[gmx-users] proper dihedrals

[Milton Taidi Sonoda]

Anton Feenstra wrote:

> Milton Taidi Sonoda wrote:
>
>> Is there a way to model a proper dihedral
>> as a sum of two or more terms of the expression
>> 4.52 of the gromacs user manual using the
>> [ dihedraltype ] section?
>
>
> Yes, simply add as many as you want for a given set of atoms.
> This will work for .itp/.top files, but may not work in .rtp files
> for all versions.
>
Anton

I've tested your advise but the results were not the
expected, at least for the .itp file.

I've created a new test ff with the dihedraltypes as

...
[ dihedraltypes ]

CT   CT   CT   CT   1   180.0  15.0  3
CT   CT   CT   CT   1   180.0  15.0  2
...

in fftestebon.itp file.
However, when processing the parameter files I've got

...
WARNING 1 [file "/usr/local/gromacs_mp/share/top/fftestebon.itp", line 12]:
  Overriding Proper Dih. parameters,
  old: 180 15 3 0 0 0
  new: CT   CT   CT   CT   1   180.0  15.0  2
...

I've tried different file formats such as

...
[ dihedraltypes ]
CT   CT   CT   CT   1   180.0  15.0  2    180.0  15.0  3
...

but gromacs only interprets the firsts four numbers.
Where did I mistake?

Milton Taidi Sonoda