Quantum simulation of molecules in solution*

Quantum chemical calculations on quantum computers have mostly focused on molecules in gas-phase. In this work we extend the Variational Quantum Eigensolver to the simulation of molecules in solution.

We represent the microscopic environment embedding the solute molecule as a polarizable continuum dielectric. Polarizable Continuum Models (PCMs) represent a good compromise between computational affordability and accuracy in describing solvation effects. Particularly, in the modified algorithm, the solute wavefuntion generated by the Quantum Computer is iteratively shaped by a classical optimization routine which minimizes the free energy in solution of the molecule instead of the molecular Hamiltonian expectation value.

We show that this additional feature does not impact the algorithmic efficiency, preserving its potential quantum advantage. Numerical results of noiseless simulations for molecular systems up to twelve qubits are presented. Furthermore, calculations performed on a simulated quantum hardware (IBM Q Mumbai), yield computed solvation free energies in fair agreement with the classical calculations without the inclusion of any error mitigation protocol.