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A theoretical study of the diffuseness of the V ( 1 B 1 u ) state of planar ethylene
Author(s) -
Lindh Roland,
Roos Björn O.
Publication year - 1989
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560350617
Subject(s) - ground state , physics , excited state , atomic physics , wave function , yield (engineering) , state (computer science) , mathematics , algorithm , thermodynamics
Abstract The ground ( N ) state and the 1 B 1 u ( V ) excited state of planar ethylene have been studied at the CPF and MR ‐ SDCI levels of theory, using an extended CGTO basis set of the ANO type. The investigation especially addresses the near‐degeneracy problem in the ground state and the coupling between the diffuse character of the π* orbital and the amount of correlation included in the wave function of the V state. The MR ‐ SDCI results yield a vertical excitation energy in the range 7.8–8.0 e V , whereas the CPF result is 7.9 e V . The best MR ‐ SDCI result for 〈1π*‖ z 2 ‖1π*〉 is 7.8, whereas CPF calculations based on MR ‐ SDCI INOS give the value 6.7. It is clear from the results that these numbers have not converged and that more extended calculations than was possible in the present work would yield an even more compact wave function.