1,720,999 research outputs found
Structural and elastic behaviour of aragonite at high-pressure: A contribution from first-principle simulations
Full text linkAragonite (CaCO3, space group Pmcn) is an important mineral for both geological and biological reasons, being one of the phases that recycles carbon in deep Earth conditions and the product of biomineralization of several terrestrial and marine organisms, respectively. Because of its ubiquity, aragonite has been the subject of several investigations to understand its elastic behaviour and stability at different P-T conditions, but the results reported in literature are still very scattered. Aiming at providing further details on this topic, in the present work we determined the structural and elastic properties of aragonite at absolute zero (0 K) within the Density Functional Theory framework, using a posteriori correction to include the weak long-range interactions. The equation of state parameters for this mineral phase, calculated between 0 GPa – 25 GPa, were K0 = 80.2(7) GPa, K’ = 4.37(10) and V0 = 223.00(6) Å3, in good agreement with the bulk modulus calculated from the elastic moduli (KR = 78.49 GPa). The results were compared to previous experimental and theoretical data, finding them in line with some specific studies, and show that some structural features (e.g., the carbonate ion aplanarity) could be related to the mechanism of phase transition to the post-aragonite phase at high pressure. The present work highlights the importance of including van der Waals interactions in the physical treatment of the structural and elastic properties of aragonite, and further extends the knowledge of the behaviour of this mineral as a function of pressure
QUANTAS: a Python software for the analysis of thermodynamics and elastic behavior of solids from ab initio quantum mechanical simulations and experimental data
Full text linkMineralogy, petrology and materials science are fundamental disciplines not only for the basic knowledge and classification of solid phases but also for their technological applications, which are becoming increasingly demanding and challenging. Characterization and design of materials are of utmost importance and usually need knowledge of the thermodynamics and mechanical stability of solids. Alongside well known experimental approaches, in recent years the advances in both quantum mechanical methods and computational power have placed theoretical investigations as a complementary useful and powerful tool in this kind of study. In order to aid both theoreticians and experimentalists, an open-source Python-based software, QUANTAS, has been developed. QUANTAS provides a fast, flexible, easy-to-use and extensible platform for calculating the thermodynamics and elastic behavior of crystalline solid phases, starting from both experimental and ab initio data
Crystal-chemical, vibrational and electronic properties of 1M-phlogopite K(Mg,Fe)3Si3AlO10(OH)2 from Density Functional Theory simulations
Full text linkTrioctahedral micas are peculiar minerals that may present interesting electronic properties that can be modulated by specific cationic substitutions. In the present work, a detailed characterization of the structural, vibrational, and electronic properties of 1M-phlogopite as a function of the FeII/MgII substitutions, with Mg/Fe ratio ≥ 2, is reported. The results were obtained from density functional theory simulations at the B3LYP-D* level of theory, which included the effect of long-range interactions, and also using all-electron Gaussian-type orbitals to describe the atoms in the mineral. The crystal structures of the different phlogopite models were in good agreement with previous X-ray and neutron diffraction data reported in the literature. In addition, the simulated Raman spectra well described the experimental ones obtained from confocal Raman micro-spectrometry, providing additional information on the atomic motions. The electronic band structure and the atom- and orbital-projected density of states were also discussed, describing the nature of the band gap and electronic transitions, and how they vary with the iron content
Thermodynamic and thermoelastic data of georesources raw minerals: Zinc sulphide and apatite
