A X-ray Absorption Near-Edge Structure (XANES) spectrum reflects the probability of X-rays being absorbed by individual atoms and exciting the core electrons (therefore leaving a core hole) into unoccupied density of states. In the decay process the photoelectron can scatter from electrons of neighboring atoms. This scattering process affects the absorption coefficient that is measured for different energies of the incoming synchrotron radiation.

CP2K is a general purpose quantum chemistry and solid state physics code based upon Density Functional Theory. In the context of X-ray spectroscopy, one of its primary advantages is its use of a mixed Gaussian and plane wave basis set (GPW and GAPW). This makes it possible to simultaneously describe the core electrons and the diffuse continuum (scattered) states associated with the above ionisation resonances.  

References associated with CP2K and details of the implementation of X-ray spectroscopy within core-hole spectroscopies can be found:

G. Lippert, J. Hutter and M. Parrinello. Theoretical Chemistry Accounts 103 (1999) 124-140

M. Iannuzzi and J. Hutter. Physical Chemistry Chemical Physics 9 (2007) 1599-1610

In this CONEXS workshop 3 presentations about the use of CP2K to simulate core hole spectra were presented:

Fernanda Nunes - Density Functional Theory and X-ray Absorption Spectroscopy

Augustin Bussy - Linear-Response Time-Dependent Density Functional Theory for X-Ray Absorption Spectroscopy in CP2K

Axel Erbing - Simulating X-ray Spectroscopies with CP2K‌

This was accompanied by workshop exercises which can be found here:

1. Connecting to the cluster
2. Single H${}_2$O molecule: DFT basics
3. Trimethylaluminium Al${}_2$(CH${}_3$)${}_6$: LR-TDDFT for XAS
4. MgS and MgO: Periodic systems and XAS
5. Liquid water: Spectra broadening and MD

Further workshop examples on the utility CP2K can be found at its homepage and another recent workshop. 

See more resources from our CONEXS Summer School. 

See our CP2K resources on gitlab.