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Our investigation focused on an in-depth examination of the physical properties of KZnH3 and NaZnH3, with lattice parameters of 4.04 and 3.72 Å, respectively. Both compounds exist stably in a cubic structure and exhibit metallic behavior with no band gap. At the Fermi level, the total and partial densities of states exhibit a significant conductivity, confirming the metallic behavior. These materials have brittle and anisotropic properties. Because of their greater bulk modulus, average shear modulus, and Young's modulus, NaZnH3 appears harder compared to KZnH3. Optical properties indicate significant absorption and optical conductivity in the energy spectrum of 6–9 eV. NaZnH3 has a greater static refractive index and reflectivity as compared to KZnH3. The research on hydrogen storage suggests that both of these materials can store hydrogen, however, NaZnH3 is a more promising candidate due to its higher hydrogen storage capability. [ABSTRACT FROM AUTHOR]

Effect of functional on structural, elastic, optoelectronic and thermoelectric characteristics of semiconducting MgX2Se4 (X = Lu, Y) spinels has been realized by WIEN2k code. The lattice constant of MgY2Se4 is slightly greater than that of MgLu2Se4, and these quantities are slightly deviated from the experimental values, where the error does not exceed 1.3%. The cohesive energy proves that both spinels are chemically stable in the normal case, and this stability is more pronounced in MgLu2Y4. The large ionic radius of Lu compared to Y explains the high bulk modulus of MgY2Se4 as well as its hardness. The spinels under study have Г → Г direct band gap located between 1.178 and 1.4 eV for all the functionals, proving their semiconductor nature. Se-s, Y-d, Lu-d states in MgY2Se4 and MgLu2Se4 dominate the upper valence band, while the first conduction band located between Fermi level and 1.5 eV is empty. There is a strong coupling between Se-p–Lu-p sites for MgLu2Se4 and Se-p–Y-p states in MgY2Se4, which reflects their hybridization. The high absorption in the ultraviolet range, the band gap between 1 and 2.4 eV and the refractive index in the range of 2.29–2.61 favour these spinels as absorbers in solar cells. Peaks of all the optical quantities studied relating to the mBJ–GGA functional are shifted to the right compared with GGA and GGA+SO approximations. The thermoelectric parameters were investigated as a function of photon energy and temperature using GGA+SO functional. [ABSTRACT FROM AUTHOR]

In our study, we create peanut-shaped boron nitride nanotubes by introducing Stone–Wales defects and applying uniaxial tensile strain. We carefully examine the structural and electronic properties by systematically applying different strain levels along the nanotubes' axial direction, both before and after introducing the defects. Our results reveal that Stone–Wales defects have a notable impact on the bond lengths and bond angles within the nanotubes. Furthermore, we conduct a detailed analysis of the band structures for both pristine nanotubes and those with Stone–Wales defects under varying strain conditions. Our findings demonstrate a clear correlation between the changes in the band structures and the density of state diagrams. Importantly, the introduction of Stone–Wales defects induces the appearance of new energy states within the band gap, leading to a significant reduction in the band gap size. Through our calculations, we provide clear evidence that the electronic properties of the nanotubes are distinctly affected by the presence of Stone–Wales defects and the application of tensile strain. [ABSTRACT FROM AUTHOR]

MgAl2O4 spinel matrix nanocomposite with TiC, AlTi3, and Al2O3 was directly fabricated using the mechanical alloying (MA) method with Mg, TiO2, Al, and graphite as the starting powder mixture. This methodology was used to synthesize magnesium aluminate spinel (MSA) matrix nanocomposite with having the advantage of no subsequent heat treatment. The mixture of the powders was milled at room temperature using a high-energy planetary ball mill with a vial rotation speed of 400 rpm in the air. The phases and morphological analysis after the MA process were characterized by X-ray diffraction and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). Followed by 20 h of ball-milling, all the desired phases of MgAl2O4, TiC, AlTi3, and Al2O3 appeared in XRD results, and also a small fraction of raw materials remained. The major reactions to synthesize MgAl2O4/TiC-AlTi3-Al2O3 spinel matrix nanocomposite were the reduction of TiO2 by Al and Mg. [ABSTRACT FROM AUTHOR]

