SPC/Fw model of water

The SPC/Fw is a variant of the SPC model for water . This model has also been re-parametrised for quantum simulations, adopting the name q-SPC/Fw . The model is given by the intra-molecular component (Eq. 2 of ):

$V^{\mathrm {intra} }={\frac {k_{b}}{2}}\left[\left(r_{\mathrm {OH} _{1}}-r_{\mathrm {OH} }^{\mathrm {eq} }\right)^{2}+\left(r_{\mathrm {OH} _{2}}-r_{\mathrm {OH} }^{\mathrm {eq} }\right)^{2}\right]+{\frac {k_{a}}{2}}\left(\vartheta _{\angle \mathrm {HOH} }-\vartheta _{\angle \mathrm {HOH} }^{\mathrm {eq} }\right)^{2}$

and the inter-molecular component (Eq. 3 of ):

$V^{\mathrm {inter} }=\sum _{ij}^{\mathrm {all~pairs} }\left\{4\epsilon _{ij}\left[\left({\frac {\sigma _{ij}}{R_{ij}}}\right)^{12}-\left({\frac {\sigma _{ij}}{R_{ij}}}\right)^{6}\right]+{\frac {q_{i}q_{j}}{R_{ij}}}\right\}$

The parameters for both of these models are given in the following table (Table I of ):

Model	$r_{\mathrm {OH} }$ (Å)	$\angle$HOH , deg	$\sigma$ (Å)	$\epsilon /k$ (K)	q(O) (e)	q(H) (e)	q(M) (e)	$r_{\mathrm {OM} }$ (Å)
SPC/Fw
q-SPC/Fw