CFOUR | Main / Spin-restricted And Partially-spin-adapted Calculations

If EXCITE=EOMEE is used together with OPEN-SHELL=SR-CC or OPEN-SHELL=PSA-CC keywords, excited state wave function will also be spin-restricted or partially spin-adapted. For excited states it might be necessary to go beyond the first-order interactive space restriction and include the so called “pseudo-triple” contributions in the wave function. This is possible with the keywords OPEN-SHELL=SR-CC_FULL and OPEN-SHELL=PSA-CC_FULL. Note that these later calculations are considerably more expensive since certain triple excited determinants are included.

Restrictions:

ORBITALS=STANDARD and SYMMETRY=OFF have to be used. The latter means that symmetry of the system can not be used.
The present version can not calculate gradients for the SR-CC or PSA-CC cases. This means that, in contrary to the ground state, calculation of the expectation value of spin operator is also not possible.