[Pw_forum] Bandstructure of a metal slab

[Paolo Giannozzi]

On Friday 16 January 2004 21:15, Marcos Verissimo Alves wrote:

> I want to calculate the phonon spectrum of PbO at the Gamma point

if you are interested to q=0 phonons only, you do not need supercells,
either using frozen phonon or using linear response (the phonon code).

If you are interested to interatomic force constants in real space, then 
you need a suitable supercell (using frozen phonon) or a suitable grid 
of q-points in the unit cell (using linear response). See for instance:

Rev. Mod. Phys. 73, 515 (2001)
(pdf file at: http://www.nest.sns.it/~giannozz/Papers/RMP_52.pdf)
Phys. Rev. B 43, 7231 (1991)
(pdf file at: http://www.nest.sns.it/~giannozz/Papers/PRB_19.pdf) 
Phys. Rep. 309, 209 (1999)
Phys. Rev. A 52, 1086 (1995) and 1096
Phys. Rev. B 35, 10337(1997) and 10555

> My questions are: why do the eigenmodes differ?

they don't, if both calculations are performed in the proper way.
Beware normalizations, atomic masses, units, degenerate
eigenvalues, and so on

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