Note

This website is presently under development. The primary website for MOPAC is still http://openmopac.net until the majority of its contents have been migrated here.

CISD

Restricts the active space to single-electron and double-electron excitations for configuration interaction calculations (i.e. Configuration Interaction Singles and Doubles).

Number of configurations for \(n\) doubly-occupied orbitals and \(m\) empty orbitals

excitation type	# of configs
none (RHF ground state)	\(1\)
1 \(\alpha\) electron	\(m n\)
1 \(\beta\) electron	\(m n\)
1 \(\alpha\) electron & 1 \(\beta\) electron	\(m^2 n^2\)
2 \(\alpha\) electrons	\(m (m-1) n (n-1)/4\)
2 \(\beta\) electrons	\(m (m-1) n (n-1)/4\)

Note

INDO calculations can also use this keyword to request double-electron excitations in MRCI calculations.