Razvan Caracas

• PhD
• Directeur de Recherche at Université de Paris

The formation and evolution of rocky planets such as the Earth are marked by the heavy bombardments that dominated the first parts of the accretions. The outcomes of the large and giant impacts depend on the critical points and liquid‐vapor equilibria of the constituent materials. Several determinations of the positions of the critical points have...

Refractory materials play an important role in lunar formation as they are some of the first components to coalesce from vaporized material that resulted from a giant impact. CaO is chemically and structurally similar to MgO and together they make up over 40% of both pyrolite and lunar composition models. In this work, we explore the liquid-vapor c...

The Moon-forming giant impact, involving a collision between the proto-Earth and a planetary body known as Theia, presents considerable challenges, particularly regarding Theia's and proto-Earth’s characteristics. By integrating impact numerical modelling with data from meteorites, we can bring further constraints on their mantle composition and Th...

Giant impacts dominate the late stages of accretion of rocky planets. They contribute to the heating, melting, and sometimes vaporizing of the bodies involved in the impacts. Due to fractionation during melting and vaporization, planet-building impacts can significantly change the composition and geochemical signatures of rocky objects. Using first...

Giant impacts dominate the late stages of accretion of rocky planets. They contribute to the heating, melting, and sometimes vaporizing of the bodies involved in the impacts. Due to fractionation during melting and vaporization, planet-building impacts can significantly change the composition and geochemical signatures of rocky objects. Using first...

Iron hydrides are a potentially dominant component of the metallic cores of planets, primarily because of hydrogen's ubiquity in the universe and affinity for iron. Using ab initio molecular dynamics, we examine iron hydrides with 0.1, 0.33, 0.5, and 0.6 mol fraction hydrogen up to 100 GPa between 3,000 and 5,000 K to describe how hydrogen content...

Giant impacts dominate the late stages of accretion of rocky planets [1, 2, 3]. They contribute to the heating, melting, and sometimes vaporization of the impacted bod- ies [4, 5, 6]. Due to fractionation during melting and vaporization, planet-building impacts can significantly change the composition and geochemical signatures of rocky objects [7,...

The moon-forming impact caused widespread melting and vaporization of the proto-Earth, leading to the formation of a protolunar disk1,2. Volatile elements trapped in the inner parts of the disk condensed together with heavier elements into a global magma ocean3,4. By subsequent cooling and degassing, volatiles contributed to the formation of the Ea...

The diffusion of noble gases in SiO2 phases is studied using ab initio molecular dynamics based on the density functional theory, covering pressure and temperature conditions from the crust to the core. Our results show that the diffusion of noble gases in SiO2 minerals is not only controlled by external conditions such as temperature and pressure...

Taking advantage of the Raman resonance effect, we employed 405 and 532 nm excitations to (1) identify sulfur species present in lazurite, haüyne, and synthetic ultramarine blue pigments and (2) investigate the enigmatic ~485 cm-1 band found previously in Raman spectra of lazurite and haüyne collected with 458 nm excitation. In spectra of lazurite...

Taking advantage of the Raman resonance effect, we employed 405 and 532 nm excitations to (1) identify sulfur species present in lazurite, haüyne, and synthetic ultramarine blue pigments and (2) investigate the enigmatic ~485 cm-1 band found previously in Raman spectra of lazurite and haüyne collected with 458 nm excitation. In spectra of lazurite...

Plain Language Summary Understanding the storage and cycling of carbon in the Earth's deep interior improves our knowledge of the Earth's formation and evolution throughout geologic time. Carbon‐bearing melts are candidate phases for carbon storage in the lower mantle and may react and mix with other melt phases at places such as the core‐mantle bo...

Constraining the diffusional behaviour of noble gases in minerals is important for many geochemical studies (e.g. thermochronometry, cycle of volatiles). SiO2 is a major component and phase in the crust and mantle, and represents up to 20% of basaltic mantle compositions. Its simple composition makes it easier to model as a large system than other...

Here we investigate how small amounts of hydrogen (much smaller than the mass of the exoplanet) above a magma ocean on a rocky exoplanet may modify the atmospheric chemistry and atmospheric escape.We use a chemical model of a magma ocean coupled to a gas equilibrium code. An energy-limited model is used to compute atmospheric escape. The compositio...

Taking advantage of the Raman resonance effect, we employed 405 and 532 nm excitations to 1) identify sulfur species present in lazurite, haüyne, and synthetic ultramarine blue pigments and 2) investigate the enigmatic ~485 cm-1 band found previously in Raman spectra of lazurite and haüyne collected with 458 nm excitation. In spectra of lazurite an...

