THEORETICAL DESIGN OF A NEW, HIGH-SPIN, ORGANIC-MOLECULE

The search for ferromagnetism in compounds only made of light elements succeeds in a very few cases. One fundamental key is to start with hi gh spin molecules as building blocks for the solid. Looking for such e ntities may be rationalised by theoretical investigations. Quantum che mistry calculations were performed on a ''virtual'' organic neutral mo lecule. This molecule is a derivative of TTF, and it is predicted to b e planar. The level of theory (semi-empirical vs. ab initio, ab initio vs. DFT), the effect of basis set quality and of electron-electron co rrelation were analysed. These results show that there is a strong evi dence for a triplet ground state. The singlet-tripler splitting ranges between 0.2 and 2 eV depending on the method. Moreover, there is a st rong tendency for these molecules to build dimers with a quintet groun d state. Consequently, this molecule, if its synthesis should be possi ble, appears to be quite attractive to build new organic ferromagnets.