[Q&A] Is bfgs_trad method have editable parameters ?

[QuantumMisaka]

Details

In ABACUS docs we can see some editable parameter for bfgs method and other geometry optimization setting, like

• relax_cg_thr
• relax_bfgs_init
• relax_bfgs_rmax
• relax_bfgs_rmin

And some users may learn ABACUS from VASP, they have initia for editing POTIM for more stable geometry relaxtion. So my question is:

• Is these parameters have effect on bfgs_trad (now the default BFGS in develop branch) ?
• Should user edit these parameters according to their structure and system ?
• Do we need guideline for learn the difference between POTIM and these parameters ?

Have you read FAQ on the online manual http://abacus.deepmodeling.com/en/latest/community/faq.html

• Yes, I have read the FAQ part on online manual.

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[19hello]

In these parameters, only relax_bfgs_rmax will affect the BFGS traditional algorithm. This parameter is used to control the maximum step size of displacement. relax_bfgs_rmin was used in the old BFGS algorithm to detect whether the trust radius was too small. If the trust radius was less than relax_bfgs_rmin twice, the optimization would stop and report an error: "trust radius is too small! Break down." However, in the BFGS traditional algorithm, this check does not exist. This means that even if the atomic displacement is already very small, the algorithm will continue running until convergence is achieved.

I asked ChatGPT about the function of POTIM. In VASP, POTIM controls the optimization step size, determining the magnitude of atomic position updates in each step. The difference between POTIM and relax_bfgs_rmax is that POTIM uniformly scales the step size of each iteration to the value of POTIM, whereas relax_bfgs_rmax only caps the step size when it exceeds relax_bfgs_rmax. If the step size is smaller than relax_bfgs_rmax, the algorithm does not modify the step size. Currently, the BFGS implementation does not include the POTIM-like functionality.

[QuantumMisaka]

@19hello Good answer, I consider whether we can update these information to docs. @mohanchen Do you have any advice?