LDA+U/GGA+U Calculations of Structural and Electronic Properties of CdTe: Dependence on the Effective U Parameter

We present a detailed assessment of the structural and electronic properties of CdTe calculated by density functional theory (DFT) with on-site Coulomb self-interaction potentials (LDA+U/GGA+U) on the Cd 4d band. We systematically calculate the lattice constants, bulk moduli, elastic constants, band structure, and density of states as a function of the U value, and compare the results with those calculated by using standard LDA/GGA and the hybrid functional (HSE06). Our study gives a more accurate account of the strong localization effect of Cd 4d electrons onto the overall electronic structure, in particular to the nature of localized Cd 4d derived bands and delocalized Te 5s derived bands and the coupling between them. We find that the s-d coupling is significant, which is underestimated within conventional DFT calculations (showing a single s-like peak, in disagreement with the experiments). LDA+U removes this discrepancy by shifting down the Cd-4d band closer to the Te-5s band, enhancing the s-d coupling, and leading to the appearance of two s-like peaks, which perfectly explains the so-called low intensity "shoulder" on the high-energy side of the Cd-4d peak in experimental spectra. Moreover, our results indicate LDA+U reveals an much more acceptable agreement with experiment at a adequate U than HSE06 does. A well balanced choice of U within LDA+U scheme is proposed to be at 7 eV.