(630d) Establishing the Zeolite SSZ-13 As Test System for Quantum Chemical Methods

Understanding the performance of various quantum chemical methods is
key in understanding the reliability in applications to realistic
systems. The typical approach to address this problem is to
investigate test systems, where high-quality experimental data is
available or high-quality quantum chemical modeling is possible. In
this contribution we describe our efforts in establishing the zeolite
SSZ-13 as a test system for quantum chemical modeling. SSZ-13 is a
zeolite in the chabazite structure, which has the smallest unit cell.
This allows the fully periodic application of various high-level
quantum chemical methods, such as the Adiabatic Connection
Fluctuation-Dissipation Theorem in its Random Phase Approximation
(RPA) and second order Møller-Plesset perturbation theory (MP2) for
total energy calculations, or GW and Bethe-Salpeter Equation for
spectroscopy.

In this work we show our efforts in describing the adsorption of
alkanes in SSZ-13. This is a particular challenging problem, since van
der Waals interactions represent the largest part of the adsorption
strength. We compare the performance of dispersion corrected density
functionals (PBE+d(2), PBE-TS, PBE-dDsC) and vdW-DF type functionals
(vdW-DF, vdW-optB86b, vdW-DF2, BEEF) to high level quantum chemical
methods (RPA, MP2). After a correction for finite temperature
effects PBE-d(2) leads to the best agreement with RPA, MP2 and
experimental measurements, while all the other methods lead to a
significant overestimation of the adsorption strength. We furthermore
explain this overestimation as a fundamental flaw in the construction
of these functionals, where non-local screening interactions are
only included implicitly.

The results presented here are highly important to arrive at a solid
understanding the performance of different quantum chemical methods in
zeolite catalysis and to judge the reliability of computational
predictions.