Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Superconducting ground state of the two-dimensional Hubbard model: a
  variational study   A trial wave function is proposed for studying the instability of the
two-dimensional Hubbard model with respect to d-wave superconductivity. Double
occupancy is reduced in a similar way as in previous variational studies, but
in addition our wave function both enhances the delocalization of holes and
induces a kinetic exchange between the electron spins. These refinements lead
to a large energy gain, while the pairing appears to be weakly affected by the
additional term in the variational wave function.

33
The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
19
The categories of this paper are: eess
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
16
The categories of this paper are: stat
9
The categories of this paper are: nlin
24
The categories of this paper are: dg-ga
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn