Structure and energetics of Li/Na, Li/K, and K/Na bimetallic hexamers

Abstract

A systematic study of neutral mixed clusters, Li6−xNax, Li6−xKx and K6−xNax (x = 0–6), was performed within the framework of density functional theory. The aim of this work is to explore the geometry variation and the energy change of homonuclear hexamers (Li6 and K6) induced by impurities. It is found that the geometry of bimetallic hexamers varies with their compositions. The geometries of resulting clusters show evolution from D4h symmetry for Li6 to D3h symmetry for Na6 and K6. The stability of bimetallic hexamers has been also explained in terms of binding energy, excess energy, the second difference in energy, and the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gaps. It is found that replacing each Li–Li bond with Li–Na or Li–K bonds decreases the cluster stability, while replacing each K–K bond by K–Na leads to stability enhancement. Examining the cluster stability, excess energy and second difference in energy reveal that among studied bimetallic hexamers, Li2Na4 is the most stable mixed hexamer.