ABINITIO HARTREE-FOCK CALCULATIONS FOR PERIODIC COMPOUNDS - APPLICATION TO SEMICONDUCTORS

The ab initio Hartree-Fock crystalline orbital program CRYSTAL is applied to diamond, silicon, BN, BP, SiC and AlP. The effects of the computational parameters controlling the accuracy of the infinite Coulomb and exchange series are analysed; the performances of five standard (but re-optimised in the valence part) molecular basis sets (STO-3G; 3-21G; 3-21G*; 6-21G; 6-21G*) are documented with reference to equilibrium binding energy, lattice parameter and bulk modulus. The analysis is then extended, with the largest basis set, to transverse optical phonon frequencies, band-structure and charge-density data. The results show trends similar to those expected from molecular calculations; typically, the mean lattice parameter and bulk modulus errors obtained at a 6-21G* level are about +1% and +10%, respectively.