Extracting Information from a Supercell Calculation

ABSTRACTA number of corrections must be made to a first-principles defect supercell calculation if the results are to be of use in calculating properties of isolated defects. These are illustrated for a tetrahedral self-interstitial in silicon, which places two electrons in the conduction band. One correction arises from the familiar Coulomb enhancement of the gap relative to local-density-approximation (LDA) calculations. The second is for the capture of these electrons in a double donor state. The third arises from the extra kinetic energy of the electrons due to their partial filling of the conduction band for a finite-sized supercell. The fourth is the partial occupation of the defect resonance, lowering the kinetic energy but increasing the Coulomb energy. A model is introduced which allows estimates of each of these corrections, with parameters which can be tuned to LDA supercell calculations. It allows then prediction of a wide range of properties dependent upon the defect in question.