Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: First-Principles Study of Electronic and Vibrational Properties of
  BaHfN$_2$   The transition metal nitride BaHfN$_2$, which consists of weakly bonded
neutral slabs of closed shell ions, has structural and chemical similarities to
other layered nitrides which have impressive superconducting T$_c$ when
electron doped: A$_x$HfNCl, A$_x$ZrNCl, A$_x$TiNCl, with $T_c= 25.5$, $15.2$
and $16.5$ K, respectively for appropriate donor (A) concentrations $x$. These
similarities suggest the possibility of BaHfN$_2$ being another relatively high
T$_c$ nitride upon doping, with effects of structure and the role of specific
transition metal ions yet to be understood. We report first-principles
electronic structure calculations for stoichiometric BaHfN$_2$ using density
functional theory with plane-wave basis sets and separable dual-space Gaussian
pseudopotentials. An indirect band gap of 0.8 eV was obtained and the lowest
conduction band is primarily of Hf 5$d_{xy}$ character, similar to
$\beta$-ZrNCl and $\alpha$-TiNCl. The two N sites, one in the Hf layer and
another one in the Ba layer, were found to have very anisotropic Born effective
charges (BEC):deviations from the formal charge (-3) are opposite for the two
sites, and opposite for the two orientations (in-plane, out of plane). LO-TO
splittings and comparison of BECs and dielectric constant tensors to those of
related compounds are discussed, and the effect of electron doping on the
zone-center phonons is reported.

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The categories of this paper are: nlin
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The categories of this paper are: astro-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: physics
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The categories of this paper are: mtrl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: funct-an
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The categories of this paper are: math-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-th
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The categories of this paper are: q-alg
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The categories of this paper are: adap-org
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The categories of this paper are: stat
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The categories of this paper are: math