Fixed error using AMOEBA 2018 with RNA (openmm#3313)

Fixed an error in condensing LJ types in CharmmPsfFile (openmm#3210)

Fixed an error in condensing LJ types in CharmmPsfFile (openmm#3210)

Updated version number to 7.6. (openmm#3182)

fix Charmm NBThole calculation bug and Improper dihedral parameter ma…

…tch issue (openmm#2952) (openmm#3087)

* nbthole

* Update charmmpsffile.py

* Update charmmpsffile.py

* Update charmmparameterset.py

fix multiple dihedral with the same periodicity and add a warning reminder for improper dihedral

* add test example for NBTHole

add system files of CYT-GUA-CYT DNA segment for testing NBThole

* Update TestCharmmFiles.py

Co-authored-by: qiuzy <[email protected]>

Fixed error using periodic exceptions with PME (openmm#2935)

Merge pull request openmm#2678 from peastman/741

Updated version number to 7.4.2.

Merge pull request openmm#2477 from peastman/7.4_branch

Updated version number to 7.4.1

Merge pull request openmm#2477 from peastman/7.4_branch

Updated version number to 7.4.1

Merge pull request openmm#2376 from peastman/methodmap

Force generators that don't use PME still accept it as a nonbonded method