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Bulk phosphorus oxynitride (PON), isoelectronic with SiO2, is confirmed to have many polymorphs as the latter. However, its 2D counterparts have not been studied. In this work, crystal structure exploration and property study are performed on 2D PON with the help of first‐principle calculation. Three 2D PON sheets are found with thermal, dynamical, and mechanical stability and all of them can be viewed as oxygen‐doped known 2D γ phosphorus nitride (γ‐PN). In the studies, it is indicated that they are indirect bandgap materials with gap values larger than 3 eV. The situations of orbital hybridization are discussed and their bonding properties are analyzed. Infrared vibrational spectra of these 2D materials are simulated and the vibrational modes at the Brillouin center are assigned by the factor group analysis. The reasons for the disappearance of some infrared peaks in the simulated spectra are revealed based on the calculated Born effective charges and vibrational eigenvectors. Their piezoelectric stress tensors are computed via density‐functional perturbation method and the piezoelectric strain tensors are also deduced via the calculated elastic constants. In the results, it is uncovered that these 2D PON sheets have considerably greater piezoelectric coefficients than the primitive 2D γ‐PN, which make them promising for nanopiezoelectric use. [ABSTRACT FROM AUTHOR]

BiOX (X = Cl, Br, I) monolayers are photocatalytic materials having many potential applications, but their basic properties are still not systematically studied. Herein, first‐principles calculations are performed to study their electronic, mechanical, and infrared properties. Band structures calculated by the Heyd–Scuseria–Ernzerhof (HSE06) functional with and without spin orbital coupling uncover that they are indirect bandgap materials. Partial densities of states of these materials are computed and compared to reveal the reason for the differences among their band structures. Studies imply that the BiO bonds are chiefly covalent while the interaction between the Bi and the X atoms is mainly ionic. Elastic constants and ideal in‐plane stresses of these materials are computed to explore their mechanical properties. Performed factor group analyses indicate that there are nine Raman‐active and six infrared‐active modes in their Brillouin zone centers. Their infrared spectra are simulated and the reason for the disappearance of some infrared peaks is given. Comparisons on the above properties are also made for these BiOX monolayers. [ABSTRACT FROM AUTHOR]

KBaBi is predicted to be a topological insulator recently, but most fundamental properties of it have not been studied. In this work, first-principles calculations were carried out to study its electronic, bonding, elastic, vibrational and dielectric properties. The results indicate that KBaBi has a band gap of 0.22 eV with the presence of spin orbital coupling. Weak p-d hybridization exists between the Ba 5d and the Bi 6p orbitals, so KBaBi has some covalent property, as revealed by the electron density difference. Studies imply that KBaBi is mechanically and dynamically stable, but it is mechanically anisotropic. KBaBi has a theoretical bulk modulus of 20.8 GPa and a shear modulus of 11.7 GPa. Group theory analysis indicates that there are six infrared- and four Raman-active modes at the Brillouin zone center of KBaBi. The vibrational frequencies and the corresponding eigenvectors were calculated and discussed. Calculation unveils that the electrons have more dielectric contribution to the total dielectric constants than the ions in the ab plane, but it is revised along the c axis. Investigations of the band structure, the Debye temperature and the phonon dispersion curves indicate that KBaBi is a promising thermalelectric material. Calculations indicate that KBaBi is metallic without SOC, but is an insulator with SOC. Theoretical studies reveal that KBaBi is mechanically and dynamically stable, Ba 5d orbital plays an important role in forming the crystal and KBaBi may be a promising thermalelectric material. Image 1 [ABSTRACT FROM AUTHOR]

