#! /bin/sh
# The computation of multiplet states corresponding to an open-shell system can
# be carried out with ADF by first computing the 'Average-of-Configuration'
# (aoc) state, where all orbitals in the open shell are degenerate and equally
# occupied. This computation is spin-restricted and serves as a fragment file
# for the multiplet run, where then different occupation numbers are assigned to
# the various orbitals in the open shell. The corresponding energies are
# computed in the field of the aoc, which is achieved by not iterating the self-
# consistency equations to convergence but only computing the orbitals in the
# initial field.
# Since ADF requires that all symmetry-partners in an irreducible representation
# (irrep) have equal occupations, the multiplet calculation, where such orbitals
# are not equally occupied, must be carried out in a formally lower point group
# symmetry. The point group to select and the appropriate occupation numbers to
# apply must be worked out by the user 'on paper' in advance.
# See the discussion of Multiplet energies in ADF manual.
# The script starts with the 'creation' of the required basic atoms, N, H, Cr
# using a fair basis set quality.
# The next step is the computation of the ammonia fragment NH3. This is not a
# crucial step here: the multiplet state computation can equally well be carried
# out by not using any intermediate compound fragments. However, it illustrates
# once more how a bigger molecule can be built up from smaller, but not trivial
# fragments.
$AMSBIN/dirac -n1 < $AMSRESOURCES/Dirac/Cr.2p
mv TAPE12 t12.rel
AMS_JOBNAME=Cr $AMSBIN/ams <