<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi,<div><br></div><div>For neutral species, I think it's straightforward (unless the paper Ran Friedman mentioned says otherwise). Just use the definition of the quadrupole moment to figure out where to put the charges and what magnitude to assign to them. The electric field from a quadrupole declines like r^-3, however, so its importance for graphene interactions seem very small to me.</div><div><br></div><div>Erik</div><div><br></div><div><br></div><div><div><div>16 jun 2011 kl. 17.10 skrev WU Yanbin:</div><br class="Apple-interchange-newline"><blockquote type="cite">Hi, Erik,<br><br>Thanks for the information.<br><br>Regarding using more than two partial charges to mimic quadrupole explicitly, is there a one-to-one relation between the quadrupole moments and "position and magnitude" of the partial charges? For example, if I would like to include quadrupole moment for carbon in graphene, which has only non-zero Q20 quadrupole component, how should I place partial charges to mimic that quadrupole moment?<br>
<br>Any hint or direction for literature is appreciated.<br><br>Best,<br>Yanbin<br><br><div class="gmail_quote">On Thu, Jun 16, 2011 at 3:24 AM, Erik Marklund <span dir="ltr"><<a href="mailto:erikm@xray.bmc.uu.se">erikm@xray.bmc.uu.se</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">Quadrupole interactions are implicit whenever you have a molecule withe more than two partial charges. You don't have to include it explicitly. There are, however, multipole expansion techniques to speed up electrostatics calculations, but that's another story.<br>
<br>
Erik<br>
<br>
15 jun 2011 kl. 23.45 skrev WU Yanbin:<br>
<div><div></div><div class="h5"><br>
> Dear GMXers,<br>
><br>
> Is there a way in GROMACS to include quadrupole-charge interaction?<br>
> Or is there a standard to way to mimic quadrupole moment using partial charge?<br>
><br>
> Thank you.<br>
><br>
> Best,<br>
> Yanbin<br>
</div></div>> --<br>
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<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div>-----------------------------------------------</div><div>Erik Marklund, PhD student</div><div>Dept. of Cell and Molecular Biology, Uppsala University.</div><div>Husargatan 3, Box 596, 75124 Uppsala, Sweden</div><div>phone: +46 18 471 4537 fax: +46 18 511 755</div><div><a href="mailto:erikm@xray.bmc.uu.se">erikm@xray.bmc.uu.se</a></div><div><a href="http://www2.icm.uu.se/molbio/elflab/index.html">http://www2.icm.uu.se/molbio/elflab/index.html</a></div></span>
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