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):064502. doi: 10.1063/1.3676409.
The influence of the choice of the exchange-correlation functional (semilocal gradient corrected or hybrid functionals) on the electronic properties of metal-exchanged zeolites has been investigated for Cu- and Co-exchanged chabazite. The admixture of exact exchange in hybrid functionals increases the fundamental gap of purely siliceous chabazite, leading to better agreement with experiment and many-body perturbation theory for close-packed SiO(2) polymorphs where detailed experimental information is available. For the metal-exchanged chabazite the increased exchange splitting strongly influences the position of the cation states relative to the framework bands-in general, gradient-corrected functionals locate the occupied cation states close to the valence-band maximum of the framework, while hybrid functionals shift the occupied cation states to larger binding energies and the empty states to higher energies within the fundamental gap. The photoluminescence spectra have been analyzed using fixed-moment total-energy calculations for excited spin states in structurally relaxed and frozen geometries. The geometrical relaxation of the excited states leads to large differences in excitation and emission energies which are more pronounced in calculations using hybrid functionals. Due to the stronger relaxation effects calculated with hybrid functionals, the large differences in the electronic spectra calculated with both types of functionals are not fully reflected in the photoluminescence spectra.
已研究了交换相关泛函（半局部梯度校正或混合泛函）的选择对金属交换沸石的电子性质的影响，分别对 Cu-和 Co-交换丝光沸石进行了研究。混合泛函中精确交换的混入增加了纯硅沸石的基本带隙，导致与实验和多体微扰理论更好地吻合，这些理论适用于具有详细实验信息的密堆积 SiO(2)多晶型体。对于金属交换丝光沸石，增加的交换劈裂强烈影响阳离子态相对于骨架能带的位置-一般来说，梯度校正泛函将占据的阳离子态定位在骨架的价带最大值附近，而混合泛函将占据的阳离子态移动到更大的结合能，将空态移动到基本带隙内更高的能量。使用结构弛豫和冻结结构的固定动量总能量计算分析了光致发光光谱。激发态的几何弛豫导致激发和发射能量的差异很大，在使用混合泛函的计算中更为明显。由于混合泛函计算的弛豫效应更强，因此两种类型泛函计算的电子光谱中的较大差异并未完全反映在光致发光光谱中。
