[Pw_forum] dynamical matrix

[Paolo Giannozzi]

On Friday 18 November 2005 11:36, Alberto Milani wrote:

> how one can change the default accuracy in the computation of 
> the dynamical matrix ?

there is no such thing as the "default accuracy" of the computation.
There are default values for the convergence thresholds, which may
or may not be appropriate in your case. These are conv_thr in the
scf calculation, tr2_ph in the phonon one. If you lower them and
the result doesn't change appreciably, this is what you get for the
particular set of approximations (i.e. cell size and geometry,
pseudopotentials, exchange-correlation functional, size of the 
plane-wave basis set, k-point grid, ....) you chose

> Unfortunately, my longitudinal acoustic frequencies are still
> not good enough 

there can be (approximately) 1001 reasons for this. If the particular 
set of approximations you chose doesn't give you satisfactory 
results, you have to examine all approximations done and verify 
their effect one at the time.

Paolo

-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050-509876, Fax:-563513 
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