SHELL - A CODE FOR LATTICE-DYNAMICS AND STRUCTURE OPTIMIZATION OF IONIC-CRYSTALS

This paper describes Shell, a program which uses lattice statics and q uasiharmonic lattice dynamics to calculate analytically the free energ y of a crystal, and its derivatives with respect to both internal and external strains, at a given temperature and pressure. These quantitie s can be used to perform efficient fully dynamic structure optimisatio n of unit cells containing hundreds of ions. Interactions are via shor t-ranged spherically symmetric pairwise and three-body potentials as w ell as the usual Coulomb terms, and polarizability effects may be acco unted for by use of the shell model. Application of the code to the ru tile phase of MgF2 is briefly described. (C) 1998 Elsevier Science B.V .