Effective one-particle energies from generalized Kohn-Sham random phase approximation: A direct approach for...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Electronic Structure Theory

Background:

• Generalized-Kohn-Sham (GKS) orbital energies from random phase approximation with semicanonical projection (spRPA) show promise for valence ionization potentials.
• Core orbital ionization energies are challenging for standard methods like GW due to significant orbital relaxation effects.

Purpose of the Study:

• Extend GKS-spRPA to accurately calculate core electron binding energies (CEBEs).
• Evaluate GKS-spRPA performance for chemical shifts and environmental effects in various molecular systems.

Main Methods:

• Self-consistent calculation of GKS-spRPA orbital energies.
• Application to benchmark datasets of 1s CEBEs for second-row elements.
• Analysis of chemical shifts in ammonia clusters and cytosine tautomers.
• Development and testing of perturbative approximations to GKS-spRPA (O(N^5), O(N^4)).
• Investigation of oxygen 1s CEBEs in condensed phases of water.

Main Results:

• GKS-spRPA yields mean absolute deviations of 0.2 eV for 1s CEBEs, surpassing GW and matching Δ-SCF.
• Accurate prediction of chemical shifts in covalent and noncovalent bonding environments.
• Agreement within 0.2-0.3 eV with high-level coupled cluster and ADC(4) methods.
• Demonstrated application to larger systems, showing a 1.6-1.7 eV lowering of O 1s CEBEs in condensed water.

Conclusions:

• GKS-spRPA is a highly accurate and versatile method for core electron binding energies.
• The method effectively accounts for orbital relaxation and environmental effects.
• Perturbative approximations offer computational efficiency for larger systems.