Questions about printing out unoccupied molecular orbitals (LUMO, LUMO+x)

marci marc... at
Wed Mar 3 09:07:27 UTC 2010


Actually, I do not think this is really a problem of the
but a misunderstanding in the definition of the MOs.
When you use the keyword ADDED_MOS together with the
diagonalization scheme,  at each SCF step all the occupied MOs
plus a number of unoccupied MOs equal to the ADDED_MOS are
computed (eigenvectors, eigenvalues, and occupation numbers).
If you print through the section
you can get the related eigenvalues and occupations, and from these
the gap.

Now, if on top of these you print through the section
and you require NLUMO different from zero,
NLUMO states are computed a posteriori, in addition to those
already computed along the SCF procedure. These are therefore higher
in energy, and do not correspond to the lowest LUMOS, but to
the lowest states laying above those already computed.
If you want the cubes of the lowest unoccupied states, and you have
different from zero, you should consider that some of them are
obtained with
the keyword NHOMO.
I agree that in this situation the keyword names NHOMO and NLUMO in
the section MO_CUBES
are misleading.

kind regards

On Mar 2, 5:17 pm, zh <vale... at> wrote:
> In my test calculations, I also found another problem:
> If the keyword "ADDED_MOS" in the section &SCF is set as 0 or 1, the
> LUMO and LUMO+1 orbitals of C6H6 molecule obtained with cp2k will be
> similar to those obtained with other codes.
> In the log file, there are two values printed out for the LUMO-HOMO
> gap.
> The first value of LUMO-HOMO gap is printed out due to the following
> keyword:
> "
>     &MO
>       &END MO
> "
> This one is reasonable. That is why I say that the unoccupied
> molecular orbitals are already obtained before calling "make_lumo()".
> The second value of LUMO-gap is printed out due to the following
> keyword:
> "
>          NHOMO  3
>          NLUMO  10
>          WRITE_CUBE .TRUE.
>       &END MO_CUBES
> "
> While the second one is quite larger than the first one.

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