The Experts below are selected from a list of 37947 Experts worldwide ranked by ideXlab platform
Francisco Colmenero - One of the best experts on this subject based on the ideXlab platform.
-
the layered uranyl silicate mineral uranophane β crystal structure mechanical properties Raman Spectrum and comparison with the α polymorph
Dalton Transactions, 2019Co-Authors: Francisco Colmenero, Jakub Plasil, Jiři SejkoraAbstract:The crystal structure, elastic properties and the Raman Spectrum of the layered calcium uranyl silicate pentahydrate mineral uranophane-β, Ca(UO2)2Si2O6(OH)2·5H2O, are studied by means of first-principles solid-state methods and compared with the corresponding information for the α polymorph. The availability of the energy optimized full crystal structure of uranophane-β, including the positions of the hydrogen atoms, made possible the computation of its elastic properties and the Raman Spectrum by using the theoretical methodology. An extended set of relevant mechanical data is reported. Uranophane-β is shown to be a weak and ductile mineral and, consequenty, is mechanically very different from the α polymorph which is a hard and brittle material. Uranophane-β exhibits the important negative Poisson's ratio (NPR) and negative linear compressibility (NLC) phenomena. The experimental Raman Spectrum of uranophane-β obtained from a natural mineral sample from pegmatite Perus, Sao Paulo, Brazil, is compared with the Spectrum determined theoretically. Since both spectra are in very good agreement, the theoretical methods are employed to assign the Raman Spectrum. Three weak bands of the experimental Spectrum of this mineral, located at the wavenumbers 2302, 2128 and 2042 cm−1, are identified as combination bands. The Raman Spectrum of uranophane-β is also compared with that of the α polymorph. While they are rather similar, a detailed analysis reveals a significant number of differences. Finally, the relative thermodynamic stability of the α and β polymorphs is evaluated. The α polymorph is more stable than the β polymorph at zero pressure and temperature by −12.0 kJ mol−1.
-
crystal structure hydrogen bonding mechanical properties and Raman Spectrum of the lead uranyl silicate monohydrate mineral kasolite
RSC Advances, 2019Co-Authors: Francisco Colmenero, Joaquin Cobos, Vicente Timon, Jakub Plasil, Jiři Sejkora, Jiři Cejka, Laura J BonalesAbstract:The crystal structure, hydrogen bonding, mechanical properties and Raman Spectrum of the lead uranyl silicate monohydrate mineral kasolite, Pb(UO2)(SiO4)·H2O, are investigated by means of first-principles solid-state methods based on density functional theory using plane waves and pseudopotentials. The computed unit cell parameters, bond lengths and angles and X-ray powder pattern of kasolite are found to be in very good agreement with their experimental counterparts. The calculated hydrogen atom positions and associated hydrogen bond structure in the unit cell of kasolite confirmed the hydrogen bond scheme previously determined from X-ray diffraction data. The kasolite crystal structure is formed from uranyl silicate layers having the uranophane sheet anion-topology. The lead ions and water molecules are located in the interlayer space. Water molecules belong to the coordination structure of lead interlayer ions and reinforce the structure by hydrogen bonding between the uranyl silicate sheets. The hydrogen bonding in kasolite is strong and dual, that is, the water molecules are distributed in pairs, held together by two symmetrically related hydrogen bonds, one being directed from the first water molecule to the second one and the other from the second water molecule to the first one. As a result of the full structure determination of kasolite, the determination of its mechanical properties and Raman Spectrum becomes possible using theoretical methods. The mechanical properties and mechanical stability of the structure of kasolite are studied using the finite deformation technique. The bulk modulus and its pressure derivatives, the Young and shear moduli, the Poisson ratio and the ductility, hardness and anisotropy indices are reported. Kasolite is a hard and brittle mineral possessing a large bulk modulus of the order of B ∼ 71 GPa. The structure is mechanically stable and very isotropic. The large mechanical isotropy of the structure is unexpected since layered structures are commonly very anisotropic and results from the strong dual hydrogen bonding among the uranyl silicate sheets. The experimental Raman Spectrum of kasolite is recorded from a natural mineral sample from the Janska vein, Přibram base metal ore district, Czech Republic, and determined by using density functional perturbation theory. The agreement is excellent and, therefore, the theoretical calculations are employed to assign the experimental Spectrum. Besides, the theoretical results are used to guide the resolution into single components of the bands from the experimental Spectrum. A large number of kasolite Raman bands are reassigned. Three bands of the experimental Spectrum located at the wavenumbers 1015, 977 and 813 cm−1, are identified as combination bands.
