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In this paper, we introduce the notions of enlarged number theory and of thermodynamically ideal liquid and calculate the temperature below which it appears. This temperature is T = 0.84Tc, where Tc is the critical temperature of a gas whose molecules are nonpolar. For such a gas, in a sufficiently wide neighborhood of the binodal, the isotherms of a gas and of a thermodynamically ideal liquid coincide with those of a van der Waals gas for the critical value of the compressibility factor Zc = 3/8. In this sense, for T ≤ 0.84Tc and the particular case Zc = 3/8, the developed theory is a generalization of the van der Waals model. A new phase transition of the second kind at the point of zero activity is described.

The dianion dimer of tetracyanoethylene (TCNE), π-[TCNE]22−, represents an unusual class of organic compounds, that possess exceptionally long C–C bonding interactions (∼2.96 A). It is twice that of conventional C–C bonds but shorter than the sum of the van der Waals radii. Experimental and computational studies best characterize the intradimer bonding as a multi-center C–C bond. A number of theoretical studies indicate that the π-[TCNE]22− dimer exhibits long, four-centers/two-electron (4c/2e) C–C bonds. However, there is still some disputation about the number of centers involved in the multicenter bonding. This work focuses on quantitative understanding of the nature of the long, multicenter bonding in the π-[TCNE]22− dimer. By the chemical bonding analysis, it is found that ∼68% of electrons in the long bond locate on the –CC– groups and the remaining locate on the –CN groups. The substituent effect is investigated by comparing the interaction energy curves of the [C2X4]22− dimer (X = H, Cl and CN). The deep local well at 3.0 A for X = CN indicates a strong bonding interaction. However, there is no obvious local well in the curves for X = H and Cl, which indicates that the [C2Cl4]22− and [C2H4]22− dimer are unstable. Herein, the –CN plays an important role in the bonding of the π-[TCNE]22− dimer, and it is more reasonable to take the long bond as 20c/2e (12 carbon plus 8 nitrogen). Moreover, we found an abnormal charge redistribution from TCNE to TCNE−, and the charge distribution of [TCNE]22− is very similar to that of TCNE−, which benefits the formation of the dianion dimer.

Chloroboron(III) and fluoroboron(III) hexa(1-alkynyl)- and hexa(2-arylethynyl)subnaphthalocyanines with a large dipole moment were prepared by Sonogashira coupling of hexaiodosubnaphthalocyanines with substituted acetylenes. Introduction of butyl or longer alkyl groups via ethynylene linkages on the periphery resulted in lower melting points and higher solubility in dichloromethane. X-ray diffraction (XRD) patterns of the cast film indicated that hexa(2-(4-hexylphenyl)ethynyl)- and hexa(2-(4-hexyloxyphenyl)ethynyl)subnaphthalocyanines with a B–F bond are packed in a discotic hexagonal columnar phase with lattice constants a = 59–64 A and stacking distance c = 4.7–4.8 A. The Q-band in visible spectra of the thin film of these B–F derivatives was blue-shifted, supporting the formation of H-aggregate in stacked columns. Polarized optical microscopy showed that these subnaphthalocyanines with a B–F bond exhibited a mesophase at 180 °C. XRD of these subnaphthalocyanines at 180 °C confirms a two dimensional hexagonal phase. XRD of the corresponding derivatives with a B–Cl bond showed that they were either amorphous or less crystalline. We suggest that the fluorine atom in the B–F group can fit into the cleft of cone-shaped subnaphthalocyanine, owing to the smaller van der Waals radius of F than Cl, to stabilize the columnar packing structure.

Biomagnification of organic pollutants in food webs has been usually associated to hydrophobicity and other molecular descriptors. However, direct information on atoms and substituent positions in a molecular scaffold that most affect this biological property is not straightforward using traditional QSPR techniques. This work reports the QSPR modeling of biomagnification factors (logBMF) of a series of aromatic organochlorine compounds using three MIA-QSPR (multivariate image analysis applied to QSPR) approaches. The MIA-QSPR model based on augmented molecular images (described with atoms represented as circles with sizes proportional to the respective van der Waals radii and having colors numerically proportional to the Pauling's electronegativity) encoded better the logBMF data. The average results for the main statistical parameters used to attest the model's predictability were r2=0.85, q2=0.72 and r2test=0.85. In addition, chemical insights on substituents and respective positions at the biphenyl rings A and B, and dibenzo-p-dioxin and dibenzofuran motifs are given to aid the design of more ecofriendly derivatives.

Columnar assembled pyridyl bis-urea macrocycles 1 provide a strong 1D supramolecular synthon to construct hierarchical assemblies. These 1D pillars contain ditopic symmetrical acceptors in the form of basic oxygen lone pairs. Herein, we probe this synthon with a series of activated halogen bond donors, the regio-isomers of diiodotetrafluorobenzenes, which vary the relative orientation of the halogen bond formers. Irrespective of the initial stoichiometry, each donor only formed one type of co-crystal with 1. In each case, similar strong pillars of assembled 1 were observed that organize the donors through the CO⋯I interaction, which were significantly shorter than the sum of the van der Waals radii of the atoms involved and among the shortest reported for neutral organic molecules. X-ray photoelectron spectroscopy characteristic core level shifts strongly indicated the formation of halogen bonding interactions. These studies suggest that this synthon can utilize both hydrogen and halogen bonding orthogonally to build complex structures.

Close contacts, defined as interatomic separations less than the sum of the respective van der Waals radii, are commonly invoked to identify attractive nonbonded interactions in crystal lattices. While this is often effective, it can also be misleading because (a) there are significant uncertainties associated with van der Waals radii, and (b) it may not be valid to attribute the interactions solely to specific pairs of atoms. The interactions within crystal lattices are Coulombic, and the strongest positive and/or negative regions do not always correspond to the positions of atoms; they are sometimes located between atoms. Examples of both types are given and discussed, focusing in particular upon σ-hole interactions.

