Calculate X-ray absorption spectra: XANES, NEXAFS

XAS is increasingly used for in situ probing of catalyst structures. X-ray absorption near-edge spectra (XANES) or near-edge X-ray adsorption fine structure spectra (NEXAFS) can be modeled for all elements with ADF. For light elements the DFT-TS approach may give accurate results at little computational effort. Accurate X-ray absorption spectra for heavier elements can be calculated with spin-orbit TDDFT in ADF by restricting the excitations to a selected window of occupied and/or virtual orbitals.

ADF features for calculating X-ray absorption spectra (XAS)

  • state-selective excitations, core excitations
  • Slater’s Transition State (DFT-TS) and transition potential (TP) methods
  • scalar and spin-orbit relativistic effects
  • all-electron Slater basis sets, diffuse functions
  • create core-hole states in molecules and periodic systems (BAND)
  • model potentials with correct long-range behavior (LB94)
  • Ligand Field DFT to include multiplet effects
  • X-ray photoelectron spectroscopy (XPS) via ΔKohn-Sham

ADF developer Mauro Stener also gave a web presentation on calculating UV/VIS and X-ray absorption.

Calculating X-ray emission spectra (XES)

The frozen orbital, one-electron ΔDFT approach to calculate X-ray emission energies has been shown to work well for V2C-XES of transition metal complexes. Contributions from quadrupole oscillator strengths can also be included.

User manual and input examples

The powerful ADF features for calculating X-ray spectroscopic properties are export options, meaning that they are not easy to set up via the graphical interface.
The manual entries form a good starting point in combination with the examples shipped with the binaries. Do let us know at support@scm.com if you have any problems or questions.

  • X-ray absorption: manual: state selection, modified excitation range, orbital energy differences (TS, TP)
  • Set up NEXAFS calculations (workflow and examples)
  • XPS or core-electron binding energies (workflow and examples)
  • X-ray emission: manual
  • ADF examples
  • BAND example: electron hole in Si