硅桥调控的聚茂钒体系电子结构和输运性质

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。

Silicon Bridge-Tuned Electronic Structures and Transport Properties of Polymetallocenes

Silicon bridge-tuned electronic structures and transport properties of polymetallocenes,V(Cp)₂(SiH₂)_n]_m (n=1 (a), n=2 (b), n=3 (c); m=∞; Cp=cyclopentadienyl), are studied using the densityfunctional theory (DFT) and non-equilibrium Green's function (NEGF) methods. As the silicon bridge islengthened, the V-V ferromagnetic (FM) coupling is weakened, while the antiferromagnetic (AFM) coupling isstrengthened. Polymetallocenes a and b favor the FM ground state, while c prefers the AFM ground state. EachV atom in the FM state of a and b has a magnetic moment of ~3.0μ_B, three times larger than that in the Vbenzeneor V-cyclopentadiene multidecker complex. The transport properties of a-c are in good agreementwith their electronic structures. Their conductivities follow the sequence c > b > a. For a and b, the spin-downstate has slightly higher conductivity than the spin-up state. Polymetallocenes a and c can both display evidentnegative differential resistance (NDR) behavior, while b cannot. This difference may originate from theorientation of the two V(Cp)₂ units, which is V-shaped for a and c (odd number of SiH₂ units), leading to ioniclikeinter-quantum dot coupling, and parallel for b (even number of SiH₂ units), leading to covalent-like interquantumdot coupling. In addition, the conductivity of a-c is sensitive to the current direction because of theasymmetric coupling between the scattering region and two electrodes.