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Isosymmetric structural phase transition (IPT, type 0), in which there are no changes in the occupation of Wyckoff positions, the number of atoms in the unit cell, and the space group symmetry, is relatively uncommon. Chlorothiazide, a diuretic agent with a secondary function as an antihypertensive, has been proven to undergo pressure-induced IPT of Form I to Form II at 4.2 GPa. For that reason, it has been chosen as a model compound in this study to determine if IPT can be predicted in silico using periodic DFT calculations. The transformation of Form II into Form I, occurring under decompression, was observed in geometry optimization calculations. However, the reverse transition was not detected, although the calculated differences in the DFT energies and thermodynamic parameters indicated that Form II should be more stable at increased pressure. Finally, the IPT was successfully simulated using ab initio molecular dynamics calculations.

Piracetam, a popular nootropic drug, widely used in the treatment of age-associated mental decline and disorders of the nervous system such as Alzheimer's disease and dementia exists under normal pressure in three polymorphic forms (P1, P2 and P3) of different stability. In this work the relative stability of piracetam polymorphs depending on the temperature was studied using the ssNMR spectroscopy combined with ab initio DFT calculations. The ssNMR spectroscopy enabled the analysis of polymorphic phase transition in the case of pure active substance as well as polymorphic form identification in the analysis of the commercial solid dosage formulations. Quantum chemical calculations of phonon density of states were performed to obtain the temperature dependence of the enthalpy, entropy and free energy of the piracetam polymorphs in a quasi-harmonic approximation. GIPAW NMR calculations combined with molecular dynamics were performed to support the chemical shift assignment. The obtained results showed that DFT calculations can be used not only to obtain the NMR parameters but also to predict the influence of the temperature on the stability order of the polymorphic forms of molecular crystals., (Copyright © 2018 Elsevier Inc. All rights reserved.)

This work presents a Density Functional Theory (DFT) study of the single perovskite CsXH 3 (X = Co, Zn). We used the CASTEP code to perform first-principles calculations and investigate the hydrogen storage properties of CsXH 3 (X = Co, Zn). We calculated the structural, Hydrogen, mechanical, electronic, optical, and thermal properties of CsXH 3 (X = Co, Zn) perovskite materials for hydrogen storage applications. Electronic properties reveal that CsXH 3 (X = Co, Zn) has a metallic behavior. The calculated value of formation energy is −0.47 eV/atom and −0.18 eV/atom for CsCoH 3 and CsZnH 3 , respectively, which means that the studied materials are synthesizable and thermodynamically stable. Our results show that CsXH 3 (X = Co, Zn) is a promising material for hydrogen storage, as it exhibits high hydrogen storage capacity. The gravimetric ratio values are 2.82 wt% and 3.09 wt% for CsCoH 3 and CsZnH 3 , respectively. The determined elastic constants show that CsXH 3 (X = Co, Zn) is mechanically stable. Our study provides valuable insights into using single perovskite CsXH 3 (X = Co, Zn) as a potential material for hydrogen storage applications. • Performance of DFT study for CsXH 3 (X = Co, Zn) perovskites materials for hydrogen storage applications. • The elastic constants values show that CsXH 3 (X = Co, Zn) is mechanically stable. • Calculated formation energy is −0.47 and −0.18 for CsCoH 3 and CsZnH 3 respectively. • The studied materials are synthesizable, thermodynamically stable and are most suitable for hydrogen storage applications. [ABSTRACT FROM AUTHOR]

Thiamine hydrochloride (THCL), also known as vitamin B1, is an active pharmaceutical ingredient (API), present on the list of essential medicines developed by the WHO, which proves its importance for public health. THCL is highly hygroscopic and can occur in the form of hydrates with varying degrees of hydration, depending on the air humidity. Although experimental characterization of the THCL hydrates has been described in the literature, the questions raised in previously published works suggest that additional research and in-depth analysis of THCL dehydration behavior are still needed. Therefore, the main aim of this study was to characterize, by means of quantum chemical calculations, the behavior of thiamine hydrates and explain the previously obtained results, including changes in the NMR spectra, at the molecular level. To achieve this goal, a series of DFT (CASTEP) and DFTB (DFTB+) calculations under periodic boundary conditions have been performed, including molecular dynamics simulations and GIPAW NMR calculations. The obtained results explain the differences in the relative stability of the studied forms and changes in the spectra observed for the samples of various degrees of hydration. This work highlights the application of periodic DFT calculations in the analysis of various solid forms of APIs. [ABSTRACT FROM AUTHOR]

