[CP2K-user] [CP2K:22353] Re: [CP2K 8.1 CDFT] Exact nonperturbative Becke/Hirshfeld weight export without entering outer SCF

['Dayu Zhu' via cp2k]

Dear CP2K developers and users,

I am following up with a much shorter version of my question.

For a fixed geometry, grid, and ATOM_GROUP definition, I need to export the
exact CP2K Becke or Hirshfeld CDFT weight function without perturbing an
already-converged electronic density.

Could you please clarify:

1. Is there a stock CP2K input option, in version 8.1 or a newer release,
that prints the weight-function grid without running the CDFT outer SCF?

2. If not, would it be methodologically valid to add a minimal diagnostic
hook that calls the existing CP2K weight builder and cube writer, and then
exits before density integration, Kohn–Sham construction,
constraint-potential application, and CDFT outer-SCF optimization?

A brief yes/no answer or a pointer to the relevant routine, example, or
newer implementation would be very helpful.

The longer message below contains the source-level details, but no detailed
review of those attachments is necessary to answer these two questions.

Thank you very much for your time.

Best regards,
Dayu Zhu

On Fri, 24 Jul 2026 at 13:12, Dayu Zhu <dayu.zhu at monash.edu> wrote:

> # CP2K 8.1 support request: exact nonperturbative Becke/Hirshfeld CDFT
> weight-grid export
>
> ## Build identity
>
> - CP2K version: `8.1`
> - Executable revision: `git:0b61f2f`
> - Container release-source HEAD: `0bfbd41a7402152da7b86a103d5d95a4184367d9
> `
> - Release tag: `v8.1.0`
> - Wrapper SHA256: `
> c786e567853dbe8fafb35a91ec25ba1ca8f5ea5c02d30f5cdf056719ce9bc2d1`
> - Input XML SHA256: `
> 728c139a1d87554490e67f0ab30f1f5c78f944dad5e87671894e1aa833f281f4`
> - Container executable: `/cp2k/exe/local/cp2k.psmp`
> - Container source root: `/cp2k/src`
>
> The wrapper/account path is intentionally omitted. The hashes above and the
> attached sanitized identity CSV are sufficient to identify the inspected
> build without exposing an HPC account path.
>
> ## Narrow technical need
>
> We need exact CP2K 8.1 Becke and Hirshfeld weight grids for offline
> integration
> of local magnetization from already-converged, unconstrained spin-density
> cubes. We want to preserve the original density and avoid running CDFT or
> an
> electronic SCF merely to obtain the geometric/partition weight grid.
>
> This request concerns method semantics and a minimal diagnostic interface
> only. It does not claim that stock CP2K is wrong, and it does not request
> scientific interpretation of any material.
>
> ## Distinctions used in this request
>
> - **Exact weight construction:** running the original CP2K 8.1 Becke or
>   Hirshfeld builder with fixed geometry, cell/PBC, grid, atom group, COEFF,
>   atom-kind, and partition parameters.
> - **Exact weight printing:** writing that already-constructed CP2K PW grid
>   through the original `cdft_print_weight_function`/cube-writer path.
> - **Nonperturbative measurement:** obtaining the weight without changing
> or
>   reoptimizing the electronic density.
> - **CDFT outer-SCF perturbation:** adding `weight * STRENGTH` to the
>   Kohn-Sham potential and updating the electronic state/multiplier.
>
> ## Exact source references inspected
>
> | Routine | CP2K 8.1 source lines |
> |---|---|
> | `read_constraint_definitions` | `qs_cdft_utils.F:534-717` |
> | `becke_constraint_init` | `qs_cdft_utils.F:100-449` |
> | `becke_constraint_low` | `qs_cdft_methods.F:142-581` |
> | `hirshfeld_constraint_init` | `qs_cdft_utils.F:966-1086` |
> | `create_shape_function` | `hirshfeld_methods.F:141-224` |
> | `hirshfeld_constraint_low` | `qs_cdft_methods.F:1153-1365` |
> | `qs_ks_cdft_constraint` | `qs_ks_apply_restraints.F:62-128` |
> | `cdft_constraint_integrate` | `qs_cdft_methods.F:772-954` |
> | `cdft_constraint_print` | `qs_cdft_utils.F:1095-1249` |
> | `cdft_print_weight_function` | `qs_cdft_utils.F:1257-1301` |
> | `qs_ks_build_kohn_sham_matrix` | `qs_ks_methods.F:207-899` |
