[gmx-users] Force Constants and Unit Systems
Justin A. Lemkul
jalemkul at vt.edu
Thu May 17 21:42:25 CEST 2012
On 5/17/12 3:32 PM, Lara Bunte wrote:
> what I meant was, that if a force constant would have the unit kcal/mol, the corresponding potential will be a coulomb potential and I said that this makes no sense. Springs has a quadratic potential, not a Coulomb Potential, like V(r) = 1/r.
> Please have a look on page 45, there you can see what is written in my supporting information (it's in English).
I just want to clarify something, though it isn't even really relevant, perhaps
it will be instructional. The 1/length issue does not mean the potential is
calculated from 1/r. In fact, neither is a Coulombic potential, though it is
proportional to this factor. The issue that was initially raised was to help
you understand that force constants for bonds must have a length term in the
denominator of the units, i.e. a 1/length (to some power) dependence.
> Do you think it is a typo?
I would suspect so. One cannot have a bond force constant that is not have a
length term in the denominator. Presumably the true units are kcal/(mol A^2),
which can be easily converted to kJ/(mol nm^2) for use in Gromacs.
Justin A. Lemkul, Ph.D.
Department of Biochemistry
jalemkul[at]vt.edu | (540) 231-9080
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