Re: Force Constant Units

From: Ramya Gamini (
Date: Wed Jun 10 2009 - 14:01:28 CDT

Hi !

[u cm-2] should mean in units of cm-2

frequency = (1/2*pi) (k/m)^(1/2)

frequency = C (velocity of light) /wavelength (in cm-1)

k is the force constant
m is the reduced mass

k = cm-2* 4*pi^2*C^2*m

[4*pi^2*C^2*m] with 'C' and 'm' in appropriate units should tally the

and, may be you have a typo but the other unit should be kcal mol-1 A-2 and
not kcal mol A-2.

hope this helps.

On Wed, Jun 10, 2009 at 12:08 PM, Kamilla Kopec <> wrote:

> Apologies as this is pretty off-topic
> - has anybody come across units of [u cm-2] before for bond stretch force
> constants? I would like to convert a literature force constant quoted in u
> cm-2 to kcal mol A-2 for comparison with one I am using in "charmm22 with
> NAMD". My dimensional analyses have failed to produce a meaningful
> conversion factor - could someone confirm that u cm-2 is a bonafide force
> constant unit?
> Many thanks....
> Milla

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