Silicon oxynitride (Si 2 N 2 O) is a functional ceramic having many possible applications. In this work, we studied the vibrational and dielectric properties and ideal strength as well as the related deformation mechanism of Si 2 N 2 O using first principles calculations. Factor group analysis was performed and vibrational frequencies were calculated to assign the observed vibrational modes. Infrared dielectric and absorption spectra were simulated and their origins were revealed. Tensile, compressive and shear strengths along the representative directions were investigated, which gave Si 2 N 2 O an ideal strength agreeing well with its experimental hardness. The calculated minimum compressive stress also coincides well with the starting amorphization pressure observed in shock experiments, providing a theoretical method to study mechanical effects of shock wave. Analyses on the deformation mechanisms at the critical strains imply that Si-O bond is stronger than other bonds, which is opposite to the previous speculation. [ABSTRACT FROM AUTHOR]

Na3OBr is expected to be a promising superionic conductor for use as solid state electrolyte in large scale energy storage systems, but its lattice dynamic and thermal conductivity properties have not been well studied till now. In this work, we performed a detailed study on these properties as well as its electronic and elastic properties using first principles method. The results indicate that Na3OBr is a direct band gap crystal. It is mechanically stable but elastically anisotropic. Its phonons at the Brillouin zone center were classified using group theory analysis and its Born effective charges, LO-TO splitting, and dielectric constants were calculated and discussed. Its phonon dispersion curves were obtained and their origins were revealed. Based on the phonon dispersion curves, its thermal conductivity as a function of temperature was predicted, which give a value of 7.30 Wm−1 K−1 at 300 K. Further study reveals that, for Na3OBr, the simple Slack's model can give almost the same thermal conductivity curve as that obtained from the phonon dispersion curves. [ABSTRACT FROM AUTHOR]

SrClF is an important optical crystal and can be used as pressure gauge in diamond anvil cell at high pressure. In this work, we performed a systematic study on the structural, electronic and elastic properties of SrClF under pressure, as well as its thermal conductivity, by first-principles calculation. Different exchange-correlation functionals were tested and PBESOL was finally chosen to study these properties of SrClF. Studies reveal that SrClF has a bulk modulus of about 56.2 GPa (by fitting equation of states) or 54.3 GPa (derived from elastic constants), which agree well with the experimental result. SrClF is mechanically and dynamically stable up to 50 GPa. Its elastic constants increase with the applied pressure, but its mechanical anisotropy deteriorates as the pressure increases. Investigation of its electronic properties reveals that SrClF is a direct band-gap insulator with a gap value of 5.73 eV at 0 GPa, which decreases with the increasing pressure and the reason is found by analysing the partial density of states. Based on the calculated phonon dispersion curves, thermal conductivity of SrClF is predicated. At ambient conditions, the predicted thermal conductivity is about 3.74 Wm−1 K−1, while that obtained using the simplified Slack model give a slightly larger value of 4.62 Wm−1 K−1. [ABSTRACT FROM PUBLISHER]

Carbon has many allotropes besides diamond and graphite. In this work, we studied the structure, elasticity, ideal strength and thermal conductivity of a pure three-dimensional sp 2 carbon crystal by first principles calculation. The results reveal that this carbon allotrope is a rare crystal with negative linear compressibility: its a axis expands while c axis shortens under hydrostatic pressure. It is mechanically stable up to 60 GPa and its elastic constant C 33 decreases at first and then increases and fluctuates with the rising pressure. Its ideal tensile, shear and compressive strengths are systematically studied and the results indicate that this pure sp 2 carbon is superhard despite of its low density. It can endure strains of 0.622 and 0.470, respectively, when tensioned and compressed. These make it a very promising shock absorbing material once synthesized. Its cracked mechanisms at the critical strains are also investigated. Our study also finds that, contrary to the common view, the direction of its weakest shear strength has no relation with that of its weakest tensile strength. Proceeding from Slack's model, we also calculated its thermal conductivity in the temperature range from 200 to 1800 K, which gives a value of about 30 Wm − 1 K − 1 at 300 K. We hope our study will provide new insight on carbon allotropes and materials with negative linear compressibility. [ABSTRACT FROM AUTHOR]

