title: Direct perturbation theory in terms of energy derivatives: scalar-relativistic treatment up to sixth order.
abstract: A formulation of sixth-order direct perturbation theory (DPT) to treat relativistic effects in quantum-chemical calculations is presented in the framework of derivative theory. Detailed expressions for DPT6 are given at the Hartree-Fock level in terms of the third derivative of the energy with respect to the relativistic perturbation parameter defined as λ(rel)=c(-2). They were implemented for the computation of scalar-relativistic energy corrections. The convergence of the scalar-relativistic DPT expansion is studied for energies and first-order properties such as dipole moment and electric-field gradient within the series of the hydrogen halides (HX, X = F, Cl, Br, I, and At). Comparison with spin-free Dirac-Coulomb calculations indicates that the DPT series exhibits a smooth and monotonic convergence. The rate of convergence, however, depends on the charge of the involved nuclei and significantly slows down for heavy-element compounds.
authors: Institut für Physikalische Chemie, Universität Mainz, 55099 Mainz, Germany. schwalbach@uni-mainz.de
authors: Werner
authors: W
authors: Schwalbach
authors: Stella
authors: S
authors: Stopkowicz
authors: Lan
authors: L
authors: Cheng
authors: Jürgen
authors: J
authors: Gauss
mesh_terms: D018054:Hydrobromic Acid / Q000737:chemistry; D006851:Hydrochloric Acid / Q000737:chemistry; D006858:Hydrofluoric Acid / Q000737:chemistry; D011789:Quantum Theory
chemical_list: D018054:Hydrobromic Acid; D006851:Hydrochloric Acid; D006858:Hydrofluoric Acid