-
periodic density functional theory study of the structure Raman Spectrum and mechanical properties of schoepite mineral
Inorganic Chemistry, 2018Co-Authors: Francisco Colmenero, Joaquin Cobos, Vicente TimonAbstract:The structure and Raman Spectrum of schoepite mineral, [(UO2)8O2(OH)12]·12H2O, was studied by means of theoretical calculations. The computations were carried out by using density functional theory with plane waves and pseudopotentials. A norm-conserving pseudopotential specific for the U atom developed in a previous work was employed. Because it was not possible to locate H atoms directly from X-ray diffraction (XRD) data by structure refinement in previous experimental studies, all of the positions of the H atoms in the full unit cell were determined theoretically. The structural results, including the lattice parameters, bond lengths, bond angles, and powder XRD pattern, were found to be in good agreement with their experimental counterparts. However, the calculations performed using the unit cell designed by Ostanin and Zeller in 2007, involving half of the atoms of the full unit cell, led to significant errors in the computed powder XRD pattern. Furthermore, Ostanin and Zeller’s unit cell contains hy...
Jiři Sejkora - One of the best experts on this subject based on the ideXlab platform.
-
the layered uranyl silicate mineral uranophane β crystal structure mechanical properties Raman Spectrum and comparison with the α polymorph
Dalton Transactions, 2019Co-Authors: Francisco Colmenero, Jakub Plasil, Jiři SejkoraAbstract:The crystal structure, elastic properties and the Raman Spectrum of the layered calcium uranyl silicate pentahydrate mineral uranophane-β, Ca(UO2)2Si2O6(OH)2·5H2O, are studied by means of first-principles solid-state methods and compared with the corresponding information for the α polymorph. The availability of the energy optimized full crystal structure of uranophane-β, including the positions of the hydrogen atoms, made possible the computation of its elastic properties and the Raman Spectrum by using the theoretical methodology. An extended set of relevant mechanical data is reported. Uranophane-β is shown to be a weak and ductile mineral and, consequenty, is mechanically very different from the α polymorph which is a hard and brittle material. Uranophane-β exhibits the important negative Poisson's ratio (NPR) and negative linear compressibility (NLC) phenomena. The experimental Raman Spectrum of uranophane-β obtained from a natural mineral sample from pegmatite Perus, Sao Paulo, Brazil, is compared with the Spectrum determined theoretically. Since both spectra are in very good agreement, the theoretical methods are employed to assign the Raman Spectrum. Three weak bands of the experimental Spectrum of this mineral, located at the wavenumbers 2302, 2128 and 2042 cm−1, are identified as combination bands. The Raman Spectrum of uranophane-β is also compared with that of the α polymorph. While they are rather similar, a detailed analysis reveals a significant number of differences. Finally, the relative thermodynamic stability of the α and β polymorphs is evaluated. The α polymorph is more stable than the β polymorph at zero pressure and temperature by −12.0 kJ mol−1.
-
crystal structure hydrogen bonding mechanical properties and Raman Spectrum of the lead uranyl silicate monohydrate mineral kasolite
RSC Advances, 2019Co-Authors: Francisco Colmenero, Joaquin Cobos, Vicente Timon, Jakub Plasil, Jiři Sejkora, Jiři Cejka, Laura J BonalesAbstract:The crystal structure, hydrogen bonding, mechanical properties and Raman Spectrum of the lead uranyl silicate monohydrate mineral kasolite, Pb(UO2)(SiO4)·H2O, are investigated by means of first-principles solid-state methods based on density functional theory using plane waves and pseudopotentials. The computed unit cell parameters, bond lengths and angles and X-ray powder pattern of kasolite are found to be in very good agreement with their experimental counterparts. The calculated hydrogen atom positions and associated hydrogen bond structure in the unit cell of kasolite confirmed the hydrogen bond scheme previously determined from X-ray diffraction data. The kasolite crystal structure is formed from uranyl silicate layers having the uranophane sheet anion-topology. The lead ions and water molecules are located in the interlayer space. Water molecules belong to the coordination structure of lead interlayer ions and reinforce the structure by hydrogen bonding between the uranyl silicate sheets. The hydrogen bonding in kasolite is strong and dual, that is, the water molecules are distributed in pairs, held together by two symmetrically related hydrogen bonds, one being directed from the first water molecule to the second one and the other from the second water molecule to the first one. As a result of the full structure determination of kasolite, the determination of its mechanical properties and Raman Spectrum becomes possible using theoretical methods. The mechanical properties and mechanical stability of the structure of kasolite are studied using the finite deformation technique. The bulk modulus and its pressure derivatives, the Young and shear moduli, the Poisson ratio and the ductility, hardness and anisotropy indices are reported. Kasolite is a hard and brittle mineral possessing a large bulk modulus of the order of B ∼ 71 GPa. The structure is mechanically stable and very isotropic. The large mechanical isotropy of the structure is unexpected since layered structures are commonly very anisotropic and results from the strong dual hydrogen bonding among the uranyl silicate sheets. The experimental Raman Spectrum of kasolite is recorded from a natural mineral sample from the Janska vein, Přibram base metal ore district, Czech Republic, and determined by using density functional perturbation theory. The agreement is excellent and, therefore, the theoretical calculations are employed to assign the experimental Spectrum. Besides, the theoretical results are used to guide the resolution into single components of the bands from the experimental Spectrum. A large number of kasolite Raman bands are reassigned. Three bands of the experimental Spectrum located at the wavenumbers 1015, 977 and 813 cm−1, are identified as combination bands.
