Solvation#

The plug-in supports all three implicit solvation models that xTB itself provides. The choice is set by the Implicit solvation parameter on every sub-step.

Solvation models#

ALPB#

Analytical Linearized Poisson-Boltzmann model. The current recommended default for xTB-family calculations with implicit solvation.

Parametrized for GFN1-xTB, GFN2-xTB, and GFN-FF. Not parametrized for GFN0-xTB; if you select GFN0 with ALPB, xtb will emit a warning or refuse to run.

Citation: Ehlert, Stahn, Spicher, Grimme, J. Chem. Theory Comput. 2021, 17, 4250.

GBSA#

The earlier Generalized Born / Surface Area model. Retained for backward compatibility with published xTB results. Use ALPB for new work unless you have a specific reason.

Parametrized for the same methods as ALPB, with the same GFN0 caveat.

Citation: same paper as ALPB (Ehlert et al. 2021).

CPCM-X#

Conductor-like Polarizable Continuum Model with extended parameterization. Uses the Minnesota Solvation Database, so it supports a wider range of solvents than ALPB / GBSA.

Citation: Stahn, Ehlert, Grimme, J. Phys. Chem. A 2023, 127, 7036.

Supported solvents#

The plug-in’s solvent dropdown lists the union of solvents supported by xTB for ALPB / GBSA. Some solvents are method-specific:

  • DMF and n-hexane are GFN2-only.

  • Benzene is GFN1-only.

xtb itself will warn or refuse at run time if you select an unsupported method/solvent combination, so trying it is safe.

For ALPB/GBSA the supported list is:

acetone, acetonitrile, benzene*, CH2Cl2, CHCl3, CS2,
DMF*, DMSO, ether, H2O, methanol, n-hexane*, THF, toluene

(* = method-specific as noted above).

CPCM-X uses the much larger Minnesota Solvation Database; the plug-in’s dropdown is enforced as an enumeration, but you can also pass a variable that resolves to a free-text solvent name if you need a solvent that is not in the dropdown.

Layout in the dialog#

When Implicit solvation is none, the Solvent widget is hidden. As soon as you select any other model, the Solvent widget appears, indented under the solvation-model row, with its default of H2O. Set it to none again and it disappears.

This makes flowcharts with no solvation visually clean while still giving you immediate access to the solvent selector when you need it.

Tips#

  • For aqueous biomolecule work, GFN2-xTB + ALPB + H2O is the standard starting point.

  • For non-aqueous solvents, the same combination works for the solvents in the supported list; for everything else, switch to CPCM-X.

  • Implicit solvation changes geometries somewhat – compare gas-phase and solvated optimized geometries if your downstream analysis is geometry-sensitive (e.g. conformer ratios).