AMBER Archive (2006)

Subject: Re: AMBER: use_pme=0 problem

From: David A. Case (case_at_scripps.edu)
Date: Wed May 24 2006 - 18:50:56 CDT

On Wed, May 24, 2006, luckyang_at_gmail.com wrote:
>
> I am trying to study a polymer system with TraPPE-united atom force field.
> Since there is no partial charge in any atom of the system, I turn off PME
> using "use_pme=0" and "eedmeth=4" to save the computer time. At the same
> time, I perform a regular simulation (NPT) with PME on and "EW_TYPE=0". I
> would expect these two simulations will give me identical or similar
> results. However, I found that the potential energy of the two systems has
> a big difference

You need to identify the source of the difference; probably just looking at a
single point will suffice. Turn on the "verbose" option in the &ewald
namelist, and look carefully at a single point calculation with both options.
Find out what's different.

[Aside, once you have everything working, setting eedmeth=5 should save a
little time compared to eedmeth=4, since you avoid some square roots.]

...regards...dac

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