> | `sum_up_and_integrate` | `qs_ks_utils.F:1195-1625` |
> | `cdft_scf` | `qs_scf.F:934-1144` |
> | `outer_loop_gradient` | `qs_outer_scf.F:102-174` |
> | `outer_loop_update_qs_env` | `qs_outer_scf.F:386-430` |
> | `cdft_control_release` | `qs_cdft_types.F:419-493` |
>
> `cdft_print_hirshfeld_density` is not present in the exact `/cp2k/src`
> tree;
> both weight types use the common `cdft_print_weight_function` route.
>
> Our revision-pinned source audit indicates that the low-level
> Becke/Hirshfeld
> builders construct weights before `cdft_constraint_integrate` reads the
> current density. The stock weight print is reached only after `cdft_scf`
> outer-loop initialization, although the print call precedes the first
> constraint-potential addition in that Kohn-Sham build. We request
> confirmation
> of the supported semantics and interface rather than asserting undocumented
> API guarantees.
>
> ## Questions
>
> 1. For CP2K 8.1, is there a supported stock-input route to initialize and
>    print exact Becke/Hirshfeld CDFT weight grids without entering the CDFT
>    outer-SCF loop?
>
> 2. For fixed geometry, real-space grid, atom group, COEFF, atom-kind, and
>    partition parameters, are the Becke/Hirshfeld weight grids completely
>    independent of the current electron density, current spin density,
> TARGET,
>    STRENGTH, and current Lagrange multiplier?
>
> 3. Does `PROGRAM_RUN_INFO/WEIGHT_FUNCTION` print exactly the same weight
> grid
>    regardless of the constrained electronic solution, even though the print
>    call occurs after outer-loop initialization?
>
> 4. Is there an officially recommended internal routine or minimal driver
> for
>    invoking the original CP2K 8.1 Becke/Hirshfeld weight builders and cube
>    writer without running CDFT or electronic SCF?
>
> 5. Would a minimal source hook that constructs the weight, writes it, and
>    exits before `cdft_constraint_integrate`, constraint-potential
> building,
>    electronic SCF, or CDFT outer-SCF optimization be considered
> semantically
>    exact?
>
> 6. For Hirshfeld CDFT in CP2K 8.1, what implementation limitations affect
>    ENERGY-only local-magnetization integration, weight printing, forces,
>    geometry optimization, and MD?
>
> 7. Can multiple `ATOM_GROUP` weight grids, for example R0/R1/R2 and a
> separate
>    HSO4 monitoring region, be generated in one invocation without
> activating
>    coupled constraints?
>
> 8. What metadata must be preserved to guarantee exact offline integration
> of
>    `integral w(r)[rho_alpha(r)-rho_beta(r)] dr` against existing
> spin-density
>    cubes, including grid origin, axes, stride, cell/PBC, atom order/kinds,
>    partition settings, group/COEFF mapping, and numeric print precision?
>
> ## Candidate minimal interface for review
>
> After normal input, subsystem, `qs_env`, MGRID, and PW-pool
> initialization:
>
> 1. allocate one weight PW grid per group using the stock lifetime pattern;
> 2. call the original Becke or Hirshfeld `init` and low-level builder;
> 3. call the original common weight cube writer;
> 4. hash/write provenance metadata;
> 5. release all temporary grids; and
> 6. exit before density integration, Kohn-Sham potential construction,
>    electronic SCF, or outer-SCF optimization.
>
> No patch, build, input, or calculation is included with this request.
>
> ## Lightweight attachments
>
> - `CP2K81_CDFT_weight_evaluator_support_request.md`
> - `CP2K81_CDFT_weight_evaluator_minimal_context.txt`
> - `CP2K81_exact_source_identity_for_support.csv`
> - `CP2K81_CDFT_weight_call_graph_compact.csv`
> - `CP2K81_weight_function_dependency_matrix.csv`
> - `CP2K81_weight_print_timing_audit.csv`
> - `CP2K81_exact_weight_extraction_options.csv`
> - `CP2K81_exact_weight_source_excerpts_compact.txt`
>
> No coordinates, WFN, trajectory, cube, binary, full source tree,
> proprietary
> data, or unrelated project details are attached.
>
>

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