Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum Monte Carlo study of the protonated water dimer   We report an extensive theoretical study of the protonated water dimer
(Zundel ion) by means of the highly correlated variational Monte Carlo and
lattice regularized Monte Carlo approaches. This system represents the simplest
model for proton transfer (PT) and a correct description of its properties is
essential in order to understand the PT mechanism in more complex acqueous
systems. Our Jastrow correlated AGP wave function ensures an accurate treatment
of electron correlations. Exploiting the advantages of contracting the
primitive basis set over atomic hybrid orbitals, we are able to limit
dramatically the number of variational parameters with a systematic control on
the numerical precision, crucial in order to simulate larger systems. We
investigate energetics and geometrical properties of the Zundel ion as a
function of the oxygen-oxygen distance, taken as reaction coordinate. In both
cases, our QMC results are found in excellent agreement with coupled cluster
CCSD(T) technique, the quantum chemistry "gold standard". Calculations on
proton transfer static barriers and dissociation energies display the same
agreement. A comparison with density functional theory (DFT) results in the PBE
approximation points out the crucial role of electron correlations for a
correct description of the PT in the dimer. Our method is able to resolve the
tiny energy differences (~ 0.1 Kcal/mol) and the corresponding structural
variations at which the proton transfer takes place; it combines these features
with a N^3-N^4 scaling with number of particles (favorable with respect to
other post-DFT methods), as proven by a benchmark calculation on a larger
protonated water cluster. The QMC approach used here represents a promising
candidate to provide the first high-level ab initio description of PT in water.

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The categories of this paper are: bayes-an
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The categories of this paper are: alg-geom
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The categories of this paper are: econ
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The categories of this paper are: math-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: funct-an
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-th
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The categories of this paper are: stat
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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: chao-dyn
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-lat