Principal Investigator Xiaoming Zheng Project g37

Theoretical Chemistry, School of Chemistry, Machine VP

University of Sydney


Quantum Mechanical Simulation of Gas/Surface Dynamics

Many industrial problems involve gaseous interaction with solid surfaces, such as thin film growth and catalysis. Understanding the dynamics of gaseous chemisorption on solid surfaces at a molecular level is crucial for practical applications. Traditional molecular dynamics techniques have been widely used for this purpose, however, the interaction potentials or forces between atoms used are often empirical. The main objective of this project is to employ a first principles molecular dynamics method to study the problems of surfaces and interfaces.

In many ways, granular particles behave similarly to atoms and molecules. Understanding the interaction between a granular particle and a solid boundary is vital in many industrial applications such as bulk material handling and transportation. More importantly, it may provide macroscopic models for interface problems of atomic system. The second objective is to employ a molecular dynamics technique to study the flows of granular particles and its interaction with boundary surfaces.


What are the basic questions addressed?

The basic questions for surfaces and interfaces of atomic systems are: what is the most stable atomic structure and its associated electronic image? How do atoms or molecules chemisorb and desorb from a surface?

For the flow of a granular material, we address the boundary slip phenomena. The basic questions are how is the boundary slip related to surface roughness and how should the parameter of surface roughness be defined

What are the results to date and future of the work?

We have examined atomic and electronic structures of hydrogen-terminated diamond (111) surface and chemisorption and desorption of hydrogen on boron-doped diamond (100) surface. We produced electronic imgaes of hydrogen-terminated diamond (111) surface which can be found in various STM experiments. The trihydride surface is found to be the smoothest and the dihydride phase is the roughest surface. We calculated atomic structures and energetics of hydrogen chemisorption on boron-doped diamond (100) surface. By comparison with hydrogen chemisorption on a clean diamond (100) surface, we anticipate that boron doping would supress the growth of diamond on (100) surface.

We have carried out simulations on inclined chute and vertical channel flows of granular materials. We found that the surface roughness parameter proposed in the literature, which characterises the extent of flowing particles "penetrating" into the boundary, is not the decisive factor for the measurement of surface roughness. The calculation on a vertical channel have been completed and the results are being analysed.

What computational techniques are used and why is a supercomputer required?

A combination of three computational techniques has been used in this project: Car-Parrinello first principles molecular dynamics approach, ab initio molecular orbital theory and classical molecular dynamics simulation. The requirement of a supercomputer stems from the demand of large CPU and memory by the first principles calculation and the modelling of system's dynamics.

Publications

X.M.Zheng, Electronic images of hydrogen-terminated diamond (111) surface, X.M. Zheng, Surface Science, accepted.

Molecular dynamics simulation of granular flows: slip along rough inclined planes X.M. Zheng and J.M. Hill, Mechanics of Materials, submitted.

Ab initio study of hydrogen chemisorption on boron-dopped diamond (100) surface J.Zeng and X.M. Zheng, Chemical Physics Letters, to be submitted.