Mixed-order schemes for molecular properties employing ADC/ISR.

Area of Science:

• Quantum chemistry
• Computational chemistry
• Theoretical chemistry

Background:

• Algebraic Diagrammatic Construction (ADC) methods are crucial for accurate electronic structure calculations.
• Intermediate State Representation (ISR) offers a pathway to efficient computation of molecular properties.
• Developing cost-effective yet accurate computational methods is essential for tackling larger molecular systems.

Purpose of the Study:

• To introduce and evaluate a novel mixed-order ADC scheme, ADC(2/1), for molecular property computations.
• To assess the accuracy and computational efficiency of the ADC(2/1) method against established ADC(2/2) benchmarks.
• To explore the potential of the ISR(1)-d scheme for enhancing computational feasibility.

Main Methods:

• Implementation of the ADC(2/1) method, integrating a first-order ISR with a second-order ADC excited state calculation.
• Benchmarking the ADC(2/1) results against the established ADC(2/2) method for molecular property calculations.
• Analysis of the computational cost associated with the ISR(1)-d scheme compared to ISR(2).

Main Results:

• The ADC(2/1) method demonstrates conserved or improved accuracy compared to the ADC(2/2) method.
• The ISR(1)-d scheme offers a significant reduction in computational cost relative to ISR(2).
• The developed method extends the applicability of ADC(2) level accuracy to larger molecular systems.

Conclusions:

• The ADC(2/1) method provides a computationally efficient and accurate approach for molecular property calculations.
• The ISR(1)-d scheme facilitates algorithmic parallelization, crucial for scaling ADC(2) calculations.
• This advancement broadens the scope of high-accuracy electronic structure investigations for complex molecules.