[molpro-user] dissociation to higher channel

[Fritz Grein]

Dear MOLPRO users,
I am encountering a problem with dissociation to a higher dissociation channel.
When dissociating O3 to O2+O, in 1-A' symmetry, then the MOLPRO calculated  CI energy (for fixed O-O distance and angle), is fine up to an O2-O separation of 2.6 A. Until here, the energy is close to the dissociated O2(3-Sigg) + O(3-P) energy. At 2.7 A, the calculated energy jumps higher, and stays higher thereafter. It appears that the O2(1-Delta) + O(1-D) level is approached.
This happens with all CI methods, RS2, MRCI, AQCC and ACPF. Interestingly, the CASSCF energy dissociates to the lowest channel. Dissociation in symmetries, like 1-A", also moves to a higher channel, although at a larger distance.
Reading the literature, there are several MOLPRO calculations described for the 1-A' dissociation of ozone, covering a large potential energy surface. Apparently, no dissociation problems as described above have been encountered. This means that there must be a way to avoid this problem.
Any help would be appreciated.
Fritz Grein
Department of Chemistry
University of New Brunswick, Canada
--------------------------------------------------------------------
     R2          ECAS                  ERS2
    2.0   -224.5573513   -225.1020581
    2.1   -224.5596135   -225.1015510
    2.2   -224.5614908   -225.1012356
    2.3   -224.5629154   -225.1009875
    2.4   -224.5639408   -225.1007287
    2.5   -224.5646529   -225.1003953
    2.6   -224.5651329   -225.0997375
    2.7   -224.5654847   -225.0134963
    2.8   -224.5656828   -225.0134413
    2.9   -224.5658012   -225.0133640
    3.0   -224.5658675   -225.0132738

***,o3-scan1
memory,100,m
symmetry,x
angstrom
geometry={o1
          o2,o1,r1
          o3,o2,r2(i),o1,a}
r1=1.22,a=120.
basis=avtz
distance2=[2.0,2.1,2.2,2.3,2.4,2.5,2.6,2.7,2.8,2.9,3.0]
i=0
do ir2=1,#distance2
i=i+1
r2(i)=distance2(ir2)
{hf;maxit,100}
{casscf;wf,24,1,0;maxit,40}
ecas(i)=energy
{rs2;wf,24,1,0;maxit,100;option,maxiti=400}
ers2(i)=energy
enddo
{table,r2,ecas,ers2
head,r2,ecas,ers2}
----------------------------------------------------------------------




-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.molpro.net/pipermail/molpro-user/attachments/20150810/d2304699/attachment.html>