  The computation of molecular excitation energies is essential for predicting
photo-induced reactions of chemical and technological interest. While the
classical computing resources needed for this task scale poorly, quantum
algorithms emerge as promising alternatives. In particular, the extension of
the variational quantum eigensolver algorithm to the computation of the
excitation energies is an attractive option. However, there is currently a lack
of such algorithms for correlated molecular systems that is amenable to
near-term, noisy hardware. In this work, we propose an extension of the
well-established classical equation of motion approach to a quantum algorithm
for the calculation of molecular excitation energies on noisy quantum
computers. In particular, we demonstrate the efficiency of this approach in the
calculation of the excitation energies of the LiH molecule on an IBM Quantum
computer.
