Atomistic forcefield

Abstract Based on an investigation of empirical links of the bond valence method to observable quantities, especially the electron density at the bond critical point as well as absolute electronic potential and hardness values in the frame of the hard and soft acids and bases concept, it is ascertained that bond valence can be understood as a functional of valence electron density. Therefrom a systematic approach for deriving bond valence parameters and related quantities such as coordination numbers and bond breaking energies is discussed that together allow for a conversion of the bond valence method to a simple effective atomistic forcefield. 

Keywords Atomistic forcefield Bond critical point Bond valence parameters Coordination numbers Electron density... 

If this is done suitably, then the (squared) bond valences can also - as demonstrated [25,26] - be linked to the absolute energy scale in static ways such as predicting energy thresholds in sohd electrolytes cf. [6], predicting NMR chemical shifts [36] or other spectroscopic properties, but also in dynamic ways as an effective atomistic forcefield. 

The computer simulation of clay minerals or other complex soil phases is often limited by the large unit cells and supercells required to properly represent the bulk or surface structure of the sorbing material. Furthermore, multicomponent substitutions in the structure, especially for clay minerals, lead to complex disordered systems that are not amenable to molecular simulation based on a simple unit cell to represent the system. Recently, Cygan and Kirkpatrick (2002) determined the sorp-tion sites of several complex clay phases based on the forcefield method of Pat-(abiraman et al. (1985). This approach allows for the evaluation of the fundamental atomistic properties that control the sorption of molecules, metals, and anions onto the internal or external surface of clays. It is possible to evaluate the influence of crystallography, cleavage surface, composition, isomorphic substitution, and sur-l ace protonation state on the relative sorption energy. 

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