Open QG-phy opened 3 months ago
This is because the default value of symmetry_prec
(1e-6) is too small for the cell-relaxed structure.
Setting symmetry_prec 1e-5
can this case converge with the original symmetry in 4 steps.
ok, then the question is how or when would someone know he/she should increase the value of symmetry_prec
? I mean this time the structure is too different and the discrepancy is too obvious. Besides, I get this message after the relaxation. Is there any signal that can be detected in advance?
how or when would someone know he/she should increase the value of symmetry_prec? Is there any signal that can be detected in advance?
There are some fatal failures result from an improper symmetry_prec
that produce warnings and suggest changing symmetry_prec
. For example:
Symmetry breaking during (cell-)relax is not regarded as a fatal failure, but it still produces warning in OUT.${suffix}/running_${calculation}.log
. In this case:
WARNING: Symmetry cannot be kept due to the lost of accuracy with atom position during cell-relax.
Continue cell-relax with a lower symmetry.
One should adjust (often increase) symmetry_prec
if the warning above is produced while symmetry-keeping is expected.
其实我还有一点问题。 如果是我设置的分别率要求太高。那么,对于一个结构其真实的空间群为A,对称性精度要求过高,应该是找到了A的 一个子群记作B。
我们已知如下两个事实:
那么问题来了,为什么在 B 子群下的优化结果是不对的?或者说不符合预期的?
那么问题来了,为什么在 B 子群下的优化结果是不对的?或者说不符合预期的?
本质上是k点在布里渊区采样不均匀造成的误差。
本质上是k点在布里渊区采样不均匀造成的误差。
OK,明白了。就是说第一步分析出的对称性是完整空间群 A, 一步离子步优化之后,第二步的对称分析为子群B, 但是不可约的K点不会更新,后面进行k点对称性还原的时候,用的群A的不可约K点,但是却用子群B的对称性操作。
那么这个难道不是个bug吗? 既然每一个离子步都做对称性分析,如果检查到和上一步对称性不同,就要进行约化 k点的更新,不更新 k 点,却只更新对称性,这个肯定就有问题。
现在的逻辑下,只要在开了对称性结构优化,后面的离子步结构与初始的结构对称性不一致,就会出现问题啊。
现在的逻辑下,只要在开了对称性结构优化,后面的离子步结构与初始的结构对称性不一致,就会出现问题啊。
也不算bug,算是误差或者近似处理。 支持更新k点是一个new feature request,需要对程序框架做不少改动,已经超出了对称性模块的范围,如有需求可以另提一个issue。但也不能为了逻辑一致让cell-relax的过程中不更新对称性,否则无法处理部分方向晶格固定的情况。
对称性和不可约k点应该是要保持一致的。 如果不一致了,我感觉怎么看都是错的。我反复思考了一下,如果非要说是近似的话,在什么样的近似下,可以让对称性和不可约k点不一致呢? 或许尺寸比较大的情况?k 点多一个少一个影响很小?感觉有点牵强。
我个人想法,可能最好的/最正确的做法,应该是更新对称性同时更新不可约k点。
至于这个是属于"new feature request" 还是bug-fix,我想具体看法可能会因人而异。至于说要不要重新提一个issue,在我看来讨论历史,算例复现等都已经在这个issue里面,应该没必要再去提一个 issue?
@mohanchen @WHUweiqingzhou 陈老师,巍青 fyi, 你们的看法呢?
我个人想法,可能最好的/最正确的做法,应该是更新对称性同时更新不可约k点
我同意。
We will discuss this issue at Issue meeting this Thursday.
I rerun the mos2 cell-relax calculation and I do confirm @maki49's statement that ABACUS doesn't increase k points sampling when the symmetry of mos2 changes from high symmetry D_6h to low symmetry C_1h starting from ION STEP 2, where the irreducible k points (nkstot_ibz) should be 254 and 42 for D_6h and C_1h (for the k-spacing provided by @QG-phy), respectively.
I will put a PR to force close symmetry
for cell-relax calculations until this bug solved.
I use ABACUS-ASE to do the cell-relax with symmetry=1, and the final structure seems no abnormal. This indicates that it is feasible to initial the symmetry in relax step. ase.zip
Describe the bug
I am using abacus to run the cell-relax job for a bulk MoS2 system. The initial structure is adopted from materials project and give honeycomb pattern viewed in c axis.
Expected behavior
No response
To Reproduce
abacus version : 3.6.0 image: registry.dp.tech/dptech/abacus:v3.6.0 mos2.bulk.tar.gz
Environment
No response
Additional Context
No response
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