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采用量子化学abinitio法和密度泛函方法对不同取代位置的嘧啶自旋耦合规律进行研究 .两种方法比较 ,用UHF方法计算导致自旋污染严重 ,而用UB3LYP方法计算 ,自旋污染则减少了许多 .计算结果得到了双自由基之间磁性耦合的拓扑规则 :共轭体系中 ,两个自由基之间以偶数个碳 (或氮 )原子耦合 ,则有效交换积分Jij<0 ,体系具有低自旋基态 ,表现为反铁磁耦合 ;两个自由基之间以奇数个碳 (或氮 )原子耦合 ,则有效交换积分Jij>0 ,体系具有高自旋基态 ,表现为铁磁耦合 .自由基性质和铁磁耦合单元的不同位置对自旋耦合的影响较大 ,这些结论为有机磁性材料的分子设计与实验合成提供了理论依据 .
Quantum chemical ab initio method and density functional method were used to study the spin-spin coupling of pyrimidine at different substituted sites. Comparing the two methods, the spin-pollutions caused by UHF method were serious, but the spin-pollutions were reduced by UB3LYP method Many results obtained the topological rules of the magnetic coupling between the two free radicals. In the conjugated system, when two free radicals are coupled with even carbon (or nitrogen) atoms, the effective exchange integral Jij <0, the system has a low Spin ground state, the performance of the anti-ferromagnetic coupling; two free radicals with an odd number of carbon (or nitrogen) atoms coupled, the effective exchange integral Jij> 0, the system has a high spin state, the performance of the ferromagnetic coupling. And the different positions of the ferromagnetic coupling unit have a great influence on the spin coupling. These conclusions provide the theoretical basis for the molecular design and experimental synthesis of the organic magnetic material.