Monte Carlo Computer Simulation Study of the Hydrophobic
effect: Potential of Mean Force for
[(CH4)2]aq
at 25oC and 50oC
Abstract:
A series of liquid-state simulations
has been performed in the system
[(CH4)2]aq
at 25oC as a function of separation R
between the dissolved
CH4 molecules. The potential functions for the
H2O - H2O,
CH4 - H2O, and
CH4 - CH4
are based on quantum-mechanical calculations of the corresponding
intermolecular interactions.
The simulation was carried out by the Monte Carlo method augmented by
convergence acceleration techniques involving force-bias and
preferential sampling.
The potential of mean force WSS(R)
for the interaction of apolar species in water was determined using umbrella
sampling orecedures on four windows in the intersolute coordinate.
Convergence accelaration was found to be necessary
for obtaining satisfactory results.
Contact and solvent-separated contributions to the statistical state of the
system are discussed in terms of radial distribution functions,
quiasi-component distribution functions for coordination number,
binding energy and pair-interaction energies.
Stereographic views of significant structures are presented,
and contributions of clathrate structures in the solvent are discussed.
The results are discussed in the context of experimentally observed
concentraion dependence of hydrophpbic effect and related theoretical
work on WSS(R)
by Marcelja, Michell, Ninham and Scully, Pratt and Chander and
Pangali, Rao and Berne.
Prosepects for quantitative study of the temperature dependence
of the hydrophobic interaction and other quantitative extensions
of the work are discussed.