[gmx-users] Question

[Mark Abraham]

On 6/01/2011 8:28 PM, Thomas Koller wrote:
> Hello,
>
> running grompp gives me this error:
>
> Program grompp, VERSION 4.0.7
> Source code file: ../../../../src/kernel/convparm.c, line: 325
>
> Fatal error:
> unknown function type 20 in ../../../../src/kernel/convparm.c line 326
>
> The two lines 325 and 326 of convparm.c are:
> break;
>    case F_VSITE2:
>
> What can be the error? I never used function type 20.

Actually, you have used it. Internal type 20 is F_IPIDIHS, ie. improper 
periodic dihedrals. The switch statement in src/kernel/convparm.c 
neglects to treat F_IPIDIHS, hence the error.

I've noted in the past that the implementation of F_IPIDIHS seems not 
quite right - see 
http://lists.gromacs.org/pipermail/gmx-users/2010-August/053262.html. 
Looking back through time with "git blame", the implementation of these 
functions was partially done in 2002 and apparently never finished 
properly. I'd lodge a Bugzilla, but we're in limbo until its replacement 
is declared available.

Meanwhile, you can work around the issue by using the corresponding 
periodic normal dihedral - the energy breakdown of proper and improper 
dihedrals reported by mdrun and g_energy won't be correct, however.

Mark