looking for headgroup charges for PC (phosphatidyl choline)

 I try to simulate lipid bilayers (POPC: Palmitoyl-oleoyl-phosphatidyl
 choline) using an X-PLOR (CHARMm) like MD program. To make the simulation as
 "good" (realistic, reliable, sound, ...) as possible I am looking for
 simulation parameters, e.g. charges for the PC headgroup atoms (extended
 So far I have three different charge sets (one from Groningen, two from our
 group) but none is really convincing.
 A literature search did not produce any results.
 Therefore I would like to ask people who are doing MD simulations of lipids
 to share their parameter sets (preferable X-PLOR rtf and parameter files, but
 any format is welcome) with me or to point me in the direction of relevant
 Thank you very much in advance,
 Servus, Helmut  (W9/DH0MAD) _________________________________________________
 heller.,at,.lisboa.ks.uiuc.edu   "Knowledge must be gathered and cannot be
 FAX:   (217)244-1080                      ZEN, one of BLAKES7
 Phone: (217)244-6914,       -------------------------------------------------
 Helmut Heller, University of Illinois at Urbana-Champaign, Beckman Institute
 Theoretical Biophysics Group, Room 3143, MC 251
 405 N. Mathews Ave., Urbana, IL 61801, U.S.A.