# CCEOM

Performs equation-of-motion (EOM) coupled cluster excited state computations.

## General

### ABCD

> Type of ABCD algorithm will be used

> - Type: string
> - Possible Values: NEW, OLD
> - Default: NEW

### CACHELEVEL

> Caching level for libdpd governing the storage of amplitudes, integrals, and intermediates in the CC procedure. A value of 0 retains no quantities in cache, while a level of 6 attempts to store all quantities in cache. For particularly large calculations, a value of 0 may help with certain types of memory problems. The default is 2, which means that all four-index quantities with up to two virtual-orbital indices (e.g., \(\left\langle ij | ab \right\rangle\) integrals) may be held in the cache.

> - Type: integer
> - Default: 2

### CACHETYPE

> The criterion used to retain/release cached data

> - Type: string
> - Possible Values: LOW, LRU
> - Default: LRU

### CC3_FOLLOW_ROOT

> Do turn on root following for CC3

> - Type: boolean
> - Default: false

### CC_NUM_THREADS

> Number of threads

> - Type: integer
> - Default: 1

### COLLAPSE_WITH_LAST

> Do collapse with last vector?

> - Type: boolean
> - Default: true

### COMPLEX_TOLERANCE

> Complex tolerance applied in CCEOM computations

> - Type: conv double
> - Default: 1e-12

### EOM_GUESS

> Specifies a set of single-excitation guess vectors for the EOM-CC procedure. If EOM_GUESS = `SINGLES`, the guess will be taken from the singles-singles block of the similarity-transformed Hamiltonian, Hbar. If EOM_GUESS = `DISK`, guess vectors from a previous computation will be read from disk. If EOM_GUESS = `INPUT`, guess vectors will be specified in user input. The latter method is not currently available.

> - Type: string
> - Possible Values: SINGLES, DISK, INPUT
> - Default: SINGLES

### EOM_REFERENCE

> Reference wavefunction type for EOM computations

> - Type: string
> - Possible Values: RHF, ROHF, UHF
> - Default: RHF

### E_CONVERGENCE

> Convergence criterion for excitation energy (change) in the Davidson algorithm for CC-EOM. See Table Post-SCF Convergence for default convergence criteria for different calculation types.

> - Type: conv double
> - Default: 1e-6

### FULL_MATRIX

> Do use full effective Hamiltonian matrix?

> - Type: boolean
> - Default: false

### LOCAL

> Do simulate the effects of local correlation techniques?

> - Type: boolean
> - Default: false

### LOCAL_CUTOFF

> Value (always between one and zero) for the Broughton-Pulay completeness check used to contruct orbital domains for local-CC calculations. See J. Broughton and P. Pulay, J. Comp. Chem. 14, 736-740 (1993) and C. Hampel and H.-J. Werner, J. Chem. Phys. 104, 6286-6297 (1996).

> - Type: double
> - Default: 0.02

### LOCAL_DO_SINGLES

> - Type: boolean
> - Default: true

### LOCAL_FILTER_SINGLES

> Do apply local filtering to singles amplitudes?

> - Type: boolean
> - Default: true

### LOCAL_GHOST

> Permit ghost atoms to hold projected atomic orbitals to include in the virtual space in local-EOM-CCSD calculations

> - Type: integer
> - Default: -1

### LOCAL_METHOD

> Type of local-CCSD scheme to be simulated. `WERNER` selects the method developed by H.-J. Werner and co-workers, and `AOBASIS` selects the method developed by G.E. Scuseria and co-workers (currently inoperative).

> - Type: string
> - Possible Values: WERNER, AOBASIS
> - Default: WERNER

### LOCAL_PRECONDITIONER

> Preconditioner will be used in local CC computations

> - Type: string
> - Possible Values: HBAR, FOCK
> - Default: HBAR

### LOCAL_WEAKP

> Desired treatment of “weak pairs” in the local-CCSD method. A value of `NEGLECT` ignores weak pairs entirely. A value of `NONE` treats weak pairs in the same manner as strong pairs. A value of MP2 uses second-order perturbation theory to correct the local-CCSD energy computed with weak pairs ignored.

