Fadda Elisa, Woods Robert J
School of Chemistry, National University of Ireland, Galway, University Road, Galway, Ireland.
School of Chemistry, National University of Ireland, Galway, University Road, Galway, Ireland; Complex Carbohydrate Research Center and Department of Chemistry, University of Georgia, Athens, GA 30602, USA.
Can J Chem. 2013 Sep 1;91(9):859-865. doi: 10.1139/cjc-2012-0542.
In this work we analyze the effect of the inclusion of an empirical dispersion term to standard DFT (DFT-D) in the prediction of the conformational energy of the alanine dipeptide (Ala2) and in assessing the relative stabilities of short polyala-nine peptides in helical conformations, i.e., α and 3 helices, from Ala4 to Ala16. The Ala2 conformational energies obtained with the dispersion-corrected GGA functional B97-D are compared to previously published high level MP2 data. Meanwhile, the B97-D performance on larger polyalanine peptides is compared to MP2, B3LYP and RHF calculations obtained at a lower level of theory. Our results show that electron correlation affects the conformational energies of short peptides with a weight that increases with the peptide length. Indeed, while the contribution of vdW forces is significant for larger peptides, in the case of Ala2 it is negligible when compared to solvent effects. Even for short peptides, the inclusion of an empirical dispersion term greatly improves accuracy of DFT methods, providing results that correlate very well with the MP2 reference at no additional computational cost.
在本工作中，我们分析了在预测丙氨酸二肽（Ala2）的构象能量以及评估从Ala4到Ala16的短聚丙氨酸肽在α和3螺旋等螺旋构象中的相对稳定性时，向标准密度泛函理论（DFT）中加入经验色散项（DFT-D）的影响。将通过色散校正的广义梯度近似（GGA）泛函B97-D获得的Ala2构象能量与先前发表的高水平二阶微扰理论（MP2）数据进行比较。同时，将B97-D在较大聚丙氨酸肽上的性能与在较低理论水平下获得的MP2、B3LYP和限制性 Hartree-Fock（RHF）计算结果进行比较。我们的结果表明，电子相关作用对短肽构象能量的影响程度随肽链长度增加而增大。实际上，虽然范德华力对较大肽的贡献显著，但对于Ala2而言，与溶剂效应相比其可忽略不计。即使对于短肽，加入经验色散项也能极大地提高DFT方法的准确性，在不增加额外计算成本的情况下提供与MP2参考值相关性很好的结果。
