Problem with Alchemical FEP

From: Jawahar Neelankatan (
Date: Mon Aug 07 2006 - 09:24:55 CDT

Hi all,
I'm trying to do an alchemical FEP simulation of an ion in TIP3P water. I'm using CHARMM parameters but I get the following error at the beginning of the simulation:

FATAL ERROR: Periodic cell has become too small for original patch grid!

I've tried pretty much everything, from increasing the margin (up to 70) to tweaking the PMEGrid sizes. It always gives the same error. The odd thing is that if I
delete the portion of the configuration file devoted to FEP simulation, and just run the simulation like a normal simulation, it works fine. Does anyone know how to get around this problem ?


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