QM, MM minimum structures of acyclic alkanes

QM versus MM minimized structures of the linear alkanes with the following force field, in which angle a2 optimized to a bad parameter of 94 degrees, not seen on the training set. All the QM and MM minimized geometries overlap though with the final RMSD in angles less than 1 degree.

1. With priors (same as 1.2, penalty_additive 1.0)

With priors (same as 1.2, penalty_additive 1.0)	Initial values	acyclic	Openff_1.3.0
b1, length, [#6X4:1]-[#6X4:2]	1.0	1.5	1.5
b1, k, [#6X4:1]-[#6X4:2]	500.0	487.7	517.2
b83, length, [#6X4:1]-[#1:2]	1.0	1.1	1.1
b83, k, [#6X4:1]-[#1:2]	700.0	699.9	754.1
*a1, angle, [:1]-[#6X4:2]-[:3]*	113.7	104.9	113.7
*a1, k, [:1]-[#6X4:2]-[:3]*	99.2	112.9	99.2
a2, angle, [#1:1]-[#6X4:2]-[#1:3]	90.0	94.1	114.3
a2, k, [#1:1]-[#6X4:2]-[#1:3]	60.0	42.2	66.6

QM - in Green

MM minima from the acyclic fit with a2 angle equilibrium at 94 degrees - in Cyan