  We investigate vapor bubble nucleation in metastable TIP4P/2005 water at
negative pressure via the Mean First Passage Time (MFPT) method using the
volume of the largest bubble as a local order parameter. We identify the
bubbles in the system by means of a Voronoi-based analysis of the Molecular
Dynamics trajectories. By comparing the features of the tessellation of liquid
water at ambient conditions to those of the same system with an empty cavity we
are able to discriminate vapor (or interfacial) molecules from the bulk ones.
This information is used to follow the time evolution of the largest bubble
until the system cavitates at 280 K above and below the spinodal line. At the
pressure above the spinodal line, the MFPT curve shows the expected shape for a
moderately metastable liquid from which we estimate the bubble nucleation rate
and the size of the critical cluster. The nucleation rate estimated using
Classical Nucleation Theory turns out to be about 8 order of magnitude lower
than the one we compute by means of MFPT. The behavior at the pressure below
the spinodal line, where the liquid is thermodynamically unstable, is
remarkably different, the MFPT curve being a monotonous function without any
inflection point.
