  We present a novel method for improving the quantum simulation of the ground
state energy of molecules. We perform a pre-processing step classically, which
reduces the dimensionality of the problem by generating a custom mapping which
excludes states which violate problem constraints. Subsequently, a specialized
measurement scheme is used to extract the expectation value of the problem
Hamiltonian through this mapping. We demonstrate that this method reduces the
amount of quantum resources needed to run a Variational Quantum Eigensolver
(VQE) algorithm without making any approximations to the physics of the quantum
chemistry problem.
