Post-Hartree-Fock methods are advanced computational techniques used in quantum chemistry to improve the accuracy of electronic structure calculations beyond the Hartree-Fock approximation. While Hartree-Fock provides a good starting point by considering single-electron wave functions, it often fails to account for electron correlation, which is crucial for accurate predictions of molecular properties. These methods, such as Møller-Plesset perturbation theory and Coupled Cluster theory, incorporate electron correlation effects by using more complex wave functions. They help chemists better understand molecular interactions, reaction mechanisms, and properties of materials, making them essential tools in theoretical and computational chemistry.