[Pw_forum] phonon frequencies with pwscf and cpmd
giannozz at nest.sns.it
Tue Mar 23 15:31:03 CET 2004
On Tuesday 23 March 2004 10:57, Massimiliano Bonomi wrote:
> I'm using both pwscf and cpmd codes with the same parameters
> (cell dimension, cutoff for the wavefunctions, number of kpoints...)
> WAVEFUNCTION CUTOFF(RYDBERG): 15.00000
> DENSITY CUTOFF(RYDBERG): (DUAL= 4.00) 60.00000
> NUMBER OF SPECIAL K POINTS (IN CARTESIAN COORDINATES): 275
> kinetic-energy cut-off = 20.0000 Ry
> charge density cut-off = 100.0000 Ry
> number of k points= 258 [..]
doesn't look the same to me. There is no reason to use a non-default
cutoff for the charge density, by the way.
> pwscf's phonon frequencies are not all positive
see http://www.pwscf.org/guide/2.0/html-node/node34.html , under
"ph.x does not yield acoustic modes with omega=0 at q=0"
> For comparison I've calculated phonon frequencies with pwscf using
> car-parrinello finite differences method moving manually each atom.
> I found negative frequencies which are in agreement with the ones
> I found with perturbation method.
which demonstrates that the phonon code works
Paolo Giannozzi e-mail: giannozz at nest.sns.it
Scuola Normale Superiore Phone: +39/050-509876, Fax:-563513
Piazza dei Cavalieri 7 I-56126 Pisa, Italy
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