I didn't work with molecules before, but have you tried Fluent? I think I saw this option in it.

What kind of simulation do you want to do G. Sakthivel? If you want to find a minimized structure on a potential energy surface as a function of time in solvent or in vacuo you can use Molecular Dynamics. The major opensource MD tools are AMBER (Scripps Instititute, USA), NAMD (University of Illinois-Champaign Urbana, USA) or GROMACS (University of the Netherlands). There are also some proprietary software that will do the same but at great expense. These include MOE (Chemical Computing Group, Canada), Accelyrs and Sybyl and a whole set of packages from Schrodinger. Accelrys offers two academic versions at lower cost. These are MODELLER and CHARM. I don't use them . GROMACS and AMBER require the Linux operating system, but NAMD has a windows version that works nicely and a stand alone viewer called VMD which is very robust in that it handles a large number of file formats.

MD is good for simulating molecules from several ps to about 10 ns on a single processor. If you have a cluster of parallel processors you can probably comfortably handle up to 40-50 ns. Any process larger than that is probably not feasible. You can use a periodic box of any size and shape and you can use implicit or explicit solvent, too (implicit solvents don't need a periodic box).

If you are interested in simulating NMR or IR spectra from an optimized structure or looking at a transition state of a reaction using ab-initio or semi-empircal methods then Gaussian (Gaussian Inc. , USA) or Spartan (Wavefunction) will work. I do not know of any open source software in this genre.

I'm sure others in this group can add to this set of programs or elaborate on my comments.

THANK LOT FOR YOUR VALUEABLE INFORMATION MIS.GLORIA ANDERLE.