High-spin electronic interaction of small lithium and sodium cluster formation in the excited states

Abstract

We have carried out the MRCI ab initio calculations for small lithium and sodium clusters, and elucidate the interaction between atoms in various high-spin electronic states, in terms of the quantum mechanical energy densities based on the regional density functional theory [Tachibana, J. Chem. Phys. 115, 3497 (2001)]. When the separated two electronic drop regions, where the electronic kinetic-energy density is positive, connect to each other, it is observed that ratios of occupation on configurations change rapidly in the Li2 molecule. These results are considered as one of the evidences that valence electrons can move around both two Li atoms freely in the meaning of classical mechanics. The shape of electronic drop region depends strongly on the electronic state and represents the characteristics of interaction clearly, and the electronic tension density also gives new images of microscopic electronic stresses. Furthermore, we have clarified the most stable structures of Li3 and Li4 for the high-spin electronic state, which are respectively different from the most stable structures for the low-spin electronic state. The stabilization energy due to taking in a Li atom is raised gradually as the number of atoms in Lin cluster increases in the initial stage of cluster propagation. The formation energies of Na2, Na3, and Na4 clusters are much smaller than that of the corresponding lithium clusters.