Title: A first principles study of the Stark shift effect on the zero-phonon line of the NV center in diamond

Abstract: Point defects in semiconductors are attractive candidates for quantum information science applications owing to their ability to act as spin-photon interface or single-photon emitters. However, the coupling between the change of dipole moment upon electronic excitation and stray electric fields in the vicinity of the defect, an effect known as Stark shift, can cause significant spectral diffusion in the emitted photons. In this work, using first principles computations, we revisit the methodology to compute the Stark shift of point defects up to the second order. The approach consists of applying an electric field on a defect in a slab and monitoring the changes in the computed zero-phonon line (i.e., difference in energy between the ground and excited state) obtained from constraining the orbital occupations (constrained-DFT). We study the Stark shift of the negatively charged nitrogen-vacancy (NV) center in diamond using this slab approach. We discuss and compare two approaches to ensure a negatively charged defect in a slab and we show that converged values of the Stark shift measured by the change in dipole moment between the ground and excited states ($\Delta \mu$) can be obtained. We obtain a Stark shift of $\Delta \mu$=2.68D using the semi-local GGA-PBE functional and of $\Delta \mu$=2.23D using the HSE hybrid-functional. The results of the slab computations are significantly different than those obtained with Modern Theory of Polarization ($\Delta \mu$=4.34D for GGA-PBE) indicating a potential issue with the combination of constrained-DFT and Modern Theory of Polarization, at least in certain codes.