**2.4.2 Interfacial tension**

In the continuum surface force (CSF) method, the interfacial tension force is calculated as

$$\mathbf{f}\_{\sigma} = \sigma \kappa \mathbf{n} \,\delta\_{\mathbf{S}'} \tag{18}$$

where is the coefficient of the interfacial tension, is the curvature, **n** is the normal to the interface, and *<sup>S</sup>* is a delta function concentrated on the interface. The interfacial tension force in Eq.(2) is calculated by using Eq.(18) and the relation **n** *<sup>S</sup> F* , which holds in the continuum limit. The curvature, , is calculated with a high degree of accuracy by using height functions (Lorstad & Fuchs, 2004), which effectively eliminates spurious currents for a static drop (Francois et al., 2006).