CdSiP 2 is a promising nonlinear optical crystal for frequency conversion in the mid-IR spectral range. In this work, the vibrational, dielectric and infrared properties of CdSiP 2 are studied by using density functional perturbation calculation. The Born effective charges of the constituent ions, the vibrational modes and the splitting of the longitudinal and transverse optical (LO–TO) frequencies at the Brillouin zone center are calculated and discussed. Its dielectric constant and dielectric spectra are also calculated, which reveals that electrons in CdSiP 2 have a larger contribution to the dielectric constant than the lattice. The theoretically obtained birefringence Δ n and the simulated infrared reflectance spectra agree well with the available experimental results. [ABSTRACT FROM AUTHOR]

BaLiF3 is an important optical crystal for use as a window material in the ultraviolet region. In this work, we studied the electronic and elastic properties of BaLiF3 with pressure effects by the generalized gradient approximation within the density-functional method. Studies indicate that BaLiF3 is mechanically stable and almost elastically isotropic up to 190 GPa, which is considerably higher than the previously reported value. The changing trends of its elastic constants, bulk modulus, B/ G ratio, Poisson ratio, and Debye temperature with pressure were systematically investigated. Electronic property calculations reveal that BaLiF3 is an ionic insulator with a bandgap of 6.14 eV at 0 GPa and the bandgap is formed by Ba-5d states and F-2p states. Two interesting phenomena are found: one is that the bandgap of BaLiF3 first increases and then decreases with increasing pressure and the reason for this is explored. Another is that Li-2s states only appear above the Fermi level in this inverted fluoroperovskite. [ABSTRACT FROM AUTHOR]

Transition metal phosphides are interesting compounds because they have many unique physical and chemical properties. Here we studied the electronic, elastic and vibrational properties of the newly synthesized marcasite-type OsP 2 by first principles calculation within the framework of local density approximation. Calculated band structure reveals that OsP 2 is a narrow indirect band gap semiconductor with a gap 0.91 eV, which agrees with the experimental value 1.13 eV. Analysis on density of states indicates that there exist covalent P–P and Os–P bonds in OsP 2 . Calculated elastic constants imply that OsP 2 is mechanically stable but anisotropic. The calculated bulk and shear moduli give a B / G ratio 1.35, suggesting that OsP 2 is brittle. Computed phonon dispersion curves show no imaginary frequency in the whole Brillion zone, indicating that OsP 2 is dynamically stable. Group theory analyses were performed and the vibrational modes of the experimentally obtained Raman spectrum were assigned. It is found that the Raman active modes only involve the vibration of the P ions while the infrared ones involve vibrations of both. [ABSTRACT FROM AUTHOR]

As a microscopic model to study ionized water, cationic water clusters are hot research subjects in these days, which also has many unique properties compared with their neutral counterparts. Here, the isomers of ( H 2 O ) 4 + cluster were searched by using particle swarm optimization method with the help of quantum chemical calculations. Eighteen stable candidates were obtained after optimization performed at the MP2/aug-cc-pVDZ level. Their relative Gibbs free energies below 350 K, the infrared spectra of the five lowest energy isomers and the electronic characteristics of the representative isomers were investigated. For these isomers, the effect of the zero point vibrational energies, the relationship between the schemes of the isomers and their energies, and the constituents of the most important orbitals were studied, which provide us with much information for further studying this kind of clusters. [ABSTRACT FROM AUTHOR]

Highlights: [•] The obtained lattice constants of CuYO2 from LDA+ U method are well consistent with the experimental data. [•] The elastic constants and mechanical properties of CuYO2 are investigated for the first time. [•] The obtained band-gap of CuYO2 is better than others and more close to the experimental value. [Copyright &y& Elsevier]

