naphtaly moro wrote:
> Dear All,
> I am trying to do an SCF calculation on GaAs with a Rocksalt
> structure. The calculations does not converge, I have tried to
> increase the Ecut up to 200Ryd but still there's no convergence. I
> have also attempted to increase the k-points with no success. What
> might be the problem?
I don't know if LDA or GGA is able to correctly predict the insulating GaAs
ground state.
Maybe the LDA gap is very small and you need to use broadening of the
occupations to
converge the calculations.
Try to use occupations='smearing' in your input file.
> My input is
>
> &control
> calculation = 'scf'
> restart_mode='from_scratch',
> prefix='GaAs',
> pseudo_dir='./'
> outdir = './',
> /
> &system
> ibrav= 2, celldm(1) =10.7, nat= 2, ntyp= 2,
> ecutwfc = 24, ecutrho = 100,
You must NOT specify ecutrho when using norm-conserving pseudos. ecutrho must
be 4*
ecutwfc (which is the default). It is of no use specifying larger values.
> nbnd = 8, nosym=.true.,
Why do you want to avoid the use of symmetries? It usually helps the
convergence.
> /
> &electrons
> diagonalization='david'
> mixing_mode = 'plain'
> mixing_beta = 0.3
> conv_thr = 1.0d-8
> electron_maxstep=1000
That's not wise to do, if it doesn't reach convergence in 100 steps it is quite
likely
that it will never do...
> /
> ATOMIC_SPECIES
> Ga 69.723 ga_ppot.gon
> As 74.9216 as_ppot.gon
Are you sure that your pseudopotentials are good? This might be another source
of
trouble... have you tried with different pseudos, for instance those on the QE
website?
HTH
GS
> ATOMIC_POSITIONS
> Ga 0.00 0.00 0.00
> As 0.50 0.50 0.50
> K_POINTS {automatic}
> 4 4 4 0 0 0
>
> PS: I am using normconserving pseudos
>
--
o ------------------------------------------------ o
| Gabriele Sclauzero, PhD Student |
| c/o: SISSA & CNR-INFM Democritos, |
| via Beirut 2-4, 34014 Trieste (Italy) |
| email: sclauzer at sissa.it |
| phone: +39 040 3787 511 |
| skype: gurlonotturno |
o ------------------------------------------------ o
