Ce Band structure

Message

elelel · #1 Post by **elelel** » Tue Aug 29, 2006 12:59 am

I have done a band structure calculation for elemental Ce, PAW, GGA as follows:
1. self-consistent step with ISMEAR=1, and,
2. non self-consistent step with ISMEAR=1.
The two respective INCAR files are shown below. My problem is that the band structure I get with these settings is wrong compared to other published band structures eg. my valence band minimum is located at the X point instead of being at the Gamma point (which happens to be 1.5 eV higher in my case). Does anyone know why this happens? I also tried to use ISMEAR = -5 with IBRION=-1 and what I got was not recognizable in any way as a Ce band structure!

INCAR 1
ISMEAR=1
SIGMA=0.1

ENCUT=400
PREC=High
NELMIN=8
ISPIN=2

LWAVE=T
LCHARG=T

IBRION=2
NSW=0
EDIFF=1E-5
EDIFFG=-0.001

INCAR 2
ISMEAR=1
SIGMA=0.1

ENCUT=400
PREC=High
NELMIN=8
ISPIN=2

LWAVE=T
LCHARG=T

IBRION=2
NSW=0
EDIFF=1E-5
EDIFFG=-0.001

ICHARG=11

Veronika · #2 Post by **Veronika** » Tue Aug 29, 2006 7:40 am

Are you using the right Potential (Ce_h)?
ENCUT 400 is not enough in this case, also EDIFF and EDIFFG are set too low. Cerium is an extremely difficult system to treat (1f electron) ...

christine1201 · #3 Post by **christine1201** » Thu Aug 31, 2006 9:12 am

i think you need to add U.

Veronika · #4 Post by **Veronika** » Mon Sep 04, 2006 8:44 am

elelel does obviously not perform an LDA+U calculation.

aron · #5 Post by **aron** » Mon Sep 11, 2006 1:57 pm

you should check that you have input the special kpoints in the correct format (cartesian or fractional) for that crystal structure type!

elelel · #6 Post by **elelel** » Wed Sep 13, 2006 5:53 am

Hi guys,
Thank you all for your suggestions. My special kpoints are all specified correctly. Yes, my accuracy settings were too stringent and I have adjusted them appropriately but I still dont get the correct bandstructure. LDA+U appears to be the way to go I think but getting the settings right is a bit of a challenge. What settings have others successfully used for the LDAU+U part of the INCAR file?
<span class='smallblacktext'>[ Edited Wed Sep 13 2006, 08:01AM ]</span>

matt_dubya · #7 Post by **matt_dubya** » Wed Sep 13, 2006 11:21 am

Hi elelel

#LDA plus U switched on
LDAU = .TRUE.
LDAUTYPE = 2
LDAUL = 3 -1
LDAUU = 5.0 0.0
LDAUJ = 0.0 0.0
LMAXMIX=6

should do it (similar to settings in published papers) assuming you have your atoms ordered Ce then O in POS(T)CAR...whether you really want to use LDA+U is a whole other ball game;)

christine1201 · #8 Post by **christine1201** » Fri Sep 15, 2006 9:59 pm

i solve the ce2o3 problem, but when i cal ceo2 with two vacancy , one week, the job can not converge.
the incar is as follow:
general:
System = CeO2
ISTART=0
ISPIN=2
GGA=91
ENCUT = 500 eV
PREC=high
ISIF=2
IBRION=1
NFREE=10
POTIM=0.2
ALGO=Fast
EDIFFG=-0.01
ISMEAR =0; SIGMA = 0.20 #-5 for accurate total energy and DOS 0 for large cell 1 for metal
NSW = 100
LREAL=A
AMIX = 0.2
BMIX = 0.0001
LMAXMIX = 6
LWAVE =.True.
VOSKOWN =1 # 0 for PBE 1 for PW91
NELM=200
NSIM=4
LDAU=.TRUE.
LDAUTYPE=2
LDAUL= 3 -1
LDAUU= 5 0
LDAUJ=0.5 0
any suggestion for me. thanks

elelel · #9 Post by **elelel** » Thu Sep 21, 2006 6:51 am

Hi Christine,

Have you tried ISIF=3 or 4? Will there be anything wrong with that? Thats what I have used in my calculations but I havent yet had a chance to test the settings Matt suggested for LDA+U - I can already see something I wasnt doing correctly though.

christine1201 · #10 Post by **christine1201** » Thu Sep 21, 2006 3:00 pm

thanks, i dont think ISIF should be 3 or 4. the job as i mentioned has been converged now.
but i have a question. if i only consider energy of the reaction, such as O vacancy formation, are the results with U and without U similar? i know DFT cant describ the band gap correctly. but for me, band gap isnot important. the energy is important. any suggestion?

elelel · #11 Post by **elelel** » Tue Sep 26, 2006 12:57 am

Dead right! Its CeO2 you are doing. I was thinking Ce2O3. No idea about other question, sorry.

jcconesa · #12 Post by **jcconesa** » Sat Oct 07, 2006 3:57 pm

The issue on the energy is probably not easy to solve (at least with VASP). See J. Phys. Chem. B 109 (2005) 22860. Fig. 1 in it, and all the discussion related to it, is interesting.

christine1201 · #13 Post by **christine1201** » Mon Oct 09, 2006 9:37 am

thanks. i have seen this paper before. but the code this group used is not vasp.

Veronika · #14 Post by **Veronika** » Tue Oct 10, 2006 8:07 am

Check the literature on Ceria in PRB, there were just recently some interesting papers about it, also in J. of Chem. Phys.

SKS · #15 Post by **SKS** » Sun Aug 04, 2013 5:45 am

In VASP, is this possible to specify Hubbard U for both the f and d orbitals of the same atom simultaneously ?