[Pw_forum] nqx in HSE

[Giuseppe Mattioli]

Dear Amin
As usual, try to increase the nqx, nqy, nqz values till the band gap  
value is stable. Such value is the accurate "HSE with Quantum  
ESPRESSO" band gap value of Zincblend, As already stated by Paolo, an  
accurate calculated value may (or not) be close to the measured one. I  
can add that in the case of wide band gap semiconductors the HSE  
standard recipe (25% of exact exchange) often leads to an  
underestimation. Moreover, I must always remember that when we compare  
the gap between occupied amd unoccupied Kohn-Sham eigenvalues and the  
measured band gap we are trying to commensurate apple and pears...  
Sometimes they can be exchanged one piece for another. More often they  
are not...

HTH

Giuseppe

Giuseppe Mattioli
ISM-CNR
Italy

Quoting Amin Torabi <mtorabi at uwo.ca>:

> Thanks, but do you have any suggestion for my input file?
>
>
> On Fri, Nov 23, 2012 at 4:22 PM, Amin Torabi <mtorabi at uwo.ca> wrote:
>
>> Dear all,
>>
>> Using the following input file, I am trying to reproduce the bandgap of
>> ZnS (wurtzite). The structure is optimized (vc-relax at 1 atm) employing
>> PBEsol, and now I am using HSE to do scf.
>>
>> Question:
>> using nqx1=nqx2=nqx3=1,  I found the bandgap to be 3.66 eV, which is
>> comparable to others (PRL 102, 226401 (2009); however, by using nqx1=nqx2=3
>> and nqx3=2, the bandgap is reduced to 3.24ev.
>>
>> Does denser auxiliary mesh not mean an improved calculation?
>> I would appreciate any comment on my input file?
>> Thanks!
>>
>>
>>
>> &CONTROL
>>          calculation     = 'scf'
>>         prefix          = 'ZnS'
>>         pseudo_dir      = '...'
>>         outdir          = '...'
>> /
>> &SYSTEM
>>         ibrav            = 0
>>         celldm(1)      = 7.20174629
>>         nat               = 4
>>         ntyp             = 2
>>         nbnd            = 20
>>         ecutwfc        = 110
>>         nqx1            = 1
>>         nqx2            = 1
>>         nqx3            = 1
>>         input_dft       = 'hse'
>>         x_gamma_extrapolation = .true
>>         exxdiv_treatment='gygi-baldereschi'
>> /
>> &ELECTRONS
>>         conv_thr        = 1.0D-7
>> /
>> ATOMIC_SPECIES
>>  Zn 65.409  Zn.pbe-nc.UPF
>>  S  32.066  S.pbe-n-nc.UPF
>> CELL_PARAMETERS (alat=  7.20174629)
>>    0.992513482   0.000001434   0.000000000
>>   -0.496255499   0.859542606   0.000000000
>>    0.000000000   0.000000000   1.628169588
>> ATOMIC_POSITIONS (crystal)
>> Zn       0.333333038   0.666666962   0.000366211
>> Zn       0.666666962   0.333333038   0.500366148
>> S        0.333333175   0.666666825   0.374633891
>> S        0.666666825   0.333333175   0.874633750
>> K_POINTS automatic
>>  6 6 4 0 0 0
>>
>>
>> --
>> ***************************************
>> Amin Torabi
>> Ph.D. Student
>> Chemistry Dept.
>> Western University
>> London, On Canada, N6A 5B7
>> Phone: 519-661-2111 Ext: 87871
>> ****************************************
>>
>>
>
>
> --
> ***************************************
> Amin Torabi
> Ph.D. Student
> Chemistry Dept.
> Western University
> London, On Canada, N6A 5B7
> Phone: 519-661-2111 Ext: 87871
> ****************************************
>