Periodic density functional theory study of the high-pressure behavior of energetic crystalline 1,4-dinitrofurazano[3, 4-b]piperazine

A detailed study of the structural, electronic, and optical absorption properties of crystalline 1,4-dinitrofurazano[3,4-b]piperazine (DNFP) under hydrostatic pressures of 0–100 GPa was performed using periodic density functional theory. As the pressure increases, the lattice constants and cell volumes calculated by LDA gradually approach those obtained by GGA-PW91. It was found that the structure of DNFP is much stiffer in the b direction than along the a and c axes, indicating that the compressibility of the crystal is anisotropic. As the pressure increases, the band gap gradually decreases, and this decrease is more pronounced in the low-pressure range than in the high-pressure region. An analysis of the density of states showed that the electronic delocalization in DNFP gradually increases under the influence of pressure. DNFP exhibits relatively high optical activity at high pressure. As the pressure increases, the bands in the fundamental absorption region of the absorption spectrum of DNFP become more numerous and intense.     

Crystal structure, energy band and optical characterizations of praseodymium monophosphate PrPO4

The structural, optical, and electronic properties of PrPO₄ have been investigated by means of single-crystal X-ray diffraction. Atomic arrangement of PrPO₄ structure is based on corner and edge sharing PrO₉ polyhedra and PO₄ tetrahedra. The energy band structure, density of states, dielectric constant, refractive index and the chemical bonds have been investigated by density functional methods (DFT). The calculated total and partial densities of states indicate that the top of valence bands is mainly built upon O-2p states which interact with P-3p states via σ(P-O) interactions, and the low conduction bands mostly originates from Pr-4f states. The P-O bond is mostly covalent in character and the interactions between Pr and O atoms are ionic.     

Pressure-induced improvement in symmetry and change in electronic properties of SnSe

To explore the structural and electronic properties of SnSe under pressure, we applied hydrostatic pressure from 0 to 8 GPa to a fully relaxed SnSe cell sample based on plane-wave pseudopotential density functional theory. The calculated results indicate that the structure of SnSe changes gradually from an irregular zigzag structure with low symmetry to a B1-like structure with regular arrangement and high symmetry under pressure. The lattice parameters and cell volume of SnSe decrease monotonically as the applied pressure increases. The energy band gap of SnSe becomes narrow under pressure and is finally closed at 6.1 GPa. Moreover, we found that SnSe exhibits non-magnetic and semi-metallic features based on analyzing its electronic state density and spin state density. This can be attributed to the decrease in the lattices constants and the enhancement of the Sn–Se bond interaction under pressure, which causes the density of electronic states to increase near the Fermi surface. Finally, the charge distribution between Se–Sn–Se along the c-axis changes gradually from asymmetric to symmetric as the pressure is increased to 6.1 GPa and beyond. This implies that enhancement of the structure symmetry of SnSe can lead to a symmetrical distribution of charges, which further affects the bonding characteristics of the Sn–Se bond.     

Theoretical analysis on the structure and properties of thiourea dioxide crystal

The equilibrium geometry, electronic structure and optical properties of thiourea S, S-dioxide crystal have been studied using DFT within generalized gradient approximation (GGA) and the local density approximation (LDA), implemented using ultrasoft pseudo-potentials. The optimum bulk geometry is in good agreement with crystallographic data. An analysis of electronic structure, charge and bond order is presented. The energy gap of thiourea dioxide with GGA and LDA calculation is 3.217 or 3.210 eV, respectively, indicating that the compound is an insulator. The calculated absorption spectrum shows a number of absorption peaks, which are believed to be associated with different exciton states, in the fundamental absorption region.     

Linear and nonlinear optical properties of azobenzene derivatives

The results of computations of spectroscopic parameters of lowest–lying electronic excited states of azobenezene derivatives are presented. The analysis of experimentally recorded spectra was supported by quantum chemical calculations using density functional theory. The theoretically determined resonant (two-photon absorption probabilities) and non-resonant (first-order hyperpolarisability) nonlinear optical properties are also discussed, with an eye towards the performance of recently proposed long-range corrected (LRC) schemes (LC–BLYP and CAM–B3LYP functionals). Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Ab initio and molecular dynamics studies of solid β-HMX: effects of hydrostatic pressure and high temperature

