[Pw_forum] lelfield and lberry (P Umari)

[umari at democritos.it]

Dear Chen,

> I am now running a calculation of strained STO  and try to calculate
> its spontaneous polarization based on Berry phase method. I try two
> different ways:
> 1) run a self-consistent calculation turning on lelfield=.true. and set
> efield=0.0
> 2) first run a self-consistent calculation and  then run a
> non-self-consistent calculation turning on lberry=.true.
> Are these two method equivalent? When I try these two methods on the same
> system, method 1) works well but method 2) fails because "probably because
> G_par is NOT a reciprocal lattice vector".

I think this is due to the fact that the berry's phase calculation 
(option lberry=.true.) is working on  parallel machines only for the
gdir =3 option. The Berry's phase polarization is also calculated through
the electric field routines which are working in parallel for any choice
of the gdir parameter. For the gdir = 3 case or for calculations
on serial machines the two methods are expected to give the same 
polarization differences.

Best regards,

Paolo Umari,
DEMOCRITOS




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