[Pw_forum] 答复: [Pw_forum] ´ð¸´: [Pw_forum] The band gap problem

[#TAO JUNGUANG#]

Yes, the gap of TiO2 is direct gap with valence band top and conduction band bottom at Gamma. 
And yes I have drawn the band structure and compared with the other guys,  they looks agree quite well. Only different is the gap value. You know, normally the band gap based on calculation is smaller than the experiment value, which is true for other guys' results but only mine not. So I am confused.
I don't know if the attachment can been seen or not. If yes ,I can attach my band structure that I have drawn.
 
Forgive my ignorance
is TiO2 known to be a direct gap insulator with valence band top and 
conduction band bottom at Gamma ?
Have you drawn the band structure on the main symmetry lines and compared with
experiment/other calculations ?

stefano

Quoting #TAO JUNGUANG# <TAOJ0003 at ntu.edu.sg>:

> Yes, it is very strange, even it agree very well with the experiment value
> (3.2eV). so I am wonder if there are something wrong. And I have double
> checked my input file, nothing I have got. So I put important part of my
> input/output file in the following, hope there is someone who can help me.
>    
> 
> 
> Input file:
>   &CONTROL
>   calculation='nscf',
>   restart_mode='from_scratch',
>    pseudo_dir='/home/tao/pseudo/',
>   prefix='TiO2',
>    tstress=.true.
>   tprnfor=.true.
> /
> &SYSTEM
>  ibrav=6, a=4.594,c=2.958, nat=6,ntyp=2,
>  ecutwfc=50,ecutrho=300,nbnd=32
> /
> &ELECTRONS
>   conv_thr=1.0d-8,
>   mixing_beta=0.7,
>   mixing_mode='plain',
> /
> 
> 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
>  .........
> Output file 
> 
>  k = 0.0000 0.0000 0.0000     band energies (ev):
> 
>    -48.0513 -48.0328 -24.6394 -24.6394 -24.5918 -24.5555 -24.4560 -24.4560
>    -10.8949  -9.9359  -9.1136  -9.1136   1.4513   1.7754   2.9432   3.3134
>      3.3134   4.5065   4.5065   4.9294   5.9502   6.2828   6.2828   6.9172
>     10.1728  10.2878  10.7490  10.7491  10.8082  12.5115  12.6253  14.3036
> 
>  10.1728-6.9172=3.2556
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