Basic Keywords

WFN = string

Acceptable values for determinant-based CI computations in PSI3 are detci and, for CASSCF, detcas.

REFERENCE = string

Most reference types allowed by PSI3 are allowed by detci, except that uhf is not supported.

DERTYPE = string

Only single-point calculations are allowed for wfn = detci. For wfn = detcas, first derivatives are also available.

CONVERGENCE = integer

Convergence desired on the CI vector. Convergence is achieved when the RMS of the error in the CI vector is less than 10**(-n). The default is 4 for energies and 7 for gradients.

EX_LVL = integer

Excitation level for excitations into virtual orbitals (default 2, i.e. CISD). In a RAS CI, this is the number of electrons allowed in RAS III.

VAL_EX_LVL = integer

In a RAS CI, this is the additional excitation level for allowing electrons out of RAS I into RAS II. The maximum number of holes in RAS I is therefore EX_LVL + VAL_EX_LVL. Defaults to zero.

FROZEN_DOCC = (integer array)

Core may be frozen by setting FREEZE_CORE. To manually select how many orbitals per irrep to freeze, use the FROZEN_DOCC keyword. Should be in psi:() or default:() sections of input. The number of lowest energy doubly occupied orbitals in each irreducible representation from which there will be no excitations. The Cotton ordering of the irredicible representations is used. The default is the zero vector.

FROZEN_UOCC = (integer array)

Should be in psi:() or default:() sections of input. The number of highest energy unoccupied orbitals in each irreducible representation into which there will be no excitations. The default is the zero vector.

RAS1 = (integer array)

Should be in psi:() or default:() sections of input. The number of orbitals for each irrep making up the RAS I space, from which a maximum of EX_LVL + VAL_EX_LVL excitations are allowed. This does not include frozen core orbitals. For a normal CI truncated at an excitation level such as CISD, CISDT, etc., it is not necessary to specify this or RAS2 or RAS3. Note: this keyword must be visible to the transqt program also so that orbitals are ordered correctly (placing it in default or psi should be adequate).

RAS2 = (integer array)

Should be in psi:() or default:() sections of input. As above for RAS1, but for the RAS II subspace. No restrictions are placed on the occupancy of RAS II orbitals. Typically this will correspond to the conventional idea of an ``active space'' in multi-reference CI.

RAS3 = (integer array)

Should be in psi:() or default:() sections of input. As above for RAS3, but for the RAS III subspace. A maximum of EX_LVL electrons are allowed in RAS III.

MAXITER = integer

Maximum number of iterations to diagonalize the Hamiltonian. Defaults to 12.

NUM_ROOTS = integer

This value gives the number of roots which are to be obtained from the secular equations. The default is one. If more than one root is required, set DIAG_METHOD to SEM (or, for very small cases, RSP or SEMTEST). Note that only roots of the same irrep as the reference will be computed. To compute roots of a different irrep, one can use the REF_SYM keyword (for full CI only).

OPDM = boolean

If TRUE, compute the one-particle density matrix for each root. By default, it will be written to disk. Except for MCSCF computations (e.g., CASSCF, RASSCF), this will also turn on computation of dipole moments by default.

TRANSITION_DENSITY = boolean

If TRUE, compute the transition density matrix from the ground state to each other state obtained in the computation. By default, this information will be written to disk. Transition dipole moments will be evaluated in detci. Note: only transition densities between roots of the same symmetry will be evaluated. detci does not compute states of different irreps within the same computation; to do this, lower the symmetry using the subgroup keyword in psi:() or default:() (see section 3.4).

DIPMOM = boolean

If TRUE, evaluate the dipole moment for each root (using the expectation value formula; orbital relaxation contributions are neglected). This is an alternative to evaluation using the oeprop module, which has more features.

REF_SYM = integer

This option allows the user to look for CI vectors of a different irrep than the reference. This probably only makes sense for Full CI, and it is not supported for unit vector guesses.

MPN = boolean

If TRUE, compute MPn energies up to nth order, where MAXNVECT = n controls the maximum order energy computed. For open-shell systems (REF = ROHF, WFN = ZAPTN), ZAPTn energies are computed.

For larger computations, additional keywords may be required, as described in the detci man pages.