Table 1. Relative Conformer Energies (kcal/mol) for the Blocked Alanine Tetrapeptide Calculated with Various ab Initio and DFT Methods and Molecular Mechanics Force Fields.
| conformer number | RI-MP2a | ωB97X-Db | M06-2Xc | OPLS-AA | OPLS-AA/L | 500 K | 1000 K | 2000 K | unweighted | ff99d | ff99sbe | ff99sb-NMRf | Amoebag |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 4.13 | 4.72 | 4.95 | 4.21 | 3.63 | 5.51 | 5.14 | 4.50 | 3.61 | 4.85 | 4.42 | 6.77 | 3.07 |
| 2 | 4.19 | 4.71 | 4.96 | 3.77 | 3.60 | 4.88 | 4.64 | 4.22 | 3.68 | 5.09 | 4.79 | 6.81 | 3.62 |
| 3 | 0.57 | 0.57 | 1.96 | 0.00 | 0.04 | 0.00 | 0.09 | 0.13 | 0.32 | 2.86 | 1.60 | 2.50 | 0.00 |
| 4 | 5.73 | 6.14 | 6.62 | 4.86 | 4.30 | 6.01 | 5.69 | 5.09 | 4.25 | 7.25 | 5.39 | 7.32 | 4.07 |
| 5 | 5.26 | 5.79 | 6.26 | 5.93 | 3.56 | 6.05 | 5.49 | 4.96 | 4.24 | 4.35 | 5.03 | 7.23 | 3.96 |
| 7 | 6.67 | 6.95 | 7.25 | 5.39 | 6.12 | 5.42 | 5.47 | 5.45 | 5.48 | 4.67 | 7.64 | ||
| 8 | 4.64 | 5.62 | 5.31 | 7.97 | 5.20 | 5.94 | 5.62 | 5.37 | 5.39 | 7.46 | 5.36 | 6.90 | 5.45 |
| 9 | 7.92 | 7.79 | 9.22 | 7.21 | 7.45 | 6.45 | 6.60 | 6.58 | 6.67 | 7.64 | 5.89 | 7.12 | 10.01 |
| 10 | 7.79 | 8.80 | 8.54 | 10.88 | 7.67 | 8.11 | 7.23 | 6.86 | 5.69 | 5.44 | 4.14 | 8.50 | 6.34 |
| 11 | 0.00 | 0.46 | 0.56 | 0.36 | 0.32 | 0.10 | 0.17 | 0.31 | 0.48 | 0.03 | 0.40 | 0.30 | 0.75 |
| 12 | 0.29 | 0.00 | 0.00 | 0.00 | 0.19 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.75 | |
| 13 | 3.66 | 4.02 | 4.34 | 2.67 | 2.69 | 3.51 | 3.34 | 3.15 | 3.02 | 3.87 | 4.07 | 5.80 | 3.56 |
| 14 | 4.68 | 4.78 | 5.36 | 3.26 | 6.38 | 5.68 | 5.30 | 4.84 | 3.02 | 4.92 | 6.52 | 4.66 | |
| 15 | 2.19 | 2.84 | 2.33 | 4.01 | 1.80 | 3.00 | 2.47 | 2.09 | 2.11 | 4.49 | 2.57 | 4.63 | 2.28 |
| 17 | 3.42 | 3.15 | 3.98 | 0.15 | 4.41 | 4.43 | 4.35 | 4.28 | 6.32 | 3.92 | 5.10 | 2.32 | |
| 18 | 1.91 | 2.42 | 2.70 | 0.72 | 0.87 | 1.30 | 1.18 | 1.22 | 1.52 | 1.57 | 2.49 | 3.95 | 2.19 |
| 19 | 3.82 | 3.97 | 4.73 | 2.34 | 2.55 | 2.47 | 2.48 | 2.52 | 2.76 | 3.59 | 3.41 | 4.79 | 4.25 |
| 20 | 1.76 | 2.46 | 3.06 | 0.40 | 3.10 | 2.47 | 2.33 | 2.31 | –0.40 | 2.31 | 3.55 | 3.18 | |
| 22 | 5.82 | 6.84 | 7.31 | 5.72 | 5.76 | 5.80 | 5.82 | 5.04 | 5.25 | 5.77 | 6.87 | ||
| 25 | 2.50 | 3.43 | 3.76 | 4.26 | 0.41 | 3.21 | 2.54 | 2.41 | 2.44 | 2.01 | 1.60 | 2.87 | |
| 26 | 0.67 | 1.89 | 2.10 | –1.00 | 2.77 | 1.87 | 1.67 | 1.59 | –2.87 | 0.65 | 1.48 | 1.6 | |
| RMS RI-MP2 | 0.60 | 0.93 | 1.54 | 1.42 | 1.03 | 0.77 | 0.71 | 0.97 | 1.74 | 1.05 | 1.70 | 0.99 | |
| RMS ωB97X-D | 0.60 | 0.60 | 1.30 | 1.78 | 0.88 | 0.86 | 0.94 | 1.38 | 1.98 | 1.32 | 1.47 | 1.12 | |
| RMS M06-2X | 0.93 | 0.60 | 1.72 | 2.04 | 1.18 | 1.20 | 1.29 | 1.75 | 2.08 | 1.52 | 1.40 | 1.25 |