[Pw_forum] error on phonon calculation (root not converged)
Paolo Giannozzi
giannozz at nest.sns.it
Mon Apr 10 18:19:01 CEST 2006
On Monday 10 April 2006 17:35, Liping YU wrote:
> Actually, for 1e-18, though unconvergence message came up
> in phonon calculation, the dielectric constant I got (see below)
> was pretty close to 1.0e-10 in the same 2*2*1 supercell.
>
> (2x2x1, tr2_ph=1.0e-18, alpha_mix=0.1)
> ( 222.132924025 0.000000000 0.000000000 )
> ( 0.000000000 222.132924025 0.000000000 )
> ( 0.000000000 0.000000000 6.253206744 )
>
> (2x2x1, tr2_ph=1.0e-10, apha_mix=0.1)
> ( 222.139158023 0.000000000 0.000000000 )
> ( 0.000000000 222.139158023 0.000000000 )
> ( 0.000000000 0.000000000 6.262166130 )
so it is not a problem of convergence. Such large values of the
dielectric constants mean that the gap is very small.
> (1x1x1, tr_ph=1.0e-18, alpha_mix=0.7)
> ( 6.296436141 0.000000000 0.000000000 )
> ( 0.000000000 6.296436141 0.000000000 )
> ( 0.000000000 0.000000000 6.296436141 ).
If you do a supercell calculation with same atomic positions and
equivalent k-point grid as in the original cell, you should get the
same Kohn-Sham eigenvalues (refolded into the appropriate
k-points) and four time the energy of the original cell. If you don't,
please check very carefully your data.
Paolo
--
Paolo Giannozzi e-mail: giannozz at nest.sns.it
Scuola Normale Superiore Phone: +39/050-509876, Fax:-563513
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