Phase stability of stress-sensitive Ag2CO3 silver carbonate at high pressures and temperature

Silver carbonate (Ag2CO3) is a material currently used for artificial carbon storage. In this work, we report synchrotron X-ray powder diffraction (XRD) experiments under high pressure and high temperature in combination with density-functional theory (DFT) calculations on silver carbonate up to 13.3 GPa. Two pressure-induced phase transitions were observed at room temperature: at 2.9 GPa to a high-pressure (HP1) phase and at 10.5 GPa to a second high-pressure phase (HP2). The facts that a) the HP2 phase can be indexed with the initial P21/m structure, b) our DFT calculations predict the initial structure is stable in the entire pressure range, and c) the HP2 phase is stable under decompression suggest that the intermediate HP1 phase is a product of the appearance of non-hydrostatic stresses in the sample. The observed structural transformations are associated to a high sensitivity of this compound to non-hydrostatic conditions. The compressibility of Ag2CO3 has also been determined, showing the c axis is the most compressible and that the bulk modulus increases quickly with applied pressure. We attribute both observations to the weak nature of the closed-shell Ag–Ag interactions in this material. The behavior of Ag2CO3 under heating at approximately 3 GPa was also studied. No temperature-induced phase transitions were found at this pressure, and the thermal expansion was determined to be relatively high for a carbonate.Authors thank the financial support from the Spanish Ministerio de Ciencia e Innovación (MICINN) and the Agencia Estatal de Investigación under projects MALTA Consolider Ingenio 2010 network (RED2018-102612-T) and PGC2021-125518NB-I00 (cofinanced by EU FEDER funds), and from the Generalitat Valenciana under projects CIAICO/2021/241 and MFA/2022/007. A.O.R. acknowledges the financial support of the Spanish MINECO RyC-2016-20301 Ramón y Cajal Grant and the project AYUD/2021/51036 of the Principality of Asturias (cofinanced by EU FEDER funds). Authors also thank the MALTA Consolider supercomputing centre and Compute Canada for computational resources and ALBA-CELLS synchrotron for providing beamtime under experiments 2020084419 and 2021024988. These experiments were performed at the MSPD beamline with the collaboration of ALBA staff

Interplay between local structure and electronic properties on CuO under pressure

The electronic and local structural properties of CuO under pressure have been investigated by means of X-ray absorption spectroscopy (XAS) at Cu K edge and ab-initio calculations, up to 17 GPa. The crystal structure of CuO consists of Cu motifs within CuO$_4$ square planar units and two elongated apical Cu-O bonds. The CuO$_4$ square planar units are stable in the studied pressure range, with Cu-O distances that are approximately constant up to 5 GPa, and then decrease slightly up to 17 GPa. In contrast, the elongated Cu-O apical distances decrease continuously with pressure in the studied range. An anomalous increase of the mean square relative displacement (EXAFS Debye Waller, \sigma$^2$) of the elongated Cu-O path is observed from 5 GPa up to 13 GPa, when a drastic reduction takes place in \sigma$^2$. This is interpreted in terms of local dynamic disorder along the apical Cu-O path. At higher pressures (P>13 GPa), the local structure of Cu$^{2+}$ changes from a 4-fold square planar to a 4+2 Jahn-Teller distorted octahedral ion. We interpret these results in terms of the tendency of the Cu$^{2+}$ ion to form favorable interactions with the apical O atoms. Also, the decrease in Cu-O apical distance caused by compression softens the normal mode associated with the out-of-plane Cu movement. CuO is predicted to have an anomalous rise in permittivity with pressure as well as modest piezoelectricity in the 5-13 GPa pressure range. In addition, the near edge features in our XAS experiment show a discontinuity and a change of tendency at 5 GPa. For P < 5 GPa the evolution of the edge shoulder is ascribed to purely electronic effects which also affect the charge transfer integral. This is linked to a charge migration from the Cu to O, but also to an increase of the energy band gap, which show a change of tendency occurring also at 5 GPa

