Ensembles
Definition of an ensemble
- Collection of microstates subject to at least one extensive constraint
“microstate” is specification of all atom positions and momenta
fixed total energy, total volume, and/or total number of molecules
unconstrained extensive quantities are represented by full range of possible values
- Probability distribution p describing the likelihood of observing each state, or the weight that each state has in ensemble average
Example: Some members of ensemble of fixed N
- isothermal-isobaric (TPN)
all energies and volumes represented