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vasp计算问题小结

本文转载自博主 一个人就是一个叠加态  ,有部分删减修改,文中对相关概念方法做了详细的总结,留坑待填… 1. 第一原理计算的一些心得 1. 第一性原理 第一性原理其实是包括基于密度泛函的从头算和基于Hartree-Fock自洽计算的从头算,前者以电子密度作为基本变量(霍亨伯格-科洪定理),通过求解Kohn-Sham方程,迭代自洽得到体系的基态电子密度,然后求体系的基态性质;后者则通过自洽求解Hartree-Fock方程,获得体系的波函数,求基态性质 2. 交换关联泛函 DFT中密度泛函的Functional, 包括LDA,GGA,杂化泛函等等 一般LDA为局域密度近似,在空间某点用均匀电子气密度作为交换关联泛函的唯一变量,多数为参数化的CA-PZ方案; GGA为广义梯度近似,不仅将电子密度作为交换关联泛函的变量,也考虑了密度的梯度为变量,包括PBE,PW,RPBE等方案,BLYP泛函也属于GGA; 还有一些杂化泛函,B3LYP等 3. 赝势 在处理计算体系中原子的电子态时,有两种方法,一种是考虑所有电子,叫做全电子法,比如WIEN2K中的FLAPW方法(线性缀加平面波);此外还有一种方法是只考虑价电子,而把芯电子和原子核构成离子实放在一起考虑,即赝势法,一般赝势法是选取一个截断半径,截断半径以内,波函数变化较平滑,和真实的不同,截断半径以外则和真实情况相同,而且赝势法得到的能量本征值和全电子法应该相同。 赝势包括模守恒和超软,模守恒较硬,一般需要较大的截断能,超软势则可以用较小的截断能即可。另外,模守恒势的散射特性和全电子相同,因此一般红外,拉曼等光谱的计算需要用模守恒势。 赝势的测试标准应是赝势与全电子法计算结果的匹配度 ,而不是赝势与实验结果的匹配度,因为和实验结果的匹配可能是偶然的。 4. 收敛测试 Ecut,也就是截断能,一般情况下,总能相对于不同Ecut做计算,当Ecut增大时总能变化不明显了即可;然而,在需要考虑体系应力时,还需对应力进行收敛测试,而且应力相对于Ecut的收敛要比总能更为苛刻,也就是某个截断能下总能已经收敛了,但应力未必收敛。 K-point,即K网格,一般金属需要较大的K网格,采用超晶胞时可以选用相对较小的K网格,但实际上还是要经过测试。 5. 磁性 一般何时考虑自旋
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VASP 的 PDOS 计算及 P4vasp 的后处理

使用的软件:VASP, Origin, SshClient, p4vasp The LDOS , or local density of states, is the the density of state at a particular site of a crystal with some asymetry. For example: A slab will have a different band structure on the surface than in the bulk region. The PDOS is a projected density of states. In the context of VASP this means site-projected DOS, where the information about the different contributions of the different orbitals is computed. You then know which states (spd) contribute at which energy. You have to select the proper LORBIT tag in the INCAR file (e.g. LORBIT=11) to get the spd decomposed DOSCAR file output. The formatting is explained in the DOSCAR file link provided. 一 PDOS 计算 在完成结构优化和静态计算后,拷贝 scf 文件夹为 pdos cp -rf scf pdos 编辑 pdos 文件夹下 INCAR INCAR SYSTEM=x ISTART=1 # change ICHARG=11 # add LORBIT=11 # add ENCUT=350 EDIFF=1E-5 IBRION=2 POTIM=0.25 NSW=0 EDIFFG=-1E-2 ISMEAR=0 SIGMA=0.05 PREC=ACCURATE ISIF=2 NPAR=4 #LWAVE=FALSE #LCHARG=FALSE LREAL=Aut

Whitesides' Group: Writing a Paper

By George M. Whitesides 1. What is a Scientific Paper ? A paper is an organized description of hypotheses, date and conclusions, intended to instruct the reader. Papers are a central part of research . If you research does not generate papers, it might just as well not have been done. “Interesting and unpublished” is equivalent to “non-existent”. Realize that your objective in research is to formulate and test hypotheses, to draw conclusions from these tests, and to teach these conclusions to others. Your objective is not to “collect data”. A paper is not just an archival device for storing a completed program; it is also a structure for planning your research in progress. If you clearly unstand the purpose and form of a paper, it can be immensely useful to you in organizing and conducting ypur research. A good outline for the paper is also a good plan for the research program. You should write and rewrite these plans/outlines throughout the course of the research. At the