Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Calculation of single-beam two-photon absorption rate of lanthanides:
  effective operator method and perturbative expansion   Perturbative contributions to single-beam two-photon transition rates may be
divided into two types. The first, involving low-energy intermediate states,
require a high-order perturbation treatment, or an exact diagonalization. The
other, involving high energy intermediate states, only require a low-order
perturbation treatment. We show how to partition the effective transition
operator into two terms, corresponding to these two types, in such a way that a
many-body perturbation expansion may be generated that obeys the linked cluster
theorem and has a simple diagrammatic representation.

23
The categories of this paper are: solv-int
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
10
The categories of this paper are: q-bio
6
The categories of this paper are: astro-ph
26
The categories of this paper are: bayes-an
34
The categories of this paper are: chem-ph
20
The categories of this paper are: acc-phys
27
The categories of this paper are: comp-gas