First-order relativistic corrections to MP2 energy from standard gradient codes: Comparison with results from density functional theory

摘要

The evaluation of the first-order scalar relativistic corrections to MP2 energy based on either direct perturbation theory or the mass-velocity and Darwin terms is discussed. In a basis set of Levy-Leblond spinors the one- and two-electron matrix elements of the relativistic Hamiltonian can be decomposed into a nonrelativistic part and a relativistic perturbation. Thus, a program capable of calculating nonrelativistic energy gradients can be used to calculate the cross-term between relativity and correlation. The method has been applied to selected closed-shell atoms (He, Be, Ne, and Ar) and molecules (CuH, AgH, and AuH). The calculated equilibrium distances and harmonic frequencies were compared with results from first-order relativistic density functional calculations. It was found that the cross-term is not the origin of the nonadditivity of relativistic and correlation effects. (C) 1998 John Wiley & Sons, Inc. [References: 36]