[QE-users] A question regarding tot_magnetization

[Giovanni Cantele]

Dear users/developers,

I've a simple question regarding the tot_magnetization keyword. I have a
system composed by the repetition of n units, each one that should carry a
1.0 magnetization. The total magnetization should be n x 1.0.
In the isolated unit, if I use, let's say, starting_magnetization(1) = 0.1,
it correctly converges towards 1.0 magnetization. However, in the system
where this unit cell is repeated n times along a given direction, the
system wants for some values of n to converge to a much higher energy with
a 5.0 magnetization per unit (so 5xn in total). To restore the correct
ground state, I set tot_magnetization = n.

The question is: the result I get "constraining" the magnetization with the
tot_magnetization keyword is necessarily the same (in terms, for example,
of electronic levels) as that I would obtain using starting_magnetization
if the system spontaneously converged to a magnetization equal to n, or the
constraint could force, in some cases, unusual occupations and so I get the
correct magnetization but this would not correspond to the ground state
with that magnetization I'm looking for?
The question arises because in some cases I get the warning
BEWARE: non-integer number of up and down electrons!
As such, I want to be sure that the "BEWARE" concerns only the "starting"
occupations, but then the convergence is to the correct ground state,
whereas it is not the case that "unusual" (or, even worse, "unphysical")
occupations are forced even though the final magnetization is the same as
that I expect.

I thank you in advance for your attention.

Giovanni

-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it <giovanni.cantele at spin.cnr.it>
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: https://sites.google.com/view/giovanni-cantele/home
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