$CIDRT group                   (required if CITYP=GUGA)                         
    This group describes the Configuration State Functions                      
(CSFs) used by the MCSCF or CI calculation.  The Distinct                       
Row Table (DRT) is the means by which the Graphical Unitary                     
Group Approach (GUGA) specifies configurations. The group                       
is spelled $DRT for MCSCF runs, and $CIDRT for CI runs.                         
The main difference in these is NMCC versus NFZC.                               
    There is no default for GROUP, and you must choose one                      
of FORS, FOCI, SOCI, or IEXCIT.                                                 
GROUP = the name of the point group to be used.  This is                        
        usually the same as that in $DATA, except for                           
        RUNTYP=HESSIAN, when it must be C1.  Choose from                        
        the following: C1, C2, CI, CS, C2V, C2H, D2, D2H,                       
        C4V, D4, D4H.  If your $DATA's group is not listed,                     
        choose only C1 here.                                                    
FORS  = flag specifying the Full Optimized Reaction Space                       
        set of configuration should be generated.  This                         
        is usually set true for MCSCF runs, but if it is                        
        not, see FORS in $MCSCF.  (Default=.FALSE.)                             
FOCI  = flag specifying first order CI.  In addition to                         
        the FORS configurations, all singly excited CSFs                        
        from the FORS reference are included.                                   
SOCI  = flag specifying second order CI.  In addition to                        
        the FORS configurations, all singly and doubly                          
        excited configurations from the FORS reference                          
        are included.  (Default=.FALSE.)                                        
IEXCIT= electron excitation level, for example 2 will                           
        lead to a singles and doubles CI.  This variable                        
        is computed by the program if FORS, FOCI, or                            
        SOCI is chosen, otherwise it must be entered.                           
INTACT= flag to select the interacting space option.  See                       
        C.F.Bender, H.F.Schaefer  J.Chem.Phys. 55,                              
        4798-4803(1971).  The CI will include only those                        
        CSFs which have non-vanishing spin couplings with                       
        the reference configuration.  Note that when the                        
        Schaefer group uses this option for high spin                           
        ROHF references, they use Guest/Saunders orbital                        
  * * the next variables define the single reference * *                        
    The single configuration reference is defined by                            
filling in the orbitals by each type, in the order shown.                       
The default for each type is 0.                                                 
       Core orbitals, which are always doubly occupied:                         
NMCC = number of MCSCF core MOs (in $DRT only).                                 
NFZC = number of CI frozen core MOs (in $CIDRT only).                           
       Internal orbitals, which are partially occupied:                         
NDOC = number of doubly occupied MOs in the reference.                          
NAOS = number of alpha occupied MOs in the reference,                           
       which are singlet coupled with a corresponding                           
       number of NBOS orbitals.                                                 
NBOS = number of beta spin singly occupied MOs.                                 
NALP = number of alpha spin singly occupied MOs in the                          
       reference, which are coupled high spin.                                  
NVAL = number of empty MOs in the reference.                                    
       External orbitals, occupied only in FOCI or SOCI:                        
NEXT = number of external MOs.  If given as -1, this will                       
       be set to all remaining orbitals (apart from any                         
       frozen virtual orbitals).                                                
NFZV = number of frozen virtual MOs, never occupied.                            
        * * the next two help with state symmetry * *                           
STSYM=  The symmetry of the electronic state.  See $DET for                     
        possible values: use AP/APP in Cs, not primes.                          
        Default is the totally symmetric representation.                        
  note: This option overwrites whatever symmetry is implied                     
        by NALP/NAOS/NBOS.  It is easier to pick STSYM than                     
        to allow its inference from the singly occupied                         
        orbitals, which is a relic of ancient input files.                      
NOIRR= controls labelling of the CI state symmetries.                           
     = 1 no labelling (default)                                                 
     = 0 usual labelling.  This can be very time consuming                      
         if the group is non-Abelian.                                           
     =-1 fast labelling, in which all CSFs with small CI                        
         coefficients are ignored. This can produce weights                     
         quite different from one, due to ignoring small                        
         coefficients, but overall seems to work OK.                            
         Note that it is normal for the weights not to sum                      
         to 1 even for NOIRR=0 because for simplicity the                       
         weight determination is focused on the relative                        
         weights rather than absolute.  However weight do                       
         not sum to one only for row-mixed MOs.                                 
     = -2,-3... fast labelling and sets SYMTOL=10**NOIRR                        
         for runs other than TRANSITN.  All irreps with                         
         weights greater than SYMTOL are considered.                            
       * * * the final choices are seldom used * * *                            
MXNINT = Buffer size for sorted integrals. (default=20000)                      
         Adjust this upwards if the program tells you to,                       
         which may occur in cases with large numbers of                         
         external orbitals.                                                     
MXNEME = Buffer size for energy matrix.  (default=10000)                        
NPRT   = Configuration printout control switch.                                 
         This can consume a HUMUNGUS amount of paper!                           
         0 = no print (default)                                                 
         1 = print electron occupancies, one per line.                          
         2 = print determinants in each CSF.                                    
         3 = print determinants in each CSF (for Ms=S-1).                       

generated on 7/7/2017