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2020-02-16

New paper on extracting chemical potential differences in the macroscopic limit from fluctuations in small systems

The paper entitled Chemical Potential Differences in the Macroscopic Limit from Fluctuations in Small Systems has been accepted for publication in the Journal of Chemical Information and Modeling.

The paper is the first in the PhD of Vilde Bråten, and written also together with Ass. Prof. S. K. Schnell. The paper presents a new method for computing chemical potential differences of macroscopic systems by sampling fluctuations in small systems. The small system method is used to create small embedded systems from molecular dynamics simulations, in which fluctuations of the number of particles are sampled. The overlapping region of two such distributions, sampled from two different systems, is used to compute their chemical potential difference. Since the thermodynamics of small systems is known to deviate from the classical thermodynamic description, the particle distributions will deviate from the macroscopic behavior as well. We show how this can be utilized to calculate the size dependence of chemical potential differences and eventually extract the chemical potential difference in the thermodynamic limit. The macroscopic chemical potential difference is determined with a relative error of 3% in systems containing particles that interact through the truncated and shifted Lennard-Jones potential. In addition to computing chemical potential differences in the macroscopic limit directly from molecular dynamics simulation, the new method provides insights into the size dependency that is introduced to intensive properties in small systems.

The figrue below displays an illustration of the method.