# CCENERGY

Computes coupled cluster energies. Called as part of any coupled cluster computation.

## General

### ABCD

> Type of ABCD algorithm will be used

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

### ANALYZE

> Do analyze T2 amplitudes

> - Type: boolean
> - Default: false

### BCCD_MAXITER

> Convert ROHF MOs to semicanonical MOs

> - Type: integer
> - Default: 50

### BRUECKNER_ORBS_R_CONVERGENCE

> Convergence criterion for Brueckner orbitals. The convergence is determined based on the largest \(T_1\) amplitude. Default adjusts depending on E_CONVERGENCE

> - Type: conv double
> - Default: 1e-5

### 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., \(\langle ij | ab \rangle\) integrals) may be held in the cache.

> - Type: integer
> - Default: 2

### CACHETYPE

> Selects the priority type for maintaining the automatic memory cache used by the libdpd codes. A value of `LOW` selects a “low priority” scheme in which the deletion of items from the cache is based on pre-programmed priorities. A value of LRU selects a “least recently used” scheme in which the oldest item in the cache will be the first one deleted.

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

### CC_NUM_THREADS

> Number of threads

> - Type: integer
> - Default: 1

### CC_OS_SCALE

> Coupled-cluster opposite-spin scaling value

> - Type: double
> - Default: 1.27

### CC_SS_SCALE

> Coupled-cluster same-spin scaling value

> - Type: double
> - Default: 1.13

### DIIS

> Do use DIIS extrapolation to accelerate convergence?

> - Type: boolean
> - Default: true

### E_CONVERGENCE

> Convergence criterion for energy. See Table Post-SCF Convergence for default convergence criteria for different calculation types.

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

### LOCAL

> Do simulate the effects of local correlation techniques?

> - Type: boolean
> - Default: false

### LOCAL_CPHF_CUTOFF

> Cutoff value for local-coupled-perturbed-Hartree-Fock

> - Type: double
> - Default: 0.10

### 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_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_PAIRDEF

> Definition of local pair domains, default is BP, Boughton-Pulay.

> - Type: string
> - Possible Values: BP, RESPONSE
> - Default: BP

### 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, NEGLECT, MP2
> - Default: NONE

### MAXITER

> Maximum number of iterations to solve the CC equations

> - Type: integer
> - Default: 50

### MP2_AMPS_PRINT

> Do print the MP2 amplitudes which are the starting guesses for RHF and UHF reference functions?

> - Type: boolean
> - Default: false

### MP2_OS_SCALE

> MP2 opposite-spin scaling value

> - Type: double
> - Default: 1.20

### MP2_SS_SCALE

> MP2 same-spin scaling value

> - Type: double
> - Default: 1.0

### NEW_TRIPLES

> Do use new triples?

> - Type: boolean
> - Default: true

### NUM_AMPS_PRINT

> Number of important \(t_1\) and \(t_2\) amplitudes to print

> - Type: integer
> - Default: 10

### PAIR_ENERGIES_PRINT

> Do print MP2 and CCSD pair energies for RHF references?

> - Type: boolean
> - Default: false

### PROPERTY

> The response property desired. Acceptable values are `POLARIZABILITY` (default) for dipole-polarizabilities, `ROTATION` for specific rotations, `ROA` for Raman Optical Activity, and `ALL` for all of the above.

> - Type: string
> - Possible Values: POLARIZABILITY, ROTATION, MAGNETIZABILITY, ROA, ALL
> - Default: POLARIZABILITY

### REFERENCE

> Reference wavefunction type

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

### RESTART

> Do restart the coupled-cluster iterations from old \(t_1\) and \(t_2\) amplitudes? For geometry optimizations, Brueckner calculations, etc. the iterative solution of the CC amplitude equations may benefit considerably by reusing old vectors as initial guesses. Assuming that the MO phases remain the same between updates, the CC codes will, by default, re-use old vectors, unless the user sets RESTART = false.

> - Type: boolean
> - Default: true

### R_CONVERGENCE

> Convergence criterion for wavefunction (change) in CC amplitude equations.

> - Type: conv double
> - Default: 1e-7

### SCSN_MP2

> Do SCS-MP2 with parameters optimized for nucleic acids?

> - Type: boolean
> - Default: false

### SCS_CCSD

> Do spin-component-scaled CCSD

> - Type: boolean
> - Default: false

### SCS_MP2

> Do spin-component-scaled MP2 (SCS-MP2)?

> - Type: boolean
> - Default: false

### SEMICANONICAL

> Convert ROHF MOs to semicanonical MOs

> - Type: boolean
> - Default: true

### SPINADAPT_ENERGIES

> Do print spin-adapted pair energies?

> - Type: boolean
> - Default: false

### T2_COUPLED

> - Type: boolean
> - Default: false

### T3_WS_INCORE

> Do build W intermediates required for cc3 in core memory?

> - Type: boolean
> - Default: false

## Expert

### AO_BASIS

> The algorithm to use for the \(\left\langle VV||VV\right\rangle\) terms If AO_BASIS is `NONE`, the MO-basis integrals will be used; if AO_BASIS is `DISK`, the AO-basis integrals stored on disk will be used; if AO_BASIS is `DIRECT`, the AO-basis integrals will be computed on the fly as necessary. NB: The `DIRECT` option is not fully implemented and should only be used by experts. Default is NONE. Note: The developers recommend use of this keyword only as a last resort because it significantly slows the calculation. The current algorithms for handling the MO-basis four-virtual-index integrals have been significantly improved and are preferable to the AO-based approach.

> - Type: string
> - Possible Values: NONE, DISK, DIRECT
> - Default: NONE

### FORCE_RESTART

> Do restart the coupled-cluster iterations even if MO phases are screwed up?

> - Type: boolean
> - Default: false

### WFN

> Wavefunction type

> - Type: string
> - Default: NONE