MOLPRO

19 THE MCSCF PROGRAM MULTI 135
transforming the final orbitals to natural orbitals (the first order density matrix is diagonalized),
to pseudo-canonical orbitals (an effective Fock-operator is diagonalized), or of localizing the
orbitals.
19.5.1 Defining the starting guess
START,record,[options];
record: dump record containing starting orbitals. As usual, record has the form irec.ifil, where
irec is the record number (e.g., 2140), and ifil the file number (usually 2). The options can be
used to select orbitals of a specific type; for details, see section 4.11.
If this card is missing, the program tries to find suitable starting orbitals as follows:
First:
Second:
Third:
Try to read orbitals from the record specified on the ORBITAL
card (or the corresponding default, see ORBITAL). All files are
searched.
Try to find orbitals from the most recent MCSCF calculation.
All files are searched.
Try to find orbitals from the most recent SCF calculation. All
files are searched.
If no orbitals are found, a starting orbital guess is generated.
It is often useful to employ MCSCF orbitals from a neighbouring geometry as starting guess
(this will happen automatically if orbitals are found, see the above defaults). Note, however,
that frozen-core orbitals should always be taken from an SCF or MCSCF calculation at the
present geometry and must be specified separately on the FROZEN card. Otherwise the program
is likely to stop with error “non-orthogonal core orbitals”. The program remembers where to
take the core orbitals from if these have been specified on a FROZEN card in a previous MCSCF
calculation.
19.5.2 Rotating pairs of initial orbitals
ROTATE,orb1.sym,orb2.sym,angle
Performs a 2×2 rotation of the initial orbitals orb1 and orb2 in symmetry sym by angle degrees.
With angle=0 the orbitals are exchanged. ROTATE is meaningful only after the START card.
See MERGE for other possibilities to manipulate orbitals.
19.5.3 Saving the final orbitals
ORBITAL,record.file
The orbitals are dumped to record record.file. Default for record is 2140 and file=2. This default
record number is incremented by one for each subsequent MCSCF calculation in the same job
(see section 4.11). Therefore, if several different MCSCF calculations at several geometries
are performed in one job, each MCSCF will normally start with appropriate orbitals even if no
ORBITAL or START card is present.
The ORBITAL card can be omitted if a NATORB, CANORB or LOCORB card is present, since
orb can also be specified on these cards (the same defaults for orb as above apply in these cases).