[Pw_forum] tetrahedra and vc-relax

[chiara.ricca at dcb.unibe.ch]

Dear Dr. Kawamura thanks a lot for the patch.


Dear Giuseppe,

after discussion of our collaborators with Paolo Giannozzi and Stefano De Gironcoli,

we learned that it is possible in QE v 6.1 to use tetrahedra for relax and vc-relax calculations for insulators/semiconductors,

especially using the the  optimized tetrahedron method (occupations='tetrahedra_opt'), as reported in the

pw.x manual for version 6.1:

 Available options are:


'smearing' :

gaussian smearing for metals;
see variables smearing<http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#smearing> and degauss<http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#degauss>


'tetrahedra' :

Tetrahedron method, Bloechl's version:
P.E. Bloechl, PRB 49, 16223 (1994)<https://journals.aps.org/prb/abstract/10.1103/PhysRevB.49.16223>
Requires uniform grid of k-points, to be
automatically generated (see card K_POINTS<http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#K_POINTS>).
Well suited for calculation of DOS,
less so (because not variational) for
force/optimization/dynamics calculations.


'tetrahedra_lin' :

Original linear tetrahedron method.
To be used only as a reference;
the optimized tetrahedron method is more efficient.


'tetrahedra_opt' :

Optimized tetrahedron method:
see M. Kawamura, PRB 89, 094515 (2014)<https://journals.aps.org/prb/abstract/10.1103/PhysRevB.89.094515>.
Can be used for phonon calculations as well.


'fixed' :

for insulators with a gap


'from_input' :

The occupation are read from input file,
card OCCUPATIONS<http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#OCCUPATIONS>. Option valid only for a
single k-point, requires nbnd<http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#nbnd> to be set
in input. Occupations should be consistent
with the value of tot_charge<http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#tot_charge>.



Best,

Chiara




________________________________
De : pw_forum-bounces at pwscf.org <pw_forum-bounces at pwscf.org> de la part de Giuseppe Mattioli <giuseppe.mattioli at ism.cnr.it>
Envoyé : mercredi 18 octobre 2017 10:48:15
À : pw_forum at pwscf.org
Objet : Re: [Pw_forum] tetrahedra and vc-relax


Dear Chiara
You should not use occupations='tetrahedra' for relax or vc-relax
calculations! The reason is clearly stated in the pw.x manual. Use
smearing instead


    Variable:       occupations

    Type:           CHARACTER
    Description:
                    Available options are:

                    'smearing' :
                         gaussian smearing for metals;
                         see variables "smearing" and "degauss"

                    'tetrahedra' :
                         especially suited for calculation of DOS
                         (see P.E. Bloechl, PRB 49, 16223 (1994)).
                         Requires uniform grid of k-points,
                         automatically generated (see below).
                         Not suitable (because not variational) for
                         force/optimization/dynamics calculations.

                    'fixed' :
                         for insulators with a gap

                    'from_input' :
                         The occupation are read from input file,
                         card "OCCUPATIONS". Option valid only for a
                         single k-point, requires "nbnd" to be set
                         in input. Occupations should be consistent
                         with the value of "tot_charge".


HTH
Giuseppe

Quoting chiara.ricca at dcb.unibe.ch:

> Dear all,
>
> I'm trying to perform a "vc-relax" calculation using the tetrahedron
> method with QE v 6.1.
>
> The calculation stops after having printed the final geometry,
> during the final scf step.
>
> It does not write any error and the scheduler only reports a
> segmentation fault.
>
> I have tried with both tetrahedra and tetrahedra_opt, but I have the
> same issue.
>
> The problem is not there if I do a "relax" calculation.
>
> Please find attached, the input and output of an example.
>
> Thanks in advance!
>
> Regards,
>
> Chiara Ricca
>
> ---
>
> Postdoctoral fellow
>
> University of Bern



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
Via Salaria Km 29,300 - C.P. 10
I-00015 - Monterotondo Scalo (RM)
Mob (*preferred*) +39 373 7305625
Tel + 39 06 90672342 - Fax +39 06 90672316
E-mail: <giuseppe.mattioli at ism.cnr.it>

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