Multiconfiguration Pair-Density Functional Theory Calculations of Low-lying States of Complex Chemical Systems with Quantum Computers
This hybrid quantum-classical method addresses the challenge of strong correlation in complex chemical systems for near-term quantum computers.
The authors combine Variational Quantum Eigensolver with Multiconfiguration Pair-Density Functional Theory to separate static and dynamic correlation, achieving chemical accuracy on benchmarks (C2 bond length error 0.006 Å, benzene excitation energy error 0.048 eV) and a bound potential for Cr2 with 48e,42o active space under hardware noise.
Accurately describing strong electron correlation in complex systems remains a prominent challenge in computational chemistry as near-term quantum algorithms treating total correlation often require prohibitively deep circuits. Here we present a hybrid strategy combining the Variational Quantum Eigensolver with Multiconfiguration Pair-Density Functional Theory to efficiently decouple correlation effects. This approach confines static correlation to a compact multireference quantum state while recovering dynamic correlation through a classical on-top density functional using reduced-density information. By enabling self-consistent orbital optimization, the method significantly reduces quantum resource overheads without sacrificing physical rigor. We demonstrate chemical accuracy on standard benchmarks by reproducing C$_2$ equilibrium bond lengths and benzene excitation energies with mean absolute errors of 0.006 Å and 0.048 eV respectively. Most notably, for the strongly correlated Cr$_2$ dimer requiring a large complete active space (48e, 42o), the framework yields a bound potential-energy curve and recovers qualitative dissociation behavior despite realistic hardware noise. These results establish that separating correlation types provides a practical route to reliable predictions on near-term quantum hardware.