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[ESPResSo] Addendum: Bug in Lennard-Jones interaction in ESPResSo versio

From: Torsten Stuehn
Subject: [ESPResSo] Addendum: Bug in Lennard-Jones interaction in ESPResSo versions 2.1.1u up to 2.1.2d
Date: Tue, 10 Mar 2009 17:15:25 +0100
User-agent: Thunderbird (X11/20080213)

Dear all,

here are some details, that will help you to find out if you were affected by 
the bug:

* if you had only one short range non bonded lennard-jones interaction e.g.:

     inter $type_1 $type_2 lennard-jones $eps $sig $rcut $shift $offset 
$cap_radius $min_radius
     , where $type_1==0 and $type_2==0 (important !)

 you were _not_ affected by the bug.

 As soon as you had additional short range non bonded interactions ($type_1 > 0 || 
$type_2 > 0)
         e.g. "inter 0 1 <whatever> ... "
 you were affected by the bug (or at least it was purely random, if you were 
affected or not,
 because the variable IA_parameters->LJ_min was not copied in copy_ia_params 
and thus was uninitialized).

Bonded interactions e.g. "inter 0 fene ..." or long range interactions e.g. "inter coulomb ..." or weather you ran ESPResSo in parallel or on one CPU only had no influence on the bug at all.

* and again: the bug was present _only_ in the "bleeding egde" CVS versions 
2.1.1u to 2.1.2d

* because somebody asked: yes, the ESPResSo testsuite detected the bug 
(testcase mass.tcl did fail)
 but somehow it could escape our attention until yesterday.


Torsten Stuehn wrote:
Dear all,

due to a bug, which appeared only in the CVS versions 2.1.1u (2009-02-09)
up to 2.1.2d (2009-03-09) some of the lennard-jones pair-interactions were not calculated correctly. All simulations that involved lennard-jones interactions (which is most likely all simulations !) and were done with these versions of
ESPResSo are most likely wrong.

The bug is fixed in version 2.1.2e (2009-03-09)

PLEASE double check your simulations, if you were using the above mentioned ESPResSo versions !!!


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