Department of Chemistry and Chemical Biology
Questions and problems?

Information about the parm frcmod option

frcmod is an option present in parm to allow the user to override or add parameters missing from the standard force field. The file consists of a title card, followed by keywords (in columns 1-4), including MASS,BOND,ANGL,DIHE, IMPR,HBON, and NONB.

Note that frcmod requires key words before each section, e.g. 

MASS
C   12.01
HC  1.008

BONDS
C -C     469.       1.394
NOTE: you cannot modify the equivalence patterns set up in the standard force field. 
Date: Tue, 1 Dec 92 08:19:44 PST
From: case@scripps.edu (David Case)
To: ross@cgl.ucsf.EDU
Subject: Re: frcmod.nmr

The file ..dat/nmr/frcmod is the one referred to as "frcmod.nmr". You are right to notice that it doesn't do very much--it is just a set of additions to the "regular" force field. Run parm with "-f parm91.dat -m frcmod".

We also generally use ..dat/nmr/all.nmr.in to make up a database (use prep) and use this database in the link step. This has the effect of reducing the charge on charged side chains from +/-1 to +/-0.2, partially mimicing solvent screening.

If you have further nmr-related questions, its probably fastest to send them to the address listed below. You can also try e-mail to Dave Pearlman, dap@vpharm.com.

...good luck.....dave case 

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