Investigation of the structural, electronic and mechanical properties of CaO–SiO_(2) compound particles in steel based on density functional theory

CaO–SiO_(2)compounds compromise one of the most common series of oxide particles in liquid steels, which could significantly affect the service performance of the steels as crack initiation sites. However, the structural, electronic, and mechanical properties of the compounds in CaO–SiO_(2)system are still not fully clarified due to the difficulties in the experiments. In this study, a thorough investigation of these properties of CaO–SiO_(2)compound particles in steels was conducted based on first-principles density functional theory. Corresponding phases were determined by thermodynamic calculation, including gamma dicalcium silicate(γ-C2S), alpha-prime(L) dicalcium silicate(αL′-C2S), alpha-prime(H) dicalcium silicate(αH′-C2S), alpha dicalcium silicate(α-C2S), rankinite(C3S2), hatrurite(C3S), wollastonite(CS), and pseudowollastonite(Ps-CS). The results showed that the calculated crystal structures of the eight phases agree well with the experimental results. All the eight phases are stable according to the calculated formation energies, and γ-C2S is the most stable. O atom contributes the most to the reactivity of these phases. The Young’s modulus of the eight phases is in the range of 100.63–132.04 GPa. Poisson’s ratio is in the range of0.249–0.281. This study provided further understanding concerning the CaO–SiO_(2)compound particles in steels and fulfilled the corresponding property database, paving the way for inclusion engineering and design in terms of fracture-resistant steels.

Effect of Exchange-Correlation Functional on the Structural, Mechanical, and Optoelectronic Properties of Orthorhombic RbSrBr3 Perovskite

In the present study, the effect of the exchange-correlation functional on the structural, mechanical, and optoelectronic properties of orthorhombic RbSrBr3 perovskite has been investigated using various functionals in Density Functional Theory (DFT) with the CASTEP code. The optimized lattice parameters are quite similar for all the functionals. The electronic properties have shown that RbSrBr3 perovskite is a wide direct band gap compound with a band gap energy ranging from 4.296 eV to 4.494 eV for all the functionals. The mechanical parameters like elastic constants, Young’s modulus, Shear modulus, Poisson’s ratio, Pugh’s ratio, and an anisotropic factor reveal that the RbSrBr3 perovskite has ductile behavior and an anisotropic nature which signifies the mechanical stability of the compound. The Debye temperature might withstand lattice vibration heat. High absorption coefficient (>104 cm−1), high optical conductivity, and very low reflectivity have been found in the RbSrBr3 perovskite for all functions. The computed findings on the RbSrBr3 perovskite suggested that the presented studied material is potentially applicable for photodetector and optoelectronic devices.

Density functional theory study of influence of impurity on electronic properties and reactivity of pyrite

The electronic property of pyrite supercell containing As,Se,Te,Co or Ni hetero atoms were calculated using density functional theory（DFT）,and the reactivities of pyrite with oxygen and xanthate were discussed by frontier orbital methods.The cell volume expands due to the presence of impurity.Co and Ni mainly affect the bands near Fermi levels,while As mainly affects the shallow and deep valence bands,and Se and Te mainly affect the deep valence bands.Electronic density analysis suggests that there exists a strong covalent interaction between hetero atom and its surrounding atoms.By frontier orbital calculation,it is suggested that As,Co and Ni have greater influence on the HOMO and LUMO of pyrite than Se and Te.In addition,pyrite containing As,Co or Ni is easier to oxidize by oxygen than pyrite containing Se or Te,and pyrite containing Co or Ni has greater interaction with collector.These are in agreement with the observed pyrite practice.

Density Functional Theory Study on Electronic and Magnetic Properties of Mn-doped （MgO）n （n=2-10） Clusters

We study the geometries, stabilities, electronic and magnetic properties of （MgO）n （n=2-10） clusters doped with a single Mn atom using the density functional theory with the gener- alized gradient approximation. The optimized geometries show that the impurity Mn atom prefers to replace the Mg atom which has low coordination number in all the lowest-energy MnMgn-1On （n=2-10） structures. The stability analysis clearly represents that the average binding energies of the doped clusters are larger than those of the corresponding pure （MgO）n clusters. Maximum peaks of the second order energy differences are observed for MnMg~_1On clusters at n=6, 9, implying that these clusters exhibit higher stability than their neighboring clusters. In addition, all the Mn-doped Mg clusters exhibit high total magnetic moments with the exception of MnMgO2 which has 3.00μB. Their magnetic behavior is attributed to the impurity Mn atom, the charge transfer modes, and the size of MnMgn- 1On clusters.

