How to output momentum/velocity matrix in ABACUS

[DzzZ1]

Background

I noticed that abacus has implemented the rt-TDDFT function in Velocity-gauge and can output current. My current requirement is to output the momentum p matrix of the system ground state under the LCAO basis set and energy eigenvalue basis set, which is very important to me. But when I was reading the manual, I did not find a label for outputting the p matrix. The p matrix I refer to here is similar to the label out_mat_r in the manual for extracting the position r matrix, but the difference from r is that the r operator now needs to be replaced by the matrix of the p operator (https://abacus.deepmodeling.com/en/latest/advanced/elec_properties/position_matrix.html#extracting-position-matrices). At the same time, I also read the second reference under the rt-TDDFT tutorial (title: Velocity-gauge real-time TDDFT within a numerical atomic orbital basis set). From formulas 7, 8 and 9 in the literature, it can be seen that calculating momentum is a prerequisite for obtaining current. I guess abacus should have calculated this item, but there is no output label.

Describe the solution you'd like

It is recommended to add labels for output momentum matrix p under the energy eigenvalue basis set.

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)

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

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Additional Context

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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.

[ESROAMER]

Your requirements can be achieved using functions in the pyatb. The function get_velocity_matrix(kpt) can obtain the velocity matrix in k-space under energy eigenstates, while the function get_velocity_basis_k(kpt) provides the velocity matrix in k-space under the atomic orbital basis. You can reach out to the developers of pyatb to learn how to use these functions correctly. Hope this helps!

[DzzZ1]

Thanks for your reply, I will do it.