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Hi,<br><br>The Coulomb energy difference that Chris Neale observed recently<br>was caused by a bug in the neighborlist assignment with the combination<br>of free energy and tip4p water optimization.<br>This bug would cause a few tip4p-tip4p charge interactions to be missing.<br>I think it has been present in all Gromacs version which have tip4p optimized loops,<br>for sure it was in 3.3.<br>I have fixed this for the upcoming Gromacs 4.0.4 release.<br><br>I assume this bug also caused the cut-off dependence that David Mobley observed.<br><br>I have done a lot of free energy calculation with tip4p and never noticed<br>any problems. This was because I always had the perturbed molecule<br>in a separate energy group, which circumvents the problem.<br><br>So for the moment and for checking if you had the problem with older Gromacs <br>versions, you can simply put the perturbed atoms and tip4p in separate energy groups.<br><br>Berk<br><br><br /><hr />What can you do with the new Windows Live? <a href='http://www.microsoft.com/windows/windowslive/default.aspx' target='_new'>Find out</a></body>
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