Abstract
An ab initio density functional theory method (DFT) with D3 dispersion corrections (DFT-D3) was employed to study the 64 possible models of the structure of hectorite intercalated with tetramethylammonium (TMA) cations with the aim to find the additional information about the structure for the energetically most suitable mutual arrangement of the TMA cations. The complex analysis of total energies showed small differences among the structural models with the lowest (L model) and the highest (H model) total energy (~50 kJ/mol). The analysis of the calculated vibrational spectrum of the L model of the TMA-H structure was conducted in detail.
Highlights
Natural or synthetic smectites, like hectorites, are important, widely abundant and low-cost materials with unique physicochemical properties, such as swelling, intercalation and ion-exchange properties
The characteristics mentioned above predetermine the hectorites for application in medicine and pharmacology, e.g., for drug delivery purposes [3,4] or as a potential sorbent of waste compounds [5]
In addition to the refined atomic positions, e.g., hydrogen atoms, which enable the study of hydrogen bonds, it is possible to analyze the vibrational modes of the individual functional groups in these structures and to help with analyzing the overlapped vibrational bands in the experimentally measured spectrum [31,32,33,34]
Summary
Like hectorites, are important, widely abundant and low-cost materials with unique physicochemical properties, such as swelling, intercalation and ion-exchange properties. In addition to the refined atomic positions, e.g., hydrogen atoms, which enable the study of hydrogen bonds, it is possible to analyze the vibrational modes of the individual functional groups in these structures and to help with analyzing the overlapped vibrational bands in the experimentally measured spectrum [31,32,33,34]. The determination of the atomic positions of the intercalated molecules/cations might be problematic as well [36], because the further experimental refinement of the atomic positions of the intercalated species is not possible This is the case for the structural refinement of the TMA hectorite (TMA-H) intercalate [37,38], where the authors used the results obtained for TMA vermiculite intercalate [39] and results from the theoretical modeling of TMA vermiculite [40] for the refinement of the TMA-H structure. DFT calculations were performed involving dispersion corrections using a D3 scheme, as recommended for the PBE functional [47]
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