Re: amber-developers: vlim errors with TIP4P-ew?

From: David A. Case <>
Date: Mon, 16 Apr 2007 15:45:37 -0700

On Mon, Apr 16, 2007, Carlos Simmerling wrote:

> we're seeing a lot of non-fatal vlim errors with tip4p that we don't get in
> comparable
> sander simulations with tip3p. These are at 320K, NPT, 1atm, 2fs time step,
> truncated oct PBC.
> has anyone else seen this?

My experience has been to see no vlimit errors with tip4p (using the default
vlimit of 20), but with different conditions:

300K (not 320), NVE (not NPT), 1 fs time step (not 2fs).

This is over more than 200 nsec of two or three small proteins.

I suspect that the principal difference is the time step, since a larger
step size would be more likely to lead to some bad forces that violate the
vlimit upper bound.

[Not sure if this helps very much, but it *is* one more data point. If you
are getting "a lot" of such errors, it might not take long to see if they go
away with the shorter time step.]

Received on Wed Apr 18 2007 - 06:07:21 PDT
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