[Pw_forum] box size in example03

[Duy Le]

On Tue, May 24, 2011 at 4:03 PM, Amin Torabi <amin.torabi at gmail.com> wrote:
> Hi all,
> ../examples/example03/README says that "The molecule is put in a cubic box
> of side 12 bohr"
> My questions are:
>
> how did you chose it to be 12? I tried different numbers and noticed that
> the total energy depends on this value.

Indeed. Energy_of_system=Energy_of_molecule+Interaction_energy_with_neighboring_molecules.
Different box sizes yield different Interaction energies.

> Is it not a calculation on an isolated molecule? cause for an isolated
> molecule, it should not be important what the size of the box is.

No, it is not. It is a calculation of bunch of molecules. By changing
box size, you change the interaction between those molecules.
Eventually, those interactions are almost negligible, you'll get
isolated molecules.

>

--------------------------------------------------
Duy Le
PhD Student
Department of Physics
University of Central Florida.

"Men don't need hand to do things"