During the project we implemented and tested different quantum chemistry methods
with the goal of identifying a promising scheme for the treatment of adsorption
and reactions of molecules in zeolites. Namely, we first added the necessary
computer routines to perform calculations with the so-called mid-range DFT
functionals into the VASP code. Unfortunately, tests with different such
functionals showed no clear winner and method that would lead to substantially
improved results.
In further work, we developed a test set for the adsorption of small molecules in
zeolites. For this dataset we obtained adsorption energies with state-of-the-art
dispersion corrected DFT functionals, the random phase approximation with singles
excitations scheme (RPA+SE), that we developed and implemented right before the
start of the MSC grant, and with the MP2 approach, which is usually considered to
offer reference quality results for adsorption in zeolites. We found that the
RPA+SE method gives results very similar to those obtained with MP2. To identify,
which one of these methods is actually better, we created an additional test
set for finite clusters cut out of the material. This allowed our collaborators
to obtain reference quality adsorption energies with the coupled cluster scheme.
These data show that the RPA with singles outperforms MP2 for the problem.
Its low cost makes it thus a very promising method for the treatment of adsorption
in zeolites. In fact, we applied the scheme to zeolite where recent experimental
data for adsorption of small molecules are available. We found a close
agreement with the reference and much improved performance compared to any other
scheme that is currently available.
Encouraged by the high quality of the results offered by the RPA with singles,
we applied it to several other problems. First, to molecular systems, where
accurate methods are also highly desirable. Moreover, they are highly relevant
for adsorption as the results reflect the accuracy of the description of the
interactions between the molecules adsorbing in the material. We again found
the best performance among all the methods that are currently available for the
treatment of molecular solids within periodic boundary conditions. Second, we
applied the scheme to systems relevant to catalysis. Namely, to the problem of
finding stable positions of extraframework ions in the zeolite matrix (siting).
Finally, we implemented a new version of the van der Waals density functional
scheme that takes explicitly into account the spin-polarisation of the material.
We also took part in the implementation of the low scaling version of the GW
approach for the calculation of electronic levels. This GW scheme can be applied
to systems with the typical cell size of zeolites.
So far, we have published two papers from the project, one more is close to being submitted.
We will publish at least one with the results for adsorption energies and at least one with the siting
results. The problems regarding the implementation of screened functionals will be also
published, once a clear conclusion can be made.
The results and project were presented at the following conferences:
* DPG Regensburg, March 2016 (oral presentation)
* JCP Frontiers, September 2016 (poster)
and following seminars:
* Faculty of Natural Sciences, Prague, April 2015
* Faculty of Mathematics and Physics, Prague, November 2015
* University College London, August 2016
* Institute of Physics, Prague, November 2016
