PSIXAS

PSIXAS simulates Near Edge X-ray Absorption Fine Structure (NEXAFS) and pump-probe PP-NEXAFS spectra using transition-potential and Δ-Kohn-Sham approaches to characterize valence- and core-excited electronic states.

Key Features:

• Integration with Psi4: Implemented as a plugin for Psi4, enabling use of Psi4 basis sets and density functionals for X-ray absorption simulations.
• Transition-Potential and Δ-Kohn-Sham Methodology: Employs the transition-potential approach alongside the Δ-Kohn-Sham method to simulate electronic transitions relevant to NEXAFS and PP-NEXAFS.
• Basis Set Considerations: Emphasizes the necessity of larger, extended basis sets to achieve precise absolute resonance positions.
• Density Functional Importance: Demonstrates that the choice of density functional critically affects PP-NEXAFS relative resonance positions and highlights the role of hybrid functionals with Hartree-Fock–like exact exchange.

Scientific Applications:

• NEXAFS and PP-NEXAFS Simulation: Simulation of NEXAFS and pump-probe PP-NEXAFS spectra for valence- and core-excited states.
• Electronic Transition Analysis: Analysis of electronic transitions that determine X-ray absorption spectral features.
• Excited-State and Pump–Probe Studies: Investigation of dynamic processes and excited-state behavior probed by PP-NEXAFS experiments.
• Density Functional Benchmarking: Assessment of density functional effects, particularly hybrid functionals, on resonance positions and spectral precision.

Methodology:

Computations use the transition-potential and Δ-Kohn-Sham methods implemented within the Psi4 framework.