Nearest-neighbor bond potential

Potential functions that have been used include the Morse type or the Lennard-Jones type. The potential function is generally minimized by the greatest number of nearest-neighbor bonds. 

Bond energy of an atom in a kink site position to the nearest neighbor Galvani potential at a point x from the Helmholtz plane Bond energy of an atom in a kink site position to the nearest neighbor, corrected for long-range forces... 

Remember that the U r) is a central force potential and must be modified in order to obtain a unidirectional force. A unit cell with a NaCl structure contains 54 nearest neighbor bonds that would have to be stretched to expand this cell in three dimensions. However, to expand it in one dimension only requires stretching 18 bonds. Therefore, since only 1/3 the number of bonds need to be stretched in a linear expansion, the stress can be written as... 

The main difficulty, therefore, lies in the construction of a suitable and cheap bias potential. Fichthorn et al. [44] developed a so-called bond-boost method, in which the boost potential is derived from the concept of bond breaking events in a solid. Thus, the boost potential in this approach is a function of all nearest-neighbor bond lengths associated with the atoms of interest. Using this technique, these authors studied the diffusion of Cu adatoms, dimers and vacancies on a Cu(OOl) surface [44]. In these simulations, average boost factors in the range lO -lO were obtained in the temperature range 230-600 K. 

In the previous section, the adaptation of the RIS model was based on the distance between next-nearest neighbor beads. This approach is obviously inadequate for CH3-CHX-CH2-CHX-CH3, because it necessarily abandons the ability to attribute different conformational characteristics to the meso and racemo stereoisomers. Therefore a more robust adaption of the RIS model to the 2nnd lattice is necessary if one wants to investigate the influence of stereochemical composition and stereochemical sequence on vinyl polymers [156]. Here we describe a method that has this capability. Of course, this method retains the ability to treat chains such as PE in which the bonds are subject to symmetric torsion potential energy functions. 

We now present results from molecular dynamics simulations in which all the chain monomers are coupled to a heat bath. The chains interact via the repiflsive portion of a shifted Lennard-Jones potential with a Lennard-Jones diameter a, which corresponds to a good solvent situation. For the bond potential between adjacent polymer segments we take a FENE (nonhnear bond) potential which gives an average nearest-neighbor monomer-monomer separation of typically a 0.97cr. In the simulation box with a volume LxL kLz there are 50 (if not stated otherwise) chains each of which consists of N -i-1... 

In our paper we are concerned with a potential energy function which is somewhat more realistic than one implied by the excluded volume effects. This potential function allows indirectly bonded chain elements which occupy adjacent lattice sites to interact with a finite energy . We call these interactions nearest-neighbor interactions, which should not be confused with interactions between near-neighbor pairs along the chain. 

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