Phase stability and dense polymorph of the BaCa(CO3)2 barytocalcite carbonate

The double carbonate BaCa(CO3)2 holds potential as host compound for carbon in the Earth?s crust and mantle. Here, we report the crystal structure determination of a high-pressure BaCa(CO3)2 phase characterized by single-crystal X-ray diffraction. This phase, named post-barytocalcite, was obtained at 5.7 GPa and can be described by a monoclinic Pm space group. The barytocalcite to post-baritocalcite phase transition involves a significant discontinuous 1.4% decrease of the unit-cell volume, and the increase of the coordination number of 1/4 and 1/2 of the Ba and Ca atoms, respectively. High-pressure powder X-ray diffraction measurements at room- and high-temperatures using synchrotron radiation and DFT calculations yield the thermal expansion of barytocalcite and, together with single-crystal data, the compressibility and anisotropy of both the low- and high-pressure phases. The calculated enthalpy differences between different BaCa(CO3)2 polymorphs confirm that barytocalcite is the thermodynamically stable phase at ambient conditions and that it undergoes the phase transition to the experimentally observed post-barytocalcite phase. The double carbonate is significantly less stable than a mixture of the CaCO3 and BaCO3 end-members above 10 GPa. The experimental observation of the high-pressure phase up to 15 GPa and 300 ºC suggests that the decomposition into its single carbonate components is kinetically hindered.Authors thank the fnancial support from the Spanish Ministerio de Ciencia e Innovación (MICINN) and the Agencia Estatal de Investigación under projects MALTA Consolider Ingenio 2010 network (RED2018-102612-T), PID2019-106383GB-C44, FIS2017-83295-P and PGC2018-097520-A-I00 (cofnanced by EU FEDER funds), and from the Generalitat Valenciana under project PROMETEO/2018/123. A.O.R. acknowledges the fnancial support of the Spanish MINECO RyC-2016-20301 Ramon y Cajal Grant. Authors also thank Dr. Nicolescu and the Mineralogy and Meteoritic Department of the Yale Peabody Museum of Natural History for providing the mineral samples, the MALTA Consolider supercomputing centre and Compute Canada for computational resources, the General Services of Research Support (SEGAI) at La Laguna University and ALBA-CELLS synchrotron for providing beamtime under experiments 2020084419 and 2021024988. Tese experiments were performed at the MSPD beamline with the collaboration of ALBA staf

Crystallographic and computational study of t-butyl N-[3-hydroxy-1-phenyl-4-(pyridin- 2-ylsulfanyl)butan-2-yl]carbamate and its pyrimidin-2-yl analogue

Abstract The crystal structure analysis of the biologically-relevant title compound (1) shows the carbonyl-O2 and amide-H atoms to be anti, and perpendicular relationships between the carbamate residue and the pyridyl ring [dihedral angle=84.60(10)°] and between the carbamate and aryl ring [74.84(11)°]; the rings are approximately co-planar [12.07(17)°]. An intramolecular hydroxyl-O–H···N(pyridyl) hydrogen bond that closes a S(7) loop is noted. Of interest is the observation that this hydrogen bond is not found in the structure of the pyrimidinyl analogue (2) which was characterised as a monohydrate, i.e. 2·H2O, in an earlier study. Density-functional theory calculations show the observed conformation in 1 is 2.0 kcal/mol more stable than the conformation where the intramolecular hydrogen bond is absent. This energy difference reduces to ca 0.5 kcal/mol in the case of 2. The differences in molecular conformations found for 1 and 2 are therefore ascribed to the dictates of overall molecular packing, in particular due to the influence of lattice water in 2·H2O.</jats:p

Structural, vibrational and electronic properties of alpha'-Ga2S3 under compression

