[molpro-user] About non-HF orbitals used in CCSD(T) calculation
knizia at theochem.uni-stuttgart.de
Mon Jan 18 06:59:33 GMT 2010
On Monday 18 January 2010 00:26, Chen Hui wrote:
> So does anybody know something about the second question?
> My question is that if CCSD(T)-F12 method can be used with the DFT
> orbital rather than the HF orbital.
> From manual, it seems that this is not right. But I am trying this and
> there is no running error yet.
There are some potential problems. Namely, under certain conditions the F12
programs use the Fock matrices stored by the SCF calculation as input; and if
this Fock matrix is not actually a Fock matrix but a Kohn-Sham matrix, then
things /will/ break. The closed-shell program may also assume that the Fock
matrix is diagonal, but it might also check and fall back to an iterative
algorithm if it is not.
In principle running these calculations on top of any kind of orbitals is
possible, but there several different places where either the single programs
or the synchronization between the open- and closed-shell programs might go
I will look up what exactly is happening in both programs (closed- and
open-shell) under various conditions, and then I'll tell you.
That being said, I'd also like to point out that it is very probable that the
F12 singles correction will just make something closely resembling a
Hartree-Fock reference function out of whatever you use as input for the
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