History#

2026.11.11 – Settings fingerprints for xTB’s model-chemistry calculations

Calculations through an xTB Model Chemistry (e.g. xTB:SQM@GFN2-xTB) now carry a fingerprint of their settings – the program and its version, the method and the accuracy – like the other codes’ calculations. Steps that reuse results, such as Thermochemistry with its fragment store, can then tell which stored xTB results match the calculation they need.
Needs seamm-mdi 2026.11.11 or later for the fingerprints; with an older seamm-mdi, xTB calculations work as before, without them.

2026.11.5 – Tight convergence on request for finite differences

Steps that take finite differences of xTB’s gradients over its MDI engine, such as the new Vibrational Analysis step, can now ask for tight convergence: every calculation then runs at accuracy 1e-4. The engine starts each SCF from the previous structure’s, and at the default accuracy that left noise depending on the previous structure (water’s anharmonic force constants: 92 cm^-1 of noise, 0.12 with the tighter accuracy).
The MDI engine takes an --accuracy option.

2026.10.20 – Bugfix: an SCF that did not converge ended the MDI engine

In the tblite MDI engine (used e.g. by the Dimer Builder), one structure whose SCF did not converge ended the engine, and with it the whole step. A failed SCF is now retried from a fresh start, then with more iterations and stronger damping, then from another starting guess – none of which changes the converged energy. If none converges, the engine returns NaN for that structure and carries on, so the step can leave the point out. For Li+ with ethylene carbonate the failures were at large separations, 7-9 Å, and the retries converged them.

2026.10.9 – Bugfix: GFN2-xTB through tblite crashed

Any GFN2-xTB calculation through tblite (the MDI engine, as used by the Dimer Builder) crashed with a segmentation fault: tblite 0.6 and 0.7 need dftd4 4.2, and that combination fails in dftd4’s polarizabilities. The environment now pins tblite-python 0.5.0 (dftd4 3.7), which works; with it the xtb program is 6.4.1. GFN1-xTB was not affected.
Internal: requires Python 3.12; CI installs with uv from PyPI (no conda test environment); the unused Docker installation option was removed.

2026.5.2: Plug-in created using the SEAMM plug-in cookiecutter.

2026.5.12: Initial working version