Clusters magnetic systems

Magnetic Field Effects on the Dynamics of the Radical Pair in a Cgo Clusters-Phenothiazine System... 

Yonemura, H., Kuroda, N., Moribe, S. and Yamada, S. (2006) Photoindiced electron-transfer and magnetic field effects on the dynamics of the radical pair in a Cgo clusters-phenofhiazine system. C. R, Chim., 9, 254-260. 

These observations in N-doped Mn and Cr clusters have relevance to the studies of the observed ferromagnetism in Mn- and Cr-doped GaN, as in these systems, it is possible that Mn and Cr atoms could cluster around N. Therefore, Curie temperatures could be enhanced since it is proportional to the square of the moment. Thus, one can expect that as an impurity (Mn or Cr) in GaN, the giant cluster magnets may play a significant role in the observed ferromagnetism in (Ga,Mn)N or (Ga,Cr)N semiconductors. 

On the other side, semiempirical model Hamiltonians have been proposed to overcome the difficulties related to symmetry restriction These methods are formulated in the real space and use localized basis so that nonperiodic systems without symmetry are easy to deal with. In the particular case of magnetic systems the selfconsistent tight-binding model has been successfully applied for the study of free and supported clusters surfaces and over lay-... 

All calculations have been performed taking fixed positions for the atoms in the structures, so that no relaxations are considered. The Siesta method, however, allows relaxations and molecular dynamics by calculating the forces on the atoms and the stress tensor from the Hellman-Feynman theorem with Pulay corrections The computational cost would be much higher than in the frozen geometry calculations, but the calculations for complex magnetic systems are cheaper than with other ab initio methods (KKR, FLAPW, LMTO). Apart from the use of pseudopotentials and a minimal basis set, the supercell construction does not require the inclusion of empty spheres as it is the case for the LMTO-ASA method. Besides, going from 2D to 3D supported clusters of similar size does not increase the computational cost like in the KKR-GF method where Green-Functions have to be computed. 

Dimers and clusters, linear chain and planar magnetic systems... 

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