HartreenFockmenetelmä

Hartreen-Fockmenetelmä, often abbreviated as HF or Hartree-Fock, is a fundamental computational quantum chemistry method used to approximate the wavefunction and energy of a many-electron system. It is a mean-field theory, meaning it treats the complex interactions between all electrons in an approximate way by considering the average interaction of each electron with all other electrons. The method starts by assuming an initial guess for the electronic wavefunction, usually constructed from atomic orbitals. This guess is then iteratively improved by solving the Hartree-Fock equations. These equations are a set of coupled, non-linear, one-electron equations. The process involves calculating the energy and wavefunction for each electron, considering the average field generated by all other electrons. This average field includes both the Coulombic repulsion and the exchange interaction, which arises from the antisymmetry requirement of the electronic wavefunction (Pauli exclusion principle). The iterative procedure continues until the energy and wavefunction no longer change significantly, reaching a self-consistent field (SCF) solution. While Hartree-Fock accounts for electron exchange, it neglects electron correlation, which is the instantaneous interaction between electrons. Therefore, the energy obtained from Hartree-Fock is an upper bound to the true ground-state energy. Despite its limitations, Hartree-Fock serves as a crucial starting point for more sophisticated methods that aim to include electron correlation.