Streamlining Diradical Calculations:
A Random Phase Approximation Approach

A Simplified Analytical Model for Predicting Diradical Properties

Understanding molecules with two unpaired electrons—diradicals—is central to advancing materials science, quantum chemistry, and quantum technologies. In this study, HQS Quantum Simulations introduces a computationally efficient method that leverages the random phase approximation (RPA) to refine the classic two-electron, two-orbital model for diradicals.

This analytical approach accurately incorporates electron correlation effects, and in benchmarking tests against advanced multi-reference methods (CASSCF and NEVPT2), it reliably predicts singlet–triplet energy splittings across diverse molecules. The RPA-corrected model achieves an average relative difference of around 40% compared to high-accuracy quantum chemistry methods, and for molecules with the smallest singlet–triplet gaps, the deviation drops below 20%.

Our framework significantly accelerates diradical modeling, enabling faster iteration and screening in quantum simulations and materials discovery.

For technical insights and detailed benchmarks, read the full publication:

“Efficient Random Phase Approximation for Diradicals”
Authors: Reza G. Shirazi, Vladimir V. Rybkin, Michael Marthaler, Dmitry S. Golubev