Extrapolation of finite cluster and crystal-orbital calculations on trans-polyacetylene

Sequences of total energies of trans-polyacetylene were obtained by either finite cluster or crystal-orbital calculations. Several different extrapolation methods were employed to improve the convergence of these two sequences. The properties of the extrapolation algorithms are discussed with emphasis on efficiency and reliability for short strings of physical input data. Four decimal digits were gained by extrapolation in the case of the finite cluster energies, but, at most, 2 decimal digits in the case of the crystal-orbital energies. The extrapolation of the finite cluster energies gave results that are almost as good as the results produced by the extrapolation of the crystal-orbital energies, and that are better than the unextrapolated crystal-orbital energies.