How to calculate surface tension properly

From: Bjoern Olausson (namdlist_at_googlemail.com)
Date: Wed Feb 08 2012 - 07:59:15 CST

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Hi,

I am wondering how to calculate the surface pressure correctly from a
NPT simulation when using values from the PRESSUREPROFILE line form
the NAMD output.

When I remember correctly the surface tension was defined as
g = Pzz - 0.5 * (Pxx+Pyy)

When googeling around an reading different papers one can find
different definitions like:
g = Lz * (Pzz - 0.5 * (Pxx + Pyy))
or
g = Lz * 0.5 * (Pzz - 0.5 * (Pxx+Pyy))

Thought the multiplication with Lz just scales the surface tension and
gets uninteresting when comparing the profiles of two simulations but
anyway, whats the proper definition?

Thanks for any thoughts on this.

Cheers,
Bjoern

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