  We construct a $k[[Q]]$-linear predifferential graded Lie algebra $L^*_{X/S}$
associated to a log smooth and saturated morphism $f: X \rightarrow S$ and
prove that it controls the log smooth deformation functor. This provides a
geometric interpretation of a construction by Chan-Leung-Ma whereof $L^*_{X/S}$
is a purely algebraic version. Our proof crucially relies on studying
deformations of the Gerstenhaber algebra of polyvector fields and interestingly
does not need to keep track of the log structure. The method of using
Gerstenhaber algebras is closely related to recent developments in mirror
symmetry.
