[gmx-users] Wrong LJ energies on Apple Mac OS X with Myrinet

[Goran Krilov]

Hi,

I have an  issue with GROMACS on Apple PPC that I am trying to
resolve. Careful analysis of our data has shown that one particular
term of the energy function (LJ short range) gives a different result,
depending on which version of GROMACS we use.

Namely, if I use the binary precompiled by GROMACS developers on  
darwin 8.2.0,
I get the result 9.99750e+03. However if I use the binaries built  
with the
Myrinet MX and Apple 4.0 compiler on 8.3.0, that were built by us
  we get  1.00229e+04 for the same term. That is a significant
difference. Especially so, because all the other energy terms are  
exactly the
same for the two versions.
Moreover, when we use GROMACS 3.3 and GROMACS 3.2.1 on Linux, we get
9.99750e+03. Also, independent calculation with a different package  
(TINKER)
gives us .99750e+03. In all cases we used the same input and data  
files, and outputs
are identical except for the difference in the energy term noted.
So it would seem our Myrinet built GROMACS gives the wrong answer.  
Any ideas what
could be going on?
Thanks!

Regards,

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Dr. Goran Krilov                    Tel. (617) 552-8927
Assistant Professor               Fax (617) 552-2705
Department of Chemistry     E-mail: goran.krilov at bc.edu
Boston College
Merkert Center, 2609 Beacon St
Chestnut Hill, MA 02467
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