Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Time-dependent renormalized natural orbital theory applied to the
  two-electron spin-singlet case: ground state, linear response, and
  autoionization   Favorably scaling numerical time-dependent many-electron techniques such as
time-dependent density functional theory (TDDFT) with adiabatic
exchange-correlation potentials typically fail in capturing highly correlated
electron dynamics. We propose a method based on natural orbitals, i.e., the
eigenfunctions of the one-body reduced density matrix, that is almost as
inexpensive numerically as adiabatic TDDFT, but which is capable of describing
correlated phenomena such as doubly excited states, autoionization, Fano
profiles in the photoelectron spectra, and strong-field ionization in general.
Equations of motion (EOM) for natural orbitals and their occupation numbers
have been derived earlier. We show that by using renormalized natural orbitals
(RNO) both can be combined into one equation governed by a hermitian effective
Hamiltonian. We specialize on the two-electron spin-singlet system, known as
being a "worst case" testing ground for TDDFT, and employ the widely used,
numerically exactly solvable, one-dimensional helium model atom (in a laser
field) to benchmark our approach. The solution of the full, nonlinear EOM for
the RNO is plagued by instabilities, and resorting to linear response is not an
option for the ultimate goal to study nonperturbative dynamics in intense laser
fields. We therefore make two rather bold approximations: we employ the
initial-state-"frozen" effective RNO Hamiltonian for the time-propagation and
truncate the number of RNO to only two per spin. Surprisingly, it turns out
that even with these strong approximations we obtain a highly accurate ground
state, reproduce doubly-excited states, and autoionization.

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The categories of this paper are: hep-lat
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The categories of this paper are: econ
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
0
The categories of this paper are: hep-ph
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The categories of this paper are: math-ph
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The categories of this paper are: funct-an
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The categories of this paper are: stat
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The categories of this paper are: astro-ph
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The categories of this paper are: adap-org
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The categories of this paper are: alg-geom
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The categories of this paper are: chem-ph
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The categories of this paper are: solv-int