Real-Space Pseudopotential Method for the Calculation of Third-Row Elements X‑ray Photoelectron Spectroscopic Signatures

X-ray photoelectron spectroscopy (XPS) is a powerful
characterization
technique that unveils subtle chemical environment differences via
core–electron binding energy (CEBE) analysis. We extend the
development of real-space pseudopotential methods to calculating 1s,
2s, and 2p3/2 CEBEs of third-row elements (S, P, and Si)
within the framework of Kohn–Sham density-functional theory
(KS-DFT). The new approach systematically prevents variational collapse
and simplifies core-excited orbital selection within dense energy
level distributions. However, careful error cancellation analysis
is required to achieve accuracy comparable to all-electron methods
and experiments. Combined with real-space KS-DFT implementation, this
development enables large-scale simulations with both Dirichlet boundary
conditions and periodic boundary conditions.