Re: FEP & node/core number

From: Brian Radak (
Date: Tue May 01 2018 - 11:58:04 CDT

Which atoms are moving to fast? Are they in the alchemical region?

Does this happen if you restart without alch on?

In general you shouldn't get instabilities just by changing the number of
nodes (an exception might be when changing to CUDA).

On Mon, Apr 30, 2018 at 11:36 AM, Francesco Pietra <>

> Hello:
> In the frame of ligand-protein FEP, the system (total 50,555 atoms) was MD
> equilibrated along 12ns on two nodes (72 cores).
> With the same hardware, or six node (216 cores), FEP immediately crashed
> because of protein atoms moving too fast.
> With four nodes (144 cores) the trial (10 min) arrived safely to step
> 72,000, with performance 0.09days/ns.
> All three simulations above were repeated with identical results.
> I am curious about that, as in the recent past I was already sporadically
> faced by FEP problems of atoms moving too fast (at the fist step, like in
> the case above) for ligand-protein systems that had been accurately
> equilibrated. At that time I did not try to change the number of
> nodes/cores.
> Memory was more than enough in all cases.
> Thanks for paying attention to that.
> francesco pietra

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