The aim of this study is to comprehensively examine the structural composition and properties of the AgAlS2 crystal during its high-pressure phase. This analysis delves into the second coordination environment of the crystal structure and elucidates the distinct transformations it undergoes during the phase transition. The band energy structure was calculated, and the origin of electronic levels was clarified. It is shown that the crystal becomes non-stratified during the phase transition. This study also determined the values of the crystal's carrier effective masses, underscoring its spatial anisotropy. It was found that the calculated optical functions are similar to the crystal in the chalcopyrite structure, and their differences are shown. Further, this study involved the calculation of the crystal's phonon spectrum, revealing the spectrum's transformation during the phase transition. The vibrational frequencies were also obtained, with a symmetrical classification of vibrational modes. Finally, this study derived the infrared and Raman spectra of the AgAlS2 crystal, thereby providing a comprehensive picture of the crystal during its high-pressure phase. [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]

The aim of this study is to comprehensively examine the structural composition and properties of the AgAlS2 crystal during its high-pressure phase. This analysis delves into the second coordination environment of the crystal structure and elucidates the distinct transformations it undergoes during the phase transition. The band energy structure was calculated, and the origin of electronic levels was clarified. It is shown that the crystal becomes non-stratified during the phase transition. This study also determined the values of the crystal’s carrier effective masses, underscoring its spatial anisotropy. It was found that the calculated optical functions are similar to the crystal in the chalcopyrite structure, and their differences are shown. Further, this study involved the calculation of the crystal’s phonon spectrum, revealing the spectrum’s transformation during the phase transition. The vibrational frequencies were also obtained, with a symmetrical classification of vibrational modes. Finally, this study derived the infrared and Raman spectra of the AgAlS2 crystal, thereby providing a comprehensive picture of the crystal during its high-pressure phase.

The effect of Cl content on total energies of W-Cl system. [Display omitted] • The monoclinic WCl 5 and the trigonal WCl 3 are the more stable phases. • WCl 6 phase may be present in two crystal forms, such as the hexagonal (P -3 m1, 164) β-WCl 6 and the hexagonal (R -3, 148) α-WCl 6. • The obtained bond distance in α-WCl 6 and β-WCl 6 are significantly longer than the mean bond distances in WCl 4 and WCl 5. • Direct Γ-Γ band gap for WCl 3 (1.78 eV), WCl 5 (0.08 eV), β-WCl 6 (1.746 eV) and α-WCl 6 (1.803 eV), while WCl 4 has the metallic character. • The atomic geometry of monoclinic WCl 4 and WCl 5 contain an ordered arrangement of W vacancies. • The PDOS profile of W and Cl are similar throughout the whole energy region, indicating the presence of hybridization between W and Cl electrons. • One shares the charge density at each point between atoms in proportion to the free atomic density, so that the distribution of bound and localized atoms resembles the molecular density. The molecular structures of WCl 6 , WCl 5 , WCl 4 , WCl 3 have been optimized by density functional theory calculations. We report the stability of the phases in the ground state, the total energies and the optoelectronic properties of the W-Cl system. We find that the material having a low tungsten concentration shows a low DOS at the Fermi level, which implies a high resistivity. Both polymorphs of WCl 6 are crystalline solids at room temperature and show the (α- WCl 6) and (β- WCl 6) phases of space group R -3 and P -3 m1 observed at 228 °C. The change in temperature influences the structural, electronic and optical properties. The object of this paper does not concern only the study of all phases, but also one controls the physical states of the molecular materials when they are subjected to polymorphic changes. Calculations on the molecular structure under symmetry indicated an orbitally degenerate ground state with bond distances in good agreement with experiment. [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]

