Subject: Charmm: drastic breakdown of Charmm potential

From: A J Turner <[email-masked]>
Date: Mon, 17 Jun 1996 16:42:34 +0100 (BST)

Hi!

I have set up a set of 10 tip3p 'molecules' randomly in a space 15A 
square.  I have used no restraints etc.

The I applied a quneched dynamic run to is, in 250 step blocks, updating 
my view in ramsol every 250 steps (running via ctcl).

To my fascination, I saw water molecules 'gluing' together,  I.E. they 
attempt to occupy the same space!

Is this a numerical problem with the VDW calculation in Charmm?  I was 
concerned that if E VDW is overflow, it would return zero and so produce 
this drastic error!

Right now I am trying smaller step sizes on the dynamics (verlet) to see 
if improving the integration, etc., stops this problem showing its self.

Has any one else seen this?

Best wishes

Alex

(I am using C24b1 on an sgi 4d25)

+--------------------------------------------------+
|Alternate E-mail [email-masked]            |
|www home @ http://www.bath.ac.uk/~chpajt/home.html|
+--------------------------------------------------+