Two-Photon Circular Dichroism in the Algebraic Diagrammatic Construction Framework

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Two-photon circular dichroism (TPCD) is a spectroscopic technique sensitive to molecular chirality.
• Accurate theoretical prediction of TPCD requires advanced quantum chemical methods.
• Algebraic diagrammatic construction (ADC) offers a systematic approach to electron correlation.
• Intermediate state representation (ISR) is a formulation within ADC for response properties.

Purpose of the Study:

• To present the calculation of rotatory strengths for TPCD using the ADC/ISR framework.
• To investigate the influence of gauge-origin dependence on TPCD calculations.
• To compare ADC/ISR results with established coupled cluster methods.

Main Methods:

• Utilized the algebraic diagrammatic construction (ADC) method with the intermediate state representation (ISR).
• Employed the recently developed Python package 'responsefun' for calculations.
• Investigated length-gauge and gauge-origin invariant formulations of TPCD.
• Compared results with literature data from coupled cluster (CC) methods.

Main Results:

• The ADC/ISR approach provides accurate calculations of TPCD rotatory strengths.
• Differences between length-gauge and invariant approaches were analyzed across perturbation orders and basis sets.
• ADC/ISR results show good agreement with coupled cluster benchmarks.
• The 'responsefun' package simplifies the calculation of sum-over-states expressions.

Conclusions:

• The ADC/ISR methodology is computationally feasible for response properties up to third order.
• This method serves as a valuable addition to high-accuracy ab initio benchmark calculations.
• The 'responsefun' package enables users to perform complex calculations without deep theoretical knowledge of ADC.