How to calculate bond force constant for CLA for molecular dynamics ?

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Justin Lemkul

Force constants are generally assigned to reproduce QM vibrational data.

Sotiris Papadatos

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.

Anthony Nash

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.