High memory usage in EXX PW

[Flying-dragon-boxing]

Details

Currently in EXX PW, ABACUS calculate 1/|k-q+G|^2 in advance, causing a resource usage in proportion to nks^2 * npw, which is unacceptable for large k-point grids.

Task list for Issue attackers (only for developers)

• Reproduce the performance issue on a similar system or environment.
• Identify the specific section of the code causing the performance issue.
• Investigate the issue and determine the root cause.
• Research best practices and potential solutions for the identified performance issue.
• Implement the chosen solution to address the performance issue.
• Test the implemented solution to ensure it improves performance without introducing new issues.
• Optimize the solution if necessary, considering trade-offs between performance and other factors (e.g., code complexity, readability, maintainability).
• Review and incorporate any relevant feedback from users or developers.
• Merge the improved solution into the main codebase and notify the issue reporter.

[Flying-dragon-boxing]

VASP only calculates |G|==0 divergence in advance, and calculates on the fly for different k-q pairs.

[Flying-dragon-boxing]

Might be mitigated using symmetry.