Evaluation of semiempirical quantum-chemical methods in solid-state applications. I. Molecular-cluster calculations of defects in silicon

Three typical semiempirical molecular-orbital methods developed by chemists; the spectroscopic version of the complete neglect of differential overlap (CNDO/S), the modified intermediate neglect of differential overlap (MINDO/3), and the modified neglect of diatomic overlap (MNDO), are evaluated in molecular-cluster model applications. The ionization energies, wave-function localizations, and equilibrium geometries of the clusters X${\mathrm{Si}}_4$ ${\mathrm{H}}_{12}$, where X is a silicon, sulfur, or oxygen atom or a vacancy, are compared with results obtained from ab initio Hartree-Fock calculations using an extended Gaussian-orbital basis set with third-order Moeller-Plesset perturbation theory. The importance of using an absolute ionization-energy scale in locating levels relative to the crystalline band gap is discussed. It is concluded that the MINDO/3 is superior among the three methods in representing defect properties using a molecular-cluster model of defects in silicon.