基于三维弹性问题的多极边界元法核函数分解

多极边界元法已经成功地应用于大规模工程计算中.得到并且证明了基于三维弹性问题的多极边界元法核函数分解的定理(定理1),完善了多击边界元法的数学理论.     

基于甲胺客体调制的混价态甲酸铁框架的构筑与磁电行为研究

N-型亚铁磁体可以在场冷时呈现负磁化行为，但在1 T强场场冷时依然能够保持负磁化行为的化合物却很罕见.本工作以CH₃NH₃⁺为客体阳离子，成功构筑了一例红砷镍矿（4⁹.6⁶）（4¹².6³）结构的混价态甲酸铁化合物[CH₃NH₃]_n[Fe^IIIFe^II（HCO₂）₆]_n（1），在1 T强场下呈现负磁化行为.1中甲酸根采用反，反模式连接Fe^II和Fe^III形成三维阴离子框架，八面体配位构型的Fe^II和Fe^III分别处于（4⁹.6⁶）和（4¹².6³）节点，而CH₃NH₃⁺则填充在框架空隙中平衡电荷.量热、介电和单晶X-射线衍射测试结果表明，1中存在由CH₃NH₃⁺无序-有序转变诱导的结构相变并伴随介电弛豫.磁性研究表明Fe^II和Fe^III之间存在较强的反铁磁耦合，但在冷却过程中Fe^II和Fe^III构成的亚晶格磁有序程度存在较大差异，且具有较小自旋的Fe^II磁矩先于Fe^III磁矩有序且平行于外加磁场，导致温度进一步降低时1呈现出负磁化行为，这表明1是一例罕见的N-型亚铁磁体.此外，1在1 T外加冷却场中依然能保持负磁化行为，表明1中存在较强的磁各向异性.值得注意的是，在100 Oe外场下冷却到17 K后，1呈现出正场调制的磁极翻转行为.进一步研究表明，1的场冷磁滞回线呈现不对称形状，并向冷却场方向发生偏转，其有效矫顽力（H_C^eff=（H⁺-H^-）/2）和交换偏置场（H_EB=（H⁺+H^-）/2）分别为21716 Oe和3322 Oe.总之，本研究表明客体分子尺寸和形状能够有效调控红砷镍矿结构中Fe^II的磁各向异性，从而实现较高的磁极翻转场、矫顽力和交换偏置场.     

二维位势问题的快速多极展开式

快速多极边界元法已经成功地应用于大规模二维三维弹性静力学问题中,有效地减少了计算时间和存储需求.将基于Taylor展式地快速多极边界元法应用到二维位势问题中,提出了二维位势问题地快速多极边界元格式,建立了二维位势问题的快速多极展开式.     

Structural optimization of Au–Pd bimetallic nanoparticles with improved particle swarm optimization method

Due to the dependence of the chemical and physical properties of the bimetallic nanoparticles(NPs) on their structures,a fundamental understanding of their structural characteristics is crucial for their syntheses and wide applications. In this article, a systematical atomic-level investigation of Au–Pd bimetallic NPs is conducted by using the improved particle swarm optimization(IPSO) with quantum correction Sutton–Chen potentials(Q-SC) at different Au/Pd ratios and different sizes. In the IPSO, the simulated annealing is introduced into the classical particle swarm optimization(PSO) to improve the effectiveness and reliability. In addition, the influences of initial structure, particle size and composition on structural stability and structural features are also studied. The simulation results reveal that the initial structures have little effects on the stable structures, but influence the converging rate greatly, and the convergence rate of the mixing initial structure is clearly faster than those of the core-shell and phase structures. We find that the Au–Pd NPs prefer the structures with Au-rich in the outer layers while Pd-rich in the inner ones. Especially, when the Au/Pd ratio is 6:4, the structure of the nanoparticle(NP) presents a standardized Pd_(core) Au_(shell) structure.