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首页> 外文期刊>Physical chemistry chemical physics: PCCP >Treating dispersion effects in extended systems by hybrid MP2 : DFT calculations - protonation of isobutene in zeolite ferrierite
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Treating dispersion effects in extended systems by hybrid MP2 : DFT calculations - protonation of isobutene in zeolite ferrierite

机译：通过混合MP2处理扩展系统中的分散效应：DFT计算-沸石镁碱沸石中异丁烯的质子化

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摘要

We propose use of a hybrid method to study problems that involve both bond rearrangements and van-der-Waals interactions. The method combines second-order Moller -Plesset perturbation theory (MP2) calculations for the reaction site with density functional theory (DFT) calculations for a large system under periodic boundary conditions. Hybrid MP2: DFT structure optimisation for a cluster embedded in the periodic model is the first of three steps in a multi-level approach. The second step is extrapolation of the MP2 energy to the complete basis set limit. The third step is extrapolating the high-level (MP2) correction to the limiting case of the full periodic structure. This is done by calculating the MP2 correction for a series of cluster models of increasing size, fitting an analytic expression to these energy corrections, and applying the fitted expression to the full periodic structure. We assume that, up to a constant, the high-level correction is described by a damped dispersion expression. Combining the results of all three steps yields an estimate of the MP2 reaction energy for the full periodic system at the complete basis set level. The method is designed for a reaction between a small or medium sized substrate molecule and a very large chemical system. For adsorption of isobutene in zeolite H-ferrierite, the energies obtained for the formation of different structures, the pi-complex, the isobutoxide, the tert-butoxide, and the tertbutyl carbenium ion, are -78, -73, -48, and -21 kJ mol(-1), respectively. This corresponds to corrections of the pure DFT (PBE functional) results by -62, -70, -67, and -29 kJ mol(-1), respectively. Hence, the MP2 corrections are substantial and, perhaps more importantly, not the same for the different hydrocarbon species in the zeolite. Coupled-cluster (CCSD(T)) calculations change the MP2 energies by -4 kJ mol(-1) (tert-butyl cation) or less (below +/- 1 kJ mol(-1) for the other species).
机译：我们建议使用混合方法来研究涉及键重排和范德华相互作用的问题。该方法将针对反应位点的二阶Moller-Plesset摄动理论（MP2）计算与针对大型系统在周期性边界条件下的密度泛函理论（DFT）计算相结合。混合MP2：针对周期性模型中嵌入的群集的DFT结构优化是多级方法中三个步骤中的第一步。第二步是将MP2能量外推到完整的基准设定极限。第三步是将高级（MP2）校正外推到完整周期结构的极限情况。这是通过为一系列大小增加的群集模型计算MP2校正，将解析表达式拟合到这些能量校正并将拟合的表达式应用于完整的周期结构来完成的。我们假定，直到一个常数为止，高阶校正由阻尼色散表达式来描述。结合所有三个步骤的结果，可以得出完整周期系统在完整基础集级别上的MP2反应能量的估算值。该方法设计用于中小型底物分子与非常大的化学系统之间的反应。为了将异丁烯吸附在沸石H-镁碱沸石中，用于形成不同结构的π-络合物，异丁醇，叔丁醇和叔丁基碳鎓离子的能量分别为-78，-73，-48和分别为-21 kJ mol（-1）。这对应于分别通过-62，-70，-67和-29 kJ mol（-1）对纯DFT（PBE功能）结果的校正。因此，MP2校正是相当大的，也许更重要的是，对于沸石中的不同烃类，MP2校正不相同。耦合簇（CCSD（T））计算会将MP2能量更改为-4 kJ mol（-1）（叔丁基阳离子）或更小（其他物种低于+/- 1 kJ mol（-1））。

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