MOLPRO

29 LOCAL CORRELATION TREATMENTS 213
print of orbital domains, and information about merged domains is
printed separately. See section 29.9.7 for further discussion of geometry
optimizations.
There are some other options which should normally not be modified:
DELBAS=ibaso
DELCOR=nshell
This parameter determines the method for eliminating redundant
functions of pair domains.
ibaso=0: The space of normalized eigenvectors of ˜S i j , which
correspond to small eigenvalues, is eliminated (default). Any other
value is not recommended and not further documented.
Activates elimination of basis functions corresponding to core orbitals.
If nshell=1, only 1s-functions are eliminated from projected
space. If nshell=2 (default) 1s functions on first-row atoms, and 1s,
2s, and 2p-functions are eliminated on second-row atoms. Nothing
is eliminated on H or He atoms. If effective core potentials are used,
nothing is deleted at the corresponding atom. Also, functions are only
deleted if the norm of the projected function is below THRCOR (default
0.1)
29.6.2 Extended domains
There are two alternative modes for domain extensions: either distance criteria REXT, REXTS,
REXTC, or REXTW can be used. These are in Bohr and refer to the minimum distance between
any atom in a standard orbital domain [i j] and another atom. If an atom is found within the
given distance, all PAOs at this atom are added to the domain [i j]. Alternatively, connectivity
criteria IEXT, IEXTS, IEXTC, or IEXTW can be used. These refer to the number of bonds
between any atom contained in the standard domain [i j] and another atom. The advantage of
distance criteria is that they select also atoms within the given radius which are not connected
to the present domain by bonds. On the other hand, the connectivity criteria are independent of
different bond lengths, e.g., for first and second-row atoms. Only one of the two possibilities
can be used, i.e., they are mutually exclusive.
REXT=value
REXTS=value
REXTC=value
REXTW=value
IEXT=value
IEXTS=value
IEXTC=value
IEXTW=value
Distance criterion for extension of all pair domains.
Distance criterion for extension of strong pair domains.
Distance criterion for extension of strong and close pair domains.
Distance criterion for extension of strong, close, and weak pair domains.
Connectivity criterion for extension of all pair domains.
Connectivity criterion for extension of strong pair domains.
Connectivity criterion for extension of strong and close pair domains.
Connectivity criterion for extension of strong, close, and weak pair
domains.
By default, domains are not extended, i.e., the default values of all parameters listed above
are zero. Note that the pair classes are determined on the basis of the standard domains, and
therefore domain extensions have no effect on the pair lists.