$ORMAS group      (required by MCSCF if CISTEP=ORMAS)                           
                               (required for CITYP=ORMAS)                       
   This group partitions an active space, defined in $DET                       
or $CIDET, into Occupation Restricted Multiple Active                           
Spaces (ORMAS).  All possible determinants satisfying the                       
occupation restrictions (and of course the space symmetry                       
restriction given in $DET/$CIDET) will be generated.  This                      
group's usefulness lies in reducing the large number of                         
determinants present in full CI calculations with large                         
active spaces.                                                                  
    There are no sensible defaults for these inputs, but if                     
the group is entirely omitted, a full CI calculation will                       
be performed.  That is, the defaults are                                        
  NSPACE=1, MSTART(1)=NCORE+1, MINE(1)=NELS, MAXE(1)=NELS                       
meaning all active orbitals are in one partition.                               
NSPACE  = number of orbital groups you wish to partition                        
          the active space (NACT in $DET/$CIDET) into.                          
MSTART  = an array of NSPACE integers.  These specify where                     
          each orbital group starts in the full list.  You                      
          must not overlook the NCORE core orbitals in                          
          computing MSTART values.  Space I runs from                           
          orbital MSTART(I) up to orbital MSTART(I+1)-1,                        
          or NACT+NCORE if I is the last space, I=NSPACE.                       
  IMPORTANT !!!!  Remember to make sure your orbitals have                      
  been reordered to suit MSTART, using NORDER in $GUESS.                        
MINE    = an array of NSPACE integers.  These specify the                       
          minimum numbers of electrons that must always                         
          occupy the orbital groups.  In other words,                           
          MINE(I) is the minimum number of electrons that                       
          can occupy space I in any of the determinants.                        
MAXE    = an array of NSPACE integers.  These specify the                       
          maximum numbers of electrons that must always                         
          occupy the orbital groups.  In other words,                           
          MAXE(I) is the maximum number of electrons that                       
          can occupy space I in any of the determinants.                        
  The number of active electrons is NELS in $DET or $CIDET,                     
  and the program will check that MINE/MAXE values are                          
  consistent with this total number.                                            
     Input for Coupled Electron Pair Approximations                             
These two keywords provide size-extensivity corrections for                     
singly and doubly excited CI calculations.  At present,                         
these approximate corrections may only be applied to a                          
single state.  The CISD may follow RHF (single reference,                       
SR) or complete active space (multireference, MR)                               
calculations.  Usually, the final ORMAS orbital space will                      
be the entire external space of the SR-CISD or MR-CISD                          
calculations.  The excitation level (MAXE) into this space                      
should only be two.  The number of electrons being                              
correlated (NELS in $CIDET) is denoted Ne.  The value of a                      
parameter G determines the weight of the approximate size-                      
extensivity correction, with the literature containing                          
several possible choices:  GVAL here sometimes is written                       
as -(1-G) in the literature.  The first order density                           
matrix for the chosen CEPA-style correction will be                             
generated, and used for property calculation.                                   
CEPA    = NONE  ordinary SR-CISD or MR-CISD (default)                           
        = CEPA0 Coupled Electron Pair Approximation,                            
                whose GVAL= 1.0                                                 
        = ACPF  Averaged Coupled Pair Functional,                               
                whose GVAL= (Ne-2)/Ne                                           
        = AQCC  Averaged Quadratic Coupled-Cluster,                             
                whose GVAL= (Ne-3)(Ne-2)/[Ne(Ne-1)]                             
        = READ  user will supply the desired GVAL.                              
GVAL    = is given only when CEPA=READ                                          
An example of the SR-AQCC size-extensivity correction for a                     
molecule with 10 chemical cores, 8 occupied valence                             
orbitals, and 163 total MOs is                                                  
 $CONTRL SCFTYP=RHF CITYP=ORMAS RUNTYP=ENERGY                                   
 $CIDET  NCORE=10 NACT=153 NELS=16                                              
 $ORMAS  CEPA=AQCC NSPACE=2                                                     
         MSPACE(1)=11,19 MINE(1)=14,0 MAXE(1)=16,2                              
A MR-CEPA case with N active electrons and M electrons in                       
filled valence orbitals should use three spaces, with NELS                      
M+N; MINE M-2,N-2,0; and MAXE M,N+2,2.                                          
Review: P.G.Szalay, in Modern Ideas in Coupled-Cluster                          
methods, R.J.Bartlett (ed), World Scientific, Singapore                         
(1997), pp 81-123.                                                              
                        * * * * *                                               
BLOCK   = a flag to request that natural orbital generation                     
          for CISTEP=ORMAS MCSCF or CITYP=ORMAS CI runs                         
          should prevent mixing between the NSPACE orbital                      
          subspaces.  This means the NOs only diagonalize                       
          the diagonal blocks of the density, and are thus                      
          not the genuine NOs.  However, these approximate                      
          NOs can be used with MOREAD to exactly reproduce                      
          the ORMAS energy, which is invariang to rotations                     
          within the orbital subspaces.  (Default=.FALSE.)                      
QCORR   = a flag to request Davidson-style +Q corrections.                      
          If this is not sensible for your CI choice, the                       
          program will not print this correction, anyway.                       
          The default is .TRUE.                                                 
FDIRCT  = a flag to choose storage in memory of some                            
          intermediates.  This is very large, and slower in                     
          the case of many occupied orbitals, but helpful                       
          with a smaller number of orbitals.  Therefore the                     
          default for this is .TRUE. for MCSCF runs, but                        
          .FALSE. during CI computations.                                       
 *** See REFS.DOC for more information on using ORMAS ***                       

generated on 7/7/2017