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7.11 Coupled-Cluster Excited-State and Open-Shell Methods

7.11.20 Non-Hartree-Fock Orbitals in EOM Calculations

(July 10, 2023)

In cases of problematic open-shell references, e.g., strongly spin-contaminated doublet, triplet or quartet states, one may choose to use DFT orbitals. This can be achieved by first doing DFT calculation and then reading the orbitals and turning Hartree-Fock off (by setting SCF_GUESS = READ MAX_SCF_CYCLES = 0 in the CCMAN or CCMAN2 job). In CCMAN, a more convenient way is just to specify EXCHANGE, e.g., if EXCHANGE = B3LYP, B3LYP orbitals will be computed and used.

Note:  Using non-HF exchange in CCMAN2 is not possible.