Aufbau Suppressed Coupled Cluster As a Post-Linear-Response Method.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Linear response (LR) methods are widely used for studying electronically excited states.
• However, LR methods can suffer from inaccuracies, especially for complex systems like charge transfer states.
• Developing post-correction methods is crucial for improving the reliability of excited state calculations.

Purpose of the Study:

• To evaluate Aufbau suppressed coupled cluster (ASCC) theory as a post-linear-response correction.
• To assess the resilience of ASCC to initial inaccuracies in the underlying LR method.
• To determine the effectiveness of ASCC in improving the accuracy of excited state energies, particularly for charge transfer states.

Main Methods:

• Application of Aufbau suppressed coupled cluster theory as a post-processing step to results from standard linear response calculations.
• Comparison of ASCC results obtained from various starting points, including those with known inaccuracies.
• Analysis of energy errors, focusing on the reduction achieved by the ASCC correction, especially for charge transfer excitations.

Main Results:

• ASCC theory demonstrates high resilience to the quality of the initial linear response calculation.
• Final ASCC results are comparable whether initiated from accurate or less accurate linear response starting points.
• Significant error reduction was observed in charge transfer states, with initial errors of several electron volts reduced to approximately 0.1 eV.

Conclusions:

• Aufbau suppressed coupled cluster theory serves as a robust post-linear-response correction for excited state calculations.
• The inherent orbital relaxation capability of ASCC minimizes the need for pre-relaxed references, simplifying calculations.
• ASCC's effectiveness, particularly for challenging charge transfer states, highlights its potential for accurate electronic structure studies.