> - Type: string
> - Possible Values: NONE, MP2, NEGLECT
> - Default: NONE

### MAXITER

> Maximum number of iterations

> - Type: integer
> - Default: 80

### NEW_TRIPLES

> Do use new triples?

> - Type: boolean
> - Default: true

### NUM_AMPS_PRINT

> Number of important CC amplitudes to print

> - Type: integer
> - Default: 5

### OVERLAP_CHECK

> Report overlaps with old excited-state wave functions, if available, and store current wave functions for later use.

> - Type: boolean
> - Default: false

### PROP_ROOT

> Root number (within its irrep) for computing properties. Defaults to highest root requested.

> - Type: integer
> - Default: 0

### PROP_SYM

> Symmetry of the state to compute properties. Defaults to last irrep for which states are requested.

> - Type: integer
> - Default: 1

### REFERENCE

> Reference wavefunction type

> - Type: string
> - Possible Values: RHF, ROHF, UHF
> - Default: RHF

### RESTART_EOM_CC3

> Do restart from on-disk?

> - Type: boolean
> - Default: false

### RHF_TRIPLETS

> Do form a triplet state from RHF reference?

> - Type: boolean
> - Default: false

### ROOTS_PER_IRREP

> Number of excited states per irreducible representation for EOM-CC and CC-LR calculations. Irreps denote the final state symmetry, not the symmetry of the transition.

> - Type: array
> - Default: No Default

### R_CONVERGENCE

> Convergence criterion for norm of the residual vector in the Davidson algorithm for CC-EOM.

> - Type: conv double
> - Default: 1e-6

### SCHMIDT_ADD_RESIDUAL_TOLERANCE

> Minimum absolute value above which a guess vector to a root is added to the Davidson algorithm in the EOM-CC iterative procedure.

> - Type: conv double
> - Default: 1e-3

### SEMICANONICAL

> Convert ROHF MOs to semicanonical MOs

> - Type: boolean
> - Default: true

### SINGLES_PRINT

> Do print information on the iterative solution to the single-excitation EOM-CC problem used as a guess to full EOM-CC?

> - Type: boolean
> - Default: false

### SS_E_CONVERGENCE

> Convergence criterion for excitation energy (change) in the Davidson algorithm for the CIS guess to CC-EOM.

> - Type: conv double
> - Default: 1e-6

### SS_R_CONVERGENCE

> Convergence criterion for norm of the residual vector in the Davidson algorithm for the CIS guess to CC-EOM.

> - Type: conv double
> - Default: 1e-6

### SS_SKIP_DIAG

> Do skip diagonalization of Hbar SS block?

> - Type: boolean
> - Default: false

### SS_VECS_PER_ROOT

> SS vectors stored per root

> - Type: integer
> - Default: 5

### T3_WS_INCORE

> Do build W intermediates required for eom_cc3 in core memory?

> - Type: boolean
> - Default: false

### VECS_CC3

> Vectors stored in CC3 computations

> - Type: integer
> - Default: 10

### VECS_PER_ROOT

> Vectors stored per root

> - Type: integer
> - Default: 12

## Expert

### EXCITATION_RANGE

> The depth into the occupied and valence spaces from which one-electron excitations are seeded into the Davidson guess to the CIS (the default of 2 includes all single excitations between HOMO-1, HOMO, LUMO, and LUMO+1). This CIS is in turn the Davidson guess to the EOM-CC. Expand to capture more exotic excited states in the EOM-CC calculation

> - Type: integer
> - Default: 2

### WFN

> Wavefunction type

> - Type: string
> - Possible Values: EOM_CCSD, EOM_CC2, EOM_CC3
> - Default: EOM_CCSD