Amber ff19ipq is not a complete/published release

[jeremyleung521]

I just noticed that OpenMMForceFields added Amber ff19ipq in the latest release. Unfortunately ff19ipq is not complete (unpublished) and the files in the Amber main repo are work-in-progress files. I would recommend "downgrading" to ff15ipq (or ff15ipq-m, which includes ff15ipq and a set of 25 protein mimetic residues).

Suggested steps:

1. I would take one of the following:
   dat/leap/cmd/leaprc.mimetic.ff15ipq (ff15ipq + a set of protein mimetic residues) paper
   dat/leap/cmd/leaprc.fluorine.ff15ipq (ff15ipq + a set of fluorinated residues) paper

   or if you really want just the vanilla ff15ipq from 2016:
   dat/leap/cmd/leaprc.protein.ff15ipq (paper-cited for ff19ipq currently)

2. I would also suggest adding in the SPC/E_b water model. The current water in openMMFF repo (from 8 years ago) is the plain SPC/E. SPC/E_b has modified eq bond length (iirc) and is what ff15ipq is parameterized for/with. paper
   dat/leap/cmd/leaprc.water.spceb

Source: I'm a Amber ff15ipq-m developer/author :) Also if you don't believe me, check https://ambermd.org/AmberModels_proteins.php.

TLDR: ff19ipq doesn't really exist, bar from those WIP files, and were not worked on for a long time.