Accurate defect levels in semiconductors and insulators from Koopmans spectral functionals

Point defects in insulating crystalline materials lead to the formation of impurity levels within the forbidden gap that play an essential role in determining the properties of electronic devices. Despite its computational feasibility, density-functional theory lacks a proper description of spectral properties and does not provide an accurate prediction of the defect binding energy, and more accurate formulations are often hindered by the size of the supercells required to damp the spurious interactions of the defect state with its periodic replicas. Here, we compute the position of defect levels using Koopmans spectral functionals [1], a novel orbital-density-dependent approach that captures the physics of the electron addition/removal process. Recent works have proven the accuracy of Koopmans functionals in predicting the band structure of semiconductors and insulators [2,3,4], laying the groundwork for a correct description of defect states.

[1] I. Dabo, A. Ferretti, N. Poilvert, Y. Li, N. Marzari, and M. Cococcioni, Phys. Rev. B 82, 115121 (2010)

[2] N. L. Nguyen, N. Colonna, A. Ferretti, and N. Marzari, Phys. Rev. X 8, 021051 (2018)

[3] R. De Gennaro, N. Colonna, E. Linscott, and N. Marzari, Phys. Rev. B 106, 035106 (2022)

[4] N. Colonna, R. De Gennaro, E. Linscott, and N. Marzari, J. Chem. Theory Comput. 18, 5435 (2022)