ab initio Studies on Molecular Conductor (BEDSe-TTF)2[Fe(CN)5NO]

In this paper the ab initio study using pseudopotential plane wave method with the local spin density functional approximation is presented for the molecular conductor (BEDSe-TTF)₂[Fe(CN)₅NO]. The mean electronic density distributions are obtained, and we find that the extended π orbital of the selenium does not affect the properties of material as assumed in other papers and the "side-by-side" type S...S interaction is the primary interaction between donors. From band structure calculations we analyze the influence of the NO groups on the electronic structure and magnetic properties of molecule. It is shown that the itinerant electrons important to electronic properties in these types of hybrids are delocalized electrons contributed by NO groups, instead of by the 3d electrons of Fe. Additionally, we have found that the localized magnetic moment is also contributed by the NO groups in this molecular conductor. From total energy calculations the molecular structure with the lowest energy is found due to the interaction between split spins, and the particular positions of the NO groups are obtained.     

ab initio Study of Electronic Structure and Magnetic Properties of a Novel Two-Dimensional Copper(II)-Radical Complex [Cu(NTTmPy)2(N3)2]n

The full-potential linearized augmented plane wave (FPLAPW) method with the generalized gradient approximations (GGA) is applied to study the compound [Cu(NTTmPy)₂(N₃)₂]_n (NITmPy=2-(3'-Pyridy1)-4, 4, 5, 5-tetramethylimidazolin-1-oxy1-3-oxide). The total density of states (DOS) and the partial density of states (pDOS) are calculated to explain the electronic and the magnetic properties of [Cu(NTTmPy)₂(N₃)₂]_n. It is found that [Cu(NTTmPy)₂(N₃)₂]_n is stable in the ferromagnetic state and the magnetic moment of the molecule mainly comes from the Cu atoms (0.518 μ_B) with partial contribution from N, O atoms of nitronyl nitroxide radicals. There exist orbital hybridization between 3d orbital of Cu and p orbitals of N(1) (from pyridyl rings of the NITmPy ligands) and N(4) (from azido group) and the weak direct exchange interactions between Cu and O atoms of nitronyl nitroxides. In addition, the bridging carbon atom (C(6)) carries a significant negative spin density (-0.019μ_B). The sign alternation of the magnetic moment along the pyridyl ring is obtained, which agrees with experiments.     

Ab initio study of magnetic property of BEST2 [Fe(CN)5NO] charge-transfer salt

By means of ab initio method of the full potential linearized augmented-plane-wave, electronic band structure and its magnetic property for a charge transfer compound of bis (ethylenediselena)-tetrathiafulvalene(BEST) with [Fe(CN)₅NO] anions are investigated for the first time, where the exchange-correlation effects of electrons are accounted in the generalized gradient approximation. The spin density of states and the magnetic moment are analyzed in detail. It is found that there exists a new antiferromagnetic coupling in the organic donors because of alternating spin population in the organic donors. Besides the localized 3d electrons of Fe in [Fe(CN)₅NO] anion, the ligand nitric oxide and the cyanogen radical play important roles in the magnetic properties of the system. Our results are in good agreement with the experimental observations.     

Photoinduced transition of [Fe(CN)5NO] nitroprusside anions to metastable states and electron localization in the (BEDT-TTF)4K[Fe(CN)5NO]2 molecular metal

The crystals of (BEDT-TTF)₄K[Fe(CN)₅NO]₂, representing a quasi-two-dimensional organic metal with conducting layers of bis(ethylenedithio)tetrathiofulvalene (BEDT-TTF) and nonconducting layers containing pho-tochromic nitroprusside anions [Fe(CN)₅NO]^2?, were studied by the method of electron spin resonance. Illuminated by light with a wavelength of 514.5 nm, the organic metal crystals feature the formation of localized paramagnetic centers in the conducting cation layers of BEDT-TTF. The phenomenon of electron localization in the BEDT-TTF layers is related to the light-induced formation of long-lived metastable states of nitroprusside anions.     

TGA-DTA and infrared spectra of potassium nitroprusside dihydrate: K2[Fe(CN)5NO] · 2H2O

The infrared spectra of the polycrystalline compound of the title, both normal and with different degrees of deuteration, at temperatures ranging between ca. 80 K and room temperature, were obtained. As no structural data are currently available for the compound, the assignment of the observed bands was accomplished supposing the existence of two different nitroprusside ions and, consequently, four inequivalent water molecules in the asymmetric unit, as suggested by the two bands found in the NO stretching region and the complexity observed in the water regions. TGA-DTA data are also presented and discussed.     

