LCAO Self-Consistent Field Calculation of the Ground State of Carbon Dioxide

LCAO molecular orbitals and ionization potentials have been calculated for the ground state of CO2 using Roothaan's LCAO self-consistent field method. The interactions of all electrons have been explicitly considered, and no extra-geometrical empirical data have been used. The calculated molecular orbitals are in general agreement with those predicted by Mulliken and Moffitt from semi-empirical considerations. The calculated ionization energies are 11.5 ev for a 1πg electron and 17.9 ev for a 2σu electron, compared with the experimental 13.8 ev, and 18.0 ev, respectively. The evaluation of the large number of integrals over atomic orbitals that occur, is discussed in an appendix. All the larger integrals were calculated exactly, the smaller ones approximated. Useful approximation methods for some of these integrals are considered.