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In the present work, the structural, magnetic, and theoretical analysis of the Fe–Si alloy prepared by melting and heat-treated was performed. The ordered FeSi simple cubic (sc) phase was obtained by melting and heat treatment processes as determined by X-ray diffraction. The presence of the superstructure peak in the (312) crystalline direction confirms the high structural order reached. Using Mossbauer spectrometry (MS), a paramagnetic behavior with quadrupole splitting of SQ = 0.53 ± 0.02 mm/s was obtained. Although MS indicates paramagnetic behavior, vibrating sample magnetometry (VSM) showed ferromagnetic behavior with a coercive field of 25 Oe, associated with a small amount of Fe3Si segregations detected by scanning electron microscopy/energy dispersive spectrometry (SEM/EDS). Using density functional theory (DFT), the crystalline structures for the simple cubic (sc) Fe50Si50, face-centered cubic (fcc) Fe3Si, and body-centered cubic (bcc) Fe3Si crystalline structures were simulated. Electron total density values were calculated to perform energetic comparisons with magnetic behavior. The electronic structures and magnetic properties of the Fe–Si alloys in different stoichiometric configurations were calculated by CASTEP, which employed first principles DFT. The density of states (DOS) and band structures were calculated together with magnetic properties. The results showed that the high value of the polarization spin for the fcc and bcc structures is due to the contribution of the high amount of Fe atoms above the Si atoms, which is reflected in an increase in the magnetic moment and that their presence could explain the ferromagnetic behavior observed by VSM.

First-principles calculations, with CASTEP code, were employed to study the effect of lithium (Li) and beryllium (Be) doping on structural stability, phase transformation, electronic band structure and optical characteristics of CaTiO3. The substitution of Ca-atoms with the Li- and Be-atoms changes the lattice parameters and hence unit cell volume and consequently the electronic band structure of CaTiO3 is modified. With 12.5% Li- and Be-doping, we observed a structural phase transformation from cubic to pseudo-cubic tetragonal structure which is in good agreement with the literature. The impact of structural phase transformation on the electronic band structure has been explained with the help of total, partial and elemental partial density of states. In case of Li-doping, the value of band gap slightly increases from 1.866 to 1.964 eV while the band gap value decreases to 1.614 eV for Be-doping. In both cases of doping, maxima of valence band are shifted from R to Z symmetry point whereas the minima of conduction band remain at G symmetry point. In pure and doped cases, the nature of the band gap remains unaltered, i.e., indirect band gap. From optical response of the doped compounds, we perceive a red shift in the absorption. With Be- and Li-doping, the static refractive index also increased from 2.48 to 2.63 and 4.1, respectively. The change in electronic structure and optical characteristic with Li- and Be-doping would make this compound a suitable candidate for future optoelectronic devices.

A novel synthesis blend of sodium carboxymethyl cellulose (CMC) with thiobarbituric acid (TBA) [CMC + TBA]B has been doped with CuO to study the optical and direct electrical (DC) properties of [CMC + TBA/CuO]C nanocomposite films. Different characterization techniques for [CMC]TF, [TBA]TF, [CMC + TBA]B and [CMC + TBA/CuO]C such as Fourier-transform infrared spectroscopy (FTIR), Ultraviolet–visible spectroscopy (UV-Vis), X-ray diffraction (XRD), Scanning electron microscopy (SEM) and optical properties have been used. SEM showed a good dispersion of copper oxide nanoparticles [CuO]NPs on [CMC + TBA]B film surface. The dielectric constant e(ω), optical conductivity σ(ω) and DC properties increased and demonstrated wave-like performance with increasing [CuO]NPs ratio at hν range of 0.7 eV – 5.0 eV. Copper content [CuO]NPs increases lead to the formation of a wide variety of 3D-semiconductor networks within [CMC + TBA]B film matrix which increase optical conductivity. The optimization was performed using density functional theory (DFT) by DMol3 and Cambridge Serial Total Energy Package (CASTEP). In Experimental section by using Tauc’s equation, the results clearly show that the values of optical energy band gap $$ {E}_g^{Opt} $$ decreases from 2.978 eV for [CMC]TF, 2.725 eV for [TBA]TF, 2.625 eV for [CMC + TBA]B to 2.488 eV for [CMC + TBA/CuO]C. The simulated FTIR, XRD, and optical properties by Gaussian software and CATSTEP are in great agreement with the experimental study. The [CMC + TBA/CuO]C presents a good candidate for optoelectronics and solar cell applications.

First-principles calculations are carried out by DFT within the CASTEP plane wave code to investigate the mechanical properties and electronic structure of N and Al doped TiC. The results show that the co-doping of nitrogen and aluminum narrows the lattice constant and nitrogen could enhance the stability of TiC, however, aluminum makes the compound unstable. The calculated elastic constants and elastic moduli reveal that aluminum reduces the elastic constants, bulk modulus B, shear modulus G and Young's modulus E, but nitrogen can enhance them. The results of B/G and C12–C44 indicate that aluminum could significantly increase the ductility of TiC. Meanwhile, the electronic structure calculations reveal that strong p–d covalent bonds exist among C-p, N-p, Ti-d and Al-p states and Al-doping causes DOS peak transfer to a higher energy level and increases the DOS above the Fermi level. The hardness is estimated by a semi-empirical model that is based on the Mulliken overlap population and bond length. The addition of Al sharply reduces the hardness of the TiC-based alloys due to the weakest bond taking a determinative role in the hardness of materials, which is the C–Al bond in those compounds.

Thioborates compounds are receiving increasing attention due to their numerous optical applications. In this work, we present a theoretical prediction of physical properties of CuBS2 and AgBS2 compounds by mean the density functional theory using the pseudo potential plane-wave method implemented in ABINIT and CASTEP codes. We investigated the structure stability and other ground state properties. The dynamical stability is also discussed from the phonon dispersion for the new hypothetical phase. We used the hybrid functional to estimate the band gap. Moreover, we present the optical anisotropy and nonlinear optical properties, both studied compounds have wide band gap, adequate optical birefringence and good second order NLO coefficients, which make them potential candidates for NLO applications.

Graphene/MoS 2 has been widely used in optoelectronic devices due to its unique optical properties. First principles calculation on the properties of graphene/MoS 2 have been performed by using density functional theory (DFT) with a plane wave basis set as implemented in the CASTEP computer code. Electronic and optical properties were further discussed comprehensively to explain the electron transfer mechanism in atomic structure of graphene/MoS 2 . The results reveal the opening in graphene’s band gap at the k-point of the Brillouin zone when MoS 2 layer is introduced in the structure. The excellent absorption characteristic in the visible to ultraviolet region demonstrates the graphene/MoS 2 as a promising candidate material for broadband operation wavelength.

