[molpro-user] Molpro and GAMESS Results Differ: CASSCF(10,10) Calculation

[rossi at york.cuny.edu]

Hello:

Can someone please help me with the following problem?

I cannot get GAMESS  and Molpro to give the same results.  It must be
something that I am overlooking.

1) When the the central bridgehead bond in bicyclobutane is stretched, a
diradical is obtained.

2) The molecule has C2V symmetry, and the diradical is in a B_1 state.

3) The calculation is CASSCF(10,10).

Here are the results:

                   GAMESS                        Molpro
-----------------------------------------------------------------------
Triplet        -154.91044949                -154.91044949
Singlet        -154.90920703                -154.72707529

Why does the Molpro calculation for the singlet diradical not agree.  The
orbitals for the CASSCF are the same in both cases.  I checked this over
and over again.

The input for the triplet CASSCF and triplet SCF (source of starting
orbitals) is given below.

Thank you so much for helping me ith this.  What am I missing or
overlooking?

Regards,

Angelo

***,bicyclobutane - diradical
memory,128,m
FILE,2,bcb_1b1_nory2.wfu,old
print,basis,orbitals

basis=6-31G*

geomtyp=xyz
geometry
   10
Bicyclobutane - Diradical
 C1      -1.0619664679   0.0000000000  -0.1207636814
 C2       1.0619664679   0.0000000000  -0.1207636814
 C3       0.0000000000   1.1269480795  -0.0595853066
 C4       0.0000000000  -1.1269480795  -0.0595853066
 H1      -2.0727315725   0.0000000000   0.2423446764
 H2       2.0727315725   0.0000000000   0.2423446764
 H3       0.0000000000   1.6996903596   0.8655887684
 H4       0.0000000000  -1.6996903596   0.8655887684
 H5       0.0000000000   1.8197114977  -0.8963535723
 H6       0.0000000000  -1.8197114977  -0.8963535723
end

{casscf
orbital,2140.2
 closed,5,2,3,0
    occ,8,5,5,2
     wf,30,2,2
   state,1; weight,1,0;
   orbprint,20
 }

put,molden,bcb_3B1.molden;
---

Starting orbitals can be obtained from the following input.

***,bicyclobutane - scf triplet
memory,128,m
FILE,2,bcb_3b1_scf.wfu,new

print,basis,orbitals

basis=6-31G*

geomtyp=xyz
geometry
   10
Bicyclobutane - Ground State
 C1      -1.0619664679   0.0000000000  -0.1207636814
 C2       1.0619664679   0.0000000000  -0.1207636814
 C3       0.0000000000   1.1269480795  -0.0595853066
 C4       0.0000000000  -1.1269480795  -0.0595853066
 H1      -2.0727315725   0.0000000000   0.2423446764
 H2       2.0727315725   0.0000000000   0.2423446764
 H3       0.0000000000   1.6996903596   0.8655887684
 H4       0.0000000000  -1.6996903596   0.8655887684
 H5       0.0000000000   1.8197114977  -0.8963535723
 H6       0.0000000000  -1.8197114977  -0.8963535723
end

{hf
wf,30,2,2}

put,molden,bcb_3b1_scf.molden;