Custom CHARMM forcefield usage problem

From: Jernej Zidar (jernej.zidar_at_gmail.com)
Date: Tue Aug 09 2011 - 23:12:04 CDT

Hi.
  Years ago we developed a CHARMM force field for lipids, that works
flawlessly within the program CHARMM. When I try to use it in NAMD
though NAMD complains about:
FATAL ERROR: UNABLE TO FIND BOND PARAMETERS FOR CEL1 CTL1 (ATOMS 8 39)

  In Charmm I would generally set the input like so:
!read topology
open read card unit 10 name top_all27_lipid.rtf
read rtf card unit 10
close unit 10
!read parameters
open read card unit 10 name par_all27_lipid.prm
read param card unit 10
close unit 10

stream toppar_all27_lipid_cholesterol.str

  In NAMD I'm using only the par_all27_lipid.prm file for NAMD
complains if I try to use the stream
toppar_all27_lipid_cholesterol.str in the conf file:
parameters par_all27_lipid.prm
parameters toppar_all27_lipid_cholesterol.str

  The error I get is:
FATAL ERROR: UNABLE TO FIND ANGLE PARAMETERS FOR HT HT OT (ATOMS 44641
44643 44642)

  I created the PSF and PDB files for the simulation using the PSFGEN
tool within VMD and using the aforementioned force field files.

  Any tips on how to solve this will be much appreciated.

Thanks,
Jernej Zidar

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