Ab initio studies of electron correlation effects in heavier closed-shell atoms: Structure of the all-electron correlation energies of Zn2+ and Zn

摘要

To provide reliable reference results for various components of the electron correlation energies of Zn2+ andnZn, which play a similar role for 3d-electron systems as Ne and Mg do for lighter atoms, we have performednextensive calculations of the all-electron correlation energy and of its various components with several stateof-nthe-art ab initio techniques. Two pairs of basis-set sequences that systematically converge to the completenbasis set (CBS) limit have been employed in the calculations. One pair [cc-pVnZ and aug-cc-pVnZ (correlationnconsistent polarized valence n-zeta and augmented cc-pVnZ with n = D, T, Q, 5, 6(−k))] is oriented towardsnthe description of valence electron correlation. The second pair of sequences [cc-pCCVnZ and aug-cc-pCCVnZn(core core-valence n-zeta, with n = D, T, Q, 5, 6(−k))] is developed for the description of all-electron correlationneffects. The correlation energies have been determined with second-order Moller-Plesset perturbation theoryn(MP2) and several single-reference coupled-cluster (CC) methods. The present correlation energies representnaccurate post-MP2 correlation energies for closed-shell atoms including 3d electrons both at the all-electron andnsubshell levels and should be useful benchmark results for various transitions.We have also employed the presentnresults for assessments of the focal-point approximation (FPA), broadly used in approximations of differencencorrelation effects for molecular interaction problems, in applications aiming at estimating correlation effectsnin heavier atoms. Our results indicate that for the systems considered, the magnitudes of the MP2 correlationnenergies overestimate the magnitudes of the CC values for all electrons correlated as well as of their variousnsubsets. For the all-electron correlation energies of the Zn atom, our result confirms the finding of S. P. McCarthynand A. J. Thakkar [J. Chem. Phys. 134, 044102 (2011)] obtained by means of non–ab initio approaches for allnheavy closed-shell atoms from Zn to Rn.We have shown that for both Zn2+ and Zn this overestimation is directlyncaused by the presence of the 3d10 electron configuration.