Abstract: Carbon is a versatile element in the periodic table because of its ability to form various stable and metastable allotropes. In the present work, an orthorhombic carbon allotrope with ‘4-membered rectangles’ is predicated by Particle Swarm Optimization method at 0GPa. Calculations indicate that this new phase is dynamically and mechanically stable although it has a high enthalpy. Its electronic and mechanical properties such as elastic constants, hardness, ideal tensile strength and shear strength are systematically studied. The results show that it is an indirect band gap crystal with a gap of 2.68eV; in spite of its elastic anisotropy, the theoretical hardness of 76.2GPa still makes it a potential superhard material; the obtained ideal tensile strength and shear strength are 69.0GPa and 75.6GPa, respectively, confirming its superhard character. The related microscopic deformation mechanisms are also detailedly analyzed through investigating the corresponding charge density, which reveals that the bonds arranged parallel to the b-axis are responsible for the breakdown of the crystal under the critical tension and shear deformations. These studies provide important information for the potential applications of the crystal once it is synthesized. [Copyright &y& Elsevier]

Highlights: [•] By employing LDA+ U calculation, an correct antiferromagnetic (AFM) insulating ground state for CeVO4. [•] Calculated magnetic moment of 1.03μB per Ce atom consists well with the experimental result. [•] The elasticity-related properties are systematically investigated for the first time. [•] Mulliken populations and charge density are studied to reveal the crystal’s bonding property. [ABSTRACT FROM AUTHOR]

Highlights: [•] Electronic properties, Fermi surface and non-magnetic property of SrCu2As2 are investigated. [•] Elastic constants and elasticity-related properties are calculated. [•] Elastic anisotropy is visually shown and analyzed. [•] Thermal properties are calculated, consisting well with the experimental data. [Copyright &y& Elsevier]

Highlights: [•] Electronic and bonding properties of CdSiP2 were investigated and analyzed. [•] Bond hardness and intrinsic Hardness of CdSiP2 were surveyed. [•] Elastic properties of CdSiP2 were studied. [•] Elastic anisotropy was calculated and shown visually. [ABSTRACT FROM AUTHOR]

[Display omitted] • Capacitive properties of boronphene related sheets with Dirac cone are detailedly studied. • Energetical, thermal and mechanical stability of these sheets are investigated. • Most of these materials are promising to be used as electrodes in supercapacitors. Borophene and related materials are of great scientific interest for their unique properties nowadays. In this work, we studied the band structures and capacitive properties of eight borophene related sheets, in which seven have Dirac cone at their Fermi levels as graphene. The results indicate that the carries in these sheets have favorable or even higher Fermi velocity compared with that of graphene. These materials have much larger differential quantum capacitance, surface storage charge and integrated quantum capacitance than graphene, which make them promising for use as electrodes superior to graphene in supercapacitors. Further studies indicate that these sheets are energetically and mechanically stable although some of them are mechanically anisotropic. Ab initio molecular dynamics simulations conducted at 400 K only exclude one sheet as good electrode. Additionally, Work functions of these materials are computed for building heterojunctions for future applications. [ABSTRACT FROM AUTHOR]

A two-dimensional rectangular carbon formed by four-, eight- and ten-membered carbon rings, named R 10 -graphene, is found by the particle swarm optimization method. Studies indicate that R 10 -graphene is metallic, possessing dynamical, thermal and mechanical stability. Its metallicity comes mainly from the p z orbital of the carbon atoms, as that in graphene. It is mechanically anisotropic, having a larger elastic constant along the a axis than that along the b axis. Calculated ideal in-plane strength along the a axis is also considerably higher than that along the b axis although the critical strains along these two directions are almost the same. Investigations reveal that it has greater differential quantum capacitance and charge storage capacity than graphene, especially at negative voltage, which make it a promising cathode material for supercapacitors. [Display omitted] • A 2D carbon with dynamical, thermal and mechanical stability is found. • It is metallic originated from the p z orbital of carbon atoms as that in graphene. • Lower density and better capacitive properties make it a promising electrode material. [ABSTRACT FROM AUTHOR]

