Three body effect molecular simulation

The importance of three-body effects in the determination of macroscopic properties has also been studied. Recently, nonadditive molecular dynamics simulation of water and organic liquids has been performed [86]. 

Computer simulation of molecular dynamics is concerned with solving numerically the simultaneous equations of motion for a few hundred atoms or molecules that interact via specified potentials. One thus obtains the coordinates and velocities of the ensemble as a function of time that describe the structure and correlations of the sample. If a model of the induced polarizabilities is adopted, the spectral lineshapes can be obtained, often with certain quantum corrections [425,426]. One primary concern is, of course, to account as accurately as possible for the pairwise interactions so that by carefully comparing the calculated with the measured band shapes, new information concerning the effects of irreducible contributions of inter-molecular potential and cluster polarizabilities can be identified eventually. Pioneering work has pointed out significant effects of irreducible long-range forces of the Axilrod-Teller triple-dipole type [10]. Very recently, on the basis of combined computer simulation and experimental CILS studies, claims have been made that irreducible three-body contributions are observable, for example, in dense krypton [221]. 

The notation Z)/ in the first term indicates a summation over all atoms in the system and Vi(r/) represents the potential in an external force field. The second term, usually called the pair potential, is probably the most important energy term in a molecular dynamics simulation. The pair potential sums over all distinct atom pairs i and j without counting any pair twice. The function V2(r/, Vj) depends only on the separation between atoms i and j and hence can also be expressed as V2(r,y). Three-body and other multibody potentials are normally avoided in molecular dynamics simulations since they are not easy to implement and can be extremely time consuming. The multi-body effects are usually taken into account by modifying the pair potential, i.e., using an effective pair potential, which is not the exact interaction potential between the two... 

In the molecular dynamics and Monte Carlo simulations which are the source of the results described herein, the overall potential energy surface was assumed to be a pairwise sum of two-body interactions. The Ar-Ar and Kr-Kr pair potentials were represented by the accurate functions determined by Aziz and Slaman, while the Ar-SF5 and Kr-SFg interactions were represented by the detailed anisotropic functions determined by Pack et alJ Although three-body forces may not be negligible in these systems, we doubt that their effects are larger than those of the uncertainties in our knowledge of the Rg-SF two-body potentials. 

Simple two-body potentials have been designed empirically or using some basis of quantum chemistry. This approach is cheap and allows one to simulate the dynamics of clusters on a microsecond time scale. Potentials including n-body effects, polarizability effects and also three-body repulsion and dispersion, allow us, nowadays, to perform molecular dynamics simulation of clusters composed of 10 -10 molecules for hundreds or thousands of ps. The accuracy of the intermolecular and intramolecular potentials is the cornerstone of the success of this approach. 

In contrast to the large number of theoretical studies, extremely few computer simulation studies of nonadditivity effects have been performed. This dearth of simulation work is due to the prohibitively large amount of central processor time required to sample N(N-l)(N-2)/3I triplets in a system of N particles. Barker and coworkers (11) have used both Monte Carlo and molecular dynamics to estimate three body contributions to... 

Extensive theory and computer simulation work has been able to clarify the molecular mechanisms of solvation dynamics in bulk liquids over the past three decades.One of the most important conclusions from this body of work is that most of the contribution to polar solvation dynamics comes from the solute s first solvation shell. This conclusion and the earlier discussion about the prominent role the solute hydration shell plays in understanding vibrational and rotational dynamics at liquid interfaces suggest that surface effects on solvation dynamics will be muted as the solute s polarity is increased. An experimental validation of this are the similar solvation dynamics of C314 at the water liquid/vapor interface and in bulk water, mentioned above, where the highly polar excited state n = 12D) implicates an interfacial hydration structure similar to the bulk. 

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