
XSPECTRA : X-ray spectra calculation

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by C. Gougoussis, O. Bunau, A. Seitsonen, F. Mauri and M. Calandra

K 
The theoretical approach on which XSpectra is based was described in:

L23 edges,

O. Bunau and M. Calandra
Projector augmented wave calculation of x-ray absorption spectra at the L2,3 edges
Phys. Rev. B 87, 205105 (2013) 

K edges

Christos Gougoussis, Matteo Calandra, Ari P. Seitsonen, Francesco Mauri,
"First principles calculations of X-ray absorption in an ultrasoft
pseudopotentials scheme: from $\alpha$-quartz to high-T$_c$ compounds",
Phys. Rev. B 80, 075102 (2009)

you should cite this work in all publications using this software.

If you use only Norm Conserving pseudopotentials, you should also
cite the following publication:

M. Taillefumier, D. Cabaret, A. M. Flank, and F. Mauri
"X-ray absorption near-edge structure calculations with the pseudopotentials: Application to the K edge in diamond 
and alpha-quartz", Phys. Rev. B 66, 195107 (2002)

The implementation of the DFT+U approximation and its application to
K-edge XAS in NiO was performed in:

C. Gougoussis, M. Calandra, A. Seitsonen, Ch. Brouder, A. Shukla, F. Mauri
" Intrinsic charge transfer gap in NiO from  Ni K -edge x-ray absorption spectroscopy", Phys. Rev. B 79, 045118 (2009)

The interface of the DFT+U+V code and the XSpectra code and its application to
oxygen K-edge XAS in LaFeO3 and LaFe0.75Ni0.25O3 is described in:

I. Timrov, P. Agrawal, X. Zhang, S. Erat, R. Liu, A. Braun, M. Cococcioni, M. Calandra, N. Marzari, D. Passerone,
"Electronic structure of pristine and Ni-substituted LaFeO3 from near edge x-ray absorption fine structure experiments 
and first-principles simulations", Phys. Rev. Research 2, 033265 (2020)

Finally you should cite properly the Quantum Espresso package.

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For more information about XSpectra read doc/INPUT_XSPECTRA
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This module uses subroutines from PW with the general infrasturcture provided by
Quantum Espresso. 

The directory XSpectra must reside immediately under the espresso directory for Makefiles to work. 

Standart compilation: Run "make xspectra" in espresso directory where XSpectra is a subdirectory
 
Directory Structure: 
src      : The source files
doc      : The documentation
examples :
tools    : small programms and scripts
           1) Plot core density for UPF pseudopotential format

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Important information for developers:

1) before starting a new development,  please contact Matteo Calandra, main 
developer of XSpectra to know if someone else is not already doing what 
you plan to do and to know what is the better way to do it (in a global 
view of the code).

2) If you plan to touch the code molecular_nexafs.f90, please contact
Guido Fratesi before.
