Python API · stjames models · API example
Relax a molecule or periodic system toward a local energy minimum at a chosen level of theory. Results include the final geometry, energy, and optimization trajectory. The starting geometry influences which minimum is found; optimization does not guarantee the lowest-energy conformer.
Molecular calculations use geomeTRIC; periodic calculations use Rowan's internal optimizer, including stress checks when the cell is relaxed.
Inspect the final geometry and convergence warning before using results. A calculation can finish and report a final geometry even when optimization has not converged.
For an unconstrained molecular minimum, a frequency calculation should show no imaginary vibrational modes. Small imaginary frequencies can reflect numerical noise or incomplete relaxation; inspect the modes and consider reoptimizing with tighter settings. A constrained minimum need not be a minimum after its constraints are removed.
In the API, set opt_settings.constraints using 1-indexed atom numbers: two for a bond, three for an angle, four for a dihedral, or a list for freeze_atoms. Omit value to freeze a coordinate at its starting value, or supply a target distance in Å or angle in degrees. See the optimization settings model.
Select "Optimize (TS)" (optimize_ts in the API) starting from a plausible transition-state guess. A reaction-coordinate scan can help generate that guess. The web form disables this task when constraints are present. Add "Frequencies" and check for exactly one imaginary mode corresponding to the intended reaction. For periodic transition states, relax the cell first and keep it fixed during the search.