First-Principles Study Of Magnetism For Organic Molecules

The subject of molecular magnet has attracted much attention by theoretic and experimental scientists both for its light in weight and easy to process as well as for its characteristic that not appear in traditional magnet.One of the most important problem in produce molecular magnet is how to improve its magnetism and critical temperature.So it's meaningful to plan theoretic study to magnetic origin and exchange mechanism of high critical temperature molecular magnet.Those study can both improve our understand to intrinsic magnetic of molecular magnet and can give guidance to find molecular magnet with better magnetic.We plan an first-principles calculation to a model system base on a series of molecular conductor.We build a possible structure according the structure and bond structure in reactions of organic molecules,and then plan a simulation to it after geometry optimize to get information of the system such as energy of ground state,charge density and density of state.And those information can be use to study the intrinsic magnetic of the model system.Through studying of TM₂TCNQ system we find that magnetic moment of this system mostly origin from transition metal atoms and organic molecule also be polarized.Ground state of V₂TCNQ system is ferromagnetic and show to have half-metallic properties. Simulation to Ni₂TCNQ system show that the system have a ground state which is antiferromagnetic and both magnet moment and critical temperature is very low.That show to us that organic anion many play an important role in magnetism of this system.Through studying of TM₂·O·DDQ system we find that Ground state of Ni₂·O·DDQ system is ferromagnetic and both magnet moment and critical temperature accord with experimental results.Fe₂·O·DDQ system may have the highest magnet moment and higher critical temperature,magnetic moment of this system also mostly origin from transition metal atoms and magnetic moment of organic molecule can't be neglect. Oxygen which among the two TM atoms exist direct exchange with both TM atom and have higher magnetic moment.Atoms of organic molecule have magnetic moment origin form their p_z state.