MOPAC Backend

MOPAC is a semiempirical quantum-chemistry backend available in PyAR through legacy optimisation routes.

When to use MOPAC

Use mopac when:

  • MOPAC is installed and available on your system

  • you specifically want a MOPAC semiempirical method

  • you are working with legacy PyAR inputs or comparisons

Example command

pyar-optimiser structure.xyz -c 0 -m 1 --software mopac

Practical notes

  • MOPAC must be installed separately.

  • Check charge, multiplicity, and method support on a small molecule before running batch calculations.

  • For new broad exploratory work, xtb is usually the simpler first choice.

AFIR/geomeTRIC status

mopac is not currently registered as an energy-gradient provider for the geomeTRIC-backed AFIR reaction route.