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A set of concepts cultivated in the past decade has substantiated the understanding of water ice compression. The concepts include the coupled hydrogen bond (O:H–O) segmental cooperativity, segmental specific-heat disparity, compressive O:H–O symmetrization and polarization, and quasisolidity. Computational and spectrometric outcome consistently justifies that the intromolecular H–O bond has a negative compressibility while the intermolecular O:H nonbond does contrastingly because of the involvement of the interionic O O repulsive coupling. Compression lowers the melting point T m (named regelation) and raises the freezing temperature T N (for instant ice formation) by inward shifting the quasisolid phase boundary through Einstein's relation, ΔΘ Dx ∝ Δ ω x , which is in contrast to the effects of electrostatic polarization and water molecular undercoordination. Theoretical reproduction of the phase boundaries in the phase diagram revealed that H–O bond relaxation dictates boundaries of negative slope, d T C /d P < 0, and that the O:H relaxation determines those of d T C /d P > 0. O:H–O bond frozen governs boundaries of constant T C such as the I C -XI boundary and the H–O and O:H energy compensation yields those of constant P C such as X-VII/VIII boundaries. The O O repulsion opposes compression minimizing the compressibility. Polarization enlarges the bandgap and the dielectric permittivity of water ice by raising the nonbonding states above the Fermi energy. Progress evidences the efficiency and essentiality of the coupled O:H–O bonding and electronic dynamics in revealing the core physics and chemistry of water ice, which could extend to other molecular crystals such as energetic materials. • O O repulsion minimizes the compressibility and polarization governs the viscosity. • Lone pair polarization widens the bandgap and raises the dielectric permittivity. • O:H or H–O relaxation discriminates phase boundaries according to their dT/dP slopes. • H–O energy governs the T m while the O:H dictates the freezing T N and vaporization T V. [ABSTRACT FROM AUTHOR]

A systematic phonon spectrometric examination revealed that the H C phonon (2966 cm−1) undergoes blueshift under both compression and heating, but the C N (921 cm−1) and the N O (1403 cm−1) bonds undergo regular thermal redshift and compression blueshift in the Nitromethene (CH 3 NO 2) assembly that is a solid under compression and a liquid under heating. An extension of the Grüneisen parameters integrates the phonon frequency shift to the intrinsic compressibility, thermal expansibility, specific heat, equilibrium bond length, atomic cohesive energy, and bonding energy density of the single bond which represents all of its sorts contributing to the spectral peak shift. The coupled hydrogen bond (HB, N (O):H–C), performs the same as the O:H–O of liquid water and ice I does in responding to heating. Results suggested that the combination of the N (O):H-C tension and the O:⇔:N repulsion stabilize the crystal structure and store energy, as they do in the cyclo- N 5 −:[4H 3 O+; 3H 3 O+ + 2NH 4 + complexes. Unlabelled Image • Both compression and heating stiffen the H C bond while the C N and N O perform regularly. • An extended Grüneisen parameter features the bonding dynamics under stimulation. • Inter- and intramolecular coupling interactions are essential to nitromethane crystals. • X:H-C tension and X:⇔:Y repulsion stabilize the molecular assembly and storage energy. [ABSTRACT FROM AUTHOR]

Considering the flexible chemical composition, tunable electronic properties and unique two-dimensional structure of layered double hydroxides (LDHs), we constructed NiFe-LDH/Cu 2 O heterostructure photocatalysts. The photocatalytic performance of NiFe-LDH/Cu 2 O heterostructure photocatalysts was evaluated by methyl blue (MB) degradation and CO 2 reduction under visible-light illumination. The removal efficiency of MB was improved from 20% for Cu 2 O and 45% for NiFe-LDH to 93% for NiFe-LDH/Cu 2 O after 30 min adsorption and 240 min visible-light irradiation. Moreover, CH 4 yield from CO 2 reduction over NiFe-LDH/Cu 2 O is about 5.6 and 6.9 times that of NiFe-LDH and Cu 2 O, respectively. Based on a detailed study of structural, electronic, optical and electrochemical properties, Z-scheme photocatalytic mechanism was proposed to explain the enhanced photocatalytic performance of NiFe-LDH/Cu 2 O. This work presents an inexpensive and flexible strategy for manufacturing heterostructure photocatalysts using earth-abundant elements. • NiFe-LDH/Cu 2 O heterostructure photocatalysts were successfully prepared by a co-precipitation method. • MB removal efficiency can be improved from 20% for Cu 2 O and 45% for NiFe-LDH to 93% for NiFe/Cu 2 O。. • CH 4 yield from CO 2 photoreduction over NiFe-LDH/Cu 2 O is 5.6 and 6.9 times of NiFe-LDH and Cu 2 O, respectively. • Z-scheme mechanism is proposed, which is responsible for promoted charge separation and higher redox potentials. [ABSTRACT FROM AUTHOR]