Using first-principles density functional theory and classical molecular dynamics (MD), the structural, electronic and mechanical properties of the energetic material β-HMX have been studied. The crystal structure optimised by the local density approximation calculations compares reasonably with the experimental data. Electronic band structure and density of states indicate that β-HMX is an insulator with a band gap of 3.059 eV. The pressure effect on the crystal structure and physical properties has been investigated in the range of 0–40 GPa. The crystal structure and electronic properties change slightly as the pressure increases from 0 to 2.5 GPa; when the pressure is above 2.5 GPa, further increment of the pressure results in significant changes in crystal structure. There is a larger compression along the b-axis than along the a- and c-axes. Isothermal–isobaric MD simulations on β-HMX were performed in the temperature range of 5–400 K. Phase transition at 360 K, corresponding to a volume interrupt, was found. The computed thermal expansion coefficients show anisotropic behaviour with a slightly larger expansion along the b- and c-axes than along the a-axis. In the temperature range of 5–360 K, β-HMX possesses good plasticity and its stiffness decreases with increasing the temperature.     

Quantum chemical investigation of nitrotyrosine (3-nitro-l-tyrosine) and 8-nitroguanine

The structural, vibrational and electronic properties of nitrotyrosine and 8-nitroguanine have been investigated theoretically by performing the molecular mechanics (MM+ force field), the semi-empirical self-consistent-field molecular-orbital (PM3), and density functional theory calculations. The geometry of the nitrotyrosine and 8-nitroguanine molecules have been optimized, the vibrational dynamics and the electronic properties calculated in their ground states in the gas phase.     

The structural, electronic, and optical properties of ladder-type polyheterofluorenes: a theoretical study

The ladder-type polyheterofluorenes were investigated theoretically by using density functional theory (DFT) to reveal their optical and electronic properties for applications in organic optoelectronic devices. The incorporation of heteroatoms (B, Si, Ge, N, P, O, and S) into the ladder-type highly fused polyfluorene backbone can influence and modify the optoelectronic properties significantly. The functionalization on the heteroatoms allows for facile derivation and incorporation of substitutes to further tune the properties. Small geometry variations between the ground, anionic/cationic, the first excited singlet and triplet states were observed due to the very rigid ladder-type coplanar backbone. Ladder-type polycarbazole was predicted to have the highest HOMO and LUMO energy levels, polyphosphafluorene oxide have the lowest HOMO energy level, polyborafluorene have the lowest LUMO energy level and bandgap, and polysulfafluorene has the highest bandgap and triplet energy. The ladder-type carbazole and borafluorene show the highest hole and electron injection abilities respectively; while sulfafluorene has the highest electron transfer rate. Most ladder-type heterofluorenes show bipolar charge transport character suggested by the reorganization energy. All of them have significantly short effective conjugation length in comparison with linear conjugated polymers. Their absorption and emission spectra were also simulated and discussed. The diversified electronic and optical properties of the ladder-type polyheterofluorenes with the different incorporated heteroatom and the substituent on it indicate their broad potential applications in organoelectronics.     

Predictive physical study of two different crystalline forms of glucose

The GGA functional PW91 were used in order to predict the structural, electronic, optical and elastic properties of α and β of d- Glucose. Such compounds, in their solid form, are widely used in chemical and pharmaceutical industry. The pure crystalline forms of glucose α-d-glucose and β-d-glucose have the same space group (McDonald and Beevers, 1950) [1]. We note that despite the fact that the two compounds have the same space group, upon cooling, the interatomic distances change and a new compound occurs. On the other hand, the cooling also influences the physical properties (structural, elastic, electronic and optical properties). The objective of this paper is associated with the control of the physical states of molecular materials when they are subjected to polymorphic changes. The laws and physical parameters that govern these transformations remain fundamentally misunderstood.     

Linear polyenes: models for the spectroscopy and photophysics of carotenoids

We have developed procedures for synthesizing dimethyl polyenes using living polymerization techniques and have initiated investigations of the spectroscopic properties of these molecules. Purification using high-performance liquid chromatography (HPLC) of the polyene mixtures resulting from the syntheses promises to provide all-trans polyenes with a wide range in the number of conjugated double bonds. Low temperature optical measurements on these model systems, both in glasses and in n-alkane mixed crystals, yield absorption and fluorescence spectra with considerably higher vibronic resolution than the spectra currently available for carotenoids with comparable conjugation lengths. The dimethyl polyenes thus allow a more precise exploration of the electronic properties of long, linearly conjugated systems. These studies can be used to verify the existence of low-lying singlet states predicted by theory and recently invoked to explain low-resolution fluorescence, Raman excitation spectra, and the transient absorption spectroscopy of carotenoids. Steady state and time-resolved optical studies of the dimethyl series will be used to better understand the energies and dynamics of the low energy electronic states relevant to the photochemistry and photobiology of all linearly conjugated systems.     

