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Project XI – Theoretical studies on the atomic scale friction and energy dissipation
Contributors: S. Ciraci, A. Baratoff
Previous studies on the atomic scale friction and quantum contacts based on the classical molecular dynamics and first-principles density functional methods [see for example, Ref’s1-3] have revealed following aspects: (i) The friction between two solid surfaces in relative motion is a complex and non equilibrium process and involves a number of physical events, such as concerted bond exchange, bond breaking and bond forming, adhesion, atomic scale reconstruction and structural transformation, complex electronic and phononic energy dissipation involving tunneling and ballistic energy transfer with novel quantum effects [4-7] (ii) The asperities, molecules and lubricants (or simply nanostructures) between the surfaces in relative motion are crucial for the friction and energy transfer. The atomic composition and structure of these nanostructures and resultant mechanical and electronic properties determine the strength and type of the coupling (also adhesion) with the surfaces. The first-principles calculations have shown that the atomic and electronic structure, vibration spectrum and frequency level spacing of a nanostructure are strongly size dependent. Moreover, details can vary depending on the pressure and temperature, and require first-principles (ab-initio) treatment.
In the proposed project we will investigate the nanostructure-surface interactions and quantum thermal conduction for different atomic composition, effects of size and external conditions, such as loading force and pressure, temperature. Efficient algorithms using the predictive power of the density functional theory and ultra soft pseudopotentials have reached a level to treat atomic systems consisting of 100-500 ions and much more electrons self-consistently at finite temperature. We believe that this is an appropriate capacity to perform ab-initio calculations on the nanaostructure-surface interactions. We plan to carry out a systematic study by addressing following questions: What is the optimal composition and size of the nanostructure which yields smallest friction and wear? How the atomic structure of the surface and nanostructure can be modified to achieve optimal friction conditions? What should the character of the nanostructure be in order to provide for the fastest transfer of energy from the place where heat is generated? Answers to these questions will contribute to our understanding of the microscopic aspects of the friction process. Furthermore, we will use the background gained from these large scale, first-principles calculations to develop models for the quantum transport of thermal energy. At the end we hope to regroup several complex and interrelated physical events playing crucial roles in friction process and to find relevant parameters to engineer friction and wear at the atomic scale. These efforts will be closely coordinated with the experimental studies.
The scope of the study: Investigation of nanostructure-surface interaction and simulation of the atomic scale friction based on the first-principles quantum molecular dynamics method at finite temperature; theoretical study of the quantum transport of thermal energy through nanostructures; theoretical study of electronic and phononic energy dissipation. Search for nanostructures, the atomic structure of which can perform periodic and reversible structural transformations in the course of relative motion of surfaces.
1. "Atomic-scale study of dry sliding friction" A. Buldum and S. Ciraci, Phys. Rev. B55, 2606 (1997)
2. "Contact, nanoindentation and sliding friction" A. Buldum, S. Ciraci and I. P. Batra, Phys. Rev. B57, 2468 (1998).
3. "Yielding and fracture mechanism of nanowires" H. Mehrez and S. Ciraci, Phys. Rev. B56, 12632 (1997).
4. "A model for phononic energy dissipation in friction" A. Buldum, D. M. Leitner and S. Ciraci, Phys. Rev. B59, 16042 (1999).
5. "Thermal conduction through a molecule" A. Buldum, D. M. Leitner and S. Ciraci, Europhys. Lett. 47, 208 (1999).
6. "Reduced density matrix approach to phononic dissipation in friction" A. Ozpineci, D. M. Leitnet and S. Ciraci, Phys. Rev. B62, 10558 (2000).
7. "Quantum effects of thermal conductance through atomic chains" A. Ozpineci and S. Ciraci, Phys. Rev. B63, xxxx (2001).
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