Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Computational Study of the Magnetic Structure of Na$_2$IrO$_3$   The magnetic structure of honeycomb iridate Na$_2$IrO$_3$ is of paramount
importance to its exotic properties. The magnetic order is established
experimentally to be zigzag antiferromagnetic. However, the previous assignment
of ordered moment to the $\bm{a}$-axis is tentative. We examine the magnetic
structure of Na$_{2}$IrO$_{3}$ using first-principles methods. Our calculations
reveal that total energy is minimized when the zigzag antiferromagnetic order
is magnetized along $\bm{g}\approx\bm{a}+\bm{c}$. Such a magnetic configuration
is explained by adding anisotropic interactions to the nearest-neighbor
Kitaev-Heisenberg model. Spin-wave spectrum is also calculated, where the
calculated spin gap of $10.4$ meV can in principle be measured by future
inelastic neutron scattering experiments. Finally we emphasize that our
proposal is consistent with all known experimental evidence, including the most
relevant resonant x-ray magnetic scattering measurements [X. Liu \emph{et al.}
{Phys. Rev. B} \textbf{83}, 220403(R) (2011)].

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The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
26
The categories of this paper are: bayes-an
11
The categories of this paper are: hep-lat
7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
35
The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio
3
The categories of this paper are: physics
19
The categories of this paper are: eess
17
The categories of this paper are: q-fin