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[Latévi Max LAWSON DAKU <max.lawson@unige.ch>]

Dear Nicola,

Many thanks for your kind answer and your detailed
explanation ! I'll follow your advices for determining
the phonons.

All  the best,
Max

Nicola Marzari wrote:
> Dear Max,
>
>
> it seems all very good and reasonable, but if phonons is what you are
> after, I'd go for a more stringent test on kpoints/smearing (as a side
> note - if the quantities you are interested in were to depend only
> on the Fermi surface, you'd need much tigher convergence tests).
>
> Since phonons are what you are looking for, just displace one or
> more atoms (by 5% on their interatomic distances, say), and
> repeat the test, until forces are converged to your desired
> tolerance (I'd say 2-3 cm-1 in the phonon frequencies).
>
>                 nicola
>
>
>
> Latévi Max LAWSON DAKU wrote:
> > Dear Abinit users,
> >
> > I would like to study a family of related metallic systems.
> > For the one with the simplest molecular formula (6 atoms
> > in the formula unit), I tried to do a convergence study in
> > order to determine the optimal value of tsmear (cold
> > smearing; occopt=5).
> >
> > 1) Without smearing, I did full geometry optimisation with
> >    nkpt = 10, 28, 60 and ecut values of 20, 30, 40, 50 Ha
> >    (and an additional test optimisation with nkpt=60 and
> >    ecut=80). For this FCC system, this gives "converged"
> >    values of acell=7.260 angstrom and Etot=-167.260 Ha.
> >    The "(tsmear=0)-convergence" in acell (> 0.001 A) is
> >    obtained for ecut=40  Ha and nkpt=28.
> >
> >
> > 2) With ecut set to 40 Ha and smearing turned on, I made
> >    vary tsmear at fixed values of nkpt (10 pts -> circles;
> >    28 pts -> squares; 60 pts -> diamonds). The attached
> >    figures gives the dependences of acell and Etot on
> >    tsmear. For tsmear <= 0.01 Ha, acell=2.589 A and
> >    Etot=-167.266 Ha; independantly of the integration
> >    grid used. The curves are actually similar in the studied
> >    range.
> >
> > 3) Given these results, I would go with a tsmear value of
> >    4 mHa and nkpt=10 for the determination of the bulk
> >    modulus and its derivative, and  also of the phonons.

--
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Latevi Max LAWSON DAKU
Departement de chimie physique 
Universite de Geneve - Sciences II
30, quai Ernest-Ansermet  
CH-1211 Geneve 4 
Switzerland 

Tel: (41) 22/379 6548 ++ Fax: (41) 22/379 6103
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