Realistic Modelling of the Effects of Solvent and Additives on Crystal Growth
The aim of this project is to investigate, at the molecular level, the interactions between the surfaces of inorganic salts and solvents/additives/foreign ions, using both interatomic potential and quantum mechanical techniques. The information from these studies will shed light on many important complex processes in crystal growth, from the role of solvent to the mode of action of growth modifiers. These processes are extremely important in many industrial processes, ranging from hydrometallurgy to the pharmaceuticals. The project requires enormous computing resources if accurate models are to be used due to the large number of atoms involved in solvent calculations and the complexity of quantum chemical calculations of additives with crystal surfaces.
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Principal Investigator Andrew RohlNanochemistry Research Institute Curtin University of Technology |
Project d64, e20 |
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Co-Investigators Damien CarterMark Ogden Stefano Piana Applied Chemistry Curtin University of Technology |
RFCD Codes 250603, 250601 |
Significant Achievements, Anticipated Outcomes and Future Work
The use of computational simulations of inorganic crystal structures and surfaces can provide valuable information for predicting the interactions between the surfaces of inorganic salts and solvents/additives/foreign ions. Density functional quantum mechanics calculations on two different crystal systems have been undertaken in this project.
There has been virtually no validation of quantum mechanical simulations with experimental data for complex inorganic surfaces. This has been due to both the lack of experimental data available and the complexity of relevant calculations. We used density functional calculations to examine relaxations of the (101) surfaces of ammonium dihydrogenphosphate (ADP) and potassium dihydrogenphosphate (KDP). We chose this system because we can compare our results to recent, high quality surface x-ray diffraction (SXRD) studies undertaken by our collaborators in Holland, led by Prof. E. Vlieg. We found a good match between our calculated values and the experimental values for the direction of atom relaxations in the surfaces. The absolute magnitudes of the relaxation did vary a little when compared to those from experiment. The good match between our calculations and the experimental values suggests our method of density functional simulations can provide an accurate model for these complex inorganic surfaces.
The reliability of the atom-atom pair potential method at surfaces has only been confirmed for simple systems. Quantum mechanics calculations have been used to check the accuracy of the interatomic potentials that have been employed to simulate the interactions between additives and complex inorganic surfaces. We have previously examined the docking of ortho-sulfonated aniline (OSA) and benzene sulfonate (BS) on the surfaces of potassium sulfate using interatomic potentials. We have performed density functional docking calculations of OSA and BS on potassium sulfate surfaces to compare to the results from this previous study and found that docking of OSA and BS is most favourable on the (001) surface and least favourable on the (010) surface. This exactly matches the docking trend found using interatomic potentials. However, the most stable orientations of BS and OSA on a particular surface did sometimes vary between the two methods. The close match in the docking trends for OSA and BS and the good match in the orientations of the docking molecules (although some variation) suggest the interatomic potentials provided a reliable method for examining complex surfaces.
This work is being currently written up in the form of a PhD thesis and a series of papers.
Computational Techniques Used
All DFT calculations were performed using the first principles program SIESTA (