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1、To set up a work function calculation Either import a structure of the bulk material from a pre-existing file or construct a new structure using the sketching and crystal building tools in the Materials Visualizer. Geometry optimize the bulk structure using CASTEP. Cleave the required crystallograph
2、ic surface using the Cleave Surface dialog so that the thickness provides a meaningful representation of the bulk. Build a vacuum slab using the Build Vacuum Slab Crystal dialog, you should ensure that the distance between the surface and the end of the vacuum is great enough that there can be no po
3、tential interactions between the surface and the next layer. Choose Modules | CASTEP | Calculation from the menu bar. Select the Setup tab. Choose the Geometry Optimization task. Fix Cartesian atomic positions of some atoms in the middle of the slab using the Edit Constraints dialog, accessible from
4、 the Modify menu. Select either the LDA or GGA Functional from the dropdown list (see the theory section for more information on functionals). Click the Run button. Follow the steps in the Displaying the averaged potential chart for work function calculations topic.,功函数计算 1。输入一个软件自带的已知体结构，或用 sketchi
5、ng 和 crystal building 工具建立一个新结构。 Geometry optimize the bulk structure using CASTEP. Cleave the required crystallographic surface using the Cleave Surface dialog so that the thickness provides a meaningful representation of the bulk. Build a vacuum slab using the Build Vacuum Slab Crystal dialog, you
6、 should ensure that the distance between the surface and the end of the vacuum is great enough that there can be no potential interactions between the surface and the next layer. Choose Modules | CASTEP | Calculation from the menu bar. Select the Setup tab. Choose the Geometry Optimization task. Fix
7、 Cartesian atomic positions of some atoms in the middle of the slab using the Edit Constraints dialog, accessible from the Modify menu. Select either the LDA or GGA Functional from the dropdown list (see the theory section for more information on functionals). Click the Run button. Follow the steps
8、in the Displaying the averaged potential chart for work function calculations topic.,功函数的计算,一、热电子发射和功函数,A：常数 W：功函数(或脱出功)，将固体中的电子移至其表面、并处于自由状态所需的最低能量。,热电子发射的电流密度为, Richardson定律,V0：真空能级（势阱的深度）,W : 26 eV。此值与晶体方向有关，变化范围约1eV。,二. 功函数的计算模型,构造如右图所示的2维无限阵列，计算的材料就是图中的板，板间是真空层。用CASTEP计算此体系的EF 和板间的静电势分布(r)，在平行表
9、面的方向上对静电势取平均，从而在板间得到V0 ，进而得到W。 由于功函数W的数值依赖于晶体结构和晶面取向，所以计算时需先优化体材料的晶体结构，再绘制2维阵列。可以优化块层表面和块层内部的原子坐标，也可以不优化。通过这些选择，人们可以研究表面弛豫对功,0.8-1 nm,slab,函数的影响。一般建议利用constraints，固定块层中间的原子，使其保留体材料的结构。,对块层进行计算时，为了反映体材料的性质，块层的厚度至少在0.8-1nm。为了避免块层相邻表面间静电势的相互干扰，并使静电势达到其渐进值，真空层的厚度至少为3nm。,计算思路：对一定的晶体结构，求出总电子能量最低的电荷密度分布(x)，再根据右式计算位置x处的电势(x)。,显示成球棒结构,转化为原胞,性质不选,优化成功,Save project, close all 打开优化后的W,恢复为晶胞，准备切面,其它不变，改厚度至9埃,切出一个厚度约9埃的表面。足够厚，表示体性质。Save project，工作窗口仅保留表面结构。,30,斜拉鼠标，选中中间的一些原子。现在弛豫表面一层的原子。严格计算应该slab取厚,检查后，恢复按照Element显示颜色,w4d4,绿色，表层原子。,另一表层，两层等价，两边对称。找不对称的。,W 4.39(111) 4.56(001),不优化,