EFFECTIVE-MEDIUM TIGHT-BINDING MODEL FOR SILICON

A method for calculating the total energy of Si systems, which is base d on the effective-medium-theory concept of a reference system, is pre sented. Instead of calculating the energy of an atom in the system of interest, a reference system is introduced where the local surrounding s are similar. The energy of the reference system can be calculated se lf-consistently once and for ah while the energy difference to the ref erence system can be obtained approximately. We propose to calculate i t using the tight-binding linear-muffin-tin-orbital scheme with the at omic-sphere approximation (ASA) for the potential, and by using the AS A with charge-conserving spheres we are able to treat open systems wit hout introducing empty spheres. All steps in the calculational method are ab initio in the sense that all quantities entering are calculated from first principles without any fitting to experiment. A complete a nd detailed description of the method is given together with test calc ulations of the energies of phonons, elastic constants, different stru ctures, surfaces, and surface reconstructions. We compare the results to calculations using an empirical tight-binding scheme.