Clathrate hydrate phases of Cl2 and Br2 guest molecules have been known for about 200 years. The crystal structure of these phases was recently re-determined with high accuracy by single crystal X-ray diffraction. In these structures, the water oxygen–halogen atom distances are determined to be shorter than the sum of the van der Waals radii, which indicates the action of some type of non-covalent interaction between the dihalogens and water molecules. Given that in the hydrate phases both lone pairs of each water oxygen atom are engaged in hydrogen bonding with other water molecules of the lattice, the nature of the oxygen–halogen interactions may not be the standard halogen bonds characterized recently in the solid state materials and enzyme–substrate compounds. The nature of the halogen–water interactions for the Cl2 and Br2 molecules in two isolated clathrate hydrate cages has recently been studied with ab initio calculations and Natural Bond Order analysis (Ochoa-Resendiz et al. J. Chem. Phys. 2016, 145, 161104). Here we present the results of ab initio calculations and natural localized molecular orbital analysis for Cl2 and Br2 guests in all cage types observed in the cubic structure I and tetragonal structure I clathrate hydrates to characterize the orbital interactions between the dihalogen guests and water. Calculations with isolated cages and cages with one shell of coordinating molecules are considered. The computational analysis is used to understand the nature of the halogen bonding in these materials and to interpret the guest positions in the hydrate cages obtained from the X-ray crystal structures.

DFT/B3LYP and CAM-B3LYP/6-311G(d,p) calculations have been performed to study a H 2 molecule inside boron-nitrogen nanotubes (BNNT) (2,2), (3,3), (4,4) and (5,5). H 2 is introduced perpendicular and parallel to the axis of nanotubes. The main difference relatively to CNTs is the disappearance of the H H bond activation zone in the BNNTs because of the absence of interactions between the π electrons and hydrogen. The most important phenomenon is the shortening of the H H bond by the interaction of the hydrogen with the repulsive zone of the van der Waals potential of the BNNT walls. This led to the appearance of a dipole moment in the inclusion complex H 2 @BNNT. The most important consequence of the existence of this dipole moment is that the IR activation of the H H vibration becomes intense. This vibration frequency may be used for detecting or assaying the H 2 contained in the nanotubes or to deduce BNNT's diameter. In this work we have examined also the consequence of the BNNT flattening on bandgap, our results show that flattening causes the reduction of a BNNT bandgap.

Focused ion beams (FIBs) are versatile tools with cross-disciplinary applications from the physical and life sciences to archeology. Nevertheless, the nanoscale patterning precision of FIBs is often accompanied by defect formation and sample deformation. In this study, the fundamental mechanisms governing the large-scale plastic deformation of nanostructures undergoing FIB processes are revealed by a series of molecular dynamic simulations. A surprisingly simple linear correlation between atomic volume removed from the film bulk and film deflection angle, regardless of incident ion energy and current, is revealed, demonstrating that the mass transport to the surface of material caused by energetic ion bombardment is the primary cause leading to nanostructure deformation. Hence, by controlling mass transport by manipulation of the incident ion energy and flux, it is possible to control the plastic deformation of nanostructures, thereby fabricating nanostructures with complex three-dimensional geometries.

The van der Waals interactions are responsible for a large diversity of structures and functions in chemistry, biology, and materials. Discussion of van der Waals interactions has focused on the attractive potential energy that varies as the inverse power of the distance between the two interacting partners. The origin of the attractive force is widely discussed as being due to the correlated fluctuations of electron charges that lead to instantaneous dipole-induced dipole attractions. Here, we use the inelastic tunneling probe to image the potential energy surface associated with the van der Waals interactions of xenon atoms.

Neutron diffraction and mechanical spectroscopy techniques were combined in one study in order to interpret structure induced anelasticity of Fe-(25–27)Me alloys where Me is Al, Ga or Ge. The following sequences of phase transitions at continuous heating in the 20–850 °C temperature range were recorded: (i) in Fe-27Al the B2 (only in water quenched state) → D0 3 → B2 → A2, (ii) in Fe-27Ga: D0 3 → L1 2 → D0 19 → A2(B2), and (iii) in Fe-25Ge: D0 19 (+A2 very limited amount) → A3 (+A2 very limited amount). At continuous cooling from 850 °C, we recorded the following transitions: (i) in Fe-27Al A2 → B2 → D0 3 , (ii) in Fe-27Ga: A2 → B2 → L1 2 (+ very limited amount of D0 19 and remaining A2 phases which underwent to D0 3 ordering), and (iii) in Fe-25Ge A3 (+A2 very limited amount) → D0 19 (+A2 very limited amount). These transition sequences determine different temperature dependencies of magnetic and anelastic properties in the studied alloys. In Fe-27Al and Fe-27Ga water quenched samples the bcc-born phases (A2, B2, D0 3 ) dominate at room temperature and a Snoek-type anelastic relaxation is recorded in both alloys. The Snoek relaxation is not recorded in Fe-25Ge alloy which has a close-packed D0 19 structure. Zener relaxation was recorded in all three systems Fe-Al, Fe-Ga and Fe-Ge both at heating and cooling. The first order irreversible D0 3 → L1 2 transition (in Fe-27Ga) at continuous heating generates internal stresses due to a huge jump-like increase of atomic volume with temperature and leads to a well-pronounced transient internal friction effect. The reversible D0 3 ↔ B2 transition (in Fe-27Al) also leads to a transient but much smaller anelastic effect. Much slower phase transition in Fe-25Ge alloy does not influence temperature dependent anelasticity in this alloy.

α-34S has been studied with X-ray crystallography within 100–363 K. Anisotropy of the evolution of the parameters of the orthorhombic unit cell has been examined. The absolute increase in the cell volume is 154 A3, and the relative one is 4.8%. It has been demonstrated that in the studied range the intramolecular S–S bond lengths are shortened at average by 0.006 A on heating. At the same time, intermolecular contacts S…S shorter than the sum of van der Waals radii demonstrate average elongation of 0.097 A.

We analyze in detail the results of experimental investigations of the evolution of the thermal vibration spectra for iron atoms in iron monosilicide FeSi depending on two external parameters, viz., temperature T (in the range 46–297 K at pressure P = 0.1 MPa) and pressure P (in the range 0.1 MPa–43 GPa at temperature T = 297 K), obtained by nuclear inelastic scattering of synchrotron radiation. The decrease of the atomic volume is accompanied by a rearrangement of the phonon spectrum, which is manifested, in particular, in the splitting of the low-energy peak in the spectrum and in an increase of the energy for all phonons. The changes of the average energy of the iron atom vibrational spectrum and of the Debye energy with decreasing atomic volume are analyzed. Different versions of FeSi electron spectrum variation, which can be used to explain the observed phonon anomalies, are considered.

