fix(lmp): avoid double qe2f in DPLR efield

[Yi-FanLi]

Summary

• remove the second qe2f multiplication when forming fix dplr efield forces
• keep the existing conversion when storing constant and equal-style efield values
• add real-unit regressions for constant and equal-style efield paths so qe2f != 1 is covered

Closes #5646.

Tests

• git diff --check
• /tmp/deepmd-check-venv/bin/ruff check .
• /tmp/deepmd-check-venv/bin/ruff format --check .

Not run

• Targeted LAMMPS DPLR pytest tests could not run in the local ad hoc venv: the lammps Python module is not installed there, and pytest startup segfaulted in the temporary environment before collection.

Summary by CodeRabbit

• Bug Fixes

  • Corrected electric-field force calculations so results are accumulated consistently in real-unit simulations.
  • Fixed related force and virial contributions to match expected values.

• Tests

  • Added coverage for electric-field behavior in real units.
  • Included checks for both constant and variable field settings to confirm force results remain accurate.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 77791842-bad2-4b67-8cc7-f52c08a4a7b1

📥 Commits

Reviewing files that changed from the base of the PR and between c1b9de1 and fb65689.

📒 Files selected for processing (2)

• source/lmp/fix_dplr.cpp
• source/lmp/tests/test_dplr.py

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📝 Walkthrough

Walkthrough

The PR removes a redundant force->qe2f multiplication in FixDPLR::post_force when computing the electric-field force term, fixing double-scaling of qe2f. It also adds a lammps_real fixture and two new tests validating DPLR efield behavior under real units.

Changes

DPLR efield qe2f fix

Layer / File(s)	Summary
Remove duplicate qe2f multiplication source/lmp/fix_dplr.cpp	tmpf[dd] now uses q[ii] * efield[dd] directly instead of applying force->qe2f twice, correcting the scaling of efield force, dfele, efield_fsum, and virial contributions.
Real-units regression tests source/lmp/tests/test_dplr.py	Adds lammps_real fixture using units="real" and two tests (test_pair_deepmd_lr_efield_constant_real, test_pair_deepmd_lr_efield_variable_real) asserting forces match expected_e_efield_constant scaled by constants.ener_metal2real for constant and variable efield configurations.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested labels: Python, LAMMPS

Suggested reviewers: njzjz, wanghan-iapcm, iProzd

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main fix: preventing double application of qe2f in DPLR efield forces.
Linked Issues check	✅ Passed	The code and tests address the linked issue by applying qe2f once and adding regression coverage for constant and equal-style efield cases.
Out of Scope Changes check	✅ Passed	The changes stay focused on the qe2f DPLR efield fix and its regression tests, with no obvious unrelated additions.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[njzjz]

LGTM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.16%. Comparing base (c1b9de1) to head (fb65689).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5732      +/-   ##
==========================================
- Coverage   81.29%   81.16%   -0.13%     
==========================================
  Files         988      988              
  Lines      110897   110897              
  Branches     4234     4236       +2     
==========================================
- Hits        90151    90009     -142     
- Misses      19220    19360     +140     
- Partials     1526     1528       +2     

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