Feature: A roadmap to improve the convergence performance of ABACUS

[WHUweiqingzhou]

Background

Current ABACUS sometimes faces convergence challenge for some complicated metal/surface and spin-polarized systems. In order to improve the convergence performance of ABACUS, we will try new algorithms in ABACUS, and a feasible roadmap is as follows:

• Step I: improve the performance of kerker preconditioner, and improve the convergence behavior for general calculations. Done. Issue #3094 PR #3133 Issue #3294 PR #3305
• Step II: separate the mixture of charge density and magnetic density. Currently, ABACUS calculate residual using charge density and magnetic density together. Ref: Journal of the Physical Society of Japan 82 (2013) 114706. This modification is expected to greatly improve the convergence calculation problem of magnetic materials. nspin=2 Done. Issue #3225 PR #3226 nspin=2 for metaGGA Done. Issue #3260 PR #3328 nspin=4 Issue #3285 PR #3330 nspin=4 angle mixing Issue #3336 PR #3356
• Step III: Mixture of density matrix. Now, ABACUS only mix charge density instead of density matrix. This modification is expected to greatly improve the convergence calculation problem of several calculations, in which use density matrix as projector, f.e. DFT+U/DeepKS/EXX. Issue #3535 PR #3549
• Step IV: (Optional) Increase history dimension in DIIS calculations. Current default value is 8 in ABACUS, which is 45 in VASP. Increasing ndim is quite important in some calculations. To this end, we need to reduce the memory cost of residual. We can make this reduction by using a cutoff in G-space, which is effective for PW calculation, but does not work in LCAO calculation.
• Step V: (Optional) Try metric of inner product. As mentioned in Ref. Physical review B, 54(16), 11169, the metric of inner product sometimes is even more important than kerker preconditioner, which is worth to try.
• Step VI: Build an automated workflow for Mixing During all above development, we will make heavy tests to make sure every modification is meaningful. During this process, we will gradually optimize an automated workflow.
• Step VII: Polish default value of mixing parameter Taking advantage of automated workflow, we will delete Charge::auto_set() and polish default value of mixing parameter. Current default value is mixing_beta=0.2, mixing_gg0=1.0 for metals; mixing_beta=0.7, mixing_gg0=1.0 for semimetals.

We just list some practical and promising choice to improve ABACUS's convergence performance, any other suggestion is welcomed to discuss.

Describe the solution you'd like

Realize this roadmap step by step.

[WHUweiqingzhou]

A Chinese handbook about convergence issue is open to the public now: https://ucoyxk075n.feishu.cn/docx/R0sqdk6T0o2RY4x5IWgcJ3RHnug?from=from_copylink

[WHUweiqingzhou]

I will close this issue now. Maybe reopen if any update of mixing method.