These are the energies of global minima I have found for various poly-alanine chains using a self-coded version of the AMBER95 force field. The two columns refer to slightly different versions of the force field, one with a dielectric constant (epsilon) of 1, the other with a "distance dependent" dielectric constant of epsilon = r, the distance between the two atoms. The "distance dependent" dielectric constant effectively screens the Coulombic term in the potential (decreases its range) and as such is supposed to partially represent the effect of water as a solvent. The energies are given in kcal/mol, and xyz files for each minimum are linked. If you believe these to be wrong, or have found a lower energy conformation for any of these polypeptides, please contact me.

All of the chains are capped at the N-terminus with an acetyl group and at the C-terminus with an -NHMe group.
 
 

Energies of global minima for Ac-(ala)n-NHMe in kcal/mol

n	epsilon = 1	epsilon = r
4	-33.162      xyz file	-6.272       xyz file
5	-36.047      xyz file	-11.115      xyz file
6	-39.567      xyz file	-12.069      xyz file
7	-41.508      xyz file	-16.178      xyz file
8	-44.397      xyz file	-20.344      xyz file
10	-51.134      xyz file	-28.785      xyz file
12	-58.994      xyz file	-37.301      xyz file
14	-69.119      xyz file	-45.858      xyz file
20	-100.231     xyz file	-71.631      xyz file
25	-126.574     xyz file	-93.154      xyz file