[Pw_forum] starting_magnetization and magnetization optimization in pwscf
Stefano de Gironcoli
degironc at sissa.it
Thu Apr 1 23:17:50 CEST 2010
Dear Jia Chen,
the starting magnetization variable is used to define the initial
charge density in a scf run in pwscf.
This density is used to build the first KS potential which thus
results to have a magnetically broken symmetry.
The resulting spin-up and spin-down hamiltonians are diagonalized and
the Fermi energy located from the constraint on the total number of
electrons (the system must be treated as a metal and a number of empty
states are present).
This determines the output density and since the potential is
"magnetically ordered" the density also is if the system likes so.
Then the code mixes in and out densities and builds a new guess for
the input density and hence the new KS potential and so on...
So starting magnetization really enters only in PW/atomic_rho.f90
which is used to build the starting guess for the input charge density as
rho_up = sum_s (1.0+starting_magnetization_atom_s)/2 *
unpolarized_rho_atom_s
rho_dw = sum_s (1.0-starting_magnetization_atom_s)/2 *
unpolarized_rho_atom_s
Hope this helps,
stefano
jia chen wrote:
> Dear All,
>
> Pwscf has a very nice feature that can set initial magnetism of a
> certain kind of atom by starting_magnetization. It is working very
> well for me. But I would like to know more about how this is really
> working in cp code, during magnetization optimization calculations. It
> is too much for me to read the code to get the answer. So I would like
> to give a guess of basic idea of this process.
>
> When we start a calculation with initial atomic wave functions. Pwscf
> code can give atomic occupations of spin up and down whose ratio
> satisfy the value of starting_magnetization. During the calculation,
> pwscf can adjust the occupation number after each diagonal step
> according to orbitals energies because pwscf goes with a bunch of
> empty states. Then there can be "electron flow" between spin up and
> down. Basically, that's I guess how pwscf does magnetization
> optimization.
>
> Can you tell me what is the actual process pwscf goes though in this
> kind of magnetization optimizations? Any comments are very welcome.
> Thank you in advance.
>
> Best Wishes
>
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