  In this letter we obtain the finite-temperature structure of 180^o domain
walls in PbTiO3 using a quasi-harmonic lattice dynamics approach. We obtain the
temperature dependence of the atomic structure of domain walls from 0K up to
room temperature. We also show that both Pb-centered and Ti-centered 180^o
domain walls are thicker at room temperature; domain wall thickness at T=300K
is about three times larger than that of T=0K. Our calculations show that
Ti-centered domain walls have a lower free energy than Pb-centered domain walls
and hence are more likely to be seen at finite temperatures.
