Multireference determinant CI calculations and CASSCF calculations on the CH3-NO2 decomposition pathway of nitromethane
| Autor: | C. Chabalowski, P. C. Hariharan, Joyce J. Kaufman, Matti Hotokka |
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| Rok vydání: | 2009 |
| Předmět: |
Nitromethane
Extrapolation Multireference configuration interaction Configuration interaction Condensed Matter Physics Atomic and Molecular Physics and Optics chemistry.chemical_compound Atomic orbital chemistry Excited state Complete active space Physical and Theoretical Chemistry Atomic physics Wave function |
| Zdroj: | International Journal of Quantum Chemistry. 28:221-235 |
| ISSN: | 1097-461X 0020-7608 |
| DOI: | 10.1002/qua.560280822 |
| Popis: | The multideterminant character of CH3NO2. at its ground-state equilibrium geometry, involving the ground SCF state plus a doubly excited (π*-like) [2] configuration out-of-plane with respect to the plane of the NO2 group, has been studied by MRD-CI (multireference determinant configuration interaction) and CASSCF (complete active space SCF) methods to elucidate the configurations required for an accurate description of the system along the decomposition pathway of the C-N bond. In the MRD-CI work, the ground and three lowest electronically excited states were investigated at a number of values of r(C-N); at each point about 850,000 configurations were generated by single and double excitations, of which ˜4500 were included explicitly in the larger MRD-CI wave function by selection criteria. Perturbation extrapolation procedures then provided the correction for the omitted configurations, and this was augmented/supplemented by a Davidson-type correction for the higher than double excitations. The CASSCF investigation included seven active orbitals. Both the MRD-CI results and the CASSCF results verified our earlier findings of the two-determinant character of CH3NO2 even in its ground electronic state at equilibrium geometry. Further, both these results indicate that a number of additional determinants become important along the C-N decomposition pathway. |
| Databáze: | OpenAIRE |
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