Photic Volume in Photobioreactors Supporting Ultrahigh Population Densities of the Photoautotroph Spirulina platensis

Characterization of the photic zone and light penetration depth in cultures with ultrahigh cell densities represents a major issue in mass cultures of phytoautotrophic microorganisms grown in enclosed photobioreactors. In a study of the effect of underwater optical properties on the penetration depth of photosynthetically active radiation, the inherent optical properties of algal suspensions, i.e., absorption and scattering coefficients, as well as their apparent optical properties, i.e., the reflectance and the vertical attenuation coefficient of downwelling irradiance, were determined by using high-spectral-resolution radiometric measurements. The vertical attenuation coefficient was used to estimate quantitatively the depth of light penetration into a reactor containing an ultrahigh cell density (chlorophyll concentration, up to 300,000 mg m(sup-3)). For such a high cell density, the photic volume in the reactor was found to be extremely small; nevertheless, it differed between the blue and red light (less than 0.06 mm) and the green light (about 0.5 mm). This suggests a singular role for green light under the unique circumstances existing in ultrahigh-cell-density cultures of photoautotrophs.     

Structure-property relationships for three indoline dyes used in dye-sensitized solar cells: TDDFT study of visible absorption and photoinduced charge-transfer processes

The electronic structures of three D-A-π-A indoline dyes (WS-2, WS-6, and WS-11) used in dye-sensitized solar cells (DSSCs) were studied by performing quantum chemistry calculations. The coplanarity of the A-π-A segment and distinct noncoplanarity of the indoline donor part of each dye were confirmed by checking the calculated geometric parameters. The relationships between molecular modifications and the optical properties of the dyes were derived in terms of the partial density of states, absorption spectrum, frontier molecular orbital, and excited-state charge transfer. 3D real-space analysis of the transition density (TD) and charge difference density (CDD) was also performed to further investigate the excited-state features of the molecular systems, as they provide visualized physical pictures of the charge separation and transfer. It was found that modifying the alkyl chain of the bridge unit near the acceptor unit is an efficient way to decrease dye aggregation and improve DSSC efficiency. Inserting a hexylthiophene group next to the donor unit leads to a complicated molecular structure and a decrease in the charge-transfer ability of the system, which has an unfavorable impact on DSSC performance.     

A large gap opening of graphene induced by the adsorption of CO on the Al-doped site

We investigated CO adsorption on the pristine, Stone-Wales (SW) defected, Al- and Si- doped graphenes by using density functional calculations in terms of geometric, energetic and electronic properties. It was found that CO molecule is weakly adsorbed on the pristine and SW defected graphenes and their electronic properties were slightly changed. The Al- and Si- doped graphenes show high reactivity toward CO, so calculated adoption energies are about ?11.40 and ?13.75 kcal mol^?1 in the most favorable states. It was found that, among all the structures, the electronic properties of Al-doped graphene are strongly sensitive to the presence of CO molecule. We demonstrate the existence of a large E_g opening of 0.87 eV in graphene which is induced by Al-doping and CO adsorption.     

Experimental and theoretical DFT (B3LYP,X3LYP,CAM-B3LYP and M06-2X) study on electronic structure,spectral features,hydrogen bonding and solvent effects of 4-methylthiadiazole-5-carboxylic acid

Detailed structural, electronic and spectroscopic study of 4-methylthiadiazole-5-carboxylic acid, one of the simplest 1,2,3-thiadiazole derivatives has been performed using density functional theory at four different functionals (B3LYP, X3LYP, CAM-B3LYP and M06-2X). The two possible conformers and their dimeric forms have been investigated for the stability and hence for the calculation of molecular properties of the title compound. Vibrational analysis has been performed with the help of experimental FT-IR and FT-Raman spectra. NBO analysis has been performed to estimate the N–H—O=C hydrogen bond strength and to evaluate the intra and inter molecular charge transfer in the system. Intermolecular hydrogen-bond strength has also been computed using Atoms in Molecules (AIM) theory. To visualise spatial domain, key sites of electron transitions and electron density difference between ground as well as excited states, and their 2D and 3D plots have been computed. Solvent effect on the intermolecular hydrogen bonding have also been investigated using solvents of different polarities. Non-linear optical properties, molecular electrostatic potential surface map (MESP), thermodynamic potentials at different temperatures have also been computed and plotted.     

