AMBER: angle bending

From: Gustavo Pierdominici Sottile <gsottile.unq.edu.ar>
Date: Thu, 19 Aug 2004 09:31:21 -0300

Hi,
    I write this mail because I have a problem and can not resolve it.
The problem is the following:
I have parametrized a couple of streching and bending parameters, and have
never have any problem. But there is a bending that seems imposible to
parametrize.
The model consists of a benzene but with a nitrogen(B) replacing an
hydrogen.
 Moreover, there is a methyl group bound to that nitrogen.
The bending I want to characterize is that between the carbon of the
ring(A), the nitrogen(B)
and the carbon of th e methyl group(C).
To do this I make an energy plot with gaussian. The points where the energy
was calculated
have the same configurations, except for the angle A-B-C.
The following step was to calculate the non bonded energy to the same
configurations.
When substracting the non bonded energy to the ab initio one, the result is
not harmonic.
I will send you some values so as to add information about the problem:
The ab initio minimum is at 120 , all the energy are in Kcal

angle ab energy non bonded difference
115 0.67 48.43 -47.76
120 0 46.99 -46.99
123 0.23 46.38 - 46.15

In other calculations I allways found a minimum value, but in this case when

the angle is below 120, the difference energy decreases instead of
increasing.

Please if someone have had this problem or kwons what is happening, write me

Thanking in advance
Gustavo


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Received on Fri Aug 20 2004 - 02:53:01 PDT
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