[QE-users] Structure optimization using rvv10-scan

[Giovani Rech]

Hello all,

Have anyone tried structure optimization using rvv10-scan?

I'm trying to optimize a structure (graphite) at 0.0 kbar taking into
account van der Waals interactions. For such, I'm using the SCAN+rVV10 by
setting "input_dft = 'rvv10-scan'". What I'm getting as a result makes no
sense, with unreasonable pressures. Here's a plot of the pressure and
volume as a function of optimization step:
[image: image.png]

When I got this values I was using version 6.4.0 and then tried again with
6.3 and finally with the latest version, 6.4.1, and got the same values
(plotted above). Here's the input that I used:

&CONTROL
>                        title = "graphite_rvv10_vcrelax" ,
>                  calculation = 'vc-relax' ,
>                 restart_mode = "from_scratch" ,
>                       outdir = "./" ,
>                   pseudo_dir = "/home/giovani/graphite/pseudo" ,
>                       prefix = "gC" ,
>                      disk_io = 'default' ,
>                    verbosity = 'default' ,
>                etot_conv_thr = 1.0D-4 ,
>                forc_conv_thr = 1.0D-3 ,
>                        nstep = 400 ,
>                      tstress = .true. ,
>                      tprnfor = .true. ,
>  /
>  &SYSTEM
>                            A = 2.47000e+00 ,
>                            C = 8.68000e+00 ,
>                          nat = 4,
>                         ntyp = 1,
>                      ecutwfc = 80 ,
>                      ecutrho = 320 ,
>                    input_dft = 'rvv10-scan' ,
>                        ibrav = 4 ,
>  /
>  &ELECTRONS
>             electron_maxstep = 200,
>                     conv_thr = 1.00000e-06 ,
>                  startingpot = "atomic" ,
>                  startingwfc = 'atomic' ,
>                  mixing_mode = "plain" ,
>                  mixing_beta = 7.00000e-01 ,
>                  mixing_ndim = 8,
>              diagonalization = 'david' ,
>               diago_thr_init = 1e-4 ,
>  /
>  &IONS
>                 ion_dynamics = 'bfgs' ,
>                ion_positions = 'from_input' ,
>                      upscale = 100 ,
>             trust_radius_max = 1.0D-3 ,
>  /
>  &CELL
>                cell_dynamics = 'bfgs' ,
>                        press = 0.0 ,
>               press_conv_thr = 0.05 ,
>                  cell_factor = 1.2 ,
>  /
> ATOMIC_SPECIES
>     C  12.0107  C.SR.ONCVPSP.PBEsol.stringent.upf
> ATOMIC_POSITIONS crystal
> C 0.0000000000 0.0000000000 0.000000000
> C 1/3          2/3          0.000000000
> C 1/3          2/3          1/2
> C 2/3          1/3          1/2
> K_POINTS automatic
>   6 6 2   0 0 0


I then tried the same optimization using PBE, by just commenting the
'input_dft' line, and got values of both pressure and volume converging to
fairly reasonable values (as plotted below) which makes me think that the
problem might be with the rVV10-scan option. Have anyone else had this kind
of problem? Any ideas on how this could be fixed?
[image: image.png]

Also, when testing and comparing the results of both approaches with
verbosity=high to investigate which contribution to the pressure was wack,
I noticed that almost all the pressure matrices were more or less similar,
except for 'exc-cor stress', that was of the same order of magnitude but
opposite signs, and 'core-core stress', which was off both in magnitude and
in sign. I'm not sure if this is relevant to the problem, but I thought it
could help in finding a solution.

Thank you for your attention,
Best regards,
Giovani Rech

Universidade de Caxias do Sul,
Caxias do Sul - RS, Brazil
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