THE 2D LOCALIZED MODES OF BIPOLARON IN cis-POLYACETYLENE

The localized vibrational modes around a bipolaron in cis-(CH)_x are studied by using a two-dimensional extension of the SSH model that includes the bond-bending term. A number of additional modes have been found, compared with the results based on the standard SSH model The amplitudes of the two directions (x and y direction) are comparable for most of the modes as in the trans-(CH)_x case. The number of localized modes and their frequencies depend not only on the coupling constant, but also on the bond-bending term and the parameter t₁ in removing the degeneracy of the ground state.