  We study the interaction of lipid bilayers with short chain alcohols using
molecular dynamics on different length scales. We use detailed atomistic
modeling and modeling on the length scale where an alcohol is just an
amphiphilic dimer. Our strategy is to calibrate a coarse--grained model against
the detailed model at selected state points at low alcohol concentration and
then perform a wider range of simulations using the coarse--grained model. We
get semiquantitative agreement with experiment for the major observables such
as order parameter and area per molecule. We find a linear increase of area per
molecule with alcohol concentration. The alcohol molecules in both system
descriptions are in close contact with the glycerol backbone. Butanol molecules
can enter the bilayer to some extent in contrast to the behavior of shorter
alcohols. At very high alcohol concentrations we find clearly increased
interdigitation between leaflets.
