Temperature control algorithms in dual control volume grand canonical molecular dynamics simulations of hydrogen diffusion in palladium

Abstract

The effectiveness of five temperature control algorithms for dual control volume grand canonical molecular dynamics is investigated in the study of hydrogen atom diffusion in a palladium bulk. The five algorithms, namely, Gaussian, generalized Gaussian moment thermostat (GGMT), velocity scaling, Nosé-Hoover (NH), and its enhanced version Nosé-Hoover chain (NHC) are examined in both equilibrium and nonequilibrium simulation studies. Our numerical results show that Gaussian yields the most inaccurate solutions for the hydrogen-palladium system due to the high friction coefficient generated from the large velocity fluctuation of hydrogen, while NHC, NH, and GGMT produce the most accurate temperature and density profiles in both equilibrium and nonequilibrium cases with their feedback control mechanisms. However, this feedback control also overestimates the self-diffusion coefficients in equilibrium systems and the diffusion coefficient in nonequilibrium systems. Velocity scaling thermostat produces slight inhomogeneities in the temperature and density profiles, but due to the dissipated heat accumulated in the control volumes it still yields accurate self-diffusion coefficients that are in good agreement with the experimental data at a wide range of temperatures while others tend to deviate.

Comparing the Efficiencies of Stochastic Isothermal Molecular Dynamics Methods

“…Using (19) to evaluate the left side of (35), and (36) followed by (21) for the right side, we obtain…”

“…If, however, the goal is to calculate time-dependent properties such as self-diffusion constants from molecular simulation, the perturbation should be small enough so as not to affect seriously the dynamics of the system on short times, while at the same time being able to rapidly drive the system into equilibrium with the thermostat, so as to give results that are effectively independent of the initial conditions with a minimal investment in computing time. It is not obvious a priori that it is possible to achieve both of these aims simultaneously, so that confidence in the validity of temporal correlation functions computed from thermostatted simulations is often low [22,12,21]; nevertheless, these methods are frequently used in practice despite the lack of a solid theoretical foundation (see e.g. [4] for a very recent example).…”

Mass Transfer through Vapor–Liquid Interfaces Studied by Non-Stationary Molecular Dynamics Simulations

“…Heat transfer through vapor–liquid interfaces during evaporation and condensation has been frequently investigated in the literature using molecular simulations − and continuum models such as density functional theory (DFT). ,,,− This inherently involves mass transfer, but the focus of the studies is different from ours; furthermore, in most of these studies, only pure components were considered. Stationary mass transfer through pores, membranes, crystals, − and homogeneous fluid phases − induced by a gradient of the chemical potential has been the subject of several studies. However, these studies do not involve vapor–liquid interfaces.…”