[gmx-users] angle force constant in mdp file?

David spoel at xray.bmc.uu.se
Mon Jun 13 21:46:55 CEST 2005

On Mon, 2005-06-13 at 12:08 -0700, David Mobley wrote:
> Dear Gromacs users and team,
> Concerning restraints, does anyone know why there isn't an option in
> the mdp files currently for changing angle restraint force constants?
> For example, dihre-fc and disre_fc are valid options and change the
> multiplier of the force constant specified in the topology file, but
> there doesn't seem to be a corresponding parameter for the angle force
> constant.
> Does such a parameter exist? If not, does anyone know why not and if
> this would be expected in the future?

It does not. Don't know why. Science isn't always rational.
Anyway you can probably emulate it's functionality by using in your

#define MULTFACTOR 1000.0
#define MYFC(x) (MULTFACCTOR*x)

And then using rather than your normal force constants

[ my_function ]
1 2 3 4 1 MYFC(3)
2 3 4 5 1 MYFC(4)


> I'm just interested in doing a bunch of runs with slightly different
> restraint forces, and it is (obviously) more annoying to have to go in
> and manually edit the topology file for each different combination of
> restraint forces than to be able to specify this in the input file.
> Thanks,
> David
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David van der Spoel, PhD, Assoc. Prof., Molecular Biophysics group,
Dept. of Cell and Molecular Biology, Uppsala University.
Husargatan 3, Box 596,          75124 Uppsala, Sweden
phone:  46 18 471 4205          fax: 46 18 511 755
spoel at xray.bmc.uu.se    spoel at gromacs.org   http://xray.bmc.uu.se/~spoel

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