Fouda Adam, Ryde Ulf
Department of Theoretical Chemistry, Chemical Centre, Lund University , P. O. Box 124, SE-221 00 Lund, Sweden.
J Chem Theory Comput. 2016 Nov 8;12(11):5667-5679. doi: 10.1021/acs.jctc.6b00903. Epub 2016 Oct 27.
We have examined how the self-interaction error in density-functional theory (DFT) calculations affects energies calculated on large systems (600-1000 atoms) involving several charged groups. We employ 18 different quantum mechanical (QM) methods, including Hartree-Fock, as well as pure, hybrid, and range-separated DFT methods. They are used to calculate reaction and activation energies for three different protein models in vacuum, in a point-charge surrounding, or with a continuum-solvent model. We show that pure DFT functionals give rise to a significant delocalization of the charges in charged groups in the protein, typically by ∼0.1 e, as evidenced from the Mulliken charges. This has a clear effect on how the surroundings affect calculated reaction and activation energies, indicating that these methods should be avoided for DFT calculations on large systems. Fortunately, methods such as CAM-B3LYP, BHLYP, and M06-2X give results that agree within a few kilojoules per mole, especially when the calculations are performed in a point-charge surrounding. Therefore, we recommend these methods to estimate the effect of the surroundings with large QM systems (but other QM methods may be used to study the intrinsic reaction and activation energies).
我们研究了密度泛函理论（DFT）计算中的自相互作用误差如何影响在包含多个带电基团的大型系统（600 - 1000个原子）上计算的能量。我们采用了18种不同的量子力学（QM）方法，包括Hartree - Fock方法，以及纯DFT、杂化DFT和范围分离DFT方法。这些方法用于计算三种不同蛋白质模型在真空、点电荷环境或连续介质溶剂模型中的反应和活化能。我们表明，从Mulliken电荷可以看出，纯DFT泛函会导致蛋白质中带电基团的电荷显著离域，通常约为0.1 e。这对周围环境如何影响计算出的反应和活化能有明显影响，表明在大型系统的DFT计算中应避免使用这些方法。幸运地是，诸如CAM - B3LYP、BHLYP和M06 - 2X等方法给出的结果在每摩尔几千焦耳的范围内一致，特别是当计算在点电荷环境中进行时。因此，我们推荐这些方法来估计大型QM系统中周围环境的影响（但也可以使用其他QM方法来研究内在反应和活化能）。
