Abstract
The cis–trans energetics of three polyacetylene isomers are studied by means of ab initio crystal orbital calculations. Systematic convergence data for optimized geometry, total energy, Koopman’s ionization potential, band gap, and population on hydrogen are given for both the minimal STO‐3G and the split valence 4‐31G basis sets with respect to the number of neighboring cells. Using a modified symmetric cutoff criterion, the relative energies of the all‐trans, cis–transoid, and trans–cisoid isomers are calculated to be 0.0, 1.8, and 1.9 kcal/mol per C2H2 units at the STO‐3G level, and 0.0, 2.1, and 3.6 kcal/mol per C2H2 units at the 4‐31G level. The STO‐3G results agree well with those of two previous works, whereas the 4‐31G calculations show a relatively accurate energy difference between cis–transoid and trans–cisoid polyacetylene. The modified symmetric cutoff procedure is proven to be suitable for calculating the energy difference between polyacetylene isomers.
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