Context. Ultrahot (>1500 K) rocky exoplanets may be covered by a magma ocean, resulting in the formation of a vapor rich in rocky components (e.g., Mg, Si, Fe) with a low total pressure and high molecular mass. However, exoplanets may have also captured a significant amount of hydrogen from the nebular gas during their formation. Ultrahot rocky exo...

This chapter highlights the power and usefulness of atomistic computer simulations in the field of mineralogy, with particular emphasis on their applications to extreme conditions in planetary interiors. The ability of density functional theory simulations to accurately predict the physical and chemical properties of minerals and melts, together wi...

The abundance of volatile elements in the silicate Earth relative to primitive chondrites provides an important constraint on the thermochemical evolution of the planet. However, an overabundance of indium relative to elements with similar nebular condensation temperatures is a source of debate. Here we use ab initio molecular dynamics simulations...

Carbonate melts have been proposed to exist in the lower mantle, but their interaction with other lower mantle melt compositions is poorly understood. To understand miscibility in the carbonate-silicate-metal melt system, we simulate endmember, binary, and ternary melt mixtures and study how their Gibbs free energies of mixing evolve with pressure....

Jadeite is frequently reported in shocked meteorites, displaying a variety of textures and grain sizes that suggest formation by either solid-state transformation or by crystallization from a melt. Some-times, jadeite has been identified solely on the basis of Raman spectra. Here we argue that additional characterization is needed to confidently id...

Electrolytes play an important role in the internal structure and dynamics of water-rich satellites and potentially water-rich exoplanets. However, in planets, the presence of a large high-pressure ice mantle is thought to hinder the exchange and transport of electrolytes between various liquid and solid deep layers. Here we show, using first-princ...

Using particle swarm optimization with density functional theory, we identify the positions of hydrogen in a hypothetical Mg-end-member of phase egg (MgSiO4H2) and predict the most stable crystal structures with MgSiO4H2 stoichiometry at pressures between 0 and 300 GPa. The particle swarm optimization method consistently and systematically identifi...

Ab initio molecular dynamics calculations on a carbonate‐silicate‐metal melt were performed to study speciation and coordination changes as a function of pressure and temperature. We examine in detail the bond abundances of specific element pairs and the distribution of coordination environments over conditions spanning Earth’s present‐day mantle....

The position of the critical point determines the top of the liquid-vapor coexistence dome, and it is a physical parameter of fundamental importance in the study of high-energy shocks, including those associated with large planetary impacts. For most major planetary materials, such as oxides and silicates, the estimated position of the critical poi...

The magma ocean was a important reservoir for Earth’s primary volatiles. Understanding the volatile fluxes between the early atmosphere and the magma ocean is fundamental for quantifying the volatile budget of our planet. Here we investigate the vaporization of carbon and hydrogen at the boundary between the magma ocean and the thick, hot early atm...

We develop a Python-based open-source package to analyze the results stemming from ab initio molecular-dynamics simulations of fluids. The package is best suited for applications on natural systems, like silicate and oxide melts, water-based fluids, various supercritical fluids. The package is a collection of Python scripts that include two major l...

We characterize the structural and transport properties of fluid iron at the low densities and high temperature conditions characteristic to the outer parts of protolunar disks, which form after giant impacts. We observe that decreasing the density and increasing the temperature decluster the fluid, which is eventually dominated by isolated atoms a...

“Cousin” worlds—slightly bigger or slightly hotter than Earth—can help us understand planetary habitability, but we need more lab and numerical experiments to make the most of this opportunity.

Jadeite is frequently reported in shocked meteorites, displaying a variety of textures and grain sizes that suggest formation by either solid-state transformation or by crystallization from a melt. Sometimes, jadeite has been identified solely on the basis of Raman spectra. Here we argue that additional characterization is needed to confidently ide...

The early Earth was marked by at least one global magma ocean. Melt buoyancy played a major role for its evolution. Here we model the composition of the magma ocean using a six‐component pyrolite melt, to which we add volatiles in the form of carbon as molecular CO or CO2 and hydrogen as molecular H2O or through substitution for magnesium. We compu...

The ab initio (ai) Gibbs ensemble (GE) Monte Carlo (MC) method coupled with Kohn–Sham density functional theory is successful in predicting the liquid–vapour equilibrium of insulating systems. Here we show that the aiGEMC method can be used to study also metallic systems, where the excited electronic states play an important role and cannot be negl...

