Effect of Electrostatic Force Truncation on Interfacial and Transport Properties of Water
Received: May 21, 1996 In Final Form: August 2, 1996 Abstract: The importance of accurately accounting for all Coulombic forces
in molecular dynamics simulations of
water at interfaces is demonstrated by comparing the Ewald summation
technique with various spherical
truncation methods. The increased structure induced by truncation
methods at 12 Å leads to water/vapor
surface tensions and surface potentials that are respectively 50% and
100% greater than obtained with Ewald.
The orientational polarization of water at the lipid/water
interface is analyzed within the Marcelja-Radic
theory of the hydration force, yielding decay parameters of 2.6 and 1.8
Å for spherical truncation and Ewald,
respectively, as compared with 1.7-2.1 Å obtained from experiment.
Bulk water transport properties such
as the viscosity and diffusion constants differ by as much as 100%
between simulations carried out with and
without truncation; this may be related to ordering in the neighborhood
of the cutoff radius. The diffusion
constant calculated from the Ewald simulation is significantly further
from experiment than the cutoff result,
pointing out the need to reparametrize the TIP3P water model for use
with Ewald summation. Appendices
describe a method for carrying out the Ewald summation on a distributed
memory parallel computer and
other computational details relevant when simulating large
systems.
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