[Pw_forum] RE : vc-md temperature increases

[BARRETEAU Cyrille]

Dear Lily,

Indeed the non magnetic ground state of iron is fcc therefore if you start from bcc your system is very unhappy.
As suggested by Mike you should set nspin=2. However do not forget that by doing vc-md you will move atoms according to a given "molecular" temperature but you will totally ignore the spin temperature which is another complicated story:-) Any hint to do a spin+molecular dynamic from ab-initio would be very welcome:-)
Some attempts to do it from empirical models have been proposed but this remains rather tricky.

good luck..
  cyrille

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Cyrille Barreteau                                 phone :      +33 (0)1 69 08 29 51
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________________________________________
De : pw_forum-bounces at pwscf.org [pw_forum-bounces at pwscf.org] de la part de Mike Mehl [Michael.Mehl at nrl.navy.mil]
Date d'envoi : lundi 5 décembre 2011 15:36
À : Lily Anh; PWSCF Forum
Objet : Re: [Pw_forum] vc-md temperature increases

Since BCC Fe is magnetic, I suspect you will get better results by adding

     nspin=2,

to your &system block.

On 12/05/2011 04:13 AM, Lily Anh wrote:
> Hi all,
>
> I am running a 'vc-md' calculation with PW.X in QE v4.1.1. The system is
> bcc-Fe supercell of 16 atoms. The target temperature were set to 600 K
> in the input file while the temperature goes up all the way to more than
> 1000 K. I tried with a much larger supercell (128 atoms), this problem
> still happens.
>
> Does anyone know how to fix this?
>
> Many thanks!
> Lily
>
>
>
> I attached my input file here:
>

> &system
> nosym=.t., ibrav = 0, celldm(1) =9.3,nat= 16, nbnd=300,ntyp= 1,
> ecutwfc=40,ecutrho=400,occupations='smearing', smearing='mp', degauss=0.02
> /
> &electrons
> mixing_mode='TF'
> mixing_beta= 0.7
> /


--
Michael J. Mehl
Head, Center for Computational Materials Science
Naval Research Laboratory Code 6390
Washington DC
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