# OCC

Performs orbital-optimized MPn and CC computations and conventional MPn computations.

## General

### 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

### CCL_ENERGY

> Do compute CC Lambda energy? In order to this option to be valid one should use “TPDM_ABCD_TYPE = COMPUTE” * option.

> - Type: boolean
> - Default: false

### CC_DIIS_MAX_VECS

> Maximum number of vectors used in amplitude DIIS

> - Type: integer
> - Default: 6

### CC_DIIS_MIN_VECS

> Minimum number of vectors used in amplitude DIIS

> - Type: integer
> - Default: 2

### CC_MAXITER

> Maximum number of iterations to determine the amplitudes

> - Type: integer
> - Default: 50

### CEPA_OS_SCALE

> CEPA opposite-spin scaling value from SCS-CCSD

> - Type: double
> - Default: 1.27

### CEPA_SOS_SCALE

> CEPA Spin-opposite scaling (SOS) value

> - Type: double
> - Default: 1.3

### CEPA_SS_SCALE

> CEPA same-spin scaling value from SCS-CCSD

> - Type: double
> - Default: 1.13

### CEPA_TYPE

> CEPA type such as CEPA0, CEPA1 etc. currently we have only CEPA0.

> - Type: string
> - Possible Values: CEPA0
> - Default: CEPA0

### CUTOFF

> Cutoff value for numerical procedures

> - Type: integer
> - Default: 14

### DO_DIIS

> Do apply DIIS extrapolation?

> - Type: boolean
> - Default: true

### DO_LEVEL_SHIFT

> Do apply level shifting?

> - Type: boolean
> - Default: true

### DO_SCS

> Do perform spin-component-scaled OMP2 (SCS-OMP2)? In all computation, SCS-OMP2 energy is computed automatically. However, in order to perform geometry optimizations and frequency computations with SCS-OMP2, one needs to set ‘DO_SCS’ to true

> - Type: boolean
> - Default: false

### DO_SOS

> Do perform spin-opposite-scaled OMP2 (SOS-OMP2)? In all computation, SOS-OMP2 energy is computed automatically. However, in order to perform geometry optimizations and frequency computations with SOS-OMP2, one needs to set ‘DO_SOS’ to true

> - Type: boolean
> - Default: false

### E3_SCALE

> Scaling value for 3rd order energy correction (S. Grimme, Vol. 24, pp. 1529, J. Comput. Chem.)

> - Type: double
> - Default: 0.25

### EA_POLES

> Do compute OCC poles for electron affinities? Only valid for OMP2.

> - Type: boolean
> - Default: false

### EKT_EA

> Do compute virtual orbital energies based on extended Koopmans’ theorem?

> - Type: boolean
> - Default: false

### EKT_IP

> Do compute occupied orbital energies based on extended Koopmans’ theorem?

> - Type: boolean
> - Default: false

### EP_EA_POLES

> Do compute EP-OCC poles for electron affinities? Only valid for OMP2.

> - Type: boolean
> - Default: false

### EP_IP_POLES

> Do compute EP-OCC poles for ionization potentials? Only valid OMP2.

> - Type: boolean
> - Default: false

### EP_MAXITER

> Maximum number of electron propagator iterations.

> - Type: integer
> - Default: 30

### 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

### IP_POLES

> Do compute OCC poles for ionization potentials? Only valid OMP2.

> - Type: boolean
> - Default: false

### LEVEL_SHIFT

> Level shift to aid convergence

> - Type: double
> - Default: 0.02

### LINEQ_SOLVER

> The solver will be used for simultaneous linear equations.

> - Type: string
> - Possible Values: CDGESV, FLIN, POPLE
> - Default: CDGESV

### MAX_MOGRAD_CONVERGENCE

> Convergence criterion for maximum orbital gradient

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

### MOGRAD_DAMPING

> Damping factor for the orbital gradient (Rendell et al., JCP, vol. 87, pp. 5976, 1987)

> - Type: double
> - Default: 1.0

### MO_DIIS_NUM_VECS

> Number of vectors used in orbital DIIS

> - Type: integer
> - Default: 6

### MO_MAXITER

> Maximum number of iterations to determine the orbitals

> - Type: integer
> - Default: 50

### MO_READ

> Do read coefficient matrices from external files of a previous OMP2 or OMP3 computation?

