[Pw_forum] problems with vc-relax

[Elie Moujaes]

Dear Xijun,
Thanks very much for your advice. I will do the necessary changes and let you know how things go.
Regards
Elie

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