Jakub Plasil - One of the best experts on this subject based on the ideXlab platform.
-
the layered uranyl silicate mineral uranophane β crystal structure mechanical properties Raman Spectrum and comparison with the α polymorph
Dalton Transactions, 2019Co-Authors: Francisco Colmenero, Jakub Plasil, Jiři SejkoraAbstract:The crystal structure, elastic properties and the Raman Spectrum of the layered calcium uranyl silicate pentahydrate mineral uranophane-β, Ca(UO2)2Si2O6(OH)2·5H2O, are studied by means of first-principles solid-state methods and compared with the corresponding information for the α polymorph. The availability of the energy optimized full crystal structure of uranophane-β, including the positions of the hydrogen atoms, made possible the computation of its elastic properties and the Raman Spectrum by using the theoretical methodology. An extended set of relevant mechanical data is reported. Uranophane-β is shown to be a weak and ductile mineral and, consequenty, is mechanically very different from the α polymorph which is a hard and brittle material. Uranophane-β exhibits the important negative Poisson's ratio (NPR) and negative linear compressibility (NLC) phenomena. The experimental Raman Spectrum of uranophane-β obtained from a natural mineral sample from pegmatite Perus, Sao Paulo, Brazil, is compared with the Spectrum determined theoretically. Since both spectra are in very good agreement, the theoretical methods are employed to assign the Raman Spectrum. Three weak bands of the experimental Spectrum of this mineral, located at the wavenumbers 2302, 2128 and 2042 cm−1, are identified as combination bands. The Raman Spectrum of uranophane-β is also compared with that of the α polymorph. While they are rather similar, a detailed analysis reveals a significant number of differences. Finally, the relative thermodynamic stability of the α and β polymorphs is evaluated. The α polymorph is more stable than the β polymorph at zero pressure and temperature by −12.0 kJ mol−1.
-
crystal structure hydrogen bonding mechanical properties and Raman Spectrum of the lead uranyl silicate monohydrate mineral kasolite
RSC Advances, 2019Co-Authors: Francisco Colmenero, Joaquin Cobos, Vicente Timon, Jakub Plasil, Jiři Sejkora, Jiři Cejka, Laura J BonalesAbstract:The crystal structure, hydrogen bonding, mechanical properties and Raman Spectrum of the lead uranyl silicate monohydrate mineral kasolite, Pb(UO2)(SiO4)·H2O, are investigated by means of first-principles solid-state methods based on density functional theory using plane waves and pseudopotentials. The computed unit cell parameters, bond lengths and angles and X-ray powder pattern of kasolite are found to be in very good agreement with their experimental counterparts. The calculated hydrogen atom positions and associated hydrogen bond structure in the unit cell of kasolite confirmed the hydrogen bond scheme previously determined from X-ray diffraction data. The kasolite crystal structure is formed from uranyl silicate layers having the uranophane sheet anion-topology. The lead ions and water molecules are located in the interlayer space. Water molecules belong to the coordination structure of lead interlayer ions and reinforce the structure by hydrogen bonding between the uranyl silicate sheets. The hydrogen bonding in kasolite is strong and dual, that is, the water molecules are distributed in pairs, held together by two symmetrically related hydrogen bonds, one being directed from the first water molecule to the second one and the other from the second water molecule to the first one. As a result of the full structure determination of kasolite, the determination of its mechanical properties and Raman Spectrum becomes possible using theoretical methods. The mechanical properties and mechanical stability of the structure of kasolite are studied using the finite deformation technique. The bulk modulus and its pressure derivatives, the Young and shear moduli, the Poisson ratio and the ductility, hardness and anisotropy indices are reported. Kasolite is a hard and brittle mineral possessing a large bulk modulus of the order of B ∼ 71 GPa. The structure is mechanically stable and very isotropic. The large mechanical isotropy of the structure is unexpected since layered structures are commonly very anisotropic and results from the strong dual hydrogen bonding among the uranyl silicate sheets. The experimental Raman Spectrum of kasolite is recorded from a natural mineral sample from the Janska vein, Přibram base metal ore district, Czech Republic, and determined by using density functional perturbation theory. The agreement is excellent and, therefore, the theoretical calculations are employed to assign the experimental Spectrum. Besides, the theoretical results are used to guide the resolution into single components of the bands from the experimental Spectrum. A large number of kasolite Raman bands are reassigned. Three bands of the experimental Spectrum located at the wavenumbers 1015, 977 and 813 cm−1, are identified as combination bands.
