Erratum: Proton Transport through Water-Filled Carbon Nanotubes [Phys. Rev. Lett.90, 105902 (2003)]

Abstract

The empirical valence bond (EVB) methodology was developed by Warshel and collaborators [1,2], extending earlier ideas of Coulson and Danielsson [3].[1] A. Warshel and R. M. Weiss, J. Am. Chem. Soc. 102, 6218 (1980).

Modelling of morphology and proton transport in PFSA membranes

“…In particular, the influence of ''structural diffusion'' on the mobility of protons in the membrane, via the Grothuss mechanism, [39][40][41] is completely neglected by standard classical force fields, and this mechanism is known to be important at high degrees of hydration, or when water is present in confined geometries. 42 Recently, a number of empirical valence bond (EVB) force fields have been produced [43][44][45] with the principal goal of studying proton diffusion in bulk water. [46][47][48][49] These have also been applied to investigate proton diffusion in PFSA systems.…”

Kinetics and Mechanism of Proton Transport across Membrane Nanopores

“…As the motion of a proton along an isolated hydrogen bonded water chain is an essentially barrier-less process, this free energy penalty is due to the desolvation energy required to extract the proton from the favorable bulk environment and move it into the less polar interior of the pore, where the excess charge is coordinated by only two water molecules. Note, however, that the effective charge of the proton and hence also its desolvation penalty are substantially reduced by the dipolar polarization of the water chain [8], as discussed below. This effect is absent…”

“…To clarify what prevents the proton from penetrating into the membrane interior despite the high proton mobility along one-dimensional water chains [8] we have calculated the free energy profile F (z) for the excess charge as a function of its position z along the tube axis as shown in Fig. 2.…”

“…To explore the fundamental question of watermediated proton transfer, and to design robust proton conducting media for technological applications, studying simpler model systems is essential. The quasi-onedimensional water chains forming inside carbon nanotubes [4] have attracted considerable attention, with computer simulations suggesting proton mobilities exceeding those even of bulk water [5,6,7,8,9,10]. However, large conductivity requires in addition a high density of charge carriers, which depends on the free energy penalty required to remove protons from the bulk liquid and introduce them into the pores.…”

“…For the interactions of the water molecules and the excess proton, we use the multistate empirical valence bond model (EVB) developed by Voth and collaborators [11] based on prior work of Warshel [12]. This model accurately describes the energetics of bond breaking and formation during aqueous proton transfer and is computationally far less expensive than ab initio methodologies [8]. The water oxygen atoms interact with the carbon atoms of the nanotube through a Lennard-Jones potential with ǫ = 0.1143 kcal/mol and σ = 3.27Å yielding a channel aperture of approximately 2Å.…”