The DFT embedding program is called by the EMBED,PROJ directive. When using this directive, the user must specify which MOs are associated with the active subsystem. This can be most directly accomplished through the ORBS option:
where orbital1 is an integer indicating that MO number orbital1 is associated with the active subsystem. The minimum input to run using the ORBS array is:
The KS calculation is performed on the full system. The EMBED,PROJ directive indicates the beginning of an embedding calculation in which subsystem A corresponds to the single MO orbital1. The HF and CCSD(T) calculations are performed on subsystem A, embedded in a subsystem interaction potential calculated at the KS level.
Alternatively to setting the ORBS array, the user can instead specify the ATOMS card:
where atom1 is the name of an atom from the geometry specification. Any MO having a Mulliken population greater than CHARGE_THRESHOLD (see subsection 62.2) on one of the listed atoms is associated with subsystem A. The minimum input to run using the ATOMS card is:
CASSCF calculations can be used as the WF method, but some care must be taken for the specification of the active space. In particular, the OCC, CLOSED, and FROZEN cards must be specified, and they must correspond to the number of OCC, CLOSED, and FROZEN orbitals within the active subsystem: