Hi,
i second Justins seond idea (creating a small box of equilibrated CCl4 and then fill the simulation box via the -cs option). Depending if you have other molecules in your system, make the simulation box a little bit bigger, because you will get some holes. In the subsequent NPT simulation these holes will vanish and your box will shrink.

The first way has the problem, that if you have holes between some CCl4 molecules, no new molecule would fit there. Then you could make a short equilibration, so that the holes gather to bigger holes and fill them again with the -ci option. If you're lucky, you will reach after a very long time the required density. (In my case i used mesitylene as a solvent and after day of the automated iteration (try to put molecules into the box, equilibrate, try to put more molecules into the box, ...) i dismissed this approach.)

greetings
thomas





James Starlight wrote:
Justin,

2012/2/6 Justin A. Lemkul<[email protected]<mailto:[email protected]>>


     Some simple calculations using the desired density and the box
     dimensions (to get the volume) will tell you exactly how many
     molecules you need.  If you only "suppose" you've got a reasonable
     number, there are better ways to be sure ;)


In accordance to my calculations I need in ~ 1000 CCl4 to obtain 1.600
g/cm^-3 density with my box dimensins

By the way way I try to define such system by

genbox -ci ccl4.gro -nmol 1000 -box 8.6 6.5 3 -o ccl4_box.gro


I've obtain memory error :(


Is there any other way to define such system with the desired size and 
n_mollecules with the less computation demands?


Two options:

1. Add them incrementally to the box (100 at a time or so, until the desired
value is reached)

2. Build a small box of solvent (a few hundred molecules), then use genbox -cs
instead of -ci to use the small solvent box to create the one of desired size.

-Justin


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