Interactions between large molecules pose a puzzle for reference quantum mechanical methods

Al-Hamdani, Yasmine S. and Nagy, Péter and Zen, Andrea and Barton, Dennis and Kállay, Mihály (2021) Interactions between large molecules pose a puzzle for reference quantum mechanical methods. NATURE COMMUNICATIONS, 12 (1). ISSN 2041-1723

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Abstract

Quantum-mechanical methods are used for understanding molecular interactions throughout the natural sciences. Quantum diffusion Monte Carlo (DMC) and coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] are state-of-the-art trusted wavefunction methods that have been shown to yield accurate interaction energies for small organic molecules. These methods provide valuable reference information for widely-used semi-empirical and machine learning potentials, especially where experimental information is scarce. However, agreement for systems beyond small molecules is a crucial remaining milestone for cementing the benchmark accuracy of these methods. We show that CCSD(T) and DMC interaction energies are not consistent for a set of polarizable supramolecules. Whilst there is agreement for some of the complexes, in a few key systems disagreements of up to 8 kcal mol−1 remain. These findings thus indicate that more caution is required when aiming at reproducible non-covalent interactions between extended molecules.

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