[gmx-users] error in converting charmm to gromacs

Justin A. Lemkul jalemkul at vt.edu
Sat Nov 21 01:47:00 CET 2009

Chanchal wrote:
> Hi All,
>     I want to create ffcharmm*.itp file from par_all36_carb.prm using 
> the script provided by Mark Abraham. While I used execute the command 
> ./convert_charmm_to_gromacs.pl <http://convert_charmm_to_gromacs.pl> 
> par_all36_carb.prm , I got this message:
> Argument "CTOFNB" isn't numeric in multiplication (*) at 
> ./convert_charmm_to_gromacs.pl <http://convert_charmm_to_gromacs.pl> 
> line 270, <GEN0> line 1382.
> Argument "EPS" isn't numeric in multiplication (*) at 
> ./convert_charmm_to_gromacs.pl <http://convert_charmm_to_gromacs.pl> 
> line 279, <GEN0> line 1382.
> How can I fix this error?

Maybe Mark will have more to say, but per the documentation of the script:

"This script was developed in conjunction with version C27. It expects
par_all27_prot_lipid.prm or par_all27_lipid.prm as input and does
convert the lipid terms (unlike the 1.0 version) but these have not been
tested by the author. It is likely to work with other versions of the
CHARMM force field, however the user is strongly encouraged to verify
the form and function of the force field by verifying the equivalence of
energy evaluations on the same structure in CHARMM and GROMACS."

Looks to me like you're attempting to do something for which the script was not 
intended.  It could be a simple matter of capitalization causing the pattern 
matching to fail.  For example, in the expected input files (mentioned above), 
terms are listed as "ctofnb" and "eps" so perhaps the nomenclature has changed 
in the .prm files.  Some re-writing of the script might be required.



Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080


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