  A self-consistent calculation with variation after parity projection is
proposed to study both ground and excited states of light nuclei. This
procedure provides description of the ground state incorporating some
correlation effects, and self-consistent solutions for the excited states of
negative parity. For flexible description of nuclear shapes, single particle
orbitals are represented on a uniform grid in the three-dimensional Cartesian
coordinates. The angular momentum projection is performed after variation to
calculate rotational spectra. To demonstrate the usefulness of the method,
results are shown for two N=Z nuclei, 20Ne and 12C, for which clustering
correlations are known to be important. In the 20Ne nucleus, both cluster-like
and shell-model-like states are described simultaneously in the present
framework. For 12C nucleus, the appearance of three-alpha clustering
correlation in the ground state is investigated in relation to the strength of
the two-body spin-orbit interaction.
