<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><blockquote type="cite"><div>From what my Professor told me it is my understanding that cutoff length is somewhat a trade-off between accuracy of the simulation and length of time to generate the simulation. A higher cut-off indicates more accuracy but will take longer to simulate. I use low cut-offs for less important simulations like energy minimizations.</div> <div> </div> <div>An increase in density would mean a larger number of simulated molecules and therefore a need for a higher cut-off for more accurate data. That is my best theory anyway.</div></blockquote>This point of view implies that the potentials used are perfect and then indeed the</div><div>longer cutoff you use the more accurate your interactions energies become. </div><div>You have to consider that current potential are parameterized to reproduce some</div><div>data (structural and thermodynamics experimental data) and this using a </div><div>given cutoff. Modifying the cutoff means that you modify the potential and </div><div>therefore the model will not necessarily (and most often) fit the experimental </div><div>data anymore. </div><div><blockquote type="cite"> <div> </div> <div>Arden Perkins<br><br></div> <div class="gmail_quote">On Sun, Dec 20, 2009 at 11:03 PM, Yanmei Song <span dir="ltr"><<a href="mailto:ysong30@asu.edu">ysong30@asu.edu</a>></span> wrote:<br> <blockquote style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex" class="gmail_quote">Dear Users:<br><br>Anyone can explain why the density of the water models increase with increase the cutoff length. I tried a couple water models in reaction-field, PME simulations.The cutoff length ranged from 0.9 to 1.5. They all show the same trend. Then there must be some reasons. Anyone can tell me why?<br clear="all"> <font color="#888888"><br>-- <br>Yanmei Song<br>Ph.D. Candidate<br>Department of Chemical Engineering<br>Arizona State University<br></font><br>--<br>gmx-users mailing list <a href="mailto:gmx-users@gromacs.org">gmx-users@gromacs.org</a><br> <a href="http://lists.gromacs.org/mailman/listinfo/gmx-users" target="_blank">http://lists.gromacs.org/mailman/listinfo/gmx-users</a><br>Please search the archive at <a href="http://www.gromacs.org/search" target="_blank">http://www.gromacs.org/search</a> before posting!<br> Please don't post (un)subscribe requests to the list. Use the<br>www interface or send it to <a href="mailto:gmx-users-request@gromacs.org">gmx-users-request@gromacs.org</a>.<br>Can't post? Read <a href="http://www.gromacs.org/mailing_lists/users.php" target="_blank">http://www.gromacs.org/mailing_lists/users.php</a><br> </blockquote></div><br> -- <br>gmx-users mailing list <a href="mailto:gmx-users@gromacs.org">gmx-users@gromacs.org</a><br><a href="http://lists.gromacs.org/mailman/listinfo/gmx-users">http://lists.gromacs.org/mailman/listinfo/gmx-users</a><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</blockquote></div><br></body></html>