Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quasi-Chemical Theory for Anion Hydration and Specific Ion Effects:
  Cl$^-$(aq) \emph{vs.} F$^-$(aq)   Anion hydration is complicated by H-bond donation between neighboring water
molecules in addition to H-bond donation to the anion. This situation can lead
to competing structures for chemically simple clusters like (H$_2$O)$_n$Cl$^-$
and to anharmonic vibrational motions. Quasi-chemical theory builds from
electronic structure treatment of isolated ion-water clusters, partitions the
hydration free energy into inner-shell and outer-shell contributions, and
provides a general statistical mechanical framework to study complications of
anion hydration. The present study exploits dynamics calculations on isolated
(H$_2$O)$_n$Cl$^-$ clusters to account for anharmonicity, utilizing ADMP
(atom-centered basis sets and density-matrix propagation) tools. Comparing
singly hydrated F$^-$ and Cl$^-$ clusters, classic OH-bond donation to the
anion occurs for F$^-$, while Cl$^-$ clusters exhibit more flexible but
dipole-dominated interactions between ligand and ion. The predicted Cl$^-$ --
F$^-$ hydration free energy difference agrees well with experiment, a
significant theoretical step for addressing issues like Hofmeister ranking and
selectivity in ion channels.

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The categories of this paper are: q-fin
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
30
The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
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The categories of this paper are: cs
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The categories of this paper are: stat
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The categories of this paper are: astro-ph
27
The categories of this paper are: comp-gas
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The categories of this paper are: adap-org
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The categories of this paper are: bayes-an
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The categories of this paper are: funct-an
9
The categories of this paper are: nlin