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Magnetic coupling in neutral and charged Cr2, Mn2, and CrMn dimers (2000)

Desmarais, N. ; Reuse, F. A.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 112 (2000), S. 5576-5584

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Theoretical ab initio studies of neutral, cationic and anionic Cr2, Mn2, and CrMn dimers have been carried out to explore the progression of magnetic coupling with the number of electrons. It is shown that while Cr2 and Cr2− have antiferromagnetically coupled atomic spins, Cr2+ has a ferromagnetic ground state closely followed by an antiferromagnetic state. On the other hand, all Mn2 dimers are ferromagnetic, irrespective of the charge. The neutral CrMn is ferrimagnetic while the charged CrMn are antiferromagnetic. In all cases, the charged dimers are found to be more stable than the neutral ones. The results are compared with available calculations and experiments and the difficulties associated with theoretical description and the experimental interpretations are discussed. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.481183

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Dissipative evolution of quantum statistical ensembles and nonlinear response to a time-periodic perturbation (2003)

Reuse, F. A. ; Maschke, K. ; Coulon, V. de ; [et al.]

Springer

The European physical journal 36 (2003), S. 573-592

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ISSN: 1434-6036

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract. We present a detailed discussion of the evolution of a statistical ensemble of quantum mechanical systems coupled weakly to a bath. The Hilbert space of the full system is given by the tensor product between the Hilbert spaces associated with the bath and the bathed system. The statistical states of the ensemble are described in terms of density matrices. Supposing the bath to be held at some - not necessarily thermal - statistical equilibrium and tracing over the bath degrees of freedom, we obtain reduced density matrices defining the statistical states of the bathed system. The master equations describing the evolution of these reduced density matrices are derived under the most general conditions. On time scales that are large with respect to the bath correlation time $\tau_{B}^{\mathrm{corr}}$ and with respect to the reciprocal transition frequencies of the bathed system, the resulting evolution of the reduced density matrix of the bathed system is of Markovian type. The detailed balance relations valid for a thermal equilibrium of the bath are derived and the conditions for the validity of the fluctuation-dissipation theorem are given. Based on the general approach, we investigate the non-linear response of the bathed subsystem to a time-periodic perturbation. Summing the perturbation series we obtain the coherences and the populations for arbitrary strengths of the perturbation.