[Pw_forum] cell optimization

[Stefano Baroni]

Dear Hania: it seems you do not know what you are doing. The acronym  
"van" in the PP file name in your input data means "Vanderbilt", i.e.  
"ultrasoft". Please, check the QE PP table for more details on the  
PP's you are using. SB

On Jun 22, 2008, at 5:35 PM, hania djani-ait aissa wrote:

> Dear Baroni,
> thank you, but it seems i am not using US pps. However, I will  
> increase ecutrho and see.
> thanks again
> hania
>
>
> From: baroni at sissa.it
> To: pw_forum at pwscf.org
> Date: Sun, 22 Jun 2008 14:32:02 +0200
> Subject: Re: [Pw_forum] cell optimization
>
> 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)
>
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> morale de la pensée - Jean Piaget
>
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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

Please, if possible, don't  send me MS Word or PowerPoint attachments
Why? See:  http://www.gnu.org/philosophy/no-word-attachments.html






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