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Cellulose acetate(CA)/graphene oxide (GO) composites have been widely used in the drug development and biosensing due to its excellent biocompatibility and strength. It is important to study their adsorption mechanisms for the application of CA/GO in detail. Here, the interaction between GO and CA was described by DFT simulations, and CA/GO composite films were characterised using tensile testing and FTIR spectroscopy. DFT calculations indicated that there is no chemical bonding between CA and GO adsorption but hydrogen bonding from hydroxyl groups facilitates the adsorption process. FTIR of CA/GO results show that the characteristic peaks of hydroxyl groups in the composite film is shifted towards high frequencies compared to the pure CA film, which is a strong evidence of hydrogen bonding of hydroxyl groups during the adsorption process. The tensile test results indicate that hydrogen bonds contribute to the tensile strength and elastic modulus of the CA/GO composite film. [ABSTRACT FROM AUTHOR]

The structural, electronic, dielectric and vibrational properties of zinc-blende (ZB) InAs were studied within the framework of density functional theory (DFT) by employing local density approximation and norm-conserving pseudopotentials. The optimal lattice parameter, direct band gap, static dielectric constant, phonon frequencies and Born effective charges calculated by treating In-4d electrons as valence states are in satisfactory agreement with other reported theoretical and experimental findings. The calculated band gap is reasonably accurate and improved in comparison to other findings. This work will be useful for more computational studies related to semiconductor devices. [ABSTRACT FROM AUTHOR]

X-ray powder diffraction studies on the secondary explosive TEX (C 6 H 6 N 4 O 8) in the temperature range 25–150 °C are reported. TEX has a triclinic structure (a = 6.850 Å, b = 7.665 Å, c = 8.826 Å, α = 82.38°, β = 75.0°, and γ = 79.30° at 25 °C), space group P 1 ¯. The crystal structure remains triclinic in this temperature range. From the temperature dependence of lattice parameters we find that thermal expansion is different along different directions. The volume thermal expansion coefficient 17.4 × 10−5 K-1 is comparable to that of a related material, CL-20. Thermal expansion along the c-direction α c is 2.2 times α a and 3 times α b. Phonon frequencies of TEX crystal at different pressures are obtained from density functional theory (DFT) calculations using CASTEP codes. The volume thermal expansion coefficient calculated using Gruneisen formalism is 6.1 × 10−5 K-1. This is the first report on the experimental determination of thermal expansion of TEX, and computation by Gruneisen formalism using DFT. • Volume thermal expansion (α V) of secondary explosive TEX is obtained from temperature dependent x-ray diffraction. • α V is also estimated using Gruneisen formalism from first principles calculations with CASTEP code. • The experimentally obtained α V = 17.4 × 10−5 K-1 is comparable to the computed value of 6.1 × 10−5 K-1. [ABSTRACT FROM AUTHOR]

This work presents a comprehensive spectroscopic analysis of crystalline isoniazid, one of the main drugs in tuberculosis chemotherapy, using a blend of spectroscopic and computational methods. Mid- and far-infrared, Raman, and inelastic neutron scattering spectroscopies, with contribution of isotopic substitution are combined with discrete and periodic DFT quantum chemical calculations. This combined approach successfully reproduces the whole spectral range, allowing a sound assignment of all the vibrational bands. Previous misassignments have been corrected and several spectral features of isoniazid crystal are reported for the first time. Virtues and limitations of the computational approach (periodic and discrete) are also discussed in light of the present state-of-the-art in the field. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To study the sensing mechanism at atomic, geometrical and electronic structural levels, Density Functional Theory (DFT) technique is useful. Based on ab initio, DFT calculations for CO gas sensing behavior on undoped and Pt doped SnO2 are done. After surface relaxation, optimum adsorption site is selected based on adsorption energy calculated for four different sites, O2C (bridging oxygen), Sn6c (6 fold Sn), Sn5c (5 fold Sn) and O3c (plane oxygen), and CO sensing behavior is observed on favorable site. For estimation of conductance, which is a measure of sensitivity of gas sensing system, analysis of related physical parameters like surface Density Of States (DOS) and Mulliken population analysis are done. Enhanced sensitivity is observed for Pt doped surface as compared to undoped ones, which is in agreement with the experimental results. Modeling and simulations help to optimize the sensor for any specific application, prior to fabrication. Conclusions help in designing the framework of SnO2-based CO gas sensor. [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]

