| Advanced
Methods for Electronic Structure
This project is working to advance the capabilities of quantum
chemical methods to describe efficiently and with controllable
accuracy the electronic structure, statistical mechanics, and
dynamics of atoms, molecules, and clusters.
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| Figure
5 Four configurations from a 1.5 ns trajectory
in which a 12-unit hydrophobic chain in water collapses
from an extended coil to a compact globule. Transparent
cubes denote vapor cells. |
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One example of molecular dynamics being studied is hydrophobic
interactions. For nearly a half century, hydrophobic interactions
have been considered the primary cause for self-assembly in
soft matter and a major source of stability in biophysical
assembly. Studying these interactions in perhaps their most
basic form, ten Wolde and Chandler used computer simulation
to demonstrate the mechanism for the collapse of a hydrophobic
polymer in water (Figure 5). They found that the mechanism
of collapse is much like that of a first-order phase transition.
The evaporation of water in the vicinity of the polymer provides
the driving force for collapse, and the rate limiting step
is the nucleation of a sufficiently large vapor bubble. This
study suggests that the kinetic effects of changing pressure
may play an important role in the hydrophobic interactions
of protein folding.
This simulation was made possible by transition path sampling
and a coarse-grained treatment of liquid water. The use of
a statistical field model of water allows the simulation of
solvent dynamics over large length and time scales that would
be impractical to study with purely atomistic simulation.
Spatially complex small length-scale fluctuations were analytically
integrated out, thus removing the most computationally costly
features from the simulation.
INVESTIGATORS
R. J. Harrison, Oak Ridge National Laboratory; M. Head-Gordon,
University of California, Berkeley, and Lawrence Berkeley
National Laboratory; W. D. Allen and H. F. Schaefer III, University
of Georgia; W. C. Ermler, University of Memphis; J. W. Evans,
M. S. Gordon, R. A. Kendall, K. Ruedenberg, and M. W. Schmidt,
Iowa State University/Ames Laboratory; W. S. Gray, Old Dominion
University; M. Minkoff, R. Shepard, and A. F. Wagner, Argonne
National Laboratory; D. L. Thompson, Oklahoma State University.
PUBLICATION
P. R. ten Wolde and D. Chandler, “Drying-induced hydrophobic
polymer collapse,” PNAS 99, 6539 (2002).
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