Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Structure and Born effective charge determination for planar-zigzag
  <beta>-poly(vinylidene fluoride) using density-functional theory   Two structures have been proposed in the literature for the b-phase of the
ferroelectric polymer, poly(vinylidene fluoride) (b-PVDF); planar-zigzag and
alternatively-deflected forms. Using density-functional theory, we have found
the planar-zigzag structure is the preferred form and upon atomic relaxation,
the alternatively-deflected structure attains a structure very similar to the
planar-zigzag structure. In order to better understand the atomic origin of the
ferroelectricity in b-PVDF, we have for the first time determined the dynamic
Born effective charges (Z*) for the planar-zigzag structure using a Berry-phase
approach. When compared to their nominal ionic values, the Z* show anomalous
differences. Using these effective charges, we describe the polarity of the
bonds with b-PVDF and show the extent of atomic-motion-induced (or dynamic)
charge transfer within this ferroelectric material. In addition, our effective
charges are different to previously-determined Mulliken charges, due to the
inherent differences between static and dynamic charges.

16
The categories of this paper are: stat
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
18
The categories of this paper are: econ
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
36
The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
10
The categories of this paper are: q-bio
9
The categories of this paper are: nlin
31
The categories of this paper are: ao-sci