Direct perturbation theory in terms of energy derivatives: Scalar-relativistic treatment up to sixth order

作者：Schwalbach Werner^*; Stopkowicz Stella; Cheng Lan; Gauss Juergen

来源：Journal of Chemical Physics, 2011, 135(19): 194114.

DOI：10.1063/1.3659316

• HF calculations
• hydrogen compounds
• molecular moments
• perturbation theory

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 lambda(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.

• 出版日期2011-11-21