Volume 121, Issue 22, 08 December 2004
Index of content:
121(2004); http://dx.doi.org/10.1063/1.1830011View Description Hide Description
We propose and test a pair potential that is accurate at all relevant distances and simple enough for use in large-scale computer simulations. A combination of the Rydberg potential from spectroscopy and the London inverse-sixth-power energy, the proposed form fits spectroscopically determined potentials better than the Morse, Varnshi, and Hulburt–Hirschfelder potentials and much better than the Lennard-Jones and harmonic potentials. At long distances, it goes smoothly to the London force appropriate for gases and preserves van der Waals’s “continuity of the gas and liquid states,” which is routinely violated by coefficients assigned to the Lennard-Jones 6-12 form.
121(2004); http://dx.doi.org/10.1063/1.1832595View Description Hide Description
Confining water in lab synthesized nanoporoussilica matrices MCM-41-S with pore diameters of 18 and 14 Å, we have been able to study the molecular dynamics of water in deeply supercooled states, down to 200 K. Using quasielastic neutron scattering and analyzing the data with the relaxing cage model, we determined the temperature variation of the average translational relaxation time and its -dependence. We find a clear evidence of an abrupt change of the relaxation time behavior at which we interpreted as the predicted fragile-to-strong liquid–liquid transition.
121(2004); http://dx.doi.org/10.1063/1.1826056View Description Hide Description
We present all-atom molecular dynamics simulations of biologically realistic transmembrane potential gradients across a DMPC bilayer. These simulations are the first to model this gradient in all-atom detail, with the field generated solely by explicit ion dynamics. Unlike traditional bilayer simulations that have one bilayer per unit cell, we simulate a 170 mV potential gradient by using a unit cell consisting of three salt-water baths separated by two bilayers, with full three-dimensional periodicity. The study shows that current computational resources are powerful enough to generate a truly electrified interface, as we show the predicted effect of the field on the overall charge distribution. Additionally, starting from Poisson’s equation, we show a new derivation of the double integral equation for calculating the potential profile in systems with this type of periodicity.