[Pw_forum] XSpectra: x-ray absorption spectra in Quantom Expresso

[matteo calandra]

> Dear all,
> Can Quantum Espresso calculate x-ray absorption spectra? or you can  
> recommend me some
> good software to calculate XAS?
> Regards
> Lily

Dear Lily,

   a new package has been included in the current CVS of the quantum
espresso distribution calculating K-edge X-ray absorption spectra.
The calculation uses gipaw and the lanczos method. Norm conserving
pseudopotentials are allowed and in september we will also upgrade to
ultrasoft pseudopotential. Spin polarised and DFT+U calculations
are allowed. The main advantage of this code is that, using the continous
fraction, it only requires the calculation of the occupied states
and thus no calculation of empty bands is necessary.
Core-hole effects are treated generating a pseudopotential
with a core-hole in the 1s state and then performing the
calculation on a supercell with a single absorbing atom.

The code is available under the directory XSpectra of the current
CVS. There is a short manual and an example is available
under the examples directory (NiO).
It requires the generation of a GIPAW pseudopotential with a
core-hole in the 1s state for the absorbing atom.
We have pseudopotentials of this kind for
several elements and they will be made public very soon.
More examples will be soon included.

The generalisation to ultrasoft pseudopotential has been terminated
and will be uploaded in september.

Please contact me if you need more informations on the code.

Matteo Calandra


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