A 152-qubit model tested by classical quantum chemistry

Classical quantum chemistry methods have now achieved an accuracy of 1 kcal/mol in modeling the FeMo cofactor, a complex structure containing eight transition metal ions and long considered a challenge beyond the reach of conventional simulation. Researchers have devised protocols combining high-order coupled cluster and density matrix renormalization group calculations to estimate the ground-state energy of a 76-orbital model. This work addresses a benchmark previously reserved for quantum computing, demonstrating a path toward precise computational understanding of the FeMo cofactor’s electronic structure and its role in nitrogenase, an enzyme central to life. High-order coupled cluster calculations, extended to quadruples with limited pentuples, now provide rigorous upper bounds on the ground-state energy of the FeMo-cofactor’s LLDUC model. These calculations, paired with density matrix renormalization group (DMRG) reaching a bond dimension of 18,000 for two candidate spin isomers, represent an advancement in classical computational…