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Ab initio calculations on urea
Author(s) -
Elbert Stephen T.,
Davidson Ernest R.
Publication year - 1974
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.560080604
Subject(s) - excited state , atomic physics , chemistry , molecular orbital , ionization energy , atomic orbital , configuration interaction , singlet state , ab initio , wave function , ground state , valence (chemistry) , ab initio quantum chemistry methods , ionization , physics , molecule , quantum mechanics , electron , ion , organic chemistry
Abstract Multiconfiguration wave functions constructed from contracted Gaussian‐lobe functions have been found for the ground and valence‐excited states of urea. ICSCF molecular orbitals of the excited states were used as the parent configurations for the CI calculations except for the 1 A 1 (π → π*) state. The 1 A 1 (π → π*) state used as its parent configuration an orthogonal linear combination of natural orbitals obtained from the second root of a three‐configuration SCF calculation. The lowest excited states are predicted to be the n π → π* and π → π* triplet states. The lowest singlet state is predicted to be the n π → π* state with an energy in good agreement with the one known UV band at 7.2 eV. The π → π* singlet state is predicted to be about 1.9 eV higher, contrary to several previous assignments which assumed the lowest band was a π → π* amide resonance band. The predicted ionization energy of 9.0 eV makes this and higher states autoionizing.