Add optional DFT-D4 support

[Growl1234]

Towards #5260.

This PR adds optional DFT-D4 support with both D4 and D4S model available through the external dftd4 package. ABACUS provides a thin wrapper that passes atomic numbers, Cartesian positions, lattice vectors, periodic flags, the functional name, and cutoff settings to the DFT-D4 library. The returned dispersion energy, gradient, and virial/sigma are converted to ABACUS energy, force, and stress units and injected through the existing vdW correction framework. DFT-D4 internal damping parameters are used; no D4 parameter table is maintained in ABACUS.

Here is a simple test that shows the consistency with reference binary: d4-test.zip

Note:

1. The dftd4 library does not support MPI parallelism, so an MPI-parallel job for large system with D4 correction would likely be slow at pre- and/or post- SCF stages. [The only solution I can see would be to implement an ABACUS-native D4 backend, with an internal EEQ solver and MPI-parallel CN, pair, and three-body dispersion loops, while still relying on the DFT-D4 library for parameters, model data, and reference results. However, this requires much more effort for an effective implementation.]
2. DFT-D4 support requires a CMake-built dftd4 library, so that ABACUS can locate it through the exported dftd4-config*.cmake (with environment variable CMAKE_PREFIX_PATH) without requiring a custom FindDFTD4.cmake on the ABACUS side. This indicates that the conda package of dftd4 (built with meson and does not provide CMake package files) would not be supported.
3. Currently with_dftd4 is not set to install for toolchain scripts regarding AMD compilers and math libs, because these build are not tested yet.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds DFT-D4 (Grimme) van der Waals dispersion support across the build/toolchain and the ABACUS runtime, including new input knobs and output reporting.

Changes:

• Toolchain: add DFT-D4 package/version wiring and a stage-4 installer script.
• Core: implement vdw_method=d4 via a new Vdwd4 backend calling the DFT-D4 C API and expose vdw_d4_xc.
• Build/IO: add ENABLE_DFTD4 CMake option + linking, update energy/stress printing, and fix VDW stress output in LCAO.

Reviewed changes

Copilot reviewed 21 out of 22 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
toolchain/toolchain_intel.sh	Adds WITH_DFTD4 option passthrough to toolchain installer.
toolchain/toolchain_gnu.sh	Adds WITH_DFTD4 option passthrough to toolchain installer.
toolchain/toolchain_gcc-mkl.sh	Adds WITH_DFTD4 option passthrough to toolchain installer.
toolchain/scripts/stage4/install_stage4.sh	Runs the new DFT-D4 stage4 install step.
toolchain/scripts/stage4/install_dftd4.sh	New installer for the DFT-D4 library.
toolchain/scripts/package_versions.sh	Adds DFT-D4 version + checksum + loader case.
toolchain/scripts/lib/version_helper.sh	Fixes export line formatting.
toolchain/scripts/lib/package_manager.sh	Declares DFT-D4 dependency and fixes formatting.
toolchain/scripts/lib/config_manager.sh	Adds dftd4 to package lists and default config.
toolchain/build_abacus_intel.sh	Enables DFT-D4 in ABACUS CMake invocation.
toolchain/build_abacus_gnu.sh	Enables DFT-D4 in ABACUS CMake invocation.
toolchain/build_abacus_gcc-mkl.sh	Enables DFT-D4 in ABACUS CMake invocation.
source/source_pw/module_ofdft/of_print_info.cpp	Prints D4 energy label when used.
source/source_lcao/FORCE_STRESS.cpp	Fixes VDW stress printing to use stress_vdw.
source/source_io/module_parameter/read_input_item_model.cpp	Adds d4 to vdw_method, introduces vdw_d4_xc, and adjusts D4 defaults.
source/source_io/module_parameter/input_parameter.h	Adds vdw_d4_xc input field.
source/source_hamilt/module_vdw/vdwd4.h	New DFT-D4 VdW backend header.
source/source_hamilt/module_vdw/vdwd4.cpp	New DFT-D4 backend implementation using the DFT-D4 C API.
source/source_hamilt/module_vdw/vdw.cpp	Adds vdw_method == "d4" factory path.
source/source_hamilt/module_vdw/CMakeLists.txt	Conditionally builds/links DFT-D4 backend when enabled.
source/source_estate/elecstate_print.cpp	Prints D4 energy label in total-energy reporting.
CMakeLists.txt	Adds ENABLE_DFTD4 option and wires find_package(dftd4)/link flags.

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[mohanchen]

Thanks for your contribution! The addition of the D4 vdW correction is greatly appreciated. However, we still require documentation explaining this new feature (put in the 'docs' directory), along with corresponding unit or integration tests to avoid future regressions.

[Growl1234]

Maybe, we should begin using toolchain in "Integration Test and Unit Test" workflow, but only for dftd4.

[Growl1234]

Unittest has been added at source/source_hamilt/module_vdw/test/vdw_test.cpp;
Regtest has been added at tests/03_NAO_multik/relax_cell_vdw4/.

Both are tested under "Integration Test and Unit Test" workflow with dftd4 library installed through toolchain.

[mohanchen]

Thanks, we will take a look.

[mohanchen]

This PR looks solid with the newly added D4 vdW functionality. However, thorough testing has not yet been completed. We recommend follow-up comprehensive validation going forward, and prompt communication for bug fixes should any issues arise.

[Growl1234]

Thank you very much for the approval! I would be very happy to receive feedback and help fix any issues that may arise.

As a longer-term follow-up, I will also consider a more native ABACUS implementation of the core D4 components, especially the EEQ solver, so that the DFT-D4 correction in ABACUS can eventually be evaluated with MPI parallelism.