Minimize-LCAO-Memory: `FFT::grid` and `rho` and `potential`

[dyzheng]

Describe the Code Quality Issue

In test of large scale LCAO base case, such as Si512 , the record of arrays with length nrxx have many different objects.

I guess some of them can be optimized to temporary memory or use other objects' memory.

Additional Context

No response

Task list for Issue attackers (only for developers)

• Identify the specific code file or section with the code quality issue.
• Investigate the issue and determine the root cause.
• Research best practices and potential solutions for the identified issue.
• Refactor the code to improve code quality, following the suggested solution.
• Ensure the refactored code adheres to the project's coding standards.
• Test the refactored code to ensure it functions as expected.
• Update any relevant documentation, if necessary.
• Submit a pull request with the refactored code and a description of the changes made.