Fakultät für Physik and Center for Computational Materials Science, Universität Wien, Sensengasse 8/12, A-1090 Wien, Austria.
J Chem Phys. 2012 Feb 14;136(6):064503. doi: 10.1063/1.3676410.
The influence of the exchange-correlation functional (semilocal gradient corrected or hybrid functional) on density-functional studies of the adsorption of CO and NO in Cu- and Co-exchanged chabazite has been investigated, extending the studies of the structural and electronic properties of these materials [F. Göltl and J. Hafner, J. Chem. Phys. 136, 064501 (2012); 136, 064502 (2012)] and including for comparison carbonyls and nitrosyls of Cu and Co. Hybrid functionals predict much lower adsorption energies than conventional semilocal functionals, in better agreement with experiment as far as data are available for comparison. The calculated adsorption energies show a strong linear correlation with the stability of the cation sites. For Cu(I)-chabazite the calculated adsorption energies span almost the interval between the adsorption energies calculated for pure neutral and positively charged Cu-carbonyls and nitrosyls. For divalent Cu(II) and Co(II) the adsorption energies at cations in chabazite are much lower than the metal-molecule binding energies in the free carbonyls or nitrosyls, especially for the most stable cation location in a six-membered ring of the chabazite structure. For the stretching modes of adsorbed CO only hybrid functionals reproduce the blueshift of the frequency reported for all Cu(I)- and Co(II)-zeolites. For Cu(II)-chabazite both types of functionals predict a blueshift, the larger value calculated with hybrid functionals being in better agreement with observation. For NO adsorbed on Cu(I)-chabazite all functionals produce a redshift, the smaller value derived with hybrid functionals being in better agreement with experiment. For NO adsorbed in Cu(II)- and Co(II)-chabazite gradient-corrected functionals produce the best agreement with experiment for cations located in a six-membered ring. Semilocal functionals tend to underestimate the frequencies, while hybrid functionals tend to overestimate. The decisive factors determining the influence of the functionals are the larger HOMO-LUMO gap and the larger bandgap of the zeolite host, as well as the larger exchange-splitting of the cation eigenstates predicted with hybrid functionals. For Co(II)-chabazite the tendency to overestimate the exchange-splitting and to stabilize a high-spin state lead to better results with semilocal functionals. Finally, a comprehensive discussion of the influence of the exchange-correlation functional on the physico-chemical properties of these complex systems, based all three papers of this series is presented.
交换相关泛函（半局域梯度修正或杂化泛函）对 CO 和 NO 在 Cu 和 Co 交换丝光沸石中吸附的密度泛函研究的影响已被研究，扩展了对这些材料的结构和电子性质的研究[F. Göltl 和 J. Hafner，J. Chem. Phys. 136, 064501 (2012); 136, 064502 (2012)]，并包括 Cu 和 Co 的羰基和亚硝酰基作为比较。杂化泛函预测的吸附能远低于传统半局域泛函，与实验结果更吻合，只要有数据可供比较。计算出的吸附能与阳离子位的稳定性呈强线性相关。对于 Cu(I)-丝光沸石，计算出的吸附能几乎涵盖了纯中性和带正电荷的 Cu-羰基和亚硝酰基的吸附能区间。对于二价 Cu(II)和 Co(II)，丝光沸石中阳离子的吸附能远低于自由羰基或亚硝酰基中的金属-分子结合能，特别是对于丝光沸石结构的六元环中最稳定的阳离子位置。对于吸附 CO 的伸缩模式，只有杂化泛函才能重现所有 Cu(I)-和 Co(II)-沸石报道的蓝移。对于 Cu(II)-丝光沸石，两种类型的泛函都预测会发生蓝移，杂化泛函计算出的较大值与观察结果更吻合。对于吸附在 Cu(I)-丝光沸石上的 NO，所有泛函都产生红移，杂化泛函得出的较小值与实验结果更吻合。对于 Cu(II)-和 Co(II)-丝光沸石中位于六元环中的阳离子，梯度校正泛函与实验结果的吻合度最好。半局域泛函往往低估频率，而杂化泛函往往高估。决定泛函影响的决定性因素是较大的 HOMO-LUMO 能隙和沸石主体较大的能带隙，以及杂化泛函预测的阳离子本征态的较大交换分裂。对于 Co(II)-丝光沸石，高估交换分裂并稳定高自旋态的趋势导致半局域泛函产生更好的结果。最后，基于本系列的三篇论文，对交换相关泛函对这些复杂体系的物理化学性质的影响进行了全面讨论。
