MOLPRO

18 ORBITAL LOCALIZATION 125
18.3 Choosing the localization method (METHOD)
METHOD,method
The localization method method can be either BOYS, PIPEK or NATURAL. This can also be
specified as argument on the LOCALI card (see above).
18.4 Delocalization of orbitals (DELOCAL)
DELOCAL
If this card is present, the orbitals are delocalized.
18.5 Localizing AOs(LOCAO)
LOCAO
If this card is present, the number of AOs contributing to each MO is minimized. This can be
useful to rotate degenerate orbitals (e.g., px, py, pz in an atom) so that pure orbitals (in this case
px, py, pz) result.
This implies Pipek-Mezey localization.
18.6 Selecting the orbital space
By default, only the valence orbitals are localized, in order to ensure invariance of subsequent
electron correlation treatments. This behaviour can be modified using the OCC and CORE directives.
18.6.1 Defining the occupied space (OCC)
OCC, o 1 , o 2 ...
defines the highest orbital o i in each symmetry i to be localized.
18.6.2 Defining the core orbitals (CORE)
CORE, c 1 , c 2 ...
The first c i orbitals in each symmetry are treated as core orbitals and not localized. Thus, orbitals
c i + 1 to o i are localized in symmetry i.
18.6.3 Defining groups of orbitals (GROUP, OFFDIAG)
GROUP,orb1,orb2,orb3,...
This card defines groups of orbitals to be localized as follows:
GROUP,1.1,2.1,3.1 a group of orbitals 1-3 in symmetry 1
GROUP,1.1,-3.1 equivalent to previous example