Ab initio Moleküldynamik von P-Verbindungen
Thema:
Ab initio Moleküldynamik von P-Verbindungen an Wasser/Mineral Grenzflächen
Einordnung:
Phosphorus (P) is central to all forms of life and its efficient use in fertilizers is one of the conditions for providing food for a rapidly increasing human population. P in the form of phosphate is the lowest mobile nutrient due to its strong reactivity with soil constituents. In general, phosphate is strongly adsorbed onto soil mineral particles such as metal oxides and metal oxyhydroxides. This strong interaction leads to deficiency in the available P with respect to required P for optimal plant growth. An effective way to increase the P mobility is to add low molecular weight organic molecules that have the ability to compete with phosphate at the soil mineral surfaces. Sorption experiments for phosphates in presence of other small organic molecules on mineral surfaces showed an improvement in the P mobility. Organic carboxylic acids are considered to be very reactive with soil mineral surfaces to enhance releasing of phosphates from surfaces. Despite presence of several studies focusing on the competition reactions between phosphates and organic compounds, molecular level understanding for the dynamics and mechanism of these reactions is still lacking. Therefore, the main objective for the present project is to unravel the nature of these competition reactions between phosphate and organic carboxylic acids at the water-mineral surface interface by applying ab initio molecular dynamics simulations.
Beschreibung:
This project is focusing on investigation the possible competition reactions that may take place at the water-surface-interface. Here, citrate will be introduced as a competitor with phosphate at the mineral surface. The most abundant FeOOH mineral surface “goethite” will be modelled.
In practice, a box containing phosphate and citrate at the goethite surface will be created and water molecules will be introduced to simulate the real soil solution. To simulate an infinite molecular system, periodic boundary conditions will be applied in all the three spatial directions. The most effective reactions in this project involving the phosphate-goethite-, citrate-goethite-, and phosphate-citrate-interactions will be studied. This will be carried out by the state of art ab initio molecular dynamics simulations. Mainly, the student will perform atomistic simulations using the existing CP2K program package by applying hybrid Gaussian and plane wave density functional theory (DFT). Furthermore, this project will be supported by sorption experiments for phosphate on goethite surface in the presence of citrate. This will be carried out in close collaboration with experimental partners. Outcomes of this work will explain at a molecular level the experimental sorption results. The work includes a general introduction to different computational chemistry and molecular dynamics approaches.
Betreuer: Dr. Ashour Ahmed