My Community

Dear admin and dear all,

I am quite new with LDA+U, so please forgive me if I say something of wrong.

I am trying to perform LDA+U calculation for GaAs.
After reading papers, I found a value for Ga in GaAs for U (d-states) which is ~ 20 eV (a huge value).

But I think this value is correct since VASP allows to correct only one state (d, in this case) at once.

I apply this value as U-J in the Dudarev approach and I do a single point calculation on a previously optimized (DFT/PAW/LDA) structure. What I got is a perfect agreement with experimental band gap (i.e. on Gamma Egap= 1.52 eV).

Now, for sake of comparison, I would like to optimize the structure from scratch at LDA+U level of calculation but what I got is a crash of the calculation.

I know that U-J =20 eV for d orbitals is a huge value and that leads to an exceptional shrinking of the cell. But, anyway I would like to have some explanations about the failure. Does it mean I can not directly fully optimize for GaAs?

I always obtain a message that tells me that POTIM should be increased (but now I am at POTIM=1.

This is my INCAR

SYSTEM = GaAs_PAW_LDA
ISTART=1
ISMEAR=-5
LReal=False
PREC=High
EDIFF=1E-5
EDIFFG=-0.01
ISPIN=2
NSW=100
ISIF=3
IBRION=1
ADDGRID=.True.
LDAU=.TRUE.
LDAUTYPE=2
LDAUL=2 -1
AMIX = 0.2
BMIX = 0.0001 ! almost zero, but 0 will crash some versions
AMIX_MAG = 0.8
BMIX_MAG = 0.0001 ! almost zero, but 0 will crash some versions
LDAUU=19.8 0.0
LDAUJ=0.0 0.0
ENCUT=287.594
ENAUG=531.356
#LMAXMIX=4

Thanks,
G

Hi,

We're sorry that we didn’t answer your question. This does not live up to the quality of support that we aim to provide. The team has since expanded. If we can still help with your problem, please ask again in a new post, linking to this one, and we will answer as quickly as possible.

Best wishes,

VASP