$CASCI group         (relevant to SCFTYP=RHF MPLEVL=2)                          
   This group carries out the Improved Virtual Orbital -                        
Complete Active Space CI method of Freed, Chaudhuri, and                        
co-workers.  IVO-CASCI starts with a RHF reference, and                         
then generates IVOs, which are used in a CI computation                         
within an active space chosen by the user.  The input                           
consists of this group, a $MCQDPT, and perhaps a $IVOORB                        
input, along with SCFTYP=RHF and MPLEVL=2.  MULT in $CONTRL                     
applies to the SCF reference, while MULT in $MCQDPT selects                     
the spin of the IVO-CASCI state(s).  Doublets are treated                       
by using a cation RHF reference.                                                
IVOCAS = a flag to turn on IVO-CASCI computation.  This is                      
         usually the only input required (default=.FALSE.)                      
MOLIST = a flag to request complete control over the                            
         active space specification.  The default uses the                      
         parameters in $MCQDPT to select from the IVOs                          
         with the lowest energy.  (default=.FALSE.)                             
DEGENR = a flag to indicate the HOMO is degenerate.                             
         The program should set this for you.                                   
PRINT  = a flag to print debugging info (default=.FALSE.)                       
The user should request IFORB=0 in $MCQDPT to suppress its                      
generation of canonical orbitals, so that the IVOs are                          
used.  A Huckel guess is usually fine.  The $MCQDPT should                      
define the active orbitals taken from the IVO set by giving                     
NMOFZC, NMODOC, and NMOACT, and the electronic state is                         
specified by that group's MULT, NSTATE, and NSTSYM.                             
D.M.Potts, C.M.Taylor, R.K.Chaudhuri, K.F.Freed                                 
  J.Chem.Phys.  114, 2592-2600(2001)                                            
R.K.Chaudhuri, K.F.Freed, S.A.Abrash, D.M.Potts                                 
  J.Mol.Spectrosc. 547, 83-96(2001)                                             
R.K.Chaudhuri, K.F.Freed                                                        
  J.Chem.Phys.  126, 114103/1-6(2007)                                           
A simple example follows,                                                       
 $contrl scftyp=rhf mplevl=2 runtyp=energy ispher=1 $end                        
 $casci  IVOCAS=.true. $end                                                     
 $mcqdpt mult=3 stsym=b1 nstate=1 iforb=0                                       
         nel=8 nmofzc=1 nmodoc=2 nmoact=2 $end                                  
 $basis  gbasis=ccd $end                                                        
 $guess  guess=huckel $end                                                      
Methylene...3-B-1 state...RHF/cc-pVDZ                                           
Cnv  2                                                                          
C   6.0   0.0  .0000000000  .0289123030                                         
H   1.0   0.0  .9813851814  .4758735367                                         
The result for the 1st order energy will be -38.9156231594,                     
which is a full CI within a two orbital space, generated by                     
the IVO process, rather than a more expensive MCSCF run.                        
$IVOORB group       (relevant if MOLIST=.T. in $CASCI)                          
In case the IVOs are not generated in the desired order,                        
this group can fully specify the orbital counts in each                         
irreducible representation.                                                     
line 1: NIRREP - gives the total number of irreps                               
line 2: NDIM, NCORE, NDOC, NUNOCC, NSING - for this irrep,                      
gives its total dimension, the number of core MOs in the                        
CASCI, and 3 parameters which define the active orbitals:                       
filled, empty, and singly occupied (0,1 only) in the                            
reference.  Repeat NIRREP times.  A 6 active e- example is                      
59 4 2 2 0                                                                      
26 0 1 1 0                                                                      

generated on 7/7/2017