Add breaks_TRS term predicate and guard compute_dynmat#1316
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antoine-levitt wants to merge 3 commits into
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Add breaks_TRS term predicate and guard compute_dynmat#1316antoine-levitt wants to merge 3 commits into
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Mirror the existing breaks_symmetries dispatch with a breaks_TRS predicate on term builders. Mark Magnetic and Anyonic as breaking TRS, and assert in compute_dynmat that no term in the model breaks TRS — the phonon response solver folds the +q and -q Sternheimer equations into one using TRS, so it is currently invalid otherwise (see #1310, Dal Corso 2019). Also document the derivation of the "ψ̄·δψ with factor 2" form used in compute_δρ from scratch (no χ₀), tracking momenta term by term and showing how TRS identifies the missing δψ̄·ψ contribution with the computed one.
Technici4n
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May 7, 2026
Technici4n
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May 7, 2026
Technici4n
reviewed
May 7, 2026
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Ended up rewriting the whole comment, AI is not great for this type of non-trivial explanation. Ready to review now. |
Technici4n
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May 8, 2026
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Summary
breaks_TRSdispatch on term builders, mirroring the existingbreaks_symmetries. Default isfalse;MagneticandAnyonicare marked as breaking TRS.compute_dynmatnow asserts that no term in the model breaks TRS. The phonon response solver folds the +q and −q Sternheimer equations into a single one at +q (with a factor of 2), which is only valid under TRS — see Phonon +q instead of -q? #1310 and Dal Corso, https://arxiv.org/abs/1906.11673.Test plan
Pkg.test("DFTK"; test_args=["minimal"])passesMagneticterm in the model