Classical Computation Reaches Chemical Accuracy in Nitrogenase Simulation

Recent research has demonstrated that classical computational methods can now model the electronic ground-state energy of the FeMo-cofactor in nitrogenase with chemical accuracy, a task previously viewed as unattainable for classical computers.

The FeMo-cofactor, located at the active site of nitrogenase, is known for its complex structure involving many unpaired electrons and transition metals. This complexity has long made it a challenging target for classical simulation approaches.

In the new study, researchers applied a classical method to a 76-orbital/152-qubit model of FeMo-co. Their approach produced rigorous or empirical upper bounds for the ground-state energy, maintaining an error within approximately 1 kilocalorie per mole, which meets the threshold for chemical accuracy.

Earlier theoretical work had suggested that only quantum computers could address the simulation challenges posed by nitrogenase’s active site. These studies proposed that quantum devices would be needed to analyze reaction mechanisms that classical computers could not handle.

What the numbers show

• The classical simulation used a 76-orbital/152-qubit model
• Chemical accuracy was achieved within ~1 kcal/mol
• Previous estimates for quantum simulation required up to a million qubits

Prior research estimated that simulating the active site of nitrogenase would require between hundreds of thousands and a million qubits on a quantum computer. This placed the problem out of reach for both classical and near-term quantum hardware until now.

The FeMo-cofactor’s complexity has been a longstanding barrier in computational chemistry. Its combination of transition metals and multiple unpaired electrons contributed to the belief that only quantum computers could provide accurate results for its electronic structure.

The recent classical computation result challenges earlier assumptions about the limitations of classical methods in modeling highly complex molecular systems. The researchers’ approach demonstrated that chemical accuracy is achievable for FeMo-co without relying on quantum hardware.

Earlier proposals in the scientific literature had highlighted the potential of quantum computers to simulate nitrogenase’s reaction mechanisms. However, the new findings indicate that classical computing can now address some of these challenges within established accuracy thresholds.

* This article is based on publicly available information at the time of writing.