Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Charge conserving approximation for excitation properties of crystalline
  materials   A charge conserving approximation scheme determining the excitations of
crystalline solids is proposed. Like other such approximations, it relies on
"downfolding" of the original microscopic model to a simpler electronic model
on the lattice with pairwise interactions. A systematic truncation of the set
of Dyson - Schwinger equations for correlators of the low energy (downfolded)
model of a material, supplemented by a "covariant" calculation of correlators
lead to a converging series of approximates. The covariance preserves all the
Ward identities among correlators describing various condensed matter probes.
It is shown that the third order approximant of this kind beyond classical and
gaussian (Hartree - Fock) is precise enough and due to several fortunate
features the complexity of calculation is surprisingly low so that a realistic
material computation is feasible. Focus here is on the electron field
correlator describing the electron (hole) excitations measured in photoemission
and other probes. The scheme is tested on several solvable benchmark models

19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
36
The categories of this paper are: cmp-lg
11
The categories of this paper are: hep-lat
16
The categories of this paper are: stat
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
1
The categories of this paper are: cs
32
The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas