First-principles calculations of pseudolocal vibrational modes: the case of Cu and Cu pairs in Si.

Pseudolocal vibrational modes (pLVMs) are defect-related vibrational modes which are localized despite being below the phonon maximum. Such modes are sometimes seen as phonon replicas in photoluminescence spectra. The pLVMs associated with two copper-related defects are calculated from first-principles density-functional theory in periodic supercells. The localization of the pLVMs is quantified using the magnitude of the eigenvectors of the dynamical matrix.