Getting Started#

Installation#

The xTB step is probably already installed in your SEAMM environment, but if not, or if you wish to check, follow the directions for the SEAMM Installer. The graphical installer is the easiest to use. In the SEAMM conda environment, simply type:

seamm-installer

or use the shortcut if you installed one. Switch to the second tab, Components, and check for xtb-step. If it is not installed, or can be updated, check the box next to it and click Install selected or Update selected as appropriate.

The non-graphical installer is also straightforward:

seamm-installer install --update xtb-step

will ensure both that the SEAMM plug-in itself and the underlying xtb executable are installed and up-to-date. By default the installer creates a dedicated seamm-xtb conda environment from conda-forge containing xtb; on first use the plug-in writes the environment location into ~/SEAMM/xtb.ini so subsequent runs can find it.

A first calculation#

The simplest useful flowchart is From SMILES → xTB → Energy:

  1. Add a From SMILES step and set the SMILES string to O (water) or any other small molecule.

  2. Add an xTB step from the Simulations menu.

  3. Open the xTB step (double-click) and inside the subflowchart add an Energy sub-step from the Calculations menu.

  4. Submit the flowchart. After a moment you should see the energy in step.out for the Energy sub-step as a Property | Value | Units table.

To do a geometry optimization, replace Energy with Optimization (or chain the two: Energy then Optimization if you want to see the change in total energy on relaxation). For vibrational frequencies and thermochemistry, use Frequencies, which by default optimizes the geometry first.

Charge and spin#

Net charge and spin multiplicity are properties of the configuration, not parameters of the xTB step. Set them when you build the structure – in From SMILES, From Structure, or Read Structure. The xTB step reads them automatically. This is what makes loops over systems with different charge/spin states trivial:

  • O2 (charge 0, multiplicity 3 – triplet ground state)

  • O2+ (charge +1, multiplicity 2 – doublet)

  • O2- (charge -1, multiplicity 2 – doublet)

are three different configurations; one xTB step can process all three in a loop without any per-system parameter editing.

Implicit solvation#

To run any of the sub-steps with implicit solvation, open the sub-step’s dialog, set Implicit solvation to ALPB (the current xTB-recommended default) or CPCM-X (broader solvent list), and choose a solvent. GFN2-xTB + ALPB + H2O is the standard starting point for aqueous work.

That should be enough to get started. For more detail about the functionality in this plug-in, see the User Guide.