Potential Energy Functions for Atomic Solids V. Application to
Alkali Metal Solids
Jian-Yun Fang, Roy L. Johnston and John N. Murrell
School of Chemistry and Molecular Sciences, University of Sussex,
Falmer, Brighton BN1 9QJ, United Kingdom.
Article: Molecular Physics 1993,78, 1405-1422.
Abstract
Empirical potential functions comprising two-body and three-body terms
have been derived for the alkali metals by fitting parameters to the
phonon frequencies, elastic constants, lattice energies and lattice
distances of the body-centred-cubic (bcc) solids. These potentials
give, in all cases, very similar energies for the bcc,
face-centred-cubic (fcc) and hexagonal closest packing (hcp) structures,
with simple cubic (sc), diamond and various two-dimensional structures
being much less stable. The lithium potential has been used to predict
structures and stabilities of neutral (Li)n microclusters. No 'magic
number' stabilities have been found. For n>=6 the structures can, in
the main, be described as face-fused tetrahedra, and ab initio
calculations support these structures in some important cases
(e.g. n = 6,7).