Gaussian Backend

Gaussian is a quantum-chemistry backend available through PyAR for users who have a licensed Gaussian installation and want higher-level electronic- structure calculations.

When to use Gaussian

Use gaussian when:

  • Gaussian is installed and accessible in your environment

  • you want DFT-style optimisation or refinement

  • you are refining a smaller set of candidates generated by cheaper PyAR searches

  • you have validated a small test calculation with your method, basis, charge, and multiplicity

Example command

Reaction search using the registered Gaussian energy-gradient route:

pyar-cli react A.xyz B.xyz -N 8 -gmin 100 -gmax 1000 --software gaussian --method B3LYP --basis 6-31G*

Practical notes

  • Gaussian must be installed separately and configured according to your local licence and system setup.

  • Confirm the executable name and output handling on a small molecule before running larger PyAR jobs.

  • Gaussian calculations are usually much slower than xTB or ML-potential runs. For screening, use xTB/AIMNet2 first and refine selected structures later.

AFIR/geomeTRIC status

gaussian is wired as a registered energy-gradient provider for the geomeTRIC-backed AFIR reaction route. This means PyAR can construct a combined Gaussian energy/gradient + AFIR bias objective for geomeTRIC. Local validation is still required because Gaussian setup and output handling depend on the installed executable and environment.