  Methods for correcting residual energy errors of configuration interaction
(CI) calculations of molecules and other electronic systems are discussed based
on the assumption that the energy defect can be mapped onto atomic regions. The
methods do not consider the detailed nature of excitations, but instead define
a defect energy per electron that that is unique to a specific atom. Defect
energy contributions are determined from calculations on diatomic and hydride
molecules and then applied to other systems. Calculated energies are compared
with experimental thermodynamic and spectroscopic data for a set of forty-one
mainly organic molecules representing a wide range of bonding environments. The
most stringent test is based on a severely truncated virtual space in which
higher spherical harmonic basis functions are removed. The errors of the
initial CI calculations are large, but in each case, including defect
corrections brings calculated CI energies into agreement with experimental
values. The method is also applied to a NIST compilation of coupled-cluster
calculations that employ a larger basis set and no truncation of the virtual
space. The corrections show excellent consistency with total energies in very
good agreement with experimental values. An extension of the method is applied
to dmsn states of Sc, Ti, V, Mn, Cr, Fe, Co, Ni and Cu, significantly improving
the agreement of calculated transition energies with spectroscopic values.
