RECLAS(n,m) 

Description

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), SC.I.(n.m), SDC.I.(n,m), or SDTC.I.(n,m). For example, to use the MOs 4,6,8,9,11,13 as the CI active space, specify the keywords C.I.(6,11) and RECLAS(4,13), with the permutation list given in the corresponding extra input section, following the first geometry, as follows (assume the HOMO is 8):

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

See also:

C.I., OPEN.