Efficient and Accurate Calculations of Electronic Excited States of the Negatively Charged NV-Center in Diamond

Electronic structure calculations of the properties of ultra-wide-bandgap materials and the effect of dopants in such materials can play an important role in the development of high-performance devices for e.g. quantum information science and ultraviolet optoelectronic emitters and detectors. Results of calculations based on the most commonly used method for electronic structure calculations of solids, density functional theory (DFT), reported in the literature on one of the most commonly used systems, the negatively charged NV-center in diamond, have been contradictory and controversial, leaving the impression that much more computationally intensive methods are needed to get accurate results [1]. This applies in particular to the excited states of the defect relevant for optical generation a pure spin state where DFT calculations from different groups have not even agreed on the ordering of the relevant energy levels, the two excited singlet states and the first excited triplet state. A new approach for calculating excited electronic states using density functionals based on direct optimisation and convergence on saddle points on the energy surface [2,3] has, however, been found to give remarkably close results to 'beyond RPA' embedding calculations and experimental data [4]. This is an important result as it opens the door for large scale, reliable calculations of other doped ultra-wide-bandgap materials without excessive computational effort. The approach presented makes calculations of excited states in materials similar in computational effort as ground state DFT calculations.<br/><br/>[1] 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).<br/><br/>[2] 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).<br/><br/>[3] A. V. Ivanov, Y. L. A. Schmerwitz, G. Levi and H. Jónsson, "Electronic Excitations of the Charged Nitrogen-Vacancy Center in Diamond Obtained Using Time-Independent Variational Density Functional Calculations", SciPost Physics scipost_202303_00008v1 (2023).<br/><br/>[4] He Ma, Marco Govoni, and Giulia Galli, "Quantum simulations of materials on near-term quantum computers", npj Computational Materials 6, 85 (2020).