This paper details a density functional theory (DFT) based ab initio study on the effect of co-doping on the dielectric function spectra and refractive indices of single-walled carbon nanotubes (SWCNTs). Dielectric function spectra of a pristine (8,0) SWCNT; (8,0) SWCNT co-doped with aluminum (Al) and phosphorus (P); (8,0) SWCNT co-doped with Al, P, and nitrogen (N); (9,0) SWCNT doped with Al; and (9,0) SWCNT co-doped with Al and boron (B) have been calculated using DFT-based Cambridge sequential total energy package (CASTEP) code. Polarized and unpolarized light as well as light through polycrystalline media have been considered. Analysis involves calculation and comparison of static refractive indices of the pristine and co-doped SWCNTs. Co-doping with Al and P results in a substantial increase in the value of the static refractive index while co-doping of Al, N, and P results in a reduction in the value of static refractive index though it does not fall lower than that of the pristine SWCNT. Thus, it can be concluded that co-doping with atoms of different combinations of elements can be evolved as a novel and effective tool for tuning the dielectric function and static refractive index values of SWCNTs. It will prove to be highly significant for effective designing of various sensitive optical devices using SWCNTs. [ABSTRACT FROM AUTHOR]

It is always difficult to assign the peaks of a vibrational spectrum in the far-infrared region. The two distinct peaks seen in many ice phases are still a mystery to date. The normal modes of ice XV were calculated using the CASTEP code based on first-principles density functional theory. On the basis of vibrational modes analysis, we divided the translational modes into three categories: four-bond vibrations, which have the highest energy levels; two-bond vibrations, which have medium levels of energy; and relative vibrations between two sublattices, which have the lowest energy. Whale et al. found that some intramolecular stretching modes include the isolated vibration of only one O−H bond, whereas the others do not vibrate in ice XV. We verified this phenomenon in this study and attributed it to local tetrahedral deformation. Analysis of normal modes, especially in the translation and stretching band of ice XV, clarified the physical insights of the vibrational spectrum and can be used with other ice phases.

The vibrational spectrum of ice II was investigated using the CASTEP code based on first-principles density functional theory (DFT). Based on good agreement with inelastic neutron scattering (INS), infrared (IR), and Raman experimental data, we discuss the translation, libration, bending, and stretching band using normal modes analysis method. In the translation band, we found that the four-bond and two-bond molecular vibration modes constitute three main peaks in accordance with INS ranging from 117 to 318 cm−1. We also discovered that the lower frequencies are cluster vibrations that may overlap with acoustic phonons. Whale et al. found in ice XV that some intramolecular vibrational modes include many isolated-molecule stretches of only one O−H bond, whereas the other O−H bond does not vibrate. This phenomenon is very common in ice II, and we attribute it to local tetrahedral deformation. The pathway of combining normal mode analysis with experimental spectra leads to scientific assignments.

