ABSTRACT
This chapter reviews the conventional determinantal treatment. It starts with the spin-free Hamiltonian used in a large number of atomic and molecular calculations. The chapter introduces the antisymmetry principle and shows the construction of antisymmetric wavefunctions using the product of spatial and spinfunctions. A frequently used approximation is the representation of the wavefunction by a single determinant in which every orbital occurs twice. The optimization of the orbitals leads to the Hartree-Fock (self-consistent-field) method. The self-consistent-field method provides an excellent first approximation. It can predict bond lengths and charge densities with great accuracy. The total energy is predicted usually with an accuracy of 99.5%. For most chemical purposes one does not need the total energy but rather energy differences as excitation energies, transition state energies and so on. The matrix elements of the Hamiltonian between determinantal functions are presented both for the case of orthogonal and non-orthogonal orbitals. The chapter reviews the basic principles of the configuration interaction method.
