NONLINEAR VIBRATIONAL EXCITATIONS IN MOLECULAR-CRYSTALS MOLECULAR MECHANICS CALCULATIONS

The coupling constant for vibrational solitons chi has been examined in a molecular mechanics model for acetanilide (ACN) molecular crystal. According to A.C.Scott, solitons can form and propagate in solid acetanilide over a threshold energy value. This can be regarded as a structural model for the spines of hydrogen bond chains stabilizing the alpha helical structure of proteins. A one dimensional hydrogen bond chain of ACN has been built, for which we have found that, even though experimental parameters are correctly predicted, the excessive rigidity of the isolated chain prevents the formation of a localized distortion around the excitation. Yet, C = O coupling value with softer lattice modes could be rather high, allowing self-trapping to take place.