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A Psi4 plugin to calculate X-ray absorption spectra (NEXAFS, PP-NEXAFS, XPS). The implemented methods are based on the Transition-Potential and Delta-Kohn-Sham approach.

For details, please refer to our paper in the Journal of Computational Chemistry and the documentation (still in progress).

Parts of the program were inspired by the psi4numpy package.

Install

Install PSI4 via Conda (using conda-forge channel)

To install the newest PSI4 version run (see also the PSI4 manual)

conda create -n psi4-new psi4 python=3.10 cmake eigen pybind11 boost gcc gxx gfortran -c conda-forge
conda activate psi4-new

Install PSIXAS

To install and use PSIXAS, you will need PSI4 already installed on your computer. You can then checkout the repository:

cd /path/to/psi4Plugins/
git clone https://github.com/Masterluke87/psixas/

then compile the Plugin:

cd psixas
$(psi4 --plugin-compile)
make

Run the Plugin

To run the plugin you just have to set the PYTHONPATH variable:

export PYTHONPATH=/path/to/psi4Plugins

Example: O-K edge of water

The following input file will perform first a ground state and then a transition potential calculation.

import psixas

molecule {
  O   0.27681793323501      0.00000014791107      0.00000000000000
  H   0.86159097690242      0.76505117501585      0.00000000000000
  H   0.86159108986257     -0.76505132292693      0.00000000000000
symmetry c1
}

set {
  basis def2-TZVP
}


set scf {
 reference uks
 scf_type MEM_DF
}

set psixas {
  prefix WATER
  MODE GS+EX+SPEC
  ORBS [0  ]
  OCCS [0.5]
  SPIN [b  ]
  DAMP 0.8
  OVL    [T]
  FREEZE [T]
}
energy('psixas',functional='PBE')

You will find a file named "WATER_b.spectrum" which can be used to plot the spectrum.