ITR/AP: Large-Scale Quantum Mechanical Molecular Dynamics Simulations: Challenges, New Directions, and Applications to Carbon-Based Nanostructures

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This award is the result of a proposal submitted to the Information Technology Research initiative. Advances in computational materials science depend on the development of efficient and reliable computational methods for large-scale quantum mechanical molecular dynamics (MD) simulations. Linear-scaling or order-N (O(N)) methods have been developed with the aim of overcoming the bottleneck associated with the N3-scaling in the computation of the total energy and atomic forces in quantum mechanics-based simulations. Despite this progress, O(N)- ab initio-MD is still limited to systems containing relatively small numbrs of atoms because of the overhead associated with the self-consistent calculations in ab initio MD. On the other hand, MD schemes based on two-center tight-binding (TB) Hamiltonians are orders of magnitude faster than O(N)-ab initio-MD methods. However, they have been found to be unsatisfactory in systems where charge transfer or bond breaking/rebonding plays a significant role. Therefore, there is a pressing need for developing transferable semi-empirical Hamiltonians that would be superior to traditional two-center TB Hamiltonians, but would include all essential ingredients of ab initio Hamiltonians without being computationally excessive. The O(N)-MD scheme using such a Hamiltonian can predict accurately the properties of complex systems of large sizes.In this research a general scheme will be developed to construct such reliable and transferable semi-empirical Hamiltonians for materials (metal or semiconductor) in the framework of linear combination of atomic orbitals (LCAO) that explicitly includes the self-consistently (SC) determined charge transfer and environment-dependent (ED) multi-center interactions. The SCED-LCAO Hamiltonian will be implemented within the O(N)-MD scheme developed previously. Using O(N)/SCED-LCAO-MD as our simulation tool, we will investigate the properties of carbon multi-wall nanotubes and carbon nanorods, and evaluate their potential as components of molecular-scale devices. Specifically, we will study the following three projects of current interest: (1) Energetics, structure, electronic, mechanical and vibrational properties of carbon multiwall nanotubes (MWNT), (2) A study of the properties of contacts between metal elctrodes and MWNT, and (3) Energetics, structure, electronic, mechanical and vibrational peoperties of carbon nanorods (CNR). Project (2) will be done in collaboration with the experimetal group of Professor Alphenar of Lousiville, whereas project (3) will be done in collaboration with the experimental group of Professor Chen of Academia Sinica (Taiwan).%%%***