A scalar-relativistic extension of the linear combination of Gaussian-type orbitals local density functional method: application to AuH, AuCl and Au₂

The linear combination of Gaussian-type orbitals local density functional (LCGTO-LDF) approach to the electronic structure of molecules has been supplemented by a self-consistent scalar-relativistic method based on external field projectors. By means of a unitary Douglas-Kroll transformation, the method decouples the large and small components correct to second order in the nuclear potential and thus yield a numerically stable two-component all-electron method. The computational effort beyond that of a nonrelativistic molecular LCGTO-LDF calculation remains moderate. The results obtained for the diatomic gold compounds Au₂, AuH and AuCl are encouraging as spectroscopic constants are found to compare well experimental data.