The article information
 Yue Gu, Jing Huang, Yujie Hu, Qunxiang Li
 顾玥, 黄静, 胡玉洁, 李群祥
 Coherent Spin Transport Through a SixCoordinate FeN
$_6$ SpinCrossover Complex with Two Different Spin Configurations  六配位FeN
$_6$ 自旋翻转化合物的自旋输运特性  Chinese Journal of Chemical Physics, 2019, 32(5): 579585
 化学物理学报, 2019, 32(5): 579585
 http://dx.doi.org/10.1063/16740068/cjcp1905104

Article history
 Received on: May 28, 2019
 Accepted on: June 2, 2019
b. School of Materials and Chemical Engineering, Anhui Jianzhu University, Hefei 230601, China;
c. Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, China
By using the electron and spin degrees of freedom at the singlemolecule level, molecular spintronics has become a rapidly developing field in recent years [14], since it holds potential applications in the next generation of electronic devices, especially in quantum computing, and the logical and memory units of computers [5, 6]. Till now, based on different singlemolecule magnets or magnetic molecules, various molecular spin devices, such as spincrossover, spin valve, spin filter, and molecular switch, have been successfully demonstrated or proposed [710].
Due to the magnetic bistability, singlemolecule spincrossover (SCO) complexes have been considered as one of the most possible building blocks in molecular spintronics [11, 12]. In general, the spin transition between the lowspin (LS) and highspin (HS) states can be achieved by external stimuli, such as magnetic or electric field, light, temperature, or strain [1316]. Among various Febased SCO complexes, the mononuclear Fe family, in which the central Fe cation is sixcoordinated via N atoms in ligands, has been best studied since their SCO electronic and transport properties are rather easily controlled. Previous research activities mainly focused on SCO behavior, photoswitching, temperaturedependent magnetism [1721], we should pay more attention to their transport properties of Fe(Ⅱ)based SCO complexes.
Very recently, Liu et al. have successfully synthesized a new mononuclear Fe(Ⅱ) SCO complex [22], namely, [Fe
Based on firstprinciples calculations combined with nonequilibrium Green's function method, we explore the SCO behavior and coherent spin transport properties of FeN
Gaussian package [23] at the metaGGA hybrid TPSSh functional level, using the triple zeta valence basis set [24], can predict reliable electronic energies and reproduce well the metalligand bond lengths of the mononuclear Fe(Ⅱ) SCO complexes [2527]. In the work, we adopt the Gaussian Package to optimize the geometric structure, to calculate electronic structure, and to describe SCO behavior of free FeN
The coherent transport through the molecular junction is explored by performing density functional theory (DFT) calculations combined with nonequilibrium Green's function (NEGF) technique, implemented in the Atomistix Toolkit (ATK) code [2830]. The TroullierMartins pseudopotential is adopted for the calculation for the inner electrons. As for the exchange and correlation functional, we use the generalized gradient approximation in the PerdewBurkeErnzerhof form [31]. To balance the calculation precision and costs, double zeta plus polarization basis set is set for all atoms, except for Au atoms, which are described by single zeta plus polarization. We employ 1
To obtain spinresolved current through the molecular junction, the transmission coefficients of the molecular junctions are calculated using
$ \begin{eqnarray} T_{\sigma}(E, V)=\textrm{Tr}[\Gamma_{\textrm{L}}G_{\sigma}\Gamma_{\textrm{R}}G_{\sigma}^{+}] \end{eqnarray} $  (1) 
where
$ \begin{eqnarray} \Gamma_{\textrm{L/R}}=\frac{i}{2}\left(\Sigma_{\textrm{L/R}}\Sigma_{\textrm{L/R}}^{\dagger}\right) \end{eqnarray} $  (2) 
and
$\begin{eqnarray} G_{\sigma}=[(E+i\eta)S_\textrm{C}H_\textrm{C}\Sigma_\textrm{R}\Sigma_\textrm{L}]^{1} \end{eqnarray} $  (3) 
here,
$ \begin{eqnarray} \Sigma_{\textrm{L/R}}=V_{\textrm{L/R}} g_{\textrm{L/R}}^s V_{\textrm{L/R}}^{\dagger} \end{eqnarray} $  (4) 
where
Then, the current through the molecular junction is obtained by
$\begin{eqnarray} I(V)=\frac{e}{h}\int T_{\sigma}(E, V)[f(E\mu_{\textrm{L}})f(E\mu_{\textrm{R}})]\textrm{d}E \end{eqnarray} $  (5) 
where
Firstly, we optimize the geometric structures of FeN
To describe the spin transition between the LS and HS states at the metaGGA hybrid TPSSh functional level, we calculate the total electronic energies of free FeN
Now we turn to analyze the frontier orbitals of free FeN
To explore the coherent transport properties through FeN
FIG. 3(b) plots the zerobias transmission spectra of FeN
As for the HS state, free FeN
We calculate the total density of states (DOS) of FeN
To make sure that the predicted molecular switching and the spinfiltering devices can work under small bias voltages, we calculate the currentvoltage (
As for the HS state, the spinup current (
In experiments, it is very difficult to design the exact anchoring structure between the central sandwiched molecule and electrodes, which always alters the transport behavior [40, 41], For example, Parashar et al. have shown that the transport properties of molecular junction depended on the adopted electrodes and the anchoringatom [42]. Here, we finally calculate the zerobias transmission curves of the HS FeN
Based on DFT calculation in combination with NEGF technique, we investigate the SCO behavior and coherent transport properties of a sixcoordinate FeN
This work was partially supported by the National Key Research & Development Program of China (No.2016YFA0200600) and the National Natural Science Foundation of China (No.21873088 and No.11634011). Computational resources are provided by Chinese Academy Sciences, Shanghai and University of Science and Technology Supercomputer Centers.
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b. 安徽建筑大学材料与化工学院，合肥 230601;
c. 中国科学技术大学合肥微尺度物质科学国家研究中心，合肥 230026