Accurate Core-Level Ionization Energies from an Affordable Second-Order Approach

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Accurate calculation of core-level ionization potentials (IPs) is crucial for understanding chemical processes.
• Existing methods often face computational challenges for extended molecular systems.

Purpose of the Study:

• To develop and assess efficient second-order methods for accurate core-level IP calculations.
• To combine core-valence separation (CVS) with iterative ADC(2) and CIS(D) methods.
• To extend these methods to double-hybrid (DH) functionals.

Main Methods:

• Implementation of core-valence separated iterative algebraic-diagrammatic construction [CVS-IP-ADC(2)] and configuration interaction singles with perturbative second-order correction [CVS-IP-CIS(D)].
• Combination with spin-scaling techniques and double-hybrid functionals.
• Efficient implementation with practically cubic scaling computational cost.

Main Results:

• The proposed methods exhibit favorable scaling, enabling calculations for extended systems.
• Iterative treatment of double excitations is essential, highlighting the utility of DH functionals.
• SOS0-PBE0-2/CVS-IP-ADC(2) shows high competitiveness with more expensive coupled-cluster methods.
• Second-order correction adds negligible computational overhead.

Conclusions:

• The developed CVS-IP-ADC(2) and CVS-IP-CIS(D) methods provide accurate and efficient calculations of core-level IPs.
• The integration with DH functionals is seamless and enhances accuracy.
• These methods are suitable for accurate computational studies of extended molecular systems.