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[交流] 【求助】castep 空带设置已有2人参与

请问在castep中electronic options这一块中有一个empty bands选项,这个选项是什么意思啊?它对计算有什么影响?比如我做BiFeO3体系，依据什么设置empty bands的大小？谢谢了。

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1楼 2009-10-16 10:44:33

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引用回帖:

Originally posted by aylayl08 at 2009-10-16 16:09:53:
我记得在MS4.4里，空带数默认设为20%，具体情况不清楚，关注一下

刚从vasp的说明书中看到了关于nband的一些有意义的信息。具体内容如下：
In iterative matrix-diagonalization schemes eigenvectors close to the top of the calculated number of vectors converge much slower than the lowest eigenvectors. This might result in a significant performance loss if not enough empty bands are included in the calculation.
Therefore we recommend to set NBANDS to NELECT/2 + NIONS/2. This setting is safe in most cases. In some cases, it is also possible to decrease the number of additional bands to NIONS/4 for large systems without performance loss, but on the other hand transition metals do require a much larger number of empty bands (up to 2*NIONS).
To check this parameter perform several calculations for a fixed potential with an increasing number of bands (e.g. starting from NELECT/2 + NIONS/2). An accuracy of 10−6 should be obtained in 10-15 iterations. Mind that the RMM-DIIS scheme is more sensible to the number of bands than the default CG algorithm.