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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