The hamiltonian is constructed and diagonalized explicitly in the primary configuration
space, which can be selected with the `PSPACE` card. The coefficients of the remaining
configurations (Q-space) are optimized iteratively using the P-space wavefunction as zeroth
order approximation.

If *thresh* is nonzero, it is a threshold for automatically selecting all configurations
as P-space configurations which have energies less then , where *emin* is
the lowest energy of all configurations. Further P-space configurations can be specified
using `CON` cards, which must follow immediately after the `PSPACE` card. These are
merged with the ones selected according to the threshold. Automatic selection can be
avoided by specifying a very small threshold. There is a sensible default value for thresh
(0.4), so you usually don't need a `pspace` card in your input. Furthermore, if the number of
configurations in the MCSCF is less than 20, all configurations go into the P-space unless
you give a PSPACE card in the input.

A P-space threshold defined on a `PSPACE` card before the first `WF`
(or `STATE`, `WEIGHT`, `SELECT`, `PUNCSF` if `WF` is not
given)
card is global, i.e., valid for all state symmetries. State-specific
thresholds
can
be defined by placing a `PSPACE` card after the corresponding `WF`
card. In the latter case the `PSPACE` card can be followed by `CON`
cards,
which define state-specific P-space configurations.

molpro@molpro.net 2018-11-18