Based on the first-principles calculations of density functional theory (DFT), the crystal structure, molecular structure, electronic properties, and optical absorption properties of methyl urotropine perchlorate under hydrostatic compression in the range of 0 ~ 100 GPa were calculated. The results show that the crystal structure of methyl urotropine perchlorate undergoes two structural transformations under hydrostatic compression. The H1A-H1B bond breaks at 25 GPa, generating two new covalent bonds N3-H1A and O1-H1B. The covalent bonds of O2A-C1 and Cl1-H3A are formed at 85 GPa. The compression ratio of lattice constants (a, b, c) and unit cell volume change abruptly at 25 GPa and 85 GPa, respectively. The conclusion that new bonds are formed under high pressure is further demonstrated by analyzing the partial density of states (PDOS) of N3, H1A, O1, H1B, O2A, C1, Cl1, and H3A atoms. The absorption spectrum showed that the absorption peak of methyl urotropine perchlorate gradually enhanced with the increase of pressure and the highest absorption peak shifted to high frequency. Highlights: The structure of methyl urotropine perchlorate was optimized, and its lattice constants (a, b, c, and V) and compression ratios at different pressures were calculated. Methyl urotropine perchlorate undergoes two structural transitions at pressurization to 25 GPa and 85 GPa, with the breaking of old bonds and the formation of new bonds. The DOS of methyl urotropine perchlorate was analyzed, further confirming the structural transformation by high pressure. The effect of high pressure on optical absorption properties was investigated. [ABSTRACT FROM AUTHOR]

The charge density, differential charge density, band structure, density of states and absorption spectra of cubic structure Ag3PO4 were calculated by Material Studio software. The best function for calculating the Ag3PO4 crystal model is PBE0 with a lattice constant of 6.004 Å. In Ag3PO4 crystal system, the force between O–Ag is weaker than that between O–P, which leads to the photo-corrosion of Ag3PO4 material. The forbidden band width of the Ag3PO4 crystal is 2.47 eV. The light absorption boundary is approximately 520 nm. At the same time, the cubic phase Ag3PO4 was successfully prepared. The light absorption boundary value of the Ag3PO4 sample measured by UV–Vis diffuse reflectance spectroscopy is about 520 nm, and the forbidden band width is 2.41 eV. The results obtained by means of photoluminescence spectroscopy, UV–Vis diffuse reflectance absorption spectroscopy and degradation of organic pollutants are consistent with theoretical calculations. calculations. [ABSTRACT FROM AUTHOR]

We present a joint experimental and computational terahertz (THz) spectroscopy study of the most stable polymorph (form I) of an antihypertensive pharmaceutical solid, felodipine (FLD). The vibrational response has been analyzed at room temperature by combining optical (THz-TDS, FT-IR, THz-Raman) and neutron (INS) terahertz spectroscopy. With the challenging example of a large and flexible molecular solid, we illustrate the complementarity of the experimental techniques. We show how the results can be understood by employing ab initio modeling and discuss current progress in the field. To this end, we employ plane wave formulation of density functional theory (plane wave DFT) along with harmonic lattice dynamics calculations (HLD) and ab initio molecular dynamics (AIMD) simulations. Based on a comprehensive theoretical analysis, we discover an inconsistency in the commonly accepted structural model, which can be linked to a distinct librational dynamics of the side ester chains. As a result, only a moderate agreement with the experimental spectra can be achieved. We, therefore, propose an alternative structural model, effectively accounting for the influence of the large-amplitude librations and allowing for a comprehensive analysis of the vibrational resonances up to 4.5 THz. In that way, we illustrate the applicability of the computationally supported THz spectroscopy to detect subtle structural issues in molecular solids. While the provided structural model can be treated as a guess, the problem calls for further revision by means of high-resolution crystallography. The problem also draws a need of extending the THz experiments toward low-temperature conditions and single-crystal samples. On the other hand, the studied system emerges as a challenge for the DFT modeling, being extremely sensitive to the level of the theory used and the resulting description of the intermolecular forces. FLD form I can be, hence, considered as a testbed for the use of more sophisticated theoretical approaches, particularly relying on an advanced treatment of the van der Walls forces and going beyond zero-temperature conditions and harmonic approximation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

