Hartree-Fock perturbed-cluster treatment of local defects in crystals: I. The EMBED program: general features

This paper is the first of a series to illustrate the characteristics of EMBED, a computer program for the ab-initio Hartree-Fock determination of the electronic structure of local defects in crystals. In its essence, the method consists in first solving the periodic problem for the host crystal, then looking for a cluster solution concerning the defect region, which is corrected self-consistently for coupling to the surroundings. A comprehensive description of the program is provided here, while deferring to subsequent papers detailed accounts of some features of the computational scheme which deserve closer analysis for a proper use of the code. The notational conventions are introduced, the basic “perturbed-cluster” equations are reported and discussed, the techniques for calculating the Fock matrix elements and for evaluating the defect formation energy are illustrated. The scheme of the program is presented subsequently. Finally, some test calculations are reported, which serve the purpose both to illustrate the scope of the method and its limitations, and to give an idea of the computational requirements.