updates on the documents: implicit solvation & detailed input & geometry optimization

[shuxiansheng2]

Dear developers,
I find some new features have been released without updating the documents.

1. Implicit Solvation
   all available solvents have been extended to GFN-FF method since 6.3.0;
   implicit solvation model GBSA for GFN0-xTB seems to be supported since 6.2.

2. Detailed Input
   currently there are automatic check and remove of duplicated atoms from the fixing or constraining list as well as sorting of the list ?

3. Geometry Optimization
   improved defaults for optimizer (RF based for less than 500 atoms, L-BFGS based otherwise) since 6.3.0.

4. Periodic Boundary Conditions
   GFN1-xTB available under periodic boundary conditions since 6.3.0.

   Finally, I sincerely hope that some examples of pathfinder and nanoreactor using metadynamics coud be included in the documents.

[awvwgk]

1. Solvation for GFN-FF and GFN0-xTB is functional but not finished, once this status changed, I will push the documentation
2. I fixed this issue some time ago, I should certainly update this part of the docs
3. There were a few changes regarding the optimization, especially w.r.t. the GFN-FF,
   @sespic have you written (or could you write) something up for this
4. Given the half-finished state of the periodic boundary conditions in xtb, I won't get to the documentation before I'm done with the actual implementation
5. I might have an example or two for the pathfinder, which I can work into a short guide

[shuxiansheng2]

Thanks a lot for your reply.

[awvwgk]

Solvation has been documented in 7cfd53d, the pathfinder has been added with 5770ce0.