Several
computational techniques for solid-state applications have
recently been proposed to enlarge the scope of computer simulations
of large molecular systems. In this contribution, we focused on two
of these, namely, HF-3c and PBEh-3c. They were recently proposed by
the Grimme’s group, as “low-cost” ab initio-based
techniques for electronic structure calculation of large systems and
were proved to be effective essentially for organic molecules. HF-3c
is based on a Hartree–Fock Hamiltonian with a minimal Gaussian
quality basis set, whereas PBEh-3c is a density functional theory
(DFT) based method with a hybrid functional and a medium-quality basis
set. Both HF-3c and PBEh-3c account for dispersion (London) interactions
and are free from the basis set superposition error due to limited
basis set size, through several pairwise semiempirical corrections.
To the best of our knowledge, despite the promising results on the
cost-accuracy side of molecular simulations of organic molecules,
these methods have been used only in few cases for solid-state applications.
In this contribution, we studied the performance of HF-3c and PBEh-3c
for predicting the properties of inorganic crystals to enlarge the
applicability of these cheap and fast methodologies. As a testing
ground, we have chosen a well-known class of material, e.g., microporous
all-silica zeolites. We benchmarked geometries, formation energies,
vibrational features, and mechanical properties by comparing the results
with literature data from both experiment and computer simulation.
For structures, HF-3c is extremely accurate in predicting the zeolites
cell volume, albeit we do not include any vibrational contribution,
neither zero point nor thermal, on the computed volumes, which may
introduce small variations in the predicted values. For the energetic,
the relative stability of the zeolites using the DFT//HF-3c approach
allows predictions within the experimental error for most of the cases
taken into consideration when the experimental enthalpies were corrected
back to electronic energies by using the HF-3c thermodynamic contributions
computed in the harmonic approximation. This strategy is particularly
convenient, as the slow step (geometry optimization) is carried out
with the cheapest HF-3c method, whereas the fast step (single point
energy evaluation) is carried out with costly DFT methods. In this
sense, the use of the DFT//HF-3c approach results to be a promising
one to predict the stability and structure of microporous materials.
Finally, the HF-3c method predicts the mechanical properties of the
zeolite set in reasonable agreement with respect to those computed
with the state-of-the-art DFT simulations, indicating the HF-3c method
as a possible technique for the mechanical stability screenings of
microporous materials.