[Pw_forum] ambiguous results with vc-relax

[Guda Karthik]

Hi,

Can you please elaborate on how you selected your ecutwfc?

regards,

On Mon, Aug 23, 2010 at 10:48 AM, jia chen <jiachen at princeton.edu> wrote:

> I did similar thing before, total energy doesn't need to converge...
>
> On Mon, Aug 23, 2010 at 2:22 AM, Guda Karthik <karthik.guda at gmail.com>
> wrote:
> > Hi,
> >
> >     The total energy doesn't converge till 80 Ryd of ecutwfc. I am using
> Ni
> > and Ti USPPs (Ti.pbe-sp-van_ak.UPF, Ni.pbe-nd-rrkjus.UPF). My
> calculations
> > become very slow while using such a large kinetic energy cutoff. am I
> doing
> > something wrong here?
> >
> > regards,
> > Karthik
> >
> > On Tue, Aug 17, 2010 at 4:46 PM, Stefano de Gironcoli <degironc at sissa.it
> >
> > wrote:
> >>
> >> please note that the two outputs that you submitted ARE NOT examples of
> >> vc-relaxation but of structural relaxation of the internal coordinates
> >> only. Your question is anyway legittimate...
> >> Are you sure to have converged the total energy of your system with
> >> respect to cutoff to a sufficient level ?
> >> when comparing  different volumes one is using different basis sets in
> >> the two cases. If convergence w.r.t. cutoff is not sufficient this  can
> >> lead to sudden decreases of the energy when increasing the volume.
> >>
> >> stefano
> >> SISSA and DEMOCRITOS
> >>
> >> Guda Karthik wrote:
> >> > Hi,
> >> >
> >> >     Here are the input and output files.
> >> >
> >> >     b19_Acklatpos_new.* - original structure
> >> >
> >> >     b19_pwscf.* - scf calculation with a structure obtained after
> >> > vc-relax
> >> >
> >> >     Please have a look if they are of help.
> >> >
> >> > regards,
> >> > Karthik
> >> >
> >> > On Sat, Aug 14, 2010 at 6:27 AM, Paolo Giannozzi
> >> > <giannozz at democritos.it>wrote:
> >> >
> >> >
> >> >> On Aug 4, 2010, at 4:41 , Guda Karthik wrote:
> >> >>
> >> >>
> >> >>> I am trying to relax an orthorhombic structure using vc-relax
> >> >>> (celldofree - xyz). I start with a structure which is at a Pressure
> >> >>> of -20.5 Kbar and at the end of the vc-relax I get a structure
> >> >>> which is at a pressure of -0.21 Kbar. Surprisingly, the structure
> >> >>> at pressure closer to zero is higher in energy than the original
> >> >>> structure by 8 * 10^-4 eV/formula unit. All the symmetry elements
> >> >>> have been conserved during relaxation and the initial and final
> >> >>> structures are the same. I am not able to make sense of this
> >> >>> result. I observe this inconsistency in my B2 structure as well.
> >> >>> Please help regarding this.
> >> >>>
> >> >> hard to help without input and output
> >> >>
> >> >> P.
> >> >> ---
> >> >> Paolo Giannozzi, Dept of Physics, University of Udine
> >> >> via delle Scienze 208, 33100 Udine, Italy
> >> >> Phone +39-0432-558216, fax +39-0432-558222
> >> >>
> >> >>
> >> >>
> >> >> _______________________________________________
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> >> >>
> >> >>
> >> >
> >> >
> >> >
> >> >
> >> >
> ------------------------------------------------------------------------
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> >
> >
> > --
> > Karthik Guda
> > Graduate Student
> > Materials Engineering
> > Purdue University
> >
> >
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> > http://www.democritos.it/mailman/listinfo/pw_forum
> >
> >
>
>
>
> --
> Jia Chen
>
> Dept of Chemistry
> Princeton University
> Princeton, NJ 08544
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>



-- 
Karthik Guda
Graduate Student
Materials Engineering
Purdue University
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