Bridging Quantum Mechanics and Biology at the Million-Atom Scale

The behaviour of proteins and other biomolecules is mainly governed by the quantum-mechanical character of their electrons. Accurately capturing the resulting interactions is essential for predicting molecular properties, obtaining spectroscopic data, and advancing drug design. However, the extreme computational cost of quantum calculations has historically limited their application to small systems of just a few hundred atoms. Here, we present a quantum-mechanical method that enables electronic structure calculations on biological systems at unprecedented scales, up to millions of atoms, while drastically reducing computational costs. We apply this approach to entire proteins and large biomolecular assemblies, including a complete bacteriophage¹ in a solution containing over 150 million electrons. Additionally, we show that atomic energies computed for AlphaFold-predicted protein structures strongly correlate with AlphaFold's confidence scores², providing a new quantum-based validation metric. The method's efficiency also allows the accurate prediction of spectroscopic properties for biomolecules previously out of reach for first-principles techniques. We present computed spectra for DNA^3,4 and the anticancer drug Actinomycin^5,6, involving hundreds to thousands of atoms, in close agreement with experimental measurements. This advance bridges quantum mechanics and biology at a previously inaccessible scale, enabling large-scale, first-principles simulations with broad applications in quantum biology, structural biology, medicine, and materials science.