From the perspective of bond order-length-strength correlation and the local bond averaging approach, we have formulated the number-of-layer resolved Raman shifts of graphene, with quantification of the referential origins from which the Raman shifts proceed and clarification of their origins. It is found that the primary D mode and the secondary 2D mode are dominated by the interaction between a specific atom and its nearest neighbors while the G mode by the dimer interaction, and therefore red shift happens to the D/2D phonons and blue shift to the G mode upon the number-of-layer is reduced. [ABSTRACT FROM AUTHOR]

The thermally softened and the mechanically stiffened graphene phonons have been formulated from the perspective of bond order-length-strength correlation with confirmation of the C-C bond length in the single-layer graphene contracting from 0.154 to 0.125 nm and the binding energy increasing from 0.65 to 1.04 eV. Matching theory to the measured temperature- and pressure-dependent Raman shift has derived that the Debye temperature drops from 2230 to 540 K, the atomic cohesive energy drops from 7.37 to 3.11 eV/atom, and the binding energy density increases from 250 to 320 eV/nm3 compared with the respective quantities of bulk diamond. [ABSTRACT FROM AUTHOR]

An innovative method is presented to estimate the size effect on the ferroelectric phase transitions in the barium titanate ceramic system. The method is based on the phenomenological thermodynamic theory with additional stress led by surface bond contraction. Two symmetry-breaking factors are introduced to correct the stress. This method has enabled us to predict the changing trends in phase transitions and the critical grain size for the disappearance of ferroelectric phase, which is beyond the prediction of existing models. [ABSTRACT FROM AUTHOR]

Although the size- and shape-induced blueshift in the photoluminescence and photoabsorption of nanostructured ZnO has been extensively investigated, the underlying mechanism remains yet unclear. Here we show that theoretical reproduction of the observed trends clarifies that the blueshift originates from the Hamiltonian perturbation due to the broken-bond-induced local strain and quantum trapping and electron-phonon coupling in the surface skin up to two atomic layers in depth while bonds in the core interior retain their bulk nature. The extent of the blue shift depends on the tunable fraction of undercoordinated atoms in the surface skin. Therefore, the quantum confinement effect is indeed more “superficial” than first thought [H. Winn, OE Mag. 8, 10 (2005)]. [ABSTRACT FROM AUTHOR]

The Hg2CuTi-type structure is found to be preferable energy wise than the Cu2MnAl-type structure for full-Heusler Cr2MnAl and exhibits half-metallic ferromagnetism based on first principles. The calculations for the mixed compounds with disorder between B and D sublattices reveal that the case of exchanging one atom maintains the half-metallicity while the case of exchanging two atoms loses it. The electronic structures of the atoms at sites A or C are affected mainly by the nearest-neighboring coordination while that of the atoms at site B are determined by the next-nearest-neighboring coordination. [ABSTRACT FROM AUTHOR]

It has long been puzzling regarding the trends and physical origins of the size-effect on the elasticity of ZnO nanostructures. An extension of the atomic “coordination-radius” correlation premise of Pauling and Goldschmidt to energy domain has enabled us to clarify that the elastic modulus is intrinsically proportional to the sum of bond energy per unit volume and that the size-induced elastic stiffening arises from (i) the broken-bond-induced local strain and skin-depth energy pinning and (ii) the tunable fraction of bonds between the undercoordinated atoms, and therefore, the elastic modulus of ZnO nanostructures should increase with the inverse of feature size. [ABSTRACT FROM AUTHOR]

