  An energy-based liquid-vapor interface detection method is presented using
molecular dynamics (MD) simulations of liquid menisci confined between two
parallel plates under equilibrium and evaporation/condensation conditions. This
method defines the liquid-vapor interface at the location where the kinetic
energy of the molecules first exceeds the total potential energy imposed by all
neighboring (liquid, vapor, and solid) atoms. This definition naturally adapts
to the location of the menisci relative to the walls and can properly model the
behavior of the liquid adsorbed layers. Unlike the density cutoff methods
frequently used in the literature that suffer from density layering effects,
this new method gives smooth and continuous liquid-vapor interfaces in
nanoconfinements. Surface tension values calculated from the equilibrium MD
simulations match the Young-Laplace equation better when using the radius of
curvatures calculated from this method. Overall, this energy-based liquid-vapor
interface detection method can be used in studies of nanoscale phase change
processes and other relevant applications.
