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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>
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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>
</div>
<br>
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<br>
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