In the last decade, graphene has been researched extensively because of its unique chemical, electronic and physical properties that can be exploited for numerous applications. Graphene has shown promise in energy storage, gas sensors, nano- devices and catalysts. [1] Recent studies have shown that the presence of naturally occurring defects can activate graphene for chemical functionalization. [2] For instance, the presence of a simple single point vacancy defect has been shown to significantly increase chemical reactivity towards H2, NOx, SO2 and NH3. [3,4] Primarily, research has been carried out with the purpose of functionalizing this active site, typically through heteroatom doping of some form. [5] We have investigated the possibility of using the innate reactivity of the single vacancy to promote the dissociation of ammonia (NH3) and achieve graphitic nitrogen doping and hydrogen gas (H2) formation. Nitrogen doped graphene is a highly sought-after material, with applications in supercapacitors and bio-sensing technology. Meanwhile, efficient production and storage of H2 gas is highly desirable for a source of renewable energy. The dissociation pathway for ammonia with single vacancy graphene was studied through a series of calculations using CASTEP, an efficient and scalable plane waves DFT code. All calculations were spin polarised and paired with vdW corrections of the Tkatchenko-Scheffler (TS) type. We have found a potential dissociation pathway which ammonia could undergo at moderate temperatures, in which hydrogen movement was dominated by hydrogen diffusion steps from the defect site. References 1 L. Rodríguez-Pérez, M. Á. Herranz and N. Martín, Chem. Commun., 2013, 49, 3721–3735. 2 S. T. Skowron, I. V. Lebedeva, A. M. Popov and E. Bichoutskaia, , DOI:10.1039/c4cs00499j. 3 S. Dandeliya and S. Anurag, IEEE Sens. J., 2019, 19, 2031–2038. 4 X.-J. Wu, Z.-J. Fei, W.-G. Liu, J. Tan, G.-H. Wang, D.-Q. Xia, K. Deng, X.-K. Chen, D.-T. Xiao, S.-W. Wu and W. Liu, Nucl. Sci. Tech., 2019, 30, 69. 5 B. Wang, L. Tsetseris and S. T. Pantelides, J. Mater. Chem. A, 2013, 1, 14927.

International audience; A crystallographic approach incorporating multinuclear high field solid state NMR (SSNMR), X-ray structure determinations, TEM observation, and density functional theory (DFT) was used to characterize two polymorphs of rubid-ium cryolite, Rb3AlF6. The room temperature phase was found to be ordered and crystallizes in the Fddd (n°70) space group with a = 37.26491(1) Å, b = 12.45405(4) Å, c = 17.68341(6) Å. Comparison of NMR measurements and computational results revealed the dynamic rotations of the AlF6 octahedra. Using in-situ variable temperature MAS NMR measurements, the chemical exchange between rubidium sites was observed. The β-phase, i.e. high temperature polymorph, adopts the ideal cubic double-perovskite structure, space group 3 ̅ , with a = 8.9930(2) Å at 600 °C. Additionally, a series of polymorphs of K3AlF6 has been further characterized by high field high temperature SSNMR and DFT computation.

Effect of anomalous behavior of beryllium (Be) on structural stability, band gap engineering and optoelectronic properties in comparison with magnesium (Mg) doped BaZrO3 perovskite have been explored. All calculations have been performed, by constructing the supercell to overcome the boundary effects, with CASTEP code, established on DFT, by Perdew-Burke-Ernzerhof-Generalized-Gradient-Approximations (PBE-GGA) exchange correlation functional and USP (ultra-soft pseudo-potential). Various properties of the doped and pure compounds are probed such as the analysis of band structure, TDOS (total density of states), PDOS (partial density of states) and their effect on dielectric function. The substitution of Ba-atom with the Mg- and Be-atom change the lattice parameters and modify electronic structure of BaZrO3. In case of Mg and Be doping the value of band gap decreases from 3.119 to 2.844 eV and 0.886 eV. Due to doping of the Mg and Be doping valence band is shifted from R to G symmetry points whereas the conduction band is shifted from G to R symmetry points, with the emergence of new symmetry points, because of Mg- and Be-s-states and showing indirect band gap. From optical properties, a red shift in the absorption edge is noticed for both doped compounds. The static refractive index is also enhanced with Be-doping from of 2.2 to 2.32. The Be and Mg doping in BaZrO3 alters electronic and optical properties emphatically and models this doped material a very prospective contestant for optoelectronic devices.

Crystalline urea undergoes polymorphic phase transition induced by high pressure. Form I, which is the most stable form at normal conditions and Form IV, which is the most stable form at 3.10 GPa, not only crystallize in various crystal systems but also differ significantly in the unit cell dimensions. The aim of this study was to determine if it is possible to predict polymorphic phase transitions by optimizing Form I at high pressure and Form IV at low pressure. To achieve this aim, a large number of periodic density functional theory (DFT) calculations were performed using CASTEP. After geometry optimization of Form IV at 0 GPa Form I was obtained, performing energy minimization of Form I at high pressure did not result in Form IV. However, employing quantum molecular isothermal&ndash, isobaric (NPT) dynamics calculations enabled to accurately predict this high-pressure transformation. This study shows the potential of different approaches in predicting the polymorphic phase transition and points to the key factors that are necessary to achieve the success.

Calculations using the density-functional theory (DFT) in combination with the single defect method were carried out to determine the heat of mixing behaviour of mineral solid solution phases. The accuracy of this method was tested on the halitesylvite (NaClKCl) binary, pyropegrossular garnets (Mg3Al2Si3O12Ca3Al2Si3O12), MgOCaO (halite structure) binary, and on Al/Si ordered alkali feldspars (NaAlSi3O8KAlSi3O8); as members for coupled substitutions, the diopsidejadeite pyroxenes (CaMgSi2O6NaAlSi2O6) and diopsideCaTs pyroxenes (CaMgSi2O6CaAlAlSiO6) were chosen for testing and, as an application, the heat of mixing of the tremoliteglaucophane amphiboles (Ca2Mg5Si8O22(OH)2Na2Mg3Al2Si8O22(OH)2) was computed. Six of these binaries were selected because of their experimentally well-known thermodynamic mixing behaviours. The comparison of the calculated heat of mixing data with calorimetric data showed good agreement for halitesylvite, pyropegrossular, and diopsidejadeite binaries and small differences for the Al/Si ordered alkali feldspar solid solution. In the case of the diopsideCaTs binary, the situation is more complex because CaTs is an endmember with disordered cation distributions. Good agreement with the experimental data could be, however, achieved assuming a reasonable disordered state. The calculated data for the Al/Si ordered alkali feldspars were applied to phase equilibrium calculations, i.e. calculating the Al/Si ordered alkali feldspar solvus. This solvus was then compared to the experimentally determined solvus finding good agreement. The solvus of the MgOCaO binary was also constructed from DFT-based data and compared to the experimentally determined solvus, and the two were also in good agreement. Another application was the determination of the solvus in tremoliteglaucophane amphiboles (Ca2Mg5Si8O22(OH)2Na2Mg3Al2Si8O22(OH)2). It was compared to solvi based on coexisting amphiboles found in eclogites and phase equilibrium experiments. (VLID)4800049

