[molpro-user] Regarding valence orbital

Gerald Knizia knizia at theochem.uni-stuttgart.de
Thu Jun 26 15:59:37 BST 2014

On Thu, 2014-06-26 at 14:38 +0530, Rameswar Bhattacharjee wrote:

> So it shows that water contain 6 valence orbital and I am not getting
> how it is possible.

It only counts atomic valence orbitals, not atomic core orbitals,
towards the valence orbitals. Each H has one valence orbital (1s), each
O has one core (1s) and four valence orbitals (2s,2px,2py,2pz). This
makes a total of six valence orbitals.

This number is, strictly speaking, not a physical quantity, and is not
used in calculations except for the definition of the full valence CAS
(e.g., if you just call "{mcscf}" without saying anthing, it will here
perform a CAS(10e,6o) calculation).

What you are referring to is the number of closed-shell orbitals. These
are the number of doubly occupied orbitals, and this is a different
concept than valence AOs. In some parts of the program the closed-shell
space is also further split into core and non-core closed-shell
Gerald Knizia

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