[Pw_forum] hybrid calculation with dexx negative

[DELLACA' Valentina (CRF)]

Dear all,
We are performing surface calculations with hybrid functional, and for the following surface structure at the moment the error saying: 'dexx is negative, error # 1 , check that exxdiv_treatment is appropriate for the system' is giving us some troubles. We already tried to change the distance between surfaces, changing celldm(3), around its optimized value 2.39, we changed also mixing_beta to 0.3, and we tried with few different k point grids. None of this attempt was successful in solving the error. We also changed the occupations to smearing, and we gave a small degauss (1d-20), but then (with many celldm(3)) it was not even converging the first scf.
Any suggestion on how to fix this error?
Thank you,
Regards,
Valentina

&CONTROL
                  calculation = 'scf',
                 restart_mode = 'from_scratch',
                       outdir = '',
                      pseudo_dir  = '',
                      prefix = 'ta2o5' ,
                      disk_io = 'default',
/
  &SYSTEM
                        ibrav = 8,
                    celldm(1) =  14.241893092,
                    celldm(2) =  0.822831603,
                    celldm(3) =  2.39,
                          nat = 38,
                         ntyp = 2,
   ecutwfc=70, nbnd=700, occupations='fixed',
     input_dft = 'PBE0',
    exxdiv_treatment = 'gygi-baldereschi'
    x_gamma_extrapolation=.true.
    nqx1 = 1 , nqx2 = 1, nqx3 = 1
/
&electrons
    conv_thr=1.0d-9, mixing_beta=0.5
/
ATOMIC_SPECIES
Ta   180.95  Ta.pbe-mt-fhi.UPF
O   15.999   O.pbe-mt-fhi.UPF



ATOMIC_POSITIONS (angstrom)
O        0.813278477   4.617988459   8.007774872
O        2.023476210   0.776972843   8.441046448
Ta       1.546871435   2.767467670   7.799599600
O        3.366054079   3.877523758   8.440539307
Ta       3.843027211   5.867856582   7.799473875
O        5.792152399   5.359043398   8.438587876
Ta       5.314346183   3.366897623   7.799507537
O        4.577766398   1.516932685   8.008262086
O        7.134074123   2.258690100   8.438344309
Ta       7.612245398   0.266340494   7.800172819
O        3.496914324   5.857316984   5.883545751
O        5.660946844   3.375012981   5.883534436
O        1.890303432   2.756178342   5.883603671
O        7.271488124   0.274248516   5.883520878
O        5.637305636   5.330921586   3.862497327
O        3.523414777   3.905957403   3.865060769
O        0.813798912   4.618557268   3.867613313
O        1.868771197   0.805909423   3.864412229
O        4.578829938   1.517577526   3.866842485
O        7.290961638   2.230024951   3.864847639
O        3.497903745   5.858106076   1.841803379
O        1.888736406   2.757775274   1.841813170
O        5.659923444   3.372905841   1.841275566
O        7.273010266   0.273369852   1.841504469
O        5.792500075   5.359007930  -0.713580871
O        3.366000630   3.876131545  -0.715282591
O        0.813543928   4.618155682  -0.280250553
O        2.025151305   0.776423231  -0.714789822
O        4.578389288   1.516157053  -0.281620473
O        7.134187444   2.259560146  -0.714019402
Ta       3.631274701   5.991239815   3.862567887
Ta       1.760248756   2.890622602   3.862584360
Ta       5.528096689   3.245167855   3.862383012
Ta       7.400881489   0.144629430   3.862458735
Ta       7.613260471   0.266812681  -0.075602588
Ta       5.314089138   3.366439123  -0.075243654
Ta       3.843827877   5.867144678  -0.074583652
Ta       1.546399836   2.767291744  -0.074953513



K_POINTS {automatic}
2 2 1  0 0 0

Valentina Dellacà
Group Materials Labs
PA&CT - Virtual Analysis & Materials Modelling


Centro Ricerche Fiat S.C.p.A.
Sede legale e amministrativa: Strada Torino, 50
10043 Orbassano (TO), Italia
Tel  +39 011 9083138
Fax +39 011 9083666

www.crf.it<http://www.crf.it>

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