Computer Physics Communications ELSEVIER Computer Physics Communications 82 (1994) 139—156 Hartree—Fock perturbed-cluster treatment of local defects in crystals I. The EMBED program: general features C. Pisani, F. Corà, R. Nada 1, R. Orlando Department of Inorganic, Physical and Materials Chemistry, University of Torino, via Giuria 5, 10125 Torino, Italy Received 6 August 1993 Abstract 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 crystal& 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. 1. Introduction For the quantum-mechanical study of local defects in crystals, the molecular-cluster [1], or the super-cell model [21 are usually adopted. One of many standard computer codes for the ab-initio quantum-mechanical treatment of molecules and crystals may then be us~d. In principle, the same problem can be solved at a more sophisticated level of approximation l~y using embedded-cluster approaches [3—7]: in this case, an isolated defect is considered, by taking its c~ystalline environment into account correctly. However, to our knowledge, no standard general-purpose computer code based on these techniques has been available to the scientific community generally up to now. It has been our purpose to fill this gap. We have implemented a comp~iter program for ab-initio embedded-cluster defect calculations, EMBED: its current version, EMBED93, is being distributed by our department [8].EMBED is based on the perturbed-cluster (PC) equations [9]which will be reviewed 1 Present address: Battelle, Pacific Northwest Laboratories, Richiand, Washington 99352, USA 0010-4655/94/$07.00 © 1994 Elsevier Science By. All rights reserved SSDI 0010-4655(94)00065-A