Quantum paradigms in hydrogen storage in nanostructures

今年，我们用模型哈密顿计算方法研究了纳米结中H2分子的转动效应。在密度泛函理论的基础上，通过第一性原理计算得到了吸附和相互作用参数。用NEGF方法计算了取向相关电流。振动效应也通过电子-声子耦合结合在一起。我们的结果恢复了以前所理解的量子点系统中的电子-声子效应，其中电流的阶梯状特征和电导的周期性峰归因于Frank-Condon激发。我们还在微观水平上推导了金属结与氢的相互作用的表达式，考虑了分子相对于结的取向。我们发现，当分子取向平行于金属表面时，电流被抑制。此外，该取向的谱函数(SF)变窄，表明结和H2之间的电子跳跃减少。这种强烈的取向效应可以在旋转平均的SF和电流中类似地看到。与J=1，m=0(正交)相比，J=0，m=0(Paro)SF更窄。在所研究的转动态中，J=1，m=1SF是最窄的。在气相中，J=1，m=0和J=1，m=1的态在能量上是简并的，这两种态的SF应该是相似的。金属结与氢之间的电子相互作用导致这些态的分裂，并导致纳米结中的各向异性电流。

This year, the rotational effects of H2 molecule in a nanojunction was investigated by means of model Hamiltonian calculations. The adsorption and interaction parameters were obtained from first principles calculations based on the density functional theory. The orientation-dependent current was calculated using NEGF formalism. Ihe vibrational effects is also incorporated through the electron-phonon coupling. Our results recovered the previously understood electron-phonon effects in the quantum dot system where step-like features in the current and periodic peaks in the conductance are attributed to the Frank-Condon excitations. We also derived an expression for the interaction between the metal junctions and H2 at a microscopic level accounting for the orientation of the molecule with respect to the junctions. We found that the current is suppressed when the molecular orientation is parallel to the surfaces of the metals. Further, the spectral function (SF) at this orientation narrows indicating the reduction of the electron hopping between the junction and H2.This strong orientation effects can be similarly seen in the rotational averaged SF and current. The J=0,m=0 (para) SF is narrow compared to J=1,m=0 (ortho). The J=1,m=1 SF is narrowest among the rotational states investigated. In the gas phase, J=1,m=0 and J=1,m=1 states are degenerate in energy and both SF of these states are expected to be the similar. The electronic interaction between the metal junctions and H2 cause the splitting of these states and results in anisotropic current in the nanojunction.