In conventional electronic structure methods (such as DFT or even DFTB), one can solve the time-independent Schrödinger equation (TISE), ĤΦ = Φ, for a given set of nuclear coordinates (R). Specifically, the electronic Hamiltonian is diagonalized to obtain a set of eigenvectors and eigenvalues that depend on the nuclear coordinates and, therefore, are known as the adiabatic eigenvectors and eigenvalues. When the TISE is solved for several sets of nuclear coordinates, we obtain the adiabatic potential energy surfaces (PESs).