Premium
Simplified methods for ab initio calculations. The valence states of CH 2 and CH 2 +
Author(s) -
Gervy D.,
Verhaegen G.
Publication year - 1977
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.560120111
Subject(s) - valence (chemistry) , ab initio , atomic physics , chemistry , gaussian , ionization energy , ab initio quantum chemistry methods , electronic correlation , ionization , physics , molecule , computational chemistry , quantum mechanics , ion
Three simplifying methodds are discussed and applied to the four lowest valence states of CH 2 ( 3 B 1 , 1 A 1 , 1 B 1 and 1 Σ g + ( 1 A 1 * )) and to the two lowest of CH 2 + ( 2 A 1 and 2 ∏ u ( 2 B 1 )). These methods concern: (1) the development of polarization functions for Gaussian‐lobe basis sets by least‐square fitting of numebrical multiconfigurational atomic fuinctions (this approach is tested also on (C 2 H 2 , (2) the use of intermediate Hamiltonians to calculate avoided crossings between potential hypersurfaces, and (3) thecalculation of correlation energies using an atoms‐in‐molecule approach. The calculated equilibrium geometries of the CH 2 States are within 0.02 Å and 5° of available experimental data. The calculated term values and ionization potentials, T e ( 1 A 1 = 0.35 eV, T e ( 1 B 1 ) = 1.22 eV, T e ( 1 Σ g + ( 1 A 1 * )) 2.48 eV, I.P. ( 2 A 1 ) = 10.39 eV and I. P. ( 2 ∏ u ( 2 B 1 )) = 10.58 eV, are in agreement with some recent theoretical studies, and are very close to existing experimental information.