[molpro-user] Open shell CC woes

[Mikael Johansson]

Hello All!

I'm trying to compute the energy difference between the doublet and sextet
states of D3h symmetric FeF3 at CCSD(T) level (in C2v). I'm having great
difficulty in converging the sextet state ROHF, which surprised me, as it
should be the ground state. The doublet I got to converge.

Now, I haven't done any open-shell calcs with Molpro before, so perhaps
I'm just doing something wrong. I would appreciate it if someone would
care to comment if even my input structure is correct. Also any general
comment on the usefulness of computing spin state splittings with RCCSD(T)
are most welcome.

For the sextet I've used the following input:

{rhf,maxit=500;
occ,14,8,5,2;
closed,12,7,4,1;
wf,53,1,5}
rccsd(t),maxit=500

And for the doublet, the following:

{rhf,maxit=500;
occ,13,7,5,2;
closed,12,7,5,2;
wf,53,1,1}
rccsd(t),maxit=500

The complete input is at the end of the mail. But as mentioned, the sextet
ROHF just refuses to converge with a basis bigger than Ahlrichs-VDZ (or
converges to a local minimum). Is it possible somehow within Molpro to
expand a converged lower basis set solution onto a larger basis set? I
tried to google for that, unsuccessfully.

I'm using 2006.1 patch level 151 in case it matters. Any help with this
would be most appreciated!

Have a nice day,
     Mikael J.
     http://www.iki.fi/~mpjohans/


***,FeF3-sextet
memory,80,m
GPRINT,orbital
GTHRESH,twoint=1.d-13
set,charge=0
geomtyp=xyz
file,1,FeF3-6-pVTZ-s.int
file,2,FeF3-6-pVTZ-s.wfu
punch,FeF3-6-pVTZ-s.punch
geometry={
    4
        FeF3 experimental D3h
Fe         0.00000        0.00000        0.00000
F          0.88150        1.52680        0.00000
F          0.88150       -1.52680        0.00000
F         -1.76300        0.00000        0.00000
}
basis={
spdfg,Fe,cc-pVTZ;C
spdf,F,cc-pVTZ;C
}
{rhf,maxit=500;
occ,14,8,5,2;
closed,12,7,4,1;
wf,53,1,5}
rccsd(t),maxit=500