An approach to constructing two-phase state regions for real gases, the state of which is described by the modified van der Waals equation in the form proposed by R.L. Fogel’son and E.R. Likhachev, has been discussed.

Tri(o-tolyl) antimony dioximates were synthesized by the reaction of tri(o-tolyl) antimony with 5-nitrofurfural and thiophen-2-carbaldehyde oximes in ether in the presence of hydrogen peroxide or tert-butylhydroperoxide (1: 2: 1 mol). Antimony atoms in the reaction products have distorted trigonal-bipyramidal coordination with the intramolecular distances Sb···N shorter than the sum of the van der Waals radii of Sb and N by ~1 A.

Weak noncovalent interactions are responsible for structure and properties of almost all supramolecular systems, such as nucleic acids, enzymes, and pharmaceutical crystals. However, the analysis of their significance and structural role is not straightforward and commonly requires model studies. Herein we describe an efficient and universal approach for the analysis of noncovalent interactions and determination of vdW radii using the Line-of-Sight (LoS) concept. The LoS allows to unambiguously identify and classify the “direct” interatomic contacts in complex molecular systems. This approach not only provides an improved theoretical base to molecular “sizes” but also enables the quantitative analysis of specificity, anisotropy and steric effects of intermolecular interactions.

Ultrahigh lattice thermal conductivity materials hold great importance since they play a critical role in the thermal management of electronic and optical devices. Models using machine learning can search for materials with outstanding higher-order properties like thermal conductivity. However, the lack of sufficient data to train a model is a serious hurdle. Herein we show that big data can complement small data for accurate predictions when lower-order feature properties available in big data are selected properly and applied to transfer learning. The connection between the crystal information and thermal conductivity is directly built with a neural network by transferring descriptors acquired through a pretrained model for the feature property. Successful transfer learning shows the ability of extrapolative prediction and reveals descriptors for lattice anharmonicity. The resulting model is employed to screen over $60\phantom{\rule{0.16em}{0ex}}000$ compounds to identify novel crystals that can serve as alternatives to diamond. Even though most materials in the top list are superhard materials, we reveal that superhard property does not necessarily lead to high lattice thermal conductivity. Large hardness means high elastic constants and group velocity of phonons in the linear dispersion regime, but the lattice thermal conductivity is determined also by other important factors such as the phonon relaxation time. What is more, the average or maximum dipole polarizability and the van der Waals radius are revealed to be the leading descriptors among those that can also be qualitatively related to anharmonicity.

First principles calculations were carried out to study the equilibrium properties of metals, including the electrons at bonding critical point, ebcp, cohesive energy, Ecoh, bulk modulus, B, and, atomic volume, V. 44 pure metals, including the s valence (alkali), p valence (groups III to V), and d valence (transition) metals were selected. In the present work, the electronic structure parameter ebcp has been considered to be a bridge connecting with the equilibrium properties of metals, and relationships between ebcp and equilibrium properties (V, and B) are established. It is easy to estimate the equilibrium properties (Ecoh, V, and B) of pure metals through proposed formulas. The relationships that were derived in the present work might provide a method to study the intrinsic mechanisms of the equilibrium properties of alloys and to develop new alloys.

We calculate the atomic and electronic structures of trirutile-type ${\mathrm{Li}}_{x}{\mathrm{FeF}}_{3}\phantom{\rule{4pt}{0ex}}(x=0,0.25,0.5,0.75,\phantom{\rule{4pt}{0ex}}\text{and}\phantom{\rule{4pt}{0ex}}1)$ by first-principles calculations and evaluate the relative stability among the optimized structures by energy analysis. ${\mathrm{Li}}_{0.5}{\mathrm{FeF}}_{3}$ is more stable than the three-phase coexistence of ${\mathrm{FeF}}_{3},{\mathrm{FeF}}_{2}$, and LiF, whereas the other compositions are unstable. The analyses of the local electron density, local atomic volume, and local atomic configurations show that the formal valence of Fe atoms decreases from trivalent (3+) to divalent (2+) after Li insertion. In addition, we calculate Fe $K$-edge x-ray absorption near-edge structure (XANES) spectra in ${\mathrm{Li}}_{x}{\mathrm{FeF}}_{3}$ and compare them with observed spectra. The calculated XANES spectra agree well with the corresponding observed spectra in areas such as the spectral shape and relative position of the main peaks associated with ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Fe}}^{2+}$. In particular, partial XANES spectra of ${\mathrm{Fe}}^{3+}$ in ${\mathrm{Li}}_{x}{\mathrm{FeF}}_{3}$, for $x=0.25,0.5$, and 0.75, have a specific peak between the main peaks, associated with ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Fe}}^{2+}$. The detailed study reveals that the energy level and intensity ratio of the ${\mathrm{Fe}}^{3+}$ main peaks depend on the adjacent cation site of Fe.

The covalent nature of strong N−Br⋅⋅⋅N halogen bonds in a cocrystal (2) of N‐bromosuccinimide (NBS) with 3, 5‐dimethylpyridine (lut) was determined from X‐ray charge density studies and compared to a weak N−Br⋅⋅⋅O halogen bond in pure crystalline NBS (1) and a covalent bond in bis(3‐methylpyridine)bromonium cation (in its perchlorate salt (3). In 2, the donor N−Br bond is elongated by 0.0954 Å, while the Br⋅⋅⋅acceptor distance of 2.3194(4) is 1.08 Å shorter than the sum of the van der Waals radii. A maximum electron density of 0.38 e Å−3 along the Br⋅⋅⋅N halogen bond indicates a considerable covalent contribution to the total interaction. This value is intermediate to 0.067 e Å−3 for the Br⋅⋅⋅O contact in 1, and approximately 0.7 e Å−3 in both N−Br bonds of the bromonium cation in 3. A calculation of the natural bond order charges of the contact atoms, and the σ*(N1−Br) population of NBS as a function of distance between NBS and lut, have shown that charge transfer becomes significant at a Br⋅⋅⋅N distance below about 3 Å.

