CRYSTAL and EMBED, two computational tools for the ab initio study of electronic properties of crystals

The present study discusses the main features of the two programs CRYSTAL a nd EMBED developed for the ab initio study of the electronic properties of perfect periodic structures and of crystals with local defects, respectivel y. After a brief historical introduction, the structure of CRYSTAL is outli ned and some specific aspects are discussed in detail: the use of local bas is functions, the way of dealing with the Coulomb and the exchange series, the exploitation of point symmetry, the possibility to adopt either the Har tree-Fock approach or one among a variety of Kohn-Sham Hamiltonians. The pr esent capabilities of the program are illustrated by a survey of selected a pplications from existing literature. Information is provided concerning wo rk in progress aimed at removing some of the limitations of the code and im proving its performance. The characteristics of EMBED are analyzed with emp hasis given to the critical aspects of the method: limits of validity of th e fundamental approximation on which the embedding technique relies, proble ms of convergence of the self-consistent procedure; and the delicate issue of the estimate of the defect formation energy. Again, a critical survey of applications clarifies the capabilities of the code. The envisaged improve ments to be introduced in a forthcoming release of EMBED are presented. The present and prospective role of the two programs in the field of computati onal studies of condensed matter problems is outlined. (C) 2000 John Wiley & Sons, Inc.