Feature `out_dm` should be deleted, and rename `out_dm1` to `out_dm`. Also feature of `init_dm` is needed.

[dyzheng]

Background

In ABACUS, out_dm feature only support gamma-only calculation, and only density matrix of gamma_point will be outputted as dense matrix, which is useless now.

I suggest to modify this feature to output real space density matrix (DMR) with non-zero matrix elements as CSR format (the feature of out_dm1).

Feature of init_dm for reading DMR file to restart SCF calculation is also needed.

Describe the solution you'd like

1. delete code of out_dm.
2. refactor code of out_dm1, use DensityMatrix::DMR to print CSR format file but not current code.
3. add feature of init_dm.

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)

No response

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

No response

Additional Context

No response

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.

[pxlxingliang]

I will refactor the interface of out_dm by using DensityMatrix.DMK instead of loc.DM