[molpro-user] Avoided crossing issue

Mon May 24 17:36:16 BST 2004

Dear Molpro user group,

I am interested in an avoided crossing that occurs between the first two 
triplet Pi_g states of O2.

I have no problem observing the avoided crossing when CASSCF is 
implemented, but when I use the RS2 (MULTIREFERENCE RAYLEIGH SCHRÖDINGER 
PERTURBATION THEORY) method, for a quick and easy improvement upon the 
correlation energy, I get an unusual result: I observe the avoided 
crossing, but it appears that either or both adiabatic states are 
displaced by a constant. (I've noticed similar results for MRCI and RS3, 
but they are not submitted here).

By this I mean that the shape of the avoided crossing is still present, 
but now the two potential energy curves overlap and cross in two places (see 
data 
below).

I'm ultimately interested in the diabatic states, so I've run the 
example of Quasi-dibatization published in the Molpro manual 
(h2s_diab1.com). Here I also notice that both the adiabatic and diabatic 
potential curves appear to be displaced: The size of the avoided 
crossing appears to be larger then expected, and the crossing of the 
diabatic states are not where the avoided crossing occurs.

Has anyone had similar issues, and can anyone point out something that I 
am overlooking? Is this a bug?

Thanks,

Yann Tambouret
BU Chemistry
Boston, MA

Here is the input file:

***, lowest two Pi g triplet O2 states
memory,20,M

file,1,o212pi.int,new;file,2,o212pi.wfu,new

basis=cc-pvtz

geometry={
O;
O,O,Bond
}

hart=27.2116
!Setting asymtoptic bond lenght and mesuring zero point energy

Bond=40

multi;
occ,4,1,1,0,4,1,1,0
closed,2,,,,2,,,,;
wf,16,6,2;state,4;

rs2;state,2;

end=energy(1)

!resetting Bond near avoided crossing

Bond=2.9

do i=1,50

r(i)=bond

multi;
occ,4,1,1,0,4,1,1,0
closed,2,,,,2,,,,;
wf,16,6,2;state,4;

mce1(i)=(energy(1)-end)*hart
mce2(i)=(energy(2)-end)*hart

rs2;state,2;
maxiter,100,100;natorb,2140.2

e1(i)=(energy(1)-end)*hart
e2(i)=(energy(2)-end)*hart

Bond=Bond+0.01

enddo

table, r,e1,e2,mce1,mce2
save,o212pi.tab,new
---

Here is the data:

       R      E1(RS2)      E2(RS2)    MCE1(MCSCF)   MCE2(MCSCF)
     2.90   1.63401957   2.83213611   12.00261447   12.50210169
     2.91   1.64087542   2.76903566   11.98600780   12.43641790
     2.92   1.64895926   2.70488861   11.96927163   12.37239260
     2.93   1.65880672   2.63866262   11.95225652   12.31013611
     2.94   1.67129533   2.56883368   11.93474662   12.24982638
     2.95   1.68787303   2.49319947   11.91642077   12.19174800
     2.96   1.71088627   2.40881107   11.89679439   12.13635019
     2.97   1.74384790   2.31256886   11.87514648   12.08431982
     2.98   1.79084818   2.20362706   11.85047876   12.03662217
     2.99   1.85330668   2.08796618   11.82164992   11.99436672
     3.00   1.92419721   1.98012421   11.78784719   11.95833548
     3.01   1.98805366   1.89456975   11.74915616   11.92841320
     3.02   2.03197341   1.83534723   11.70656012   11.90358793
     3.03   2.05331181   1.79760299   11.66135068   11.88254040
     3.04   2.05625941   1.77451344   11.61463095   11.86414080
     3.05   2.04633761   1.76076596   11.56717976   11.84758453
     3.06   2.02799032   1.75291296   11.51950550   11.83233834
     3.07   2.00427225   1.74884249   11.47193226   11.81805407
     3.08   1.97718055   1.74726053   11.42466672   11.80450189
     3.09   1.94800268   1.74736211   11.37784166   11.79152657
     3.10   1.91757488   1.74863269   11.33154303   11.77902055
     3.11   1.88644771   1.75073379   11.28582651   11.76690722
     3.12   1.85498953   1.75343742   11.24072779   11.75513066
     3.13   1.82344992   1.75658224   11.19626918   11.74364905
     3.14   1.79200120   1.76005587   11.15246374   11.73243044
     3.15   1.76076208   1.76377539   11.10931814   11.72144984
     3.16   1.72981641   1.76767837   11.06683451   11.71068747
     3.17   1.69922177   1.77172098   11.02501174   11.70012731
     3.18   1.66901895   1.77586529   10.98384636   11.68975626
     3.19   1.63923589   1.78008301   10.94333324   11.67956339
     3.20   1.60989093   1.78435280   10.90346602   11.66953951
     3.21   1.58099596   1.78865557   10.86423743   11.65967676
     3.22   1.55255802   1.79297881   10.82563960   11.64996842
     3.23   1.52458025   1.79731194   10.78766421   11.64040862
     3.24   1.49706239   1.80163929   10.75030258   11.63099217
     3.25   1.47000307   1.80595626   10.71354592   11.62171453
     3.26   1.44339863   1.81025827   10.67738523   11.61257162
     3.27   1.41724484   1.81453719   10.64181153   11.60355979
     3.28   1.39153628   1.81878987   10.60681608   11.59467528
     3.29   1.36626628   1.82301550   10.57238931   11.58591589
     3.30   1.34142845   1.82721070   10.53852259   11.57727841
     3.31   1.31701658   1.83137974   10.50520730   11.56875982
     3.32   1.29302267   1.83551363   10.47243422   11.56035844
     3.33   1.26943888   1.83962004   10.44019494   11.55207152
     3.34   1.24625659   1.84370975   10.40848092   11.54389676
     3.35   1.22347307   1.84777834   10.37728376   11.53583187
     3.36   1.20107449   1.85187354   10.34659523   11.52787436
     3.37   1.17905759   1.85596882   10.31640713   11.52002167
     3.38   1.15741532   1.86009824   10.28671146   11.51227062
     3.39   1.13614086   1.86432964   10.25750036   11.50461704