Abstract
We study the polarization behavior of water under geologically-relevant
extreme aqueous environments along four equidistant supercritical
isotherms, 773 ! T (K) ! 1373, and over a wide pressure range,
0 < P(GPa) ! 30 , by isobaric-isothermal molecular dynamics simulations
of the Gaussian Charge Polarizable (GCP ) water model, to unravel and
discuss the underlying link between two precisely defined orientational
order parameters and the magnitude of the average induced dipole moment
of water. The predicted behavior indicates an isothermal linear dependence
(a) between the magnitude of the average induced dipole moment μind and
the average system density ! , (b) between the magnitude of the average
induced dipole μind and that of the total dipole μtot , resulting from (c) a
compensating (inverse) dependence between the permanent-to-induced
dipolar angle ! and the magnitude of the average induced dipole moment
μind . Moreover, we interpret this behavior in terms of the evolution of the
state dependent tetrahedral order parameter qT and the corresponding
bond-order parameter Q6 , supplemented by the microstructural analysis
based on the three site-site radial distribution functions of water and the
distance-ranked nearest-neighbors distributions. Finally, we show that
while water exhibits a dramatic microstructural transformation from an
open four-coordinated hydrogen-bonded network at normal conditions to a quasi close-packed coordination, it still preserves a significant degree of hydrogen bonding.