Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Surface energy and elementary excitations of the XXZ spin chain with
  arbitrary boundary fields   The thermodynamic properties of the XXZ spin chain with integrable open
boundary conditions at the gaped region (i.e., the anisotropic parameter $\eta$
being a real number) are investigated.It is shown that the contribution of the
inhomogeneous term in the $T-Q$ relation of the ground state and elementary
excited state can be neglected when the size of the system $N$ tends to
infinity. The surface energy and elementary excitations induced by the
unparallel boundary magnetic fields are obtained.

8
The categories of this paper are: hep-ex
32
The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
11
The categories of this paper are: hep-lat
16
The categories of this paper are: stat
5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
27
The categories of this paper are: comp-gas