High‐pressure studies of the micro‐Raman spectra of iron cyanide complexes: Prussian blue (Fe4[Fe(CN)6]3), potassium ferricyanide (K3[Fe(CN)6]), and sodium nitroprusside (Na2[Fe(CN)5(NO)]·2H2O)

The pressure dependences of the peaks observed in the micro‐Raman spectra of Prussian blue (Fe₄[Fe(CN)₆]₃), potassium ferricyanide (K₃[Fe(CN)₆]), and sodium nitroprusside (Na₂[Fe(CN)₅(NO)]·2H₂O) have been measured up to 5.0 GPa. The vibrational modes of Prussian blue appearing at 201 and 365 cm⁻¹ show negative dν/dP values and Grüneisen parameters and are assigned to the transverse bending modes of the Fe C N Fe linkage which can contribute to a negative thermal expansion behavior. A phase transition occurring between 2.0 and 2.8 GPa in potassium ferricyanide is shown by changes in the spectral region 150–700 cm⁻¹. In the spectra of the nitroprusside ion, there are strong interactions between the FeN stretching mode and the FeNO bending and the axial CN stretching modes. The pressure dependence of the NO stretching vibration is positive, 5.6 cm⁻¹ GPa⁻¹, in contrast to the negative behavior in the iron(II)‐meso‐tetraphenyl porphyrinate complex. Copyright © 2011 John Wiley & Sons, Ltd.     

配合物型分子导体（PyH）［Ni（dmit）2］2的能带结构及其导电性

采用EHMO紧束缚方法计算了配合物型分子导体 (PyH) [Ni(dmit) 2 ] 2 二维阴离子导电层中相邻两 [Ni(dmit) 2 ] - 0 .5 的HOMO轨道的重叠积分 ,并进行了二维能带计算 .计算结果与其单晶变温电导率测试结果一致 ,表明该配合物型分子导体为窄能隙半导体 .在能带计算基础上讨论了该类分子导体导电性与结构的关系 .分子导体的晶体结构对其能带结构和导电性能影响极大 ,分子柱的均匀化 (包括沿分子轴方向的错动尽可能小和面间距均一 )以及小的导电组元分子面间距是有利于增加分子导体的导电性的结构因素     

Mössbauer parameters of the two long-lived metastable states in Na2[Fe(CN)5NO]·2H2O single crystals

We have measured the quadrupole splitting, isomer shift and line broadening of the ground and two metastable states in Na₂[Fe(CN)₅NO]·2H₂O single crystals. Pure state II could be observed by Mössbauer spectroscopy after irradiation of state I with light in the near infrared spectral region. The difference between the two nearly infinitely long-lived electronic states is shown. A possible change of the Fe(3d, 4s, 4p) electron densities is discussed on the basis of the Mössbauer parameters and thev(FeN) andv(NO) stretching vibrations. The resulting new orbital population allows to explain the observed properties of state I. A rearrangement of the electron density due to state II would lead to a contradiction with the vibrational behaviour of the molecule. The larger line width of both metastable states could not yet be interpreted.     

2,7-二辛基[1]苯并噻吩并[3,2-b]苯并噻吩/Ni(100)的界面能级结构随薄膜厚度的演化

利用紫外光电子能谱、X射线光电子能谱以及原子力显微镜系统研究了2,7-二辛基[1] 苯并噻吩并[3,2-b]苯并噻吩(C8-BTBT)生长在单晶Ni(100)上的能级结构随着薄膜厚度的演化以及薄膜的生长方式. 发现第一层C8-BTBT平躺生长且与Ni基底发生了化学吸附反应. 从第二层起分子直立生长且呈现岛状生长模式. 这种平躺至直立的分子取向转变, 导致薄膜的能级结构在第一层与第二层间发生阶梯式的变化, 真空能级与最高占据能级同步下降. 此后能带结构随着薄膜厚度的增加逐渐向下弯曲, 功函数随着膜厚的增加而减小. 同时还发现由于直立生长的C8-BTBT其层间电导率较差导致实验中的能级未能收敛. 实验结果提示对基于Ni和C8-BTBT的自旋器件需要插入缓冲层并尽可能减少C8-BTBT的层数.     

Thermal behavior and vibrational spectra of cesium nitroprusside monohydrate,Cs2[Fe(CN)5NO].H2O

The infrared spectra of the title compound in the polycrystalline state, both normal and with different degrees of deuteration, were obtained at room and low temperatures. An infrared polarized spectrum of a monocrystalline plate was also obtained as well as the Raman spectrum of the powder. The anion and water molecule vibrational bands were assigned. The data show that the anion is located in sites of C_s symmetry and that the hydration water molecule is strongly asymmetric, forming two H-bonds of different strength. TGA-DTA data on the compound are also presented.     

Molecular beam epitaxy growth of monolayer hexagonal MnTe2 on Si(111) substrate

Monolayer MnTe₂ stabilized as 1T structure has been theoretically predicted to be a two-dimensional (2D) ferromagnetic metal and can be tuned via strain engineering. There is no naturally van der Waals (vdW) layered MnTe₂ bulk, leaving mechanical exfoliation impossible to prepare monolayer MnTe₂. Herein, by means of molecular beam epitaxy (MBE), we successfully prepared monolayer hexagonal MnTe₂ on Si(111) under Te rich condition. Sharp reflection high-energy electron diffraction (RHEED) and low-energy electron diffraction (LEED) patterns suggest the monolayer is atomically flat without surface reconstruction. The valence state of Mn⁴⁺ and the atom ratio of ([Te]:[Mn]) further confirm the MnTe₂ compound. Scanning tunneling spectroscopy (STS) shows the hexagonal MnTe₂ monolayer is a semiconductor with a large bandgap of ~2.78 eV. The valence-band maximum (VBM) locates at the Γ point, as illustrated by angle-resolved photoemission spectroscopy (ARPES), below which three hole-type bands with parabolic dispersion can be identified. The successful synthesis of monolayer MnTe₂ film provides a new platform to investigate the 2D magnetism.     

81Br NQR Study of [NH3(CH2) n NH3]CdBr4 (n = 4 and 5) and [NH3(CH2) n NH3]ZnBr4 (n = 5 and 6)

⁸¹Br NQR frequencies and differential scanning calorimetry (DSC) were measured as a function of temperature. [NH₃(CH₂)₄ NH₃]CdBr₄ (1) and [NH₃(CH₂)₅NH₃]CdBr₄ (2) showed a doublet and quartet ⁸¹Br NQR spectrum, respectively. [NH₃(CH₂)₅NH₃]ZnBr₄ (3) and [NH₃(CH₂)₆NH₃]ZnBr₄ (4) exhibited a four-line ⁸¹Br NQR spectrum. From the NQR results, it is inferred that (1) and (2) consist of infinite two-dimensional sheets of corner-sharing CdBr₆ octahedra, whereas (3) and (4) have isolated [ZnBr₄]²⁻ tetrahedra. All of the crystals except (1) showed at least one structural phase transition above 380 K.     

Mössbauer, nuclear inelastic scattering and density functional studies on the second metastable state of Na2[Fe(CN)5NO]·2H2O

The structure of the light-induced metastable state SII of Na₂[Fe(CN)₅NO]·2H₂O was investigated by transmission Mössbauer spectroscopy (TMS) in the temperature range between 85 and 135 K, nuclear inelastic scattering (NIS) at 98 K using synchrotron radiation and density functional theory (DFT) calculations. The DFT and TMS results strongly support the view that the NO group in SII takes a side-on molecular orientation and, further, is dynamically displaced from one eclipsed, via a staggered, to a second eclipsed orientation. The population conditions for generating SII are optimal for measurements by TMS, yet they are modest for accumulating NIS spectra. Optimization of population conditions for NIS measurements is discussed and new NIS experiments on SII are proposed.     

Light-induced structural changes in sodiumnitroprusside (Na2(Fe(CN)5NO)·2D2O) at 80 K

Groundstate and electronic excited state (MS_I) of deuterated sodiumnitroprusside (Na₂(Fe(CN)₅NO)·2D₂O) have been investigated by neutron diffraction as well as by optical and Mössbauer techniques. Significant structural changes occur predominantly in the O–N–Fe–C-bond. It has been shown, that the N–O bond-length is not the order parameter, as expected from other studies. We found an increase in the bond lengths Fe–N4 of 0.019(2) Å and N–O of 0.004(4) Å respectively, which is in qualitative agreement with changes determined by Raman spectroscopy and predictions based on diatomic correlations (Badger/Herschbach/Laurie). Additionally we observed a change in the Fe–C1 bond length of 0.012(3) Å in agreement with Raman meaurements.     

Possible reaction coordinates in the metastable states of sodiumnitroprusside Na2[Fe(CN)5NO]2H2O: a discussion based on neutron diffraction- and spectroscopic measurements

The metastable states of sodiumnitroprusside are extremely stable at temperatures below 200 K. It is possible to allocate structural changes measured by neutron diffraction to measured spectroscopic parameters, but the amount of the structural change is relatively small for a reaction co-ordinate as the metastable states have an extremely long lifetime. New hypotheses for related systems try to explain such a phenomena in two ways: The first way is a bending of the NO-bond in the metastable state, the second one an exchange of the oxygen and nitrogen atoms in the NO-bond (which can be regarded as an bending). As such changes would be possible also from our density functional calculations, we re-investigated our neutron diffraction data using the new models. However, our results are not compatible with one of these models. On the contrary, the neutron diffraction data show partially opposite tendencies. We compare both models with EXAFS measurements, with vibrational spectroscopic results and the data found by M?ssbauer spectroscopy. We propose a potential scheme for all three states (GS, and ) extracted from absorption and thermodynamic data to explain the electronic and energetic rearrangement, and the population dynamics. Received: 23 June 1997 / Accepted: 13 October 1997     

Ab initio study of the electronic structure of the molecule-based ferromagnet Co[N(CN)2]2

We have investigated the electronic and magnetic properties of the molecule-based magnet Co[N(CN)₂]₂ using the full potential linearized augmented plane wave (FP-LAPW) method. The relative stability of the ground state, density of states and charge distributions were examined. Total energy calculations reveals that the ferromagnetic phase is a stable ground state for Co[N(CN)₂]₂ in agreement with the previous experimental findings. It is noteworthy that we predict the Co[N(CN)₂]₂ is a ferromagnetic semiconductor with a small band gap of 0.027 eV, and the semiconductor property can be connected to the strong crystal field splitting of Co²⁺ 3d states for Co[N(CN)₂]₂. Such a molecule-based ferromagnetic semiconductor would offer a potential for semiconductor applications, therefore, an experimental confirmation of our theoretical predictions is encouraged.     

First-Principles Studies for the Electronic Structures of Diluted Magnetic Semiconductors (Ga, Fe)As

First-principles LMTO-ASA band calculations are performed for Ga1-xFexAs (x = 1, 1/4, 1/8) by assuming supercell structures. It is found that the antiferromagnetic (AFM) state is stable for x = 1/4. For x = 1/8, ferromagnetic(FM) state is more stable than AFM state, and no stable magnetic state exists for x = 1. In both the cases the magneticmoments of As and Ga atoms are parallel to those of the nearest Fe atoms due to the p-d hybridization. Further, theband structure shows rather localized Fe 3d state in the gap, and the parallel polarization is confined rather in thevicinity of Fe site.     

应变对单层二硫化钼能带影响的第一性原理研究

采用密度泛函理论框架下的第一性原理平面波赝势方法,研究了双轴拉应变下单层二硫化钼晶体的电子结构性质．本文的计算结果表明对单层二硫化钼晶体施加一个很小的应变（0．5％）时,其能带结构由直接带隙转变为间接带隙．随着应变的增加,能带仍然保持间接带隙的特征,且禁带宽度呈现线性下降的趋势．通过对单层二硫化钼晶体态密度和投影电荷密度的进一步分析,揭示了单层二硫化钼晶体能带变化的原因．     

First-Principles Studies for the Electronic Structures of Diluted Magnetic Semiconductors （Ga, Fe）As

First-principles LMTO-ASA band calculations are performed for Ga1-xFezAs (x = 1, 1/4, 1/8) by assuming supercell structures. It is found that the antiferromagnetic (AFM) state is stable for x = 1/4. For x = 1/8, ferromagnetic (FM) state is more stable than AFM state, and no stable magnetic state exists for x = 1. In both the cases the magnetic moments of As and Ga atoms are parallel to those of the nearest Fe atoms due to the p-d hybridization. Fhrther, the band structure shows rather localized Fe 3d state in the gap, and the parallel polarization is confined rather in the vicinity of Fe site.