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VASP+EAM的Mg合金层错能计算+文献综述

时间:2017-12-06 21:28来源:毕业论文
重点通过VASP、EAM计算得到其层错能,并比较这两种方法的计算结果,分析差异原因,通过三种不同方法计算镁未掺杂、掺杂时的层错能,这些方法分别为基于赝势平面波基组的密度泛函程
摘要目前通过三种不同方法计算镁未掺杂、掺杂时的层错能,这些方法分别为基于赝势平面波基组的密度泛函程序VASP计算法,嵌入原子法EAM,堆垛层错能热力学模型法。由于热力学模型法需实验测量其有效层错能值,本课题只作该方法的相应介绍,重点通过VASP、EAM计算得到其层错能,并比较这两种方法的计算结果,分析差异原因。
使用VASP程序时,用户需设置KPOINTS、INCAR、POSCAR、POTCAR文件以及晶格常数优化脚本,其中INCAR、KPOINTS文件经调试后得到,而POTCAR文件可从数据库中调用,主要设置POSCAR文件。POSCAR文件内容为确定三个基矢坐标、晶胞内不同种类原子对应的原子数目及其坐标。晶格常数优化脚本将晶格常数设为一定范围内的变量,计算不同晶格常数所对应的晶胞能量后得到一系列值,取最低能量对应的晶格常数为优化后的晶格常数。用户应首先计算常态晶胞能量,然后添加层错面计算层错态晶胞能量,两者相减即为该晶胞对应的层错能,用层错能比层错面面积表示单位面积层错能。16255
嵌入原子法认为晶体中的每个原子可以视为镶嵌在由其它原子组成的基体里的一个“杂质”,单个原子能量为其嵌入能与电子间的静电相互作用势之和,晶体的总能量可以表示为所有单个原子能量之和。嵌入能仅与其他原子在该原子所在处产生的背景电子密度有关,电相互作用势与原子间距有关。根据理论研究,h.c.p.金属的原子电子密度及相互作用势可由材料的晶格常数,平衡态原子体积,结合能,单空位形成能,体弹性模量和剪切模量计算得到。
堆垛层错能热力学模型法着眼于组分含量对堆垛层错能的影响。在两平行局部位错的特殊情况中,有效堆垛层错能与理想堆垛层错能,剪切模量,泊松比,堆垛层错面法线方向上的应变有关。我们通过实验测量材料的有效层错能,进而得到其理想层错能值,随后改变合金元素的掺杂率得到一系列理想层错能值,从而确定理想层错能与合金元素掺杂率的关系式。
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关键词  堆垛层错能  VASP  EAM  热力学模型
毕业设计说明书(论文)外文摘要
Title     Calculation of Magnesium Stacking-Fault Energy       
Abstract
Currently stacking fault energies of un-doped and doped magnesium are calculated by three methods, which are respectively the program VASP based on the density functional theory of pseudo-potential plane waves basis set, the embedded atom method EAM and the thermodynamic model for stacking fault energies. Because the thermodynamic model needs to obtain the effective stacking fault energy of the material, this project only presents the corresponding introduction of it, and mainly uses VASP and EAM to calculate the stacking fault energy and compare the results obtained from these two methods, then analyze the reason for the disparity.
When operating the program VASP, users need to configure INCAR, KPOINTS, POSCAR, POTCAR files and a script for the optimization of the lattice constant, where INCAR, KPOINTS, POTCAR files are usually called from the data base, we mainly configure POTCAR file. The content of POSCAR file is about the coordinates of three basis vectors, the number of atoms per species and their coordinates. The script for the optimization of the lattice constant set the lattice constant as a variable and obtain a series of cell energy values with corresponding lattice constants through computation, then treat the lattice constant with the lowest cell energy as the optimized one. Users should calculate the normal cell energy, then add stacking fault planes to calculate the faulted cell energy. The difference value of them is the stacking fault energy of the cell, and get the stacking fault energy per unit area by piding the stacking fault energy by the area of the stacking fault plane. VASP+EAM的Mg合金层错能计算+文献综述:http://www.lwfree.cn/cailiao/20171206/17525.html
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