This paper presents a first principles study on the effect of co-doping on various optical spectra of a zigzag single-walled carbon nanotube (SWCNT). Optical spectra of a pristine SWCNT, SWCNT co-doped with Aluminum (Al) & Phosphorus (P) and another one co-doped with Al, P and Nitrogen (N) have been calculated using density functional theory (DFT).The theory has been implemented using the Cambridge sequential total energy package (CASTEP) code available as a userfriendly module with the software ‘Material Studio’. Polarized and unpolarized light as well as light through polycrystalline media have been considered. The dependence of various spectra on the status of incident light presents a clear evidence of anisotropicity in the optical properties. Analysis of the simulated spectra involves calculation and comparison of different optical properties like dielectric function, reflectivity, refractive index, conductivity and loss function for the pristine and co-doped SWCNTs. Noticeable variations are observed in the optical properties on simultaneously doping the SWCNT with Al and P and then further introducing N atom into the structure so that it can be concluded that co-doping (simultaneous doping with different combinations of dopants) can be evolved as a novel and effective tool for tailoring the optical properties of SWCNTs as per the requirements while designing an optical device. It will prove to be highly significant for effective designing of SWCNT based sensitive optical devices for a variety of technological applications. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study of pristine single walled carbon nanotube (SWCNT) and SWCNT co- doped with combinations of Aluminum (Al), Phosphorous (P) and Nitrogen (N) along with their dielectric function spectra and calculated refractive indices. Dielectric function spectra of a pristine SWCNT and the SWCNT co-doped with Aluminum (Al) & Phosphorus (P) and another one co-doped with Al, P and Nitrogen (N) have been calculated using density functional theory implemented through the Cambridge sequential total energy package (CASTEP). The spectra show the variation of real and imaginary part of the dielectric function with frequency of the incident light. Polarized and unpolarized light as well as light through polycrystalline media has been considered. The value of static refractive index has been calculated using these curves. A substantial increase in the value of the static refractive index is observed when a pristine SWCNT is co-doped with Al and P but if in addition N atom is also introduced, a reduction in the value of static refractive index is observed though it does not fall lower than that of the pristine SWCNT. Thus, we propose that co-doping with atoms of different combinations of elements can be used as a novel and effective tool to manipulate the dielectric function and refractive index of SWCNTs and can pave the way to effective designing of various sensitive optical devices using SWCNTs for a variety of technological applications. [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]

[Display omitted] • First ever theoretical investigation of CsSiBr 3 has been done using CASTEP module under Density Functional Theory. Material showed conducting behavior, promising candidate for photovoltaic and solar cell applications. Br-p state visibly prominent and showing maximum conduction, in result gives maximum photon energy for photovoltaic applications. In recent paper, density functional theory (DFT) based CASTEP first principles calculations has been studied for CsSiBr 3 perovskite for solar cell and photovoltaic applications. Admittedly, discussed and examined the optical, structural and electronic properties of the CsSiBr 3 perovskites compound, using GGA-PBE calculations. Furthermore, the consequences and influence of the lattice constant of the CsSiBr 3 perovskites on the band gap values have been examined. Also we observed the physical properties of the calculated materials and noticed that the optimized lattice constant is equal to 5.057 Å for CsSiBr 3 perovskite compound having supercell of pm3m. It is examined that for CsSiBr 3 compound the band gap value is 0.996 eV. Optical properties, electronic and structural parameters shows that CsSiBr 3 is a capable material aimed to solar cell and photovoltaic applications with promising parameters. [ABSTRACT FROM AUTHOR]

[Display omitted] • Density Functional Theory (DFT) framework has been used to explore XCdCl 3 (X = Na, K, Rb and Cs) chloroperovskites. • Single-crystal elastic constant and associated mechanical parameters indicate that all of the compounds are mechanically stable, ductile, and soft. • All the chloroperovskites are found as semiconducting nature with an indirect bandgap energy. • Bandgap energies are preferable for visible light absorption and their application in photovoltaic technology. • Optical parameter analysis consisted of the electronic band structure analysis. The structural, elastic, mechanical and optoelectronic properties of XCdCl 3 (X = Na, K, Rb and Cs) chloroperovskites have been investigated by using the Density Functional Theory (DFT) framework through the CASTEP code. The GGA, GGA-U and LDA functionals have been used to explore XCdCl 3 (X = Na, K, Rb and Cs) chloroperovskites. All of the computational results of structural parameters are in good accord with the available experimental data, indicating that our work is reliable. The elastic stiffness constants C ij use the essential circumstances to show that the XCdCl 3 perovskite structures are mechanically stable. The elastic modulus and other reliable features indicate the XCdCl 3 chloroperovskites are mechanically ductile and soft. All the materials exhibit indirect bandgap and their bandgap energy decrease with X-site cation variation from Na to Cs. Optical conductivity and absorption for visible and ultraviolet imply their wide application in photovoltaic technology. [ABSTRACT FROM AUTHOR]

