adding charges to NEP

[brucefan1983]

Many users hope to have this feature.

How to set up the charges:

• Fixed charges?
  • let the user to specify?
  • let SNES to optimize?
• Dynamic charges?
  • a separate NN is needed
  • need to study the literature

How to evaluate the interactions from the charges?

• the simple DSF method (damped shifted force); I like this
• the canonical Ewald summation; the golden standard

[ZKC19940412]

Hi, it is definitely a major step ahead to include charges. Here is a review from the HDNNP by Professor Jörg Behler (https://pubs.acs.org/doi/abs/10.1021/acs.chemrev.0c00868) and page 15 - 20 goes over their latest scheme of incorporating charges and might be useful for brainstorm the charge implementations for NEP. Just want to add a comment that while adding this new features, might be useful to do benchmarking on efficiency too? I love NEP because it is always the best in terms of balancing efficiency and accuracy. I would love to see NEP is always the fastest code for large scale MD simulations.

[brucefan1983]

Thanks for the comments. This review is very helpful! I also hope to keep the superior speed of NEP, so I was thinking a non-Ewald way to evaluate the Coulomb forces.

[brucefan1983]

Aim to achieve this within GPUMD-v4.0.