MOLPRO

29 LOCAL CORRELATION TREATMENTS 217
The orbitals located at these atoms will be treated at the level specified in method. The remaining
orbitals will be treated as defined in default. If not given by the user, the latter option will be set
to HF.
The orbital selection can be done in two ways. If type is set to INCLUSIVE, any orbital containing
one of the atoms in its domain centre list will be included. If type is set to EXCLUSIVE,
the program will only add orbitals whose domains are exclusively covered by the given atoms.
Any local correlation treatment can be given as method, with the restriction that only MP2 and
HF can be used as default method. Up to two REGION directives may be included in a single
calculation, ordered according to the correlation level (method) specified for the region. The
highest level region should be given last.
It is advisable to check the region orbital list and the orbital domains printed by the program.
The use of regions may significantly reduce the computation time, and, provided the active
atoms are sensibly chosen, may give still sufficiently accurate results for the active group, e.g.
bond lengths and bond angles.
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.
29.8.7 Energy partitioning for molecular cluster calculations (ENEPART)
The local character of occupied and virtual orbitals in the local correlation treatment also offers
the appealing possibility to decompose the intermolecular interaction energy of molecular
clusters into individual contributions of different excitation classes. This allows to distinguish
between intramolecular-, dispersive-, and ionic components of the correlation contribution to
the interaction energy (cf. M. Schütz, G. Rauhut and H.J. Werner, J. Phys. Chem. 102, 5197
(1998)). The energy partitioning algorithm is activated either by supplying the ENEPART directive:
ENEPART,[epart],[iepart]
or by giving the parameters as options on the command line.