Small cluster model of the NV centre in diamond

The singlet 1E and 1A1 energy levels of the Nitrogen-Vacancy centre’s ground state configuration each need two Slater determinants in theoretical models, posing difficulties for Density-Functional Theory (DFT) and Hartree-Fock approaches. Configuration Interaction (CI) can handle such states, but not the C284H144N− and C163H100N− clusters of our recent DFT study as CI computer time and memory scale worse than DFT with system size. Using smaller clusters to model bulk diamond introduces size errors. We examine the smaller diamond cluster C42H42N− using DFT to quantify the size error: if not too large it opens the way to CI calculations of these states.