MOLPRO

20 THE CI PROGRAM 149
ROTREF=value
If value=0 the cluster corrections are not printed for the rotated
reference energies (cf. Section 20.7). If value=1 all corrections
are printed. If value=-1 the 2009.1 behaviour is recovered.
20.1 Introduction
The internally contracted MRCI program is called by the CI command. This includes as special
cases single reference CI, CEPA, ACPF, MR-ACPF and MR-AQCC. For closed-shell reference
functions, a special faster code exists, which can be called using the CISD, QCI, or CCSD
commands. This also allows to calculate Brueckner orbitals for all three cases (QCI and CCSD
are identical in this case).
With no further input cards, the wavefunction definition (core, closed, and active orbital spaces,
symmetry) corresponds to the one used in the most recently done SCF or MCSCF calculation.
By default, a CASSCF reference space is generated. Other choices can be made using
the OCC, CORE, CLOSED, WF, SELECT, CON, and RESTRICT cards. The orbitals are taken
from the corresponding SCF or MCSCF calculation unless an ORBITAL directive is given. The
wavefunction may be saved using the SAVE directive, and restarted using START. The EXPEC
directive allows to compute expectation values over one-electron operators, and the TRAN directive
can be used to compute transition matrix elements for one-electron properties. Natural
orbitals can be printed and saved using the NATORB directive.
For excited state calculations see STATE, REFSTATE, and PROJECT.
20.2 Specifying the wavefunction
20.2.1 Occupied orbitals
OCC,n 1 ,n 2 ,...,n 8 ;
n i specifies numbers of occupied orbitals (including CORE and CLOSED) in irreducible representation
number i. If not given, the information defaults to that from the most recent SCF,
MCSCF or CI calculation.
20.2.2 Frozen-core orbitals
CORE,n 1 ,n 2 ,...,n 8 ;
n i is the number of frozen-core orbitals in irrep number i. These orbitals are doubly occupied
in all configurations, i.e., not correlated. If no CORE card is given, the program uses the same
core orbitals as the last CI calculation; if there was none, then the atomic inner shells are taken
as core. To avoid this behaviour and correlate all electrons, specify
CORE
20.2.3 Closed-shell orbitals
CLOSED,n 1 ,n 2 ,...,n 8
n i is the number of closed-shell orbitals in irrep number i, inclusive of any core orbitals. These
orbitals do not form part of the active space, i.e., they are doubly occupied in all reference CSFs;
however, in contrast to the core orbitals (see CORE), these orbitals are correlated through single