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1. Tracing the origin of the amide issue

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One easy fix of the problem is using simple targets, whose torsion profiles have parabolic shape near the minimum (planar geometry at the minimum). + Expecting that this experiment to be one proof of the need for using simple-as-possible torsiondrive targets in general torsion parameter fitting.

2. Filtering out non-planar structures at the minimum geometry

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v1.2.0

fb-fit2 (scheme 2)

fb-fit3 (scheme3)

fb-fit4 (scheme 4)

non-filtered Unfiltered

test cal 1

144.59

91.81

82.39

88.84 

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test cal 2

25.37

15.62

14.75

14.15

23.21

test cal 2-1 simple

7.10

6.21

7.49

8.29

11.04

test cal 2-2 complex

18.26

9.40

7.26

6.87

12.17

final X2 (fitting)

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1.31e+02 → 2.22e+01 

1.30e+02 → 1.73e+01

2.09e+02 → 3.01e+01

5.28e+02 → 6.90e+01

(1) N-methylacetamide

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(2) Test set 1 (N-methyacetamide, non-planar molecules in the 1st gen. Roche torsion set)

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ID, SMIRKS

 Initial guess

fb-fit2

fb-fit3

fb-fit4

t69a [*:1]-[#7X3:2]-[#6X3$(*=[#8,#16,#7]):3]~[*:4]

k1 = 2.5

k1= 1.6793e+0

k1 = 1.3647e+0

k1 = 1.7786e+0

t70 [#1:1]-[#7X3:2]-[#6X3:3]=[#8,#16,#7:4]

k1 = 3.4592e+0

k2 = 1.3570e+0

(from 1.2.0)

k1 = 3.5662e-1

k2 =1.3542e+0

k1 = 2.4868e-1

K2 = 9.4280e-1

k1 = -1.3577e+0

k2 = 1.2663e+0

t70b [*:1]-[#7X3:2]-!@[#6X3:3](=[#8,#16,#7:4])-[#6,#1]

k1 = 2.5

k1 = 4.1692e+0

k1 = 4.4151e+0

k1 = 4.1071e+0

t70c [#1:1]-[#7X3:2]-!@[#6X3:3](=[#8,#16,#7:4])-[#6,#1]

k1 = 2.5

k2 = 2.0

k1 = 1.2406e+0

k2 = 9.0656e-1

k1 = 1.5283e+0

k2 = 7.3406e-1

k1 = 1.1159e+0

k2 = 7.6465e-1

t70d [*:1]-[#7X3:2]-!@[#6X3:3](=[#8,#16,#7:4])-[#7X3]

k1 = 2.5

k1= 1.3031e+0

k1 = 1.6149e+0

k1 = 1.1680e+0

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Although the k1 value for t70a seems unphysical, the result below shows the plots got improved after the optimization. checked improvement for all of the four fitting targets.

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4. Conclusions

* Fitting torsion parameters to simpler torsion targets (with less + Selecting simple geometries (no strong electrostatic interaction) might be needed for the next round fittingmay need to be considered in the next torsion training dataset selection procedure.