-Abstract: In this work, electronic and elastic properties along with the pressure effects of the unconventional superconductor Sr2RuO4 are investigated by first principles calculation. Band structure calculation reveals that Sr2RuO4 is a weak metal. The characteristic of the band structure has also been analyzed. The calculated elastic constants reproduce the experimental data well. Analyses disclose that Sr2RuO4 is mechanically stable but anisotropic. The calculated Debye temperature 475.0K is in good agreement with the experimental results. Surveys of the pressure effect on the lattice constants reveal that the a axis is less compressible than the c axis, as found in the experiment. Further investigations illustrate that Sr2RuO4 is mechanically stable up to 50GPa till the elastic constant C 44 fails to meet the mechanical stability criterion. The pressure-dependent elastic parameters are also investigated to know their behaviors under pressure. In addition, the bonding properties of Sr2RuO4 at 0GPa and 50GPa are analyzed to explain its elastic behavior under pressure. [ABSTRACT FROM AUTHOR]

The structural stabilities, phase transitions and thermodynamic properties of 2 under high pressure and temperature are investigated by first-principles calculations based on plane-wave pseudopotential density functional theory method within the local density approximation. The calculated lattice parameters of 2 in all four phases under zero pressure and zero temperature are in good agreement with the existing experimental data and other theoretical results. Our results demonstrate that 2 undergoes a series of structural phase transitions from rutile (P42/mnm)→2-type (Pnnm)→ fluorite (Pa-3)→ ( Pnam) under high pressure and the obtained transition pressures are in fairly good agreement with the experimental results. The temperature-dependent volume and thermodynamic properties of 2 in the rutile phase at 0 GPa are presented and the thermodynamic properties of 2 in the rutile, 2-type, modified fluorite and cotunnite phases at 300 K are also predicted using the quasi-harmonic approximation model (QHA) and the quasi-harmonic Debye model (QHD), respectively. Moreover, the partial density of states and the electronic density of the four phases under the phase transition are also investigated. [ABSTRACT FROM AUTHOR]

Up to now, at least 806 carbon allotropes have been proposed theoretically. Three interesting carbon allotropes (named Pbam-32, P6/mmm, and) were recently uncovered based on a random sampling strategy combined with space group and graph theory. The calculation results show that they are superhard and remarkably stable compared with previously proposed metastable phases. This indicates that they are likely to be synthesized in experiment. We use the factor group analysis method to analyze their Γ -point vibrational modes. Owing to their large number of atoms in primitive unit cells (32 atoms in Pbam-32, 36 atoms in P6/mmm, and 94 atoms in), they have many Raman- and infrared-active modes. There are 48 Raman-active modes and 37 infrared-active modes in Pbam-32, 24 Raman-active modes and 14 infrared-active modes in P6/mmm, and 34 Raman-active modes and 35 Raman- and infrared-active modes in. Their calculated Raman spectra can be divided into middle frequency range from 600 cm−1 to 1150 cm−1 and high frequency range above 1150 cm−1. Their largest infrared intensities are 0.82, 0.77, and 0.70 (D/Ĺ)2/amu for Pbam, P6/mmm, and , respectively. Our calculated results provide an insight into the lattice vibrational spectra of these sp3 carbon allotropes and suggest that the middle frequency Raman shift and infrared spectrum may play a key role in identifying newly proposed carbon allotropes. [ABSTRACT FROM AUTHOR]

