regarding some basic molecular dynamics

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1

Dear MD-guys,

First of all I want to say that this Qs might be very basic, please excuse me.

Recently I was trying to see the differences of a system in different temperature and pressure condition, for my case I took water TIP4P/2005 model and equlibriated water at 1atm, 100 atm and 200 atm pressure with temperature 300, 350 and 400 K respectively, my confusions are

  1. As different pressure conditions I saw that the total energy (etotal) is more or less same in three cases. But total energy should be different in different P and T, isn’t not ? If I increase P i.e. target equlibration pressure, the kinetic contribution part and virial contribution part will be increase to adjust with P i.e. kinetic energy should increase, isn’t it ?

  2. Apart from structural property ( getting from rdf ) what are the main difference of that three system which I can observe ?

Thank you for your attention.

2

200 atm is probably not high enough pressure to expect much structural difference in condensed phase systems like water. You might see some small effects if you look carefully enough, but don't expect anything drastic unless you really crank up the pressure. Of course, then you have to worry about whether your model will be valid at high pressure.

Kinetic energy should certainly change with increased temperature though, I don't know why you wouldn't be seeing any big difference there as you increase T.

3

You can try raising temperatures and pressures to be safely within the supercritical fluid region. Then you should be able to see the breakdown of the hydrogen bond network but persistence of pair HBs.

Regards

Tatiana Kuznetsova