XAS input

marci marcella.ia... at psi.ch
Thu Oct 30 09:14:46 UTC 2008

Hi Carlo,

when running core level spectroscopy simulations, you should specify
from which core state the electron is extracted. This is done
by giving the index of the atom on which the core state is located and
type of the state, for example 1s.
Then the corresponding molecular orbital has to be identified.
The search is limited to the lowest n MOS, as given by the input
Typically, first a localization procedure is run only over these n MOS
and then the
location and character of each rotated MOS is verified.
Once the desired state has been identified, its occupation number is
changed and a new SCF is started,
using  the ground state MOS as initial guess.

For the emission spectrum (XES) only the occupied valence orbitals are
needed. Instead,
a certain number of unoccupied states should be added to obtain a
absorption spectrum.
The implemented method is suitable for near-edge-XAS, i.e. within a
range of about 20÷30 eV above the homo.
This is why the  ADDED_MOS keyword is present in the XAS section.
The number you give indicates how many states are added to the initial
set of MOS that has been used for the ground state calculation.
It is duplicated because in principle you do not need many unoccupied
states for the ground state calculation.
If you already added unoccupied states for the ground state
calculation, say 10, the number of states given in XAS%ADDED_MOS, say
is added to the first 10, i.e. the new SCF with the excited core state
is run with 110 unoccupied states.

I hope this clarifies your doubts,


On Oct 30, 9:36 am, "c.pignedoli" <c.pig... at gmail.com> wrote:
> Dear all,
> I'm not so sure to fully understand the input cards of the XAS
> section.
> In particular, I don't know the meaning of
> and the meaning of ADDED_MOS if another card ADDED_MOS is present in
> the SCF section
> Can anybody help me?
> Ciao
> Carlo

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