  We consider the Kramers--Smoluchowski equation at a low temperature regime
and show how semiclassical techniques developed for the study of the Witten
Laplacian and Fokker--Planck equation provide quantitative results. This
equation comes from molecular dynamics and temperature plays the role of a
semiclassical paramater. The presentation is self-contained in the one
dimensional case, with pointers to the recent paper \cite{Mi16} for results
needed in higher dimensions. One purpose of this note is to provide a simple
introduction to semiclassical methods in this context.
