[Pw_forum] Occupation numbers in CP and FPMD

Paolo Giannozzi giannozz at nest.sns.it
Mon May 19 19:41:46 CEST 2003

On Monday 19 May 2003 16:45, Eyvaz Isaev wrote:
> Dear all,
> Now I am trying to do some calculations with CP and
> FPMD. But I was surprised very much due to the
> "occupations" option. It turned out that they are
> fixed, i.e. valance and conduction bands are separated
> as in semiconductors and and insulators. At least,
> smearing is not used in CP and FPMD. Does it mean that
> this kind of calculations could not be carried out for
> metallic systems?

Car-Parrinello dynamics and metallic systems don't
go along very well: see for instance
G. Pastore, E. Smargiassi, F. Buda,  Phys. Rev. A 44, 6334 (1991).
In order to perform CP simulations in systems with
very small or no gap, one has to use Nose' thermostats 
on electronic degrees of freedom, or similar techniques. 
Such techniques may require some serious experience.

By the way: there is a bug in the CP distribution on the web
that may cause a crash or a memory leak (invariably leading
to a crash): lines 2039-2040 of CPV/cprsub.f90:
        end if
should be reversed:
        end if


Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050509412
Piazza dei Cavalieri 7      Fax:     +39/050509417, 050563513     
I-56126 Pisa, Italy         Office:  Lab. NEST, Via della Faggiola 19

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