Quantum Chemical Modeling of Photoadsorption Properties of the Nitrogen-Vacancy Pint Defect in Diamond

Quantum chemical Calculations of geometric and electronic structure and vertical transition energies for several low-lying excited states of the neutral and negatively charged nitrogen-vacancy point defect in diamond (NV0 and NV-) have been performed employing various theoretical methods and basis Sets and using finite model NCnHm clusters. Unpaired electrons in the ground doublet state of NV0 and triplet state of NV- are found to be localized mainly on three carbon atoms around the vacancy and the electronic density on the nitrogen and rest of C atoms is only weakly disturbed. The lowest excited states involve different electronic distributions on molecular orbitals localized close to the vacancy and their wave functions exhibit a strong multireference character with significant contributions from diffuse functions. CASSCF calculations underestimate excitation energies for the anionic defect and overestimate those for the neutral system. The inclusion of dynamic electronic correlation at the CASPT2 level leads to a reasonable agreement (within 0.25 eV) of the calculated transition energy to the lowest excited state with experiment for both systems. Several excited states for NV- are found in the energy range of 2-3 eV, but only for the 1(3)E and 5(3)E states the excitation probabilities from the ground state are significant, with tile first absorption band calculated at similar to 1.9 eV and the second lying 0.8-1 eV higher in energy than the first one. For NV0 we predict the following order of electronic states: 1(2)E (0.0), 1(2)A(2) (similar to 2.4 eV), 2(2)E (2.7-2.8 eV), 1(2)A(1), 3(2)E (similar to 3.2 eV and higher). (C) 2008 Wiley Periodicals, Inc. J Comput Chem 30: 119-131, 2009