Showing papers by "Julia Contreras-García published in 2009"
TL;DR: Calculations on this P6(3)/mmc (hP4) structure as a function of pressure show three isostructural transitions and three distinctive types of chemical bonding: free electron, ionic, and metallic.
Abstract: Experimentally, we have found that among the ``complicated'' phases of potassium at intermediate pressures is one which has the same space group as the double hexagonal-close-packed structure, although its atomic coordination is completely different. Calculations on this $P{6}_{3}/mmc$ ($hP4$) structure as a function of pressure show three isostructural transitions and three distinctive types of chemical bonding: free electron, ionic, and metallic. Interestingly, relationships between localized metallic structures and ionic compounds are found.
93 citations
TL;DR: Overall, the results clearly correlate with chemical intuition: periodic trends are revealed, cores are almost incompressible and do not contribute appreciably to the macroscopic compressibility, and lone pair basins are rather easier to compress than bond basins.
Abstract: The ability of the electron localization function to perform a partition of the unit cell volume of crystalline solids into well-defined, disjoint, and space-filling regions enables us to decompose the bulk compressibility into local contributions with a full chemical meaning. This partition has been applied to a set of prototype crystals of the chemical elements of the first three periods of the periodic table, and the equations of state for core, valence, bond, and lone electron pairs have been obtained. Solids are unequivocally classified into two groups according to their response to hydrostatic pressure. Those with sharing electrons (metals and covalent crystals) obey a simple relationship between the average valence electron density and the zero pressure bulk modulus. The stiffness of the closed-shell systems (molecular and ionic solids) is rationalized resorting to the Pauli principle. Overall, the results clearly correlate with chemical intuition: periodic trends are revealed, cores are almost incompressible and do not contribute appreciably to the macroscopic compressibility, and lone pair basins are rather easier to compress than bond basins.
30 citations
TL;DR: In this paper, a microscopic analysis of mechanistic aspects in the pressure-induced ZrSiO-4 phase transition of the scheelite was performed under a martensitic scheme at the thermodynamic boundary.
Abstract: Based on accurate quantum-mechanical calculations, a microscopic analysis of mechanistic aspects in the pressure-induced $\text{zircon}\ensuremath{\rightleftharpoons}\text{scheelite}$ phase transition of ${\text{ZrSiO}}_{4}$ is performed under a martensitic scheme at the thermodynamic boundary. Gibbs energy profiles, atomic displacements, bonding reconstruction, and lattice strains are computed across two different transition pathways. After application of a minimum displacement criterion to the atomic positions of consecutive steps in the proposed paths, the trajectories of the 24 atoms involved in each of the unit cells are disclosed. Using the common $I{4}_{1}/a$ symmetry, we show that the group-subgroup relationship between two phases displaying the same metal coordinations is not a sufficient condition to characterize a phase transformation as displacive. A very high activation barrier (236 kJ/mol) accompanies the breaking and formation of four primary Zr-O bonds with oxygen displacements as large as $1.29\text{ }\text{\AA{}}$ from the zircon to the scheelite structure for this tetragonal path. A lower activation energy (80 kJ/mol) is required to nucleate the scheelite phase from zircon according to our fully optimized monoclinic $C2/c$ transition path. Only two oxygen atoms surrounding Zr have similar displacements in this mechanism, yielding the breaking and formation of two primary Zr-O bonds and revealing the reconstructive character of the transformation. Interestingly enough, ${\text{SiO}}_{4}$ tetrahedra are preserved with similar bond lengths and angles when rotating from the zircon to the scheelite phase across the more favorable monoclinic transition pathway.
26 citations
TL;DR: This work presents a novel computational procedure, general, automated, and robust, for the analysis of local and global properties of the electron localization function (ELF) in crystalline solids, which successfully faces the two main shortcomings of the ELF analysis in crystals.
Abstract: We present a novel computational procedure, general, automated, and robust, for the analysis of local and global properties of the electron localization function (ELF) in crystalline solids. Our algorithm successfully faces the two main shortcomings of the ELF analysis in crystals: (i) the automated identification and characterization of the ELF induced topology in periodic systems, which is impeded by the great number and concentration of critical points in crystalline cells, and (ii) the localization of the zero flux surfaces and subsequent integration of basins, whose difficulty is due to the diverse (in many occasions very flat or very steep) ELF profiles connecting the set of critical points. Application of the new code to representative crystals exhibiting different bonding patterns is carried out in order to show the performance of the algorithm and the conceptual possibilities offered by the complete characterization of the ELF topology in solids.
