Combining the maximum overlap method with multiwavelets for core-ionisation energy calculations.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Accurate computation of core-ionization energies is crucial for interpreting X-ray photoelectron spectroscopy (XPS) experiments.
• Traditional methods using Atomic Orbitals (AOs) face challenges like slow convergence and numerical instabilities for core-hole states, especially in larger systems.
• Existing Multiwavelet calculations often rely on pseudopotentials, limiting their applicability and accuracy.

Purpose of the Study:

• To present a novel protocol for computing molecular core-ionization energies.
• To enable precise reproduction of X-ray photoelectron spectroscopy experiments.
• To overcome limitations of previous computational methods for core-ionization energy calculations.

Main Methods:

• Utilizing Multiwavelets and Density-Functional Theory (DFT) to compute electronic structures of ground and core-ionised states.
• Employing the Delta Self-Consistent Field (ΔSCF) method to determine core-ionization energies.
• Implementing the Maximum Overlap Method (MOM) to stabilize core-hole states and avoid pseudopotentials.

Main Results:

• The protocol allows for the first all-electron calculation of core-ionization energies using Multiwavelets.
• Results demonstrate higher precision compared to Atomic Orbital calculations and are consistent with previous Multiwavelet calculations using pseudopotentials.
• The method is applicable to relatively large molecules and supports both closed-shell and open-shell systems.

Conclusions:

• The developed protocol offers a robust and precise method for calculating core-ionization energies.
• This approach overcomes significant numerical challenges associated with AO basis sets and pseudopotentials.
• The protocol enhances the accuracy of simulating XPS experiments and extends computational capabilities to larger molecular systems.