AMBER Archive (2008)

Subject: Re: AMBER: ff02 in nmode gives error "too many dihedrals" ?

From: David A. Case (
Date: Wed Nov 12 2008 - 09:13:45 CST

On Mon, Nov 10, 2008, Jacob Kongsted wrote:
> Im am doing minimization using sander and ff02. After the minimization I
> would like to enter the nmode part of the code in order to do a vibrational
> analysis in order to get estimates of the vibrational entropy. The sander
> minimization runs fine, but upon entering nmode I get the following error
> meassage:
> "too many dihedrals"

I don't think anyone has used polarizable nmode much (if you have: please
chime in here). And, I don't know what the restriction means.

But, you could try to just allocate more space and see what happens.
The allocation of ni14 occurs in pol.h: change the "15" there to a larger
value, then make comparable changes in new_stuff.f (didn't Jim have wonderful
file names!) and rdparm.f. The nature of Newton-Raphson minimization and
normal mode calculation is such that you can generally tell if things are
working or not (e.g. you can reach low RMS gradients, and get six zero
frequency modes, etc.)

...good luck...dac

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