Coupled Cluster Methods
The Configuration Interaction (CI) Approach
The CI method is the simplest electronic structure method to comprehend
from a conceptual viewpoint but one of the hardest to efficiently implement
on modern computer workstations. An understanding of the theoretical basis
of CI theory may be approached from two distinct but complementary viewpoints:
it can be viewed as the matrix mechanics solution of the Schrödinger
equation or as the variational minimization of a linear combination of
N-electron basis functions. In order to provide the clearest possible
picture of the CI method, both viewpoints, starting with the matrix mechanics
approach, are presented in this section.