[Pw_forum] scf and nscf and smearing

Stefano de Gironcoli degironc at sissa.it
Tue Dec 28 12:21:11 CET 2004

If you want to compute total energy (scf calculation) of a  metal you 
need to specify some
strategy to deal with the Fermi energy. You have to specify either 
(that requires the use of an automatically generated k-ponit grid) or 
(in this case also smearing and degauss variables must be set;  see 
INPUT_PW for their definitions).

When you do a band structure (nscf) calculation  the scf potential is 
read from file and the
(previously computed) scf  hamiltonian is diagonalized on the k-points 
specified in the nscf input..
The Fermi energy is not computed, nor it is the charge density or the 
Thus, you don't need to specify occupations, smearing or degauss but 
they don't harm.
If you leave them in the input file they will (should) be simply ignored.

best wishes,
Stefano de Gironcoli

W. YU wrote:

>Dear PW users,
>For metal system, in scf calculation, it is required
>to use occupation='smearing'. Do we still required to
>include  it and the same other parameters such as
>degause in the following nscf calculations as we do in
>the scf calculation?
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