[Pw_forum] box size in example03

Duy Le ttduyle at gmail.com
Tue May 24 22:14:10 CEST 2011

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"

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