Tuesday, 24 May 2005 - 2:45 PM

This presentation is part of: Electronic Structure in Chemistry II

On the fly orbital localization in ab initio molecular dynamics and its application in the reaction of organic molecules with semiconductor surfaces

Mark E. Tuckerman, New York University, New York, NY

The methodology of ab initio molecular dynamics, wherein finite-temperature dynamical trajectories are generated using forces computed ``on the fly'' from electronic structure calculations, has benefited significantly from its combination with maximally localized electronic orbitals. The latter exploit the unitary invariance of the total energy to generate orbitals with maximum spatial locality. These orbitals resemble the classic textbook picture of molecular orbitals and, hence, are useful tools for analyzing electronic structure. In addition, maximally localized orbitals, expanded in localized basis sets, are a key component in linear scaling methods. In this talk, it will be shown how techniques from quantum field theory can be used to reformulate ab initio molecular dynamics in such a way that maximally localized orbitals are generated automatically and dynamically as the calculation proceeds. It will be seen how the resulting trajectory of maximally localized orbitals can be used to elucidate the mechanism of a chemical process on the Si(100)-2x1 surface, namely, the addition of a conjugated diene. Such processes are opening new inroads into molecular electronics and nanoscale devices. Covalent attachment of organic molecules to semiconductor surfaces can yield active devices such as molecular switches as well as passive insulating layers. Finally, we will show that it is possible to ``reverse engineer'' specific molecules to yield lower free energy barriers to detachment, which hold promise for applications in, for example, surface lithography.

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