  Circuit depth reduction is of critical importance for quantum chemistry
simulations on current and near term quantum computers. This issue is tackled
by introducing a chemically aware strategy for the Unitary Coupled Cluster
ansatz. The objective is to use the chemical description of a system to aid in
the synthesis of a quantum circuit. We combine this approach with two flavours
of Symmetry Verification for the reduction of experimental noise. These method
enable the use of System Model H1 for a 6-qubit QSE (Quantum Subspace
Expansion). We present (i) calculations to obtain CH4 optical spectra; (ii) an
atmospheric gas reaction simulation involving
$[$CH$^{\cdot}_3$--H--OH$^{\cdot}]^{\ddagger}$. Using our chemically aware UCC
state-preparation strategy in tandem with state of the art symmetry
verification methods, we improve device yield for CH4 at 6-qubits. This is
demonstrated by a 90% improvement in two-qubit gate count and reduction in
relative error to 0.2% for electronic energy calculated on System Model H1.

Quantum Physics;Materials Science