cceom(1)

✨ cceom(1) ✨ — equation of motion coupled cluster energy program 💖

okay bestie, welcome to the group chat for cceom. this is the manual page, but make it make sense. no cap. 🫶

🌸 DESCRIPTION 🌸

The program cceom calculates EOM-CCSD energies using a Davidson algorithm to solve for the right-hand eigenvectors of the CC Hamiltonian. that's the whole vibe. periodt. 💅

🦋 COMMAND LINE ARGUMENTS 🦋

real talk: after internal coordinates are detected or generated, optking will enter a run-time mode dependent on command line arguments. yes, that's what it says. i'm just the messenger. 😭

• --dot_with_Lg — check the orthogonality of the excited right-hand eigenvector with the ground state left eigenvector, lambda. cclambda must be run first for this to work. no cclambda first? then it's not gonna work, bestie. 🙈

🦋 REFERENCES 🦋

1. The equation of motion coupled-cluster method. A systematic biorthogonal approach to molecular excitation energies, transition probabilities, and excited state properties, J. F. Stanton and R. J. Bartlett, J. Chem. Phys. 98, 7029 (1993).

now for the settings that are literally right after the references in the original. slay. ✨

• EOM_REFERENCE = integer — specifies the algorithm used by cceom. useful for debugging. also must currently be set to ROHF, if you want to get triplet excited states from a singlet ground state. the default is whatever "REFERENCE" is.
• STATES_PER_IRREP = array of integers — specifies the number of states of each irreducible representation desired. for example, in C2v symmetry, (0 2 0 0) specifies two excited states of A2 symmetry to be solved, regardless of the symmetry of the ground state.
• PROP_SYM = integer — specifies the symmetry of the state that should be used to compute properties. defaults to the last irrep for which states are requested.
• PROP_ROOT = integer — specifies the number of the root (within its irrep) that should be used to compute properties. defaults to the highest root requested.
• EXCITATION_RANGE = excitation_range — used to generate initial guesses. the larger the value, the more initial guesses are made in the Davidson algorithm.
• RESIDUAL_TOL = integer — Davidson algorithm will converge until the norm of the residual vector is less than 10^(-integer). default if 4.
• EVAL_TOL = integer — Davidson algorithm will converge until the change in the excitation energy is less than 10^(-integer). default if 6.

mwah 💋 that's the whole page, bestie. this manual page is from cceom(1), dated Sept 2002. source/version + date, delivered with love. go off. 👑🎀