Investigations of phase transition, elastic and thermodynamic properties of GaP by using the density functional theory

The phase transition of gallium phosphide （GAP） from zinc-blende （ZB） to a rocksalt （RS） structure is investigated by the plane-wave pseudopotential density functional theory （DFT）. Lattice constant a0, elastic constants cij, bulk modulus B0 and the pressure derivative of bulk modulus B0 are calculated. The results are in good agreement with numerous experimental and theoretical data. From the usual condition of equal enthalpies, the phase transition from the ZB to the RS structure occurs at 21.9 GPa, which is close to the experimental value of 22.0 GPa. The elastic properties of GaP with the ZB structure in a pressure range from 0 GPa to 21.9 GPa and those of the RS structure in a pressure range of pressures from 21.9 GPa to 40 GPa are obtained. According to the quasi-harmonic Debye model, in which the phononic effects are considered, the normalized volume V/Vo, the Debye temperature 8, the heat capacity Cv and the thermal expansion coefficient a are also discussed in a pressure range from 0 CPa to 40 GPa and a temperature range from 0 K to 1500 K.

Density-functional theory study of the effect of pressure on the elastic properties of CaB_6

Under high pressure, the long believed single-phase material CaB6 was latterly discovered to have a new phase tI56. Based on the density-functional theory, the pressure effects on the structural and elastic properties of CaB6 are obtained. The calculated bulk, shear, and Young’s moduli of the recently synthesized high pressure phase tI56-CaB6 are larger than those of the low pressure phase. Moreover, the high pressure phase of CaB6 has ductile behaviors, and its ductility increases with the increase of pressure. On the contrary, the calculated results indicate that the low pressure phase of CaB6 is brittle. The calculated Debye temperature indicates that the thermal conductivity of CaB6 is not very good. Furthermore, based on the Christoffel equation, the slowness surface of the acoustic waves is obtained.

Structures and electronic properties of Si_m N_(8-m)(0

The geometries, electronic structures and related properties of SimN8-m（0 〈 m 〈 8） clusters are studied using density functional theory （DFT） with hybrid functional B3LYP. The calculated results reveal several trends. For any stoichiometric clusters, the lowest energy isomers with an alteration of N and Si atoms are favourable in energy if the numbers of Si and N atoms are large enough to form ... Si N-Si-N... alternative chains. The bond lengths of single Si-N bonds are very close to the corresponding values of the bulk and other SiN clusters. The geometries for N-rich and Si4N4 clusters are planar structures, but three-dimensional structures are favourable in energy for Si-rich clusters. With the increase of m, the isotropic polarizability and average polarizability increase, the total binding energies generally decrease, the HOMO-LUMO gap and vertical ionization potential oscillate with increasing number of valence electrons, and their values with even valence electrons are larger than those with odd valence electrons. The atomic charges, IR and Raman properties are also reported.

Pressure-dependent physical properties of cubic SrΒO3(Β=Cr,Fe)perovskites investigated by density functional theory

We perform the first-principles investigations of the structural,elastic,electronic,and optical properties of SrBO3(B=Cr,Fe)perovskites under pressure based on density functional theory(DFT).This is the first detailed pressure-dependent study of the physical properties for these compounds.The calculated structural parameters are consistent with the existing experimental results and slightly decrease with the application of pressure.The mechanical properties are discussed in detail and reveal that the SrCrO3 is harder than SrFeO3.Without pressure,these compounds behave like half-metals,confirmed by their band structure and density of states.Although the SrCrO3 retains its half-metallic nature under pressure,SrFeO3 becomes metallic for both up-spin and down-spin configuration.Both charge density and bond overlap population reveal the covalent nature of Cr–O bond and Fe–O bond in the studied compounds.The optical properties of SrBO3,also discussed for the first time,reveal some interesting results.

High-throughput calculations combining machine learning to investigate the corrosion properties of binary Mg alloys

Magnesium(Mg)alloys have shown great prospects as both structural and biomedical materials,while poor corrosion resistance limits their further application.In this work,to avoid the time-consuming and laborious experiment trial,a high-throughput computational strategy based on first-principles calculations is designed for screening corrosion-resistant binary Mg alloy with intermetallics,from both the thermodynamic and kinetic perspectives.The stable binary Mg intermetallics with low equilibrium potential difference with respect to the Mg matrix are firstly identified.Then,the hydrogen adsorption energies on the surfaces of these Mg intermetallics are calculated,and the corrosion exchange current density is further calculated by a hydrogen evolution reaction(HER)kinetic model.Several intermetallics,e.g.Y_(3)Mg,Y_(2)Mg and La_(5)Mg,are identified to be promising intermetallics which might effectively hinder the cathodic HER.Furthermore,machine learning(ML)models are developed to predict Mg intermetallics with proper hydrogen adsorption energy employing work function(W_(f))and weighted first ionization energy(WFIE).The generalization of the ML models is tested on five new binary Mg intermetallics with the average root mean square error(RMSE)of 0.11 eV.This study not only predicts some promising binary Mg intermetallics which may suppress the galvanic corrosion,but also provides a high-throughput screening strategy and ML models for the design of corrosion-resistant alloy,which can be extended to ternary Mg alloys or other alloy systems.

