Excited singlet and triplet states of the negatively charged NV-center in diamond calculated using a variation density functional approach

The first two excited singlet states and the first excited triplet state as well as the triplet ground state of the negatively charged NV-center in diamond have been calculated using a novel approach based on convergence to the corresponding saddle points on the electronic energy surface. The method makes use of direct optimization of the orbitals in a cell subject to periodic boundary conditions [1]. The PBE density functional is used with PAW representation of the inner electrons. After spin purification has been applied, the calculated energy differences between the states are found to be in remarkably close agreement with recent RPA calculations as well as a cluster calculation using a multiconfigurational approach [3]. The approach used here makes calculations of excited states in materials similar in computational effort as ground state DFT calculations.

[1] A. V. Ivanov, G. Levi, E. Ö. Jónsson and H. Jónsson,"Method for Calculating Excited Electronic States Using Density Functionals and Direct Orbital Optimization with Real Space Grid or Plane-Wave Basis Set",J. Chem. Theory Comput. 17, 5034 (2021).

[2] He Ma, Marco Govoni, and Giulia Galli, "Quantum simulations of materials on near-term

quantum computers", npj Computational Materials 6, 85 (2020).

[3] Churna Bhandari, Aleksander L. Wysocki, Sophia E. Economou, Pratibha Dev, and Kyung-

wha Park, "Multiconfigurational study of the negatively charged nitrogen-vacancy center in

diamond", Phys. Rev. B 103, 1 (2021).