Feature: Support calculation of multi-k point band-decomposed charge density under LCAO basis.

[AsTonyshment]

Background

Currently, ABACUS only supports multi-k point calculation of band-decomposed charge density under PW basis, while under LCAO basis the calculation can be carried out only when gamma_only is set to be true. It is necessary to support calculation of multi-k point charge density under LCAO basis when INPUT keyword is set as calculation = get_pchg.

Describe the solution you'd like

Changes of INPUT keywords:

1. Delete INPUT keyword nbands_istate.
2. Add a new INPUT parameter bands_to_print(similar to ocp_set), which enables users to choose which band to calculate.
3. Add a new INPUT boolean parameter out_all_kpt, which enables users to choose whether to calculate all k-points or gamma point only.

Possible changes of source code: source/module_io/istate_charge.cpp. Currently the calculation of density matrix under LCAO basis set is still using old-fashioned data structure. We plan to rewrite these codes with new density matrix using HContainer (see source/module_elecstate/module_dm/density_matrix.cpp).

Task list only for developers

• Notice possible changes of behavior
• Explain the changes of codes in core modules of ESolver, HSolver, ElecState, Hamilt, Operator or Psi

Notice Possible Changes of Behavior (Reminder only for developers)

No response

Notice any changes of core modules (Reminder only for developers)

Only source code in module_io will be changed. See solution description.

Notice Possible Changes of Core Modules (Reminder only for developers)

No response

Additional Context

For a more detailed description (formulae etc.), see Feishu doc https://xmywuqhxb0.feishu.cn/docx/FBHldIvHxoP99axSZeLcHIenntg. One can ask @AsTonyshment for access permission.

Task list for Issue attackers (only for developers)

• Review and understand the proposed feature and its importance.
• Research on the existing solutions and relevant research articles/resources.
• Discuss with the team to evaluate the feasibility of implementing the feature.
• Create a design document outlining the proposed solution and implementation details.
• Get feedback from the team on the design document.
• Develop the feature following the agreed design.
• Write unit tests and integration tests for the feature.
• Update the documentation to include the new feature.
• Perform code review and address any issues.
• Merge the feature into the main branch.
• Monitor for any issues or bugs reported by users after the feature is released.
• Address any issues or bugs reported by users and continuously improve the feature.

[WHUweiqingzhou]

Look forward to it!
b.t.w, there is a similar PR #3501 for PW basis recently.

[WHUweiqingzhou]

And This issue will be close as Issue #3266

[WHUweiqingzhou]

@AsTonyshment can we close this issue now?

[AsTonyshment]

The implementation for multi-k is not yet complete and must wait for other refactoring tasks to be finished (for example, getting rid of class LocalOrbitalCharge).

[hongriTianqi]

@AsTonyshment LOC has been removed. Would you take care of this issue in near future?

[AsTonyshment]

@hongriTianqi This has already been implemented, as you may have just seen in the Feishu doc (which includes a detailed benchmark with VASP). The PR will follow next week.