As the piperidin-1-ium group is nearly orthogonal to the quinolinyl residue in each of the two independent cations of the title salt solvate, these cations are l-shaped. Supra­molecular chains arise in the crystal as a result of charge-assisted O—H⋯O and N—H⋯O hydrogen bonding., The asymmetric unit of the centrosymmetric title salt solvate, 2C17H17F6N2O+· C4H4O4 2−·CH3CH2OH, (systematic name: 2-{[2,8-bis­(tri­fluoro­meth­yl)quinolin-4-yl](hy­droxy)meth­yl}piperidin-1-ium butane­dioate ethanol monosolvate) comprises two independent cations, with almost superimposable conformations and each approximating the shape of the letter L, a butane­dioate dianion with an all-trans conformation and an ethanol solvent mol­ecule. In the crystal, supra­molecular chains along the a-axis direction are sustained by charge-assisted hy­droxy-O—H⋯O(carboxyl­ate) and ammonium-N—H⋯O(carboxyl­ate) hydrogen bonds. These are connected into a layer via C—F⋯π(pyrid­yl) contacts and π–π stacking inter­actions between quinolinyl-C6 and –NC5 rings of the independent cations of the asymmetric unit [inter-centroid separations = 3.6784 (17) and 3.6866 (17) Å]. Layers stack along the c-axis direction with no directional inter­actions between them. The analysis of the calculated Hirshfeld surface reveals the significance of the fluorine atoms in surface contacts. Thus, by far the greatest contribution to the surface contacts, i.e. 41.2%, are of the type F⋯H/H⋯F and many of these occur in the inter-layer region. However, these contacts occur at separations beyond the sum of the van der Waals radii for these atoms. It is noted that H⋯H contacts contribute 29.8% to the overall surface, with smaller contributions from O⋯H/H⋯O (14.0%) and F⋯F (5.7%) contacts.

(Pu) has an unusually rich phase diagram that includes seven distinct solid state phases and an unusually large 25% collapse in volume from its delta phase to its low temperature alpha phase via a series of structural transitions. Despite considerable advances in our understanding of strong electronic correlations within various structural phases of Pu and other actinides, the thermodynamic mechanism responsible for driving the volume collapse has continued to remain a mystery. Here we utilize the unique sensitivity of magnetostriction measurements to unstable f electron shells to uncover the crucial role played by electronic entropy in stabilizing delta-Pu against volume collapse. We find that in contrast to valence fluctuating rare earths, which typically have a single f electron shell instability whose excitations drive the volume in a single direction in temperature and magnetic field, delta-Pu exhibits two such instabilities whose excitations drive the volume in opposite directions while producing an abundance of entropy at elevated temperatures. The two instabilities imply a near degeneracy between several different configurations of the 5f atomic shell, giving rise to a considerably richer behavior than found in rare earth metals. We use heat capacity measurements to establish a robust thermodynamic connection between the two excitation energies, the atomic volume, and the previously reported excess entropy of delta-Pu at elevated temperatures., Comment: 38 pages with 10 figures

Thickness is not a well-defined quantity for two-dimensional (2D) materials. Hence, there are several choices adopted widely to assign the thickness of a 2D nanosheet: (a) the interlayer distance in layered bulk crystals; (b) the vertical distance between outmost atoms; (c) the value of (b) plus atomic van der Waals radius. Except these definitions of thickness, we determine the effective thickness of 2D pnictogen nanosheets based on continuum elastic theory combined with first principle calculations, from which the tension rigidities are extracted by fitting the strain energies of biaxially stretched samples with a quadratic relation on the lateral and transversal strains for blue phosphorene, arsenene, and antimonene. Whereas the bending rigidities are computed from the pnictogen nanotubes rolled from flat 2D nanosheets. Given the tension and bending rigidities, the effective thickness could be determined from the ratio between these two quantities. Our results indicate that the effective thickness, being much smaller than the widely used interlayer distance in the corresponding bulk material, is suited to describe mechanical properties of 2D nanosheets in a consistent way.

Controlling glass-glass interfaces in metallic nanoglasses is essential for tuning their mechanical properties and in particular, the ability to inhibit severe strain localization through distributed shear band formation. In this paper, molecular dynamics are employed to quantify the structural characteristics of interfaces in a scalable nanoglass model produced through hydrostatic compression of amorphous nanoparticles. Using a framework for distinguishing interfaces from amorphous grains based on the correlation between dilatation and atomic volume distributions, we show that the interfaces in our nanoglass model exhibit a volume fraction of 0.36, a width of approximately 2 nm, excess free volume of 1--2%, and full icosahedral (FI) fraction roughly 30% that of a bulk metallic glass counterpart. While these characteristics are quantitatively unique relative to other nanoglass models (e.g., planar interfaces and Poisson-Voronoi constructions), they are consistent with experimental results reported for nanoglasses consolidated from glassy nanoparticles produced through inert gas condensation. Increasing the consolidation temperature enhanced the FI fraction with a strong bias to the interfaces, thus demonstrating a route for tuning interfacial properties in nanoglasses.

The adsorption geometry, the electronic properties, and the adsorption energy of the prototype organic molecule 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on a monolayer of hexagonal boron nitride (hBN) grown on the Cu(111) surface were determined experimentally. The perylene core is at a large height of 3.37 $\AA{}$ and only a minute downward displacement of the functional anhydride groups (0.07 \AA{}) occurs, yielding adsorption heights that agree with the sum of the involved van der Waals radii. Thus, already a single hBN layer leads to a decoupled (physisorbed) molecule, contrary to the situation on the bare Cu(111) surface.

We report the high-pressure behavior of plasmon in polycrystalline Li up to 15 GPa at room temperature studied by inelastic x-ray scattering and ab initio calculation. The plasmon energy () increases with decreasing atomic volume (), and the slope exhibits a discontinuity at bcc → fcc structural phase boundary reflecting the electronic band structure change. The plasmon peak width () versus momentum transfer (q) curve of bcc-Li below 6.5 GPa keeps similar parabola-like shape. Above 8.4 GPa, where Li is in fcc, it changes from that of bcc-Li and has a convex shape., A B acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (FIS2016-76617-P) and the Department of Education, Universities and Research of the Basque Government and the University of the Basque Country (IT756-13).