The anisotropic BaFe12−xCoxO19 (x = 0, 0.3, 0.6, 0.9) (BFCO) samples were synthesized. We investigated the crystal structure, microstructure, and magnetic properties of BFCO. And the potential application value at millimeter waveband was discussed. The magnetic anisotropy field is successfully decrease from 17 kOe to 10 kOe by substituting Cobalt, which lower the Ferromagnetic resonance frequency and benefit for extending the bandwidth for the circulator. With the cobalt substitution, the saturation inevitably decreases from 60 emu/g to 45 emu/g. The site preference of cobalt in five crystallographically inequivalent Fe ions was calculated using software castep. The influence of site preference on lattice parameters and magnetic saturation was calculated and discussed. The result show cobalt mainly sites 2a and 12k position.

The molecular structure of 2,4−dinitroanisole (DNAN) is optimized using Gaussian 09W program, two stable molecular structures with different methoxy group orientations are obtained and vibrational frequencies are calculated for the two optimized molecular structures. DNAN crystal structure is optimized using CASTEP and VASP codes and phonon frequencies are calculated and assigned. Computed frequencies compare well with experimental values. Pressure dependent phase transformation in DNAN is investigated by Raman spectroscopy and X-ray diffraction. Differences between the Raman spectra of DNAN and trinitrotoluene (TNT) point to a larger phonon energy gap in DNAN to be a possible reason for the lower impact sensitivity of DNAN. Appearance of new Raman bands and discontinuity of the bands above 1.3 GPa indicates a phase transformation. Changes in the X-ray diffraction patterns confirm the phase transformation. The transformation of the ambient monoclinic to an orthorhombic structure starts at around 2 GPa. At 6.8 GPa the monoclinic structure completely transforms into orthorhombic with a volume collapse of 10%. Bulk moduli for the monoclinic and orthorhombic phases are estimated as ∼12 GPa and 27 GPa respectively, pointing to a lower impact sensitivity of the orthorhombic phase.

Powders of Fe50Al30Ni20 (wt%) are being milled in a P7 high-energy planetary ball mill to determine the effect of milling time on magnetic properties. In order to track changes in morphology and magnetic properties, SEM, magnetic measurements, and Mossbauer spectroscopy were employed during milling. Multiple phases are present; B2-(Fe, Ni)Al dominates, and Fe(Ni, Al) is second in strength. This indicates that they are paramagnetic at room temperature based on the Mossbauer effect spectra after 8 h of milling. The coercivity Hc and saturation magnetization, on the other hand, remains finite values in magnetic measurements. The CASTEP (Cambridge Serial Total Energy Package) code was used to investigate magnetic behavior further.

The CASTEP program based on density functional theory was used to study the effect of shear deformation on the structure, electronic and optical properties of hydrogenated silicene. The calculation results show that the hydrogenated silicene can still remain stable under the action of shear deformation. After the hydrogenation of silicene, the forbidden band width increases to 2.204 eV, and the electrical conductivity is significantly improved. Shear deformation significantly affects the energy band structure characteristics of hydrogenated silicene. The resulting band gap gradually decreases as the deformation increases. The shear deformation causes the red shift of the imaginary part of the dielectric function of the hydrogenated silicene to the direction of lower energy. Shear deformation improves the luminous efficiency of the system. The peak range of the reflection spectrum gradually widens with the increase of the deformation. These properties may be applied to optoelectronic devices in the future.

The influence of the reaction gas composition during the DC magnetron sputtering process on the structural, chemical and optical properties of Ce-oxide thin films was investigated. X-ray diffraction (XRD) studies confirmed that all thin films exhibited a polycrystalline character with cubic fluorite structure for cerium dioxide. X-ray photoelectron spectroscopy (XPS) analyses revealed that cerium is present in two oxidation states, namely as CeO2 and Ce2O3, at the surface of the films prepared at argon-oxygen flow ratios between 0–7%, whereas the films are completely oxidized into CeO2 as the aforementioned ratio increases beyond 14%. Various optical parameters for the thin films (including an optical band gap in the range of 2.25 – 3.1 eV) were derived from the UV-Vis reflectance. A significant change in the band gap was observed as the oxygen pressure was raised from 7% to 14% and this finding is consistent with the high-resolution XPS analysis of Ce 3d that reports a mixture of Ce2O3 and CeO2 in the films. Density functional theory (DFT+U) implemented in the Cambridge Serial Total Energy Package (CASTEP) was carried out to simulate the optical constants of CeO2 clusters at ground state. The computed electronic density of states (DOSs) of the optimized unit cell of CeO2 yields a band gap that agrees well with the experimentally measured optical band gap. The simulated and measured absorption coefficient (α) exhibited a similar trend and, to some extent, have similar values in the wavelength range from 100 to 2500 nm. The combined results of this study demonstrate good correlation between the theoretical and experimental findings.

The structures of Si2P2O and Ge2P2O with the space group Cmc21 are derived. The structural, mechanical, elastic anisotropy, electronic and optoelectronic properties are calculated by first principles calculations based on density functional theory (DFT) with generalized gradient approximation (GGA) at high pressure for Si2P2O and Ge2P2O. By using the elastic stability criteria, it is shown that their structures are all stable. The phonon dispersion spectra are researched throughout the Brillouin zone as implemented in the CASTEP code, which indicates that the optimized structures are stable dynamically. The brittle/ductile behaviors are assessed in the pressures from 0 GPa to 50 GPa. Our calculations present that the performances of them become ductile with pressure rise. Moreover, the anisotropies of them are discussed by the Young's moduli at different pressure, and the results indicate that the anisotropies of them are obvious. The direct band structures of Ge2P2O and the indirect band gap of Si2P2O show that Si2P2O and Ge2P2O present semiconducting character at 0 GPa and 50 GPa. The band structures of Si2P2O are changed obviously with the increase of pressure. The total DOS originate mainly from O ‘s’ states, O ‘p’ states, P ‘s’ states and P ‘p’ states and M ‘p’ states (M=Si, Ge). The trends of DOS for Si2P2O and Ge2P2O display many similarities, and the change of DOS is obviously affected by the pressure for Si2P2O. The optoelectronic properties of them are researched. The calculated static dielectric constants, ɛ1(0), are 3.2 at 0 GPa and 6.4 at 50 GPa for Si2P2O, and the values of Ge2P2O are 10.2 and 9.2 at 0 GPa and 50 GPa.

