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Non-equilibrium simulations of thermally induced electric fields in water

Wirnsberger, P; Fijan, D; Šarić, A; Neumann, M; Dellago, C; Frenkel, D; (2016) Non-equilibrium simulations of thermally induced electric fields in water. Journal of Chemical Physics , 144 (22) , Article 224102. 10.1063/1.4953036. Green open access

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Abstract

Using non-equilibrium molecular dynamics simulations, it has been recently demonstrated that water molecules align in response to an imposed temperature gradient, resulting in an effective electric field. Here, we investigate how thermally induced fields depend on the underlying treatment of long-ranged interactions. For the short-ranged Wolf method and Ewald summation, we find the peak strength of the field to range between 2 × 107 and 5 × 107 V/m for a temperature gradient of 5.2 K/Å. Our value for the Wolf method is therefore an order of magnitude lower than the literature value [J. A. Armstrong and F. Bresme, J. Chem. Phys. 139, 014504 (2013); J. Armstrong et al., J. Chem. Phys. 143, 036101 (2015)]. We show that this discrepancy can be traced back to the use of an incorrect kernel in the calculation of the electrostatic field. More seriously, we find that the Wolf method fails to predict correct molecular orientations, resulting in dipole densities with opposite sign to those computed using Ewald summation. By considering two different multipole expansions, we show that, for inhomogeneous polarisations, the quadrupole contribution can be significant and even outweigh the dipole contribution to the field. Finally, we propose a more accurate way of calculating the electrostatic potential and the field. In particular, we show that averaging the microscopic field analytically to obtain the macroscopic Maxwell field reduces the error bars by up to an order of magnitude. As a consequence, the simulation times required to reach a given statistical accuracy decrease by up to two orders of magnitude.

Type: Article
Title: Non-equilibrium simulations of thermally induced electric fields in water
Open access status: An open access version is available from UCL Discovery
DOI: 10.1063/1.4953036
Publisher version: http://dx.doi.org/10.1063/1.4953036
Language: English
Additional information: The following article appeared in: Wirnsberger, P; Fijan, D; Šarić, A; Neumann, M; Dellago, C; Frenkel, D; (2016) Non-equilibrium simulations of thermally induced electric fields in water. Journal of Chemical Physics, 144 (22), Article 224102, and may be found at: http://dx.doi.org/10.1063/1.4953036. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.
Keywords: Electrostatics, Quadrupoles, Carrier density, Electric fields, Maxwell equations
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/1518730
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