The most complicated term in eq. 2.7 is the electron-electron interaction (𝑉 ̂ee ). In principle, the electrons move in a correlated fashion, that means their movement depends on all other electrons at every point in time. However, it is often enough to capture this correlated movement in an approximate manner. In the so-called mean-field approximation, the Schrödinger equation is solved for one electron by considering the other electrons as a background field (instead of computing the interaction with every single one of the other electrons explicitly). The result of this approximation are the HF equations (eq. 2.9) where one Schrödinger equation for each electron exists (the one-electron Hamiltonian is now called the Fock operator 𝐹 ̂ and the one-electron wavefunction is the molecular orbital) which implicitly depends on all other One-Electron-Schrödinger equations through the HF potential (the above-mentioned mean-field). These interdependent equations have then to be solved in an iterative mannerthe self-consistent field (SCF) approach.