Study on lattice vibrational properties and Raman spectra of Bi_2Te_3 based on density-functional perturbation theory

We present a variational density-functional perturbation theory （DFPT） to investigate the lattice dynamics and vibra- tional properties of single crystal bismuth telluride material. The phonon dispersion curves and phonon density of states （DOS） of the material were obtained. The phonon dispersions are divided into two fields by a phonon gap. In the lower field, atomic vibrations of both Bi and Te contribute to the DOS. In the higher field, most contributions come from Te atoms. The calculated Born effective charges and dielectric constants reveal a great anisotropy in the crystal. The largest Born effective charge generates a significant dynamic charge transferring along the c axis. By DFPT calculation, the greatest LO-TO splitting takes place in the infrared phonon modes and reaches 1.7 THz in the Brillouin zone center. The Raman spectra and peaks corresponding to respective atomic vibration modes were found to be in good agreement with the experimental data.

Electronic and Optical Properties of Rocksalt CdO: A first-Principles Density-Functional Theory Study

The structural, electronic and optical properties of rocksalt CdO have been studied using the plane-wave-based pseudo-potential density functional theory within generalized gradient approximation. The calculated lattice parameters are in agreement with previous experimental work. The band structure, density of states, and Mulliken charge population are obtained, which indicates that rocksalt CdO having the properties of a halfmetal due to an indirect band gap of -0.51eV. The mechanical properties show that rocksalt CdO is mechanically stable, isotropic and malleable. Significantly, we propose a correct value for ε1(0) of about 4.75, which offers theoretical data for the design and application for rocksalt CdO in optoelectronic materials.

Structures, stabilities, and electronic properties of F-doped Sin （n=1～12） clusters：Density functional theory investigation

The geometries, stabilities, and electronic properties of FSin （n=1～12） clusters are systematically investigated by using first-principles calculations based on the hybrid density-functional theory at the B3LYP/6-311G level. The geometries are found to undergo a structural change from two-dimensional to three-dimensional structure when the cluster size n equals 3. On the basis of the obtained lowest-energy geometries, the size dependencies of cluster properties, such as averaged binding energy, fragmentation energy, second-order energy difference, HOMO–LUMO （highest occupied molecular orbital–lowest unoccupied molecular orbital） gap and chemical hardness, are discussed. In addition, natural population analysis indicates that the F atom in the most stable FSin cluster is recorded as being negative and the charges always transfer from Si atoms to the F atom in the FSin clusters.

Structure,electronic,and nonlinear optical properties of superalkaline M_(3)O(M=Li,Na)doped cyclo[18]carbon

Cyclo[18]carbon has received considerable attention thanks to its novel geometric configuration and special electronic structure.Superalkalis have low ionization energy.Doping a superalkali in cyclo[18]carbon is an effective method to improve the optical properties of the system because considerable electron transfer occurs.In this paper,the geometry,bonding properties,electronic structure,absorption spectrum,and nonlinear optical(NLO)properties of superalkaline M_(3)O(M=Li,Na)-doped cyclo[18]carbon were studied by using density functional theory.M_(3)O and the C_(18) rings are not coplanar.The C_(18) ring still exhibits alternating long and short bonds.The charge transfer between M_(3)O and C_(18) forms stable[M_(3)O]+[C_(18)]-ionic complexes.C_(18)M_(3)O(M=Li,Na)shows striking optical nonlinearity,i.e.,their first-and second-order hyperpolarizability(βvec andγ||)increase considerably atλ=1907 nm and 1460 nm.

Crystal Structure and Density Functional Theory Studies of (p-Methoxyphenyl) Thiosemicarbazide

The title compound [CH3OC6H4NHNHCSNH2] has been characterized by ele- mental analysis, IR, electronic absorption spectra and X-ray single-crystal diffraction. It crystallizes in the monoclinic system, space group C2/c with a = 25.071(5), b = 5.9292(12), c = 14.938(3) ?, β = 118.40(3)o, Mr = 197.26 (C8H11N3OS), V = 1953.3(7) ?3, Z = 8, Dc = 1.342 g/cm3, F(000) = 832, μ = 0.296 mm-1, R = 0.0647 and wR = 0.1433. In the crystal lattice, there exist some intermolecular hydrogen bonds, π-π stacking interactions and C–H…π supramolecular interactions to stabilize the crystal structure. The density functional theory (DFT) calculations at the B3LYP/6-31G* level, charge distributions and thermodynamic properties at different temperature have been performed, showing the sulfur and nitrogen atoms have bigger negative charges because they are the potential sites reacting with the metallic ions.

