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<br><br>> Date: Thu, 19 Feb 2009 01:53:47 +1100<br>> From: Mark.Abraham@anu.edu.au<br>> To: gmx-users@gromacs.org<br>> Subject: Re: [gmx-users] ewald_rtol parameter question<br>> <br>> Claus Valka wrote:<br>> > Hello,<br>> > <br>> > I would like to ask you a (simple) clarification question:<br>> > Reading the manual and equations 4.158 up to 4.160 there is a <br>> > convergence parameter b (with hellenic letters â).<br>> > I would like to ask you whether this parameter is the same as the <br>> > ewald_rtol that I come accross in the manual.<br>> <br>> No.<br>> <br>> > If it is not, is there any <br>> > function between those two quantities?<br>> <br>> Yes. It's something like erfc(R)/R <= ewald_rtol for R = beta * <br>> rcoulomb. That is, beta is controlled by the value of the two parameters <br>> so that the contributions to the direct-space sum from charges outside <br>> rcoulomb are negligibly small. Check the Darden papers referenced from <br>> the GROMACS manual for details. GROMACS reports the value of 1/beta in <br>> the .log file, IIRC.<br>> <br>> Mark<br><br><br>ewald_rtol sets the relative magnitude of the direct space eletrostatics part<br>at the cut-off (as described briefly in the mdp options manual pages), i.e.:<br>erfc(rcoulomb)/rcoulomb = ewald_rtol<br><br><br>We should add a few lines on this to the manual.<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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