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TUNA: A streamlined quantum chemistry program for atoms and diatomics

Harry Brough

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.

TUNA: A streamlined quantum chemistry program for atoms and diatomics

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 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.

Paper Structure

This paper contains 7 sections, 4 equations, 3 figures, 2 tables.

Table of Contents

  1. Introduction
  2. A common framework for response properties
  3. Calculation types
  4. Electronic structure methods and basis sets
  5. Implementation
  6. Summary and perspectives
  7. Acknowledgements

Figures (3)

  • Figure 1: Molecular orbital plots calculated in TUNA. The HF/6-31G $\pi^*$ LUMO of carbon monoxide (left) and a 4d virtual orbital from PBE/cc-pVQZ on the hydrogen atom (right). The orbital phases are shown in red and blue, separated by white nodes. The symmetry of diatomic molecules means that molecular orbitals can be fully described in two dimensions.
  • Figure 2: The dihydrogen potential energy surface calculated by electronic structure methods in the STO-3G basis set with a SCAN calculation in TUNA, shown with the SCANPLOT and ADDPLOT keywords (left). The anharmonic vibrational wavefunctions (increasing red intensity with energy) calculated with CCSD/def2-TZVP and shown with the VIBPLOT keyword (right).
  • Figure :