Localization of polarons: A calculation in the adiabatic approximation

We have calculated the properties of an extra charge carrier in a polar medium in using a realistic self-consistent tight-binding molecular-dynamics method at finite temperature. This approach permits a quantitative, realistic study of polaron structure at finite temperatures. Using rutile titanium dioxide, as an example, we report numerical data on the participation ratio as a function of temperature. The results are consistent for a transition from a delocalized to a localized polaron at a temperature below about 100 K. We interpret the observed localization as arising from an Anderson-like mechanism in which the disorder associated with the thermal motion of the atoms localizes the electron. We briefly discuss implications for transport.