No full textThis article reports a dataset on the thermodynamic and elastic properties of two important raw minerals exploited in georesources and ore mining. The presented data refers to two zinc sulphide polymorphs, namely zinc-blende (low-pressure polymorph, space group F4−3m) and rock-salt (high-pressure polymorph, space group Fm3−m) [1], and of type-A carbonated apatite, [CAp, Ca10(PO4)6CO3, space group P1] [2]. The data here reported were calculated from ab initio quantum mechanical simulations at the DFT/B3LYP level, all-electron Gaussian-type orbitals basis sets and from the analysis of the phonon properties of the zinc sulphide polymorphs and of type-A CAp by means of the quasi-harmonic approximation. In addition, a correction to take into account the effects of dispersive forces was considered to obtain the dataset of type-A carbonated apatite. This dataset, which was validated against experimental thermodynamic data reported in literature, has been employed to construct the phase diagram between the two zinc sulphide polymorphs and discuss their stability over the temperature and pressure range 0–800 K and 0–25 GPa. The thermodynamic and thermoelastic data of CAp were obtained between 0 and 600 K and 0–3 GPa, below the temperature of thermal decomposition of the mineral. The reported data can be of use in several application fields, for instance fundamental georesource exploration and exploitation, and also in applied mineralogy, geology, material science, and as a reference to assess the quality of other theoretical approaches. Furthermore, the data of type-A carbonated apatite could be useful for designing and processing new biomaterials with tailored properties
Equation of state and second-order elastic constants of portlandite Ca(OH)2 and brucite Mg(OH)2
No full textHydroxide minerals brucite Mg(OH) 2 and portlandite Ca(OH) 2 (space group P3 ̄ m1) are very important phases for several geological and industrial applications which often require the knowledge of the mechanical properties. In the present work, the equation of state (EoS) and the second-order elastic constants of the two minerals were calculated by ab initio quantum mechanical methods. The aims are extending the knowledge of their important applicative mechanical properties and providing a consistent relative dataset. In addition, the simple crystal-chemical composition and structure of Ca(OH) 2 and Mg(OH) 2 is ideal to simulate and characterize the effect of the proton disorder on the elastic properties, which could be useful for the comprehension of more complex hydrous minerals and synthetic phases. The third-order Birch–Murnaghan EoS parameters obtained in the present study were V 0 = 39.59(1) Å 3 , K 0 = 48.0(9) GPa and K′ = 9.1(3), and V 0 = 54.0(7) Å 3 , K 0 = 30.1(9) GPa and K′ = 8.5(4) for Mg(OH) 2 and Ca(OH) 2 , respectively. Axial compressibilities were found to be in ratio β(a):β(c) = 1.000:3.600 for brucite, and 1.000:3.777 for portlandite. The theoretical results agree with the general trend experimentally observed in the available literature, and further extend the knowledge of the mechanical properties of the two phases. The results could be very helpful for petro-geological investigations and for the synthesis and use of concrete nanocomposites and layered double hydroxides with tailored mechanical properties
Study of the variation of the optical properties of calcite with applied stress, useful for specific rock and material mechanics
Full text linkCalcite (CaCO3, trigonal crystal system, space group R3 ̄ c) is a ubiquitous carbonate phase commonly found on the Earth’s crust that finds many useful applications in both scientific (mineralogy, petrology, geology) and technological fields (optics, sensors, materials technology) because of its peculiar anisotropic physical properties. Among them, photoelasticity, i.e., the variation of the optical properties of the mineral (including birefringence) with the applied stress, could find usefulness in determining the stress state of a rock sample containing calcite by employing simple optical measurements. However, the photoelastic tensor is not easily available from experiments, and affected by high uncertainties. Here we present a theoretical Density Functional Theory approach to obtain both elastic and photoelastic properties of calcite, considering realistic experimental conditions (298 K, 1 atm). The results were compared with those available in literature, further extending the knowledge of the photoelasticity of calcite, and clarifying an experimental discrepancy in the sign of the p41 photoelastic tensor component measured in past investigations. The methods here described and applied to a well-known crystalline material can be used to obtain the photoelastic properties of other minerals and/or materials at desired pressure and temperature conditions
Interaction at the nanoscale of fundamental biological molecules with minerals
No full textThe availability of advanced nanotechnological methodologies (experimental and theoretical)
has widened the investigation of biological/organic matter in interaction with substrates. Minerals are good
candidates as substrates because they may present a wide variety of physico-chemical properties and surface
nanostructures that can be used to actively condense and manipulate the biomolecules. Scanning Probe
Microscopy (SPM) is one of the best suited techniques used to investigate at a single molecule level the
surface interactions. In addition, the recent availability of high performance computing has increased the
