Systematic study of electron localization in an amorphous semiconductor

We investigate the electronic structure of gap and band tail states in amorphous silicon. Starting with two 216-atom models of amorphous silicon with defect concentration close to the experiments, we systematically study the dependence of electron localization on basis set, density functional, and spin polarization using the first-principles density-functional code SIESTA. We briefly compare three different schemes for characterizing localization: information entropy, inverse participation ratio, and spatial variance. Our results show that to accurately describe defected structures within self-consistent density-functional theory, a rich basis set is necessary. Our study revealed that the localization of the wave function associated with the defect states decreases with larger basis sets and there is some enhancement of localization from generalized gradient approximation relative to local-density approximation. Spin localization results obtained via local spin-density approximation (LSDA) calculations are in reasonable agreement with experiment and with previous LSDA calculations on a-Si:H models.