# Particle-particle ladder based basis-set corrections applied to atoms and molecules using coupled-cluster theory

## TL;DR

This paper introduces a basis-set correction method for coupled cluster calculations that reduces computational cost while maintaining accuracy for atoms and molecules, especially in energy calculations.

## Contribution

The study applies a finite basis-set correction based on the particle-particle ladder term to coupled cluster theory, enabling reduced basis sets without loss of accuracy.

## Key findings

- Basis set reductions by two cardinal numbers are feasible for atomization energies, ionization potentials, and electron affinities.
- Reaction energies can be accurately computed with basis set reductions by one cardinal number.
- The correction technique is adaptable to other many-electron theories without complex integrals.

## Abstract

We investigate the basis-set convergence of electronic correlation energies calculated using coupled cluster theory and a recently proposed finite basis-set correction technique. The correction is applied to atomic and molecular systems and is based on a diagrammatically decomposed coupled cluster singles and doubles correlation energy. Only the second-order energy and the particle-particle ladder term are corrected for their basis-set incompleteness error. We present absolute correlation energies and results for a large benchmark set. Our findings indicate that basis set reductions by two cardinal numbers are possible for atomization energies, ionization potentials and electron affinities without compromising accuracy when compared to conventional CCSD calculations. In the case of reaction energies we find that reductions by one cardinal number are possible compared to conventional CCSD calculations. The employed technique can readily be applied to other many-electron theories without the need for three- or four-electron integrals.