Morse potential
Potential form of the Morse potential is,
E_{ij}(R_{ij}) = D_{ij} \left\{ [\exp (\alpha_{ij} (R_{0,ij} -R_{ij}))-1]^2 -1\right\} \end{equation*}$$ The potential requires a parameter file `in.params.Morse` that has the following format. ``` # isp, jsp, D_ij, alpha_ij, R0_ij 1 1 3.7 2.0 1.68 1 2 3.2 1.9 2.5 2 2 2.5 2.1 2.3 ``` In the above case, there are three interactions between 1-1, 1-2 and 2-2. Each interaction has three parameters: - `D_ij`: depth of the potential curve (eV) - `alpha_ij`: related to the width of the potential well (Ang.^{-1}). - `R0_ij`: position of the potential minimum (Ang.)