$DETPT group      (relevant if SCFTYP=MCSCF and MPLEVL=2)                       
    This input group applies to the determinant-based                           
multi-reference perturbation theory program, if chosen by                       
MRPT=DETMRPT in $MRMP.                                                          
    When applied to only one state, the theory is known as                      
multi-reference Moller-Plesset (MRMP), but the term MCQDPT                      
is used when this theory is used in its multi-state form.                       
Please note that this perturbation theory is not the same                       
thing as the CASPT2 theory, and should -NEVER- be called                        
that.  A more complete discussion may be found in the                           
'Further Information' chapter.                                                  
NVAL   = number of filled valence orbitals in the MCSCF to                      
         be included in the dynamic correlation treatment.                      
         This is analogous to NMODOC in the $MCQDPT input.                      
         The number of frozen cores orbitals is found by                        
         subtracting NVAL from NCORE in $DET, so that you                       
         need not specify the chemical core's size.  Also,                      
         there is no input for specifying the active space,                     
         which is inherited from $DET.  The default for                         
         NVAL correlates valence orbitals, but freezes any                      
         chemical cores.                                                        
NEXT   = number of external orbitals to use.  The default                       
         means to use all of them (default=-1).                                 
NOS    = a flag to use MCSCF natural orbitals rather than                       
         canonicalized orbitals as the basis of the PT.                         
         This changes the numerical results!!!                                  
Omitting NPTST, IPTST, and WPTST is the simplest option,                        
meaning that any state with a non-zero WSTATE in $DET is                        
included in the pertubation.  Canonicalization of the                           
orbitals is normally done by the MCSCF program, see CANONC                      
in $MCSCF.  However, if not, or if the state weights are                        
changed, the canonicalization is done in the perturbation                       
code, according to CANON in this group.  The default is the                     
most computationally efficient.                                                 
CANON  = flag to request canonicalization.  Default=.TRUE.                      
         Turning off canonicalization is for experimental                       
         purposes, so most runs should not avoid it.  The                       
         canonicalization will be done in the perturbation                      
         code under three circumstances,                                        
             RDVECS=.TRUE. was used, at the first geometry,                     
             the MCSCF step skipped canonicalization, or                        
             you enter NPTST/IPTST/SPTST information.                           
         Canonicalization uses the state averaged density                       
         matrix to build the "standard Fock operator", and                      
         involves diagonalizing its diagonal sub-blocks.                        
NPTST  = the number of states to include in generation of                       
         the unperturbed CAS states.  If NPTST is chosen,                       
         spins of the states will be ignored, like using                        
         PURES=.F. in $DET, so you must be careful in your                      
         matching IPTST input.                                                  
IPTST  = an array of CAS-CI states to be included in the                        
         perturbation theory, give NPTST values.                                
WPTST  = an array of state weights.  Like NPTST/IPTST, the                      
         default for WPTST is derived from WSTATE in $DET.                      
example: NPTST=3 IPTST(1)=1,3,5 might be used to include                        
three singlets, S0,S1,S2 in a MCQDPT-type treatment, but                        
skip over T1 and T2.  You will have done an earlier CI or                       
MCSCF run, in order to know that you need NPTST five or                         
higher to capture the lowest three singlets, and that these                     
singlets appear where they do.  NSTATE in $DET must be at                       
least 5 in this example, to find enough roots.                                  
EDSHFT  is the same as the same keyword in $MCQDPT.  The                        
        denominators D are changed to D + EDSHFT/D.                             
        Reasonable values are 0.02 to 1D-4, if you need                         
        any shift at all.  The default is 0.0.                                  

generated on 7/7/2017