  The Martini model, a coarse-grained forcefield for biomolecular simulations,
has experienced a vast increase in popularity in the past decade. Its
building-block approach balances computational efficiency with high chemical
specificity, enabling the simulation of various organic and inorganic
molecules. The modeling of coarse-grained beads as Lennard-Jones particles
poses challenges for the accurate reproduction of liquid-vapour interfacial
properties, which are crucial in various applications, especially in the case
of water. The latest version of the forcefield introduces refined interaction
parameters for water beads, tackling the well-known artefact of Martini water
freezing at room temperature. Additionally, multiple sizes of water beads are
available for simulating the solvation of small cavities, including the
smallest pockets of proteins. This work focuses on studying the interfacial
properties of Martini water, including surface tension, surface thickness, and
bulk densities for the liquid and vapour phases. Employing the test-area
method, we systematically compute the liquid-vapour surface tension across
various combinations of water bead sizes and for temperatures in the range from
300 to 350 K. Our findings provide a comprehensive characterization of Martini
3.0 water intefacial properties. These findings are of interest to the Martini
community as they allow users to account for the low interfacial tension of
Martini water by properly adjusting observables computed via coarse-grained
simulations (e.g., capillary forces) to allow for accurate matching against
all-atom or experimental results. Surface tension data are also interpreted in
terms of local enrichment of the various mixture components at the
liquid-vapour interface by means of Gibbs' adsorption formalism
