  The method of Monte Carlo configuration interaction (MCCI) [1,2] is applied
to the calculation of multipole moments. We look at the ground and excited
state dipole moments in carbon monoxide. We then consider the dipole of NO, the
quadrupole of the nitrogen molecule and of BH. An octupole of methane is also
calculated. We consider experimental geometries and also stretched bonds. We
show that these non-variational quantities may be found to relatively good
accuracy when compared with FCI results, yet using only a small fraction of the
full configuration interaction space. MCCI results in the aug-cc-pVDZ basis are
seen to generally have reasonably good agreement with experiment. We also
investigate the performance of MCCI when applied to ionisation energies and
electron affinities of atoms in an aug-cc-pVQZ basis. We compare the MCCI
results with full configuration-interaction quantum Monte Carlo [3,4] and
`exact' non-relativistic results [3,4]. We show that MCCI could be a useful
alternative for the calculation of atomic ionisation energies however electron
affinities appear much more challenging for MCCI. Due to the small magnitude of
the electron affinities their percentage errors can be high, but with regards
to absolute errors MCCI performs similarly for ionisation energies and electron
affinities.

Chemical Physics;Computational Physics