Recently it was shown that the WAC model for liquid silica [L. V. Woodcock, C. A. Angell, and P. Cheeseman, J. Chem. Phys. 65, 1565Phys. 65, (1976] is remarkably close to having a liquid-liquid critical point (LLCP). We demonstrate that increasing the ion charge separates the global maxima of the response functions, while reducing the charge smoothly merges them into a LLCP; a phenomenon that might be experimentally observable with charged colloids. An analysis of the Si and O coordination numbers suggests that a sufficiently low Si/O coordination number ratio is needed to attain a LLCP.PACS numbers: 64.70.Ja, 61.20.JaTetrahedral liquids tend to display a range of phenomena that are anomalous in comparison to "simple" liquids [1]. The showcase example here is liquid water, which displays a large number of anomalies, such as an increase of the self-diffusion upon compression (diffusion anomaly) and an increase of the density as it is cooled (density anomaly). In water, many of these anomalies are highly pronounced in the supercooled regime, far below the melting line. Of particular interest are the seemingly divergent behaviors of both the isobaric heat capacity C P [2, 3] and isothermal compressibility K T [4] upon cooling. Unfortunately these experiments are limited by homogeneous nucleation, and crystallization rapidly occurs as the temperature approaches −40To explain both the anomalies and this divergent behavior, several scenarios have been proposed [5][6][7] among which the liquid-liquid critical point (LLCP) scenario [6] has received the most attention [8,9]. According to this scenario two metastable liquids exist deep in the supercooled regime: a high-density liquid phase (HDL) that is highly diffusive, and a low-density liquid phase (LDL) that is more structured and less diffusive. These two metastable phases are separated by a first-order-like liquid-liquid phase transition (LLPT) line that ends at a critical point. In the one-phase region beyond any critical point the response functions remain finite and display a locus of maxima or minima that near the critical point merges with the locus of correlation length maxima, known as the Widom line [10][11][12]. According to this scenario it is the response function extrema originating from the LLCP that account for many of the anomalies of water.The LLCP scenario could also explain the anomalies found in other tetrahedral liquids. For example, a LLCP has been found in the Stillinger-Weber model for liquid silicon [13,14]. Another candidate is liquid silica, SiO 2 . Simulations of the BKS silica model [15] and the WAC silica model [16] show hints of a possible LLCP at low temperatures [17][18][19], however, more recent studies have questioned its existence in these models [20,21]. Nonetheless, in the P T -plane the isochores of the WAC model are remarkably close to crossing. As the crossing of isochores is a clear indicator of a phase transition [20,22], one may therefore conclude that the WAC model is remarkably close to having a LLCP.It is important to ...