr3 result from relativistic effects. Volatilities of the oxytrihalides in comparison with the corresponding pentahalides were considered using results of the present calculations. Higher ionic character and lower covalency as well as the presence of dipole moments in MOX3 (X=Cl, Br) molecules compared to analogous MX5 ones are the factors contributing to their lower volatilities.

A detailed study of the electronic structure and bonding of the pentahalides of group 5 elements V, Nb, Ta, and element 105, hahnium (and Pa) has been carried out using relativistic molecular cluster Dirac–Slater discrete-variational method. A number of calculations have been performed for different geometries and molecular bond distances. The character of the bonding has been analyzed using the Mulliken population analysis of the molecular orbitals. It is shown that hahnium is a typical group 5 element. In a great number of properties it continues trends in the group. Some peculiarities in the electronic structure of HaCl5 result from relativistic effects.