Aufbau suppressed coupled cluster as a post-linear-response method

TL;DR

Aufbau suppressed coupled cluster theory effectively improves excited state calculations by acting as a robust post-linear-response correction, especially for charge transfer states, even from less accurate initial methods.

Contribution

The paper demonstrates that Aufbau suppressed coupled cluster can serve as a resilient post-linear-response correction, reducing errors significantly regardless of the initial linear response method used.

Findings

Highly resilient to initial method inaccuracies

Reduces charge transfer state errors to ~0.1 eV

Performs orbital relaxation independently

Abstract

We investigate the ability of Aufbau suppressed coupled cluster theory to act as a post-linear-response correction to widely used linear response methods for electronically excited states. We find that the theory is highly resilient to shortcomings in the underlying linear response method, with final results from less accurate starting points nearly as good as those from the best starting points. This pattern is especially stark in charge transfer states, where the approach converts starting points with multi-eV errors into post-linear-response results with errors on the order of 0.1 eV. These findings highlight the ability of Aufbau suppressed coupled cluster to perform its own orbital relaxations and raise the question of whether initializing it with an orbital relaxed reference is worth the trouble.