Quantum chemical calculations of geometrical 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-) were performed

by using 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- were found to be localized mainly on three carbon atoms around the vacancy,

while the electronic density on the nitrogen and rest of the C atoms was only

slightly disturbed. The lowest excited states involved different electronic

distributions on molecular orbitals localized close to the vacancy, and their wave

functions exhibited a strong multireference character; with significant contributions

arising from diffuse functions. CASSCF calculations under-estimated the

excitation energies for the anionic defect and over-estimated those for the neutral

system. The inclusion of dynamic electronic correlations at the CASPT2 level led

to a reasonable agreement (within 0.25eV) of the calculated transition energy to the

lowest excited state with experimental results for both systems. Several excited

states for NV- were found in the energy range of 2 to 3eV, but the excitation

probabilities from the ground state were significant only for the 13E and 53E states;

with the first absorption band calculated to be at approximately 1.9eV and the

second lying 0.8 to 1eV higher in energy than the first one. For NV0, the order of

electronic states was predicted to be: 12E (0.0), 12A2 (approximately 2.4eV), 22E

(2.7 to 2.8eV), 12A1, 32E (approximately 3.2eV and higher).

Quantum Chemical Modeling of Photo-Adsorption Properties of the Nitrogen-

Vacancy Point Defect in Diamond. A.S.Zyubin, A.M.Mebel, M.Hayashi,

H.C.Chang, S.H.Lin: Journal of Computational Chemistry, 2009, 30[1], 119-31