Sum-of-products form of the molecular electronic Hamiltonian and application within the MCTDH method

We introduce two different approaches to represent the second-quantized electronic Hamiltonian in a sum-of-products form. These procedures aim at mitigating the quartic scaling of the number of terms in the Hamiltonian with respect to the number of spin orbitals, and thus enable applications to larger molecular systems. Here we describe the application of these approaches within the multi-configuration time-dependent Hartree framework. This approach is applied to the calculation of eigen energies of LiH and electronic ionization spectrum of H2O.