Kaolinite is an essential mineral with numerous applications across many sectors. One of them is in the agricultural industry, in which it is a crucial component in the method of controlled-release fertilizer. This manuscript reports the use of different functionals and basis sets on the structural and electronic properties of kaolinite's surface, intending to find reliable methods among those tested. Four different functionals, B3LYP, CAM-B3LYP, M06-2X, TPSSTPSS, complemented with various basis sets, were used in this study. The results show that TPSSTPSS complement with 6-311G** provides good agreement with previous research and experimental results among different functionals and basis sets used. The quantitative analysis was done to optimize the kaolinite molecule. Selected extrema points were used to place the urea molecule for the interaction of urea-kaolinite studies. The urea's interaction with kaolinite was reported at a different interaction site in the gas phase and different orientations of the urea molecule. Urea molecule was optimized above the Al–O and Si–O surfaces with their energy difference calculated. Our results showed that both surfaces act as promising adsorbents among the different orientations of the urea on both the Al–O and Si–O surfaces. However, Al–O, and Si–O had another preferable interaction site to the urea molecules.

The disubstituted thiourea compounds have shown its reliability on their usages in various industries compared to the thiourea compounds. However, they also show capability to exist in different configurations, which would render them to possess different properties and hence affect their usability by unsuspected users. In this study, investigation was carried out on the polymorphism of five disubstituted thiourea compounds in which the phenyl rings and arylhalide acted as substituents. Using the B3LYP/DEF2-TZVP model chemistry with D3-BJ and gCP correctional schemes, the energetic analysis on the possible structural arrangements of the compounds was performed. The topology analysis of non-covalent interaction and electrostatic potential surfaces was used for understanding the interaction and reactivity of the constitute molecules of the compounds. Energetic results show that for all interested compounds, CT and TT configurations may coexist. Between the two types of substituents, phenyl substituted molecules are more flexible with better capability to be nucleophilic compounds. On the other hand, the arylhalide substituted molecules form better electrophilic compounds. The reactive sites of the molecules rotated to the stable new configurations are similar to the molecules in their original configurations observed from experiments.

Polymorphism is the ability of a compound to form more than one crystalline form in the solid state. Compounds having this ability would display different stabilities for different forms, hence affecting its applicability. Symmetrically substituted thiourea derivatives have been shown to be polymorphic due to the flexibility of the C-N bond. One of this type of compounds, known as 1,3-bis(1-(4-methylphenyl)ethyl)thiourea, is studied on its stabilities and ability to exist in different forms. Since the molecule of this compound was experimentally found to exist in trans-trans configuration, the stability of the cis-trans and cis-cis configurations are assessed using theoretical calculations. Rotations along the C-N bonds are performed using Gaussian 09 suite program. Level of method B3LYP, complemented by basis set DEF2-TZVP, is used. The stability of the molecules in different configurations is then studied in terms of its interactions using reduced density gradient. Apart from the original trans-trans configuration, with the difference of 0.024 eV, cis-trans configuration are also possible to exist. Next possible configuration is cis-cis with relative energy 1.8412 eV. Both the non-covalent CH … HN and CH … S interactions are found to provide stabilising effect in the cis-trans and trans-trans configurations.