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Fix: correct My sign in noncollinear Mulliken magnetism - #8250
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Correct the nspin=4 Mulliken My sign for the conj-first density matrix convention. Add a regression test covering nonzero My for several noncollinear spin directions. Keep the nspin=1/2 paths unchanged.
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The My sign now matches the conj-first density matrix and the production overlap contraction. No new implementation defect found. Static review only; no build or runtime tests were run.
Non-blocking: Please record the exact configure/build and test commands, including the command or sign-revert procedure used to check the old-sign failure.
Corrected comment to reflect the proper matrix operation in the code.
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Reminder
AGENTS.mdanddocs/developers_guide/agent_governance.md.source/changes.Summary
Fix the incorrect sign of the y-component of Mulliken magnetization (
My) for noncollinear calculations (nspin=4).The previous implementation used a sign convention inconsistent with the conjugate-first density matrix representation and Pauli-matrix decomposition in ABACUS.
The corrected expression is:
My = Im(mud_ud - mud_du)Previously:
My_old = -Im(mud_ud) + Im(mud_du)Changes
Mysign fornspin=4.collect_MW_nspin4().Mx,Mz, and thenspin=1/2paths unchanged.Verification
Unit Tests
The Mulliken unit tests passed, including the new regression test
OutputMullikenSpinTest.Nspin4MyFollowsPauliConvention.Verification command:
ctest --test-dir build-test -R MODULE_IO_mulliken_test --output-on-failureResult: 1/1 CTest target passed.
Integration Tests
Two independent ABACUS versions were compiled and compared:
0223bfeb0e2a8728f0OMP_NUM_THREADS=1The converged noncollinear Fe example (
examples/04_noncollinear/01_Fe_noncollinear) was tested with initial magnetization along +y andout_mul 1.SCF converged in 11 iterations with final DRHO =
8.2125e-06.Myagrees with the prescribed magnetization direction.Mx,Mz, atomic charges, and total energy remain unchanged.Result: PASS
The existing
tests/17_DS_DFTU/02_LCAO_SPIN_S4_XYZcase was also tested. It confirmed the exactMysign reversal with unchanged other quantities, but did not reach SCF convergence due to its existing numerical stability issue.Conclusion
The Mulliken
Mysign correction is verified by unit tests and a converged noncollinear Fe integration calculation. The fix affects only the reportedMycomponent and does not alter the SCF calculation.No automated integration regression case was added.