A hybrid QM:QM method (MP2:(PBE+D2) + ΔCCSD(T)) is employed that reaches chemical accuracy (±4 kJ mol⁻¹) for periodic systems. Three mechanisms are considered and evidence is produced that cracking proceeds via protonation of a CC bond at the Brønsted acid site. For H-FER, H-MFI, and H-CHA, the deviations between predictions (uncertainty ± 4 kJ mol⁻¹) and experiment (error ± 5 kJ mol⁻¹) are between −3 and +8 kJ mol⁻¹. The predicted apparent enthalpy barriers for H-FER, H-MFI, H-CHA, and H-FAU at 650 K are 153, 153, 160, and 182 kJ mol⁻¹, respectively. Their variation with the pore size is dominated by the adsorption enthalpies (−55, −47, −40, and −29 kJ mol⁻¹, respectively), whereas the intrinsic enthalpy barriers vary within a narrow range of 10 kJ mol⁻¹ only. Routine PBE+D2 calculations show large errors, −16 to −20 and −40 to −60 kJ mol⁻¹ for adsorption enthalpies and enthalpy barriers, respectively.

采用了混合QM：QM方法（MP2：（PBE + D2）+ΔCCSD（T）），该方法可达到周期性系统的化学精度（±4 kJ mol ^-1）。考虑了三种机理，并且产生了通过在布朗斯台德酸位点处的C C键的质子化来进行裂解的证据。对于H-FER，H-MFI和H-CHA，预测（不确定度±4 kJ mol ^-1）和实验（误差±5 kJ mol ^-1）之间的偏差在-3和+8 kJ mol ^-1之间。H-FER，H-MFI，H-CHA和H-FAU在650 K时的预测表观焓垒分别为153、153、160和182 kJ mol ^-1。它们随孔径的变化主要受吸附焓（-55，-47，-40和-29 kJ mol^-1），而固有焓垒仅在10 kJ mol ^-1的狭窄范围内变化。常规PBE + D2计算显示出较大的误差，分别是吸附焓和焓垒的-16至-20和-40至-60 kJ mol ^-1。