RECLAS — Reorder MOs.

RECLAS()`n,m`

When CI is explicitly or implicitly invoked, the CI-active MOs are explicitly or
implicitly defined as a contiguous range of MOs. If the desired CI-active MOs do not lie in a
contiguous range, then it is necessary to specify how to reorder the MO list so that the
desired MOs do lie in a contiguous range. This is done using the
RECLAS(* n,m*) keyword. The MOs n through m are reordered after the
SCF but before the selection of the CI-active MOs. The permuted order is typically defined so
that the desired active space MOs are consecutive after permutation and is specified in the
AMPAC input file as extra input following the geometry
specification with the header

$$ reclas - ci permutation of mos

or simply

$$ reclas

RECLAS(* n,m*) is often used together with
C.I.(

`n,m`

`n.m`

`n,m`

`n,m`

$$ reclas - ci permutation of mos 5,7,4,6,8,9,11,13,10,12 ... $$ end of extra data

For multi-geometry input files, e.g., for CHAIN jobs, all of the geometries will use the same MO permutation order, so it
should only be specified for the first one. MOs with different occupancies cannot be permuted,
i.e., doubly occupied MOs cannot be permuted with partially occupied or virtual MOs and
partially occupied MOs cannot be permuted with doubly occupied MOs or virtual MOs. See
Chapter 11, *Configuration Interaction* for a more complete discussion of
AMPAC’s CI capability.

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