<html>
<head>
<style><!--
.hmmessage P
{
margin:0px;
padding:0px
}
body.hmmessage
{
font-size: 10pt;
font-family:Tahoma
}
--></style>
</head>
<body class='hmmessage'><div dir='ltr'>
Dear Xijun,<div><br></div><div>Thanks very much for your advice. I will do the necessary changes and let you know how things go.</div><div><br></div><div>Regards</div><div><br></div><div>Elie<br><br><div><div id="ecxSkyDrivePlaceholder"></div>> Date: Wed, 7 Sep 2011 15:58:37 -0400<br>> From: xijunw@gmail.com<br>> To: pw_forum@pwscf.org<br>> Subject: Re: [Pw_forum] problems with vc-relax<br>> <br>> On Wed, Sep 7, 2011 at 3:28 PM, Elie Moujaes <elie.moujaes@hotmail.co.uk> wrote:<br>> > Dear all,<br>> ><br>> <br>> Dear Elie,<br>> <br>> ><br>> > I am relaxing a 60 atom supercell (graphene grain boundary) to make the<br>> > total force on atoms mainly 0.001 Ry/au. However the vc-relax stopped after<br>> > 4 days of execution and without reaching the desired force threshold. The<br>> > following output was obtained :<br>> ><br>> > Please can anyone advice me on this? Shall I start with the new<br>> > configuration and start relaxing again?<br>> ><br>> <br>> I'm also doing some cell relaxation. As I understand, cell<br>> optimization is not very easy, and it is common that it does not<br>> converge after a very long run.<br>> <br>> Surely you should restart the calculation to achieve your convergence<br>> criteria. You can just change the "restart_mod = 'from_scratch' " to<br>> "restart_mode = 'restart' ", and submit the job again to continue from<br>> where you stopped. Please be advised that pw.x will read cell<br>> parameters / atomic positions, initial density, pseudopotentials from<br>> the folder of GBphonon.save, so make sure you copy the folder to<br>> computing-nodes.<br>> <br>> However, I highly suggest you do something to accelerate the<br>> convergence. For example, if you do not expect the cell angle to<br>> change (i.e. keep angles=90), you may add the following keywords to<br>> the &CELL section.<br>> <br>> cell_dofree = xyz<br>> <br>> This will greatly reduce the uncertainty of the geometry optimization.<br>> and reduce energy/force oscillation.<br>> <br>> Another great idea is to manually choose x, y and z, then do a<br>> relaxation of atomic positions only. and plot the total energy changes<br>> with x, y and z. However, be noted that different volume means<br>> different numbers of PW basis function, and energy comparison in this<br>> way could be a little confusing. Anyway, if volume change is not<br>> large, still this would help a lot.<br>> <br>> Since I'm also a learner, any more comments or correction to my<br>> comments are welcome. Thanks<br>> <br>> Xijun<br>> <br>> ><br>> > Regards<br>> ><br>> ><br>> ><br>> > Elie Moujaes<br>> ><br>> > University of Nott<br>> ><br>> > University Park<br>> ><br>> > NGT 3RD<br>> ><br>> ><br>> ><br>> > _______________________________________________<br>> > Pw_forum mailing list<br>> > Pw_forum@pwscf.org<br>> > http://www.democritos.it/mailman/listinfo/pw_forum<br>> ><br>> ><br>> <br>> <br>> <br>> -- <br>> Department of Chemistry and Biochemistry, Concordia University<br>> 7141 Sherbrooke Ouest, Montreal, QC H4B 1R6<br>> Tel: 514-848-2424-#5835 (Lab) TA office: SP175.23<br>> _______________________________________________<br>> Pw_forum mailing list<br>> Pw_forum@pwscf.org<br>> http://www.democritos.it/mailman/listinfo/pw_forum<br></div></div> </div></body>
</html>