possibility to study quantum mechanically the interaction phenomena extending the number of atoms
involved in the simulation. In the present paper, firstly we will briefly introduce new SPM technological
developments and applications to investigate mineral surfaces and mineral-biomolecule interaction, then we
will present results on the specific RNA-mineral interaction and recent basics and applicative achievements
in the field of the interactions between other fundamental biological molecules and mineral surfaces from
both an experimental and theoretical point of view
3D meso-nanostructures in cleaved and nanolithographed Mg-Al-hydroxysilicate (clinochlore): Topology, crystal-chemistry, and surface properties
No full textThe peculiar physico-chemical properties that a solid surface can present, unlike the bulk, are the key for a huge amount of important and widespread processes, including for instance, contaminant and biomolecules adsorption, solid-state and ion exchange reactions, soil aggregation, adhesion in micro and nanodevices. In this regard, the development of new materials and three-dimensional nanofabrication technologies becomes a fundamental challenge. Here, the authors present both natural and synthetic three-dimensional meso-nanostructures of a particular Mg-Al-hydroxysilicate (mineral clinochlore) produced by scanning probe microscopy related methods. Topology, crystal-chemistry, and surface properties were addressed by experimental and theoretical methodologies on nanocleaved and nanolithographed clinochlore. Scanning probe microscopy revealed a meso-nanostructured heterogeneous surface in terms of morphology, hydrophilic/phobic character and surface potential. The possibility to arbitrarily tailor and fabricate surface nanopatterns by SPM-based nanolithography is reported. Quantum mechanical simulations of the crystal-chemical structure and material properties supported and corroborated the experimental data. These findings suggest that the heterogeneous three-dimensional meso-nanostructured surface of clinochlore can represent an optimal effective substrate for exploring specific and innovative catalytic, electrochemical and biological processes at the nanoscale
Benchmarking dispersion-corrected DFT methods for the evaluation of materials with anisotropic properties: Structural, electronic, dielectric, optical and vibrational analysis of calcite (CaCO3, space group: R 3 c)
Full text linkCalcite (CaCO3, space group R3c) is a solid phase whose well-known highly anisotropic physical properties can be exploited to compare and calibrate various theoretical simulation methods. In this work, to benchmark different ab initio Density Functional Theory approaches that include for the first time corrections for dispersive forces, a systematic analysis of structural, electronic, dielectric, optical and vibrational properties of calcite is performed. The simulations considered the generalized-gradient approximation functional PBE and the hybrid B3LYP and PBE0, whereas the DFT-D2 and DFT-D3 schemes were adopted to account for the long-range interactions. This study suggests an overall better agreement between the theoretical results obtained with the DFT functionals corrected for the dispersive forces, with a better performance of hybrid functionals over PBE
SEM-EDS MICROANALYSIS OF ULTRATHIN GLASS AND METAL FRAGMENTS: MEASUREMENT STRATEGY BY MONTE CARLO SIMULATION IN CULTURAL HERITAGE AND ARCHAEOLOGY
Full text linkScanning electron microscopy (SEM) combined with energy dispersive X-ray spectrometry (EDS) has a very wide range of applications in cultural heritage and archaeology, because of the capability to provide morphological analysis with high spatial resolution, combined with chemical information at the microscale. However, when the size of the materials analyzed approaches the micro- and submicrometre scale, as often found in cultural heritage and archaeology investigations, several effects related to electron and X-ray generation and transport had to be considered to avoid quantification errors. In this work, Monte Carlo simulations are presented for the study of the effects of thickness and shape on quantitative microanalysis by SEM-EDS of ultrathin glass and metal alloys fragments, as usually found in cultural heritage and archaeology. Glass fragments with different chemical composition, elongated shapes, square section and thicknesses from 0.1 to 10 micrometers, and micro/nanoscale gold alloy fragments were simulated in realistic experimental conditions. The simulations showed an important contribution from the fragments thickness and shape on the X-ray intensity measured by EDS, which in turn affect the quantitification procedure. The results of this study are of general meaning and application, and can be used to develop the most appropriate specific measurement strategy and avoid analytical errors and misinterpretations
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