24 citations
TL;DR: The study confirms that the topology of the bonding network in the pseudopolymeric phases points toward the incipient formation of the new bonds in the higher pressure polymers, including the birth of a new intermolecular C--O bond controlled by the oxygen lone pairs.
Abstract: We present a novel quantitative strategy for monitoring chemical bonding transformations in solids from the topology of their electronic structure. Developed in the context of the electron localiza...
13 citations
TL;DR: A new form of CaTe2O5 (ɛ) has been synthesized by hydrothermal method and its crystal structure has been solved and refined from single crystal X-ray diffraction data.
12 citations
TL;DR: In this article, it was argued that mainly the selenium sublattice determines the overall compressibility of the cubic spinel selenides, AB2Se4, and that the bulk modulus for these compounds is about 100 GPa.
Abstract: It is argued that mainly the selenium sublattice determines the overall compressibility of the cubic spinel selenides, AB2Se4, and that the bulk modulus for these compounds is about 100 GPa. The hypothesis is supported by experiments using high-pressure X-ray diffraction and synchrotron radiation, and by first-principles calculations using density functional theory.
8 citations
TL;DR: In this article, the transformation of the chemical bonding network of SiO2 across the pressure-induced α-cristobalite→stishovite phase transition is rigorously analyzed using the topology of the electron localization function (ELF).
Abstract: The transformation of the chemical bonding network of SiO2 across the pressure-induced α-cristobalite→stishovite phase transition is rigorously analyzed using the topology of the electron localization function (ELF). Under a martensitic approach, the simultaneous and concerted atomic displacements can be theoretically modeled by means of a transition path of P41212 symmetry. For the parent and the product phases, as well as for selected structures of this mechanism, the characterization of ELF critical points and the integration of basin properties of the ELF attractors have allowed us to study how the nature of the bonding network and the charges and volumes of shells, bonds and lone pairs evolve along this transformation. The change in the Si environment from tetrahedral to octahedral coordination is accompanied by a significant increase in the bond ionicity and by a decrease in the crystal compressibility due to the greater electron density of the oxygen valence shell in the stishovite phase.
5 citations
TL;DR: In this paper, the authors used available ab initio calculations for the complete alkali halides (AX) family in the rock salt phase and some selected spinels to find that the pressure at the limit of stability of the crystal matches exactly those of the individual ions (or group of ions), pointing to the conclusion that the ionic volumes at the equilibrium define the relative compressibilities of the ions in the crystal at all pressures.
Abstract: The theory of atoms in molecules leads to a convenient partition of the crystalline space into atomic regions that are space filling and allow a decomposition of the bulk compressibility of a crystal as a volume-weighted sum of local compressibilities. Using available ab initio calculations for the complete alkali halides (AX) family in the rock salt phase and some selected spinels, we find that the pressure at the limit of stability of the crystal matches exactly those of the individual ions (or group of ions), pointing to the conclusion that the ionic volumes at the equilibrium define the relative compressibilities of the ions (or group of ions) in the crystal at all pressures. We also analyse the functional dependence between the ionic compressibilities and volumes for the AX family. We show that these ions exhibit universal behaviour when the local bulk moduli are correlated with the pressure referred to the spinodal pressure value, instead of volume. This fact allows us to define a generalised equati...
4 citations
TL;DR: In this paper, the chain of bonding changes induced by pressure in molecular phases of CO2 is analyzed in order to shed light into the controversial process of polymerization of simple molecular crystals under pressure.
Abstract: The chain of bonding changes induced by pressure in molecular phases of CO2 is analyzed in order to shed light into the controversial process of polymerization of simple molecular crystals under pressure. The evolution of the bonding network in the pseudo-molecular CO2-II phase is found to point towards an incipient stabilization of six-fold coordinated carbon at high pressure (stishovite-like) as proposed by Iota et al. [V. Iota, C.-S. Yoo, J.-H. Klepeis, Z. Jenei, W. Evans, and H. Cynn, Nat. Mater. 6 (2007), pp. 34–38]. The relevance of secondary interactions in the polymerization is identified as a polarization of the oxygen lone pairs that gives rise to a synchronic birth of a new intermolecular C− O bond along with the weakening of the intramolecular (C= O) double bond. These results have been derived thanks to a new computational code developed in our laboratory that allows us to perform general topological analysis of the electron localization function in crystalline solids.
2 citations