By means of density functional theory (DFT) calculations, we have systematically investigated the effect of hydrostatic pressure on the structural, electronic and elastic properties of barium-doped silicon clathrate Ba8Si46 in the type-VIII structure (α phase). Physical properties are calculated under different conditions of pressure (0 GPa to 45 GPa) using the GGA-PBE functional. Those calculations have been performed using the Cambridge serial total energy package CASTEP within the Materials Studio package. Electronic properties have shown that type-VIII Ba8Si46 has metal-like properties with a fundamental bandgap of 1 eV. Under pressure the fundamental bandgap increases slightly and the positions of the valence band maximum VBM and the conduction band minimum CBM remain unchanged when pressure is changed from 0 to 25 GPa, but when pressure is set to 30 GPa the CBM is transited from its initial position (Γ-H segment) towards the Γ(0,0,0) point, this indicates that the bandgap nature of this material can be tuned through strain engineering. We found that the compound is mechanically stable under the pressure range and might be unstable or collapse when pressure exceeds 44 GPa. These findings need to be confirmed experimentally through synthesis, a comparison with the type-I and the guest-free counterparts has exhibited promising features for the type-VIII Ba8Si46. [ABSTRACT FROM AUTHOR]

Magnesium diboride (MgB2) superconductor with excellent physical properties continues to attract the attention of researchers since its discovery. It derives its versatility from the absence of weak links, large coherence length, and small anisotropy. On the other hand, reports of superconductivity in small-diameter single-walled carbon nanotubes (SWCNTs) suspended between superconducting contacts and proximity induced supercurrents in Ta/SWNTs/Au junctions have also aroused great interest in the scientific community. Proximity induced superconductivity in SWCNTs has opened up new frontiers of research which will lead to many novel discoveries. This paper reports ab initio investigations on the proximity effect of MgB2 on the electronic structure of a SWCNT. Condensation of electronic states is observed in the electronic band structure of the pristine SWCNT when MgB2 is held in proximity. An additional band gap is generated below the lowest energy state of the valence band of the pristine CNT which we suggest, is due to Cooper pair formation. This leads to the prediction that SWCNTs will show superconducting properties in proximity of MgB2. We envision MgB2-coated SWCNTs as a novel nanomaterial that has a combination of proximity induced superconductivity and inherently unique mechanical and optical properties of SWCNTs. [ABSTRACT FROM AUTHOR]

We used the CASTEP program with a GGA+ U method to study the effects of Cu doping on the formation energy, electronic and optical properties of V-doped ZnO. The calculated enthalpies show that Cu inclines stay near V. The formation energy shows Cu and V codoping is easy to form in an oxygen atmosphere. Vanadium introduces an impurity band level and Cu widen the level. The relation between the band and density of states (DOS) has been discussed. The calculated absorption coefficient ( α( ω)) shifts to lower energy (red shift). The absorption coefficient also has a broad increased peak in the green energy region (around 530 nm). We also calculated the other optical constants of Cu and V codoped ZnO. The relation between the optical properties and DOS has been discussed. Our calculations not only can explain the experiment and but also clarify the mechanism and role of Cu on the optical properties of V-doped ZnO. Our study provides a reference and method for improving codoping content and absorption in the visible region of V-doped ZnO. We also provide a reference in designing optical devices base on V-doped ZnO. [ABSTRACT FROM AUTHOR]

Superconductivity in carbon nanotubes is attracting worldwide attention because of the reported high superconducting transition temperature in small-diameter single-walled carbon nanotubes (SWCNTs). However, it is well known that superconductivity in low-dimensional (quasi-1D) systems is not so common due to low density of states (DOS), strong quantum fluctuations and other phenomena in such systems. In this paper, we present theoretical investigations of the proximity effect of superconducting niobium carbide on single-walled carbon nanotube using density functional theory (DFT). The relaxed structure shows that Nb atoms are held around the SWCNT, forming a layer through weak van der Waals' forces. The stability of the structure has been confirmed by Hirshfeld analysis and Mullikan population analysis as well. The study of the electronic band structure of the pristine and modified SWCNT shows a fascinating condensation of electronic states and a striking shift in the Fermi level. Further, two additional band gaps have appeared below the valence band suggesting some kind of pairing mechanism being operational. This indicates the possibility of superconducting behaviour in SWCNT in proximity of niobium carbide. The relaxed structure thus envisions the feasibility and stability of NbC-coated SWCNTs which will have superconducting properties as well as the remarkable mechanical and optical properties of SWCNTs. This prediction seeks interest of the researchers to try and develop such a novel nanomaterial which, if realized, will prove to be highly significant for many technological applications. [ABSTRACT FROM AUTHOR]

