[Pw_forum] oscillating scf accuracy in relax run

[Ari P Seitsonen]

Dear pulkit rai,

  1) Please remember to include your affiliation next time

  2a) I think that the cut-off energy is (far) too low for the pseudo 
potentials that you use, I would assume > 120 Ry to be necessary for 
reasonable convergence, at least,

  2b) Is there possibility for spin polarisation?

  2c) Please try using tighter mixing; also, you might try a bit larger 
value of 'degauss' (the default method for smearing is Gaussian 
broadening, and the unit of 'degauss' is Ry).

     Greetings from Montrouge,

        apsi

PS You do not seem to start your endeavours with QE from the easiest 
material... Good Luck! :)

PS^2 The 'cosAB'/'cosBC'/'cosAC' are not used with 'ibrav = 8' anyway, but 
I guess that including them does not harm

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   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 Wed, 6 Jan 2016, pulkit rai wrote:

> Hello everyone,
> 
> I am trying to relax the structure of the compound HoMnO3.
> 
> The scf run converged in 27 iterations but the relax run does not converge
> and keeps on oscillating in scf accuracy.
> 
> Why is this happening ? Is it because of the pseudopotentials ?
> 
> I am new to quantum espresso. Please give some suggestions.
> 
> I have attached my input file below.
> 
> Thank you.. !
>  
> 
> 
>  &control
>     calculation='scf'
>     restart_mode='from_scratch',
>     tstress = .true.
>     tprnfor = .true.
>     prefix='HoMn_lda_scf',
>     pseudo_dir = '/home/HoMnCr/QEpseudo',
>     outdir='/lustre/01/HoMnO3/'
>     disk_io='low'
> 
>  &system
> ecutwfc=  80.00
> ibrav=8, A= 5.616838, B= 7.458766, C= 5.242448, cosAB=0,cosBC=0,cosAC=0,
> nat=20
> ntyp=4,
> occupations='smearing'
> degauss=0.005
> 
>  &electrons
> electron_maxstep=200
> conv_thr=1.0e-8
> 
> ATOMIC_SPECIES
> O     15.99     O.pz-hgh.UPF
> Mn   51.99     Mn.pz-sp-hgh.UPF
> Ho    164.93   Ho.pz-sp-hgh.UPF
> ATOMIC_POSITIONS (crystal)
> O        0.30916       0.05393      -0.30577
> O        0.19084      -0.05393       0.19423
> O       -0.30916       0.55393       0.30577
> O        0.80916       0.44607       0.80577
> O       -0.30916      -0.05393       0.30577
> O        0.80916       0.05393       0.80577
> O        0.30916       0.44607      -0.30577
> O        0.19084       0.55393       0.19423
> O        0.46235       0.25000       0.10381
> O        0.03765       0.75000       0.60381
> O       -0.46235       0.75000      -0.10381
> O        0.96235       0.25000       0.39619
> Mn      0.50000       0.00000       0.00000
> Mn      0.50000       0.50000       0.00000
> Mn      0.00000       0.00000       0.50000
> Mn      0.00000       0.50000       0.50000
> Ho       0.07091       0.25000      -0.01203
> Ho       0.42909       0.75000       0.48797
> Ho      -0.07091       0.75000       0.12030
> Ho       0.57091       0.25000       0.51203
> K_POINTS automatic
> 8 6 8  1  1  1
> 
> 
>