Roberto Dovesi - One of the best experts on this subject based on the ideXlab platform.
-
the Raman Spectrum of grossular garnet a quantum mechanical simulation of wavenumbers and intensities
Journal of Raman Spectroscopy, 2014Co-Authors: Lorenzo Maschio, Roberto Orlando, Raffaella Demichelis, Marco De La Pierre, Agnes Mahmoud, Roberto DovesiAbstract:Raman spectroscopy is a standard and powerful investigation technique for minerals, and garnet is one of the most observed and visible minerals, undoubtfully important both as a witness of our planet's evolution and as a main component in many high-tech applications. This paper presents the Raman Spectrum of grossular, the calcium–aluminium end-member of garnets (Ca 3Al 2Si 3O12), as computed by using an ab initio quantum-mechanical approach, an all-electron Gaussian-type basis set and the hybrid B3LYP functional. The wavenumbers of the 25 Raman active modes are in excellent agreement with the available experimental measurements, with the mean absolute difference being between 5 and 8 cm − 1. The apparent disagreement between a few experimental vs calculated data can be easily justified through the analysis of the corresponding calculated peak intensities, which is very low in all of these cases. The intensities of the Raman active modes of grossular were calculated here for the first time, thanks to a recent implementation by some of the present authors that allow for accurate predictions of the Raman spectra of minerals. To the authors’ knowledge, there are no tabulated data sets for Raman intensities of grossular, although qualitative information can be extracted from the published spectra. This study can then be considered as an accurate reference data set for grossular, other than a clear evidence that quantum-mechanical simulation is an actual tool to predict spectroscopic properties of minerals. Copyright © 2014 John Wiley & Sons, Ltd.
-
Raman Spectrum of naalsi2o6 jadeite a quantum mechanical simulation
Journal of Raman Spectroscopy, 2014Co-Authors: Mauro Prencipe, Lorenzo Maschio, Bernard Kirtman, Simone Salustro, Alessandro Erba, Roberto DovesiAbstract:The Raman Spectrum of NaAlSi2O6 jadeite is simulated and compared with two recent experimental data sets. In one experiment, only 17 (out of 30 symmetry allowed) peaks and a qualitative estimate of the intensities are provided. In the second case, the digitalized Spectrum is available, from which we have been able to extract 20 evident peaks and an estimate of the relative intensities. The present calculation is based on an ab initio quantum mechanical treatment. Using an all-electron Gaussian-type basis set, together with the hybrid B3LYP density functional, the full set of 30 active modes and their (polycrystalline and polarized) intensities are obtained. The simulated intensities (not available in a previous study of the same system) permit the two experimental spectra to be reconciled and explain why the missing peaks were not seen. This ultimately leads to excellent agreement between experiment and theory. By artificially varying the mass of the Na + and Al3 + cations in the simulations, which can be performed automatically and at essentially no computational cost, the vibrational modes to which these ions contribute are identified. We conclude that quantum mechanical simulation can be a very useful complementary tool for the interpretation of experimental Raman spectra. Copyright © 2014 John Wiley & Sons, Ltd.
