$DET/$CIDET

$DET group (required for SCFTYP=MCSCF if CISTEP=ALDET)
$GEN group (required for SCFTYP=MCSCF if CISTEP=GENCI)
$CIDET group (required if CITYP=ALDET)
$CIGEN group (required if CITYP=GENCI)

This group describes the determinants to be used in a full MCSCF or CI wavefunction.

For $DET or $CIDET, a full list of determinants is generated, i.e. the MCSCF is of FORS (also known as CAS) type, or this is to be a full CI. For $GEN and $CIGEN you must input an arbitrary set of determinants, according to the keyword GLIST.
Determinants contain several spin states, in contrast to configuration state functions.
The Sz quantum number of each determinant is the same, but the Hamiltonian eigenvectors will have various spins S=Sz, Sz+1, Sz+2, ... so NSTATE may need to account for states of other spin symmetry. In Abelian groups, you can specify the exact spatial symmetry you desire.
GLIST = general determinant list option
The keyword GLIST must not be given in a $DET or $CIDET input group!
These both generate full determinant lists, automatically.
= INPUT means an input $GCILST group will be read.
= EXTRNL means the list will be read from a disk file GCILIST generated in an earlier run.
= SACAS requests generation of sevaral CAS spaces of different space symmetries, specified by the input IRREPS. This option is intended for state averaged calculations for cases of high symmetry, where degenerate irreps of the true group may fall into different irreps of the Abelian subgroup used.
The next three determine the symmetry of the states:
GROUP = name of the point group. The default is to copy this from $DATA, if that group is Abelian (C2, Ci, Cs, C2v, C2h, D2, or D2h). If not, the group is set to C1 (no symmetry used).
ISTSYM = specifies the spatial symmetry of the state. This table is exactly the same as in $DRT input.
ISTSYM=   1    2    3    4    5    6    7    8
C1        A
Ci        Ag  Au
Cs        A'  A''
C2        A   B
C2v       A1  A2   B1    B2
C2h       Ag  Bu   Bg    Au
D2        A   B1   B2    B3
D2h       Ag  B1g  B2g   B3g  Au   B1u  B2u  B3u
Default is ISTSYM=1, the totally symmetric state.
IRREPS = specifies the symmetries of the GLIST=SACAS space determinant list.
This variable should always be an array, as a single symmetry is more quickly obtained by the regular full CI code. The values given have the same meaning as the ISTSYM table.

The next four define the filled and active orbital space.
There is no default for NCORE, NACT, and NELS:
NCORE = total number of orbitals doubly occupied in all determinants.
NACT = total number of active orbitals.
NELS = total number of active electrons.
SZ = azimuthal spin quantum number for each of the determinants, two times
SZ is therefore the number of excess alpha spins in each determinant.
The default is SZ=S, extracted from the MULT=2S+1 given in $CONTRL.
* * * the following control the diagonalization * * *
NSTATE = Number of CI states to be found, the default is 1. The maximum number of states is 100.
PRTTOL = Printout tolerance for CI coefficients, the default is to print any larger than 0.05.
ITERMX = Maximum number of Davidson iterations per root. The default is 100. A CI calculation will fail if convergence is not obtained before reaching the limit. MCSCF computations will not bomb if the iteration limit is
reached, instead the last CI vector is used to proceed into the next orbital update. In cases with very large active spaces, it may be faster to input ITERMX=2 or 3 to allow the program to avoid fully converging the CI
eigenvalue problem during the early MCSCF iterations. For small active spaces, it is best to allow the CI step to be fully converged on every iteration.
CVGTOL = Convergence criterion for Davidson eigenvector routine. This value is proportional to the accuracy of the coeficients of the eigenvectors found. The energy accuracy is proportional to its square. The default is 1.0E-5.
NHGSS = dimension of the Hamiltonian submatrix which is diagonalized to obtain the initial guess eigenvectors. The determinants forming the submatrix are chosen on the basis of a low diagonal energy, or if needed to complete a
spin eigenfunction. The default is 300.
NSTGSS = Number of eigenvectors from the initial guess Hamiltonian to be included in the Davidson's iterative scheme. It is seldom necessary to include extra states to obtain convergence to the desired states. The default equals
NSTATE.
MXXPAN = Maximum number of expansion basis vectors in the iterative subspace during the Davidson iterations before the expansion basis is truncated. The default is the larger of 10 or 2*NSTGSS. Larger values might help
convergence, do not decrease this parameter below 2*NSTGSS.

* * * the following control the 1st order density * * *
These are ignored during MCSCF, but are used during a CI.

$DET/$CIDET

IROOT = the root whose density is saved on the disk file for subsequent property analysis. Only one root can be saved, and the default value of 1 means the ground state. Be sure to set NFLGDM to form the density of the state you are interested in!
NFLGDM = Controls each state's density formation. 0 do not form density for this state. 1 form density and natural orbitals for this state, print and punch occ.nums. and NOs. 2 same as 1, plus print density over MOs.
The default is NFLGDM(1)=1,0,0,...,0 meaning only ground state NOs are generated.

                       * * * the following control the state averaged * * *
                            1st and 2nd order density matrix computation

Usually ignored by CI runs, these are relevant to MCSCF.
PURES = a flag controlling the spin purity of the state avaraging. If true, the WSTATE array pertains to the lowest states of the same S value as is given by the MULT keyword in $CONTRL. In this case the value of NSTATE will
need to be bigger than the total number of weights given by WSTATE if there are other spin states present at low energies. If false, it is possible to state average over more than one S value, which might be of interest in
spin-orbit coupling jobs. The default is .TRUE.
WSTATE = An array of up to 100 weights to be given to the densities of each state in forming the average. The default is to optimize a pure ground state, WSTATE(1)=1.0,0.0,...,0.0 A small amount of the ground state can help
the convergence of excited states greatly. Gradient runs are possible only with pure states. Be sure to set NSTATE above appropriately!