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    <div class="moz-cite-prefix">Hello George,<br>
      I had a look at this using small basis sets and I found results
      similar to yours, ie the CASSCF energies are not size-consistent
      in this case. So `trivial' errors such as incorrect convergence or
      getting the wrong electronic states should be excluded.<br>
      Specifically:<br>
      <br>
      1) Using the small STO-3G basis set CASSCF is FCI in the valence
      space, and in this case the energies *are* size consistent. I get
      using MCSCF E1=-73.804150 for O, E2=-73.443584 for O+,
      E1+E2=-147.247734 which is also the value I get for O2+ at r=100
      a0.<br>
      <br>
      2) Using 6-31G or cc-pVDZ the sum of the atomic energies is lower
      than the energy of stretched O2+ by about 0.0047 Eh, as you
      reported in the aug-cc-pV5Z basis set.<br>
      On the other hand if we do FCI using the MCSCF orbitals we get
      size-consistent energies (attached outputs).<br>
      As suggested by Kirk, perhaps different virtual orbitals enter
      into the active space (AS) in the molecular and atomic cases. If
      you want to investigate this further I'd have a look at the
      orbital expansion coefficients (use ORBPRINT) in the atomic and
      molecular cases (using the smallest basis set which reproduces the
      problem, eg 6-31G or even smaller) and see if you can understand
      what is going into the AS.<br>
      <br>
      I also point out that in this sistem there are lots of
      degeneracies. In the atomic calculation (attached) I average over
      the spacial components (3 components for oxygen 3P and 1 component
      for oxygen+ 4S^o), while for the molecule I average over the two
      degenerate components of the 2Pi_g term. At r=infty a part from
      2Pi_g there is also a 2Pi_u and two 2Sigma_g^+ terms, as well as
      {2Pi_g, 2Pi_u, 2x2Sigma_g^+} quadruplets and sextets, I wonder if
      the size-consistency violation you observed is related to which
      states are included and averaged over.<br>
      <br>
      Lorenzo<br>
      <br>
      On 10/02/16 18:36, george wrote:<br>
    </div>
    <blockquote
cite="mid:CA+H8_LFbGAA0HBNZu35G5XDmgNUXdbmibUY0JNt4_Sz263rgGg@mail.gmail.com"
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          <div>Dear molpro users<br>
            <br>
            <br>
          </div>
                 I am computing potential energy curve for ground state
          O2+ at multi level using av5z basis set. This dissociates to
          O(3P)+O+(4S) fragments. Now I add the energies of these two
          fragments and get -149.18369960 hartrees at the same level.
          When I look at the energies of curve at 100 angstrom, the
          multi value at this long distance is  -149.13557933 hartrees.
          I wonder why and how this numerical discrepancies arise? My
          input file is very simple without any complicated keyworkds.
          Am I missing something relevent to this type of problem? Any
          suggestion please.<br>
          <br>
          <br>
        </div>
        My input<br>
        <br>
         ***,o2+<br>
         memory,125,m<br>
         print,orbitals,civector<br>
                                                                                        
        !file,1,o2+_<a moz-do-not-send="true"
          href="http://ci_d2h_6_1_mar5.int">ci_d2h_6_1_mar5.int</a><br>
                                                                                        
        !file,2,o2+_ci_d2h_6_1_mar5.wfu<br>
                               
        !symmetry,nosym                                                                                
        !symmetry,x<br>
                                                                
!rcm=[1.11780256,0.7,0.75,0.8,0.85,0.9,0.95,1,1.025,1.05,1.075,1.1,1.110,\<br>
                                                                                   
        !      1.125,1.15,1.175,1.2,1.25,1.3,1.35,1.4,1.5,1.6,\<br>
         !     
        1.7,1.8,1.9,2,2.125,2.25,2.5,2.75,3,3.25,3.375,3.5,3.625,3.75,4,4.25,4.5,4.75,5,5.25,5.5,5.75,6,6.5,7,7.5,8,9,10,11,12,13,14,15,16,18,20,21,22,23,24,25]
        ANG<br>
         rcm=[100] ANG<br>
        <br>
         geometry                                                                       
        !geometry specification, using z-matrix<br>
         o1<br>
         o2,o1,r<br>
         end<br>
        <br>
         basis=aug-cc-pV5Z<br>
        <br>
         do i=1,#rcm<br>
        <br>
         r=rcm(i)<br>
        <br>
         {multi;maxiter,40;config;pspace,0.1;wf,15,7,1;dm}<br>
         emulti_gs(i)=energy(1)<br>
                                                                                        
        !{ci;option,maxiti=10000;wf,15,6,1}<br>
                                                                                        
        !eci_gs(i)=energy(1)<br>
                                                                                        
        !eci_david(i)=energd(1)<br>
        <br>
         {table,rcm,emulti_gs<br>
         Title,Results for O2+ dissociation 2Pi_g state<br>
         format,'(f15.8,f30.15)'}<br>
        <br>
                                                                                        
        !{table,rcm,eci_gs<br>
                                                                                        
        !format,'(f15.8,f30.15)'}<br>
        <br>
                                                                                        
        !{table,rcm,eci_david<br>
                                                                                        
        !format,'(f15.8,f30.15)'}<br>
        <br>
         end do<br>
        <br>
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