A scaled force field for polyenes derived from ab initio calculations including electron correlation effects

Geometries and harmonic force constants were calculated for trans‐ and gauche‐butadiene and for trans‐ hexatriene using SCF and electron correlation (ACPF) methods. By comparing the results of these two procedures trends in the errors of the SCF values are discussed. Although diagonal SCF force constants are usually too large in relation to correlated results, the opposite is true (in absolute value) for several off‐diagonal force constants referring to the carbon backbone. Scaling techniques are used in order to correct for these deficiencies and also for anharmonicity effects. On that basis scaled SCF force fields and vibrational frequencies were calculated for trans‐polyenes up to 14 carbon atoms and for the infinite chain.