Table 2.

Interaction Energies $\mathbf{IE}({\mathbf{Gly}}_{\mathit{m}}{:\mathrm{Gly}}_{\mathit{n}})$ of Glycine Dipeptide Oligomers ${\mathbf{Gly}}_{\mathit{m}}{:\mathrm{Gly}}_{\mathit{n}}$ Calculated by $\omega B97X-\mathbf{D}$/aTZ and Molecular Mechanical Force Fields (kcal/mol)^a

$\omega \text{B97X}-\mathrm{D}$/aTZ		pGM-perm	pGM-ind	Amoeba13	ff12pol	ff19SB	ff15ipq	ff03
$\text{Gly:Gly}$
$\alpha \mathrm{R}$ b	−14.73	−16.21 (−1.48)d	−16.09 (−1.36)	−12.98 (1.75)	−12.91 (1.81)	−16.04 (−1.31)	−19.08 (−4.35)	−15.35 (−0.62)
$\mathrm{a}\beta$ b	−14.53	−16.01 (−1.48)	−16.13 (−1.60)	−13.82 (0.71)	−14.67 (−0.15)	−13.60 (0.92)	−16.31 (−1.78)	−11.83 (2.70)
$\beta$ b	−17.36	−19.24 (−1.88)	−19.28 (−1.92)	−14.16 (3.20)	−17.82 (−0.46)	−15.69 (1.67)	−18.85 (−1.48)	−14.78 (2.58)
${\text{Gly:Gly}}_2$
$\alpha \mathrm{R}$ b	−17.90	−19.21 (−1.31)	−19.11 (−1.22)	−15.38 (2.52)	−14.94 (2.96)	−17.90 (−0.01)	−21.30 (−3.40)	−17.09 (0.80)
$\mathrm{a}\beta$ b	−16.00	−17.26 (−1.26)	−17.38 (−1.38)	−14.89 (1.11)	−15.68 (0.32)	−14.06 (1.94)	−16.83 (−0.83)	−12.28 (3.72)
$\beta$ b	−18.99	−20.64 (−1.65)	−20.67 (−1.69)	−15.42 (3.57)	−18.97 (0.02)	−16.19 (2.80)	−19.45 (−0.46)	−15.26 (3.73)
${\text{Gly:Gly}}_3$
$\alpha \mathrm{R}$ b	−19.06	−20.32 (−1.26)	−20.23 (−1.18)	−16.26 (2.80)	−15.68 (3.37)	−18.42 (0.63)	−21.93 (−2.87)	−17.57 (1.48)
$\mathrm{a}\beta$ b	−16.12	−17.36 (−1.24)	−17.47 (−1.35)	−14.95 (1.17)	−15.74 (0.38)	−14.09 (2.03)	−16.86 (−0.74)	−12.31 (3.81)
$\beta$ b	−19.16	−20.79 (−1.63)	−20.83 (−1.67)	−15.56 (3.61)	−19.08 (0.08)	−16.25 (2.91)	−19.52 (−0.36)	−15.31 (3.85)
${\text{Gly}}_2{\text{:Gly}}_2$
$\alpha \mathrm{R}$ b	−22.11	−23.20 (−1.09)	−23.12 (−1.01)	−18.54 (3.57)	−17.71 (4.40)	−20.30 (1.81)	−24.16 (−2.04)	−19.36 (2.75)
$\mathrm{a}\beta$ b	−17.72	−18.75 (−1.03)	−18.85 (−1.13)	−16.21 (1.51)	−16.88 (0.84)	−14.61 (3.11)	−17.49 (0.23)	−12.80 (4.92)
$\beta$ b	−21.02	−22.34 (−1.33)	−22.40 (−1.38)	−16.98 (4.03)	−20.27 (0.75)	−16.77 (4.25)	−20.14 (0.87)	−15.80 (5.22)
${\text{Gly}}_3{\text{:Gly}}_3$
$\alpha \mathrm{R}$ b	−25.73	−26.68 (−0.96)	−26.63 (−0.90)	−21.27 (4.45)	−20.09 (5.64)	−21.91 (3.82)	−26.11 (−0.39)	−20.86 (4.87)
$\mathrm{a}\beta$ b	−18.03	−18.99 (−0.97)	−19.09 (−1.07)	−16.37 (1.66)	−17.04 (0.98)	−14.69 (3.33)	−17.57 (0.46)	−12.90 (5.12)
$\beta$ b	−21.47	−22.74 (−1.27)	−22.80 (−1.32)	−17.33 (4.14)	−20.56 (0.91)	−16.92 (4.55)	−20.33 (1.14)	−15.94 (5.53)
RMSE		1.35	1.37	2.91	2.28	2.67	1.87	3.78
MAE		1.32	1.34	2.65	1.54	2.34	1.43	3.45
max devc		−0.96	−0.90	4.45	5.64	4.55	1.14	5.53
min devc		−1.88	−1.92	0.71	−0.46	−1.31	−4.35	−0.62

^aThe formula for the interaction energies $\text{IE}({\text{Gly}}_m{\text{:Gly}}_n)$ is shown in eq 21.

^b$\alpha \mathrm{R}$, $\mathrm{a}\beta$, and $\beta$ represent $\alpha$-helix, anti-parallel $\beta$-sheet, and parallel $\beta$-sheet conformations, respectively.

^cThe maximum and minimum deviations with $\omega \text{B97X}-\mathrm{D}$/aTZ results.

^dThe values in parentheses are differences between the values calculated by molecular mechanical force fields and corresponding values calculated by the $\omega \text{B97X}-\mathrm{D}$/aTZ method.