[Pw_forum] problems with pressure calculation

[Paolo Giannozzi]

Please provide input data (and pseudopotentials if not available
somewhere)

P.

On Mon, 2013-04-01 at 14:28 -0400, Eduardo Ariel Menendez Proupin wrote:
> Dear colleagues, 
> 
> 
> I have found strange differences in results for the calculation of
> pressure using pwscf in versions 4.3 and 5.0.N (N=1,2).  We are
> calculating wurtzite CdSe, using the following UPF files. 
> 
> PAW calculation
>    Cd  112.40000  Cd.pbe-dn-kjpaw_psl.0.2.UPF 
>    Se   78.96000  Se.pbe-n-kjpaw_psl.0.2.UPF 
> 
> 
> 
> Ultrasoft PP calculation
>    Cd  112.40000  Cd.pbe-dn-rrkjus_psl.0.2.UPF 
>    Se   78.96000  Se.pbe-n-rrkjus_psl.0.2.UPF 
> 
> 
> 
> 
> For the PAW calculations, the convergence of pressure with the density
> cutoff (euctrho) shows jumps  (see the attached  figure paw-press.eps)
> and no convergence in the case of version 5.0.N, while there is
> convergence with version 4.3. For both versions the total energies are
> the same. 
> 
> The jumps are associated with differences in the number of symmetry
> operations detected. The message 
> 
>  "         (note:  6 additional sym.ops. were found but ignored
>            their fractional translations are incommensurate with FFT
> grid)"
> 
> is associated with higher pressures (33 kbar). Lower pressures ~ 26
> kbar) are found when the FFT grid is commensurate and all 12 sym. ops.
> are used. 
> In the calculations with version 4.3 the pressures are somewhat lower,
> but apparently convergent. Also, there are less symmetry operations
> detected or used than for version 5.0.N. 
> 
> 
> 
> In the ultrasoft calculations, (see figure uspp-press), both versions
> 4.3 and 5.0.N produce convergent pressures vs ecutrho, but the
> pressures differ almost by 10 kbar. (The total energies are almost
> equal, as expected). 
> 
> 
> 
> Thanks for any comment. 
> 
> 
> -- 
> Eduardo Menendez Proupin
> Departamento de Fisica, Facultad de Ciencias, Universidad de Chile 
> URL: http://fisica.ciencias.uchile.cl/~emenendez
> "Lograremos el anhelado desarrollo cuando sea la ciudadanía, y no los
> científicos, la que pida más ciencia para Chile." J. Babul
> 
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