SIMULATION OF UREA−HYDROXYAPATITE BY USING DENSITY FUNCTIONAL THEORY (DFT)

Nitrogen and phosphorus are the main macronutrients needed by crops.Due to environmental factors, these nutrients can be easily washed off before reaching the crops.Slow-release fertilisers have been introduced to solve these problems as it helps release nutrients slowly to the plants.Many experimental studies have been conducted on the effectiveness of urea and hydroxyapatite as a slow-release fertiliser.In a complementary manner, this computational study concentrated on the details of interactions between urea and hydroxyapatite in relative stability, as well as the structural and electronic properties by using density functional theory (DFT) at the level of B3LYP/6-31G(d,p).The calculations were performed using the Gaussion 09 and Multiwfn programmes.The hydroxyapatite cluster was modelled to interact with one urea molecule, which was placed at strategic positions on the cluster's surface.All structures in this investigation are found to form bonding between the N atom in urea and Ca atom in hydroxyapatite.In addition, the interaction energies between urea and hydroxyapatite range from -0.09719 eV to -1.2245 eV.Meanwhile, for the newly-formed bond between N and Ca, the bond lengths range between 2.64 Å -2.85 Å.Our results confirmed the experimental findings that urea molecules can react favorably with the surfaces of hydroxyapatite.