AMBER Archive (2006)

Subject: Re: AMBER: use_pme=0 problem

From: luckyang_at_gmail.com
Date: Wed May 24 2006 - 19:20:35 CDT

Dear Dr. Case,

I have identified the source of the difference. The main difference comes
from the EVDW term. How does use_pme affect VDW energy? In attachment please
find the file contains the differences.

Thanks.

Lu Yang

On 5/24/06, David A. Case <case_at_scripps.edu> wrote:
>
> 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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