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Estimates of the structure and dimerization energy of polyacetylene from ab initio calculations on finite polyenes

✍ Scribed by H. Guo; J. Paldus

Publisher
John Wiley and Sons
Year
1997
Tongue
English
Weight
242 KB
Volume
63
Category
Article
ISSN
0020-7608

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✦ Synopsis

Ž .

Ab initio calculations at the Hartree᎐Fock HF and the second-order Møller᎐Plesset Ž . MP2 levels are performed for finite polyenes C H to estimate the structure and 2 n 2 nq2 Ž . dimerization energy E of polyacetylene. The effect of electron correlation on the dim structure of finite polyenes is analyzed in detail. The MP3r6-31G* CsC and C-C bond lengths in polyacetylene are estimated by a simple extrapolation method using empirical ẘ Ž . corrections for the MP2 deficiencies, yielding values CsC MP3 ; 1.36 A and ˚Ž . x Ž C-C MP3 ; 1.44 A that are in a good agreement with experiment CsC s 1.36 A and ˚. C-C s 1.44᎐1.45 A . Comparison is also made with other theoretical estimates of polyacetylene structure. E is approximated by the energy difference between the dim equilibrium and hypothetical polyenic structures. It is estimated that E is ; 1.4᎐1.5 dim Ž . kcalrmol 0.06᎐0.07 eV per carbon᎐carbon bond at the HF level with 4-21G and 6-31G* Ž . basis sets and ; 0.3᎐0.5 kcalrmol 0.013᎐0.022 eV at the MP2 level with the 6-31G* basis set. It is concluded that E is very sensitive to the level of approximation dim employed so that a proper treatment of electron correlation is essential to obtain a reliable estimate of the dimerization energy.

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