Perovskite materials possess promising application prospects in photovoltaics and are most likely to replace the dominance of silicon-based solar photovoltaic materials. (K 0.5 Na 0.5 )NbO 3 – x Fe 2 O 3 perovskite ferroelectric ceramics ( x = 0, 0.01, and 0.05) were prepared using a conventional solid-state reaction method. We systematically analyzed the structural, morphological, electric, magnetic, and optical properties. Structural and morphological features of the as-prepared ceramics show that the phases of the materials all are orthorhombic. The appropriate amount of Fe 2 O 3 introduced will improve the electrical properties. Magnetic switching corresponding to a diamagnetic-ferromagnetic transformation was observed. Bandgap ( E g ) modulation was achieved in the Fe 2 O 3 -doped KNN ceramics, with the E g exhibiting a drastic decrease as the doping content increased in experiment where the E g = 2.886, 2.232, and 2.061 eV when x = 0, 0.01, and 0.05, and the CASTEP calculation shows a similar trend, indicating that the materials exhibit a higher performance with the absorption in visible light.

Sorption of Se(IV) and Se(VI) species onto Mg-rich biotite (phlogopite) and calcite surfaces was investigated using molecular modelling techniques. A CASTEP code implemented into Materials Studio was used to calculate the periodic systems, site densities and site types on the phlogopite and calcite surfaces. According to the results, the Se oxyanions attach to both edge and basal surfaces of phlogopite via an oxygen atom. However, calculated sorption energies indicate that surface complexation reactions via hydrogen bonding happen on the edge surfaces of phlogopite while cation exchange reactions happen on the basal surfaces of phlogopite. These reactions occur on the so-called weak sites according to the PHREEQC modelling. On the calcite surface, only cation exchange reactions are possible, and only for neutral Se species which do not occur in low saline groundwater conditions with pH 8–10. Biotite which is an abundant mineral in crystalline rock works fairly well as a sorbent but calcite which often exists on fracture surfaces of bedrock does not act as a sorbent for Se species.

Calculations using the density-functional theory (DFT) in combination with the single defect method were carried out to determine the heat of mixing behaviour of mineral solid solution phases. The accuracy of this method was tested on the halite–sylvite (NaCl–KCl) binary, pyrope–grossular garnets (Mg3Al2Si3O12–Ca3Al2Si3O12), MgO–CaO (halite structure) binary, and on Al/Si ordered alkali feldspars (NaAlSi3O8–KAlSi3O8); as members for coupled substitutions, the diopside–jadeite pyroxenes (CaMgSi2O6–NaAlSi2O6) and diopside–CaTs pyroxenes (CaMgSi2O6–CaAlAlSiO6) were chosen for testing and, as an application, the heat of mixing of the tremolite–glaucophane amphiboles (Ca2Mg5Si8O22(OH)2–Na2Mg3Al2Si8O22(OH)2) was computed. Six of these binaries were selected because of their experimentally well-known thermodynamic mixing behaviours. The comparison of the calculated heat of mixing data with calorimetric data showed good agreement for halite–sylvite, pyrope–grossular, and diopside–jadeite binaries and small differences for the Al/Si ordered alkali feldspar solid solution. In the case of the diopside–CaTs binary, the situation is more complex because CaTs is an endmember with disordered cation distributions. Good agreement with the experimental data could be, however, achieved assuming a reasonable disordered state. The calculated data for the Al/Si ordered alkali feldspars were applied to phase equilibrium calculations, i.e. calculating the Al/Si ordered alkali feldspar solvus. This solvus was then compared to the experimentally determined solvus finding good agreement. The solvus of the MgO–CaO binary was also constructed from DFT-based data and compared to the experimentally determined solvus, and the two were also in good agreement. Another application was the determination of the solvus in tremolite–glaucophane amphiboles (Ca2Mg5Si8O22(OH)2–Na2Mg3Al2Si8O22(OH)2). It was compared to solvi based on coexisting amphiboles found in eclogites and phase equilibrium experiments.

The phase composition, crystal structure and microwave dielectric properties of (1-x) (3ZnO-Nb2O5)-xGeO2 were investigated systematically. The phase composition and phase transformation of (1-x) (3ZnO-Nb2O5)-xGeO2 ceramics were confirmed by XRD refinement, SEM micrographs and EDS analysis. All sintered samples were composed of Zn3Nb2O8 and ZnNb2O6 phases. Phase transition between Zn3Nb2O8 and ZnNb2O6 was closely related the introduction of GeO2. When the doping content was low (x = 0–0.007), the phase transformation from ZnNb2O6 to Zn3Nb2O8 occurred, which was discovered for the first time. To clarify the phase transition, the local charge density and band structures were calculated using the CASTEP program. With the substitution of Ge4+, part of the electrons transferred from the oxygen atom to the middle of 'niobium-oxygen' and 'zinc-oxygen'. According, the covalency of 'niobium-oxygen' and 'zinc-oxygen' was enhanced. The shrinkage of ZnO6 octahedron resulted in a decrease in the coordination number of zinc atoms. At last, the relationships between phase transition, crystal structure and the microwave performance were established. The system of 2.73ZnO-0.91Nb2O5-0.09GeO2 sintered at 1150 °C for 6 h had excellent microwave dielectric properties: er = 21.3, Qf = 99,140 GHz, τf = −54 ppm/°C, which, to our best knowledge, the best performance with relative lower sintering temperature.

