Force Field, Virial Calculation of Stress

Interactions both between non-bonded united atoms (CH2) on different chain segments and between united atom pairs separated by four or more bonds in the same chain segment were calculated using a Lennard-Jones potential with a cut-off distance = 2.5 tlj. In addition, three types of bonded interactions are included, accounting for the stiffness in the bond length, bond angle and torsion. The interaction potentials are, in that order, 

For each of the force field contributions described above, there is a corresponding contribution to the total instantaneous stress tensor t, which is expressed in terms of the individual virial contributions. Explicit expressions for these contributions can be found in [26,29]. When using Lennard-Jones interactions for total energy calculations or for virial calculations of the stresses, long range corrections need to be included, as discussed by In t Veld et al. [26]. 

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