SEAMM xTB Plug-in

A SEAMM plug-in for the xTB family of extended tight-binding methods from the Grimme group.

• Free software: BSD-3-Clause
• Documentation: https://molssi-seamm.github.io/xtb_step/index.html
• Code: https://github.com/molssi-seamm/xtb_step

Features

• Single-point energies, geometry optimizations, and harmonic vibrational frequencies for molecular (non-periodic) systems.

• The full set of xTB Hamiltonians and the GFN-FF force field:

  • GFN2-xTB (default) -- self-consistent, multipole electrostatics, density-dependent dispersion. Recommended for general use.
  • GFN1-xTB -- earlier self-consistent method.
  • GFN0-xTB -- non-self-consistent, useful for robust screening.
  • GFN-FF -- generic force field, automatically parameterized.

• Implicit solvation with all three xTB-supported models:

  • ALPB -- analytical linearized Poisson-Boltzmann (Ehlert et al., J. Chem. Theory Comput. 2021, 17, 4250).
  • GBSA -- generalized-Born model.
  • CPCM-X -- conductor-like polarizable continuum (Stahn et al., J. Phys. Chem. A 2023, 127, 7036).

  with the standard xTB solvent list (water, methanol, DMSO, acetonitrile, etc.).

• Net charge and spin multiplicity are read from the configuration, so the same flowchart works unchanged across O₂, triplet O₂, and O₂⁺ -- a single loop can scan a list of systems with different charge/spin states.

• Optimization with all eight xTB convergence levels (crude through extreme) and flexible structure handling: overwrite the current configuration in place, store the optimized structure as a new configuration, store it in a new system, or discard.

• Vibrational analysis using xTB's analytic Hessian, with the optimize-then-Hessian (--ohess) workflow recommended by xTB (or --hess alone if the geometry is already at a stationary point). Thermochemistry quantities (ZPE, H(T), T*S, S, G(T), total free energy) are reported in chemist-friendly units of kJ/mol and J/mol/K, not E_h.

• Tabulated results in the local step.out and storage in the SEAMM property database using the standard <name>#xTB#{model} property-naming convention, so downstream plug-ins (Thermochemistry, Reaction Path, ...) can pick up the values.

• Automatic citation tracking. The principal xTB program reference, the active GFN method reference, the DFT-D4 dispersion references (for GFN2-xTB), and the implicit-solvation reference are all added to the run's reference list automatically.

• Automatic installation of the xtb executable into a dedicated seamm-xtb conda environment via the standard SEAMM Installer.

Acknowledgements

This package was created with the molssi-seamm/cookiecutter-seamm-plugin tool, which is based on the excellent Cookiecutter.

Developed by the Molecular Sciences Software Institute (MolSSI), which receives funding from the National Science Foundation under award CHE-2136142.