SPC/Fw model of water

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The SPC/Fw is a flexible variant of the rigid SPC model for water [1]. This model has also been re-parametrised for quantum simulations, adopting the name q-SPC/Fw [2]. The model is given by the intra-molecular component (Eq. 2 of [2]):

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^{\mathrm{eq}}_{\angle \mathrm{HOH}}  \right)^2

and the inter-molecular component (Eq. 3 of [2]):

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 [2]):

Thee site water model.png


Model k_b r^{\mathrm {eq}}_{\mathrm {OH}} (Å) k_a \vartheta^{\mathrm{eq}}_{\angle \mathrm{HOH}} (deg) \sigma_{\mathrm {OO}} (Å) \epsilon_{\mathrm {OO}} (kcal mol-1) q(O) (e) q(H) (e)
SPC/Fw 1059.162 1.012 75.90 113.24 3.165492 0.1554253 -0.82 0.41
q-SPC/Fw 1059.162 1.000 75.90 112.0 3.165492 0.1554252 -0.84 0.42

where the unit of k_b is kcal.mol-1Å-2 and the unit of k_a is kcal.mol-1rad-2.

Dielectric constant[edit]

The dielectric constant has been calculated by Raabe and Sadus [3].

References[edit]

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