Dear CP2K developers and users, While testing METHOD GAPW_XC with r2SCAN in CP2K 2026.2 (git:c92cc08), I found that the analytic forces and stress do not agree with RUN_TYPE DEBUG finite differences, whereas GAPW, and GAPW_XC with PBE, pass the same check. I may be missing something in my setup, so I would be grateful if you could take a look. All inputs and outputs, a short analysis script (numpy only) and a README with the full tables are attached (cp2k_GAPW_XC_mGGA_report.zip). **Setup** 302-atom ZnO–P2O5–Al2O3 glass (cubic, a = 16.06 Å, Γ point), TZVP-MOLOPT-SCAN-GTH + GTH-SCAN for all elements, `MGGA_X_R2SCAN` + `MGGA_C_R2SCAN` (libxc) + D3(BJ), CUTOFF 1100 / REL_CUTOFF 60, EPS_SCF 1e-7, analytical stress. RUN_TYPE DEBUG checks one Al, O, P and Zn atom and the stress tensor. Between the inputs, only METHOD, GAPW_ACCURATE_XCINT, FORCE_PAW or the functional changes. Without FORCE_PAW, O and Zn are PAW kinds and Al and P are treated by GPW. **Results** (analytic − finite difference; force: max over x, y, z, meV/Å; stress: GPa) | functional | METHOD | ACCURATE_XCINT | Al | O | P | Zn | ΔS diagonal | ΔS off-diagonal | |---|---|---|---|---|---|---|---|---| | r2SCAN | GAPW | T | 0.02 | 0.03 | 0.23 | 0.03 | 0.004 | 0.001 | | r2SCAN | GAPW | F | 0.02 | 0.03 | 0.23 | 0.04 | 0.004 | 0.001 | | r2SCAN | **GAPW_XC** | T | 11.5 | 91.5 | 23.3 | **410** | **+23.7** | 0.008 | | r2SCAN | **GAPW_XC** | F | 18.2 | 261 | 37.6 | **458** | **+28.8** | 0.004 | | PBE | GAPW_XC | T | 0.03 | 0.01 | 0.23 | 0.00 | 0.005 | 0.001 | | PBE | GAPW_XC | F | 0.02 | 0.01 | 0.23 | 0.00 | 0.004 | 0.001 | - The checked forces are 2000–3600 meV/Å, so the Zn error is about 20 %. The stress error is an isotropic shift of the diagonal; the off-diagonal components agree. - The *finite-difference* forces of GAPW_XC and GAPW agree to within 2.6 meV/Å (with and without ACCURATE_XCINT), so the GAPW_XC energy itself looks fine; only the analytic derivatives seem to be affected. - The largest errors are on the PAW kinds (Zn, then O). Adding `FORCE_PAW` (so Al and P also become PAW atoms) does not change the numbers. - So the problem seems specific to the combination GAPW_XC + meta-GGA, and does not depend on GAPW_ACCURATE_XCINT. In the v2026.2 regtests, the GAPW_XC finite-difference checks (`regtest-acc-1/h2o-gapw_xc-force-1.inp`, `h2o-gapw_xc-stress-debug-1.inp`) use PBE, and the meta-GGA (TPSS) checks use GAPW with USE_FINER_GRID, so I could not find a test that covers this combination. I have not tested the current master, other meta-GGAs or a smaller system. My questions: 1. Is this a known issue, or is GAPW_XC not meant to be used with meta-GGA forces and stress? 2. If it is a bug, would a small reproducer help (for example H2O with TPSS, based on `h2o-gapw_xc-force-1.inp`)? I would be happy to prepare one, or to open a GitHub issue. For now I use GAPW (or GPW with USE_FINER_GRID), which pass the same checks. Thank you very much for your time and for CP2K. Best regards, Wei LIU -- You received this message because you are subscribed to the Google Groups "cp2k" group. To unsubscribe from this group and stop receiving emails from it, send an email to <a href="mailto:cp2k+unsubscribe@googlegroups.com">cp2k+unsubscribe@googlegroups.com</a>. To view this discussion visit <a href="https://groups.google.com/d/msgid/cp2k/c6c055e8-358f-426b-b287-dd02f4d2399an%40googlegroups.com?utm_medium=email&utm_source=footer">https://groups.google.com/d/msgid/cp2k/c6c055e8-358f-426b-b287-dd02f4d2399an%40googlegroups.com</a>.