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Hi,<br><br>I don't know how you currently supply your dihedral (multiple periodic dihedral terms?).<br>But you can supply the whole potential, including the constant term, using a Ryckaert-Bellemans dihedral.<br>The manual gives some conversion formulas.<br><br>Berk<br><br>> From: a.kukol@herts.ac.uk<br>> To: gmx-users@gromacs.org<br>> Date: Tue, 26 May 2009 09:29:36 +0100<br>> Subject: [gmx-users] constant term in dihedral potential function<br>> <br>> Dear all,<br>> <br>> I included the following dihedral potential function in a topology:<br>> <br>> V(phi2) = -5.865 + 7.470 [1+cos(phi2-180°)] + 3.99 [1+cos(2 phi2)] + 1.1 [1+cos(3 phi2-180°)]<br>> <br>> The problem is about representing the constant term -5.865. Using equation 4.61 (Gromacs 4.0 manual):<br>> <br>> V(phi) = k * (1 + cos (n phi - phis) )<br>> <br>> I specified:<br>> <br>> V = -5.865 * (1 + cos (0 - 90) ) = -5.865 with multiplicity n=0<br>> <br>> That leads to the entry in the topology file:<br>> 22 23 24 25 1 90 -5.685 0<br>> <br>> This worked fine in Gromacs 3.3, but in Gromacs 4.05 I get the error message (from Grompp):<br>> <br>> Fatal error:<br>> Value of 'multiplicity' in Proper Dih. is 0, which is smaller than the minimum of 1<br>> <br>> I wonder, if this is a bug in Gromacs 4.05, or if there is any better way to specify a constant term in a dihedral potential function.<br>> <br>> Many thanks<br>> Andreas<br>> _______________________________________________<br>> gmx-users mailing list gmx-users@gromacs.org<br>> http://www.gromacs.org/mailman/listinfo/gmx-users<br>> Please search the archive at http://www.gromacs.org/search before posting!<br>> Please don't post (un)subscribe requests to the list. Use the <br>> www interface or send it to gmx-users-request@gromacs.org.<br>> Can't post? Read http://www.gromacs.org/mailing_lists/users.php<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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