**From:** Ramya Gamini (*ramyabhargavi_at_gmail.com*)

**Date:** Wed Jun 10 2009 - 14:01:28 CDT

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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

dimension.

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.

Ramya

On Wed, Jun 10, 2009 at 12:08 PM, Kamilla Kopec <ozero22_at_yahoo.co.uk> wrote:

*> Apologies as this is pretty off-topic
*

*>
*

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