Algorithm for multireference unitary coupled-cluster quantum computations of molecule systems

We present an efficient algorithm for the MultiReference Unitary Coupled-Cluster (MR-UCC) approach that integrates quantum computing techniques with particle number conserved (PNC) gates. This algorithm makes it possible to use sophisticated MR wave functions with minimal use of computer resources to calculate the ground-state energies of LiH, ${\mathrm{BeH}}_{2}$, and ${\mathrm{H}}_{6}$. The higher-order correlations in the subsequent UCC calculations can be included requiring only Single and Double excitations of the wave operator. This algorithm achieves a higher accuracy compared with other available sophisticated quantum computational models, using a single quantum circuit across the entire bond length including the dissociation length region.