7.4. Simulation in micro canonical ensemble (NVE)

This ensemble is not commonly used in MC simulation. Keeping N & V constant throughout the simulation is relatively easy and convenient than keeping E constant. At any given T, E of the system is supposed to fluctuate across a mean value. Therefore, this ensemble is not suitable. If in any situation, this ensemble is to be used, the following procedure may be adopted based on the demon algorithm proposed by Creutz (Ref. 4).  Here, a random walk on the configuration space is attempted keeping total energy (E#) constant.  Usually, E# is set higher than the configurational energy, Ei. An additional degree of freedom, the demon energy, ED is introduced to carry the remainder (E#- Ei) of the energy.

7.5. Simulation in NPT ensemble

This is one of the widely used ensembles. The simulation is carried out at a constant temperature and pressure, where, volume is subject to vary. It is usually done by one volume change move coupled with the particle displacement moves in an MC step, as we did in NVT ensemble simulation. NPT ensemble is advantageous over NVT ensemble to study phase transition, since experimentally, phase transition is studied keeping P and T constant.