PSIMRCC

Performs multireference coupled cluster computations. This theory should be used only by advanced users with a good working knowledge of multireference techniques.

General

CC_NUM_THREADS

Number of threads

  • Type: integer
  • Default: 1

CORR_ANSATZ

The ansatz to use for MRCC computations

  • Type: string
  • Possible Values: SR, MK, BW, APBW
  • Default: MK

CORR_CCSD_T

The type of CCSD(T) computation to perform

  • Type: string
  • Possible Values: STANDARD, PITTNER
  • Default: STANDARD

CORR_CHARGE

The molecular charge of the target state

  • Type: integer
  • Default: 0

CORR_MULTP

The multiplicity, \(M_S(M_S+1)\), of the target state. Must be specified if different from the reference \(M_s\).

  • Type: integer
  • Default: 1

CORR_WFN

The type of correlated wavefunction

  • Type: string
  • Possible Values: PT2, CCSD, MP2-CCSD, CCSD_T
  • Default: CCSD

COUPLING

The order of coupling terms to include in MRCCSDT computations

  • Type: string
  • Possible Values: NONE, LINEAR, QUADRATIC, CUBIC
  • Default: CUBIC

COUPLING_TERMS

Do include the terms that couple the reference determinants?

DAMPING_PERCENTAGE

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

  • Type: double
  • Default: 0.0

DIAGONALIZE_HEFF

Do diagonalize the effective Hamiltonian?

DIAGONAL_CCSD_T

Do include the diagonal corrections in (T) computations?

DIIS_MAX_VECS

Maximum number of error vectors stored for DIIS extrapolation

  • Type: integer
  • Default: 7

DIIS_START

The number of DIIS vectors needed before extrapolation is performed

  • Type: integer
  • Default: 2

E_CONVERGENCE

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

FAVG_CCSD_T

Do use the averaged Fock matrix over all references in (T) computations?

FOLLOW_ROOT

Which root of the effective hamiltonian is the target state?

  • Type: integer
  • Default: 1

HEFF4

Do include the fourth-order contributions to the effective Hamiltonian?

HEFF_PRINT

Do print the effective Hamiltonian?

LOCK_SINGLET

Do lock onto a singlet root?

MAXITER

Maximum number of iterations to determine the amplitudes

  • Type: integer
  • Default: 100

MP2_CCSD_METHOD

How to perform MP2_CCSD computations

  • Type: string
  • Possible Values: I, IA, II
  • Default: II

MP2_GUESS

Do start from a MP2 guess?

NO_SINGLES

Do disregard updating single excitation amplitudes?

OFFDIAGONAL_CCSD_T

Do include the off-diagonal corrections in (T) computations?

PERTURB_CBS

Removed in 1.4. Will raise an error in 1.5.

PERTURB_CBS_COUPLING

Removed in 1.4. Will raise an error in 1.5.

PT_ENERGY

The type of perturbation theory computation to perform

  • Type: string
  • Default: SECOND_ORDER

R_CONVERGENCE

Convergence criterion for amplitudes (residuals).

SMALL_CUTOFF

  • Type: integer
  • Default: 0

TIKHONOW_MAX

The cycle after which Tikhonow regularization is stopped. Set to zero to allow regularization in all iterations

  • Type: integer
  • Default: 5

TIKHONOW_OMEGA

The shift to apply to the denominators, {it c.f.} Taube and Bartlett, JCP, 130, 144112 (2009)

  • Type: double
  • Default: 0.0

TRIPLES_ALGORITHM

The type of algorithm to use for (T) computations

  • Type: string
  • Possible Values: SPIN_ADAPTED, RESTRICTED, UNRESTRICTED
  • Default: RESTRICTED

TRIPLES_DIIS

Do use DIIS extrapolation to accelerate convergence for iterative triples excitations?

USE_SPIN_SYM

Do use symmetry to map equivalent determinants onto each other, for efficiency?

WFN_SYM

The symmetry of the target wavefunction, specified either by Schönflies symbol, or irrep number (in Cotton ordering)

  • Type: string
  • Default: 1

ZERO_INTERNAL_AMPS

Do zero the internal amplitudes, i.e., those that map reference determinants onto each other?

Expert

TIKHONOW_TRIPLES

Do use Tikhonow regularization in (T) computations?

USE_SPIN_SYMMETRY

Whether to use spin symmetry to map equivalent configurations onto each other, for efficiency