  In this manuscript, we calculate the ground state energy of benzene under
spatial deformations by using the variational quantum eigensolver (VQE). The
primary goal of the study is estimating the feasibility of using quantum
computing ansatze on near-term devices for solving problems with large number
of orbitals in regions where classical methods are known to fail. Furthermore,
by combining our advanced simulation platform with real quantum computers, we
provided an analysis of how the noise, inherent to quantum computers, affects
the results. The centers of our study are the hardware efficient and quantum
unitary coupled cluster ansatze (qUCC). First, we find that the hardware
efficient ansatz has the potential to outperform mean-field methods for extreme
deformations of benzene. However, key problems remain at equilibrium,
preventing real chemical application. Moreover, the hardware efficient ansatz
yields results that strongly depend on the initial guess of parameters - both
in the noisy and noiseless cases - and optimization issues have a higher impact
on their convergence than noise. This is confirmed by comparison with real
quantum computing experiments. On the other hand, the qUCC ansatz alternative
exhibits deeper circuits. Therefore, noise effects increase and are so extreme
that the method never outperform mean-field theories. Our dual simulator/8-16
qubits QPU computations of qUCC appears to be a lot more sensitive to hardware
noise than shot noise, which give further indications about where the
noise-reduction efforts should be directed towards. Finally, the study shows
that qUCC method better captures the physics of the system as the qUCC method
can be utilized together with the Huckel approximation. We discussed how going
beyond this approximation sharply increases the optimization complexity of such
a difficult problem.
