[Pw_forum] Total energy does not converge with respect to ecut variation

[Ari P Seitsonen]

Dear Seyed Mojtaba Rezaei Sani,

   I would assume the Cu-HTH-pseudo potential to require a cut-off energy 
higher than 100 Ry, they are quite hard ones. If you are able to use the 
PAW method, you can find the data sets for example in the PSlibrary of 
Andrea Dal Corso, http://qe-forge.org/gf/project/pslibrary/ .

     Greetings from Trieste,

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
   Ecole Normale Supérieure (ENS), Département de Chimie, Paris
   Mobile (F) : +33 789 37 24 25    (CH) : +41 79 71 90 935


On Sun, 25 Jan 2015, Seyed Mojtaba Rezaei Sani wrote:

> Dear all
> I was performing an optimizing calculation for the kinetic energy cutoff of  wavefunctions expansion for Cu3N compound with a cubic structure using
> QE v.5.1.
> Results don't show any convergence neither in total energies nor in differences.
> Here is the table for the calculation result
> 
> 25.out:!    total energy              =    -224.54499924 Ry
> 30.out:!    total energy              =    -231.56190061 Ry
> 35.out:!    total energy              =    -239.33860506 Ry
> 40.out:!    total energy              =    -247.75926085 Ry
> 45.out:!    total energy              =    -256.35103303 Ry
> 50.out:!    total energy              =    -264.81580643 Ry
> 55.out:!    total energy              =    -272.59279950 Ry
> 60.out:!    total energy              =    -279.38896704 Ry
> 
> I chose these PPs:
> 
> Cu.pbe-d-hgh.UPF
> N.pbe-hgh.UPF
> 
> and this an input file:
> 
> &CONTROL
>   calculation = 'scf'
>   verbosity = 'high'
>   restart_mode = 'from_scratch'
>   wf_collect = .TRUE.
>   nstep =  100 
>   tstress = .TRUE.
>   tprnfor = .TRUE.
>   outdir = './tmp'
>   prefix = 'Cu3N'                       
>   etot_conv_thr = 0.0001
>   forc_conv_thr = 0.0001
>   pseudo_dir = '/home/rezaei/work/cu_pnictide/pseudo'
> /
> &SYSTEM
>   ibrav = 1
>   celldm(1) = 7.217
>   nat = 4
>   ntyp = 2
>   ecutwfc = 25
>   ecutrho = 100.0
>   occupations = 'smearing'
>   degauss = 0.02D0
>   smearing = 'mv'
> /
> &ELECTRONS
>   electron_maxstep = 100
>   conv_thr = 1.0d-6
>   mixing_mode = 'TF'
>   mixing_beta = 0.7D0
>   diagonalization = 'cg'
> /
> ATOMIC_SPECIES
>   Cu   63.5460  Cu.pbe-d-hgh.UPF
>   N    14.0067  N.pbe-hgh.UPF
> ATOMIC_POSITIONS {alat}
>   N        0.000000000   0.000000000   0.000000000
>   Cu       0.000000000   0.500000000   0.000000000
>   Cu       0.500000000   0.000000000   0.000000000
>   Cu       0.000000000   0.000000000   0.500000000
> K_POINTS {automatic}
>   10 10 10  1 1 1
> 
> I appreciate any help in advance.
> 
>  Best regards,
> 
> --
> Seyed Mojtaba Rezaei Sani
> 
> Institute for Research in Fundamental Sciences (IPM)
> School of Nano-Science
> Shahid Farbin Alley
> Shahid Lavasani st
> P.O. Box 19395-5531
> Tehran, Iran
> Tel: +98 21 2310  (3069)
> 
>