Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Microscopic origin of isotropic non-Heisenberg behavior in highly
  correlated systems   We have reanalyzed the microscopic origin of the isotropic deviations that
are observed from the energy spacings predicted by the HDVV Hamiltonian.
Usually, a biquadratic spin operator is added to the HDVV Hamiltonian to
account for such deviations. It is shown here that this operator cannot
describe the effect of the excited atomic non-Hund states which brought the
most important contribution to the deviations. For systems containing more than
two magnetic centers, non-Hund states cause additional interactions that are of
the same order of magnitude as the biquadratic exchange and should have
significant effects on the macroscopic properties of extended systems.

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The categories of this paper are: hep-ex
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The categories of this paper are: quant-ph
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
22
The categories of this paper are: chao-dyn
34
The categories of this paper are: chem-ph
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The categories of this paper are: astro-ph
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
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The categories of this paper are: adap-org
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The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg