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1.
The molecular effect in the ionization of inner shell electrons of aluminum atoms by energetic H+2 molecules has been calculated. We distinguish between the molecular effect in Al and Al2O3. We conclude that in the case of Al the protons of the cluster have a definite orientation but in the case of Al2O3 the orientation is at random. 相似文献
2.
Mahdi Rezaei-Sameti 《Physica B: Condensed Matter》2012,407(1):22-26
In this work, an armchair model of the (4,4) boron phosphide nanotubes (BPNTs) with a 1-nm length and consisting of 32 B and 32 P atoms is considered to study the influence of doping three atoms of aluminum in sites of boron (B3AlPNTs) and three atoms of nitrogen in sites of phosphors (BP3NNTs) on the electrostatic structure properties. The mouths of nanotubes are capped by hydrogen atoms in order to saturate the dangling bonds of the boundaries and to decrease the calculation time. The structures of BPNTs, B3AlPNTs and BP3NNTs are optimized by performing the level of density functional theory (DFT) using 6-31G? basis set. The optimized structures are used for calculating the chemical shielding (CS) tensors and nuclear magnetic resonance parameters such as isotropic chemical shielding (CSI) and anisotropic chemical shielding (CSA). The results reveal that in both models of B3AlPNTs and BP3NNTs by doping N atoms the chemical shielding parameters of P and B atoms, which are directly connected to the Al and N atoms decreased and the other sites significantly changed. 相似文献
3.
N.S. Golosov A.M. Tolstik L.Ya. Pudan 《Journal of Physics and Chemistry of Solids》1976,37(3):273-277
On the basis of the general theory developed with the account of a four-particle correlation of atoms in the tetrahedron cluster sites the atomic ordering is considered in the Fe-Al system with 0–50 at % Al. The calculated equilibrium diagram of the phases Fe3Al(DO3), FeAl(B2) and short-range order phases α(A2) are in agreement with the diagram proposed by Rudman. The temperature dependences of short- and long-range order parameters in the case of Fe3Al and Fe13Al3 compositions are discussed. 相似文献
4.
采用密度泛函理论中的广义梯度近似(DFT-GGA)对ConAl (n= 1–8)合金团簇进行了系统的几何、 电子结构和磁性质研究. 研究结果表明Al原子倾向于与Co原子形成最大的成键数, 即Al原子均处在团簇原子拥有最大配位数的位置上. Al掺杂后ConAl团簇的稳定性减弱, 磁性降低. 磁性降低的幅度与实验上对较大ConAlM团簇的磁性检测结果获得了很好地符合. 在所有ConAl团簇的最稳定结构中, 除Co4Al外, Al与近邻Co原子均呈现反铁磁性耦合. 相对于纯Co团簇,非磁性Al元素的掺入以及Al掺杂后Co原子整体自旋极化的减弱 是导致ConAl团簇磁性的降低主要原因.
关键词:
nAl合金团簇')" href="#">ConAl合金团簇
几何结构
磁性
自旋极化 相似文献
5.
The crystal structure, electronic structure and hydrogen site occupancy of LaNi4.5Al0.5Hy intermediate phase (y=2.0, 3.0, 4.0) have been investigated using the full-potential linearized augmented plane wave (FLAPW) method. For the first time we analyzed the interstitial site occupation of hydrogen atoms. The H atoms were found to prefer the 6m, 3f and 12n sites, while no 4h sites were occupied. A narrowed Ni-d band is found due to the lattice expansion: the total DOS at EF increases with y, which indicates that the compounds become less stable. The interaction between Al and Ni, with H plays a dominant role in the stability of LaNi4.5Al0.5Hy intermediate phase. The smaller the shift of EF towards the higher energy region, the more stable the compounds will be. Our results are compared with experimental data and discussed in the light of previous works. 相似文献
6.
建立了镁合金纯净晶界及其析出Mg17Al12相的晶界原子集团,应用实空间的递归方法计算了铝、稀土元素在晶界的偏聚能,晶界处铝、稀土原子间相互作用能和不同体系的费米能级.讨论了铝、稀土在晶界的偏聚行为,铝、稀土原子间的相互作用与有序化的关系及稀土对镁合金晶间应力腐蚀影响的物理本质.研究发现:铝、稀土原子偏聚于晶界;铝原子间相互排斥,在晶界区形成有序相Mg17Al12,稀土原子间互相吸引,形成原子团簇;稀土原子团吸引铝原子,使铝原子渗入稀土团簇中,形成稀土化合物.因此,稀土具有抑制铝在晶界形成导致应力腐蚀的阴极相Mg17Al12的作用,提高镁合金的晶间应力腐蚀抗力.
关键词:
电子理论
镁合金
应力腐蚀
稀土 相似文献
7.
Density functional theory study on LaNi4.5Al0.5 hydride phase: electronic properties and sites occupation*
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In this paper the crystal structure, electronic structure and hydrogen site occupation of LaNi4.5Al0.5Hy hydride phase (y = 5.0, 6.0) have been investigated by using full-potential linearized augmented plane wave method. The hydrogen atoms were found to prefer the 6m, 12o and 12n sites, while no 4h sites were occupied. A narrowed Ni-d band is found due to the lattice expansion, the total density of states at EF increases with y, which indicates that the compounds become less stable. The interaction between Al and Ni, H plays a dominant role in the stability of LaNi4.5Al0.5 hydride phase. The smaller the shift of EF towards the higher energy region, the more stable the compounds will be. The obtained results are compared with experimental data and discussed in the light of previous works. 相似文献
8.
《Journal of Physics and Chemistry of Solids》2014,75(4):528-534
The geometries, stabilities, and magnetic properties of PdnAl (n=1–8) neutral clusters are studied using density functional theory with generalized gradient approximation. The growth pattern for different sized PdnAl (n=1–8) clusters is Al-substituted Pdn+1 clusters and it keeps the similar framework of the most stable Pdn+1 clusters except n=6 and 8. Al atoms in the ground state PdnAl isomers tend to occupy the most highly coordinated position. The analysis of stabilities shows that doping an Al atom can enhance the stabilities of the host Pd clusters and the magic number characteristic of Pd4 cluster cannot be changed, the Pd3Al cluster has a higher stability. Charges are transferred from Al atom to Pd atoms in all PdnAl clusters, so the Al atom is the electron donor, and Pd atoms are the electron accepters. Doping an Al atom decreases the average atomic magnetic moments of the host Pd clusters. 相似文献
9.
C. H. Yao S. F. Zhao J. R. Li Y. W. Mu J. G. Wan M. Han G. H. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,57(2):197-205
The lowest-energy geometries and electronic-structure properties have been
obtained for AlnHn (n=1-10) clusters within the
density-functional theory using the generalized gradient approximation for
the exchange correlation potential. The resulting geometries show that the
hydrogen atoms tend to occupy outside positions and no hollow positions are
found. The subunit Aln of AlnHn (n=1-5) have little
distortion, in comparison with corresponding pure Aln cluster, whereas
the subunit Aln have large distortion from n=6. The stability has been
investigated by analyzing the binding energy per atom and the second
difference in energy, indicating that Al8H8 exhibit higher
stability than others. The bonding property has been analyzed by calculating
the Mulliken charges and Al–H distances. The calculated energy gap between
the highest occupied molecular orbital and the lowest unoccupied molecular
orbital (HOMO-LUMO), the vertical ionization potential, and the vertical
electron affinity also confirm that Al8H8 is a stable cluster. The
density of states (DOS) shows that AlnHn exhibit changes from
molecular-like (Al1H1) to band-like structure (Al10H10)
as n increases. 相似文献
10.
Hongzhi Fu Feng Peng Tao Gao Xiangdong Yang 《Journal of Physics and Chemistry of Solids》2007,68(8):1598-1602
The electronic structures of the ternary (Hume-Rothery) L21-phase compound AlCo2Ti are calculated by first-principles using full potential linearized augmented plane wave (FLAPW) method with the generalized gradient approximation (GGA). The ab initio results are analyzed with a simplified model for Al-based compounds containing transition metal (TM) atoms. The results show that the total DOS depends strongly on the positions of TM atoms, and the TM d DOS plays a crucial role in hybridization with other element valence electrons. However, the Al 3s states are repelled far away from the Fermi energy in studied sample, and the Al 3d states are far more extended-like in the character than the d states. Furthermore, the total DOSs are modulated by Al 3p states and the Al 3p states are more sensitive than d states to change in the electronic interactions. Then, the Al 3p is also important for the ternary stability of the intermetallic compound. The Co-Ti interaction becomes stronger by the doping element Zr in the Al4Co8Ti3Zr structure. Especially, the doping Al4Co8Ti3Zr alloy has a larger value DOS at the Fermi level and makes the total DOS gap smaller than the AlCo2Ti. 相似文献
11.
Ling Guo 《Journal of nanoparticle research》2011,13(5):2029-2039
The chemisorptions of hydrogen on aluminum arsenide clusters are studied with density functional theory (DFT). The on-top
site is identified to be the most favorable chemisorptions site for hydrogen. And the Al-top site is the preferred one in
the most cases for one hydrogen adsorption in (AlAs)
n
(n = 2, 5, 6, 8–15) clusters. Top on the neighboring Al and As atoms ground-state structures are found for two hydrogen adsorption
on (AlAs)
n
except for (AlAs)2 cluster. The Al–As bond lengths decrease generally as the size of the cluster increases. And there is a slight increase in
the mean Al–As bond lengths after H adsorption on the lowest-energy sites of the most AlAs clusters. In general, the binding
energy of H and 2H are both found to decrease with an increase in the cluster size. And the result shows that large binding
energies (BE) of a single hydrogen atom on small AlAs clusters and large highest occupied and lowest unoccupied molecular-orbital
gaps for (AlAs)H and (AlAs)3H make these species behaving like magic clusters. Calculations on two hydrogen atoms on (AlAs)
n
clusters show large BE for (AlAs)
n
H2 with an odd number of n. The stability of these complexes is further studied from the fragmentation energies. (AlAs)7H2 and (AlAs)9H2 clusters are again suggested to be the stable clusters. On the other hand both the fragmentation energy and the binding energy
for (AlAs)13H are close to the lowest values. 相似文献
12.
The low-energy structures of Al8Sim (m = 1–6) have been determined by using the genetic algorithm combined with density functional theory and the Second-order Moller-Plesset perturbation theory (MP2) models. The results show that the close-packed structures are preferable in energy for Al–Si clusters and in most cases there exist a few isomers with close energies. The valence molecular orbitals, the orbital level structures and the electron localisation function (ELF) consistently demonstrate that the electronic structures of Al–Si clusters can be described by the jellium model. Al8Si4 corresponds to a magic number structure with pronounced stability and large energy gap; the 40 valence electrons form closed 1S21P61D102S21F142P6 shells. The ELF attractors also suggest weak covalent Si–Si, Si–Al and Al–Al bonding, and doping Si in aluminium clusters promotes the covalent interaction between Al atoms. 相似文献
13.
Local structure of AlSb2Te3 thin film was studied by experiments and theoretical calculations. Results show that both Sb and Te atoms are likely to be replaced by Al to form Al–Sb and Al–Te covalent bonds. At a smaller dopant concentration, Al atoms presumably incorporate into Sb2Te3 matrix by substitute Sb or Te atoms without spoiling its structural unit. Compared together with other reported data, for Al doping Sb2Te3 PCM material, optimizing Al content is a key criteria for its phase stability and electric performance. 相似文献
14.
Corinne Lacaze-Dufaure Christine Blanc Georges Mankowski Claude Mijoule 《Surface science》2007,601(6):1544-1553
A DFT study of the electronic properties of copper doped aluminum clusters and their reactivity with atomic oxygen is reported. Firstly we performed calculations for the pure Cun and Aln (n = 4, 9, 10, 13, 25 and 31) clusters and we determined their atomization energy for some frozen conformations at the B3PW91 level. The calculated work functions and M-M (M = Cu, Al) bond energies of the largest clusters are comparable with experimental data. Secondly, we focused our attention on the change of the electronic properties of the systems upon the substitution of an Al atom by a Cu one. This latter stabilizes the system as the atomization energy of the 31-atoms cluster increases of 0.31 eV when the substitution is done on the surface and of 1.18 eV when it is done inside the cluster. We show that the electronic transfer from the Al cluster to the Cu atom located at the surface is large (equal to 0.7 e−) while it is negligible when Cu is inserted in the Aln cluster. Moreover, the DOS of the Al31 and Al30Cu systems are compared. Finally, the chemisorption energies of atomic oxygen in threefold sites of the Al31, Cu31 and Al30Cu clusters are calculated and discussed. We show that the chemisorption energy of O is decreasing on the bimetallic systems compared to the pure aluminum cluster. 相似文献
15.
通过自编软件建立了铝氧化膜与基体铌界面的原子集团模型,用递归法计算了合金的原子埋置能、原子结合能等电子参数,从电子层面分析铌合金高温氧化机理.研究表明:铝通过晶界扩散偏聚在合金表面,并与氧结合生成致密的Al2O3氧化膜,阻挡氧向铌基体扩散.晶界和稀土元素能提高氧化膜与基体间的原子结合能,增加其界面的结合强度,加强氧化膜与基体铌间的黏附性.因此,通过在合金中添加稀土元素或细化合金晶粒均能提高铌合金的抗高温氧化性能. 相似文献
16.
L. A. Pérez X. López-Lozano I. L. Garzón 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,52(1-3):123-126
The adsorption of the cysteine amino acid (H–SCβH2–CαH–NH2–COOH) on the Au55 cluster is investigated through density functional theory calculations. Two isomers, with icosahedral (Ih) and chiral (C1) geometries, of the Au55 cluster are used to calculate the adsorption energy of the cysteine on different facets of these isomers. Results, only involving the S(thiolate)-Au bonding show that the higher adsorption energies are obtained when the sulfur atom is bonded to an asymmetrical bridge site at the facet containing Au atoms with the lowest coordination of the C1 cluster isomer. 相似文献
17.
Influences of Al doping on the electronic structure of Mg(0001) and dissociation properties of H2 总被引:1,自引:0,他引:1
By using the density functional theory method, we systematically study the effects of the doping of an Al atom on the electronic structures of the Mg(0001) surface and on the dissociation behaviors of H2 molecules. We find that for the Al-doped surfaces, the surface relaxation around the doping layer changes from expansion of a clean Mg(0001) surface to contraction, due to the redistribution of electrons. After doping, the work function is enlarged, and the electronic states around the Fermi energy have a major distribution around the doping layer. For the dissociation of H2 molecules, we find that the energy barrier is enlarged for the doped surfaces. In particular, when the Al atom is doped at the first layer, the energy barrier is enlarged by 0.30 eV. For different doping lengths, however, the dissociation energy barrier decreases slowly to the value on a clean Mg(0001) surface when the doping layer is far away from the top surface. Our results well describe the electronic changes after Al doping for the Mg(0001) surface, and reveal some possible mechanisms for improving the resistance to corrosion of the Mg(0001) surface by doping of Al atoms. 相似文献
18.
Effects of the doping atom (O, Al, and (Al, O)) on structural and electronic properties of the monolayer WS2 have been studied by using first-principles calculations. Results show that the covalent character of W–S bonding has been enhanced after doping. Meanwhile, W–O, Al–S and W–S bonds of (Al, O) co-doped WS2 monolayer have higher covalent character compared with O-doped and Al-doped WS2 monolayer of this work. After doping with Al (or Al, O) atoms, Fermi level moves close to the valence band and the dopant atoms produce the defect energy levels, indicating that Al doped and (Al, O) co-doped WS2 monolayer both have p-type conductivity. O-doped and (Al, O) co-doped WS2 ultrathin films was prepared on Si substrates. Results of Raman spectra show the formation of the O-doped and (Al, O) co-doped WS2 films. Moreover, compared with the pure WS2, the approximate reduction of 0.43 eV and 0.46 eV for W 4f and S 2p in binding energy after (Al, O) co-doped shows that p-type doping of (Al, O) co-doped WS2 has been verified. 相似文献
19.
The reaction mechanism of methane dehydrogenation on monomeric Rh center located on (100) γ-alumina has been theoretically investigated at the PBE0/cc-pVTZ, SDD level. The (100) face of γ-alumina support is represented by an Al8O26H28 cluster, which is cut out from the ideal crystal structure. Then, two model Rh/γ-Al2O3 catalysts, in which Rh center interacts with one oxygen or two oxygen atoms of the (100) surface of γ-Al2O3, have been compared and denoted as Rh/Al8O26H27 and Rh/Al8O26H26, respectively. Toward methane activation, the model catalyst Rh/Al8O26H27 exhibits better performance than Rh/Al8O26H26. For the first CH bond cleavage of methane, the lowering of activation barriers on Rh/Al8O26H27 is mainly caused by lower substrate activation strain ΔE≠strain[substr], which is from substrate equilibrium geometry to the geometry it adopts in the TS, in comparison with that on Rh/Al8O26H26. These results are in qualitative agreement with the experimental results, where the partially reduced Rh+ is one of the active sites for methane dissociation. 相似文献
20.
The reaction mechanisms between Al and Fe3O4 powders were investigated. Differential thermal analysis revealed that a two-step displacement reaction between Al and Fe3O4 took place during sintering. Initially, the Fe3O4 was converted to amorphous FeO at ~720°C and some of the Al was oxidized to amorphous Al2O3. In the final stage, when the temperature reached ~840°C, crystalline Al2O3 particles were produced in the molten Al–Fe liquid. The effects of cooling rate on the microstructures were studied. When the Al–Fe liquid was furnace-cooled to room temperature, proeutectic Al3Fe plates, plate-like divorced eutectic Al3Fe and Al2O3 particles were in situ formed in the Al(Fe) matrix. While quenching from 700°C, nanometer-sized Al dendrites and Al–Al6Fe eutectic lamellae were produced in the Al matrix. However, when it was rapidly quenched from 900°C, the size of the proeutectic Al3Fe phases was further reduced and Al6Fe nanorods were found in the Al–Al6Fe eutectics. A model was proposed to describe the transformation of the Al–Fe intermetallics during solidification. 相似文献