This paper reports a vibrational spectroscopic study on a zigzag single-walled carbon nanotube (SWCNT) using the first-principles method based on density functional theory (DFT). The most suitable exchange correlation functional for DFT analysis was determined by comparing the predicted value of band gap of the SWCNT under study with the experimental value reported in the literature. General gradient approximation functional in combination with revised Perdew-Burke-Ernzerh sub-functional was found to give the best results. Using this optimum combination, phonon density of states and phonon dispersion curves have been determined. The analysis of results obtained focuses on symmetry considerations, group theory analysis, segregation of Raman active and infrared (IR) active vibrational modes and interpretation of the Raman and IR spectra obtained. The earlier approaches to the problem rely upon the zone folding technique and force constant models in which structural relaxation factor is not taken care of. An ab initio approach has been adopted by the authors in this work, which is advantageous as it neither depends on some predefined parameter nor does it ignore the structural relaxation factor. Analysis of the Raman spectrum reveals some additional peaks other than the commonly known radial breathing mode, D, G, and G′ bands in the SWCNT spectra, which have been recently reported to be observed experimentally also. Similarly, the theoretically developed IR spectrum for the simulated SWCNT is also in agreement with experimental observations. The methodology presented thus provides a very useful and novel simulation route to predict the vibrational modes, Raman spectra, and IR spectra of SWCNTs theoretically. [ABSTRACT FROM AUTHOR]

The effect of lithium intercalation on the structural and electronic properties of layered LiFeSO 4 OH and layered FeSO 4 OH cathode material is investigated using first-principle calculations. Results of Mulliken analysis, band gap, density of state, and charge density before and after intercalation are discussed. The importance of the strong covalent character of S–O and Fe–O bonds in high charge/discharge cycles and thermodynamic stabilities is confirmed. Analysis of the partial density of state reveals that the main contributor to the strong S–O covalent bond is the hybridization between the S 3s, S 3p electron state and the O 2p electron state. The Fe 3d orbital also plays an important role in cathode performance because it dominates the conduction and valence bands and radically changes upon the removal and insertion of lithium ion inside the cathode materials. The charge density elucidates the ionic and covalent characters of the bond inside the cathode. [ABSTRACT FROM AUTHOR]

Experimental and computational (DFT) approaches were carried out to investigate oxygen vacancies on cerium dioxide. Computational result indicates oxygen vacancies can shorten the band gap of CeO 2 and enhance the absorption for visible light because Ce (III) created by generation of oxygen vacancies is easier for excitation than Ce (IV) under same irradiation. The order of calculated band gap for Ce 16 O 31 , (111) < (113) < (133), and the absorption data suggests that (111) plane may be the most ideal position for oxygen vacancies to enhance photocatalytic activity. The result has been tested and verified by experimental study, including UV–Vis spectra, XPS, XRD and PL. The enhanced hydrogen productions of CeO 2 samples, from 34.8 μmol to 63.0 μmol, are 2.0–3.5 times as high as that of commercial CeO 2 (17.8 μmol). [ABSTRACT FROM AUTHOR]

Structural, optical and electronic properties, elastic constants of Be 1− x Zn x Te alloys have been studied by employing Castep program based on density functional theory (DFT). The Generalized Gradient Approximation (GGA) and Local Density Approximation (LDA) were utilized as exchange correlation. Using elastic constants for compounds, bulk modulus, forbidden band gap, Fermi energy and Kramers–Kronig relations; dielectric constants, the refractive index, absorption coefficient, energy loss function have been found through calculations. Apart from these results the elastic constants and bulk modulus were obtained experimentally, using X-ray measurement and Vegard׳s law with aim comparison. These properties of ternary alloys were explored using the properties of binary alloys. It is seen that results obtained from both methods are all in agreement. Be 1− x Zn x Te alloy also shows the alloy ionic character for x =0.25. When the Zn is increased, the ionic property of all alloys is increases. Furthermore, as the alloy with x =0.25 shows a flexible characteristic property, other alloys become brittle one. [ABSTRACT FROM AUTHOR]