Assertion Supported AI assessment confidence: 95% certainty 4/5 debate potential 2/5

Classical computers cannot simulate molecular systems more complex than two atoms

Mark Cupta · Quantum computing could be a critical climate solution · Dec 16, 2021 · at 27:16

Mark Cupta, a venture capitalist and former materials scientist, discusses the computational limits of classical computing for materials science and molecular modeling.

0:00 / 0:38exact quote · 38.0s

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“We do not have the capability currently with our classical computers to simulate anything more complicated Than a two-body problem or a two-atom molecule, and we're really good at simulating hydrogen, so we can take that, put it into a computer, and understand all the energy states and figure out how that hydrogen atom would interact with physical properties. You start getting bigger than that, maybe a lithium-hydrogen combination, we can do that fairly well, but as you get to more and more complicated molecules and all the different electrons that flow around those, we have no idea how to truly simulate that Perfectly”

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The claim, plainly

Classical computers lack the capability to perfectly simulate molecular systems more complicated than simple two-body or two-atom molecules due to electron interactions.

a quote alone can be ambiguous, so this restates it with the references and context of the conversation around it resolved. AI-written; the tape below the player is the source.

Assessment

The claim asserts that classical computers lack the capability to perfectly (exactly from first principles) simulate molecular systems more complicated than two-body or two-atom molecules due to electron-electron interactions. In quantum chemistry and computational physics literature, obtaining exact solutions to the electronic Schrödinger equation without approximations requires Full Configuration Interaction (FCI). Because the Hilbert space of electronic configurations scales factorially/exponentially with the number of electrons and basis orbitals, exact classical FCI simulations on modern supercomputers are practically constrained to systems of 16 to 22 electrons in active spaces—limiting exact classical simulation strictly to diatomic, triatomic, or minimal-hydride molecules (e.g., H2, LiH, N2). Any larger molecular systems necessitate polynomial-scaling approximations such as Density Functional Theory or Coupled Cluster methods.

Literature across quantum chemistry (e.g., Aspuru-Guzik et al., Science 2005) confirms that exact Full Configuration Interaction (FCI) calculations on classical computers scale exponentially, limiting exact simulations to diatomic and triatomic molecules.
State-of-the-art supercomputer FCI benchmarks (such as ABCI in 2024 and Fugaku in 2025) handle up to 1-3 trillion determinants, which only accommodates small systems like LiH, NaBH4, or N2 in limited basis sets.
All classical simulations of larger molecular systems rely on approximations (DFT, HF, CCSD(T)) rather than exact ab initio solutions due to the exponential scaling of electron correlation.

Checked against

[1] acs.org [2] uchicago.edu [3] acs.org [4] harvard.edu [5] arxiv.org [6] utah.edu [7] researchgate.net [8] arxiv.org

FCI "triatomic" "diatomic" "classical computers" quantum chemistry classical simulation exact molecular systems Full CI limit number of atoms electrons Full Configuration Interaction largest molecule classical supercomputer exact quantum chemistry simulation classical limit FCI water benzene exact ab initio classical simulation molecules limit two atoms "Full configuration interaction" "exponential" limit number of atoms classical "limiting such full configuration interaction" "diatomic"

assessed as of 2026-09-03

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Mentioned

classical computers material science

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