Browsing by Author "Zyubin, A. S."

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Potential energy surfaces for the lowest excited states of the nitrogen-vacancy point defects in diamonds: A quantum chemical study
(2008-09-10)
Zyubin, A. S.
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Mebel, A. M.
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Chang, H. C.
;
Lin, S. H.
;
應用化學系
Quantum chemical calculations of geometry relaxation in lowest excited states of neutral (NV(O)) and negatively charged (NV) nitrogen-vacancy point defects in diamond have been performed employing the CASSCF method with a finite NC(19)H(28) model cluster. Vibrations activated by the electronic transitions are determined by comparing calculated atomic displacements in the excited states with normal mode vectors, and the activated frequencies are evaluated as similar to 600 cm (1). The barrier for N migration through the vacancy in NV is estimated at the TD-B3LYP level and no significant decrease of this barrier (similar to 5 eV in the ground state) is found due to electronic excitations. (c) 2008 Elsevier B. V. All rights reserved.
Quantum Chemical Modeling of Photoabsorption Properties of Two- and Three-Nitrogen Vacancy Point Defects in Diamond
(2009-06-18)
Zyubin, A. S.
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Mebel, A. M.
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Hayashi, M.
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Chang, H. C.
;
Lin, S. H.
Quantum chemical calculations of the geometric and electronic structures and vertical transition energies for several low-lying excited states of the neutral and negatively charged vacancy-related point defects in diamond containing two and three nitrogen atoms (N(2)V(0), N(2)V(-), and N(3)V(0)) have been performed employing various theoretical methods (time-dependent density functional theory, equation-of-motion coupled cluster, and multireference perturbation theory) and different basis sets and using C(21)H(28), C(35)H(36), and C(51)H(52) finite model clusters. In the;round states, the vacancy-related atoms are found to be shifted away from the vacancy center by similar to 0.1 angstrom, whereas the positions of atoms from the second layer around them vacancy remain nearly unchanged, indicating a local character of geometry relaxation due to defects. The lowest excited states are formed with participation of the stretched (N(2)V) or broken (N(3)V) C-C bond and nonbonding combinations of nitrogen lone pairs as donors, with the C-C antibonding molecular orbital (MO) in N(2)V(0), broken C-C bond in N(3)V(0), and diffuse vacancy-related MOs serving as acceptors. Normally, the first excited states have a valence character, but the diffuse states are rather close in energy, especially for N(3)V(0) (2(2)A(1) and 1(2)E excited states). The first optically active excitation in the N(2)V(0) defect with the calculated energy of similar to 2.6 eV (in close agreement with the experiment) is formed by the electronic transition from the stretched C-C bond to the antibonding C-C MO, with an additional contribution from the combination of nitrogen lone pairs. For the negatively charged N(2)V(-) system, the lowest excitation to the 1(2)A(1) state is predicted to occur from the singly occupied antibonding b(1) MO to the empty diffuse a(1) orbital, but the CASPT2 calculated excitation energy, similar to 0.9 eV, underestimates the experimental zero phonon line observed at 1.26 eV. The lowest excited states of N(3)V(0), 2(2)A(1), and 1(2)E correspond to transitions from the singly occupied MO (SOMO) to the diffuse lowest vacant orbital and from the nonbonding combination of nitrogen lone pairs to SOMO, respectively, and have similar energies of about 3.1-3.3 eV, in agreement with the experimental photoabsorption band maximum at similar to 3 eV.
Quantum Chemical Modeling of Photoadsorption Properties of the Nitrogen-Vacancy Pint Defect in Diamond
(2009-01-15)
Zyubin, A. S.
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Mebel, A. M.
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Hayashi, M.
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Chang, H. C.
;
Lin, S. H.
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 (NV(0) and NV(-)) have been performed employing various theoretical methods and basis Sets and using finite model NC(n)H(m) clusters. Unpaired electrons in the ground doublet state of NV(0) 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 NV(0) 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
Quantum Chemical Modeling of Photoadsorption Properties of the Nitrogen-Vacancy Pint Defect in Diamond
(2009-01-15)
Zyubin, A. S.
;
Mebel, A. M.
;
Hayashi, M.
;
Chang, H. C.
;
Lin, S. H.
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