Long-range interactions computational aspects

Computer simulations have been applied to studies of the structure of molten salts along two lines one is the fi ee standing application of the computer simulation to obtain the partial pair correlation functions, the other is the refining of x-ray and neutron diffraction and EXAFS measurements by means of a suitable model. In both cases a suitable potential function for the interactions of the ions must be employed, as discussed in Sect. 3.2.4. Such potential functirms are employed in both the Monte Carlo (MC) and the molecular dynamics (MD) simulation methods. A further aspect that has been considered in the case of molten salts is the long range coulombic interaction that exceeds the limits of the periodic simulation boxes usually involved (for 1000 ions altogether), requiring the Ewald summation that is expensive in computation time and is prone to truncation errors if not applied carefully. 

Atomistic MD implements predetermined potential functions, also referred as force fields (FFs), either empirical or derived from independent electronic stmcture calculations. An important aspect in any MD simulation is how to describe or approximate the interatomic interactions. Usually, the potentials that describe these interactions are determined a priori and the full interaction is partitioned into two-, three-, and many-body contributions, long- and short-range terms, and so on, for which suitable analytical functional forms are devised. There are arguments that empirically fitted potentials are more reliable since they include in an implicit way the many-body effects. In principle, by comparing the results of computer and laboratory experiments, we can improve and refine the theoretical model. 

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