SPC/Fw model of water

2016-09-16T17:03:15Z

Efremdan1: Corrected units of k_a.

The '''SPC/Fw''' is a flexible variant of the rigid [[SPC]] model for [[water]]
<ref>[http://dx.doi.org/10.1063/1.2136877 Yujie Wu, Harald L. Tepper and Gregory A. Voth "Flexible simple point-charge water model with improved liquid-state properties", Journal of Chemical Physics '''124''' 024503 (2006)]</ref>.
This model has also been re-parametrised for quantum simulations, adopting the name '''q-SPC/Fw'''
<ref name="q-SPC/Fw">[http://dx.doi.org/10.1063/1.2386157 Francesco Paesani, Wei Zhang, David A. Case, Thomas E. Cheatham, III and Gregory A. Voth "An accurate and simple quantum model for liquid water", Journal of Chemical Physics '''125''' 184507 (2006)]</ref>.
The model is given by the intra-molecular component (Eq. 2 of <ref name="q-SPC/Fw"> </ref>):

:<math>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 </math>

and the inter-molecular component (Eq. 3 of <ref name="q-SPC/Fw"> </ref>):

:<math>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\} </math>

The parameters for both of these models are given in the following table (Table I of <ref name="q-SPC/Fw"> </ref>):

[[Image:Thee_site_water_model.png‎|center|400px]]

{| style="width:75%; height:100px" border="1"
|-
| Model || <math>k_b</math> || <math>r^{\mathrm {eq}}_{\mathrm {OH}}</math> (Å)|| <math>k_a</math> || <math>\vartheta^{\mathrm{eq}}_{\angle \mathrm{HOH}}</math> (deg)|| <math>\sigma_{\mathrm {OO}}</math> (Å)|| <math>\epsilon_{\mathrm {OO}}</math> (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 <math>k_b</math> is kcal.mol-1Å-2 and the unit of <math>k_a</math> is kcal.mol-1rad-2.
==Dielectric constant==
The dielectric constant has been calculated by Raabe and Sadus <ref>[http://dx.doi.org/10.1063/1.3600337 Gabriele Raabe and Richard J. Sadus "Molecular dynamics simulation of the dielectric constant of water: The effect of bond flexibility", Journal of Chemical Physics '''134''' 234501 (2011)]</ref>.
==References==
<references/>
{{numeric}}
[[category: water]]
[[category: models]]

SklogWiki - User contributions [en]

SPC/Fw model of water