[gmx-users] periodic improper dihedral

[Eric Smoll]

Thank you Mark,

We are having difficulty adding new parameters to the oplsaa forcefield in
"share/gromacs.top." We have a "[ dihedraltypes ]" directive where I add
fourier dihedral parameters (function type 5) and a "[ dihedraltypes ]"
directive where I add periodic improper dihedrals (function type 4). We
have itp/top files that contain two corresponding "[ dihedrals ]" directive.

Grompp is complaining that "No default proper/improper dihedral type."
Grompp also complains when the improper terms are represented with a proper
dihedral (function type 2).

Do you have any idea how I could trouble shoot this problem?

Best,
Eric

On Wed, Dec 16, 2015 at 4:54 PM, Mark Abraham <mark.j.abraham at gmail.com>
wrote:

> Yes
>
> On Thu, 17 Dec 2015 05:39 Eric Smoll <ericsmoll at gmail.com> wrote:
>
> > Hello GROMACS users,
> >
> > I have a question about specifying periodic improper dihedrals in
> GROMACS.
> >
> > In the GROMACS manual (chapter 5, table 5.5), the parameters of the
> > periodic improper dihedral are listed as follows:
> >
> > phi_s ( deg ); k_phi (kJ mol^-1); multiplicity
> >
> > In the GROMACS manual (chapter 4, equation 4.60), the form of the
> periodic
> > improper dihedral is specified as
> >
> > V_d( phi_ijkl ) = k_phi ( 1 - cos(n*phi - phi_s))
> >
> > Am I correct in assuming that "n" shown is the "multiplicity" listed
> above?
> >
> > Best,
> > Eric
> > --
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