HF orbital splitting

[wcwang]

Dear All,

I report a very unusual problem about HF correction. I dope impurity into an insulator which has monoclinic geometry. For PBE calculation, I found three impurity levels. For each level, it has two states for electrons to occupy based on electron intergration in DOSCAR. However, when I do HSE correction, one of the three levels splits into two peaks. And each of the two peaks only shows single occupied behavior based on the electron occupation in DOSCAR. that means the spliting peak can only be occupied by one electron.

Why does the correction lead to the states splitting, it is very strange to me. BTW, it only happens in netrual charge system. It becomes normal when I add or remove electroncs fromt the system. I mean there is no single occupied states any more.

I did not includes spin in the system. and I also checked regular DFT calcualtion with and without spin. both did not show any state splitting. I guess it relates to HSE correction. I post the INCAR as the following.
######

ISTART =1

ICHARG =1

ISMEAR = 0

SIGMA=0.02

NEDOS=2000

LREAL= Auto


# HF calculation

LHFCALC=.TRUE.

HFSCREEN=0.2

ENCUTFOCK=0

NKRED=2

AEXX = 0.22

#AGGAX= 0.77

ALGO=Damped

NBANDS=400

TIME=0.04

#####
Any comment is appreciated.

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