In this paper, we have study the structural, elastic, electronic, mechanical, optical and thermodynamic properties of NdPb3 intermetallic compound using density functional theory (DFT) with CASTEP code for the first time. The structural and other physical properties of NdPb3 compared with the results where available and show well accord. The optimized lattice parameters show a good agreement with the experimental data. The elastic constants C i j , bulk modulus B, shear modulus G, Young's modulus Y and Poisson's ratio v are optimized and discussed by using the Voigt-Reuss-Hill (VRH) approximation. The elastic constants show that NdPb3 is a mechanical stable compound. Cauchy pressure, Pugh's ratio and Poisson's ratio indicate that NdPb3 is also a ductile compound associated with ionic bonding nature. Zener's anisotropy index and universal anisotropic index show the anisotropic characteristics of this compound. The density of states (DOS) at Fermi level is high which is mainly contributed by Nd 4f indicates the metallic behavior of this compound. The metallic behavior also characterized by band structure and conductivity. This compound is a good reflector at low energies also have a good quality of absorption at visible region. We also determined the Debye temperature from elastic constants, minimum thermal conductivity, melting temperature sound velocities and D u l o n g − P e t i t l i m i t .

First-principles calculations were performed to explore the structural, elastic and electronic properties of the ternary indium chalcogenides AInQ 2 (A: K, Rb and Q: S, Se, Te) in both monoclinic and triclinic phases. This study is carried out by using the first-principles pseudopotential plane-wave (PP–PW) method as implemented in CASTEP code. Both the generalized gradient approximation of Perdew–Burke–Ernzerhof scheme (GGA–PBE) and the Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional were used to treat the exchange-correlation interactions. In order to confirm the previous reports and to understand the effect of symmetry in determining the physical properties of these layered materials we have calculated the structural and the electronic properties at the equilibrium lattice constant for both the systems. The single-crystal elastic constants C i j are calculated using the stress-strain approach. The elastic moduli of the polycrystalline aggregates and their related properties are obtained in the framework of Voigt–Reuss–Hill approximations. Electronic band structure indicates the semiconducting behaviour with a direct band gap at Γ–Γ. The results obtained from the (HSE06) hybrid functional are in excellent agreement with the available experimental data and computed results for the monoclinic and triclinic structures.

First principles calculations are applied in the study of FeMP (M = Ti, Zr, Hf) compounds. We investigate the structural, elastic, mechanical and electronic properties by combining first-principles calculations with the CASTEP approach. For ideal polycrystalline FeMP (M = Ti, Zr, Hf) the shear modulus, Young’s modulus, Poisson’s ratio, elastic anisotropy indexes, Pugh’s criterion, elastic wave velocities and Debye temperature are also calculated from the single crystal elastic constants. The shear anisotropic factors and anisotropy are obtained from the single crystal elastic constants. The Debye temperature is calculated from the average elastic wave velocity obtained from shear and bulk modulus as well as the integration of elastic wave velocities in different directions of the single crystal. Keywords: FeTP, FeHfP, Electronic band structure, Bulk moduli

Sr2 CeO4 phosphors with different crystalline sizes were synthesized by the sol-gel method or the solid-state reaction. Their crystalline size, luminescence intensity of O2- -Ce4+ charge transfer and energy gaps were obtained through the characterization by X-ray diffraction, photoluminescence spectra, as well as UV-visible diffuse reflectance measurements. An inverse relationship between photoluminescence (PL) spectra and crystalline size was observed when the heating temperature was from 1000°C to 1300°C. In addition, band energy calculated for all samples showed that a reaction temperature of 1200°C for the solid-state method and 1100°C for sol-gel method gave the largest values, which corresponded with the smallest crystalline size. Correlation between PL intensity and crystalline size showed an inverse relationship. Band structure, density of states and partial density of states of the crystal were calculated to analyze the mechanism using the cambrige sequential total energy package (CASTEP) module integrated with Materials Studio software.

As a newly discovered member of the tungstate family, InWO4 hollow nanospheres with a monoclinic wolframite structure were synthesized successfully. The crystal phase of InWO4 was investigated via a combination of CASTEP geometric optimization and experimental simulation. InWO4 has a space group of P2/c with two InWO4 formula units per unit cell. The optimized cell dimensions are a = 5.16 A, b = 5.97 A, and c = 5.23 A, with α = 90°, β = 92.11°, γ = 90°, giving a unit cell volume of 161.10 A3, which is consistent with the experimental measurements. More importantly, InWO4 was a promising host material for different Ln3+ (Ln = Eu and Yb/Er) ions. For InWO4:Yb3+/Er3+ excited at 980 nm, transitions from the 4G11/2 (384 nm), 2H9/2 (411 nm), and 4F7/2 (487 nm) levels to the ground state (4I15/2) of Er3+ were observed. In addition to the aforementioned properties, the InWO4 hollow nanospheres can be used to improve the performance of dye-sensitized solar cells, which is chiefly attributed to theirlight scattering.

Using surface photovoltaic and electric-field-induced surface photovoltaic techniques, as well as a CASTEP simulation method, we have studied the photo-excited and field-induced charge transfer (CT) behaviors of anatase nano-TiO2 particles adsorbed by O2, N2, and water vapor. Our results suggest that the photo-generated carriers transport process is strongly influenced by the adsorbates on the TiO2 nanoparticles. Oxygen molecules enhance the main-band-gap CT transition at 345 nm and inhibit the sub-band-gap CT transition at 419 nm. This can be explained by the 1 π g electrons in adsorbed O2 and the widened bandgap after adsorbing O2. Nitrogen molecules inhibit the main-band-gap and the sub-band-gap CT transitions differently. This can be explained by the 3 σ g and 1 π g electrons of adsorbed N2, which may cause more new surface states in between the bandgap and decrease the valence band edge of nano-TiO2, as suggested by the CASTEP simulation. The influence of adsorbed water molecule on the main-band-gap CT transition is much stronger than that on the sub-band-gap CT transition.

Data presented in this article are related to the research article entitled O2−–V5+ charge transfer band, chemical bond parameters and R/O of Eu3+ doped Ca(VO3)2 and Ca3(VO4)2: A comparable study[ing Li, Yu Pan, Wenjun Wang, Zihao Wen, Xuanxi Leng, Qi Wang, Liqun Zhou, Haibing Xu, Qinghua Xia, Li Liu, Hongping Xian, Xiaoguang Liu]. The data present the fitting results of the broad excitation spectra of Ca(VO3)2:1%Eu and Ca3(VO4)2:1%Eu using the Gaussian model, the O/R values using the experimental PL emission results. The data compares the optimized cell parameters for Ca(VO3)2: 1%Eu and Ca3(VO4)2:1%Eu through the CASTEP geometry optimization with their initial cell parameters.

