Dear Hungie
This is simply a matter of symantics - The force is the differential of the
potential energy and thus if the potential energy is defined as:
E = K(r-req)^2
Then the force is:
F = 2K(r-req)
Often people refer to K as being the force constant which in the above
example isn't strictly correct. The force constant is 2K. If however you
express the energy in terms of K/2 then the force is K(r-req) and so K in
this case is the force constant.
So really it is just how you choose to define the force constant. Since K is
a constant the only difference is in what you define it's value to be. I.e
in the first example the value of K would be half that of the second
example. As long as you are consistent in your definition and assignment of
the constants it doesn't strictly matter which form you use.
I hope this helps.
All the best
Ross
/\
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|\oss Walker
| Department of Molecular Biology TPC15 |
| The Scripps Research Institute |
| Tel:- +1 858 784 8889 | EMail:- ross.rosswalker.co.uk |
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http://www.rosswalker.co.uk/ | PGP Key available on request |
-----Original Message-----
From: owner-amber.scripps.edu [mailto:owner-amber.scripps.edu] On Behalf Of
A. Hungie
Sent: 02 January 2004 04:29
To: amber.scripps.edu
Subject: AMBER: force field
Dear All,
As I have seen in the literatures, the feature of force field of AMBER, for
example bond term is
summation { Kb(l-l0)^2}
whereas in some book it is
summation {Kb/2(l-l0)^2} , i.e. there is a term of 1/2
Could you please tell me why they are different?
Thank you very much in advance for your kindness.
Best Regards,
Hungie
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Received on Wed Jan 14 2004 - 15:53:13 PST
