Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: X-ray Magnetic and Natural Circular Dichroism from first principles:
  Calculation of K- and L1-edge spectra   An efficient first principles approach to calculate X-ray magnetic circular
dichroism (XMCD) and X-ray natural circular dichroism (XNCD) is developed and
applied in the near edge region at the K-and L1-edges in solids. Computation of
circular dichroism requires precise calculations of X-ray absorption spectra
(XAS) for circularly polarized light. For the derivation of the XAS cross
section, we used a relativistic description of the photon-electron interaction
that results in an additional term in the cross-section that couples the
electric dipole operator with an operator $\mathbf{\sigma}\cdot
(\mathbf{\epsilon} \times \mathbf{r})$ that we name spin-position. The
numerical method relies on pseudopotentials, on the gauge including projected
augmented wave method and on a collinear spin relativistic description of the
electronic structure. We apply the method to the calculations of K-edge XMCD
spectra of ferromagnetic iron, cobalt and nickel and of I L1-edge XNCD spectra
of $\alpha$-LiIO3, a compound with broken inversion symmetry. For XMCD spectra
we find that, even if the electric dipole term is the dominant one, the
electric quadrupole term is not negligible (8% in amplitude in the case of
iron). The term coupling the electric dipole operator with the spin-position
operator is significant (28% in amplitude in the case of iron). We obtain a
sum-rule relating this new term to the spin magnetic moment of the p-states. In
$\alpha$-LiIO3 we recover the expected angular dependence of the XNCD spectra.

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The categories of this paper are: math-ph
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The categories of this paper are: hep-ex
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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: q-alg
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The categories of this paper are: chao-dyn
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The categories of this paper are: stat
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The categories of this paper are: cs
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The categories of this paper are: nucl-ex
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The categories of this paper are: gr-qc
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The categories of this paper are: comp-gas
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-th
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The categories of this paper are: adap-org
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The categories of this paper are: eess