can one specify the fermi level manually for GW ?

[askhetan]

Dear All,

I've been trying to run GW simulations for slab system. After usinhg algo=exact and writing the wavecar and waveder files when I start the GW simulations I get this message:
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The Fermi energy was updated, please check that it is located mid-gap
values below the HOMO (VB) or above the LUMO (CB) will cause erroneous energies
E-fermi : -5.1602
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What does vasp mean by "check that it is located mid-gap" ? Does it give us the freedom in someway to manually specify this ? The updated value of Fermi-level from vasp may be actually wrong and very slighly below my homo level, which i can see from the OUTCAR at some kpoints in the spin down case of the algo=exact run as:

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1 band eigenvalue occupancy
104 -5.2955 1.00000
105 -5.1602 0.11470
106 -5.1038 0.00000

2 band eigenvalue occupancy
104 -5.2954 1.00000
105 -5.1600 0.07003
106 -5.1037 0.0000

3 band eigenvalue occupancy
104 -5.2955 1.00000
105 -5.1601 0.08712
106 -5.1039 0.00000

4 band eigenvalue occupancy
104 -5.2955 1.00000
105 -5.1600 0.07239
106 -5.1037 0.00000
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As you can see, the fermi-level is not loacted "mid-gap" and there are slight partial occupancies just above the fermi level from kpoints cases 2/3/4. I know from literature that this system is actually an insulator with only a few surface conducting states. However my GW simulations tell me that this system is insulating and i should check for errors.
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CHECK_OCCUPATIONS: ERROR, system is not insulating.
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When I look at the OUTCAR printed after the GW simulations, the QP-energy values are very jumbled up:
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k-point 1 : 0.0000 0.0000 0.0000
band No. KS-energies QP-energies sigma(KS) V_xc(KS) V^pw_x(r,r') Z occupation
107 -6.2351 -8.1418 -19.6414 -14.5476 -27.5015 0.3743 1.0000 0.5362
108 -6.2351 -8.1418 -19.6414 -14.5476 -27.5015 0.3743 1.0000 0.5362
109 -5.8506 14.5640 -19.5989 -58.9072 -24.6618 0.5193 1.0000 0.3996
110 -5.4056 16.1812 -20.8656 -63.0062 -26.6991 0.5123 1.0000 0.2933
111 -5.4056 16.1812 -20.8656 -63.0062 -26.6991 0.5123 1.0000 0.2933
112 -5.4056 16.1812 -20.8656 -63.0062 -26.6991 0.5123 1.0000 0.2933
113 -4.3664 10.6058 -15.9067 -42.8719 -13.5373 0.5552 0.0000 -0.1952
114 -4.1893 9.3321 -16.1200 -41.6748 -13.0745 0.5291 0.0000 -0.2624
115 -4.1893 9.3321 -16.1200 -41.6748 -13.0745 0.5291 0.0000 -0.2624
116 -4.1893 9.3321 -16.1200 -41.6748 -13.0745 0.5291 0.0000 -0.2624
117 -2.5895 3.3566 -14.7629 -27.3238 -10.8450 0.4734 0.0000 -0.3563
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Here is my INCAR for the GW simulations:
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ALGO = GW0
ENCUTGW = 150
NOMEGA = 180
ISMEAR = 0
ISPIN = 2
SIGMA = 0.001
LREAL = .FALSE.
NELM = 1
LORBIT = 11
LOPTICS = .TRUE.
PRECFOCK = FAST
LWANNIER90 = .TRUE.
LWRITE_UNK = .TRUE.
LPEAD = .TRUE.
MAXMEM = 256000
KPAR = 3
NBANDS = 288
GGA = PS
OMEGAMIN = 0.001
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Could anyone suggest what might be going wrong or how to remedy this situation?

Thanks and Best Regards

[support_vasp]

Hi,

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