5.5. Polar & Non-polar interaction:

Polar interaction: Basically coulomb potential

Non-polar interaction: van der Waals potential, such as L-J potential, hard spheres etc

For polar interaction, r_c is higher than non-polar interaction and thus, polar interaction is known as long-range interaction and non-polar interaction is known as short-range interaction.

Usually, we consider pair-wise interaction (viz. two-body interaction) only. In simulation, we implement as follows: find the distance between any two atoms/molecules/particles and then check if the distance, r_ij is within the allowable range (> & < r_c ). If yes, calculate the potential, else discard the calculation.

5.6. Review on Partition Function, Ensemble, etc:

We have already discussed partition function, ensembles in module II. Here, we briefly review on these basic concepts.

Partition function Z

is proportional to the probability of having a system at the energy , the probability is

Once the Z is known, almost every thermodynamic parameter can be measured.

For example, free energy, F is related with the partition function through the relation:

Once, free energy is determined, all thermodynamic properties can be easily estimated .