Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Analytic energy, gradient, and hessian of electrostatic embedding QM/MM
  based on electrostatic potential fitted atomic charges scaling linearly with
  the MM subsystem size   Electrostatic potential fitting method (ESPF) is a powerful way of defining
atomic charges derived from quantum density matrices fitted to reproduce a
quantum mechanical charge distribution in the presence of an external
electrostatic potential. These can be used in the Hamiltonian to define a
robust and efficient electrostatic embedding QM/MM method. The original
formulation of ESPF QM/MM contained two main approximations, namely, the
neglect of grid derivatives and the non-conservation of the total QM charge.
Here, we present a new ESPF atomic charge operator which solves these drawbacks
at virtually no extra computational cost. The new charge operators employ
atom-centered grids and conserve the total charge when traced with the density
matrix. We present an efficient and easy-to-implement analytic form for the
energy, gradient, and hessian that scale linearly with the MM subsystem size.
We show that grid derivatives and charge conservation are fundamental to
preserve the translational invariance properties of energies and its
derivatives and exact conditions to be satisfied by the atomic charge
derivatives. As proof of concept, we compute the transition state that leads to
the formation of hydrogen peroxide during cryptochrome's reoxidation reaction.
Last, we show that the construction of the full QM/MM hessian scales linearly
with the MM subsystem size.

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The categories of this paper are: nucl-ex
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-th
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The categories of this paper are: hep-lat
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The categories of this paper are: solv-int
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The categories of this paper are: comp-gas
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The categories of this paper are: supr-con
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The categories of this paper are: cmp-lg
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The categories of this paper are: alg-geom
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The categories of this paper are: funct-an
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The categories of this paper are: q-alg
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The categories of this paper are: hep-ex
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The categories of this paper are: mtrl-th
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The categories of this paper are: eess
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The categories of this paper are: adap-org
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The categories of this paper are: chem-ph