Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Variational method for the calculation of critical distance between two
  Coulomb centers in graphene   The supercritical instability in a system of two identical charged impurities
in gapped graphene described in the continuous limit by the two-dimensional
Dirac equation has been studied. The case where the charge of each impurity is
subcritical, but their sum exceeds the critical value calculated in the version
with a single Coulomb center, is considered. Using the developed variational
method, the dependence of the critical distance $R_{\rm cr}$ between the
impurities on their total charge is calculated. The $R_{\rm cr}$-value is found
to grow as the total impurity charge increases and the quasiparticle band gap
decreases. The results of calculations are compared with those obtained in
earlier researches.

8
The categories of this paper are: hep-ex
19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
25
The categories of this paper are: patt-sol
5
The categories of this paper are: gr-qc
36
The categories of this paper are: cmp-lg
27
The categories of this paper are: comp-gas
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
13
The categories of this paper are: quant-ph
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin