I am using Gromacs and I want to edit the ffbonded.itp in oplsaa.ff directory. I have by literature the bond length but I can't find the force constant. Is there a way to calculate it?
Force constants are generally assigned to reproduce QM vibrational data.
OK, so I have to do QM calculations, right?
If I want to use a molecule.itp instead of changing the force field, is this constant obligatory or optional?
You need the force constant unless the bond is going to be constrained. You can either add it as a new parameter in ffbonded.itp or in the molecule.itp file itself.
Hi Justin,
I've always wondered how does one go from the vibrational frequency analysis performed, say HF/6-31+g (I think that's the chemistry model for the Amber forcefield), to a set of force constants. It's something I will need to consider very shortly. Any thoughts? Thanks.
I use CHARMM, so I can't comment on the AMBER directly, but for us it's MOLVIB:
http://www.charmm.org/documentation/c39b1/molvib.html
We have a pretty comprehensive force field, so the initial guess (e.g. in CGenFF) comes from the most chemically similar parameter, then is refined empirically to match the vibrational analysis from MOLVIB.
- Badges
- Science topic