Virtual Force Field method

In the IBM, the presence of the solid boundary (fixed or moving) in the fluid can be represented by a virtual body force field -rp( ) applied on the computational grid at the vicinity of solid-flow interface. Considering the stability and efficiency in a 3-D simulation, the direct forcing scheme is adopted in this model. Details of this scheme are introduced in Section II.B. In this study, a new velocity interpolation method is developed based on the particle level-set function (p), which is shown in Fig. 20. At each time step of the simulation, the fluid-particle boundary condition (no-slip or free-slip) is imposed on the computational cells located in a small band across the particle surface. The thickness of this band can be chosen to be equal to 3A, where A is the mesh size (assuming a uniform mesh is used). If a grid point (like p and q in Fig. 20), where the velocity components of the control volume are defined, falls into this band, that is... 

Dynamics). The field of molecular simulations grew up independently from that of NMR structural studies and developed its own level of molecular detail. Many such force fields use the united atom representation of a molecule, in which all heavy atoms are present but only polar hydrogens are treated explicitly.12-14 An NMR restraint, however, may well refer to an aliphatic proton not explicitly treated. To handle this situation, van Gunsteren et al., applied what was called the virtual atom.ls With this method, one can take the force that one would want to impose on the proton and redistribute it on to the atoms present. For example, one may have a potential V defined in terms of the coordinates of a proton H. The force as a function of that proton s coordinates would be written as follows ... 

The application of ab initio methods in the calculation of harmonic force fields of transition metal complexes has been hampered by the size of these systems and the need to employ costly post-Hartree-Fock methods, in which electron correlation is taken into account. Thus, the fruitful symbiosis between ab initio theory and experiment, to determine empirically scaled quantum mechanical force fields, has been virtually absent in studies of transition metal complexes. 

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