Basis-set limit binding energies ofBenandMgn(n=2,3,4)clusters

Abstract

The general applicability of the basis set and correlation-dependent extrapolation method [J. Chem. Phys. 118, 3035 (2003)], which fits two successive correlation energies with correlation-consistent cc-pVXZ and cc-pV(X+1)Z basis sets [X=D(2),T(3),Q(4)] by (X+k){sup -3} with varying k according to basis-set quality and correlation level, was explored by examining the basis-set limit binding energies of the metallic clusters of Be{sub n} and Mg{sub n} (n=2,3,4) at the MP2 (second-order Moller-Plesset perturbation theory) and CCSD(T) (single and double coupled cluster method with perturbative triple correction) level. The comparison of the extrapolated basis-set limit estimates with the highly accurate reference basis-set limits suggests that the extrapolation of correlation contributions of binding energies with only cc-pVDZ and cc-pVTZ basis sets already yields the basis-set limit estimates close to the reference complete basis-set limits within 1 m-hartree in most cases, signifying the utility of this extrapolation method in the study of larger clusters. The natural extension of this extrapolation method to all electron correlated computations including core electrons with core-valence cc-pCVXZ basis sets is also made, which shows the similar accuracy of the extrapolated estimates for all electron correlated results as the valence electron only correlated results. The comparison of the MP2 and CCSD(T) basis-setmore » limit binding energies with DFT (density-functional theory) results manifests the capability and limitation of the current DFT methods in studying the binding of such clusters.« less