Department of Physical Chemistry, Palacky University, 771 46 Olomouc, Czech Republic.
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, 166 10 Prague, Czech Republic.
J Chem Theory Comput. 2011 Mar 8;7(3):685-9. doi: 10.1021/ct200005p. Epub 2011 Feb 10.
The dispersion energy term in the symmetry-adapted perturbation theory based on the density functional theory (DFT-SAPT) converges rather slowly with basis set size. Accurate results for large complexes, where only calculations in small basis sets are practical, can be obtained by extrapolation to the complete basis set limit (CBS). In this paper, we propose an extrapolation scheme with the variable exponent optimized specifically for the DFT-SAPT calculations in correlation-consistent basis sets with diffuse functions. Another way to improve the accuracy term at no additional cost is to scale the dispersion term by a fixed amount. We present the scaling factors averaged over a balanced set of 10 model complexes. The results of these schemes are compared to the high-quality DFT-SAPT/CBS interaction energies in small complexes obtained by fitting to a series of basis sets up to aug-cc-pV5Z and to the CCSD(T)/CBS interaction energies. It is shown that even the cheapest extrapolation scheme yields results that are limited by the accuracy of the DFT-SAPT approach rather than by the basis set convergence. Scaling the dispersion term allows accurate interaction energies as well as their components to be obtained using just the aug-cc-pVDZ basis set; such a calculation can be applied to complexes consisting of up to 50 first-row atoms.
基于密度泛函理论的对称自适应微扰理论（DFT-SAPT）中的色散能项随基组大小的增加而收敛得相当缓慢。对于大型配合物，只能在小基组中进行计算，因此需要通过外推到完全基组极限（CBS）来获得准确的结果。在本文中，我们提出了一种特定于具有弥散函数的相关一致基组中 DFT-SAPT 计算的变指数外推方案。另一种无需额外成本即可提高精度项的方法是按固定量缩放色散项。我们给出了在一组平衡的 10 个模型配合物上平均的缩放因子。这些方案的结果与通过拟合至 aug-cc-pV5Z 系列基组并与 CCSD(T)/CBS 相互作用能得到的小配合物中高质量的 DFT-SAPT/CBS 相互作用能进行了比较。结果表明，即使是最便宜的外推方案，其结果也受到 DFT-SAPT 方法的精度限制，而不是基组收敛性的限制。缩放色散项允许使用仅 aug-cc-pVDZ 基组获得准确的相互作用能及其分量；这样的计算可以应用于由最多 50 个第一行原子组成的配合物。
