User Guide#
The xTB plug-in lets a SEAMM flowchart drive the xTB family of extended tight-binding methods from the Grimme group. It is a fast, robust route to single-point energies, geometry optimizations, and harmonic vibrational frequencies for molecular (non-periodic) systems, with optional implicit solvation.
The plug-in is a container step with a subflowchart of sub-steps.
You add the top-level xTB step to your flowchart, then open it
and add one or more sub-steps inside it. Three sub-steps are
available in this release:
Energy – a single-point energy at a fixed geometry.
Optimization – minimize the geometry with xTB’s ANC (approximate normal coordinate) optimizer.
Frequencies – compute the analytic Hessian (optionally after a geometry optimization) and report harmonic vibrational frequencies, IR intensities, and thermochemistry.
The Hamiltonian, accuracy, and solvation settings are common to all three sub-steps and are described in:
Methods – choosing between GFN0-xTB, GFN1-xTB, GFN2-xTB (the default), and GFN-FF.
Solvation – using ALPB, GBSA, or CPCM-X implicit solvation, and the supported solvent list.
A summary of the properties produced and where they end up:
Results – the table of energies, orbital energies, dipole moment, vibrational data, and thermochemistry quantities, with their units and how they are stored in the SEAMM property database.
A note on charge and spin#
Net charge and spin multiplicity are not parameters of the
sub-steps. They are properties of the configuration (the SEAMM
data model treats O2, triplet O2, and
O2+ as different chemical species). Set them
when you build the structure – e.g. in From SMILES or
From Structure – and every downstream xTB step will pick them up
automatically. This is what makes loops over systems with different
charge/spin states trivial.