[Pw_forum] Choice of Pseudopotential

[Elham]

I confused about choice of pseudo potential for system about this atoms
(C,N,O,Fe)

first I used ultra soft pseudo potential
C  12.0107     C.pbe-van_ak.UPF
Fe 55.8450     Fe.pbe-sp-van_ak.UPF
N  14.0067     N.pbe-van_ak.UPF
[image: Inline image 1]
Ecut optimum:   ecutwfc   = 60.0,  ecutrho   = 600.0,

This Ecut is too high for ultra soft pseudo potential.

I use another ultra soft pseudo potential
C  12.0107     C.pbe-n-rrkjus_psl.0.1.UPF
Fe 55.8450     Fe.pbe-nd-rrkjus.UPF
N  14.0067     N.pbe-n-rrkjus_psl.0.1.UPF

Ecut optimum:   ecutwfc   = 40.0,  ecutrho   = 400.0
[image: Inline image 2]

I use from this comment Prof. Stefano  in this question from forum.

"My recommended strategy to fix ecutwfc and ecutrho is to perform total  energy
(and possibly, force and stress) convergence test increasing ecutwfc
keeping ecutrho at its default vaule (=4*ecutwfc)  until satisfactory
stability is reached (typically ~1 mry/atom in the energy, 1.d-4 ry/au in
the forces, a fraction of a KBar in the stress) ...  this fixes the
converged value of ecutrho to 4 times the resulting ecutwfc.

Now keeping this value for ecutrho one can try to reduce ecutwfc and see
how much this can be done without deteriorating the convergence."
I use PAW pseudo potential .

first I use Ecutrho in default (4*Ecut)
but don't reach difference of energy from mRy.

[image: Inline image 3]

second I select Ecutrho=256 and fix Ecut rho and changed Ecut wfc .
and Ecutwfc=52 and Ecut rho=256 is nearly converged.

in higher Ecut wfc oscillation of energy is seen.
[image: Inline image 4]

Any help would be appreciated.

Elham
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