Hi,
Because of PBC you'll always get three, close to zero,
frequencies corresponding to the translation modes.
If you insist in forcing strict zero frequencies -not
necessarily advisable, due to the numerical errors
inherent to the evaluation of the force constants matrix-,
then you can modify the *.FC (force constansts matrix)
accordingly, and feed that to Vibra.
Regards,
Roberto
On Fri, 26 Nov 2010, "Fran?ois Varchon" wrote:
<!-- @page { margin: 2cm }
P { margin-bottom: 0.21cm } --> Dear Siesta users,
I am currently calculating the vibration frequencies of one molecule on a
Cu(111) surface using SIESTA and Vibra codes. I have just one broad question.
I was wondering if there is a way to impose the acoustic sum rule (i.e. impose
the three acoustic modes to be equal to 0) in SIESTA ?
Regards,
Fran?ois Varchon
UCL/IMCN/NAPS, Louvain-la-neuve, Belgium
