| 查看: 1970 | 回复: 34 | |||
| 当前只显示满足指定条件的回帖，点击这里查看本话题的所有回帖 | |||
[交流]
六角晶系结构参数的优化问题
|
|||
| 由于初学VASP，不知道如何优化六角晶系结构参数，看侯老师讲义上的内容，还是不明白。真诚地希望各位高手们帮忙指教，谢谢！！ |
回复此楼» 猜你喜欢
售SCI一区文章，我:8.O.55.1.O.54,科目齐全,可伽急
已经有5人回复
-
售SCI文章，我:8O5.5.1.O.54,科目齐全,可+急
已经有3人回复
-
售SCI一区T0P文章，我:8O.55.1.O.54,科目全,可伽急
已经有3人回复
-
售SCI文章，我:8O5.5.1.O.54,科目齐全,可+急
已经有3人回复
-
售SCI一区T0P文章，我:8O.55.1.O.54,科目全,可伽急
已经有3人回复
-
售SCI一区文章，我:8.O.551.O.5.4,科目全,可伽急
已经有4人回复
-
售SCI一区T0P文章，我:8.O.55.1.O.54,科目齐全,可+急
已经有3人回复
-
售SCI-T0P文章，我:8O.5.5.1.O.54,科目齐全,可+急
已经有4人回复
-
售SCI一区T0P文章，我:8O.55.1.O.5.4,科目齐全,可+急
已经有6人回复
-
售SCI文章，我:8O.5.5.1O.54,科目全,可十急
已经有4人回复
» 本主题相关价值贴推荐，对您同样有帮助:
- 关于根据电子衍射图样求六角晶系轴长比c/a的问题
已经有3人回复
- 结构优化参数设置
已经有6人回复
- 结构优化中问题
已经有6人回复
- VASP优化结构遇到的问题。
已经有9人回复
- 结构优化中遇到的问题
已经有9人回复
- 【求助】VASP怎么做晶格参数的结构优化
已经有17人回复
- 【求助】六角晶系中[11-20]与(11-20)为什么不垂直？
已经有11人回复
- 【求助】一个结构优化的问题
已经有11人回复
- 【求助】侯老师的vasp入门的晶格优化部分没看懂，问一下
已经有25人回复
- 【求助成功】计算能带结构时出现错误，请教
已经有19人回复
- 【求助】利用侯博的方法优化结构出现的问题（求验证）
已经有11人回复
- 【请教】请教一个六方晶系的问题
已经有12人回复
- 【求助】siesta中关于几何结构优化的问题【完结】
已经有17人回复
★ ★ ★ ★ ★
奋力拼搏(金币+1): 谢谢参与
WDD880227: 金币+1, 多谢指教 2012-08-17 08:43:59
奋力拼搏: 金币+3, 非常感谢您的回复！！谢谢！1 2012-08-19 17:39:42
奋力拼搏(金币+1): 谢谢参与
WDD880227: 金币+1, 多谢指教 2012-08-17 08:43:59
奋力拼搏: 金币+3, 非常感谢您的回复！！谢谢！1 2012-08-19 17:39:42
|
看你对精度有啥要求，如果要求不是太高的话，直接设置ISIF=3，弛豫就可，最后的结构就是优化后的结果 如果要求精度较高，就得做V-E曲线，vasp manual上的： Accurate bulk relaxations with internal parameters (one) The general message is: whenever possible avoid volume relaxation with the default energy cutoff. Either increase the basis set by setting ENCUT manually in the INCAR file, or use method two suggested below, which avoids doing volume relaxations at all. If volume relaxations are the only possible and feasible option please use the following step by step procedure (which minimizes errors to a minimum): Relax from starting structure (ISMEAR should be 0 or 1, see section 6.38). Start a second relaxation from previous CONTCAR file (re-relaxation). As a final step perform one more energy calculation with the tetrahedron method switched on (i.e. ISMEAR=-5), to get very accurate and unambiguous energies (no relaxation for the final run). The final calculation should be done with PREC=High, to get very accurate energies. A few things should be remarked here: Never take the energy obtained at the end of a relaxation run, if you allow for cell shape relaxations (the final basis set might not be isotropic). Instead perform one additional static run at the end. The relaxation will give a structure which is correct to first order, the final error in the energy of step 3 is of second order (with respect to the structural errors). If you take the energy directly from the relaxation run, errors are usually significantly larger. Another important point is that the most accurate results for the relaxation will be obtained if the starting cell parameters are very close to the final cell parameters. If different runs yield different results, then the run which started from the configuration which was closest to the relaxed structure, is the most reliable one. We strongly recommend to do any volume (and to lesser extend cell shape) relaxation with an increased basis set. ENCUT=1.3 default cutoff is reasonable accurate in most cases. PREC=High does also increase the energy cutoff by a factor 1.25. At an increased cutoff the Pulay stress correction are usually not required. Accurate bulk relaxations with internal parameters (two) It is possible to avoid volume relaxation in many cases: The method we have used quite often in the past, is to relax the structure (cell shape and internal parameters) for a set of fixed volumes (ISIF=4). The final equilibrium volume and the groundstate energy can be obtained by a fit to an equation of state. The reason why this method is better than volume relaxation is that the Pulay stress is almost isotropic, and thus adds only a constant value to the diagonal elements of the stress tensor. Therefore, the relaxation for a fixed volume will give an almost correct structure. The outline for such a calculation is almost the same as in the previous section. But in this case, one has to do the calculations for a set of fixed volumes. At first sight this seems to be much more expensive than method number one (outlined in the previous section). But in many cases the additional costs are only small, because the internal parameters do not change very much from volume to volume. Select one volume and relax from starting structure keeping the volume fixed (ISIF=4 see sec. 6.24; ISMEAR=0 or 1, see section 6.38). Start a second relaxation from previous CONTCAR file (if the initial cell shape was reasonable this step can be skipped, if the cell shape is kept fixed, you never have run VASP twice). As a final step perform one more energy calculation with the tetrahedron method switched on (ISMEAR=-5), to get very accurate unambiguous energies (no relaxation for the final run). The method has also other advantages, for instance the bulk modulus is readily available. We have found in the past that this method can be used safely with the default cutoff. (see also section 9.2). |
35楼2012-08-16 23:16:05
9楼2012-08-13 07:10:47
