Structural and electronic characteristic dataset of the water on basal surface the cis- and trans-vacant variety of a montmorillonite

The data given in the paper were obtained using CASTEP based on the density functional theory (DFT) applying a basis set of plane waves and PBE exchange-correlation functional. Van der Waals interactions were considered by the Grimme-D2 semi-empirical correction. The data include the optimized geometry and electronic properties of the equilibrium state of the non-hydrated cis- and trans-vacant variety of a Na-montmorillonite (MMT) and its state after the adsorption of water molecules. The data on hydration shells formed by the Na+ cation on the basal surface of MMT are also presented. The data are presented on the behavior of crystalline hydroxyl groups and water molecules during their adsorption. Data files of the optimized crystal structures and electronic properties can be read by the public text editors.


Subject
Surfaces and Interfaces Specific subject area Surface and Interface Chemistry of Clay Minerals Type of data Graph Figure How the data were acquired Sampling of the initial configurations of the adsorbed molecules on the montmorillonite surface was performed using Monte Carlo method implemented in the Adsorption Locator module of Material Studio software.
The most stable states with the minimum system energy were further optimized.The final equilibrium geometry of the non-hydrated crystal structure of montmorillonite and its structure after the adsorption of water molecules on the basal surface, as well as their electronic properties, were obtained using CASTEP program.

Value of the Data
• The data contains structural and electronic characteristics of cis-and trans-vacant montmorillonite with a single isomorphic substitution Mg 2 + → Al 3 + in the octahedral position.• It can be used to build scale models for solving tasks related to the interface phenomena.
They make it possible to study the effect of the bound water on adsorption processes and contact phenomena.• Data on the electronic structure (partial density of then electronic states) of the models makes it possible to evaluate changes in the state of the system atoms, related to the adsorption processes.

Objective
The models and related data were obtained during a theoretical study of the role of OHcrystalline groups in cis -and trans -vacant positions in the montmorillonite octahedral layer during the adsorption of water molecules.The obtained data were used to interpret the changes caused by the adsorption of water molecules on the basal surface of montmorillonite.

Data Description
Fig. 1 shows non-hydrated crystal structures of montmorillonite with a single isomorphic substitution Mg 2 + → Al 3 + in the octahedral position with cis -and trans-vacant states.Na + cation was used to compensate the charge, appeared in the structure due to the isomorphic substitution.
The given geometric structures of montmorillonite (MMT) are optimized to achieve an equilibrium state.The dispersion forces were taken into account as a correction to the calculated total system energy.Consideration of this correction was required for the correct description of  preliminary sample of possible states with the lowest total energy was performed with Monte Carlo method.For the selected states, geometric optimization was performed using DFT method.The data is presented on the hydration shells formed around Na + cation with the indicated interatomic distances.
The partial densities of the electronic states (PDOS) of crystalline OH groups that characterize non-hydrated MMT models, models with an adsorbed layer of the water molecules, and the absorption water layer itself are shown in Fig. 3 -5 .Fig. 3 shows PDOS of the H and O atoms included in the upper and lower crystalline OH groups with respect to the MMT basal surface in the area of isomorphic Mg 2 + → Al 3 + substitution.Fig. 4 shows PDOS of crystalline OH group atoms that allow evaluating the changes related to the adsorption of the water molecules on the basal surface of MMT.Fig. 5 shows PDOS data for H and O atoms of the adsorbed water molecules.The obtained data make it possible to evaluate the changes connected with the process of adsorption of the water molecules on the basal surface of MMT.

Experimental Design, Materials and Methods
The non-hydrated model of the montmorillonite was created on the basis of two primitive unit cells forming a Si 16 Al 7 Mg 1 O 40 (OH) 8 Na supercell of 81 atoms with the sizes 10.36 ×8.89 ×15 Å. Montmorillonite with an adsorption layer of the water molecules consisting of 12 water molecules has the following configuration: Si 16 Al 7 Mg 1 O 40 (OH) 8 Na12(H 2 O).
The preliminary structure of the adsorption layer of the water molecules was obtained using Monte Carlo method implemented in the Adsorption Locator module of the Material Studio program [1] .The Metropolis algorithm with automatic temperature control was applied [ 2 , 3 ].The  calculation was done for 10 cycles with 10 0,0 0 0 steps in each cycle.The total energies calculation was fulfilled using ClayFF force field [4] .

Limitations
Not applicable.

Ethics Statements
This article does not contain any studies with human, animals subjects or any data collected from social media platforms.The datasets used in the article are open to the public.For the usage of these datasets, proper citation rules should be maintained.

Fig. 3 .
Fig. 3. PDOS of OH-groups atoms of cis -and trans -vacant montmorillonite with a single Mg 2 + → Al 3 + substitution in the octahedral position.

Fig. 4 .
Fig. 4. PDOS of OH-groups atoms of cis -and trans -vacant montmorillonite with the water molecules adsorbed on the basal surface.

Fig. 5 .
Fig. 5. PDOS of atoms of water molecules adsorbed on the basal surface of cis -and trans -vacant montmorillonite with a single substitution Mg 2 + → Al 3 + in the octahedral position.