29.8.6 Domain Merging (MERGEDOM)

The restriction of the virtual space in local calculations may result in discontinuities for reaction path calculations due to changes of the geometry dependent domains. This may be avoided by the use of a MERGEDOM directive

MERGEDOM,[NEIGHBOUR=value],[CENTERS=[atom1, atom2...]], [RECORD=...],CHECK

This directive provides augmented domains, which can be saved (using option or directive SAVE, see section 29.8.3) for later use in reaction paths or in single point calculations (in cases where the orbital domain description is unbalanced). The use of the neighbour option works in the same way as the local option MERGEDOM, with value specifying the number of coincident centres. If the centres option is used, an atom list should be given (enclosed by square brackets). The domains of all orbitals located exclusively at these atoms will be merged, and the resulting merged domains will be used for all these orbitals.

One may also give a record number from a previously saved local calculation. The domain list contained in the record will be matched to the current one, and orbital domains augmented (merged) to include both sets. This domain definition should then be adequate for calculations on both points (and all those in between). This procedure can be repeated to include more geometries. In this way domains can be defined that are appropriate for a whole range of geometries (e.g. a reaction path), and if these domains are used in all calculations a strictly smooth potential energy surface is obtained.