AB Initio Configuration Interaction Calculations on the States of HF(-)

The principles that form the basis of all quantum mechanics were first introduced in 1926 by Schroedinger. Since that time these principles have been extended to become the framework of the theory used today. Although the simplicity of the theory cannot be questioned, practical implementation of the basic concepts has often proven difficult. For certain applications, including the hydrogen atom as well as other one electron systems, the Schroedinger Theory allows exact analytic solution. For larger systems, approximations are necessary. The first approximation that is generally incorporated into the Schroedinger Theory is known as the Born Oppenheimer Approximation. The use of this approximation allows the separation of electronic and nuclear motions. Further simplification can be achieved through a method for dealing with the electron-electron interaction potential. This approach was first suggested by Hartree, and was subsequently extended by Fock to include exchange effects. In molecular orbital theory, an electron orbital is replaced by a one-electron wave function delocalized over the whole molecule. This concept, together with the Pauli principle and the work of Hartree and Fock allow the wavefunction to be expressed in a single Slater determinant.