The role of dynamical polarization of the ligand to metal charge transfer excitations in {\em ab initio} determination of effective exchange parameters

The role of the bridging ligand on the effective Heisenberg coupling parameters is analyzed in detail. This analysis strongly suggests that the ligand-to-metal charge transfer excitations are responsible for a large part of the final value of the magnetic coupling constant. This permits to suggest a new variant of the Difference Dedicated Configuration Interaction (DDCI) method, presently one of the most accurate and reliable for the evaluation of magnetic effective interactions. This new method treats the bridging ligand orbitals mediating the interaction at the same level than the magnetic orbitals and preserves the high quality of the DDCI results while being much less computationally demanding. The numerical accuracy of the new approach is illustrated on various systems with one or two magnetic electrons per magnetic center. The fact that accurate results can be obtained using a rather reduced configuration interaction space opens the possibility to study more complex systems with many magnetic centers and/or many electrons per center.Comment: 7 pages, 4 figure

Exchange coupling inversion in a high-spin organic triradical molecule

The magnetic properties of a nanoscale system are inextricably linked to its local environment. In ad-atoms on surfaces and inorganic layered structures the exchange interactions result from the relative lattice positions, layer thicknesses and other environmental parameters. Here, we report on a sample-dependent sign inversion of the magnetic exchange coupling between the three unpaired spins of an organic triradical molecule embedded in a three-terminal device. This ferro-to-antiferromagnetic transition is due to structural distortions and results in a high-to-low spin ground state change in a molecule traditionally considered to be a robust high-spin quartet. Moreover, the flexibility of the molecule yields an in-situ electric tunability of the exchange coupling via the gate electrode. These findings open a route to the controlled reversal of the magnetic states in organic molecule-based nanodevices by mechanical means, electrical gating or chemical tailoring

Isoenzimas de Eucalyptus: técnicas para extracao e eletroforese.

Visou-se, com este estudo, determinar os metodos mais adequados para a extracao e a separacao eletroforetica de isoenzimas de E. . Examinaram-se zimogramas em gel de amido, obtidos a partir de extrato de folhas,de polen, de plantulas mantidas por micropropagacao e de plantulas obtidas de sementes. Testaram-se quatro metodos mecanicos para a maceracao dos tecidos vegetais, cinco sistemas-tampao para a extracao das enzimas e 16 combinacoes de sistemas-tampao gel/eletrodo para a eletroforese. Sao apresentados e discutidos os resultados obtidos com o uso desses sistemas-tampao para a identificacao de 34 enzimas nos quatro materiais mencionados. Este trabalho fornece uma escolha de marcadores isoenzimaticos aplicaveis ao melhoramento de Eucalyptus.Edição dos Anais do Congresso Florestal Brasileiro, 6., 1990, Campos do Jordão