In this work, we use molecular dynamics simulations to study the stress overshoots of metallic glass Cu50Zr50 in three scenarios (unloading-reloading, slide-stop-slide, and stress serrations) that are associated with shear band relaxation. We found that, after the elastic recovery effect is factored out, atomic volume in the shear band barely changes during compressive relaxation but decreases during tensile relaxation, while local fivefold symmetry increases consistently for both cases. We propose that the atomistic mechanism for the related stress overshoots is due to the relaxation of structural symmetry, instead of free volume, in the shear band. Upon unloading, a propagating shear band continues for some time before arrested, which results in a stress undershoot and could contribute to material fatigue under cyclic elastic loads. We did not directly observe stress serrations via molecular dynamics simulations due to the very high simulated strain rates. While athermal quasistatic simulations produce serrated flow stress, we note that such serrations result from global avalanches of shear events rather than the relaxation of the shear band. Our studies provide atomistic insights on shear-banding dynamics and deepen the understanding of inhomogeneous mechanical response of metallic glasses.

Molecular dynamics simulations have been carried out to determine the equation of state of helium inside nanobubbles embedded into a UO2 matrix. The parameters of the equation of state are fitted with the Brearley and MacInnes hard-sphere model based on the formalism of Carnahan-Starling used in fuel performance codes. This new equation of state takes into account the interactions between the surrounding UO2 matrix and the helium atoms. Four nanobubble sizes (diameters: 1, 2, 5, and 10 nm) have been investigated over four temperatures (300, 500, 700, and 900 K) and for initial helium concentration inside the bubble ranging from 0.33 × 10 5 to 3.9 × 10 5 mol.m−3 (corresponding to helium-to-vacancy ratio of 0.3–3.3, respectively). We find that helium atoms are inhomogeneously distributed inside the bubble. A boundary layer of 1 nm thickness appears at the bubble surface in which helium atoms are more concentrated and diffuse into the UO2 matrix. We also find a saturation concentration of the helium atoms that can be incorporated into the bubble. This concentration limit is equal to 1.6 helium atom per vacancy in UO2. It corresponds to an atomic volume of 7.8 × 10 − 30 m3, which is almost half of the value proposed with the original Brearley and MacInnes model ( 13 × 10 − 30 m3). For this threshold concentration and for bubble of diameter higher than 5 nm, nano-cracks and dislocations appear at the bubble surface. However, experimental observation is needed to confirm this finding. We calculated the critical pressures inside the bubble which yields to this onset of crack in UO2. These critical pressures are in good agreement with those calculated with the Griffith criterion for brittle fracture.

Understanding of interactions among molecules is essential to elucidate the binding of pharmaceuticals on receptors, the mechanism of protein folding and self-assembling of organic molecules. While interactions between two aromatic molecules have been examined extensively, little is known about the interactions between two antiaromatic molecules. Theoretical investigations have predicted that antiaromatic molecules should be stabilized when they stack with each other by attractive intermolecular interactions. Here, we report the synthesis of a cyclophane, in which two antiaromatic porphyrin moieties adopt a stacked face-to-face geometry with a distance shorter than the sum of the van der Waals radii of the atoms involved. The aromaticity in this cyclophane has been examined experimentally and theoretically. This cyclophane exhibits three-dimensional spatial current channels between the two subunits, which corroborates the existence of attractive interactions between two antiaromatic π-systems., Little is known about interactions between two antiaromatic molecules. Here, the authors synthesised a cyclophane, in which two antiaromatic porphyrin moieties adopt a stacked face-to-face geometry with a distance shorter than the sum of the van der Waals radii of the atoms involved.

We have explored the suitability of an O,N,N&ndash, donor Schiff base (H2SB) for obtaining dinuclear complexes with heavy metal ions such as Cu2+, Zn2+, Ni2+, and Co2+ (borderline acids) as well as Pd2+ and Cd2+ (soft acids). Spectroscopic studies demonstrated that the complexation of H2SB and Cu2+, Zn2+, Ni2+, Co2+, Pd2+, and Cd2+ occurred at a 1:1 stoichiometry. We have found two square planar centers with Pd-N-Pd angles of 93.08(11)&deg, and a Pd&ndash, Pd distance of 3.0102(4) &Aring, in Pd2(SB)2&middot, Me2CO. This Pd&ndash, Pd distance is 30% shorter than the sum of the van der Waals radii, which is in accordance with a strong palladophilic interaction. Fluorescence studies on H2SB-M2+ interaction showed that H2SB can detect Cu2+ ions in a sample matrix containing various metal ions (hard, soft, or borderline acids) without interference. Determination of binding constants showed that H2SB has a greater affinity for borderline acids than for soft acids.

The main asset of small molecules for application in organic electronics lies in the tunability of their electronic properties owing to the precise control of their molecular design. Semiconducting properties in organic compounds are for instance closely linked to the molecular planarity degree, including when considering various redox states. Among those species, the π-extended TTF (exTTF: 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene) presents fascinating redox and structural properties, which have been extensively studied in various fields of organic electronics. Here we show that S-exTTF, a sulfur enriched π-isoelectronic dithieno analogue of pristine exTTF, synthesized through a Horner–Wadsworth–Emmons olefination, presents a much higher π-donating ability than its exTTF homologue, associated to a higher planarity degree in the neutral or in the oxidized states. This is demonstrated by a combined experimental/theoretical approach. Solution studies (cyclic voltammetry and thin layer cyclic voltammetry) as well as solid-state analyses (X-ray structures of neutral S-exTTF and of the electrocrystallized cation radical salt ([S-exTTF][PF6]·THF)) were performed, and systematically compared with those of the pristine exTTF analogue. An in-depth computational study, carried out on the neutral state as well as on oxidized states of S-exTTF, confirms the prominent role of intramolecular S⋯S interactions in dictating a planar conformation, which is manifested by exceptionally short S⋯S distances in the X-ray structure (2.82 A, i.e., shorter, by far, than the sum of the van der Waals radii for S atoms (3.60 A)), and in promoting HOMO destabilization compared to the parent exTTF.

