Quantum chemistry and large systems – a personal perspective

Abstract This perspective offers a personal reflection on the evolution, current status, and open challenges of quantum chemistry in the context of large molecular systems. Beginning with Dirac’s famous 1929 prophecy, I revisit the historical trajectory of our discipline, from the development of early conceptual models to the emergence of density functional theory and correlated wavefunction methods. While enormous progress has been made in algorithmic sophistication, enabling accurate calculations on systems with thousands of atoms, I argue that accurate energies alone do not solve the entirety of chemical problems. Real-world applications demand more than electronic structure: solvation, entropy, conformational complexity, and the sheer complexity of large molecules challenge our methods and our assumptions. Equally important are the conceptual and philosophical tensions that continue to shape the field, especially the difficult balance between prediction and understanding. I advocate for a more integrative approach that values models, insight, and falsifiability alongside numerical precision. Finally, I briefly consider the emerging role of machine learning and the implications of automation for the future of theory. This article is not a review but a dialogue – with the field, with its history, and with its practitioners.