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Ab Initio Molecular Dynamics


Ab Initio Molecular Dynamics is currently the most powerful computational technique that captures the dynamics of any physiochemical reacting system using only the knowledge of its elemental composition – hence ‘Ab Initio’.  The basic workhorse -- the quantum density functional theory (Q-DFT), is used to compute the atomic forces via the Hellman Feynman theorem, which when neglecting the electron motion (assumed to be too fast on the time-scale of ion-motion – the Born Oppenheimer approximation), solves Newton’s equations of motion to obtain a time-dependent trajectory.  This technique has lead to our understanding of a range of complex material systems, such as the interaction of water with oxide surfaces for fuel cell applications and chemical reactions of battery electrolytes on electrodes for Li-ion batteries, among other challenging systems studied at ORNL. The usefulness of the technique is accelerated by the availability of Q-DFT codes that scale very well on some of the world’s fastest supercomputers. Another class of quantum dynamics simulations introduces a time-dependent Hamiltonian for electrons, enabling description of (a) externally driven systems and molecules that are subject to a strong laser field for which a linear response approximation is not valid, (b) processes with coupling and energy transfer between nuclear and electronic degrees of freedom, and (c) non-equilibrium processes such as electron transfer in redox reactions.

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