Quantum Simulation of Molecules in Solution

Quantum chemical calculations on quantum computers have
been focused
mostly on simulating molecules in the gas phase. Molecules in liquid
solution are, however, most relevant for chemistry. Continuum solvation
models represent a good compromise between computational affordability
and accuracy in describing solvation effects within a quantum chemical
description of solute molecules. In this work, we extend the variational
quantum eigensolver to simulate solvated systems using the polarizable
continuum model. To account for the state dependent solute–solvent
interaction we generalize the variational quantum eigensolver algorithm
to treat non-linear molecular Hamiltonians. We show that including
solvation effects does not impact the algorithmic efficiency. Numerical
results of noiseless simulations for molecular systems with up to
12 spin-orbitals (qubits) are presented. Furthermore, calculations
performed on a simulated noisy quantum hardware (IBM Q, Mumbai) yield
computed solvation free energies in fair agreement with the classical
calculations.