If true, a machine-learned force field is used to pre-optimize the geometry,
once, before the actual optimization starts.
Currently, only uses MatterSim. This is not compatible with GOCalculator=mattersim.
Requires Octopus to be compiled with MatterSim; the default is no otherwise.
The default is also no for GOCalculator=mattersim, and when relaxing
the cell of a system which is not periodic along all three directions.
The pre-optimization keeps the coordinates fixed by GOConstrains and
GOCenter, as well as the atoms of a fixed species.