Initial guess of the density matrix

marci marc... at pci.uzh.ch
Thu Feb 11 22:59:39 CET 2010


Hi

something in the direction of a biased initial guess is already
present in QS.
The ATOMIC guess is normally based on the construction of a first
density matrix
by occupation of atomic orbitals according to the electronic
configuration
of each element.
However, there is the possibility to modify this procedure by
subtracting or adding
valence electrons (NEL) from specific channels (identified by N and
L ) of selected elements.
This can be done independently for spin up (ALPHA) and spin down
(BETA).
Have a look at the reference inputs in cp2k/tests/QS/regtest-bs.
This might provide a better initial guess, also for charged systems.
As a safety check, if the resulting density matrix amounts to the
wrong number of  electrons,
it is rescaled by  a proper factor, and the calculation proceeds.
This trick is only used for the initial guess, no further constraints
are applied afterwards.
Hence, there is no guarantee that the selected configuration is kept
during the SCF.

Kind regards
Marcella


On Feb 11, 9:12 pm, Simone Piccinin <piccini... at gmail.com> wrote:
> Dear CP2K users,
>
> I'm studying a large molecule containing 4 Ru atoms. These are
> arranged as to form two pairs. I'd like to study the molecule in a
> singlet state, and see if the coupling within each pair is
> ferromagnetic (FM) or antiferromagnetic (AF). Is there a way in
> quickstep to guide the scf cycle toward the FM or AF solution, for
> example through an appropriate initial guess of the density matrix?
>
> Thanks for your help.
>
> Best wishes,
>
> Simone Piccinin
> CNR-IOM Democritos (Trieste)



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