Monte Carlo Potential Energy Sampling for Molecular Entropy in Zeolites

Zeolites are widely
applied as molecular sieves and porous host
materials for active sites in heterogeneous catalysis. Adsorption
and reaction kinetics depend critically on the molecular entropy in
the zeolite. In this work, we introduce a method to calculate the
entropy of molecules in zeolites using Monte Carlo integration of
the semiclassical partition function. The method is demonstrated for
N2 and CH4 in chabazite and MFI silicalites.
We find that the molecular entropy is lowered by a factor between 1/3 and 1/2 with respect to
the gas-phase value. The results are corroborated by explicit molecular
dynamics simulations revealing the active molecular degrees of freedom.
The possibility of accurate entropy estimations opens up for an improved
description of catalytic reactions and sorption phenomena in zeolites.

沸石（Zeolites）作为分子筛与多相催化中活性位点的多孔主体材料，已获得广泛应用。吸附与反应动力学极大程度上依赖于沸石内部的分子熵。本研究提出一种基于半经典配分函数的蒙特卡洛（Monte Carlo）积分法，用于计算沸石内分子的熵。该方法以菱沸石（chabazite）与MFI型硅沸石（MFI silicalite）中的N₂和CH₄为演示案例。研究结果表明，相较于气相条件下的分子熵值，沸石内分子的熵会降至原有的1/3至1/2。该结论通过揭示分子活性自由度的显式分子动力学模拟得到验证。精准熵估算的实现，为沸石内催化反应与吸附现象的精细化描述开辟了新的路径。