We discuss major challenges in modeling giant impacts between planetary bodies, focusing on the equations of state (EOS). During the giant impact stage of planet formation, rocky planets are melted and partially vaporized. However, most EOS models fail to reproduce experimental constraints on the thermodynamic properties of the major minerals over...

Giant impacts are disruptive events occurring in the early stages of planetary evolution. They may result in the formation of a protolunar disk or of a synestia. A central planet and one or several moons condense upon cooling bearing the chemical signature of the silicate mantles of the initial bodies; the iron cores may partly vaporize, fragment a...

The position of the vapor‐liquid dome and of the critical point determine the evolution of the outermost parts of the protolunar disk during cooling and condensation after the Giant Impact. The parts of the disk in supercritical or liquid state evolve as a single thermodynamic phase; when the thermal trajectory of the disk reaches the liquid‐vapor...

The degree to which the Earth’s mantle stores and cycles water in excess of the storage capacity of nominally anhydrous minerals is dependent upon the stability of hydrous phases under mantle-relevant pressures, temperatures, and compositions. Two hydrous phases, phase D and phase H, are stable to the pressures and temperatures of the Earth’s lower...

To improve our understanding of the Earth's global carbon cycle, it is critical to characterize the distribution and storage mechanisms of carbon in silicate melts. Presently, the carbon budget of the deep Earth is not well constrained and is highly model‐dependent. In silicate melts of the uppermost mantle, carbon exists predominantly as molecular...

With ab initio molecular dynamics simulations on a Na‐, Ca‐, Fe‐, Mg‐, and Al‐bearing silicate melt of pyrolite composition, we examine the detailed changes in elemental coordination as a function of pressure and temperature. We consider the average coordination as well as the proportion and distribution of coordination environments at pressures an...

We discuss major challenges in modeling giant impacts between planetary bodies, focusing on the equations of state (EOS). During the giant impact stage of planet formation, rocky planets are melted and partially vaporized. However, most EOS models fail to reproduce experimental constraints on the thermodynamic properties of the major minerals over...

The Raman Experiments for Astrobiology and Planetology REAP database of the Laboratoire de Géologie de Lyon is based on a collection of Raman spectra of representative minerals from the original “Handbook of Raman spectra for geology” web database. Now it is incremented with Raman spectra of organic compounds having an astrobiology interest. Eventu...

A formulation of the response of a system to strain and electric field perturbations in the pseudopotential-based density functional perturbation theory has been proposed by Hamann et al. [D. R. Hamann, X. Wu, K. M. Rabe, and D. Vanderbilt, Phys. Rev. B 71, 035117 (2005)], using an elegant formalism based on the expression of density functional the...

The crystallization of a magma ocean (MO) early in Earth's history shaped the entire evolution of our planet. The buoyancy relations between the forming crystals and the residual melt is the most important but also the most unknown parameter affecting the large-scale structure and evolution of the MO. The accumulation of crystals, near the depth of...

Current estimates of the carbon flux between the surface and mantle are highly variable, and the total amount of carbon stored in closed hidden reservoirs is unknown. Understanding the forms in which carbon existed in the molten early Earth is a critical step towards quantifying the carbon budget of Earth's deep interior. Here we employ first-princ...

Geometrical and vibrational characterization of magnesium hydroxide were performed using Density Functional Theory. Four possible crystal symmetries were explored: P\bar3 (No. 147, point group -3), C2/m (No. 12, point group 2), P3m1 (No. 156, point group 3m) and P\bar3m1 (No. 164, point group -3m) which are the currently accepted geometries found i...

All the different phases of water ice between 2 GPa and several megabars are based on a single body-centered cubic sub-lattice of oxygen atoms. They differ only by the behavior of the hydrogen atoms. In this study, we investigate the dynamics of the H atoms at high pressures and temperatures in water ice from first-principles molecular dynamics sim...

The Raman frequencies of quartz are used to evaluate deviatoric stresses in rocksalt-structure media in diamond-anvil cell experiments to pressures up to 20 GPa. The piezospectroscopic effect in quartz is modeled by first-principles calculations. Non-hydrostatic stresses measured in halogen salts give yield strength estimates of 3 GPa in the B1 str...

Terrestrial planets are thought to experience episode(s) of large-scale melting early in their history. Fractionation during magma-ocean freezing leads to unstable stratification within the related cumulate layers due to progressive iron enrichment upward, but the effects of incremental cumulate overturns during MO crystallization remain to be expl...

