Rotational symmetry enforcement for third-order force constants

hiPhive
1

Hello,

Thank you for developing and maintaining HiPhive, it is a very powerful and useful tool.

I have a question regarding rotational invariance. As far as I understand, HiPhive can enforce translational and rotational sum rules for second-order force constants. Is it also possible to enforce rotational invariance directly on existing third-order force constant matrices, similar to the second-order case? If not, are there recommended approaches or plans to support this feature in HiPhive?

Thanks a lot for your guidance!

Best regards,
Yuwen Zhang

2

Thanks :slight_smile:

That’s correct, the Huang rule only applies to second order afaik. The Born-Huang sum rule is also only applied for second order but can be generalized to include higher orders as you say. This is not implemented at the moment as it is seldom requested and I haven’t seen it make a difference but there might be recent results showing otherwise.

I think the other force constant softwares like tdep supports it so maybe check those.

Do you know it is needed or do you just want to be on the safe side? :slight_smile:

Best
Fredrik