Quantum HF/DFT-Embedding Algorithms for Electronic Structure Calculations: Scaling up to Complex Molecular Systems

TL;DR

This paper introduces a quantum embedding method combining classical HF/DFT calculations with quantum algorithms to efficiently simulate complex molecules, demonstrating improved accuracy over traditional methods.

Contribution

It presents a novel quantum embedding approach that integrates classical HF/DFT calculations with quantum VQE algorithms for scalable molecular simulations.

Findings

Achieved energy corrections for pyridine surpassing CASSCF results.

Demonstrated the method's potential to scale quantum simulations to larger molecules.

Validated the approach with successful energy calculations on complex molecular systems.

Abstract

In the near future, material and drug design may be aided by quantum computer assisted simulations. These have the potential to target chemical systems intractable by the most powerful classical computers. However, the resources offered by contemporary quantum computers are still limited, restricting the chemical simulations to very simple molecules. In order to rapidly scale up to more interesting molecular systems, we propose the embedding of the quantum electronic structure calculation into a classically computed environment obtained at the Hartree-Fock (HF) or Density Functional Theory (DFT) level of theory. We achieve this by constructing an effective Hamiltonian that incorporates a mean field potential describing the action of the inactive electrons on a selected Active Space (AS). The ground state of the AS Hamiltonian is determined by means of the Variational Quantum Eigensolver (VQE) algorithm. With the proposed iterative DFT embedding scheme we are able to obtain energy correction terms for a single pyridine molecule that outperform the Complete Active Space Self Consistent Field (CASSCF) results regardless of the chosen AS.