The structural, elastic, electronic, Vickers-Hardness, vibrational, Optical and thermo dynamical properties of potentially technologically important superconductors BaRh 2 P 2 and SrIr 2 As 2 are calculated using density functional theory (DFT) with CASTEP code for the first time. The structural and other physical properties of BaRh 2 P 2 and SrIr 2 As 2 are compared with the results where available and show well accord. The phonon dispersion curve is calculated and the dynamical stability of this compound is investigated. Both the compounds show mechanically stable under the Born stability conditions. For the above condition BaRh 2 P 2 behaves ductile nature and SrIr 2 As 2 indicates the brittle nature. The Mulliken dislocation bonding population and charge density maps show stronger bond between As-Ir compared with Ir-Ir bond. The overall superior conversation reflects that the chemical bonding in BaRh 2 P 2 and SrIr 2 As 2 superconductors can be denominated as an extremely anisotropic connection between ionic, covalent and metallic interactions. At the Fermi level valence band and conduction bands overlapped, so the compounds are metal. From the Fermi surface and charge density map it is observed that both ionic and covalent bond exist. Vickers hardness reveals the both superconductors relatively soft with compare to Diamond. The optical and acoustic modes are observed clearly. We calculate the Helmholtz free energy ( F ), internal energy ( E ), entropy ( S ), and specific heat capacity ( C v ) from the phonon density of states. Various optical parameters are also calculated. The reflectance spectrum shows that this compound has the potential to be used as an efficient solar reflector. Debye temperature of BaRh 2 P 2 and SrIr 2 As 2 superconductors are 273.91 K and 341.03 K calculated by using present elastic constants data. The superconducting parameter indicates the phonon-mediated medium coupled BCS superconductors. The acquired results in present investigation could provide a great spur for future studies.

The aim of this study was to determine whether the periodic density functional theory (DFT) calculations can be used for accurate prediction of the influence of the increased pressure on crystal structure and stability of molecular solids. To achieve this goal a series of geometry optimization and thermodynamic parameters calculations were performed for γ-glycine and δ-glycine structures at different pressure values using CASTEP program. In order to perform most accurate geometry optimization various exchange-correlation functionals defined within generalized gradient approximation (GGA): PBE, PW91, RPBE, WC, PBESOL as well as defined within local density approximation (LDA), i.e. CAPZ, were tested. Geometry optimization was carried out using different dispersion correction methods (i.e. Grimme, TS, OBS) or without them. The linear response density functional perturbation theory (DFPT) was used to obtain the phonon dispersion curves and phonon density of states from which thermodynamic parameters, such as: free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were evaluated. The results of the geometry optimization depend strongly on the choice of the DFT functional. Calculated differences between the free energy of the studied polymorphic forms at the studied pressure values were consistent with experimental observations on their stability. The computations of thermodynamic properties not only confirmed the order of stability of two studied forms, but also enabled to predict the pressure at which this order is reversed. The results obtained in this study have proven that the plane-wave basis set first principles calculations under periodic conditions is suitable for accurate prediction of crystal structure and stability. © 2018 Wiley Periodicals, Inc.

The structural, elastic, optical and electronic behavior of CaSiO3 monoclinic polymorph are estimated utilizing ultrasoft pseudo-potential technique operated in CASTEP code. The calculated lattice parameters, such as lattice constants, angle β, and unit cell volume, are in excellent agreement with the experimental data. The computed elastic constant shows that CaSiO3 monoclinic is mechanical stable according to Born criteria. In addition, the polycrystalline properties such as bulk modulus, shear modulus, Young's modulus, Poisson's ratio, elastic anisotropy, compressibility and Debye temperature are determined based on the computed values of the elastic constants. Cauchy pressure and Poisson's ratio indicating a dominant ionic nature of the brittle CaSiO3 monoclinic. An Indirect band gap E (C-Г) = 5.02 eV, E (C-B) = 5.26 eV, and a direct gap E (Г-Г) = 5.06 eV were obtained. Finally, optical properties, such as dielectric function, absorption coefficient, refractive index, conductivity, loss function, and reflectivity have been predicted for polarized incident radiation with electrical vector E parallel to the crystalline b-axis.

A variety of uniform and well-dispersed one-dimensional Zn2GeO4:Mn2+ phosphors have been synthesized via a facile solvothermal process with H2O/EG as solvent. During the synthesis process, the component of solvent and the addition of PEG surfactant play an important role in determining the structure, particle size, and morphology of the final product. Under ultraviolet light excitation, the pure Zn2GeO4 sample shows bluish-white emission which is attributed to the native defects present in the Zn2GeO4 host. When Zn2+ ions are partially substituted by Mn2+, the as-synthesized Zn2GeO4:Mn2+ samples exhibit intense green emission that corresponds to the d-d transition (4T1→6A1) of Mn2+ ions. The luminescence mechanisms of the Zn2GeO4:Mn2+ samples were investigated in detail by using the CASTEP code based on density functional theory (DFT). It is expected that the as-synthesized Zn2GeO4:Mn2+ phosphors can be potentially applied in lighting, optical displays, and optoelectronic devices.

Important performance parameters of macro-structure exponential-doping Ga0.37Al0.63As are measured and some optical properties of micro-structure Ga0.37Al0.63As is calculated by quantum mechanics CASTEP software package based on the first principle density function theory. The relationships of properties and characteristics between micro-structure and macro-structure is inferred and investigated. We infer the threshold energy of quantum efficiency is the function of energy of band gap by comparing their close values and approximately equals the energy of vacuum level. The inference that electron escape probability is not always increasing as energy increase after a certain large energy with the comparison of adsorption coefficient trend diagram and reflectivity trend diagram is conducted, which we think the optical parameters of both would affect nv(E). Quantum efficiency is also related to optical properties of microstructure as shown in equations.

Glycine is a common amino acid with relatively complex chemistry in solid state. Although several polymorphs (α, β, δ, γ, e) of crystalline glycine are known, for NMR spectroscopy the most important is a polymorph, which is used as a standard for calibration of spectrometer performance and therefore it is intensively studied by both experimental methods and theoretical computation. The great scientific interest in a glycine results in a large number of crystallographic information files (CIFs) deposited in Cambridge Structural Database (CSD). The aim of this study was to evaluate the influence of the chosen crystal structure of α glycine obtained in different crystallographic experimental conditions (temperature, pressure and source of radiation of α glycine) on the results of periodic DFT calculation. For this purpose the total of 136 GIPAW calculations of α glycine NMR parameters were performed, preceded by the four approaches ("SP", "only H", "full", "full+cell") of structure preparation. The analysis of the results of those computations performed on the representative group of 34 structures obtained at various experimental conditions revealed that though the structures were generally characterized by good accuracy (R

A series of single component Sr3LuNa(PO4)3F:Eu2+,Mn2+ phosphors with tunable colours have been firstly obtained through solid state reactions. Structure optimization and electronic structure analysis of the host were performed by density functional theory using the CASTEP code. Sr3LuNa(PO4)3F:Eu2+ phosphors can be efficiently excited by n-UV light and give bright blue emission with good colour purity. Utilizing the Eu2+ → Mn2+ energy transfer, the Mn2+ ion was well sensitized and single component Sr3LuNa(PO4)3F:Eu2+,Mn2+ phosphors with tunable colours have been obtained successfully. The energy transfer mechanism was investigated by Dexter's energy transfer theory and the critical distance for the doped ions was calculated using the spectral overlap method. Moreover, by coating our prepared typical samples on 405 nm UV chips, white LED devices have been fabricated and the corresponding luminescence performance was studied. The investigation results on the properties of the as-prepared samples revealed that the Sr3LuNa(PO4)3F:Eu2+,Mn2+ phosphors might have potential application in n-UV WLEDs.

