Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A "mean-field approximation" on the phase transitions of
  three-dimensional Lennard-Jones model   It is difficult to derive the solid-fluid transition theoretically from
microscopic models, although this phenomenon itself has been investigated for a
long time. We previously constructed an exactly-solvable model with the
solid-fluid transition. This model resembles the infinite-range (or mean-field)
model in spin systems in some points, hence it can be called a "mean-field
model" of the solid-fluid transition. In the present paper, we construct a
"mean-field approximation" of the solid-fluid transition by using the
"mean-field model" introduced in our previous study, and tries to describe the
phase transitions of the three-dimensional Lennard-Jones model as an example.
This approximation succeeds in describing the phase diagram which contains
three (gas, liquid, and fcc-solid) phase, at least qualitatively.

5
The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
15
The categories of this paper are: nucl-ex
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The categories of this paper are: nlin
30
The categories of this paper are: q-alg
31
The categories of this paper are: ao-sci
23
The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
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The categories of this paper are: adap-org
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The categories of this paper are: astro-ph
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The categories of this paper are: funct-an
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The categories of this paper are: comp-gas
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The categories of this paper are: physics
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The categories of this paper are: math-ph