We study the hydrogen mobility in ringwoodite and wadsleyite considering multiple charge-balanced defects, including Mg < = > 2H, Si < = > Mg + 2H, and the hydrogarnet defect, Si < = > 4H, using molecular dynamics simulations based on the density functional theory at transition zone pressures and temperatures between 1500 and 2500 K. We determine t...

Terrestrial planets are thought to experience episode(s) of large-scale melting early in their history. Fractionation during magma-ocean freezing leads to unstable stratification within the related cumulate layers due to progressive iron enrichment upwards, but the effects of incremental cumulate overturns during MO crystallization remain to be exp...

In various shocked meteorites, low-pressure silica polymorph a-cristobalite is commonly found in close spatial relation with the densest known SiO 2 polymorph seifertite, which is stable above B80 GPa. We demonstrate that under hydrostatic pressure a-cristobalite remains untransformed up to at least 15 GPa. In quasi-hydrostatic experiments, above 1...

Supplementary Figures, Supplementary Tables and Supplementary References

Water-rich planetary bodies including large icy moons and ocean exoplanets may host a deep liquid water ocean underlying a high-pressure icy mantle. The latter is often considered as a limitation to the habitability of the uppermost ocean because it would limit the availability of nutrients resulting from the hydrothermal alteration of the silicate...

The newly described hydrous phase H, MgSiO4H2, is stable to the pressures and temperatures of the Earth's lower mantle, suggesting that the Earth's lower mantle may participate in the cycling of water. We present the results of ab initio calculations on the stability of this phase within the phase H–δAlOOH–SiO2 system between 20 and 60 GPa, explori...

The newly described hydrous phase H, MgSiO4H2, is stable to the pressures and temperatures of the Earth's lower mantle, suggesting that the Earth's lower mantle may participate in the cycling of water. We present the results of ab initiocalculations on the stability of this phase within the phase H-delta AlOOH-SiO(2)system between 20 and 60GPa, exp...

Sound velocities of bridgmanite measured in the laboratory are a key to deciphering the composition of the lower mantle. Here, we report Debye sound velocities determined using nuclear inelastic scattering (NIS) for one majorite composition (Mg0.82Fe0.18SiO3) and five bridgmanite compositions (Mg0.82Fe0.18SiO3, Mg0.86Fe0.14Si0.98Al0.02O3, Mg0.88Fe0...

Knowledge of potential carbon carriers such as carbonates is critical for our understanding of the deep-carbon cycle and related geological processes within the planet. Here we investigated the high-pressure behavior of (Ca,Mn)CO3 up to 75 GPa by synchrotron single-crystal X-ray diffraction, laser Raman spectroscopy, and theoretical calculations. M...

The mechanical properties of C-doped hexagonal-close packed (hcp) iron are studied at high pressure from first-principles calculations. The energy required for doping with C as an interstitial impurity is 246 meV/1wt%C at 120 GPa for one unit cell of hcp Fe, and increases almost linearly with pressure. The density deficit of the inner core can be m...

In the present study single crystals of rhombohedral α-B were investigated under pressure to 60 GPa by means of single-crystal X-ray diffraction. The bulk modulus of α-B was found to be K = 224(7) GPa (K´ = 3.0(3)). Measurements of interatomic distances as a function of pressure revealed that the intericosahedral two-center two-electron (2c-2e) bon...

From first-principles molecular dynamics, we investigate the relation between the superionic proton conduction and the behavior of the O─H⋯O bond (ice VII′ to ice X transition) in body-centered-cubic (bcc) H2O ice between 1300 and 2000 K and up to 300 GPa. We bring evidence that there are three distinct phases in the superionic bcc stability field....

Iron isotopes constrain core chemistry The overall composition of Earth's core is an important constraint on the chemistry and evolution of our planet's interior. A longstanding problem has been determining the minor element contribution to its predominately iron-nickel alloy. Based on the iron isotope fractionation of various iron alloys with pres...

The Fe-based solid crystalline structure(s) present in Earth's core is(are) compact, whether hexagonal or cubic. The nature of the light element (or elements) has been the subject of considerable speculation because of its bearing on the overall bulk composition of Earth, the conditions under which the core formed, the temperature regime in the cor...

Abstract: Vibrational spectroscopic techniques, including Raman, infrared (IR), and inelastic neutron scattering (INS) or x-ray scattering (IXS) spectroscopies, are coupled with ab initio or first principles calculations to study the vibrational lattice dynamics and to predict and elucidate the thermodynamic behavior of minerals under high-pressure...