Department of Microtechnology and Nanoscience (MC2), Chalmers University of Technology, SE-41296 Gothenburg, Sweden.
J Chem Phys. 2018 May 21;148(19):194115. doi: 10.1063/1.5012870.
The vdW-DF-cx0 exchange-correlation hybrid design [K. Berland , J. Chem. Phys. , 234106 (2017)] has a truly nonlocal correlation component and aims to facilitate concurrent descriptions of both covalent and non-covalent molecular interactions. The vdW-DF-cx0 design mixes a fixed ratio, , of the Fock exchange into the consistent-exchange van der Waals density functional, vdW-DF-cx [K. Berland and P. Hyldgaard, Phys. Rev. B , 035412 (2014)]. The mixing value is sometimes taken as a semi-empirical parameter in hybrid formulations. Here, instead, we assert a plausible optimum average value for the vdW-DF-cx0 design from a formal analysis; A new, independent determination of the mixing is necessary since the Becke fit [A. D. Becke, J. Chem. Phys. , 5648 (1993)], yielding ' = 0.2, is restricted to semilocal correlation and does not reflect non-covalent interactions. To proceed, we adapt the so-called two-legged hybrid construction [K. Burke , Chem. Phys. Lett. , 115 (1997)] to a starting point in the vdW-DF-cx functional. For our approach, termed vdW-DF-tlh, we estimate the properties of the adiabatic-connection specification of the exact exchange-correlation functional, by combining calculations of the Fock exchange and of the coupling-constant variation in vdW-DF-cx. We find that such vdW-DF-tlh hybrid constructions yield accurate characterizations of molecular interactions (even if they lack self-consistency). The accuracy motivates trust in the vdW-DF-tlh determination of system-specific values of the Fock-exchange mixing. We find that an average value ' = 0.2 best characterizes the vdW-DF-tlh description of covalent and non-covalent interactions, although there exists some scatter. This finding suggests that the original Becke value, ' = 0.2, also represents an optimal average Fock-exchange mixing for the new, truly nonlocal-correlation hybrids. To enable self-consistent calculations, we furthermore define and test a zero-parameter hybrid functional vdW-DF-cx0p (having fixed mixing ' = 0.2) and document that this truly nonlocal correlation hybrid works for general molecular interactions (at reference and at relaxed geometries). It is encouraging that the vdW-DF-cx0p functional remains useful also for descriptions of some extended systems.
vdW-DF-cx0 交换相关杂化设计 [K. Berland, J. Chem. Phys., 234106 (2017)] 具有真正的非局域相关分量，旨在促进共价和非共价分子相互作用的同时描述。vdW-DF-cx0 设计混合了固定比例的 Fock 交换到一致交换范德华密度泛函 vdW-DF-cx [K. Berland 和 P. Hyldgaard, Phys. Rev. B, 035412 (2014)] 中。混合值在杂化配方中有时被视为半经验参数。在这里，我们从形式分析中主张 vdW-DF-cx0 设计的合理最佳平均值；由于 Becke 拟合 [A. D. Becke, J. Chem. Phys., 5648 (1993)] 仅限于半局域相关，并且不反映非共价相互作用，因此需要对新的、独立的混合值进行确定。为了继续进行，我们将所谓的双足杂化结构 [K. Burke, Chem. Phys. Lett., 115 (1997)] 应用于 vdW-DF-cx 功能的起点。对于我们的方法，称为 vdW-DF-tlh，我们通过结合计算 Fock 交换和 vdW-DF-cx 中的耦合常数变化来估计精确交换相关泛函的绝热连接规范的性质。我们发现，即使缺乏自洽性，此类 vdW-DF-tlh 杂化结构也能准确描述分子相互作用。准确性促使人们信任 vdW-DF-tlh 对特定系统的 Fock 交换混合的确定。我们发现，平均值 '= 0.2 可以最好地描述 vdW-DF-tlh 对共价和非共价相互作用的描述，尽管存在一些分散。这一发现表明，原始的 Becke 值 '= 0.2 也代表了新的真正非局域相关杂化的最佳平均 Fock 交换混合。为了实现自洽计算，我们还定义并测试了一个零参数杂化功能 vdW-DF-cx0p（具有固定混合 '= 0.2），并记录到该真正非局域相关杂化适用于一般分子相互作用（在参考和松弛构象下）。令人鼓舞的是，vdW-DF-cx0p 功能对于一些扩展系统的描述也仍然有用。
