Extended Second-Order Multireference Algebraic Diagrammatic Construction Theory for Charged Excitations.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Strongly correlated molecular systems pose significant challenges for electronic structure calculations.
• Accurate simulation of electron attachment and ionization is crucial for understanding molecular properties and reactions.

Purpose of the Study:

• To develop and implement a new multireference algebraic diagrammatic construction (MR-ADC) method for electron attachment and ionization.
• To introduce computationally efficient approximations (MR-ADC(2)-X) with improved scaling for strongly correlated systems.

Main Methods:

• Implementation of second-order MR-ADC for electron attachment (EA-MR-ADC(2)).
• Development of extended second-order approximations (EA- and IP-MR-ADC(2)-X) incorporating partial third-order correlation.
• Efficient algorithm for solving first-order amplitude equations, avoiding four-particle reduced density matrices.

Main Results:

• EA- and IP-MR-ADC(2)-X demonstrate low computational scaling with basis set size.
• The new methods achieve accuracy comparable to strongly contracted NEVPT2.
• Efficient access to transition properties is provided.

Conclusions:

• The developed EA/IP-MR-ADC(2)-X methods provide an accurate and efficient approach for studying electron attachment and ionization in strongly correlated molecules.
• These methods offer a favorable balance between accuracy and computational cost, particularly for larger systems.