[CP2K:1508] Re: XAS input

[carlo antonio pignedoli]

Ciao Marcella,
that's more or less all I needed, thanks a lot!!
In addition.. if I am interested only in the core level shift in a
bulk calculation,
what would be your suggestion for a reasonable number of  ADDED_MOS
(depending on the
size of the system)?

Thanks again

Carlo

On Thu, Oct 30, 2008 at 10:14 AM, marci <marcella.ia... at psi.ch> wrote:
>
> 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
> the
> 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
> keyword STATE_SEARCH.
> 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
> reasonable
> 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
> 100,
> 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,
>
> ciao
> Marcella
>
>
> 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
>>
>> STATE_SEARCH  n
>>
>> and the meaning of ADDED_MOS if another card ADDED_MOS is present in
>> the SCF section
>>
>> Can anybody help me?
>>
>> Ciao
>>
>> Carlo
> >
>