# How to output Berry connection and identify the gauge by changing VASP or QE source code?

Usually, the first-principles packages like VASP and QE involve many aspects to totally figure out what their subroutines do. For example, to output Berry connection $$\mathcal{A}^\alpha_{nn}$$ used by these codes to calculate electronic polarization is hard and time-consuming, especially for those like me who don't read these source codes. So my question here resorts to those people who read these source codes. Namely, how to output Berry connection and identify the gauge by modifying the VASP or QE source code?

• Did you figure this one out? Are you still working on this? Let us know! I gave my +1 long ago. Feb 6 at 18:44
• @NikeDattani Not yet.
– Jack
Feb 7 at 1:19
• Are you still working on it? Feb 7 at 2:10