[Pw_forum] why I can not get the correct band gap of TiO2?

[#TAO JUNGUANG#]

My input file is as following,

 &CONTROL

  calculation='nscf',

  restart_mode='from_scratch',

  

  pseudo_dir='/home/tao/pseudo/',

   tstress=.true.

  tprnfor=.true.

/

&SYSTEM

 ibrav=6, a=4.594,c=2.958, nat=6,ntyp=2,

 ecutwfc=16,

/

&ELECTRONS

  conv_thr=1.0d-8,

  mixing_beta=0.7,

  mixing_mode='plain',

/

&IONS

  ion_dynamics='bfgs',

  upscale=10

  /

 

ATOMIC_SPECIES

 Ti  47.867   Ti.vdb.UPF

 O   15.9994  O.vdb.UPF

 

ATOMIC_POSITIONS crystal

Ti 0.00 0.00 0.00

Ti 0.5  0.5  0.5

O  0.3053 0.3053 0.00

O  0.6947 0.6947 0.00

O  0.1947 0.8053 0.50

O  0.8053 0.1947 0.50

K_POINTS 

36

0.5 0.5 0.5  1

0.4 0.4 0.4  1

0.3 0.3 0.3  1

0.2 0.2 0.2  1

0.1 0.1 0.1  1

0.0 0.0 0.0  1

0.0 0.0 0.1  1

0.0 0.0 0.2  1

0.0 0.0 0.3  1

0.0 0.0 0.4  1

0.0 0.0 0.5  1

0.0 0.0 0.6  1

0.0 0.0 0.7  1

0.0 0.0 0.8  1

0.0 0.0 0.9  1

0.0 0.0 1.0  1

0.0 0.1 1.0  1

0.0 0.2 1.0  1

0.0 0.3 1.0  1

0.0 0.4 1.0  1

0.0 0.5 1.0  1

0.0 0.6 1.0  1

0.0 0.7 1.0  1

0.0 0.8 1.0  1

0.0 0.9 1.0  1

0.0 1.0 1.0  1

0.0 0.9 0.9  1

0.0 0.8 0.8  1

0.0 0.7 0.7  1

0.0 0.6 0.6  1

0.0 0.5 0.5  1

0.0 0.4 0.4  1

0.0 0.3 0.3  1

0.0 0.2 0.2  1

0.0 0.1 0.1  1

0.0 0.0 0.0  1

 

And the output file is:

 

.......

.... End of band structure calculation

 

          k = 0.5000 0.5000 0.5000     band energies (ev):

 

   -48.0011 -47.9986 -24.3665 -24.3599 -23.9018 -23.9017 -23.6774
-23.6773

    -9.6133  -9.6128  -9.5064  -9.5063   3.0737   3.0742   3.4060
3.4062

     4.6156   4.6161   5.5717   5.5719   6.6187   6.6188   6.7179
6.7182

 

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