Screened configuration interaction method for open-shell excited states applied to NV centers

We present a computational approach, based on density functional theory and screened configuration interaction, able to accurately treat highly correlated electron spins localized around semiconductor defects, typically occurring in the context of qubit implementations. The method is computationally not more demanding than a usual density functional theory calculation, which makes it suitable for the calculation of isolated defects, or defect complexes, typically requiring large simulation cells. We illustrate the approach by applying it to the three different charge states of the nitrogen vacancy defect in diamond and obtain very good agreement with experiment.