[QE-users] Flat band structure

[Leo Yang]

Dear QE Users,
  
 I am trying to simulation a system with cell parameter represented below:
  
 &SYSTEM
    a     =  9.66639e+00
    b     =  1.08037e+01
    c     =  1.65553e+01
    cosab =  1.72500e-01
    cosac =  1.52180e-01
    cosbc =  1.69516e-02
    ibrav = 14
    nat   = 182
    ntyp  = 5
  
 And I choose the uniform k grid as 6x6x6 for SCF calculation. But the eigenvalue between each k point (same band) are almost same. I also try calculate the band structure with k path:
  
        0.0000000000    0.0000000000    0.0000000000    1.0
        0.0000000000    0.0000000000    0.1666666667    1.0
        0.0000000000    0.0000000000    0.3333333333    1.0
        0.0000000000    0.0000000000    0.5000000000    1.0
        0.0000000000    0.1000000000    0.4000000000    1.0
        0.0000000000    0.2000000000    0.3000000000    1.0
        0.0000000000    0.3000000000    0.2000000000    1.0
        0.0000000000    0.4000000000    0.1000000000    1.0
        0.0000000000    0.5000000000    0.0000000000    1.0
        0.0000000000    0.3750000000    0.0000000000    1.0
        0.0000000000    0.2500000000    0.0000000000    1.0
        0.0000000000    0.1250000000    0.0000000000    1.0
        0.0000000000    0.0000000000    0.0000000000    1.0
       -0.1000000000    0.0000000000    0.0000000000    1.0
       -0.2000000000    0.0000000000    0.0000000000    1.0
       -0.3000000000    0.0000000000    0.0000000000    1.0
       -0.4000000000    0.0000000000    0.0000000000    1.0
       -0.5000000000   -0.0000000000   -0.0000000000    1.0
       -0.5000000000   -0.1000000000   -0.1000000000    1.0
       -0.5000000000   -0.2000000000   -0.2000000000    1.0
       -0.5000000000   -0.3000000000   -0.3000000000    1.0
       -0.5000000000   -0.4000000000   -0.4000000000    1.0
       -0.5000000000   -0.5000000000   -0.5000000000    1.0
       -0.4166666667   -0.4166666667   -0.4166666667    1.0
       -0.3333333333   -0.3333333333   -0.3333333333    1.0
       -0.2500000000   -0.2500000000   -0.2500000000    1.0
       -0.1666666667   -0.1666666667   -0.1666666667    1.0
       -0.0833333333   -0.0833333333   -0.0833333333    1.0
        0.0000000000    0.0000000000    0.0000000000    1.0
       -0.0833333333   -0.0833333333    0.0000000000    1.0
       -0.1666666667   -0.1666666667    0.0000000000    1.0
       -0.2500000000   -0.2500000000    0.0000000000    1.0
       -0.3333333333   -0.3333333333    0.0000000000    1.0
       -0.4166666667   -0.4166666667    0.0000000000    1.0
       -0.5000000000   -0.5000000000   -0.0000000000    1.0
       -0.5000000000   -0.4000000000   -0.1000000000    1.0
       -0.5000000000   -0.3000000000   -0.2000000000    1.0
       -0.5000000000   -0.2000000000   -0.3000000000    1.0
       -0.5000000000   -0.1000000000   -0.4000000000    1.0
       -0.5000000000    0.0000000000   -0.5000000000    1.0
       -0.4000000000    0.0000000000   -0.4000000000    1.0
       -0.3000000000    0.0000000000   -0.3000000000    1.0
       -0.2000000000    0.0000000000   -0.2000000000    1.0
       -0.1000000000    0.0000000000   -0.1000000000    1.0
        0.0000000000    0.0000000000    0.0000000000    1.0
        0.0002800000   -0.1005580000    0.0986140000    1.0
        0.0005600000   -0.2011160000    0.1972280000    1.0
        0.0008400000   -0.3016740000    0.2958420000    1.0
        0.0011200000   -0.4022320000    0.3944560000    1.0
        0.0014000000   -0.5027900000    0.4930700000    1.0  
  
 The band structure in the plot is flat. What is reason for that? Is there any mistake I made during the simulation? It will be very appreciated if you solve my question. Thank you.
  
 Best,
 Yang Zhou
  
  
 Yang Zhou
 PhD student
 University of Leeds
 United Kingdom 
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