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Multistage Optimization

Python API · stjames models · API example

How it works

Optimize a molecular geometry through one or more methods, then optionally refine its energy with a final single-point calculation. Each optimization starts from the previous stage's geometry; the single point evaluates that geometry without moving the atoms. Results include the stage calculations and, when requested, frequencies and thermochemical corrections at the final optimization level.

Settings

  • Stages: "Multistage opt. settings" lets you select a preset or add, edit, reorder, and remove optimization stages and the optional final single point. Include at least one optimization and at least two stages in total.
  • Solvent: each stage can have its own solvent model. "Solvent (all steps)" applies the selected solvent to every solvent-capable stage; the models may differ between methods.
  • Frequencies: "Calculate frequencies?" evaluates vibrations at the last optimization method, even when a higher-level single point follows. This is off by default.
  • Transition state: "Transition state?" searches for a saddle point from a suitable transition-state guess instead of optimizing a minimum.
  • Constraints: hold selected atoms, distances, angles, or dihedrals fixed, where supported by the chosen methods.

Modes

The current web presets are shown below. Frequencies are optional for each protocol.

PresetOptimization stages, in orderSingle point
RecklessGFN-FFGFN2-xTB
RapidGFN2-xTBr²SCAN-D4/vDZP
Carefulr²SCAN-D4/vDZPωB97X-3c
Meticulousr²SCAN-D4/vDZP → ωB97X-3cωB97M-D3BJ/def2-TZVPPD

Rapid is the web default. Add an inexpensive optimization stage if the starting geometry needs preparation. API mode helpers can use different protocols; check the actual stage settings when reproducing a calculation.

Notes

Check convergence and the final geometry. For an unconstrained structure, a minimum should have no imaginary vibrational frequencies; a transition state should have one imaginary mode along the intended reaction. Constrained geometries need additional care when interpreting frequencies.

Molecular optimizations use the geomeTRIC optimizer, including transition-state optimizations with supported xTB methods. A final single point does not verify that the geometry is stationary at its own level of theory.

Submission video

Further reading