fix bfgs bug

[19hello]

Reminder

• Have you linked an issue with this pull request?
• Have you added adequate unit tests and/or case tests for your pull request?
• Have you noticed possible changes of behavior below or in the linked issue?
• Have you explained the changes of codes in core modules of ESolver, HSolver, ElecState, Hamilt, Operator or Psi? (ignore if not applicable)

Linked Issue

Fix #...

Unit Tests and/or Case Tests for my changes

• A unit test is added for each new feature or bug fix.

What's changed?

• Example: My changes might affect the performance of the application under certain conditions, and I have tested the impact on various scenarios...

Any changes of core modules? (ignore if not applicable)

• Example: I have added a new virtual function in the esolver base class in order to ...

[Copilot]

Pull request overview

This PR fixes an early-return condition in the BFGS-based ionic relaxation update step by checking the maximum absolute displacement component, avoiding incorrect termination when all displacement components are negative.

Changes:

• Replace max_element(dpos) threshold check with a max_abs_dpos computation using std::abs.
• Prevent erroneous early return in Ions_Move_BFGS2::Update() when displacements are negative but non-negligible.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[mohanchen]

LGTM