Physics conducted a simulation of molecular dynamics of modification of ice-VII and found that the protons inside it can move through the crystal lattice under the action of an external electric field. This behavior is typical for not so long ago discovered experimentally superionic ice, the existence of which is possible on cold planets such as Uranus and Neptune. But the emergence of superiormost under the action of electric fields of high tension extends the range of celestial bodies, which the possible existence of this exotic state. In particular, according to the study of superionic ice could exist on Venus. Article published in Science Advances.
Most of the ice on Earth is an ice-Ih, which has a hexagonal crystal lattice. But there are 17 modifications of water ice, characterized by arrangement of molecules in the elementary cells. In one of them, called ice VII, the molecules are located in the nodes of the cubic lattice. Such a phase appears in a wide range of temperatures at pressures above 2 GPA and differs from other modifications by the possibility of transition to the superionic state. In this state, oxygen atoms of water molecules inside the crystal lattice remain fixed, while the protons gain the ability to move across the unit cell and even beyond.
The existence of such state of the physics predicted in 1987, and to observe it in the laboratory succeeded only in 2018. But even before laboratory synthesis, researchers advanced the theory that the superionic ice-VII can exist in the mantles of giant planets such as Uranus and Neptune, as the pressure and temperature inside them allow to exist this crystal modification. Prior to this, scientists also showedthat the structure of ice and the occurrence of superiormost can influence, among other things, the external electric field.
Researchers from Ireland, Canada and the Czech Republic under the leadership of Niall English (Niall J. English) from University College Dublin has conducted theoretical modeling of the motion of protons in the crystal lattice of ice VII using the method of ab initio non-equilibrium molecular dynamics. Ab initio approaches differ from other methods of quantum-mechanical simulations that do not use empirical data, but based only on physical laws. As the physical basis of calculations the authors used the density functional method. He is making several approximations, according to which all electrons in the system equally interacts with each other, and functional to a certain point in space depends only on the electron density in it. In contrast to the Hartree-Fock methodin the density functional theory of many-electron function is replaced by the electronic density, which allows to solve a more simple one-particle Schrodinger equation for each element of the system.
The authors found that under the action of an electric field strength of less than 0.33 volts per Angstrom, superiormost in this form of ice will not arise. But at higher values of tension in the system began to appear is characteristic of the superionic state of the “jumping” of protons on the mechanism of Grothus. Under this mechanism, formed after the dissociation of water hydrogen ions are attached to others, medicationabana, molecules with the formation of a positively charged hydronium H3O+. This particle is rather unstable, so the proton is split off from her and moves to the neutral molecule. Thus hydrogen ions can endlessly move around the crystal lattice as long as necessary for the existence of this phenomenon conditions.
In addition to theoretical calculations, the researchers built the vibrational spectra of ice VII under the influence of an external electric field. They also showed that the increase of the electric field the water molecules appear fluctuations associated with the appearance of superionic mechanism of diffusion of protons.
Based on earlier detection of electric fields on Venus and the presence on it of water, the study authors concluded that ice-VII superionic state can exist not only on cold planets, but also on more hot celestial bodies having a strong electric field, such as Venus. It should be noted that ice-VII along with the ice-X, in contrast to other modifications, may exist at high temperature, up to nearly 700 degrees Celsius, although this required a high pressure of 10 GPA.
Ice-VII, like many other modifications exist at high pressure or very low temperature. However, even in the familiar phase of ice I coexist two different combinations of cubic and hexagonal. Metastable cubic modification and get it in its pure form, scientists are still failed. Recently, however, researchers have set a record: they created the ice-I, in which the content of cubic phases have reached 80 percent.