Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Theoretical X-Ray Absorption Debye-Waller Factors   An approach is presented for theoretical calculations of the Debye-Waller
factors in x-ray absorption spectra. These factors are represented in terms of
the cumulant expansion up to third order. They account respectively for the net
thermal expansion $\sigma^{(1)}(T)$, the mean-square relative displacements
$\sigma^2(T)$, and the asymmetry of the pair distribution function
$\sigma^{(3)}(T)$. Similarly, we obtain Debye-Waller factors for x-ray and
neutron scattering in terms of the mean-square vibrational amplitudes $u^2(T)$.
Our method is based on density functional theory calculations of the dynamical
matrix, together with an efficient Lanczos algorithm for projected phonon
spectra within the quasi-harmonic approximation. Due to anharmonicity in the
interatomic forces, the results are highly sensitive to variations in the
equilibrium lattice constants, and hence to the choice of exchange-correlation
potential. In order to treat this sensitivity, we introduce two prescriptions:
one based on the local density approximation, and a second based on a modified
generalized gradient approximation. Illustrative results for the leading
cumulants are presented for several materials and compared with experiment and
with correlated Einstein and Debye models. We also obtain Born-von Karman
parameters and corrections due to perpendicular vibrations.

31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
19
The categories of this paper are: eess
1
The categories of this paper are: cs
9
The categories of this paper are: nlin
13
The categories of this paper are: quant-ph
14
The categories of this paper are: math-ph
18
The categories of this paper are: econ
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th
10
The categories of this paper are: q-bio