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<body class='hmmessage'><div style="text-align: left;"><br></div><br><br><br><hr id="stopSpelling">> Date: Wed, 12 Mar 2008 17:20:19 +0100<br>> From: andreas.frank@ch.tum.de<br>> To: gmx-users@gromacs.org<br>> Subject: Re: [gmx-users] Re: DMSO G53a6 FF in Gromacs<br>> <br>> Dear all,<br>> <br>> I think I found the reason for the deviation after "hunderds of small <br>> runs"...:-): I normally used Dispersion Correction for both the energy <br>> and pressure because in the manual the following is noted:<br>> <br>> "...The pressure correction in contrast is very large and can not be <br>> neglected. Although it is in principle possible to<br>> parameterize a force field such that the pressure is close to 1 bar even <br>> without correction, such a method makes<br>> the parameterization dependent on the cut-off and is therefore <br>> undesirable. Please note that it is not consistent to<br>> use the long range correction to the dispersion without using either a <br>> reaction field method or a proper long range<br>> electrostatics method such as Ewald summation or PPPM."<br>> <br>> Maybe I got it wrong (and I am still a little bit confused) but because <br>> I used the reaction-field approximation I turned on DispCorr for <br>> Pressure. However, it seems that the Gromos DMSO FF was established in a <br>> way that the correction is "included" in the parameter set which was / <br>> is not clear to me when reading the DMSO paper.<br><br>Reaction-field is for electrostatics and has nothing to do with dispersion correction,<br>which is for Van der Waals interactions.<br><br>Gromos force fields never use a dispersion correction.<br><br>Berk.<br><br><br /><hr />Express yourself instantly with MSN Messenger! <a href='http://clk.atdmt.com/AVE/go/onm00200471ave/direct/01/' target='_new'>MSN Messenger</a></body>
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