Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The statistical description of the electron system on the liquid helium
  surface   It is known that homogeneous distribution of particles in Coulomb-like
systems can be unstable, and spatially inhomogeneous structures can be formed.
A simple method for describing such inhomogeneous systems and obtaining spacial
distributions of electron density is proposed and applied to the case of
two-dimensional electron systems on surface of liquid helium. A free energy
functional for the model in mean field approximation is obtained. Creation of
various types of structures, such as long-range periodical modulation and
multi-electron dimples, is predicted by minimizing this functional.

2
The categories of this paper are: math
19
The categories of this paper are: eess
18
The categories of this paper are: econ
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
21
The categories of this paper are: adap-org
0
The categories of this paper are: hep-ph
13
The categories of this paper are: quant-ph
8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
16
The categories of this paper are: stat