[Pw_forum] cell optimization

[Eyvaz Isaev]

Hi again,

Please discard my previous mail regarding "alat".
It seems to be correct, as I did not pay attention 
that you used celldim(1) and celldim(3). Please
remember that celldim(3) is c/a. 

Nevertheless "conv_thr = 1e-6" looks quite high, use
1.e-8. For complex systems "mixing_mode=local-TF"
keyword is very useful. 

Bests,
Eyvaz.

--- Stefano Baroni <baroni at sissa.it> wrote:

> I may be wrong, but your problem could be due to
> subtelties of the US  
> PP formalism. Using US PPs, I am afraid that PW
> calculations are  
> variational with respect to PW expansion
> coefficients only when the  
> augmentation charge is at convergence. Convergence
> with respect to the  
> augmentation charge usually is a rather delicate
> issue. For sure, the  
> cutoff for the charge-density distribution (ecutrho)
> should be taken  
> larger (sometimes much larger) than the default
> value for norm- 
> conserving PPs (4 x ecutwfc). In yor calculation,
> you seem to use just  
> this value, which may turn out to be inadequate.
> Have you tried to  
> test the convergence of your calcs wrt echutrho
> (keeping ecutwfc  
> fixed)? SB
> 
> On Jun 22, 2008, at 11:06 AM, hania djani-ait aissa
> wrote:
> 
> > Dear Nicola,
> > I have tried startingwfc='random' and it gave me
> the same energies  
> > values as for startingwfc='atomic' with still the
> same problem of  
> > drop and rise of total energy. I also increase
> Ecutoff to 40Ry, the  
> > energies values are actually more accurate but the
> problem persist.
> >
> > Hania
> >
> >
> >  &control
> >     calculation  = 'scf'
> >     restart_mode = 'from_scratch'
> >     pseudo_dir   = '/root/pwscf/pseudo/'
> >     outdir       = '/root/tmp/'
> >  /
> >  &system
> >     ibrav=7
> >     celldm(1)=7.33, celldm(3)=8.54
> >     nat=19
> >     ntyp=3
> >     ecutwfc=25.0
> >     ecutrho=100.0
> >  /
> >  &electrons
> >     conv_thr = 1e-6,
> >     mixing_beta=0.2,
> >     startingwfc=’random’
> >  /
> > ATOMIC_SPECIES
> >   Bi    208.98    Bi.pbe-d-mt.UPF
> >   Ti    47.867    Ti.pbe-sp-van_ak.UPF
> >   O     15.9994   O.pbe-van_ak.UPF
> > ATOMIC_POSITIONS
> >  Bi 0.00000000 0.00000000 0.5713404
> >  Bi 0.00000000 0.00000000 7.9816596
> >  Bi 0.00000000 0.00000000 1.8072489
> >  Bi 0.00000000 0.00000000 6.7457511
> >  Ti 0.00000000 0.00000000 3.1757289
> >  Ti 0.00000000 0.00000000 5.3772711
> >  Ti 0.00000000 0.00000000 4.2765000
> >  O  0.50000000 0.00000000 0.0000
> >  O  0.00000000 0.50000000 0.0000
> >  O  0.50000000 0.00000000 2.13825
> >  O  0.50000000 0.00000000 6.41475
> >  O  0.00000000 0.00000000 3.771873
> >  O  0.00000000 0.00000000 4.781127
> >  O  0.00000000 0.00000000 2.7241305
> >  O  0.00000000 0.00000000 5.8288695
> >  O  0.50000000 0.00000000 1.0049775
> >  O  0.50000000 0.00000000 7.5480225
> >  O  0.00000000 0.50000000 1.0049775
> >  O  0.00000000 0.50000000 7.5480225
> > K_POINTS {automatic}
> >   4 4 4 1 1 1
> >
> >
> >
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> 
> 
> 
> ---
> Stefano Baroni - SISSA  &  DEMOCRITOS National
> Simulation Center -  
> Trieste
> http://www.sissa.it/~baroni / [+39] 040 3787 406
> (tel) -528 (fax) /  
> stefanobaroni (skype)
> 
> La morale est une logique de l'action comme la
> logique est une morale  
> de la pensée - Jean Piaget
> 
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> Why? See: 
>
http://www.gnu.org/philosophy/no-word-attachments.html
> 
> 
> 
> 
> 
> 
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> 


-------------------------------------------------------------------
Prof. Eyvaz Isaev, 
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
Condensed Matter Theory Group, Uppsala University, Sweden 
Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com