Equilibrium geometries of low-lying isomers of some Li clusters,within Hartree-Fock theory plus bond order or MP2 correlation corrections

摘要

In a recent study by Kornath et al [J.Chem.Phys.118,6957 (2003)],the Li_n clusters with n = 2,4,and 8 have been isolated in argon matrices at 15 K and characterized by Raman spectroscopy.This has prompted us to carry out a theoretical study on such clusters up to n= 10,using Hartree-Fock theory,plus low-order M011er-Plesset perturbation corrections.To check'against the above study of Kornath et ai,as a by-product we have made the same approximations for n = 6 and 8 as we have for n = 10.This has led us to emphasize trends with n through the Li_n clusters for (i) ground-state energy,(ii) HOMO-LUMO energy gap,(iii) dissociation energy,and (iv) Hartree-Fock eigenvalue sum.The role of electron correlation in distinguishing between low-lying isomers is plainly crucial,and will need a combination of experiment and theory to obtain decisive results such as that of Kornath et al for Li_8.In particular,it is shown that Hartree-Fock theory plus bond order correlations does account for the experimentally observed symmetry T_d symmetry for Li_8.