[gmx-users] g_angle and a dihedral

[Justin Lemkul]

On Sep 6, 2015 11:09 AM, "Vitaly V. Chaban" <vvchaban at gmail.com> wrote:
>
> I compute a dihedral using g_angle.
>
> g_angle -h:
> It should be noted that the index file must contain atom triplets for
angles
> or* atom quadruplets for dihedrals*. If this is not the case, the program
> will
> crash.
>
> I get:
>
> Program g_angle_mpi, VERSION 4.6.1
> Source code file: /root/workdir_kn/gromacs-4.6.1/src/tools/gmx_angle.c,
> line: 228
>
> Fatal error:
> number of index elements not multiple of 3, these can not be angle
triplets
>
> For more information and tips for troubleshooting, please check the
GROMACS
> website at http://www.gromacs.org/Documentation/Errors
>
> My index.ndx:
> [ angles ]
> 16 8 7 46
>
> Is it healable?

You need to add -type dihedral to the command, otherwise g_angle assumes it
is a normal valence angle.

-Justin

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