$CEEIS group  (optional, for extrapolation to FCI limit)                        
     The method termed Correlation Energy Extrapolation by                      
Intrinsic Scaling (CEEIS) allows one to extrapolate                             
sequences of CI energies, computed with the ORMAS program,                      
to what is effectively the full CI limit for a given basis                      
set.  Typically, the energy for SD and SDT excitation                           
levels using all orbitals (m=M, meaning occupied + all                          
virtuals) is combined, using certain scaling relations,                         
with explicit computations using m orbitals for quadruple,                      
quintuple... excitations (x), using a smaller m for each                        
higher excitation, to obtain the extrapolated FCI limit,                        
within an estimated error bar.  When this is done for                           
several basis sets, it is possible to extrapolate the                           
individual full CI energies to the limit of the complete                        
basis set.                                                                      
     A series of papers combines complete basis set CEEIS                       
energies with scalar relativistic, spin-orbit, and long                         
range electrostatic corrections to produce a very accurate                      
rotational-vibrational spectrum of F2, see                                      
L.Bytautas, T.Nagata, M.S.Gordon, K.Ruedenberg                                  
        J.Chem.Phys. 127, 164317/1-20 (2007)                                    
L.Bytautas, N.Matsunaga, T.Nagata, M.S.Gordon, K.Ruedenberg                     
        J.Chem.Phys. 127, 204301/1-12 (2007)                                    
L.Bytautas, N.Matsunaga, T.Nagata, M.S.Gordon, K.Ruedenberg                     
        J.Chem.Phys. 127, 204313/1-19 (2007)                                    
L.Bytautas, K.Ruedenberg                                                        
        J.Chem.Phys. 130, 204101/1-14 (2009)                                    
     The input description below is quite terse.  A full                        
description of how to use CEEIS with ORMAS is provided in a                     
separate file (a Word document) named                                           
containing a much more detailed description of how to do                        
this kind of calculation.  This document explains how to                        
use an Excel spreadsheet to allow visual checking of the                        
energy data that are being extrapolated.  Several input                         
examples are given in the same directory.                                       
ENREF  = reference energy, usually either a zero-excited                        
         ORMAS reference wavefunction, or some SCF level                        
         energy (if the reference is one determinant).                          
ISTPEX = highest excitation level considered by the CEEIS,                      
         the default is 8 (octuple excitations).                                
M1M2EX = an array to specify the various ORMAS computations                     
         to be performed, at each excitation level x.                           
         0's start the specification of m values for each                       
         level x=3,4,...ISTPEX.  Some examples follow,                          
  M1M2EX(1)= 0,0,0,                                                             
             0,7,10,-14   ISTEPX=5                                              
The final two zero's on the first (SDT) line mean do the                        
SDT computations with the entire virtual space, and also                        
for all m values used at the higher excitations.  The SDTQ                      
energies are found for m=7,10,11,12,13,14,20, that is, the                      
minus sign implies all values in the range 10-14.  The                          
SDTQ5 computations do not include m=20.  If there is not                        
enough memory to do the entire SDT calculation, this can be                     
extrapolated (losing accuracy in the entire CEEIS process),                     
by input such as                                                                
  M1M2EX(1)= 0,7,10,-14,20,27,                                                  
             0,7,10,-14   ISTEPX=5                                              
Changing the 0,0 part of the triples line to what is shown                      
extrapolates from m=27.  Note that it is an error not to                        
include the same m values that higher excitations will use.                     
There is no input for doubles, as in all cases the program                      
will generate the SD energy for the entire virtual space,                       
and additional SD energies for the m values chosen for use                      
by the higher excitation levels.                                                
  M1M2EX(1)= all 0's will carry out a fully automated CEEIS                     
using MMIN to MMIN+4, testing convergence, possibly adding                      
MMIN+5 to MMIN+9 and so forth.                                                  
IDELTM = range increment for the m1,m2 ranges given as                          
         {m1,-m2} in M1M2EX.  Default=1.                                        
ISCHME = extrapolation choice (the default is 1) for energy                     
         increments (DEMAT = differences of EMAT values):                       
       = 1 means extrapolate excitation level "x" by                            
              DEMAT(m,x) = a*DEMAT(m,x-2) + b                                   
       = 2 means extrapolate quadruples as above, but                           
           x=5+6 or x=7+8,... are extrapolated together:                        
              DEMAT(m,x) = A*DEMAT(m,2) + B*DEMAT(m,3) + C                      
           In this case energies for odd excitation levels                      
           are not needed, and their computation can be                         
           avoided by making the odd levels in M1M2EX be                        
           the same input for 5+6, 7+8, ...                                     
MMIN   = "m" value of the lowest virtual orbital to be                          
         considered in the extrapolation.  The default is                       
         NCORE + 1 + MAX(no. valence e-, no. valence orbs),                     
         which is in fact the lowest "m" that should ever                       
         be used.                                                               
XTRTOL = an array of thresholds for each extrapolated                           
         energy E(x), if the automated CEEIS is being used.                     
         default = 2D-4 Hartree for all levels x.                               
NSEXT  = an array containing NSPACE entries.  Each entry                        
         corresponds to an ORMAS orbital group defined by                       
         MSTART in $ORMAS, and can be either 0 or 1.                            
         An entry of 1 means include excitations from this                      
         space during the CEEIS.  0 means do not include                        
         any such excitations, meaning electrons in this                        
         subspace are NOT being correlated, apart from the                      
         correlation built into the original ORMAS.  The                        
         final entry in the list is the virtual space, and                      
         must be given as 1.  The default is all 1's.                           
RESTRT = a flag to say that the CEEIS calculation is being                      
         restarted, in which case energies provided in the                      
         $CEDATA input are read, and only the missing                           
         energies will be calculated.  Default = .FALSE.                        
IEXPND = expands the excitation level in restarts, e.g. if                      
         the previous data was computed for ISTPEX=6, and                       
         you now wish to use ISTPEX=8, enter IEXPND=2 to                        
         add two more columns to the matrix EMAT(m,x) being                     
         read in $CEDATA.                                                       
$CEDATA group    (optional restart data for CEEIS runs)                         
This group contains previously computed ORMAS energies,                         
forming the EMAT array, to be used to restart CEEIS runs.                       
It is required if RESTRT in $CEEIS is true.                                     

generated on 7/7/2017