Optimization#

The Optimization sub-step minimizes the geometry using xTB’s ANC (approximate normal coordinate) optimizer. After the run the optimized geometry is harvested from xtbopt.xyz and applied to the SEAMM configuration according to your Structure handling choice.

Dialog#

The dialog has two panels.

Hamiltonian Parameters#

The same panel as in the Energy sub-step: xTB method, Accuracy, Implicit solvation, and (when solvation is on) Solvent.

Optimization#

Optimization level

The xTB --opt preset, in order of increasing convergence tightness: crude, sloppy, loose, lax, normal (default), tight, vtight, extreme. The presets set both the energy and the gradient convergence criteria. normal is appropriate for general use; use tight or tighter before a frequency calculation if you are not using the Frequencies sub-step’s --ohess workflow.

Maximum iterations

Maximum number of optimization iterations. Set to default to let xTB decide based on system size, or enter an integer to override.

Optimized structure

What to do with the optimized geometry:

  • Overwrite the current configuration (default) – replace the coordinates of the input configuration in place. The input geometry is lost. Most common choice for a simple optimization step.

  • Add a new configuration – keep the input geometry as a configuration of the system, and store the optimized geometry as a new configuration of the same system. Useful if you want to compare initial and optimized structures.

  • Add a new system – store the optimized geometry as a configuration of a freshly created system.

  • Discard the optimized structure – compute the optimized energy but throw the geometry away. Useful if you only want energetics and want to keep the input geometry sacred.

Output#

The Optimization sub-step prints the same results table as the Energy sub-step (total and electronic energy, gap, dipole) but with values at the optimized geometry.

The work directory contains, in addition to the Energy files, xtbopt.xyz (the optimized geometry) and xtbopt.log (the optimization trajectory in XMOL format – each frame is one optimization step).