The heat capacities of Al, Si ordered alkali feldspars of different Na, K compositions were calculated using the density functional theory. The effect of the Na, K distribution, if random, ordered or clustered, on the resulting heat capacity was investigated on different cells with AbOr composition. For all compositions and distributions studied, the excess heat capacity of mixing is positive at low temperatures with a maximum at ~60 K. This produces an increasing excess vibrational entropy that reaches a constant value above ~200 K. The amount of the excess heat capacity of AbOr, however, depends on the Na, K distribution. Best agreement with measured excess heat capacities is achieved, if the distribution of Na and K is either ordered or clustered. The positive excess heat capacities can be attributed to a strong softening of the acoustic and the lowest optical modes related to a strong increase of Na-O bond lengths in samples with intermediate compositions. The softening of the lowest optical mode is, however, not reflected by thoroughly measured literature IR data. Comparing calculated and measured IR spectra suggests that the resolution of the measured spectra was insufficient for detecting the lowest IR-active modes. [ABSTRACT FROM AUTHOR]

The CASTEP program was used to study the effects of Cu on the structure, magnetic moment and electronic properties of V-doped ZnO. The calculated enthalpies showed that the Cu atoms were inclined to stay near the V atoms. Cu neutralized the delocalized electrons in V-doped ZnO. Cu also suppressed the magnetic moments of Zn and O more than those of the V ions. The different amounts of suppression caused the moments to concentrate on the V atoms. The magnetic moments decreased in Cu and V co-doped ZnO. The suppressions of the magnetic moments and concentrations of the Cu atoms were verified with density of states calculations. The states showed that Cu increased the conduction in V-doped ZnO. The calculated spin isospheres showed that Cu improved the concentration of the magnetic moments on the V sites. The improved concentration enhanced the performance of diluted magnetic semiconductors based on V-doped ZnO. These results help in understanding the role of Cu in V-doped ZnO. They also provide a reference for preparing diluted magnetic semiconductors based on V-doped ZnO [ABSTRACT FROM AUTHOR]

Co-crystals formed between benzoic acid and 4,6-dimethyl-2-aminopyrimidine in 1:1 molar ratio (C6H9N3C7H6O2) have been prepared and studied. According to single crystal XRD analysis, the structure is monoclinic, P21/ c, a = 6.7019(9) Å, b = 7.647(1) Å, c = 25.285(3) Å, β = 91.36(2)°, V = 1295.4(3) Å3, Z = 4. The asymmetric unit contains 2-amino-4,6-dimethylpyrimidine and benzoic acid molecules linked to each other by two hydrogen bonds [O1-H1N1, HN = 1.819 Å; N3-H3AO2, HO = 2.157 Å]. Calculations of band structure, density of states, absorption and reflectivity spectra have been performed in the frame of density functional theory using the CASTEP code, and the corresponding experimental optical properties have been investigated. The theoretical results indicate that (C6H9N3C7H6O2) single crystal is a wide band-gap semiconductor with the theoretical direct band gap 3.0271 eV. The title co-crystal may become promising host for fluorescence-emitting; it can absorb ultraviolet radiation. [ABSTRACT FROM AUTHOR]

The internal energies and entropies of 21 well-known minerals were calculated using the density functional theory (DFT), viz. kyanite, sillimanite, andalusite, albite, microcline, forsterite, fayalite, diopside, jadeite, hedenbergite, pyrope, grossular, talc, pyrophyllite, phlogopite, annite, muscovite, brucite, portlandite, tremolite, and CaTiO3-perovskite. These thermodynamic quantities were then transformed into standard enthalpies of formation from the elements and standard entropies enabling a direct comparison with tabulated values. The deviations from reference enthalpy and entropy values are in the order of several kJ/mol and several J/mol/K, respectively, from which the former is more relevant. In the case of phase transitions, the DFT-computed thermodynamic data of involved phases turned out to be accurate and using them in phase diagram calculations yields reasonable results. This is shown for the Al2SiO5 polymorphs. The DFT-based phase boundaries are comparable to those derived from internally consistent thermodynamic data sets. They even suggest an improvement, because they agree with petrological observations concerning the coexistence of kyanite + quartz + corundum in high-grade metamorphic rocks, which are not reproduced correctly using internally consistent data sets. The DFT-derived thermodynamic data are also accurate enough for computing the P-T positions of reactions that are characterized by relatively large reaction enthalpies (> 100 kJ/mol), i.e., dehydration reactions. For reactions with small reaction enthalpies (a few kJ/mol), the DFT errors are too large. They, however, are still far better than enthalpy and entropy values obtained from estimation methods. [ABSTRACT FROM AUTHOR]