[QE-users] SCF calculations on WN supercell not converging

Ari P Seitsonen Ari.P.Seitsonen at iki.fi
Sun Jun 21 20:09:41 CEST 2020


Dear Coralie,

   Besides the concern of the possibly errorneous pseudo potential, I 
would recommend that you begin with a simpler system at the beginning if 
you are not yet familiar with the (periodic) DFT calculations, in 
particular the broadening, empty bands, choice of k points and so on.

   In particular here, it seems that you have been trying to use quite many 
k points in the directions corresponding to the surface plane (earlier 
2x2, now 4x4 will consume plenty of computing time), and in particular in 
the direction corresponding to the surface normal, where you have (in 
principle) no periodicity there is no need to specify more than "1" in the 
k points. I would also recommend to try if you can make the laterally 1x1 
unit cell, without the adsorbate to converge, before going to such large a 
slab. Are you sure about the values of the 'starting_magnetization()' on 
the nitrogen and tungsten atoms - 60 % polarisation on the latter for 
example (please notice that this is in _relative_ units, so the tungsten 
atoms have a magnetic moment of 0.6 * 14 valence electrons in the 
initial electron density - the magnetisation is larger than the "true 
valence" of four electrons of W)? The initial electronic structure might 
be very far from the final, self-consistent one that you are trying to 
reach. What is the magnetic ordering in the bulk, is it ferro-magnetic?

     Greetings from Paris,

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/


On Fri, 19 Jun 2020, Coralie Khabbaz wrote:

