Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Reduced-density-matrix-based ab initio cavity quantum electrodynamics   A reduced-density-matrix (RDM)-based approach to {\em ab initio} cavity
quantum electrodynamics (QED) is developed. The expectation value of the
Pauli-Fierz Hamiltonian is expressed in terms of one- and two-body electronic
and photonic RDMs, and the elements of these RDMs are optimized directly in
polynomial time by semidefinite programming techniques, without knowledge of
the full wave function. QED generalizations of important ensemble
$N$-representability conditions are derived and enforced in this procedure. The
resulting approach is applied to the description of classic ground-state strong
electron correlation problems, augmented by the presence of ultrastrong
light-matter coupling. First, we assess cavity-induced changes to the
singlet-triplet energy gap of the linear oligoacene series; for a heptacene
molecule modeled under experimentally feasible coupling strengths, this gap can
change by as much as 1.9 kcal mol$^{-1}$ (or 15\%). We also explore the
metal-insulator transition in linear hydrogen chains and demonstrate that
strong electron-photon interactions increase the insulating character of these
systems under all coupling strengths considered.

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The categories of this paper are: chem-ph
4
The categories of this paper are: cond-mat
27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
36
The categories of this paper are: cmp-lg
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