[Pw_forum] nk1,nk2,nk3 selection rule for HCP

[Stefano de Gironcoli]

without additional knowledge of the electronic structure of the system I 
think a reasonable criterion is that the density of points in all 
directions is more or less the same.
so I would say that in an hcp with c/a ~ 1.6 a more balanced grid could 
have been 18 18 12 (~18/1.6) 0 0 0.
but how many points are needed depends on the dispersion of the band 
structure in the different directions.
If on a given direction the band structure varies strongly and in 
another it is almost flat It is likely you'll need many more k-points in 
the former direction than in the latter.

The golden rule is as usual to check convergence in your particular case 
and if the behavior of your convergence test does not agree with your 
expectation think which of the assumptions you based your expectation on 
does not apply.

hope this helps, regards,

stefano

On 05/03/2012 01:28 PM, Divya Srivastava wrote:
> Dear QE Developers/Users
>
> I have used K_POINTS (automatic)  18 18 18 0 0 0 for HCP (hexagonal close packed) lattice  in scf calculation. My lattice parameters are a= 4.0 a. u. and c/a = 1.59. I would like to know  whether I can use  nk1=nk2=nk3 for the HCP lattice or not.  If not what is the criteria for choosing them in case of non cubic (HCP) lattices.
>
> Sincerely,
> Sincerely,
>
> Dr. Divya Srivastava
> Research Associate
> TSU, JNCASR
> Jakkur, Bangalore-64
>
> Tel: +9122082834
>
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