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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 28: Condensed Matter Simulations augmented by Advanced Statistical Methodologies I (joint session DY/CPP)

CPP 28.5: Vortrag

Dienstag, 13. März 2018, 12:00–12:15, BH-N 334

Hyperdynamics approach to the non-equilibrium states coupled to the thermal bath — •Yuri S. Nagornov and Ryosuke Akashi — University of Tokyo, Department of Physics, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Efficient numerical simulation method for rare events driven by thermal fluctuation has long been a hot topic in a wide range of fields in condensed-matter physics. The target phenomena in this context, such as crystal nucleation, atomic diffusion etc., occur in time scales of microseconds or even longer and are intractable by atomistic molecular dynamics simulation. Solutions to this problem have long been attempted by introducing collective variables to seek for escape paths and/or efficiently sampling the phase space to represent the canonical ensemble. However, an ideal approach is rather desired (i) not to respect the prior knowledge of appropriate collective variables and (ii) not to require the system to reach the thermal equilibrium since many of the above mentioned phenomena can occur under non-equilibrium situations. Along the line of the Langer's theory, we formulate a differential equation for the distribution of the variables that evolve on an elevated potential surface under thermal fluctuation, from which its real probability of realization can be retrieved. This formalism enables us non-empirical exploration of rare events and evaluation of its probability to occur simultaneously. An algorithm with a modified form of the Langevin molecular dynamics is thereby constructed, which is in spirit an extension of the hyperdynamics approach. Applications to simple model systems will be presented.