[molpro-user] UCCSD-F12 with CASSCF orbitals

[Gerald Knizia]

binjiang.nju wrote:
> I am trying to do a uccsd(t) calculation with CASSCF orbitals in 
> Molpro.2010.1, it will be useful when two quasi-degenerate states 
> exist and sometimes improve the convergence, comparing to the 
> uccsd(t)/hf strategy. 
>  
> It works fine when I use only normal uccsd(t) option, but it fails 
> when I use uccsd(t)-f12 option. I have tried to change the basis set, 
> active space, as well as the type of CASSCF orbitals (Natural, 
> Canonical), all of these do not help. Then I find some information for 
> such problem, but still no suitalbe answer.
>  
> Gerald Knizia has mentioned that the F12 methods do request RHF 
> reference functions, but he would try to fix this. (I cite his words 
> in the following, hopefully he would not mind)

I have semi-fixed this in the current development version (i.e., it is 
there possible to use such orbitals now, but it requires some persuation 
with rhf,maxit=1). However, this turned out to be more complicated than 
anticipated, which is why I did not backport the changes to the 
production version. In the current production version both CCSD-F12 
programs will give (different) wrong energies when used with non-HF 
orbitals. I would prefer to leave this issue open until the next Molpro 
production version (i.e., the one from the current development version, 
where this will work automatically), unless there is very strong 
interest in having this feature available.
-- 
Gerald Knizia