The partial atomic volume of hydrogen, vH, is a fundamentally important thermodynamic parameter of interstitial metal hydrides in which dissociated H occupies interstices in the metal lattice. Such an important property should be able to be reliably calculated by a suitable theory or model in order to explain and understand its origin. In practice, vH is typically obtained by means of ab initio calculations founded on density functional theory (DFT), where the equilibrium lattice constant at zero temperature is found by minimising the Born-Oppenheimer energy. While the absolute lattice constants calculated in this way depend quite strongly on the DFT scheme employed, the present work showed that vH is rather robust against differing calculational approaches, thus making a meaningful comparison of theory and experiment possible. Comparing vH for PdnH (0

The pressure effect on structures and properties of a Fe78Si9B13 metallic glass was investigated by in situ high-pressure synchrotron Fe Kβ x-ray emission spectroscopy and x-ray diffraction, and electrical resistivity measurements up to ∼51 GPa. The study reveals a reversible and continuous pressure-induced high- to low-spin crossover of Fe atoms in an amorphous structure. The changes of the local spin moment can be scaled to match its average atomic distance shrinkage very well during compression. The crossover of electronic spin states in the Fe78Si9B13 metallic glass resembles that of typical crystalline Fe-bearing materials but without a sharp atomic volume collapse and an abrupt electrical resistivity jump. These findings could help guide applications of Fe-based metallic glasses as a soft ferromagnetic material at extreme conditions and also improve our understanding of magnetism and coupling of its changes with disordered atomic structures and other properties in metallic glasses.

The Cux(Ge30Se70)100−x (0 ≤ x ≤ 12 at.%) chalcogenide alloys have been synthesized by the conventional melt quenching technique. The physical properties such as the mean coordination number, density, molar volume, compactness, overall bond energy, and cohesive energy were estimated for the Cu doped Ge-Se glassy alloys. The chemical bond approach (CBA) was used to predict the type and proportion of the formed bonds in the studied glasses. Subsequently, several structural and physical properties have been estimated. The results show that the studied glasses are rigidly connected, having an average coordination number increase from 2.6 to 2.77. The density and glass compactness show an increase with the Cu content, whereas the main atomic volume decreases. The cohesive energy and the heat of atomization show a similar behavior trend with the enhancement of Cu % in the Ge-Se binary glasses. The optical band gap was estimated theoretically compared with the previously published experimental values for the Cux(Ge30Se70)100−x (0 ≤ x ≤ 12 at.%) thin films. The covalency parameter >91% for the studied glasses so that the compositions may be used as a stable glass former. Furthermore, the mechanical properties as the elastic bulk modulus, Poisson's ratio, Young's modulus, micro-hardness, and Debye temperature were investigated as a function of the Cu content. © 2021 The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University , Saudi Arabia, for funding this work through the General Research Project Under Grant Number ( GRP/146/42 ).

We measured the atomic volume of Ag in a toroidal diamond anvil cell to a maximum pressure of 416 GPa and calculated the atomic volume and elastic constants of Ag up to 750 and 460 GPa, respectively. Our density functional theory calculations at 0 K utilize an all-electron fully relativistic method and agree well with our volume measurements, particularly at pressures above ∼75 GPa. We corrected our experimental results for non-hydrostaticity using a line shift analysis, and the resulting Vinet equation of state (EOS) parameters are reported. We find that the uniaxial stress sustained by Ag increases linearly up to 4.5 GPa at a pressure of 416 GPa. Our experimental results indicate that the fcc structure of Ag remains stable to at least 416 GPa at room temperature. Our theoretical results show that C44 increases as pressure increases and reaches a maximum at ∼100 GPa above which it begins to decrease, a sign that the fcc structure of Ag is becoming unstable, and at V/V0 = 0.30, the bcc structure is lower in energy than fcc.

In this work, an ionic liquid (IL), 1-naphthylammonium tetrachloroferrate (III), was synthesized and characterized using different characterization techniques. The IL existed as solid at room temperature and hence it was explored as an adsorbent for the removal of methylene blue (MB) and rose bengal (RB) dyes from aqueous solutions. The adsorption capacity of the adsorbent at equilibrium was found to be 6.443 mg/g for MB and 20.70 mg/g for RB. Furthermore, the adsorption isotherms were fitted into Langmuir isotherm model indicating that the two dyes were homogenously adsorbed on the surface of the material and the adsorption kinetics followed pseudo-second-order kinetic model with R2 value above 0.99. In addition, density functional theory (DFT) calculation confirmed the experimental findings showing energy gap (ΔE) of 3.572 eV and 4.084 eV for MB and RB respectively, and after complexation, a shift of 1.261 eV was observed in MB compared to 0.484 eV in RB in basic medium, indicating higher tendency of MB adsorption. The adsorption energies exhibited a greater affinity for MB with 13.2 kcal/mol, while RB in acidic condition with a value of 20.2 kcal/mol and 2.806 A binding distances for RB which is lower than the Van der Waals radii, 2.990 A showing Lewis acid-base interaction.

Based on first-principles simulations, we have studied systematically the interaction of transition elements (TEs) with hydrogen (H) in interstitial lattice and vacancy in molybdenum. The results indicated that the stable position of H can be remarkably affected by the TEs, which can be attributed to the valence electron density redistribution surrounding the TEs. The interactions between H and TEs display mainly the attraction, which is explained by the elastic mechanism and the Pauling electronegativity. The elastic mechanism mainly characterizes the H-TE interaction for the TE atoms with the small atomic volume and the large electronegativity in comparison with molybdenum, the opposite cases can be explained by the Pauling electronegativity viewpoint. The appearance of one H atom around the TE atom can affect negatively the binding of the second H. The positive binding energy among H, vacancy and TE can easily lead to the H-TE-vacancy cluster formation in molybdenum. The existence of the TE atom in the vicinity of vacancy can affect the interaction between H and vacancy, while the presence of the H atom around vacancy may influence the interplay between TE and vacancy. The present results give a detailed physical analysis on the interaction between H and TE as well as among H, vacancy and TE in molybdenum and could further help us design the future Mo-based material with regard to the choice of alloy composition for the consideration of the H retention.

