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利用密度泛函理论和非平衡格林函数的方法对硅桥调控后的聚茂钒体系([V(Cp)_2(SiH2)_n]_m(n=1(a),n=2(b),n=3(c);m=∞;Cp=环戊二烯基))的电子结构和输运性质进行了研究。研究结果表明:随着硅桥的增长,V-V的铁磁性耦合变弱而反铁磁性耦合增强。a和b证实为铁磁性基态,而c更倾向为反铁磁性基态。a和b的铁磁性基态中的每个钒原子的磁距为3.0μ_B,超过钒-苯络合物或者纯聚茂钒体系的3倍。a-c的输运性质同它们的电子结构相一致,导电性变化规律为c>b>a。对于a和b,自旋向下状态的导电性略强于自旋向上状态。a和c都发生了明显的负微分电阻效应而b却没有,这主要是由于两个二茂钒的排列取向不同:a和c(SiH2为奇数)中二茂钒呈V-型取向排列,进而导致了类似于离子键的量子点耦合,而b(SiH2是偶数)中二茂钒是平行-型取向排列,从而导致了类似于共价键的量子点耦合。此外,由于散射区和两个电极之间的不对称耦合,a-c的导电性对电压施加方向较敏感。
The density functional theory and the non-equilibrium Green’s function method were used to study the silicon-bridge-controlled poly (vanadium) vanadium system ([V (Cp) _2 (SiH2) _n] n = 3 (c); m = ∞; Cp = cyclopentadienyl)) have been studied. The results show that with the increase of silicon bridge, the ferromagnetic coupling of V-V becomes weak and the anti-ferromagnetic coupling increases. a and b are confirmed as ferromagnetic ground state, while c is more inclined to antiferromagnetic ground state. The magnetic distance of each vanadium atom in the ferromagnetic ground state of a and b is 3.0 μ B, which is more than 3 times that of the vanadium-benzene complex or the pure polyvararene system. The transport properties of a-c are consistent with their electronic structure, and the conductivity variation is c> b> a. For a and b, the spin-down state is slightly more conductive than the spin-up state. a and c both have significant negative differential resistance effect and b do not, which is mainly due to the different orientation of the two metallocene vanadium: a and c (SiH2 is an odd number) in the vanadyl vanadium was V-type orientation, Which in turn leads to quantum dot coupling similar to ionic bonds and vanadium vanadium in b (SiH2 is even) is aligned in a parallel-type orientation, resulting in a quantum dot coupling similar to a covalent bond. In addition, due to the asymmetric coupling between the scattering region and the two electrodes, the conductivity of a-c is more sensitive to the voltage application direction.