📰 Towards a better quantum description of water


The quantum description of interacting molecules leads to notoriously complex calculations as soon as their number exceeds a few units. Thanks to an important campaign of quantum simulations, physicists have nevertheless managed to reproduce the dynamic quantities ofwater (Water is an omnipresent chemical compound on Earth, essential for everyone …) liquid (The liquid phase is a state of matter. In this form, matter is …) as the diffusion (In common parlance, the term diffusion refers to a notion of …) and viscosity.

The continued increase of power (The word power is used in several fields with a particular meaning 🙂 computer for 60 years has made significant progress physicist (Physics (from the Greek φυσις, nature) is etymologically the …) of the it matters (Matter is the substance that makes up any body having a tangible reality. Its …) condensate making it possible to simulate assemblies of particles in interaction (An interaction is an exchange of information, affect or energy between two agents within …) from the fundamental equations of physics. This “physics digital (Digital information is information …)“thus allowed us to understand how fluids organize and evolve at the molecular level, and how the macroscopic properties we know of them emerge from these microscopic characteristics: density (The density or relative density of a body is the ratio of its density to the …)viscosity, surface tension (On the surface of a dense medium (liquid or solid) or at the interface between two mediums …)etc.

In many cases, the equations of classical physics are sufficient to obtain excellent predictions for the thermodynamic and dynamic properties of simple fluids up to complex polymer mixtures. However, in some cases, a quantum treatment of molecular interactions turns out to be necessary when, for example, the conditions of pressure (Pressure is a fundamental physical notion. You can think of it as a reported force …) and / or of temperature (Temperature is a physical quantity measured using a thermometer and …) become exceptional, or when quantum signatures specifically escape the simplified description of the mechanic (In everyday language, mechanics is the field of machines, engines, vehicles, organs, etc.) classic.

Despite our familiarity with it, and its abundance everywhere Land (Earth is the third planet in the Solar System in order of distance …)water is a perfect example where this complexity (Complexity is a concept used in philosophy, epistemology (for …) what is done day (The day or day is the interval between sunrise and sunset; it is the …): the interactions between molecules have two faces, being on the one hand similar to the so-called van der Waals attractions, generic between molecules, and on the other very specific to molecule (A molecule is an electrically neutral chemical set of at least two atoms, which …) H.2Or, directional and selective, the so-called “hydrogen (Hydrogen is a chemical element with the symbol H and atomic number 1.)“, because by temporarily connecting the atoms (An atom (from the Greek ατομος, atomos, “which cannot be …) H from one molecule aloxygen (Oxygen is a chemical element of the chalcogen family, of …) Or a nearby molecule. This “two-headed” nature of the interactions is of purely quantum origin and has an impact on the macroscopic properties of water, the best known being undoubtedly the abnormal lower density of the water. Ice (Ice is solid water.) of water compared to liquid water which preserves the life (Life is the name given 🙂 in the lakes of cold regions.

When the Quantum mechanics (Quantum mechanics is the branch of physics that aims to study and … becomes a necessary ingredient of the physical description, the simulation work undergoes a real leap in complexity, and still today challenges the power of the largest computers.

In this context (The context of an event includes the circumstances and conditions surrounding it; the …)researchers of theInstitute (An institution is a permanent organization created for a specific purpose. It is …) light (Light is the set of electromagnetic waves visible to the eye …) subject (ILM, CNRS / University Claude Bernard (Claude Bernard, born on 12 July 1813 in Saint-Julien (Rhone) and died on …) Lyon 1), in collaboration with scientists from theUniversity (A university is a higher education institution whose goal is the …) from Zurich have just played a major country (The countryside, also called rural environment, designates all the cultivated areas …) quantum simulations on liquid water for a wide range of temperatures. They show that computers today are powerful enough for the quantum computing schemes used by physicists (including the “theory (The word theory comes from the Greek theorein, which means “to contemplate, observe, …) of the functional (In mathematics, the term functional refers to certain functions ….) density “, or DFT) can quantitatively explain the viscosity of water and its diffusion properties, from one approach from the beginning.

Their calculations also allow to prioritize the various known DFT approaches, some diagrams ofapproximation (An approximation is an approximate representation, i.e. missing …) also failing to describe the viscosity of water at any temperature. Finally, they show that the dynamic properties of water can be deduced from the analysis ofentropy (In thermodynamics, entropy is a state function introduced in 1865 by Rudolf Clausius …) of the liquid on a scale of a few molecules, which allows their calculation to be considerably accelerated, as the structural properties are faster to calculate than essentially dynamic quantities.

What is at stake is important, the possibility of faithfully describing the water, in its structure and in its dynamic (The word dynamic is often used to designate or qualify what refers to movement. It …), being for example a crucial issue for the advancement of the understanding of nanofluidic flows. These results are published in Proceedings of the National Academy of Sciences.

Connection between dynamic and structural properties of water: Insights from ab initio simulations.
C. Herrero, M. Pauletti, G. Tocci, M. Iannuzzi, L. Joly; PNASreleased on May 19, 2022.
DOI: 10.1073 / pnas.2121641119
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