Excited-State DMRG Made Simple with FEAST

We introduce DMRG­[FEAST], a new method
for optimizing excited-state
many-body wave functions with the density matrix renormalization group
(DMRG) algorithm. Our approach applies the FEAST algorithm, originally
designed for large-scale diagonalization problems, to matrix product
state wave functions. We show that DMRG­[FEAST] enables the stable
optimization of both low- and high-energy eigenstates, therefore overcoming
the limitations of state-of-the-art excited-state DMRG algorithms.
We demonstrate the reliability of DMRG­[FEAST] by calculating anharmonic
vibrational excitation energies of molecules with up to 30 fully coupled
degrees of freedom.