Initial guess of the density matrix

Simone Piccinin piccini... at gmail.com
Fri Feb 12 09:27:06 CET 2010


Dear Marcella,

thanks a lot for the answer.
I'm not sure I understand how to use these feature, though.

The relevant section of the cu2cl6_m1_clp6cud9.inp file in the test/QS/
regtest-bs folder is this:

    &KIND  Cu1
      ELEMENT Cu
      BASIS_SET  DZVP-MOLOPT-SR-GTH
      POTENTIAL  GTH-BLYP-q11
      &BS
        &ALPHA
          NEL -1   0
          L    0   2
          N    4   3
        &END
        &BETA
          NEL -1  -2
          L    0   2
          N    4   3
        &END
      &END
    &END

Does this mean that we are removing, from the alpha channel of Cu1, 1
electron from the 4s and in the beta channel 1 electron from the 4s
and 2 electrons from the 3d?
If so, Cu1 now has 4 electrons less than the neutral atom. A similar
treatment is done for Cu2. For Cl, on the other hand, it seems that we
are adding 2 alpha
electrons and 2 beta electrons in the 3p orbitals. Since we have 6 Cl
and 2 Cu atoms in the molecule, the overall charge should be 2*4-6*4 =
-16, resulting
in a wrong number of electrons. Is this what is done, or did I
misunderstand something?

Thanks a lot.
Best wishes,
Simone


On 11 Feb, 22:59, marci <marc... at pci.uzh.ch> wrote:
> 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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