AMBER Archive (2006)

Subject: Re: AMBER: A problem with Amber force field new parameter derivation

From: FyD (
Date: Fri Feb 24 2006 - 00:27:31 CST


> But, when it comes to the angle bends (A-M-B, B-M-C, etc.), we
> can't change the value of one angle without affecting the other
> angle(s), so the computed energy can no longer be fitted to a single
> k*x**2 term. (i.e. Contributions come from more than one angle bend).
> So, how does one go about determining each of the angle bend k's
> separately?

You apply the same strategy than for bond stretches except that will get
several terms.

Eqm-Emm(non-bond)=k1(x1-x1o)2 + k2(x2-x2o)2 + ...

When you fit instead to have a single unknown k1 (bond stretches), you have
several ones i.e. two or three for organic molecules for instance... In your
case, may be more...

regards, Francois

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