[EN] We report a joint experimental and theoretical study of the low-pressure phase of ¿¿-Ga2S3 under compression. Theoretical ab initio calculations have been compared to X-ray diffraction and Raman scattering measurements under high pressure carried out up to 17.5 and 16.1 GPa, respectively. In addition, we report Raman scattering measurements of ¿¿-Ga2S3 at high temperature that have allowed us to study its anharmonic properties. To understand better the compression of this compound, we have evaluated the topological properties of the electron density, the electron localization function, and the electronic properties as a function of pressure. As a result, we shed light on the role of the Ga¿S bonds, the van der Waals interactions inside the channels of the crystalline structure, and the single and double lone electron pairs of the sulphur atoms in the anisotropic compression of ¿¿-Ga2S3. We found that the structural channels are responsible for the anisotropic properties of ¿¿-Ga2S3 and the A¿(6) phonon, known as the breathing mode and associated with these channels, exhibits the highest anharmonic behaviour. Finally, we report calculations of the electronic band structure of ¿¿-Ga2S3 at different pressures and find a nonlinear pressure behaviour of the direct band gap and a pressure-induced direct-to-indirect band gap crossover that is similar to the behaviour previously reported in other ordered-vacancy compounds, including ß-Ga2Se3. The importance of the single and, more specially, the double lone electron pairs of sulphur in the pressure dependence of the topmost valence band of ¿¿-Ga2S3 is stressed.The authors thank the financial support from the Spanish Research Agency (AEI) under projects MALTA Consolider Team network (RED2018-102612-T) and projects MAT2016-75586-C4-2/3-P, FIS2017-83295-P, PID2019-106383GB-42/43, and PGC2018-097520-A-100, as well as from Generalitat Valenciana under Project PROMETEO/2018/123 (EFIMAT). A. M. and P. R.-H. acknowledge computing time provided by Red Espanola de Supercomputacion (RES) and MALTA-Cluster and E. L. D. S. acknowledges Marie Sklodowska-Curie Grant No. 785789-COMEX from the European Union's Horizon 2020 research and innovation program. J. A. S. also wants to thank the Ramon y Cajal fellowship (RYC-2015-17482) for financial support. We also thank the ALBA synchrotron light source for funded experiment 2017022088 at the MSPD-BL04 beamline.Gallego-Parra, S.; Vilaplana Cerda, RI.; Gomis, O.; Lora Da Silva, E.; Otero-De-La-Roza, A.; Rodríguez-Hernández, P.; Muñoz, A.... (2021). Structural, vibrational and electronic properties of alpha'-Ga2S3 under compression. Physical Chemistry Chemical Physics. 23(11):6841-6862. https://doi.org/10.1039/d0cp06417cS68416862231

The importance of Au⋯π(aryl) interactions in the formation of spherical aggregates in binuclear phosphane gold(I) complexes of a bipodal thiocarbamate dianion: a combined crystallographic and computational study, and anti-microbial activity

Binuclear phosphane gold(I) complexes of a bipodal thiocarbamate dianion, (R3PAu)2L, R = Et (1), Ph (2) and Cy (3), where LH2 is {1,4-[MeOC([double bond, length as m-dash]S)N(H)]2C6H4}, have been synthesised, and characterised spectroscopically (NMR and IR) and by X-ray crystallography. The gold atoms are linearly coordinated within a P-,S-donor set, and are oriented toward the central ring to form intramolecular Au⋯π(aryl) interactions, rather than the intramolecular Au⋯O interactions normally observed in mononuclear analogues. This phenomenon has been investigated by theory (LC-ωPBE-XDM) for 1 which revealed that the geometry optimised species with two Au⋯π(aryl) interactions is more stable by at least 12 kcal mol−1 compared to conformations having one or more Au⋯O interactions instead. The disk diffusion, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) methods were used to observe the inhibitory effect of complexes 1–3. The disk diffusion results demonstrated that 1 exhibited a broad spectrum of anti-bacterial activity toward 24 strains of Gram-positive and Gram-negative bacteria. By contrast, the anti-bacterial activity of 2 and 3 was limited to Gram-positive bacteria. Further evaluation showed that 1 exhibited marked bactericidal activity against B. cereus, B. subtilis, E. faecalis, L. monocytogenes, S. aureus, S. saprophyticus and methicillin resistant S. aureus cf. standard antibiotics tetracycline and chloramphenicol

Advanced capabilities for materials modelling with Quantum ESPRESSO

Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudo-potential and projector-augmented-wave approaches. Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement theirs ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software

Search for dark matter at √s=13 TeV in final states containing an energetic photon and large missing transverse momentum with the ATLAS detector

Results of a search for physics beyond the Standard Model in events containing an energetic photon and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. As the number of events observed in data, corresponding to an integrated luminosity of 36.1 fb−1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, is in agreement with the Standard Model expectations, model-independent limits are set on the fiducial cross section for the production of events in this final state. Exclusion limits are also placed in models where dark-matter candidates are pair-produced. For dark-matter production via an axial-vector or a vector mediator in the s-channel, this search excludes mediator masses below 750–1200 GeV for dark-matter candidate masses below 230–480 GeV at 95% confidence level, depending on the couplings. In an effective theory of dark-matter production, the limits restrict the value of the suppression scale M∗ to be above 790 GeV at 95% confidence level. A limit is also reported on the production of a high-mass scalar resonance by processes beyond the Standard Model, in which the resonance decays to Zγ and the Z boson subsequently decays into neutrinos