[QE-users] Discrepancy between QE and VASP when including Efield in slab system

[Carlos Polanco Garcia]

Dear Michal
Thanks for your reply.

> First of all, version 5.4 is ancient. Have you tried with the latest QE? I
have not tried the newest version. Although I did look for emails stating
problems including Efield in older versions of QE and I did not find any.
So I'm assuming for now that my problem is not due to the QE version.
> Assuming both calculations are performed correctly, the difference may
stem
> from different pseudopotentials. Are you using some old norm-conserving
> pseudos? Are you sure your cutoff is large enough? Have you tried SSSP
> pseudos? I have tried several pseudopotentials: 1) PAW PBE:
Mo.pbe-spn-kjpaw_psl.1.0.0.UPF, S.pbe-n-kjpaw_psl.1.0.0.UPF 2) PAW PBEsol:
Mo.pbesol-spn-kjpaw_psl.1.0.0.UPF, S.pbesol-n-kjpaw_psl.1.0.0.UPF 3) USPP
PBE: Mo.pbe-spn-rrkjus_psl.1.0.0.UPF, S.pbe-nl-rrkjus_psl.1.0.0.UPF 4) PW
LDA: Mo.pw-mt_fhi.UPF, S.pw-mt_fhi.UPF 4) USPP LDA:
Mo.pz-spn-rrkjus_psl.0.2.UPF, S.pz-n-rrkjus_psl.0.1.UPF All these trials
tend to agree relatively well, meaning that the change in bandgap with
Efield from all the simulations is within 10-20%. The change in bandgap
with Efield for LDA pseudopotentials tends to be a bit slower than that for
GGA pseudopotentials. The cut off energy I'm using (80 Ry) is around or
above what other calculations in the literature are using. So I'm assuming
that increasing the cut off energy will not be enough to increase the
change in bandgap with Efield that I'm getting by four times (what is
obtained with VASP). Also, as I mention before, my QE calculations agree
decently with other independent calculations in the literature (Ref [3] and
[4] of the initial email).
Anyway, are you expecting reasonable results for this system from PBE? I
choose the PBE results because the bandstructrure at Efield=0 resembles
other bandstructures in the literature.
Best regards,
Michal Krompiec, Merck Electronics

-- 
Carlos Andrés Polanco García
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