Page Comparison

Note: This post will be moved to Force Field / FF releases / Parsley minor release(s) once it is ready to be shared.

Fitting Data and Results

• Fitting targets: 2nd generation training sets (link for the details of the training set generation scheme: http://doi.org/10.5281/zenodo.3777278)

...

• Direct parameter comparison has found no significant differences in equilibrium bond lengths and equilibrium angles while showing notable differences in k values of some angle/ torsion parameters.

• Angle terms with significant different final k values between RC1 and RC2:

  • a6([#1:1]-[*;r3:2]~;!@[*:3], k value in SMIRNOFF99Frosst: 100 kcal/mol/radian²)

  • a3([*;r3:1]1~;@[*;r3:2]~;@[*;r3:3]1, k value in SMIRNOFF99Frosst: 200 kcal/mol/radian²)

  • a15([#8X1:1]~[#6X3:2]~[#8:3], k value in SMIRNOFF99Frosst: 126 kcal/mol/radian²)

: Based solely on my intuition without no strong evidence, RC2 angle k values for the angle terms(doesn’t change much from 1.1.0 during the optimzation) seem physical; 400kcal/mol/radian² for angle seems too large compare to other angle k values. Final gradients for the angle k values are also higher in RC1 (a6: 5.580e+00 , a15 : 4.750e+00) compared to the gradients in RC2 (a6: 1.599e+00 , a15 : 1.391e+00)

...

: But scatter plot seems slight better in RC1. Also one thing I noticed is that due to the larger equilibrium angle over QM angle values in v1.1.0, RC2 which used v1.1.0 as its initial guess also ended up having large equilibrium value (~ 135 degree) compared to the resulting equilibrium value in RC1 ( ~ 129 degree). ( The optimization issue about resulting in final equilibrium values substantially off from QM values is one of the known problems that we are currently working on. )

...

But it seems like having final equilibrium angle different with the angles in QM optimized geometries are not always frustrating. Here’s one example of it. Having larger equilibrium angle (~ 147 degree. ~ 110 degree in QM optmized geometries) for a38 is found to be benefitial in locating hydroxyl hydrogen in phosphono group far away enough from its neighboring oxygens, preventing unphysical intermolecular H-bonding.

...

• Torsion terms with significant different final k values between RC1 and RC2:

  • t146, t147: 6 periodicities

  • t15 ([*:1]-[#6X4;r3:2]-@[#6X4;r3:3]-[*:4]), t16 ([#6X4;r3:1]-[#6X4;r3:2]-[#6X4;r3:3]-[*:4]): in-ring rotation

...

Specific improvement in certain functional groups(phosphono group, sulfamate acetate) found in RC1 is also shown in RC2.

• TODO: revert WRMSE → objective value

...

...

QM optimized geometry of CC(O)([P@@](=O)(O)[O-])[P@](=O)(O)[O-]. ( orange: MM optimized geometry with v1.1.0 force field, green: v1.2.0-RC1 force field, magenta: v1.2.0-RC2 force field)

(4) v1.2.0-RC1 vs. v1.2.0-RC2: Relative energies between conformers at “QM optimized geometries”

...