looking for headgroup charges for PC (phosphatidyl choline)



Hello,
 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
 good
 simulation parameters, e.g. charges for the PC headgroup atoms (extended
 atoms).
 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
 literature.
 Thank you very much in advance,
 Servus, Helmut  (W9/DH0MAD) _________________________________________________
 heller.,at,.lisboa.ks.uiuc.edu   "Knowledge must be gathered and cannot be
 given"
 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.