Efficient Protocol for Computing MCD Spectra in a Broad Frequency Range Combining Resonant and Damped CC2 Quadratic...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Coupled cluster response theory enables high-accuracy spectroscopic property calculations.
• Divergence and slow convergence hinder calculations for electronic transitions in high-energy regions with dense states.

Purpose of the Study:

• To address convergence issues in magnetic circular dichroism (MCD) calculations.
• To implement damped quadratic response theory and resonant response theory for MCD.
• To provide an efficient strategy for broad-frequency MCD spectra.

Main Methods:

• Implementation of damped quadratic response theory for resolution-of-identity coupled cluster singles-and-approximate-doubles (RI-CC2).
• Implementation of the MCD $$ term from resonant response theory.
• Application to zinc tetrabenzoporphyrin (2-8 eV) and comparison with experimental data.

Main Results:

• Combined damped and resonant response theory efficiently yields MCD spectra across a wide frequency range.
• The protocol is effective for highly symmetric molecules with degenerate excited states.
• Calculation time is dominated by building blocks for MCD ellipticity, not the resonant/damped approaches themselves.

Conclusions:

• Damped and resonant response theory offer an efficient strategy for calculating MCD spectra.
• The method successfully calculates MCD for systems with dense electronic states.
• Recommendations for using the developed procedure are provided.