Using a combination of first-principles calculations, special quasi-random structures and quasi-harmonic Debye model methods, we investigated the structural properties, magnetic moments, phase stability, electronic structure, mechanical properties and thermodynamic properties of fcc and bcc FeNi1-xCrx disordered alloys. The results show that the volume per atom and lattice constant of fcc and bcc FeNi1-xCrx alloys exhibit different nonlinear decreasing trends with increasing Cr content, which can be understood by the coupling effect of the composition-dependent antiferromagnetic interaction and atomic volume. Only fcc FeNi1-xCrx alloys with x less than 0.25 are relatively easy to synthesize, while FeNi1-xCrx alloys with other compositions all have a strong tendency to phase separation. The DOS of fcc and bcc FeNi1-xCrx alloys gradually moves to the shallower energy level with the increase of Cr content, which makes TDOS narrow. As the Cr content increases, the hardness and rigidity of fcc FeNi1-xCrx (x = 0, 0.125, and 0.25) alloys gradually increase, while the toughness, ductility and compression resistance gradually weaken. Increasing Cr content is beneficial to reduce the volumetric thermal expansion coefficient of fcc FeNi1-xCrx (x = 0, 0.125, and 0.25) alloys, which also can decrease Debye temperature and weaken interaction between atoms.

The disorder-order phase transition of NaBH4 from the cubic to tetragonal structures has been studied based on density functional theory. The disordered high temperature phase is expressed as a statistical average of three substructures with a hypothesis that each BH4− tetrahedron has a fixed orientation. Our calculations show that the phase transition is mainly induced by synergic rotation of BH4− ion and the energy barrier is sensitive to volume change. We also investigated the role of van der Waals corrections in describing phase transition with DFT-D2 and vdW-DF methods.

Ionic liquids (ILs) are chemicals that are nonvolatile and hence have the potential to replace volatile organic compounds in industrial applications. A large number of ILs, through the combination of different cations and anions, can potentially be synthesized. In this context, it will be useful to intelligently design customized ILs through computer-aided methods. Practical limitations dictate that any successful attempt to design new ILs for industrial applications requires the ability to accurately predict their melting point and viscosity as experimental data will not be available for the designed structures. In this paper, we present two new correlations for precise prediction of melting point and viscosity of ILs solely based on inputs from quantum chemistry calculations (no experimental data or simulation results are needed). To develop these correlations we utilized data related to size, shape, and electrostatic properties of cations and anions that constitutes ILs. In this work, new descriptors such as dielectric energy of cations and anions as well as the values predicted by an ‘ad-hoc’ model for the radii of cations and anions (instead of their van der waals radii) were used. A large number of correlation equations consisting different combination of descriptors (as inputs to the model) were tested and the best correlation for viscosity and melting point were identified. The average relative errors were estimated as 3.16% and 6.45% for melting point, Tm, and ln(vis), respectively.

In the presence of methanol (or ethanol) and acetone molecules, a zinc(II)–salphen [salphen = N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-phenylenediamine] building block gives rise to discrete supramolecular dimers involving both intermolecular hydrogen bonding and unique oxygen···oxygen interactions, that is, the O···O distances are much shorter than twice the van der Waals radius of an oxygen atom. These types of unexpected self-assembled structures have been studied thoroughly through a combination of experimental (X-ray diffraction, IR spectroscopy, solid-state UV/Vis absorption spectroscopy, and elemental analysis) and theoretical [DFT and natural bond orbital (NBO) calculations] studies. However, their solution structures involve different equilibrating species according to variable-temperature 1H NMR spectroscopy. The replacement of the methanol (or ethanol) and acetone molecules by bulkier isopropyl alcohol and 2-butanone, respectively, leads to structures with no oxygen···oxygen interactions. An infinite supramolecular polymeric chain stabilized by hydrogen bonding is obtained in the presence of water. The present study highlights that even well-explored molecules can provide extremely interesting possibilities for metallo-supramolecular chemistry.

Three polymeric group 11 transition metal polymers featuring metallophilic interactions were obtained directly via self-assembly of metal ions and 4-pyridinethiol ligands. In the cationic [Cu2(S-pyH)4]n2+ with [ZnCl4]n2− counterion (1) and in the neutral [Ag(S-py) (S-pyH)]n (2) 4-pyridinethiol (S-pyH) and its deprotonated form (S-py) are coordinated through the sulfur atom. Both ligands are acting as bridging ligands linking the metal centers together. In the solid state, the gold(I) polymer [Au(S-pyH)2]Cl (3) consists of the repeating cationic [Au(S-pyH)2]+ units held together by aurophilic interactions. Compound 1 is a zig-zag chain, whereas the metal chains in the structures of 2 and 3 are linear. The protonation level of the thiol ligand had an impact on the crystallization of polymers. Both nature of the metal center and reaction conditions affected the polymerization. QTAIM analysis confirmed direct metal-metal contacts only in polymers 1 and 3. In polymer 2, no theoretical evidence of argentophilic contacts was obtained even though the Ag⋅⋅⋅Ag distance was found to be less than sum of the Bondi's van der Waals radius of silver. peerReviewed

The rotational spectrum of the weakly bound complex 3,5-difluoropyridine⋯CO2 has been observed using pulsed-nozzle Fourier transform microwave spectroscopy. Spectroscopic constants are reported for the parent and 13CO2 isotopologues. The data indicate a planar structure in which the nitrogen approaches the carbon of the CO2 with either a C2v or effectively C2v geometry in the ground vibrational state. The N⋯C van der Waals bond distance is 2.8245(16) A and the oxygen⋯ortho-hydrogen distance is 3.091(2) A. The N⋯C van der Waals bond length is 0.027(8) A longer than that previously determined for pyridine–CO2, but is still considerably shorter than the 2.998 A distance in HCN⋯CO2. M06-2X/6-311++G(3df,3pd) calculations place the binding energy of the complex at 4.3 kcal/mol (4.1 kcal/mol with counterpoise correction). The calculations further indicate that a secondary interaction between the ortho-hydrogens of the ring and the CO2 oxygens account for ∼50% of the total binding energy.

