Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Structural instability and the Mott-Peierls transition in a
  half-metallic hollandite : K$_{2}$Cr$_{8}$O$_{16}$   In order to explore the driving mechanism of the concomitant metal-insulator
and structural transitions in quasi-one-dimensional hollandite
K$_{2}$Cr$_{8}$O$_{16}$, electronic structures and phonon properties are
investigated by employing the {\it ab initio} density functional theory (DFT)
calculations. We have found that the imaginary phonon frequency reflecting the
structural instability appears only in the DFT+$U$ ($U$: Coulomb correlation)
calculation, which indicates that the Coulomb correlation plays an essential
role in the structural transition. The lattice displacements of the softened
phonon at X explain the observed lattice distortions in K$_{2}$Cr$_{8}$O$_{16}$
perfectly well, suggesting the Peierls distortion vector {\bf Q} of X (0, 0,
1/2). The combined study of electronic and phonon properties reveals that
half-metallic K$_{2}$Cr$_{8}$O$_{16}$, upon cooling, undergoes the
correlation-assisted Peierls transition to become a Mott-Peierls ferromagnetic
insulator at low temperature.

14
The categories of this paper are: math-ph
12
The categories of this paper are: nucl-th
24
The categories of this paper are: dg-ga
23
The categories of this paper are: solv-int
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
0
The categories of this paper are: hep-ph
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
13
The categories of this paper are: quant-ph
34
The categories of this paper are: chem-ph