Computer simulation studies of a square-well fluid in a slit pore. Spreading pressure and vapor-liquid phase equilibria using the virtual-parameter-variation method
Hl. Vortler et Wr. Smith, Computer simulation studies of a square-well fluid in a slit pore. Spreading pressure and vapor-liquid phase equilibria using the virtual-parameter-variation method, J CHEM PHYS, 112(11), 2000, pp. 5168-5174
We study model square-well fluids with well-width parameter lambda=1.5 conf
ined to hard planar slits. We derive a general computer simulation method f
or numerically calculating an arbitrary first derivative of the canonical e
nsemble partition function with respect to a simulation parameter, which we
call the virtual-parameter-variation method. Two special cases of this app
roach are the Widom test-particle insertion method for calculating the exce
ss chemical potential, and a method for calculating the pressure due to Epp
enga and Frenkel [Mol. Phys. 52, 52, 1303 (1984)]. We use this approach to
calculate the volume derivative parallel to the slit walls of the Helmholtz
free energy in an (N,V,T) Monte Carlo simulation, and show that this sprea
ding pressure is numerically consistent with the thermodynamic pressure obt
ained by integration of the Gibbs-Duhem equation using the simulated chemic
al potentials of the confined fluid as a function of density. We obtain new
simulation results for the spreading pressure and the phase equilibrium pr
operties of the confined square-well fluid, and we also estimate its critic
al point properties, observing a decrease of the critical temperature in co
mparison to the bulk fluid. (C) 2000 American Institute of Physics. [S0021-
9606(00)50510-8].