> - Type: boolean
> - Default: false

### MO_STEP_MAX

> Maximum step size in orbital-optimization procedure

> - Type: double
> - Default: 0.5

### MO_WRITE

> Do write coefficient matrices to external files for direct reading MOs in a subsequent job?

> - Type: boolean
> - Default: false

### MP2_OS_SCALE

> MP2 opposite-spin scaling value

> - Type: double
> - Default: 6.0

### MP2_SOS_SCALE

> MP2 Spin-opposite scaling (SOS) value

> - Type: double
> - Default: 1.3

### MP2_SOS_SCALE2

> Spin-opposite scaling (SOS) value for optimized-MP2 orbitals

> - Type: double
> - Default: 1.2

### MP2_SS_SCALE

> MP2 same-spin scaling value

> - Type: double
> - Default: 1.0

### NAT_ORBS

> Do compute natural orbitals?

> - Type: boolean
> - Default: false

### OCC_ORBS_PRINT

> Do print OCC orbital energies?

> - Type: boolean
> - Default: false

### OEPROP

> Do compute one electron properties?

> - Type: boolean
> - Default: false

### OPT_METHOD

> The optimization algorithm. Modified Steepest-Descent (MSD) takes a Newton-Raphson (NR) step with a crude approximation to diagonal elements of the MO Hessian. The ORB_RESP option obtains the orbital rotation parameters by solving the orbital-reponse (coupled-perturbed CC) equations. Additionally, for both methods a DIIS extrapolation will be performed with the DO_DIIS = TRUE option.

> - Type: string
> - Possible Values: MSD, ORB_RESP
> - Default: ORB_RESP

### ORB_OPT

> Do optimize the orbitals?

> - Type: boolean
> - Default: true

### ORB_RESP_SOLVER

> The algorithm will be used for solving the orbital-response equations. The LINEQ option create the MO Hessian and solve the simultaneous linear equations with method choosen by the LINEQ_SOLVER option. The PCG option does not create the MO Hessian explicitly, instead it solves the simultaneous equations iteratively with the preconditioned conjugate gradient method.

> - Type: string
> - Possible Values: PCG, LINEQ
> - Default: PCG

### ORTH_TYPE

> The algorithm for orthogonalization of MOs

> - Type: string
> - Possible Values: GS, MGS
> - Default: MGS

### PCG_BETA_TYPE

> Type of PCG beta parameter (Fletcher-Reeves or Polak-Ribiere).

> - Type: string
> - Possible Values: FLETCHER_REEVES, POLAK_RIBIERE
> - Default: FLETCHER_REEVES

### PCG_CONVERGENCE

> Convergence criterion for residual vector of preconditioned conjugate gradient method.

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

### PCG_MAXITER

> Maximum number of preconditioned conjugate gradient iterations.

> - Type: integer
> - Default: 30

### RELAXED

> Do consider orbital response contributions for PDMs and GFM?

> - Type: boolean
> - Default: true

### RMS_MOGRAD_CONVERGENCE

> Convergence criterion for RMS orbital gradient. Default adjusts depending on E_CONVERGENCE

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

### R_CONVERGENCE

> Convergence criterion for amplitudes (residuals).

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

### SCS_TYPE

> Type of the SCS method

> - Type: string
> - Possible Values: SCS, SCSN, SCSVDW, SCSMI
> - Default: SCS

### SOS_TYPE

> Type of the SOS method

> - Type: string
> - Possible Values: SOS, SOSPI
> - Default: SOS

### SYMMETRIZE

> Do symmetrize the GFM and OPDM in the EKT computations?

> - Type: boolean
> - Default: true

### TPDM_ABCD_TYPE

> How to take care of the TPDM VVVV-block. The COMPUTE option means it will be computed via an IC/OOC algorithm. The DIRECT option (default) means it will not be computed and stored, instead its contribution will be directly added to Generalized-Fock Matrix.

> - Type: string
> - Possible Values: DIRECT, COMPUTE
> - Default: DIRECT

### WFN_TYPE

> Type of the wavefunction.

> - Type: string
> - Possible Values: OMP2, OMP3, OCEPA, OMP2.5
> - Default: OMP2