Molecular dynamics simulation of water beween two ideal classical metal walls

Abstract

We have simulated a slab of water with two-dimensional periodic boundary conditions between two metallic walls. The entire compliment of charges, arising from periodic reproductions and from classical images in the metal, are included explicitly by mapping onto a problem with three-dimensional periodicity which is handled by usual Ewald summation methods. Results are presented for charged and uncharged surfaces, permitting an estimate of the differential capacitance arising from the layer of water near the walls. The estimate is about a factor of 2 smaller than the observed differential capacitance of metal–aqueous electrolyte interfaces.

Fluctuations of local electric field and dipole moments in water between metal walls

“…The surface charge densities are then equal to E z (x, y, 0)/4π at z = 0 and −E z (x, y, H)/4π at z = H, where E z = −∂Φ/∂z is the electric field along the z axis. Their lateral averagesσ λ = dxdy σ λ (x, y)/L 2 (λ = 0, H) are related to M z by 23,27 …”

“…(3) vanishes at z = 0 and H, leading to Eq.(2). The electrostatic energy U m is written as the sum [23][24][25][26] ,…”

“…We can apply the 3D Ewald method due to the summation over h fully accounting for the image charges [23][24][25][26][27] . If the charge positions r i are shifted infinitesimally by dr i and E a by dE a , U m is changed by…”

“…In such studies, the Ewald method has been used to efficiently sum the electrostatic interactions 12,14 . Furthermore, we mention simulations on dipoles (and ions) in applied electric field [23][24][25][26][27][28][29][30][31] . Some groups [23][24][25][26][27] introduced image charges outside the cell to realize constant electric potentials at z = 0 and H under the periodic boundary condition in the x and y axes.…”

Phase diagram of water between hydrophobic surfaces

“…There are many computational studies on confined water, [4][5][6][7][8][9][10][11][12] some of the pioneering works date back to 1980s. 4 One of the earlier computer simulations focusing on liquidsolid phase transitions 13 showed that water between hydrophobic surfaces freezes into a bilayer form of crystalline ice when temperature is lowered under a fixed normal pressure.…”