A series of Ce3+/Tb3+ doped Li3Sc2(PO4)3 phosphors has been obtained using high temperature solid state reactions. Density functional theory (DFT) calculations using the CASTEP module have given an insight into the bandgap and electronic structures of the hosts. The phase formation and the crystal structure of the prepared samples were verified using X-ray diffraction and Rietveld structure refinement analysis. Samples singly doped with Ce3+ ions had an intense emission centered at 350 nm under UV light irradiation, while samples singly doped with Tb3+ ions exhibited a typical green emission under 230 nm irradiation. Efficient Ce3+→Tb3+ energy transfer can cause the Li3Sc2(PO4)3:Ce3+,Tb3+ samples to have an intense green emission at very low Tb3+ concentrations under 285 nm excitation, making Li3Sc2(PO4)3:Ce3+,Tb3+ an efficient UV-excited green phosphor. The mechanism and critical distance for Ce3+→Tb3+ energy transfer in the phosphor were determined by detailed luminescence decay curve analysis utilizing the I-H model. Moreover, a WLED device was fabricated using our prepared green phosphor.

Considering that graphene is one layer of graphite, which has some amazing properties. It is expected that graphene-like lamellar porous carbons (PCs) can be directly formed by a simple thermal treatment, which has not been realized. Here, we present a simple and scalable synthesis of graphene-like lamellar PCs via thermal transformation of asphalt at the temperature of 700–1600 °C. The electronic properties of PCs under different temperatures are calculated by CASTEP simulations based on density functional theory (DFT). The results show reduction in band gap for PC700, PC900, PC1200 and PC1600, which are 1.781, 1.624, 1.486 and 1.33 eV, respectively. Moreover, the values of electron density difference for PC700, PC900, PC1200 and PC1600 are 4.004 × 10−2, 4.849 × 10−2, 3.077 × 10−2, 8.368 × 10−2 Bohr−3, respectively. These results imply that the PC1200 possesses the higher conductivity, smallest electron density difference and more even electron distribution. Interesting enough, the experimental results are in good agreement with this theoretical prediction. That is to say, the 1200 °C thermally-treated PC (PC1200) exhibits higher specific capacitance of 162 F g−1 at 1 A g−1 and excellent cycling stability (remain 94% after 10,000 cycles) in aqueous electrolyte and Li-ion capacitors (LICs). As a result, the PC1200 materials are promising for large-scale and practical applications in LICs.

Barium tungstate (BaWO4) has fascinating applications in the area of laser technology, solar cell, super capacitor, electronic devices and in photoluminescence. Electronic and optical behavior of BaWO4 is the reasons behind all of these fascinating applications. This research work provides the evaluation of electronic and optical properties of BaWO4 at the optimized cut-off energy value of 1200 eV by the implementation of Density Functional Theory (DFT) within the framework of CASTEP in Material STUDIO. The direct band gap and diamagnetic behavior of semiconductor BaWO4 have been evaluate by band structure, PDOS and TDOS calculation. O 2p of V.B and W, Ba 5d of C.B are the occupied electronic states of BaWO4. The highest band gap value of BaWO4 corresponds to highest loss function and smallest value of dielectric constant. Absorption spectrum exhibits that BaWO4 is an excellent UV absorber so it suitable for the formation of sensor, filter and for transparent conducting film for window layers on solar cell, solar control, and warming coatings. High refractive index value of BaWO4 makes it useful for detector for dark matter and for scintillators.

In order to better understand the doping process at A site and B site, we have researched the X (Sr2+, Zn2+, Nd3+, Ni2+, Zr4+, Hf4+) doping of barium titanate (BaTiO3) by using the CASTEP. This work computed the distinct optical, structural, and electrical characteristics before and after doping and analyzed them in depth. After doping, the addition of Sr, Zn and Nd causes the low energy level and conduction band of the system to shift to the direction of low energy, and narrows the band gap. While after the B-site ion replaces Ti, the width and intensity of the conduction band state density also widen and increase. What's more, after doping, the cubic phase rises to the tetragonal phase, increasing the quality of BaTiO3. The optical spectra have dramatically different energy characteristics, making doped BaTiO3 promising for applications in a variety of optical and optoelectronic installations.

In modern days silicon is being extensively used in making electronic semiconductor-based chips and IC’s. In this research, the change in different thermodynamic properties of silicon like lattice heat capacity, molar enthalpy and Debye temperature at constant pressure, with the change in temperature, has been investigated by using molecular dynamics (MD) simulation method. Knowing silicon’ thermodynamic functions are quite important, because many electronic companies are nowadays trying a lot to reduce the heat generated by their semiconductor chips as excessive heating of the chip not only warms up the device quickly but also reduces the chip life. The results obtained from this simulation help engineers to design electronic chips more efficiently. For simulation “Accelrys Materials Studio” (Version 5.0) software has been used. The simulation was run for silicon FCC diamond structured cell. The analysis tool used in the simulation is known as CASTEP (Cambridge Sequential Total Energy Package). This tool is specialized for performing molecular level thermodynamic analysis to generate data and graphs for the change in different temperature dependent properties of the molecular system. The interaction between silicon atoms was expressed by the Kohn-Sham potential and MD calculation was conducted on crystalline state of silicon at temperatures between 0 and 1000 K. Here, density function theory (DFT) based tool has been used to derive density of state relations. Results obtained by the simulation were compared with published experimental values and it was found that the simulation results were close to the experimental values.

