Electrostatics

Electrostatics describes the force resulting from the interaction between two charged particles. The electrostatic energy between two atoms i and j is described by Coulomb's Law as

$$E_{\text{elec}} = \epsilon_{14} \frac{C q_i q_j}{\epsilon_0 \vert\vec{r}_{ij}\vert}$$

where

• $\epsilon_{14}$ = Scaling factor for 1-4 interactions. This is zero for 1-2 and 1-3 interactions and is equal to 1.0 for any interaction other than a modified 1-4 interaction. The value used for modified 1-4 interactions is specified in the configuration file using the 1-4scaling parameter. (See section 4.)
• C = 2.31 $\times$ 10^-19 J nm
• q_i = charge of atom i from the PSF file
• q_j = charge of atom j from the PSF file
• $\epsilon_0$ = Dielectric constant specified in the configuration file using the parameter dielectric. (See section 4.)
• $\vec{r}_{ij} = \vec{r}_j - \vec{r}_i$, the vector from atom i to atom j
• $\vert\vec{r}_{ij}\vert$ = length of $\vec{r}_{ij}$, which is equal to the calculated distance between atoms i and j