> Hello,
> Thank you so much for your response. Do you think it will converge if I use the PAW pseudopotential instead of
> the ultrasoft?
> 
> On Fri, 19 Jun 2020 at 04:15, Andrea Urru <aurru at sissa.it> wrote:
>       Dear Coralie, 
> the issue you are facing is most likely due to the W pseudopotential, which gives convergence issues if
> used in slab systems 
> with vacuum space, as reported here: https://dalcorso.github.io/pslibrary/PP_list.html
> 
> The behavior you describe might be due to a ghost state, but I am not deeply expert in pseudopotentials
> and I cannot swear. 
> I would suggest you to try a different pseudopotential. If you wish to use Ultrasoft pseudopotentials you
> may try the one from 
> Pslibrary 0.3.1. 
> 
> Best regards, 
> 
> Andrea Urru
> 
> Ph. D. Student in Condensed Matter 
> SISSA - Trieste (Italy)  
>
>       Il giorno 17 giu 2020, alle ore 23:31, Coralie Khabbaz <khabbaz.coralie at gmail.com> ha
>       scritto:
> 
> Hello,
> I am doing an scf calculation on a tungsten nitride (WN) slab (catalyst), with a methane molecule 5
> Angstrom away from the surface. The energy values are not converging, even after 533 iterations.
> The energy values are very negative, and then they increase to a positive value then decrease a lot
> again. Before building the supercell, I had a WN unit cell with 433 K-points. Then, I built the
> super cell by using a scaling of 333 and miller indices of 100. I tried using K points of 111 and
> 222 for my super cell, but the calculations didn't converge for both. 
> 
> This is the input file I am using:
> 
> &CONTROL
>     calculation  = "scf"
>     max_seconds  =  1.72800e+05
>     pseudo_dir   = "/home/coralee/projects/def-jkopysci/coralee/.pseudopot"
>     restart_mode = "from_scratch"
> /
> 
> &SYSTEM
>     a                         =  1.24907e+01
>     angle1(1)                 =  0.00000e+00
>     angle1(2)                 =  0.00000e+00
>     angle2(1)                 =  0.00000e+00
>     angle2(2)                 =  0.00000e+00
>     b                         =  1.34803e+01
>     c                         =  2.52767e+01
>     cosab                     =  6.12323e-17
>     cosac                     =  6.12323e-17
>     cosbc                     = -1.85547e-01
>     degauss                   =  1.00000e-02
>     ecutrho                   =  4.50000e+02
>     ecutwfc                   =  5.00000e+01
>     ibrav                     = 14
>     nat                       = 113
>     nspin                     = 2
>     ntyp                      = 4
>     occupations               = "smearing"
>     smearing                  = "gaussian"
>     starting_magnetization(1) =  2.00000e-01
>     starting_magnetization(2) =  6.00000e-01
>     starting_magnetization(3) =  0.00000e+00
>     starting_magnetization(4) =  0.00000e+00
> /
> 
> &ELECTRONS
>     conv_thr         =  1.00000e-06
>     diagonalization  = "david"
>     electron_maxstep = 528
>     mixing_beta      =  4.00000e-01
>     startingpot      = "atomic"
>     startingwfc      = "atomic+random"
> /
> 
> K_POINTS {automatic}
>  4  4  2  0 0 0
> 
> ATOMIC_SPECIES
> N      14.00674  N.pbe-n-rrkjus_psl.1.0.0.UPF
> W     183.84000  W.pbe-spn-rrkjus_psl.1.0.0.UPF
> C      12.01070  C.pbe-n-rrkjus_psl.1.0.0.UPF
> H       1.00794  H.pbe-rrkjus_psl.1.0.0.UPF
> 
> ATOMIC_POSITIONS {angstrom}
> N       2.481849   0.418242  14.837784
> N       6.645429   0.418242  14.837784
> N      10.809008   0.418242  14.837784
> N       2.481849   4.911686  14.837784
> N       6.645429   4.911686  14.837784
> N      10.809008   4.911686  14.837784
> N       2.481849   9.405131  14.837784
> N       6.645429   9.405131  14.837784
> N      10.809008   9.405131  14.837784
> W       2.481849   2.628097  14.748648
> W       6.645429   2.628097  14.748648
> W      10.809008   2.628097  14.748648
> W       2.481849   7.121541  14.748648
> W       6.645429   7.121541  14.748648
> W      10.809008   7.121541  14.748648
> W       2.481849  -1.865347  14.748648
> W       6.645429  -1.865347  14.748648
> W      10.809008  -1.865347  14.748648
> N       0.400059   3.110895  14.468179
> N       4.563639   3.110895  14.468179
> N       8.727218   3.110895  14.468179
> N       0.400059   7.604339  14.468179
> N       4.563639   7.604339  14.468179
> N       8.727218   7.604339  14.468179
> N       0.400059  -1.382549  14.468179
> N       4.563639  -1.382549  14.468179
> N       8.727218  -1.382549  14.468179
> W       0.400059   0.783425  14.415413
> W       4.563639   0.783425  14.415413
> W       8.727218   0.783425  14.415413
> W       0.400059   5.276869  14.415413
> W       4.563639   5.276869  14.415413
> W       8.727218   5.276869  14.415413
> W       0.400059   9.770314  14.415413
> W       4.563639   9.770314  14.415413
> W       8.727218   9.770314  14.415413
> N       2.481849   3.081849  12.630078  0 0 0
> N       6.645429   3.081849  12.630078  0 0 0
> N      10.809008   3.081849  12.630078  0 0 0
> N       2.481849   7.575293  12.630078  0 0 0
> N       6.645429   7.575293  12.630078  0 0 0
> N      10.809008   7.575293  12.630078  0 0 0
> N       2.481849  -1.411595  12.630078  0 0 0
> N       6.645429  -1.411595  12.630078  0 0 0
> N      10.809008  -1.411595  12.630078  0 0 0
> W       2.481849   0.798260  12.540942  0 0 0
> W       6.645429   0.798260  12.540942  0 0 0
> W      10.809008   0.798260  12.540942  0 0 0
> W       2.481849   5.291704  12.540942  0 0 0
> W       6.645429   5.291704  12.540942  0 0 0
> W      10.809008   5.291704  12.540942  0 0 0
> W       2.481849   9.785148  12.540942  0 0 0
> W       6.645429   9.785148  12.540942  0 0 0
> W      10.809008   9.785148  12.540942  0 0 0
> N       0.400059   1.281057  12.260473  0 0 0
> N       4.563639   1.281057  12.260473  0 0 0
> N       8.727218   1.281057  12.260473  0 0 0
> N       0.400059   5.774502  12.260473  0 0 0
> N       4.563639   5.774502  12.260473  0 0 0
> N       8.727218   5.774502  12.260473  0 0 0
> N       0.400059  10.267946  12.260473  0 0 0
> N       4.563639  10.267946  12.260473  0 0 0
> N       8.727218  10.267946  12.260473  0 0 0
> W       0.400059   3.447032  12.207706  0 0 0
> W       4.563639   3.447032  12.207706  0 0 0
> W       8.727218   3.447032  12.207706  0 0 0
> W       0.400059   7.940476  12.207706  0 0 0
> W       4.563639   7.940476  12.207706  0 0 0
> W       8.727218   7.940476  12.207706  0 0 0
> W       0.400059  -1.046412  12.207706  0 0 0
> W       4.563639  -1.046412  12.207706  0 0 0
> W       8.727218  -1.046412  12.207706  0 0 0
> N       2.481849   1.252012  10.422372  0 0 0
> N       6.645429   1.252012  10.422372  0 0 0
> N      10.809008   1.252012  10.422372  0 0 0
> N       2.481849   5.745456  10.422372  0 0 0
> N       6.645429   5.745456  10.422372  0 0 0
> N      10.809008   5.745456  10.422372  0 0 0
> N       2.481849  10.238900  10.422372  0 0 0
> N       6.645429  10.238900  10.422372  0 0 0
> N      10.809008  10.238900  10.422372  0 0 0
> W       2.481849   3.461867  10.333236  0 0 0
> W       6.645429   3.461867  10.333236  0 0 0
> W      10.809008   3.461867  10.333236  0 0 0
> W       2.481849   7.955311  10.333236  0 0 0
> W       6.645429   7.955311  10.333236  0 0 0
> W      10.809008   7.955311  10.333236  0 0 0
> W       2.481849  -1.031577  10.333236  0 0 0
> W       6.645429  -1.031577  10.333236  0 0 0
> W      10.809008  -1.031577  10.333236  0 0 0
> N       0.400059   3.944664  10.052766  0 0 0
> N       4.563639   3.944664  10.052766  0 0 0
> N       8.727218   3.944664  10.052766  0 0 0
> N       0.400059   8.438108  10.052766  0 0 0
> N       4.563639   8.438108  10.052766  0 0 0
> N       8.727218   8.438108  10.052766  0 0 0
> N       0.400059  -0.548780  10.052766  0 0 0
> N       4.563639  -0.548780  10.052766  0 0 0
> N       8.727218  -0.548780  10.052766  0 0 0
> W       0.400059   1.617195  10.000000  0 0 0
> W       4.563639   1.617195  10.000000  0 0 0
> W       8.727218   1.617195  10.000000  0 0 0
> W       0.400059   6.110639  10.000000  0 0 0
> W       4.563639   6.110639  10.000000  0 0 0
> W       8.727218   6.110639  10.000000  0 0 0
> W       0.400059  10.604083  10.000000  0 0 0
> W       4.563639  10.604083  10.000000  0 0 0
> W       8.727218  10.604083  10.000000  0 0 0
> C      10.809008   2.628097  19.750000
> H      10.177000   1.997000  20.383000
> H      11.443000   1.997000  19.117000
> H      10.177000   3.263000  19.117000
> H      11.443000   3.263000  20.383000
> 
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