[QE-users] Bandstructure with HSE provides wrong eigenvalues

[Stefan Seidl]

Dear All,
I am calculating with QUANTUM ESPRESSO the BANDSTRUCTURE of Silicon with HYBRID FUNCTIONAL HSE.

My calculation contains 3 steps:

1: pw.x 	< si.scf.in 				> si.scf.out
2: pw.x 	< si.scf_instead_bands.in 	> si.scf_instead_bands.out
3: bands.x 	< bands.in 			> bands.out

to 1: I am using an explicit kpoint list with a correspoinding qpoint grid
       all kpoints (12 12 12 mesh )are equal weighted with 1 (which provides the weight 2/(12**3) )
#######################################################
&control
    calculation   = 'scf'
    prefix        = 'silicon',
    pseudo_dir    = './',
    outdir        = './calculation'
    verbosity     = 'high',
 /
 &system    
    ibrav       = 2,
    celldm(1)   = 10.2612, 
    nat         = 2, 
    ntyp        = 1,
    ecutwfc     = 40.0,  
   ! nbnd       = 8,
    input_dft   ='hse', 
    nqx1        = 4, 		
    nqx2        = 4, 
    nqx3        = 4,
    occupations = 'smearing',   
    smearing    = 'gaussian',
    degauss     = 0.001, 

    nosym       = .TRUE.,    
    noinv       = .TRUE.,	
 /
 &electrons
    mixing_beta = 0.7 
 /

ATOMIC_SPECIES
 Si  28.0855  Si_NCv0.4_PBE_stringent.upf
ATOMIC_POSITIONS
 Si 0.00 0.00 0.00 
 Si 0.25 0.25 0.25
K_POINTS tpiba
     1728
  0.0000000   0.0000000   0.0000000 1
 -0.0833333   0.0833333  -0.0833333 1
 -0.1666667   0.1666667  -0.1666667 1
 -0.2500000   0.2500000  -0.2500000 1
 -0.3333333   0.3333333  -0.3333333 1
 -0.4166667   0.4166667  -0.4166667 1
  0.5000000  -0.5000000   0.5000000 1
  0.4166667  -0.4166667   0.4166667 1
  0.3333333  -0.3333333   0.3333333 1
  0.2500000  -0.2500000   0.2500000 1
  0.1666667  -0.1666667   0.1666667 1
  0.0833333  -0.0833333   0.0833333 1
  0.0833333   0.0833333   0.0833333 1
  0.0000000   0.1666667   0.0000000 1
 -0.0833333   0.2500000  -0.0833333 1
 -0.1666667   0.3333333  -0.1666667 1
...




to 2: here I am just specifying the special kpoint path
#######################################################

&control
    calculation   = 'scf'
    prefix        = 'silicon',
    pseudo_dir    = './',
    outdir        = './calculation'
    verbosity     = 'high',
 /
 &system    
    ibrav       = 2,
    celldm(1)   = 10.2612, 
    nat         = 2, 
    ntyp        = 1,
    ecutwfc     = 40.0,  
    nbnd        = 8,
    input_dft   ='hse', 
    nqx1        = 1, 		
    nqx2        = 1, 
    nqx3        = 1,
    occupations = 'smearing',   
    smearing    = 'gaussian',
    degauss     = 0.001, 

    nosym       = .TRUE.,
    noinv       = .TRUE.,	
 /
 &electrons
    mixing_beta = 0.7 
 /

ATOMIC_SPECIES
 Si  28.0855  Si_NCv0.4_PBE_stringent.upf
ATOMIC_POSITIONS
 Si 0.00 0.00 0.00 
 Si 0.25 0.25 0.25
K_POINTS tpiba
       50
   0.50000000  0.50000000  0.50000000     1 
   0.44444444  0.44444444  0.44444444     2 
   0.38888889  0.38888889  0.38888889     3
   0.33333333  0.33333333  0.33333333     4
   0.27777778  0.27777778  0.27777778     5
   0.22222222  0.22222222  0.22222222     6
   0.16666667  0.16666667  0.16666667     7
   0.11111111  0.11111111  0.11111111     8
   0.05555556  0.05555556  0.05555556     9
   0.00000000  0.00000000  0.00000000     10
   0.00000000  0.00000000  0.00000000     11
 ...
  


The eigenvalues from my 1st calculation si.scf.out are correct !
But the eigenvalues of the 2nd calculation si.bands.out are wrong !
E.g. the HOMO-LUMO distance at the Gamma point is just too big (compared to VASP results which are proven to be right)!

Where is the mistake in my input file si.bands.in for the 2nd calculation ??

Thanks a lot, best
Stefan


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