# On the distinguishable cluster approximation for triple excitations

## TL;DR

This paper extends the distinguishable cluster approximation to triple excitations in coupled cluster methods, significantly enhancing energy accuracy while maintaining computational efficiency and desirable theoretical properties.

## Contribution

It introduces a novel application of the distinguishable cluster approximation to triples, improving coupled cluster results with manageable computational scaling.

## Key findings

- Improved absolute and relative energies in coupled cluster calculations.
- Method is orbital invariant and size extensive.
- Exact for three-electron systems.

## Abstract

The distinguishable cluster approximation applied to coupled cluster doubles equations greatly improves absolute and relative energies. We apply the same approximation to the triples equations and demonstrate that it can also improve results of the coupled cluster with singles, doubles and triples. The resulting method has a nominal computational scaling of ${\cal O}(N^7)$ in the real-space representation, is orbital invariant, size extensive, and exact for three electrons.