Studies of n-Octanol/water Partition Coefficients (lgK_(ow)) for Organophosphate Compounds by Density Functional Theory

Optimized calculation of 35 dialkyl phenyl phosphate compounds （OPs） was carded out at the B3LYP/6-31G^＊ level in Gaussian 98 program. Based on the theoretical linear solvation energy relationship （TLSER） model, the obtained parameters were taken as theoretical descriptors to establish the novel QSPR model for predicting n-octanol/water partition coefficients （lgKow） of OPs. The new model achieved in this work contains three variables, i.e., molecular volume （Vm）, dipole moment of the molecules （μ） and enthalpy （H^0）. For this model, R^2 = 0.9167 and SD = 0.31 at large t values. In addition, the variation inflation factors （VIF） of variables are all close to 1.0, suggesting high accuracy of the predicting model. And the results of cross-validation test （q^2 = 0.8993） and method validation also showed the model of this study exhibited optimum stability and better predictive power than that from semi-empirical method. The model achieved can be used to predict IgKow of congeneric compounds.

Density Function Theory Study of Electronic,Optical and Thermodynamic Properties of CaN_2,SrN_2 and BaN_2

We put forward a first-principles density-functional theory about the impact of pressure on the structural and elastic properties of bulk CaN2,SrN2 and BaN2.The ground state properties of three alkaline earth diazenides were obtained,and these were in good agreement with previous experimental and theoretical data.By using the quasi-harmonic Debye model,the thermodynamic properties including the debye temperature ΘD,thermal expansion coefficient α,and gruneisen parameter y are successfully obtained in the temperature range from 0 to 100 K and pressure range from 0 to 100 GPa,respectively.The optical properties including dielectric function ε（ω）,absorption coefficient α（ω）,reflectivity coefficient R（ω）,and refractive index n（ω） are also calculated and analyzed.

Structures and electronic properties of Mo_(2n)N_n(n=1-5):a density functional study

The lowest-energy structures and the electronic properties of Mo2nNn （n=1-5） clusters have been studied by using the density functional theory （DFT） simulating package DMol3 in the generalized gradient approximation （GGA）. The resulting equilibrium geometries show that the lowest-energy structures are dominated by central cores which correspond to the ground states of Mon （n = 2, 4, 6, 8, 10） clusters and nitrogen atoms which surround these cores. The average binding energy, the adiabatic electron affinity （AEA）, the vertical electron affinity （VEA）, the adiabatic ionization potential （AIP） and the vertical ionization potential （VIP） of Mo2nNn （n=1-5） clusters have been estimated. The HOMO LUMO gaps reveal that the clusters have strong chemical activities. An analysis of Mulliken charge distribution shows that charge-transfer moves from Mo atoms to N atoms and increases with cluster size.

Structural,Electronic and Magnetic Properties of ConO(n=2-10)Clusters:A Density Functional Study

The structural, electronic, and magnetic properties of ConO （n = 2- 10） clusters have been systematically investigated within the framework of the generalized gradient approximation density functional theory. The results indicate that the O atom occupies the surface-capped position on ConO （n = 2-10） clusters. The stabilities of the host clusters are improved by adding one O atom. Maximum peaks of the second-order difference energy of the ground-state ConO clusters are found at n = 3, 6 and 8, indicating higher stability than their neighboring clusters. Compared with corresponding pure Con clusters, the O-doped cobalt clusters have larger gaps between the HOMO and LUMO energy levels, indicating their higher chemical stabilities. In addition, the doping of O atom exhibits different influence on the magnetism of the clusters. This is also further investigated by the local magnetic moment, deformation charge density and partial local density of states analysis.

Theoretical Study on the Optical Properties for 2,7- and 3,6-Linked Carbazole Trimers by Time-dependent Density Functional Theory

Electronic properties, such as HOMO and LUMO energies, band gaps, ionization potential （IP） and electron affinity （EA） of 2,7- and 3,6-1inked carbazole trimers, two conjugated oligomcrs with different linkages of carbazole, were studicd by the density functional theory with Becke-Lee-Young-Parr composite exchange correlation functional （B3LYP）. The absorption spectra of these compounds were also investigated by time-dependent density functional theory （TD-DFT） with 6-3 IG＊ basis set. The calculated results indicated that the HOMO and LUMO of the 2,7- and 3,6-1inked carbazole trimers are both slightly destabilized on going from methyl substitution to sec-butyl substitution. Both IP and EA exhibit their good hole-transporting but poor electronaccepting ability. The presence of alkyl groups on the nitrogen atoms does not affect the intra-chain electronic delocalization along the molecular frame. Thus no significant effect on the band gap and absorption spectra of compounds has been found.