A model has been developed for the P-E hysteresis behavior from the perspective of dipole switching. Hysteresis loops have been reproduced with the model to agree reasonably well with the experimental data measured from various ferroelectric thin films. The model can also predict asymmetric hysteresis loop measured under unconventional situation. Additionally, the mathematical description can be easily combined with electronic design automation software in circuit simulation of ferroelectric capacitor or ferroelectric field effect transistor. [ABSTRACT FROM AUTHOR]

The optical limiting (OL) properties of a novel coordination polymer {[Et4N][Ag2I3]}n with a ladder-like framework were investigated using 532-nm nanosecond laser pulses. The coordination polymer in dimethylformamide solution exhibits better OL performance than C60 in toluene. The results were discussed using a phenomenological model based on excited-state nonlinear absorption. [ABSTRACT FROM AUTHOR]

Combining bond–band–barrier (BBB), density‐functional theory (DFT) and zone‐selective electron spectroscopy (ZES) correlations, we investigate the bonding mechanisms at Na/Ta(110) and Ta/Na(110) interfaces. When the Ta metal coverage on the Na(110) surface is increased from 7/9 ML to 8/9 ML, the Ta surface distribution changed from one‐dimensional chains to two‐dimensional ring structures. Moreover, the Ta‐induced shifts in the surface binding energy (BE) on the Na(110) surface were dominated by quantum entrapment, whereas the Na‐induced shifts in the BE on the Ta(100) surface are dominated by polarization. DFT calculations reveal that the Ta atomic chain is more stable than the structure of the Ta atomic ring. The adsorption of Ta atoms on the Na(110) surface is more stable than the structure of the Na atoms adsorbing on the Ta(110) surface. The 1D chain formations and 2D ring structures on the Na(110) surface are identified and explained in this paper. [ABSTRACT FROM AUTHOR]

Regelation, i.e., ice melts under compression and freezes again when the pressure is relieved, remains puzzling since its discovery in 1850's by Faraday. Here we show that hydrogen bond (O:H-O) cooperativity and its extraordinary recoverability resolve this anomaly. The H-O bond and the O:H nonbond possesses each a specific heat ηx(T/ΘDx) whose Debye temperature ΘDx is proportional to its characteristic phonon frequency ωx according to Einstein's relationship. A superposition of the ηx(T/ΘDx) curves for the H-O bond (x = H, ωH ~ 3200 cm−1) and the O:H nonbond (x = L, ωL ~ 200 cm−1, ΘDL = 198 K) yields two intersecting temperatures that define the liquid/quasisolid/solid phase boundaries. Compression shortens the O:H nonbond and stiffens its phonon but does the opposite to the H-O bond through O-O Coulomb repulsion, which closes up the intersection temperatures and hence depress the melting temperature of quasisolid ice. Reproduction of the Tm(P) profile clarifies that the H-O bond energy EH determines the Tm with derivative of EH = 3.97 eV for bulk water and ice. Oxygen atom always finds bonding partners to retain its sp3-orbital hybridization once the O:H breaks, which ensures O:H-O bond recoverability to its original state once the pressure is relieved. [ABSTRACT FROM AUTHOR]

Review: 514 refs. [ABSTRACT FROM AUTHOR]

It has long been a puzzle regarding the atomistic origin of the thermally driven elastic softening of a solid specimen since the pioneering works of Anderson in 1966 and Watchman in 1961. Here we present an analytical solution developed from the perspective of the local bond average. It is shown that the thermally driven elastic softening of crystals can be directly related to the geometric and energetic response of the representative bonds or their average of the given specimen to the temperature variation. Reproduction of the experimental results of Ag, Au, MgO, Mg2SO4, Al2O3, KCl, Si, Ge and diamond crystals has been realized giving rise to information on the mean atomic cohesive energy without involving any hypothetical parameters used in classical thermodynamics or in continuum mechanics. [ABSTRACT FROM AUTHOR]