Layered crystal Bi2O2Te has recently been found to have high electron mobility and excellent thermoelectric properties for technical applications; however, its other properties are not well studied yet. In this work, the electronic, elastic and optical properties of Bi2O2Te are systematically studied using the density functional method. The results indicate that Bi2O2Te is a narrow band gap semiconductor. The gap is formed by the Te 5p orbital at the top of the valence band and the Bi 6p orbital at the bottom of the conduction band. There are both ionic and covalent interactions within the Bi–O layers, and these layers are linked by the ionic Bi–Te bonds forming the crystal. Bi2O2Te is mechanically stable but anisotropic. It is easy to fracture along the c axis under shear stress. Its shear modulus is far smaller than its bulk modulus, so shape deformation is easier to occur than pure volume change. Its melting point is predicted to be 1284.0 K based on an empirical formula. The calculated refractive index at zero frequency reveals that Bi2O2Te is a negative uniaxial crystal with a birefringence of 0.51, making it a potential tuning material for optical application. The characteristics and origins of other optical properties are also discussed. [ABSTRACT FROM AUTHOR]

KCdCO 3 F is a newly synthesized promising ultraviolet nonlinear optical crystal, but its structure is disputed and its fundamental properties have not been well studied. Here our first-principles study indicates that the structure with the space group P 6 ¯ c 2 is energetically more stable than the P 6 ¯ m 2 phase. We systematically investigated its electronic, optical, vibrational, infrared, and elastic properties. The results reveal that KCdCO 3 F is a direct-band-gap insulator with rather flat bands below the Fermi level. Analyses of its partial density of states revealed that the top (bottom) of its valence (conduction) band is formed by the O 2p (Cd 5s) orbital. It is a negative uniaxial crystal with ionic-covalent nature. Both infrared-active and Raman-active modes exist at its Brillouin zone center, and ions contribute more to its static dielectric constants. Its optical spectra in the visual and infrared ranges were studied, and their origins were revealed. Calculations indicate that KCdCO 3 F is mechanically stable but anisotropic since it is more vulnerable to shear stress and is easy to cleave along the c axis. [ABSTRACT FROM AUTHOR]

Carbon is a versatile element having many allotropes with unique properties in the periodic table. In this work, we predicted a tetragonal carbon allotrope formed by five-membered carbon cages. We studied its electronic, vibrational, dielectric, elastic, hardness and ideal strengths using first principles calculation. The results indicate that it is dynamically stable but higher in energy than graphite. It is a semiconductor having both Raman and infrared vibrational modes in its Brillouin zone center. Calculated dielectric properties reveal that it is an electronic dielectric material. It is mechanically stable but has a noticeable elastic anisotropy. Investigations of the ideal strengths indicate that c axis is more resistant against tension than a axis, but it is reversed in the case of compression. The minimum ideal strength is about 42.5/40.0 GPa occurring in the [010](100) slip system, which agrees well with the calculated hardness 41.2/39.2 GPa, so it may be a superhard material. The related fracture mechanisms at the critical strains were also discussed and illustrated by maps of electron density difference. [ABSTRACT FROM AUTHOR]

ZrBeSi is the prototype of the ZrBeSi‐type of crystals, but its fundamental properties have not been well studied till now. In this work, a systematic study on the electronic, elastic, and vibrational properties of ZrBeSi under zero and high pressures has been performed by first‐principles calculation. Calculated electronic properties indicate that ZrBeSi is metallic dictated mainly by the Zr 4d state. Its metallicity weakens as the pressure increases. Studies reveal that sp2 hybridization exists in the Be atoms and their 2p orbitals accept electrons from the Zr atoms, leading them to have an unusual negative valency. Calculated elastic properties imply that ZrBeSi is mechanically stable but anisotropic up to 175 GPa. It has a bulk modulus of 144.4 (142.5) GPa deduced from the third‐order Birch–Murnaghan equation of state (elastic constants) at 0 GPa. Its elastic moduli and elastic anisotropy increase with the rising pressure. Group theory analysis unveils that there are six infrared‐active and four Raman‐active modes at the Brillouin zone center of ZrBeSi. The vibrational patterns of these modes are presented and discussed. Studies further reveal that the frequencies of these modes increase with the rising pressure. [ABSTRACT FROM AUTHOR]