Page Comparison

...

• ['TIG0', 'TIG1a', 'TIG1b'] - General torsions

• ['TIG1c', 'TIG1d', 'TIG2', 'TIG3', 'TIG4', 'TIG5a', 'TIG5b', 'TIG6', 'TIG7', 'TIG8'] - interpolated

Fit4.1: For each of the interpolated parameter a general torsion parameter is created where the central bond can be a single, aromatic or double bond (denoted by letters p,q,r at the end of parameter id). Due to lack of enough training data that match those patterns only a subset of those are trained and here are the parameters optimized.

...

• ['TIG0', ‘TIG1a', ‘TIG1b',
  ‘TIG3p’, ‘TIG3r', ‘TIG4p', ‘TIG5ap’, ‘TIG5bp’, ‘TIG1cp’, ‘TIG6p’, ‘TIG7p’, ‘TIG8p’, ‘TIG2p’, 'TIG2r’, 'TIG1dp’ ] - General torsions

So, fit4.1 has two parameters extra when compared to fit4, and all are general torsion parameters. The total number of torsion parameters in [openff-1.3.0, fit4, fit4.1] are [167, 170, 172] respectively. And the parameters that are replaced with interpolated parameters are [t43, t44, t45, t48, t69, t69a, t70d, t76, t77, t78] based on smarts patterns.

...

For clarity adding more plots with subset of data:

...

Simpler Fits

Simple_fit1

Replacing t43, t44, t45 with an interpolated torsion parameter for the smarts pattern: “[*:1]~[#6X3:2]~[#6X3:3]~[*:4]” and fitting this FF to 170 targets from 14 datasets (listed below under fit0) that have a dihedral that matches this pattern. The objective function value is compared to the zeroth iteration of various other FFs and fits:

Performance on Benchmarking set of molecules:

...

To check whether the BM set is a good dataset to test these interpolated fits checked the performance on 'OpenFF Primary Benchmark 1 Torsion Set' from QCA:

...