Theoretical study of polaron binding energy in conformationally disrupted oligosilanes.

Density functional theory was used for a quantum chemical study of oligo[methyl(phenyl)silylene] structures containing a conformational defect: a kink in the silicon backbone. Oligomers were studied in the neutral state as well as in the form of positive (P(+)) and negative (P(-)) polaron quasiparticles. Computations performed using the B3LYP model and the 6-31G(d) basis set revealed that the charge distribution is not influenced by the presence of the kink, but the positive charge on the Si backbone differs slightly in P(+) and P(-) quasiparticles. On the other hand, the spin density is significantly shifted away from the chain part that contains the kink, and this effect is more intense in P(-) polarons. Changes in electron density are also evident from the frontier molecular orbital distribution. The deformation energy (which is associated with the relaxation of polarons) decreases with the number of atoms in the oligomer backbone in P(+) but shows the opposite behavior for P(-) quasiparticles.