Molecular dynamics-modified neglect of diatomic overlap study of the thermal isomerization mechanism from cis to trans form in polyacetylene

In the present work we have studied the thermal isomerization process of polyacetylene (PA) from the trans-cisoid (TC) and cis-transoid (CT) forms to the trans-transoid (TT) form. We have used the molecular dynamics-modified neglect of diatomic overlap (MD-MNDO) method, which combines a molecular dynamics algorithm with the MNDO approximation. The thermal isomerization mechanism from TC-to-TT form is fully described. In our simulation, starting from the CT form in its ground state and heating the system up to T=450 K, there is no evidence of an isomerization process. However, a model, which simulate the subtraction of some charge from the double bonds of the PA chains, is able to give important insights into the isomerization mechanism from the CT to the TT form. This charge subtraction is essential to induce a CT-to-TC local transformation followed by the TC-to-TT isomerization.