  The existence of a first-order phase transition between a low-density liquid
(LDL) and a high-density liquid (HDL) forms of supercooled water has been a
central and highly debated issue of physics and chemistry in the last three
decades. We present a computational study that allows to determine the
free-energy landscapes of supercooled water over a wide range of pressure and
temperature conditions, using the accurate TIP4P/2005 force field. Our approach
combines topology-based structural transformation coordinates, state-of-the-art
free-energy calculation methods, and extensive unbiased molecular dynamics
simulations. All our results indicate that transitions between the LDL and HDL
forms are smooth throughout the so-called "no man's land", and that free-energy
barriers do not appear until the onset of the solid, non-diffusive amorphous
forms.
