DOS does not go to zero in the gap

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dkanan

DOS does not go to zero in the gap

#1 Post by dkanan » Wed Jan 13, 2010 9:12 pm

Hello,
I am running HSE calculations on a small rhombohedral cell of a wide band gap insulator (Transition metal oxide to be exact) using vasp 5.2

Using the same INCAR,POSCAR,POTCAR, and converged KPOINT mesh/file I have found that the DOS does not go to zero in the case where the tetrahedron method is used for the BZ integration, whereas it does go to zero in the gap for the case where gaussian smearing is used!

Some suggestions in other threads say to make sure the gamma point is included, which I have done. I have even looked at various k-meshes including:
gamma centered 12x12x12
MP 12x12x12

in combination with both ISMEAR=0 and ISMEAR=-5, both with a very small SIGMA=0.01

Can you please help/explain why this is the case? I have seen this problem in other calculations as well.
Last edited by dkanan on Wed Jan 13, 2010 9:12 pm, edited 1 time in total.

dkanan

DOS does not go to zero in the gap

#2 Post by dkanan » Thu Jan 14, 2010 3:27 pm

By the way, I see that in other threads the suggestion is also to make sure the k-points on the BZ boundary are included. I am not sure how this should be checked. I assume that the automatically generated k-mesh in vasp already takes care of this. Is this correct?
Last edited by dkanan on Thu Jan 14, 2010 3:27 pm, edited 1 time in total.

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DOS does not go to zero in the gap

#3 Post by VASP001 » Fri Jan 15, 2010 3:11 am

Maybe ,you can see the HOMO and LOMO in the OUTCAR ,because the DOS is affected by the pepole ,because ,it's can be tunned by hand to choose some parameters ,for example sigma etc .
[quote author=0 and ISMEAR=-5, both with a very small SIGMA=0.01

Can you please help/explain why this is the case? I have seen this problem in other calculations as well.[/quote]
Last edited by VASP001 on Fri Jan 15, 2010 3:11 am, edited 1 time in total.

dkanan

DOS does not go to zero in the gap

#4 Post by dkanan » Fri Jan 15, 2010 5:39 am

VASP001, thank you for your help. however, I could not understand what you meant in your reply. Do you mean the DOS is affected by different people? as in the user. What about the HOMO and LUMO should I check?

Do you think this is a problem with VASPs implementation of the tetrahedron method or with the use of the tetrahedron method for this case??
Last edited by dkanan on Fri Jan 15, 2010 5:39 am, edited 1 time in total.

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DOS does not go to zero in the gap

#5 Post by VASP001 » Fri Jan 15, 2010 7:40 am

[quote="dkanan"]VASP001, thank you for your help. however, I could not understand what you meant in your reply. Do you mean the DOS is affected by different people? as in the user. What about the HOMO and LUMO should I check?

Do you think this is a problem with VASPs implementation of the tetrahedron method or with the use of the tetrahedron method for this case??[/quote]
I mean some facors about the parameters when you draw the pictures of the DOS ,and it's affected by the people .Besides that ,the energy zero is be substracted by the fermi level or not ?

I'm sorry .I make a mistake ,when you see the occupancy in the OUTCAR ,the gamma point only is used and the Direct energy gap at the gamma point ,and you can see the energy gap from the OUTCAR .
Last edited by VASP001 on Fri Jan 15, 2010 7:40 am, edited 1 time in total.

dkanan

DOS does not go to zero in the gap

#6 Post by dkanan » Fri Jan 15, 2010 4:40 pm

Sorry, but I am not sure that you have understood my question. So to clarify it I am not concerned about the fermi level here, I do subtract all the energies by the fermi level in order to shift my DOS plot as you refer to.
However my problem is more serious than that because I am modeling a wide gap insulator, but the calculation results in a DOS that is not zero IN the gap. This is only true when the tetrahedron method with blochl corrections is used for BZ integration, for gaussian smearing the DOS is fine.
Last edited by dkanan on Fri Jan 15, 2010 4:40 pm, edited 1 time in total.

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DOS does not go to zero in the gap

#7 Post by VASP001 » Sat Jan 16, 2010 3:33 am

[quote="dkanan"]Sorry, but I am not sure that you have understood my question. So to clarify it I am not concerned about the fermi level here, I do subtract all the energies by the fermi level in order to shift my DOS plot as you refer to.
However my problem is more serious than that because I am modeling a wide gap insulator, but the calculation results in a DOS that is not zero IN the gap. This is only true when the tetrahedron method with blochl corrections is used for BZ integration, for gaussian smearing the DOS is fine.[/quote]
If it's like this ,I don't know the reason.

Best wishes.
Last edited by VASP001 on Sat Jan 16, 2010 3:33 am, edited 1 time in total.

dkanan

DOS does not go to zero in the gap

#8 Post by dkanan » Sat Jan 16, 2010 9:01 am

thank you for trying, I hope admin can address my issue
Last edited by dkanan on Sat Jan 16, 2010 9:01 am, edited 1 time in total.

schani

DOS does not go to zero in the gap

#9 Post by schani » Mon Feb 01, 2010 3:04 pm

Have you tried to look at the eigenvalues themselves?
Last edited by schani on Mon Feb 01, 2010 3:04 pm, edited 1 time in total.

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DOS does not go to zero in the gap

#10 Post by admin » Wed Feb 10, 2010 8:26 am

1) HOMO and LUMO are not valid input parameters in vasp.
2) as schani proposed: please check the eigenvalue spectrum at each k-point. for a wide gap insulator, the number of occupied bands has to be exactly the same at each k-point, all below the gap. Otherwise the tetrahedra will be interpolated between HOMO and LUMO states.
Last edited by admin on Wed Feb 10, 2010 8:26 am, edited 1 time in total.

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