Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Higher-order effective Hamiltonian for light atomic systems   We present the derivation of the effective higher-order Hamiltonian, which
gives $m \alpha^6$ contribution to energy levels of an arbitrary light atom.
The derivation is based on the Foldy-Wouthuysen transformation of the
one-particle Dirac Hamiltonian followed by perturbative expansion of the many
particle Green function. The obtained results can be used for the high
precision calculation of relativistic effects in atomic systems.

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The categories of this paper are: hep-lat
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-th
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The categories of this paper are: math
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The categories of this paper are: hep-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: q-alg
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The categories of this paper are: mtrl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: eess
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The categories of this paper are: nlin
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-ex