Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High-order density-matrix perturbation theory   We present a simple formalism for the calculation of the derivatives of the
electronic density matrix at any order, within density functional theory. Our
approach, contrary to previous ones, is not based on the perturbative expansion
of the Kohn-Sham wavefunctions. It has the following advantages: (i) it allows
a simple derivation for the expression for the high order derivatives of the
density matrix; (ii) in extended insulators, the treatment of
uniform-electric-field perturbations and of the polarization derivatives is
straightforward.

5
The categories of this paper are: gr-qc
2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
19
The categories of this paper are: eess
33
The categories of this paper are: plasm-ph
32
The categories of this paper are: atom-ph
0
The categories of this paper are: hep-ph
29
The categories of this paper are: funct-an
26
The categories of this paper are: bayes-an
36
The categories of this paper are: cmp-lg
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
24
The categories of this paper are: dg-ga
9
The categories of this paper are: nlin
21
The categories of this paper are: adap-org