[Pw_forum] cell optimization

[Gebauer Ralph]

Hania,

Apart from the (too small) cutoff you are using, I think that you
experience the well known problem of a discontinuous energy-volume graph.
See for example here:
http://www.quantum-espresso.org/wiki/index.php/Methodological_Background#Stress
and in the reference given in that wiki.

Greetings!

Ralph

-----

Ralph Gebauer
The Abdus Salam International Centre for Theoretical Physics (ICTP)
Condensed Matter Section           Tel: (+39).040.2240.344
Strada Costiera 11                 Fax: (+39).040.224163
I-34014 Trieste (Italy)            e-mail: rgebauer at ictp.trieste.it



-- 


>
> Hi, thanks for your fast response.actually, I am using Bi-mt-PPs, so 25Ry
> is too small.here is my input:
>  &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, /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.UPFATOMIC_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
> 7.5480225K_POINTS {automatic}  4 4 4 1 1 1
> Hania Djani-AitAissa
> CDTA, Algiers, Algeria