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[matthieu verstraete <matthieu.jean.verstraete@gmail.com>]

As Pierre-Matthieu said, it depends what you want to look at, and how
severe you need to be. In the case of elphon, the problem is that you
need to use matrix elements of the perturbed potential, which contain
explicit wavefunctions (not integrated over k or bands). Therefore,
the tolwfr ensures that the wavefunctions will be converged as well,
not just the energy or potential or forces. Globally speaking tolwfr
is the slowest quantity to converge, although as PMA said you can
always find pathological cases where one tolwfr is converged but
tolvrs not (I have seen this) or the other way around (seen that too).
So: always check your final ETOT line and think about what you are
calculating and what needs to be precise!

Matthieu

On Mon, Jun 8, 2009 at 9:23 AM, St Druid<tq02ksu@gmail.com> wrote:
> Dear PMA, LUO
> Thank you for your reply, i got it.
> tolvrs is a very good convergent criterion. But one can relax the
> system using voldfe to get relevant stable coordination at first time.
>
> OK. thank you.
>
> sincerely.
>
>
> --
> B.W. Dong
> State Key Laboratory of Superhard Materials,
> Jilin University, Changchun, China. 130012
>
> tq02ksu@gmail.com [ dbw07@mails.jlu.edu.cn ]
>



-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF)
Dpto. Fisica de Materiales,
U. del Pais Vasco,
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Mail : matthieu.jean.verstraete@gmail.com
http://www-users.york.ac.uk/~mjv500