[Pw_forum] HSE vs PBE

[Giuseppe Mattioli]

Dear Giacomo

> is it OK? can I do it? I.e., using PBE psudopotential for HSE calculations?

A the present time, there is no other way to perform hybrid calculations but with GGA (norm 
conserving) pseudopotentials. In this regard, I suppose that a 95 Ry wfc cutoff may be poor for 
copper (with semicore 3s and 3p). You should test the convergence of your PBE results before 
attempting HSE calculations.

> and then use the same for HSE (same pseudopotentials at PBE, taken from the
> PwSCF website)

I'm quite puzzled... There is no NC pseudopotential for copper in the website. Do you mean the 
pslibrary?

>     input_dft='hse', nqx1= 2, nqx2= 2, nqx3= 2,

You should check the convergence of your results wrt the blend of k points and q points, and this is 
the most painful task when using hybrid functionals (and metals are very sensitive to k points...).
In practice, be sure to the convergence of k points in the PBE calculation, and starting from

nqx1= 1, nqx2= 1, nqx3= 1,

try to reach convergence (or reach the most bloody-cpu-consuming grid you can afford) wrt the q 
points.

> nspin=2

Copper is nonmagnetic, and you have an even number of atoms. Save (a lot of) time with nspin=1.

> nbnd = 80
> occupations='smearing'

The latter provide already a fair number of unoccupied states, you do not need to use the former.

HTH

Giuseppe


On Thursday 24 May 2012 04:45:14 giacsport at libero.it wrote:
> Dear All,
>             I am using the development version of PWscf.
> 
> I would like to ask you this question.
> 
> I want to make HSE hybrid calculations (vc-relax) using pseudopotential at
> PBE level.
> I want indeed test the impact of the hybrid functional in the lattice
> parameter (this is the case of Copper)
> 
> I mean is it a correct procedure to optimize the system with such initial
> settings
> 
> /
> &system
>     ibrav=  2, celldm(1) = 6.830792531
>     nat=  4, ntyp= 1, nspin=2,
>     ecutwfc = 95.,  nbnd = 80, occupations='smearing',
>     degauss=0.01,smearing='gaussian', starting_magnetization(1)=1
> /
> 
> and then use the same for HSE (same pseudopotentials at PBE, taken from the
> PwSCF website)
> 
> /
> &system
>     ibrav=  2, celldm(1) = 6.830792531
>     nat=  4, ntyp= 1, nspin=2,
>     ecutwfc = 95.,  nbnd = 80, occupations='smearing',
>     degauss=0.01,smearing='gaussian', starting_magnetization(1)=1
>     input_dft='hse', nqx1= 2, nqx2= 2, nqx3= 2,
>     x_gamma_extrapolation = .TRUE.
> /
> 
> is it OK? can I do it? I.e., using PBE psudopotential for HSE calculations?
> 
> 
> Thanks in advance for any suggestion!
> 
> Best,
> Giacomo

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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
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