-
Raman Spectrum of pyrope garnet a quantum mechanical simulation of frequencies intensities and isotope shifts
Journal of Physical Chemistry A, 2013Co-Authors: Lorenzo Maschio, Bernard Kirtman, Simone Salustro, Claudio M Zicovichwilson, Roberto Orlando, Roberto DovesiAbstract:The Raman Spectrum of pyrope garnet is simulated in ab initio quantum mechanical calculations, using an all-electron Gaussian-type basis set and the hybrid B3LYP functional. Frequencies calculated for the 25 Raman-active modes are in excellent agreement with the several sets of experimental data, with the mean absolute difference ranging from 4 to 8 cm(-1). Comparison of the computed and experimental Spectrum shows excellent agreement for most of the intensities as well. Modes missing from experiment are shown to be characterized by low (computed) intensity. Spurious peaks in the experimental spectra are also identified. The isotopic effect has been simulated for (24)Mg → (26)Mg substitution and shows excellent agreement with shifts reported in one of the experiments. Agreement is excellent for all but one mode, which turns out to be attributed to the wrong symmetry in the experiment.
-
ab initio quantum mechanical simulation of the Raman Spectrum of grossular
Journal of Raman Spectroscopy, 2009Co-Authors: Roberto Dovesi, Claudio M Zicovichwilson, Loredana Valenzano, Fabien Pascale, Roberto OrlandoAbstract:The Raman Spectrum of the grossular garnet Ca3Al2Si3O12 has been simulated with the periodic ab initio CRYSTAL code by adopting an all-electron Gaussian-type basis set and the B3LYP Hamiltonian. The wavenumbers of the 25 Raman active modes (3 of A1g, 8 of Eg and 14 of F2g symmetry) are in excellent agreement with two sets of accurate experimental data. Isotopic substitution is used to measure the participation of Ca and Si (Al is constrained in a centro-symmetric position) to the various modes. Copyright © 2008 John Wiley & Sons, Ltd.
Laura J Bonales - One of the best experts on this subject based on the ideXlab platform.
-
crystal structure hydrogen bonding mechanical properties and Raman Spectrum of the lead uranyl silicate monohydrate mineral kasolite
RSC Advances, 2019Co-Authors: Francisco Colmenero, Joaquin Cobos, Vicente Timon, Jakub Plasil, Jiři Sejkora, Jiři Cejka, Laura J BonalesAbstract:The crystal structure, hydrogen bonding, mechanical properties and Raman Spectrum of the lead uranyl silicate monohydrate mineral kasolite, Pb(UO2)(SiO4)·H2O, are investigated by means of first-principles solid-state methods based on density functional theory using plane waves and pseudopotentials. The computed unit cell parameters, bond lengths and angles and X-ray powder pattern of kasolite are found to be in very good agreement with their experimental counterparts. The calculated hydrogen atom positions and associated hydrogen bond structure in the unit cell of kasolite confirmed the hydrogen bond scheme previously determined from X-ray diffraction data. The kasolite crystal structure is formed from uranyl silicate layers having the uranophane sheet anion-topology. The lead ions and water molecules are located in the interlayer space. Water molecules belong to the coordination structure of lead interlayer ions and reinforce the structure by hydrogen bonding between the uranyl silicate sheets. The hydrogen bonding in kasolite is strong and dual, that is, the water molecules are distributed in pairs, held together by two symmetrically related hydrogen bonds, one being directed from the first water molecule to the second one and the other from the second water molecule to the first one. As a result of the full structure determination of kasolite, the determination of its mechanical properties and Raman Spectrum becomes possible using theoretical methods. The mechanical properties and mechanical stability of the structure of kasolite are studied using the finite deformation technique. The bulk modulus and its pressure derivatives, the Young and shear moduli, the Poisson ratio and the ductility, hardness and anisotropy indices are reported. Kasolite is a hard and brittle mineral possessing a large bulk modulus of the order of B ∼ 71 GPa. The structure is mechanically stable and very isotropic. The large mechanical isotropy of the structure is unexpected since layered structures are commonly very anisotropic and results from the strong dual hydrogen bonding among the uranyl silicate sheets. The experimental Raman Spectrum of kasolite is recorded from a natural mineral sample from the Janska vein, Přibram base metal ore district, Czech Republic, and determined by using density functional perturbation theory. The agreement is excellent and, therefore, the theoretical calculations are employed to assign the experimental Spectrum. Besides, the theoretical results are used to guide the resolution into single components of the bands from the experimental Spectrum. A large number of kasolite Raman bands are reassigned. Three bands of the experimental Spectrum located at the wavenumbers 1015, 977 and 813 cm−1, are identified as combination bands.