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Exact and Optimal Quantum Mechanics/Molecular Mechanics Boundaries

Sun, Qiming and Chan, Garnet Kin-Lic (2014) Exact and Optimal Quantum Mechanics/Molecular Mechanics Boundaries. Journal of Chemical Theory and Computation, 10 (9). pp. 3784-3790. ISSN 1549-9618. doi:10.1021/ct500512f.

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Motivated by recent work in density matrix embedding theory, we define exact link orbitals that capture all quantum mechanical (QM) effects across arbitrary quantum mechanics/molecular mechanics (QM/MM) boundaries. Exact link orbitals are rigorously defined from the full QM solution, and their number is equal to the number of orbitals in the primary QM region. Truncating the exact set yields a smaller set of link orbitals optimal with respect to reproducing the primary region density matrix. We use the optimal link orbitals to obtain insight into the limits of QM/MM boundary treatments. We further analyze the popular general hybrid orbital (GHO) QM/MM boundary across a test suite of molecules. We find that GHOs are often good proxies for the most important optimal link orbital, although there is little detailed correlation between the detailed GHO composition and optimal link orbital valence weights. The optimal theory shows that anions and cations cannot be described by a single link orbital. However, expanding to include the second most important optimal link orbital in the boundary recovers an accurate description. The second optimal link orbital takes the chemically intuitive form of a donor or acceptor orbital for charge redistribution, suggesting that optimal link orbitals can be used as interpretative tools for electron transfer. We further find that two optimal link orbitals are also sufficient for boundaries that cut across double bonds. Finally, we suggest how to construct “approximately” optimal link orbitals for practical QM/MM calculations.

Item Type:Article
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URLURL TypeDescription Info
Sun, Qiming0000-0003-0528-6186
Chan, Garnet Kin-Lic0000-0001-8009-6038
Additional Information:© 2014 American Chemical Society. ACS Editors' Choice. Received: June 12, 2014. Published: July 25, 2014. This work was primarily supported by the Department of Energy, Office of Science, through grant no. DE-SC0010530. Additional support was provided by the Department of Energy, Office of Science, through grant no. DE-SC0008624. The authors declare no competing financial interest.
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0010530
Department of Energy (DOE)DE-SC0008624
Issue or Number:9
Record Number:CaltechAUTHORS:20170106-131952689
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73306
Deposited By: Donna Wrublewski
Deposited On:06 Jan 2017 21:42
Last Modified:11 Nov 2021 05:14

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