Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Binding and excitations in Si$_x$H$_y$ molecular systems using quantum
  Monte Carlo   We present high-accuracy correlated calculations of small Si$_x$H$_y$
molecular systems both in the ground and excited states. We employ quantum
Monte Carlo (QMC) together with a variety of many-body wave function approaches
based on basis set expansions. The calculations are carried out in a
valence-only framework using recently derived correlation consistent effective
core potentials. Our primary goal is to understand the fixed-node diffusion QMC
errors in both the ground and excited states with single-reference trial wave
functions. Using a combination of methods, we demonstrate the very high
accuracy of the QMC atomization energies being within $\approx$ 0.07 eV or
better when compared with essentially exact results. By employing proper
choices for trial wave functions, we have found that the fixed-node QMC biases
for total energies are remarkably uniform ranging between $1-3.5$ % with
absolute values at most $\approx$ 0.2 eV across the systems and several types
of excitations such as singlets and triplets as well as low-lying and
Rydberg-like states. Our results further corroborate that Si systems, and
presumably also related main group IV and V elements of the periodic table (Ge,
Sn, etc), exhibit some of the lowest fixed-node biases found in valence-only
electronic structure QMC calculations.

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The categories of this paper are: q-alg
36
The categories of this paper are: cmp-lg
0
The categories of this paper are: hep-ph
14
The categories of this paper are: math-ph
18
The categories of this paper are: econ
13
The categories of this paper are: quant-ph
25
The categories of this paper are: patt-sol
1
The categories of this paper are: cs
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
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The categories of this paper are: comp-gas
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The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th
33
The categories of this paper are: plasm-ph