model-chemistry-step 2026.7.31

SEAMM Model Chemistry Plug-in

A SEAMM plug-in for defining the model chemistry for subsequent steps

• Free software: BSD-3-Clause

• Documentation: https://molssi-seamm.github.io/model_chemistry_step/index.html

• Code: https://github.com/molssi-seamm/model_chemistry_step

History

2026.7.31 – Bugfix: crash and stale picker on Type change / direct-entry edits

• Fixed a crash (“TypeError: object of type ‘NoneType’ has no len()”) when changing the Type selector (e.g. to DFT) in the Model Chemistry dialog.

• Editing the model-chemistry string in direct-entry mode and then switching back to the guided picker now correctly reflects the edit. A component that isn’t a currently offered choice (e.g. a method not advertised by any installed program) is now shown blank, instead of the picker silently substituting some other, unrelated valid choice – which made an edit look like it had been ignored.

2026.7.30 – $variables in the Type/Method/Basis selectors

• The Type and Method (e.g. DFT functional) selectors now accept typed text, including a ‘$variable’ or ‘=expression’, so a preceding Loop step can vary the model chemistry from one iteration to the next.

• A ‘$variable’ typed into any of Type, Method, Program, or Basis is now actually evaluated at run time. Previously only a variable that was the entire model-chemistry value was dereferenced; one embedded in a composed string (e.g. the Basis field alone) was passed through to downstream steps as the literal, unresolved text.

• Added a checkbox to enter the whole model-chemistry string directly as text, instead of using the Type/Method/Program/Basis picker – by far the simplest way to use a ‘$variable’, since it sidesteps the picker’s discovery/validation entirely. The dialog switches to this mode automatically when the stored value can’t be decomposed by the picker (e.g. it is itself a ‘$variable’).

2026.6.28 – Basis-set selection

• Added a basis-set field to the dialog for levels of theory that use a basis (HF, DFT, MP2, coupled cluster), using the shared Basis Set Exchange picker (choose elements on a periodic table, then a covering basis). It is hidden for methods that use no basis (semiempirical, forcefield, MLFF).

• The basis is the user’s free choice – any Basis Set Exchange basis (stored as ‘bse:NAME’), not just the few a program advertises. A level of theory is accepted as long as a program offers its type and method.

• The model-chemistry grammar accepts a ‘bse:’ prefix on the basis.