The title compound, C27H38ClN2+·C32H12BF24−, was synthesized by reacting the product formed from a previous reaction between 1,3-bis(2,6-diisopropylphenyl)imidazolinium-2-carboxylate (SIPrCO2), and SOCl2, with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBARF). In the cation, the imidazole ring is in a half-chair conformation and the formerly carbene carbon atom is bonded in a distorted trigonal–planar geometry with N—C—Cl angles of 122.96 (16) and 122.21 (16)° and an N—C—N angle of 114.83 (18)°. In the crystal, weak C—H...F hydrogen bonds link the cations and anions, forming a three-dimensional network. In addition, a short Cl...F contact of 3.213 Å and several short F...F contacts less than the sum of the van der Waals radii [1.47 Å + 1.47 Å = 2.94 Å] are observed. The F atoms of two of the CF3groups were refined as disordered over four sets of sites.

Transforming the fluorine gauche effect from an academic curiosity into a powerful acyclic conformational control strategy has enriched molecular design. This expansive approach to modulating structure has proven to be particularly valuable in the construction of functional small molecules, thereby finding application in diverse disciplines, ranging from therapeutic medicine to enantioselective catalysis. In contrast to the well-established arsenal of conformational control tactics, in which conformer populations result from minimising nonbonding interactions, (e.g., A1,3- or A1,2-strain), the fluorine gauche effect is attributable to stabilising interactions comprised of two components: stereoelectronic and electrostatic. Conformer populations are partially determined by favourable, hyperconjugative interactions involving proximal electron-rich σ-bonds, π-systems, and nonbonding electron pairs with the antibonding orbital of the C−F σ-bond: σ→σ*, π→σ*, and n→σ*, respectively. Electrostatic, charge-dipole interactions (e.g., N+⋅⋅⋅Fδ−) also play a crucial role in stabilising what are often counter-intuitive conformations. These noncovalent interactions, permissible on account of the low van der Waals radius and high electronegativity of the fluorine atom, render this effect fundamentally important and practically valuable in structural chemistry. In this contribution to the Rosarium Philosophorum in honour of Prof. Jack David Dunitz FRS, we endeavour to delineate, albeit in an abridged form,[1] the evolution of the fluorine gauche effect from a fundamental spectroscopic study to a ubiquitous component of physical organic chemistry.

The title compound features an amine-N-capped octa­hedral coordination geometry for YbIII defined by an N4O3 donor set. The packing features supra­molecular layers sustained by C—H⋯O, C—H⋯π(ar­yl) and C—Cl⋯π(ar­yl) inter­actions., The YbIII atom in the title complex, [Yb(C27H24Cl3N4O3)] [systematic name: (2,2′,2′′-{(nitrilo)­tris­[ethane-2,1-di­yl(nitrilo)­methylyl­idene]}tris­(4-chloro­phenolato)ytterbium(III)], is coordinated by a trinegative, hepta­dentate ligand and exists within an N4O3 donor set, which defines a capped octa­hedral geometry whereby the amine N atom caps the triangular face defined by the three imine N atoms. The packing features supra­molecular layers that stack along the a axis, sustained by a combination of aryl-C—H⋯O, imine-C—H⋯O, methyl­ene-C—H⋯π(ar­yl) and end-on C—Cl⋯π(ar­yl) inter­actions. A Hirshfeld surface analysis points to the major contributions of C⋯H/ H⋯C and Cl⋯H/H⋯Cl inter­actions (along with H⋯H) to the overall surface but the Cl⋯H contacts are at distances greater than the sum of their van der Waals radii.

The crystal structure of a Li+ salt of a glucosyl derivative of lithocholic acid (lithium 3α-(α- d -glucopyranosyl)-5β-cholan-24-oate) has been solved. The crystal belongs to the orthorhombic system, P212121 spatial group, and includes acetone and water in the structure with a 1:1:2 stoichiometry. Monolayers, having a hydrophobic interior and hydrophilic edges, are recognized in the crystal structure. Li+ is coordinated to three hydroxyl groups of three different glucose residues, with two of them belonging to the same monolayer. A fourth molecule, located in this monolayer, is involved in the coordination of the cation through the carboxylate ion by an electrostatic interaction, thus completing a distorted tetrahedron. All Li+-oxygen distances values are very close to the sum of the ionic radius of Li+ and van der Waals radius of oxygen. Each steroid molecule is linked to other five steroid molecules through hydrogen bonds. Water and acetone are also involved in the hydrogen bond network. A hierarchical organization can be recognized in the crystal, the helical assembly along 21 screw axes being left-handed.

This investigation is based on an atomic equation of state which takes into account the excluded volume of the atom being considered. Study of solid rare gases allows following the packing factor of the solid in equilibrium with the gas at different temperatures and of the solid and the liquid in the case of solid–liquid equilibria. The application of a pressure to the solid up to 9800 MPa allows determining the decrease in atomic volume and thus the compressibility. Such a study leads to proposing a new expression through dividing the pressure derivative (as a function of the excluded volume) by the pressure. This new coefficient is a pressure-independent constant but varies with the atom considered. Multiplied by the initial atomic volume, this coefficient has a unique value for all the rare gases. Furthermore, this is also true for the series of alkali metals with however a lower value of the coefficient. The atomic configurations of the two series are very different with one free electron for the alkali metals but closed shells for the rare gases. The alkali metals are therefore more complex than the rare gases. It is worthwhile to note that study of the equilibrium has not required the use of the principles of thermodynamics.

An improved algorithm for the calculation of the volume of internal cavities within protein structures and virus capsids as well as the volumes occupied by single amino acid residues were presented. The geometrical approach was based on atomic van der Waals radii. The results obtained with two sets of the radii, those proposed by Pauling and those determined by Tsai et al were compared. The main improvement compared with our previous approach is a more elaborate treatment of the regions at the very boundary of the cavities, which yields a more accurate volume estimate. The cavity volume of a number of Plant Pathogenesis-Related proteins of class 10 (PR-10) were reevaluated and the volumes and other geometrical parameters for about 400 capsids of icosahedral viruses were reported. Using the same approach the volumes of amino acid residues in polypeptides as mean values averaged over multiple conformations of the side chain were also estimated. Proteins 2016; 84:1275-1286. © 2016 Wiley Periodicals, Inc.