Dear MMC,<br><br>The supercell I used is a simple cubic one (let ibrav=8 celldim(1,2,3)=20bohr). Because the molecule is isolated, I think the kpoint sampling should be irrelevant. And I used gamma point for the calculation.
<br><br>I increased ecut to 25Ry, and celldim to 30bohr) the number of negative modes increase by 9 (to 21modes)!<br>OMG, there must be sth wrong!<br>I'll attach my input and see if someone can give some comments.<br>!-----------------------omega-------------------
<br> omega( 1) = -123.660534 [THz] = -4124.898815 [cm-1]<br> omega( 2) = -122.070631 [THz] = -4071.865015 [cm-1]<br> omega( 3) = -109.408034 [THz] = -3649.483445 [cm-1]<br> omega( 4) = -103.611190
[THz] = -3456.120267 [cm-1]<br> omega( 5) = -100.288151 [THz] = -3345.274863 [cm-1]<br> omega( 6) = -86.921490 [THz] = -2899.408087 [cm-1]<br> omega( 7) = -86.648147 [THz] = -2890.290289 [cm-1]
<br> omega( 8) = -78.536226 [THz] = -2619.703943 [cm-1]<br> omega( 9) = -63.552993 [THz] = -2119.913758 [cm-1]<br> omega(10) = -60.437624 [THz] = -2015.995524 [cm-1]<br> omega(11) = -
59.290658 [THz] = -1977.736621 [cm-1]<br> omega(12) = -59.022664 [THz] = -1968.797246 [cm-1]<br> omega(13) = -58.953578 [THz] = -1966.492750 [cm-1]<br> omega(14) = -46.326804 [THz] = -1545.306104
[cm-1]<br> omega(15) = -31.263942 [THz] = -1042.859776 [cm-1]<br> omega(16) = -31.093207 [THz] = -1037.164629 [cm-1]<br> omega(17) = -27.758798 [THz] = -925.939988 [cm-1]<br> omega(18) = -
27.694407 [THz] = -923.792135 [cm-1]<br> omega(19) = -24.097859 [THz] = -803.823410 [cm-1]<br> omega(20) = -20.675736 [THz] = -689.672916 [cm-1]<br> omega(21) = -20.064562 [THz] = -669.286187
[cm-1]<br> omega(22) = 15.218497 [THz] = 507.637805 [cm-1]<br> omega(23) = 16.277849 [THz] = 542.974191 [cm-1]<br> omega(24) = 20.249558 [THz] = 675.457041 [cm-1]<br> omega(25) =
21.320279 [THz] = 711.172668 [cm-1]<br> omega(26) = 22.104349 [THz] = 737.326626 [cm-1]<br> omega(27) = 23.427206 [THz] = 781.452687 [cm-1]<br> omega(28) = 30.392570 [THz] = 1013.793763
[cm-1]<br> omega(29) = 43.644315 [THz] = 1455.827328 [cm-1]<br> omega(30) = 55.006552 [THz] = 1834.833267 [cm-1]<br> omega(31) = 57.997854 [THz] = 1934.613035 [cm-1]<br> omega(32) =
61.898591 [THz] = 2064.728462 [cm-1]<br> omega(33) = 68.862483 [THz] = 2297.020463 [cm-1]<br> omega(34) = 68.979827 [THz] = 2300.934652 [cm-1]<br> omega(35) = 69.303015 [THz] = 2311.715098
[cm-1]<br> omega(36) = 69.697807 [THz] = 2324.884051 [cm-1]<br><br><div><span class="gmail_quote">On 11/19/06, <b class="gmail_sendername">Miguel Martínez Canales</b> <<a href="mailto:wmbmacam@lg.ehu.es" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">
wmbmacam@lg.ehu.es</a>> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Hi Jin,<br><br>Jin Zhang escribió:<br>> The thing I cannot understand is, there're 12 negative frequencies
<br>> existing. I know 3 of them are purely translational modes and another 3<br>> are rotational ones. But what about the rest 6? I'm a little confused<br>> and hopefully someone can help.<br>><br>> The eigenvals are pasted below and thanks in advance!
<br>><br>> (the result may not be accurate due to a only-15Ry ecut I used, but it<br>> should not give out qualitative different result)<br><br>For a start, I wouldn't think 15 rydbergs is enough. Have you tested the
<br>pseudopotentials for ecut convergence? 25 or 30 would probably be a better<br>choice. Anyway, what you probably are missing most in your calculations is<br>k-point sampling convergence. Translational and rotational frequencies are
<br>a bit too large. What happens if you increase your k-point grid? Anyway,<br>don¡t forget to relax your molecule with the new parametres.<br><br>BTW: What kind of cell are you using? I've never done molecular normal mode
<br>calculations but I guess that in the case of bencene using an hexagonal<br>supercell might make sense.<br><br>--<br>----------------------------------------<br>Miguel Martínez Canales<br> Dto. Física de la Materia Condensada
<br> UPV/EHU<br> Facultad de Ciencia y Tecnología<br> Apdo. 644<br> 48080 Bilbao (Spain)<br>Fax: +34 94 601 3500<br>Tlf: +34 94 601 5437<br>----------------------------------------<br><br> "The problem with Renault is that they dont have
<br> the skills to convince FIA that the mass damper<br> is just a brake cooler."<br><br>Annonymous<br><br>_______________________________________________<br>Pw_forum mailing list<br><a href="mailto:Pw_forum@pwscf.org" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">
Pw_forum@pwscf.org</a><br><a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">http://www.democritos.it/mailman/listinfo/pw_forum</a><br></blockquote>
</div><br><br clear="all"><br>-- <br>Jin Zhang<br>Dep. of Physics,
<br>Peking Univ.