Structural, elastic, electronic, optical and thermodynamic properties of laves phase intermetallic SrRh2 compound with prototype MgCu2 were investigated by using the first principle calculations. The calculations stand on density functional theory (DFT) from CASTEP code. The calculated lattice parameters are consistent with the experimental values. The significant elastic properties, like as bulk modulus B, shear modulus G, Young's modulus E and the Poisson's ratio v are determined by applying the Voigt-Reuss-Hill (VRH) approximation. The analysis of Cauchy pressure and Pugh's ratio shows the ductile nature of cubic laves phase intermetallic SrRh2 compound. Metallic conductivity is observed for SrRh2 compound. The ionic character of SrRh2 is revealed from Sr Rh bonds. Most of the contribution originates from Rh-4d states at Fermi level in DOS. The study of bonding properties of this compound exhibits the existence of covalent, ionic and metallic bonds. The maximum reflectivity occurs in low energy region which reveals the characteristics of high conductance. Absorption quality is good in the visible region. The Debye temperature of SrRh2 is 270.85 K which has been evaluated by using the calculated elastic constants. We also predicted the thermal conductivity and melting temperature of this compound.

Gas detecting and sensing is a largely studied field of knowledge, but total understanding is not yet achieved and the ideal device is still far in the future. Many experimental efforts have been devoted to find the minimum optimal temperature and operational conditions for SnO 2 to sense hydrocarbons; different methods to build gas-detecting devices keep being developed all around the world, from paste-based bulk devices to nanostructured thick and thin films, but little effort has been aim to characterize the reactions by calculating their related enthalpies. Computational methods have been widely used to characterize, understand and model many physicochemical interactions. In this regard, three main courses can be followed: Ab initio (first principles of quantum mechanics), DFT (Density Functional Theory) and MD (Molecular Dynamics) simulation. In this research, DFT modelling tool is employed to understand and characterize the gas-sensing reactions of Tin Oxide when exposed to an atmosphere with Methane. In CASTEP, a robust DFT module of the Materials Studio suite, one SnO 2 (110) crystal plane is exposed to CH 4 and the structure is optimized many times for each possible step of the reaction, recording the energies related with each optimization stage, in sum giving us the Transition State (TS) of the reaction. Based on the data, a promising reaction-path is proposed and analyzed for the (110) surface.

The first principles calculations were performed to study the sit preferences and effects on elastic properties with the Cambridge sequential total energy package (CASTEP) code for the Ni3Al system doped with the alloying element M (Ti, Nb). It was found that all the alloying elements were preferred to replace the Al sites but Ni sites at 0 K. element M (Ti, Nb) would increase the bulk, shear and Young’s modulus in Ni3Al poly-crystalline alloy, and decrease the bulk/shear modulus ratios (B/G), while all of which were larger than 1.75, indicating that Ni3Al, Ni24Al7Nb and Ni24Al7Ti poly-crystalline alloys were ductility materials. Through analyzing the electronic Structure of the calculated Ni3Al alloys, we found that the covalent bonds between alloying atom M (Ti, Nb) and their neighbor atoms Ni were considered to be the mainly strengthening mechanism of alloying elements M in Ni3Al alloys.DOI: http://dx.doi.org/10.5755/j01.ms.23.4.17051

Full inorganic perovskite solar cell materials have shown significantly improved performance in recent years. To reduce their reliance on Pb, alkaline-earth metal ions (Ba, Sr, Ca, and Mg) have been employed for the exchange of Pb in α-CsPbI 3 . In this study, density functional theory calculations were used to study the structures, band structures, and optical absorption properties of these alkaline-earth-metal doped α-CsPbI 3 materials with CASTEP (2017) and Dmol 3 (2017). The calculation also investigated the effect of spin-orbit coupling. Alkaline-earth metal doping can enlarge the band gap of α-CsPbI 3 and convert α-CsPbI 3 from a direct gap semiconductor to an indirect gap semiconductor. After alkaline-earth metal doping, the sun-light absorption increased. Among all the alkaline-earth metals studied here, Mg-doped α-CsPbI 3 showed the most improved indirect gap band structure, ideal band gap (compared to α-CsPbI 3 ), and sun-light absorption.

A new calcium magnesium orthosilicate with the composition Ca3MgSi2O8 was synthesized by a solid-state reaction process at 1.2 GPa and 1373 K for 7 days. We refined the crystallographic structure of this new compound using single-crystal X-ray data, and obtained some of its thermodynamic properties by performing some first-principles simulations. Our single-crystal X-ray analysis has shown that this new compound is monoclinic with the space group C2/c, and its unit-cell parameters are a = 9.344(4) A, b = 5.3308(3) A, c = 13.290(6) A, α = 90°, β = 92.072(7)°, γ = 90°, and V = 658.7(6) A3. The compressibility of this new compound was studied with the CASTEP code using density functional theory and planewave pseudopotential technique, which led to an isothermal bulk modulus B0 of 99(2) GPa with a pressure derivative B 0 ′ of 3.5(5). The phonon dispersions and vibrational density of the states (VDoS) of this new compound were calculated by using density functional perturbation theory. Subsequently, the VDoS was combined with a quasi-harmonic approximation to compute the isobaric heat capacity (Cp) and standard vibrational entropy ( S 298 0 ), yielding Cp = 3.927(2) × 102 – 1.159(6) × 103T−0.5 – 1.054(4) × 107T−2 + 1.362(8) × 109T−3 J mol−1 K−1 for the T range of 298–1000 K and S 298 0 = 270.5(60) J mol−1 K−1.

Thermodynamic calculation, ab initio molecular dynamics (AIMD) and vacuum decomposition experiments were performed to study the volatilization behaviors of Mo and S from molybdenite concentrate by vacuum decomposition. In thermodynamic calculation, starting decomposition temperatures of reactions were calculated, and saturated vapor pressures of Mo, S and MoS2 were also analyzed. In AIMD, geometries of the S n (n≤8), Mo m (m≤8) and Mo m S n (m+n≤8) clusters have been optimized using density functional theory (DFT) with generalized gradient approximation (GGA). And these clusters were simulated in DFT with Cambridge Sequential Total Energy Package (CASTEP) code of Material Studio software. Structures and stabilities of these clusters before and after molecular dynamics simulations were discussed, and diffusion coefficients were also calculated. In vacuum decomposition experiments, relationship between heat preservation time and volatilization rate of Mo and S was obtained, while the constant temperature and chamber pressure were 1823 K and 5–35 Pa, respectively. Above all, both the theoretical and experimental results showed that volatilization behaviors of Mo and S during vacuum decomposition process of molybdenite concentrate were as follows: Mo could partly evaporate into the condensate in the form of clusters, and S could easily evaporate into the condensate.