[QE-users] Question regarding mixing of PBE and PBESOL PP

[Holzwarth, Natalie]

We are slowly updating our ATOMPAW webpage http://pwpaw.wfu.edu to include
LDA and PBESOL PAW datasets that are more reliable when used with Quantum
Espresso.    I just added Ca and could add more as needed.       Of course,
although similar datasets have been used in the past,   the new ones always
need to be tested.

N. A. W. Holzwarth                                       email:
natalie at wfu.edu
Department of Physics                                  web:
http://www.wfu.edu/~natalie
Wake Forest University                                 phone:
1-336-758-5510
Winston-Salem, NC 27109 USA                     office: Rm. 300 Olin
Physical Lab


On Sat, May 4, 2019 at 12:27 AM Yeon, Jejoon <jyeon at udel.edu> wrote:

> Hello
>
>
> I ran several DFTs few times before, but I only have limited amount of
> knowledge and experience in DFTs.
>
>
> I have Pyrope (Mg3Al2Si3O12) and Grossular (Ca3Al2Si3O12) unit cell, and
> wish to preform relax and vc-relax. After I get the relaxed atomic
> structure and cell size, I wish to make an energy curve of Pyrope /
> Grossular structure w.r.t. compression and expansion of volume, using
> expanded / compressed unit cells. Purpose of this DFT is to get the
> database for the parametrization of empirical force field, especially for
> mechanical properties like stress-strain curve and elastic constants.
>
>
> Now, I have PBE-PAW(kjpaw) and PBESOL-PAW(kjpaw) PPs for all atom types. I
> have no problem about Pyrope, I can run it with PBESOL. But Grossular is an
> issue. For Ca, PBE is only available option from QE PP webpage, there is
> no PBESOL for Ca yet. Accordingly, if I want to calculate energies of
> Grossular structure, I have three options as far as I know:
>
> 1) input_dft = 'PBE', while mix the PBE (Ca) and PBESOL (Al, Si, O)
>
> 2) inout_dft = 'PBESOL', while mix the PBE (Ca) and PBESOL (Al, Si, O)
>
> 3) just use PBE PPs for all 4 atom types.
>
>
>
> At this point, I'm not sure what would be the good choice for my purpose. I
> wish to use PBESOL because it is known to have better prediction for solid
> properties. But I'm not sure if I can mix them with PBE, and if I mix,
> which input_dft option should I need to choose.
>
>
> I ran test relaxations for 3 cases, and I found that the final atom
> coordinates of all 3 cases are very similar, they are mostly the same up
> to second decimal point numbers. Their final optimized energies are
> different, but as far as I know I can't compare them, isn't it? I'm not
> sure on which criteria should I need compare and select the best one
> from those three options.
>
>
> Or, if anyone had a similar experience, I welcome any advises or
> suggestions.
>
>
> Just in case, following is my example in file.
>
>
> &CONTROL
>   prefix="03_Relax_Grossular_80_800_PBESOL",
>   calculation='relax',
>
> outdir="/scratch/jj/20190501_QEDFT_Grossular_EoS/03_Relax_Grossular_80_800_PBESOL/tmp",
>   pseudo_dir="/home/QE_pseudo/",
>   restart_mode= 'from_scratch',
>   nstep = 1000
> /
>
> &SYSTEM
>   ibrav=0,
>   nat=20,
>   ntyp=4,
>   ecutwfc=80,
>   ecutrho=800,
>   occupations='smearing',
>   smearing='methfessel-paxton',
>   degauss=0.005000,
>   input_dft='PBESOL'
> /
>
> &ELECTRONS
>   diagonalization='cg',
>   conv_thr=1d-07,
>   mixing_mode='plain',
>   mixing_beta=0.100,
> /
>
> &IONS
>   ion_dynamics = 'bfgs',
> /
>
> ATOMIC_SPECIES
>   Ca 40.078000 Ca.pbe-spn-kjpaw_psl.1.0.0.UPF
>   Al 26.981539 Al.pbesol-n-kjpaw_psl.1.0.0.UPF
>   Si 28.085500 Si.pbesol-n-kjpaw_psl.1.0.0.UPF
>   O 15.999400 O.pbesol-n-kjpaw_psl.1.0.0.UPF
>
> ATOMIC_POSITIONS {angstrom}
> Ca    1.480750    0.000000    2.961500
> Ca    2.961500    1.480750    0.000000
> Ca    0.000000    2.961500    1.480750
> Al    0.000000    0.000000    0.000000
> Al    2.961500    2.961500    2.961500
> Si    0.000000    2.961500    4.442250
> Si    4.442250    0.000000    2.961500
> Si    2.961500    4.442250    0.000000
> O     0.450148    5.393484    1.791116
> O     1.791116    0.450148    5.393484
> O     5.393484    1.791116    0.450148
> O     3.491016    2.511352    4.752616
> O     2.511352    4.752616    3.491016
> O     4.752616    3.491016    2.511352
> O     5.472852    0.529516    4.131885
> O     4.131885    5.472852    0.529516
> O     0.529516    4.131885    5.472852
> O     2.431984    3.411648    1.170385
> O     3.411648    1.170385    2.431984
> O     1.170385    2.431984    3.411648
>
> K_POINTS {automatic}
>   4 4 4 0 0 0
>
> CELL_PARAMETERS {angstrom}
>    5.923000000   0.000000000   0.000000000
>    0.000000000   5.923000000   0.000000000
>    0.000000000   0.000000000   5.923000000
>
> Thank you
>
>
>
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