The knowledge of geometries and chemistry of functional motifs that causes particular materials behavior is crucial for the rational development of novel materials and materials based technologies. X-ray photoelectron spectroscopy (XPS) measures the binding energy (BE) changes that are induced on an atom by its surrounding ligands and by comparing to them to databases. However, in many cases the reference materials available in the databases are limited to limited to common/model compounds, while actual materials designed may have more complicated chemistries. Furthermore, the big spread in the reported values of BE due to various ways to charge calibrate spectra and also sensitivity of BE to secondary environments present a big problem for accurate identification of unknown peaks in spectra.

 

Being able to calculate binding energy shifts based on molecular structure can be very important tool for identifying structural motifs in materials. There are only a few studies reporting density-functional-theory (DFT) calculations of BE energies due to challenges that are associated with the treatment of core electrons. Their high kinetic energy can require to include relativistic effects especially for heavy elements and absolute values of binding energies cannot be expected to be accurate. Furthermore the differences in reference state complicate the direct comparison between experiment and theory.

 

A possible solution to these challenges is to compare BE to a reference system that is accessible both in experiment and theory. We will report on BE shift that have been calculated and compared to experimentally obtained values for metallic, bimetallic and covalent systems. For metallic Pd (111) system, surface layers have lower binding energy, while sub-surface is bulk like. For bimetallic PdZn system, Pd(3d) and Zn(2p) shift upwardwith respect to fcc-Pd(3d) and for hcp-Zn(2p), respectively. Magnitudes of shifts are very similar to that obtained experimentally. For covalent system, such as metal-less and metal-containing porphyrins, shift for N 1s BE in Co 2p environment compared to N 1s without metal is also very close to that obtained experimentally.