Combining rules

In computational chemistry and molecular dynamics, the combination rules or combining rules are equations that provide the interaction energy between two dissimilar non-bonded atoms, usually for the part of the potential representing the van der Waals interaction. In the simulation of mixtures, the choice of combining rules can sometimes affect the outcome of the simulation. In computational chemistry and molecular dynamics, the combination rules or combining rules are equations that provide the interaction energy between two dissimilar non-bonded atoms, usually for the part of the potential representing the van der Waals interaction. In the simulation of mixtures, the choice of combining rules can sometimes affect the outcome of the simulation. The Lennard-Jones Potential is a mathematically simple model for the interaction between a pair of atoms or molecules. One of the most common forms is where ε is the depth of the potential well, σ is the finite distance at which the inter-particle potential is zero, r is the distance between the particles. The potential reaches a minimum, of depth ε, when r = 21/6σ ≈ 1.122σ. The Lorentz rule was proposed by H. A. Lorentz in 1881: The Lorentz rule is only analytically correct for hard sphere systems. The Berthelot rule (Daniel Berthelot, 1898) is given by: These rules are the most widely used and are the default in many molecular simulation packages, but are not without failings. The Waldman-Hagler rules are given by: