Surface tension

The surface tension, $\gamma$, is a measure of the work required to create a surface.

Thermodynamics

In the Canonical ensemble: two phases;

$\gamma =\frac{\partial A(N,V,T,\mathcal{A})}{\partial \mathcal{A}}$;

where

• $N$ is the number of particles
• $V$ is the volume
• $T$ is the temperature
• $\mathcal{A}$ is the surface area
• $A$ is the Helmholtz energy function

Computer Simulation

A review on different techniques to compute surface (interface) tension can be found in the paper by Gloor et al.

Liquid-Vapour Interfaces of one component systems

• Binder procedure

For given conditions of volume and temperature, the Helmholtz energy function is computed as a function of the number of molecules:

$A(N;V,T)$

The calculation is usually carried out using Monte Carlo simulation

If liquid-vapour equilibrium occurs, the plot of the chemical potential, $\mu \equiv (\partial A/\partial N{)}_{V,T}$, as a function of $N$ shows a loop.

Using basic thermodynamic procedures (Maxwell construction) it is possible to compute the densities of the two phases; ${\rho }_v,{\rho }_l$

• Explicit interface

References

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