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Prof. Giovanni Ciccotti
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Department of Physics
Università degli Studi di Roma La Sapienza
Piazzale Aldo Moro 2, I-00185 Roma
Italy
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ciccotti@roma1.infn.it |
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MD of complex systems: nonhamiltonian, constrained, quantum-classical
In the last years it has become apparent that an efficient and sound
treatment of molecular dynamics simulations for complex systems cannot be
obtained without a suitable generalization of statistical mechanics to
dynamical systems not derivable from a hamiltonian. This generalization is
needed to understand and apply correctly the new dynamics in generalized
ensemble (constant temperature, constant pressure, etc). Another consequence
of this new approach is a better understanding of the nature of mechanical
systems subjected to holonomic constraints. The last have been of wide use in
simulations of macromolecular systems and their statistical mechanical
behavior deserves a correct treatment. In the first two lectures I will derive
the statistical mechanics for nonhamiltonian systems; apply it to Nose'-Hoover
and related 'iso'-stats (thermostat, barostat etc); interpret in this new
language the statistical behavior of constrained dynamics. As an important
aside I will also discuss the most rigorous family of algorithms used to
integrate the equations of motion: Trotter-derived unitary integrators; SHAKE
and related implementations. The third lecture will be devoted to discuss the
most-needed generalization of molecular dynamics to treat interacting systems
composed of quantum and classical subsystems. The problem is far from trivial
but recent progresses permit to hope to have soon tractable but rigorous
algorithms to compute the statistical properties of such systems.
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