TUNA: A streamlined quantum chemistry program for atoms and diatomics

TL;DR

TUNA is an open-source quantum chemistry program optimized for atoms and diatomics, offering a broad set of methods and properties through a simple, transparent interface, ideal for teaching and benchmarking.

Contribution

It introduces a specialized, open-source quantum chemistry tool for diatomic systems with comprehensive methods and an intuitive interface, facilitating education and method development.

Findings

Supports density functional theory, perturbation theory, and coupled cluster methods.

Enables calculation of energies, optimizations, vibrational frequencies, and more.

Provides a transparent platform for benchmarking and developing electronic structure methods.

Abstract

We present TUNA, an open-source quantum chemistry program specifically designed for atoms and diatomic molecules. Within this narrow molecular domain, a broad and consistent set of electronic structure methods and calculation types is available. Energies, optimisations, vibrational frequencies, response properties, coordinate scans and ab initio molecular dynamics trajectories can be accessed through an intuitive command-line interface. A single principle underlies TUNA: once a method can be used to evaluate the energy, all properties follow from numerical differentiation. This makes the program both a transparent teaching platform and a compact environment for benchmarking methods on diatomics $\unicode{x2014}$ among the most simple yet instructive systems in quantum chemistry. Reference implementations including density functional theory, many-body perturbation theory and coupled cluster theory, supported by detailed theoretical documentation, make TUNA an accessible foundation for developing improved methods and algorithms in electronic structure.