Extended Basis-Set LCSTO—MO—SCF Calculations on the Ground State of Carbon Dioxide

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Abstract
Extended basis‐set SCF—STO—MO wavefunctions for the ground state of CO2 are reported. In particular, the effect of doubling the number of 2pσ basis functions and the effect of changing their orbital exponents has been investigated, together with the effect of addition of 3dσC basis functions. The effect of expanding the π basis set by addition of extra 2pπC basis functions and 3dπO1, O2 basis functions is also shown. A wave‐function using the best σ basis set together with the best π basis set used in these calculations would give a molecular energy of approximately 9 eV below that obtained from a `best atom' minimal basis‐set calculation. This is to be compared with the estimated Hartree—Fock molecular energy which is approximately 24 eV below the ``best atom'' minimal basis‐set value. This highlights the importance of the choice of basis functions and minimization of the total energy with respect to orbital exponents in the case that the number of basis functions out of which MO's can be constructed is limited. The quadrupole moment of CO2 is computed from two of the wavefunctions reported.