[gmx-users] Re: Energetics in collision

Janne Hirvi janne.hirvi at joensuu.fi
Thu Apr 19 14:51:19 CEST 2007

First thanks for your reply!

>>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 300K.
>>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
>Don't know for sure, but incorrect comm removal springs to mind.

I wont remove COM motion so that translational velocity is not disturbed.

>>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?      
>Wouldn't that stabilizing energy be part of the total energy?

That sounds realistic but I just tried to figure out some reason for decreased
total energy, which actually in case of porous surface decrease little by
little while water molecules intrude the pores and stabilize just after the
bottom of the pores is reached.

Then it should be so that extra stabilization from droplet-surface interactions
in potential energy would be equally out of water-water interactions if
temperature wont change. In that case what makes the droplet stay on surface
with specific contact angle? Now I am so confused that I dont know anything -
hopefully someone can explain it to me...

>>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
>>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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