DENSITY-FUNCTIONAL BASED STRUCTURE OPTIMIZATION FOR MOLECULES CONTAINING HEAVY-ELEMENTS - ANALYTICAL ENERGY GRADIENTS FOR THE DOUGLAS-KROLL-HESS SCALAR RELATIVISTIC APPROACH TO THE LCGTO-DF METHOD

The self-consistent scalar-relativistic linear combination of Gaussian -type orbitals density functional (LCGTO-DF) method has been extended to calculate analytical energy gradients. The method is based on the u se of a unitary second order Douglas-Kroll-Hess (DKH) transformation f or decoupling large and small components of the full four-component Di rac-Kohn-Sham equation. The approximate DKH transformation most common in molecular calculations has been implemented; this variant employs nuclear potential based projectors and it leaves the electron-electron interaction untransformed. Examples are provided for the geometry opt imization of a series of heavy metal systems which feature a variety o f metal-ligand bonds, like Au-2, AuCl, AuH, Mo(CO)(6) and W(CO)(6) as well as the d(10) complexes [Pd(PH3)(2)O-2] and [Pt(PH3)(2)O-2]. The c alculated results, obtained with several gradient-corrected exchange-c orrelation potentials: compare very well with experimental data and th ey are of similar or even better accuracy than those of other high qua lity relativistic calculations reported so far.