Bowling Green State University

Molecular Dynamics Studies of the Collisions of Small Clusters

Brief summary-- Classical molecular dynamics is used to simulate the behavior of small clusters of Ar atoms (with 2-25 atoms per cluster.) The primary interest is in the collision of such clusters with either another Argon atom or with another small cluster. The collisions are generally at relatively low energy. A relatively large number of collisions are studied to map the growth and fragmentation patterns in such collisions.

What is a molecular Cluster?

It is a small group of molecules

• perhaps 3-50 molecules
  • small enough that is does not really behave like ordinary liquid or solid.
• what kind of molecules?
  • the simplest molecules are monoatomic
    • we mostly study clusters of Argon atoms
  • as a rule, cluster work is limited to relatively small molecules
  • some clusters are mixed (contain more than one type of molecule)
  • some clusters are charged (perhaps formed from an ion and neutral molecules)

• We are interested in the forces that typically cause nonpolar gas molecules to condense and form liquids
• Such forces are quite weak compared to
  • chemical bonds
  • attractions and repulsions between ions
    • in solution
    • in ionic crystals
  • interactions involving polar molecules
    • attractions between polar molecules
      • hydrogen bonding is an extremely strong example
    • atractions between ions and polar molecules
  • intera.tomic interactions within metals
• Neutral Molecules or Atoms are attracted by forces known under several names
  • Van DerWaals forces
  • London Forces
  • Dispersion Forces
  • Weak Attraction

• These terms are really best applied to large ensembles of molecules. Small clusters tend to behave differently and such labels as solid or liquid don't apply exactly. Likewise, if a cluster is alone in space, it might also be convidered a form of gas or part of an aerosol.