Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Density-Matrix Algorithm for Phonon Hilbert Space Reduction in the
  Numerical Diagonalization of Quantum Many-Body Systems   Combining density-matrix and Lanczos algorithms we propose a new optimized
phonon approach for finite-cluster diagonalizations of interacting
electron-phonon systems. To illustrate the efficiency and reliability of our
method, we investigate the problem of bipolaron band formation in the extended
Holstein Hubbard model.

17
The categories of this paper are: q-fin
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
24
The categories of this paper are: dg-ga
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
1
The categories of this paper are: cs
30
The categories of this paper are: q-alg
7
The categories of this paper are: hep-th
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph
15
The categories of this paper are: nucl-ex