# DCT¶

Performs density cumulant (functional) theory computations

## General¶

### ALGORITHM¶

Algorithm to use for the density cumulant and orbital updates in the DCT energy computation. Two-step algorithm is usually more efficient for small systems, but for large systems simultaneous algorithm (default) is recommended. If convergence problems are encountered (especially for highly symmetric systems) QC algorithm can be used.

• Type: string

• Possible Values: TWOSTEP, SIMULTANEOUS, QC

• Default: SIMULTANEOUS

### AO_BASIS¶

Controls whether to avoid the AO->MO transformation of the two-electron integrals for the four-virtual case ($$\langle VV|| VV \rangle$$) by computing the corresponding terms in the AO basis. AO_BASIS = DISK algorithm reduces the memory requirements and can significantly reduce the cost of the energy computation if SIMULTANEOUS algorithm is used. For the TWOSTEP algorithm, however, AO_BASIS = DISK option is not recommended due to extra I/O.

• Type: string

• Possible Values: NONE, DISK

• Default: DISK

### DCT_FUNCTIONAL¶

Chooses appropriate DCT method

• Type: string

• Possible Values: DC-06, DC-12, ODC-06, ODC-12, ODC-13, CEPA0

• Default: ODC-12

### DCT_TYPE¶

What algorithm to use for the DCT computation

• Type: string

• Possible Values: CONV, DF

• Default: CONV

### DF_BASIS_DCT¶

Auxiliary basis set for DCT density fitting computations. Defaults to a RI basis.

• Type: string

• Possible Values: basis string

• Default: No Default

### DIIS_START_CONVERGENCE¶

Value of RMS of the density cumulant residual and SCF error vector below which DIIS extrapolation starts. Same keyword controls the DIIS extrapolation for the solution of the response equations.

### E_CONVERGENCE¶

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

### GUESS_R_CONVERGENCE¶

Convergence criterion for the density cumulant and orbital guess for the variationally orbital-optimized DFT methods. Currently only available for ALGORITHM = SIMULTANEOUS.

### MAXITER¶

Maximum number of macro- or micro-iterations for both energy and response equations

• Type: integer

• Default: 40

### ODC_GUESS¶

Whether to perform a guess DC-06 or DC-12 computation for ODC-06 or ODC-12 methods, respectively. Currently only available for ALGORITHM = SIMULTANEOUS.

### OPDM¶

Compute a (relaxed) one-particle density matrix? Can be set manually. Set internally for property and gradient computations.

### QC_COUPLING¶

Controls whether to include the coupling terms in the DCT electronic Hessian (for ALOGRITHM = QC with QC_TYPE = SIMULTANEOUS only)

### QC_TYPE¶

Controls the type of the quadratically-convergent algorithm (effective for ALGORITHM = QC). If set to TWOSTEP the Newton-Raphson equations are only solved for the orbital updates, the cumulant is updated using the standard Jacobi algorithm. If set to SIMULTANEOUS both cumulant and orbitals are updated in a single Newton-Raphson step.

• Type: string

• Possible Values: TWOSTEP, SIMULTANEOUS

• Default: SIMULTANEOUS

### REFERENCE¶

Reference wavefunction type

• Type: string

• Possible Values: UHF, RHF, ROHF

• Default: RHF

### RESPONSE_ALGORITHM¶

Algorithm to use for the solution of DC-06 response equations in computation of analytic gradients and * properties

• Type: string

• Possible Values: TWOSTEP, SIMULTANEOUS

• Default: TWOSTEP

### R_CONVERGENCE¶

Convergence criterion for the RMS of the residual vector in density cumulant updates, as well as the solution of the density cumulant and orbital response equations. In the orbital updates controls the RMS of the SCF error vector

### THREE_PARTICLE¶

Whether to compute three-particle energy correction or not

• Type: string

• Possible Values: NONE, PERTURBATIVE

• Default: NONE

## Expert¶

### CACHELEVEL¶

Controls how to cache quantities within the DPD library

• Type: integer

• Default: 2

### DAMPING_PERCENTAGE¶

The amount (percentage) of damping to apply to the orbital update procedure: 0 will result in a full update, 100 will completely stall the update. A value around 20 (which corresponds to 20% of the previous iteration’s density being mixed into the current iteration) can help in cases where oscillatory convergence is observed.

• Type: double

• Default: 0.0

### DCT_GUESS¶

Whether to read the orbitals from a previous computation, or to compute an MP2 guess.

• Type: string

• Possible Values: CC, BCC, MP2, DCT

• Default: MP2

### DIIS_MAX_VECS¶

Maximum number of error vectors stored for DIIS extrapolation

• Type: integer

• Default: 6

### DIIS_MIN_VECS¶

Minimum number of error vectors stored for DIIS extrapolation

• Type: integer

• Default: 3

### ENERGY_LEVEL_SHIFT¶

Level shift applied to the diagonal of the density-weighted Fock operator. While this shift can improve convergence, it does change the DCT energy.

• Type: double

• Default: 0.0

### INTS_TOLERANCE¶

Schwarz screening threshold. Mininum absolute value below which TEI are neglected.

### ORBITAL_LEVEL_SHIFT¶

The shift applied to the denominator in the orbital update iterations

• Type: double

• Default: 0.0

### RELAX_GUESS_ORBITALS¶

Controls whether to relax the guess orbitals by taking the guess density cumulant and performing orbital update on the first macroiteration (for ALOGRITHM = TWOSTEP only)

The number of vectors that can be added simultaneously into the subspace for Davidson’s diagonalization in stability check

• Type: integer

• Default: 20

### STABILITY_AUGMENT_SPACE_TOL¶

The value of the rms of the residual in Schmidt orthogonalization which is used as a threshold for augmenting the vector subspace in stability check

### STABILITY_CHECK¶

Performs stability analysis of the DCT energy

### STABILITY_CONVERGENCE¶

Controls the convergence of the Davidson’s diagonalization in stability check

### STABILITY_MAX_SPACE_SIZE¶

The maximum size of the subspace for the stability check. The program will terminate if this parameter is exceeded and the convergence (STABILITY_CONVERGENCE) is not satisfied

• Type: integer

• Default: 200

### STABILITY_N_EIGENVALUES¶

The number of Hessian eigenvalues computed during the stability check

• Type: integer

• Default: 3

### STABILITY_N_GUESS_VECTORS¶

The number of guess vectors used for Davidson’s diagonalization in stability check

• Type: integer

• Default: 20

### TIKHONOW_OMEGA¶

The shift applied to the denominator in the density cumulant update iterations

• Type: double

• Default: 0.0