Fomin potential

The Fomin potential was firstly introduced as (Eq. 2):

$\Phi _{12}\left(r\right)=\left({\frac {d}{r}}\right)^{n}+{\frac {\epsilon }{2}}(1-\tanh(k_{0}(r-\sigma _{s})))$

where $\Phi _{12}\left(r\right)$ is the intermolecular pair potential, Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle r:=|\mathbf {r} _{1}-\mathbf {r} _{2}|} is the distance between site 1 and site 2, $n=14$ and Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle k_0=10} . Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle d} is the diameter of the hard core, Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \sigma_s} is the width of the repulsive shoulder, Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \epsilon} is the height of the shoulder. As such, this model can be viewed as a softened square shoulder model.

Later it was generalized to the form  :

Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle \Phi _{12}\left(r\right)=\left({\frac {d}{r}}\right)^{n}+\lambda _{0}+\sum _{i=1}^{i=i_{max}}\lambda _{i}\tanh(k_{i}(r-\sigma _{i})))}

By varying coefficients Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \lambda_i } one can add repulsive shoulders or attractive wells to the potential.