[gmx-users] CMAP Dihedrals and free energy perturbations

[Mark Abraham]

On 16/08/11, "Wright, Louise" <Louise.Wright at warwick.ac.uk> wrote:

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> Hi
> I was wondering if anyone could help me.  I am trying to use Gromacs 4.5.4 to do some free energy calculations.  I am using the CHARMM forcefield with CMAP and keep getting the error message:
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> Fatal error:
> Function type CMAP Dih. not implemented in ip_pert
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> I noticed that someone had posted a while ago about a similar message for Improper Dihs. and that the solution to this was an extra line added to topsort.c.  I think I need to add a line to topsort.c too for F_CMAP but am slightly unsure of what to do.
> Any help would be appreciated.  Is there an easy way to carry to carry out free energy perturbation calculations in Gromacs when using CMAP in the potential was well?
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Looking at the code suggests to me that FEP of the CMAP parameters is not implemented (if that even makes sense, I dunno). Also, FEP on some other parameters when CMAP is active is not implemented properly. To get the latter working, I suggest inserting
 
    case F_CMAP:
        bPert = FALSE;
        break;
  
immediately before the "default:" clause in ip_pert() in src/gmxlib/topsort.c 
 
Mark 
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