Ethylene Molecule in a Gaussian Basis. I. A Self-Consistent-Field Calculation

Abstract

A series of nonempirical calculations are reported for the ethylene molecule, using the LCAO—SCF method with Gaussians as the basic expansion functions. Ground-state calculations on the planar molecule at its experimental equilibrium position are reported for ten basis sets of different sizes. The pi orbitals are found to be relatively independent of the sigma orbitals, with excitation energies for the lowest 1Ag and 3B3u states giving fair agreement with experiment, the lowest 1B3u state being too high. Calculations on the twisted and stretched molecule using a small basis set give structural parameters in good agreement with experiment.