[gmx-users] Energetics in collision

Janne Hirvi janne.hirvi at joensuu.fi
Thu Apr 19 12:50:12 CEST 2007

Hello gmx-users!

I am studying the effect of impact velocity of a water droplet in collision with
a frozen surface in NVE ensemble. A droplet has extra translational energy,
which corresponds to a specific velocity, in addition to thermal energy at

I supposed that at the collision extra translational energy of the droplet will
change to potential and kinetic energy of the droplet so that total energy of
the system is conserved. However, even I observe increase in potential and
kinetic energy, total energy of the system (~300 000kJ/mol) first decreases
slightly (<100kJ - exact value depends on the velocity) and just after that
reverts partly, but stabilizes value lower than at the beginning.

The total energy should be conserved but on the other hand it sounds logical
that there will be stabilizing energy from the droplet-surface interactions
which prevents the droplet to bounce away and makes it to equilibrate on the
surface. I am wondering if this is the case or have I done some mistake which
disturbs the energy conservation?      

The other question concerns about the intrusion of the droplet into the pores of
the structured surface. The situation is otherwise the same but now the total
energy continues to decrease after first touch and wont stabilize until the
bottom of the pore is reached. It again sounds like a consequence of the
stabilizing energy from the droplet-surface interactions, but now when these
interactions are larger than without the intrusion also slight increase (2-3K)
in the droplet temperature is observed. It sounds little bit strange that water
molecules in the pores would have higher temperature. So again is it really the
truth or have I done something what I shouldnt have?   

Thanks for your time and assistance,


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