Diagonalizing Hamiltonians is the main task of all quantum mechanics. If one can achieve the exact diagonalization of the Hamiltonian for all DOFs, the exact answer is returned, given a complete basis set. In reality, one is unable to achieve this due to the basis set limitations and/or the complexity of the many-body problem itself. As such, one seeks to find the best alternative toward providing approximate solutions to the many-body problem that returns the correct physics. For the electronic Hamiltonian, the community at large has spent nearly 90 years working on this problem providing methods such as Hartree-Fock theory (HF), density functional theory (DFT), configuration interaction (CI), coupled cluster (CC), among others including their excited state analogues like time-dependent DFT (TD-DFT). Each of these methods returns, to varying degrees of computational expense and accuracy, the solutions to the electronic Hamiltonian.