Thermal,structural, optical,and photon shielding studies of cerium-doped barium tellurite glasses

A series of tellurite-based glasses are prepared by using a melt-quenching method. The effect of cerium on the physical, thermal, structural, optical, spectroscopic, and shielding properties of barium tellurite glass samples is studied. It has been observed that the thermal stability factor increases with increasing cerium ion (Ce³⁺) concentration. The density and other physical parameters such as ion concentration and molar volume are calculated using the Archimedes principle. An increase in optical band gap and density suggests a decrement in non-bridging oxygens. These results are in accordance with Raman results. The blue emission in prepared glasses is studied in terms of International Commission on Illumination chromaticity coordinates. Moreover, various shielding properties such as mass attenuation coefficient, linear attenuation coefficient, effective atomic number, half-value layer, and tenth-value layer have also been determined to understand the photon shielding characteristics of as-prepared glass samples.     

Size Confinement Effects on Electronic and Optical Properties of Silver Halide Nanocrystals as Probed by Cryo-EFTEM and EELS

Cryo-energy-filtering transmission electron microscopy and electron energy-loss spectroscopy have been applied to study size confinement effects on electronic, dielectric, and optical properties of Ag(Br, I) nanocrystals. The dielectric permittivity, optical joint density of states, refractive index, extinction, and absorption for nanocrystals derived via Kramers–Kronig relations have been compared with experimental data for Ag(Br, I) tabular microcystals and ab initio linear muffin-tin orbital method in its atomic spheres approximation calculations for AgBr. Contrast tuning with the selected energy window between 0 and 100 eV enabled visualizing valence electron excitations in silver halides because of plasmons superimposed with interband transitions and Mott–Wannier excitons. The nonuniform contrast of nanocrystals revealed by cryo-energy-filtering transmission electron microscopy was referred to a size-confined coupling of surface and volume losses that could lead to oscillations of the image intensity with the nanocrystal size. A size-dependent enhancement of interband transitions at 4 eV correlated with the enhancement of exciton luminescence from nanocrystals because of contributions to the energy-level structure from carrier confinement and surface states.     

Electronic, magnetic and optical properties of Cu, Ag, Au-doped Si clusters

The structural, optical and magnetic properties of Cu, Ag, Au-doped Si₇ Clusters have been systematically investigated using density functional theory calculations. The global optimized structures of Cu, Ag, Au-doped Si clusters are predicted to have a lower HOMO–LUMO gap and higher magnetic moment. M-doping (M?=?Cu, Ag, Au) in Si cluster widens a range of adsorption wavelength, especially Au-doping. The characteristics in electronic density of states (DOSs) show that C_5v-Si₆Cu has a big asymmetrical spin-up and spin-down. The average atomic moment is 0.428 mμ_B per atom for the Si₆Cu cluster with C_5v symmetry, while the average paramagnetic moment is 0.143 mμ_B per atom for other M-doped (M?=?Cu, Ag, Au) Si₇ clusters.     

Effect of structural modifications on the spectroscopic properties and dynamics of the excited states of peridinin

The spectroscopic properties and dynamics of the lowest excited singlet states of peridinin and two derivatives have been studied by steady-state absorption and fast-transient optical spectroscopic techniques. One derivative denoted PerOlEs, possesses a double bond and a methyl ester group instead of the r-ylidenebutenolide of peridinin. Another derivative denoted PerAcEs, is the biosynthetic precursor of peridinin and possesses a triple bond and a methyl ester group corresponding to the r-ylidenbutenolide function. Ultrafast time-resolved spectroscopic experiments in the visible and near-infrared regions were performed on the molecules and reveal the energies and regarding the structural features and interactions responsible for the unusual solvent-induced changes in the steady-state and transient absorption spectra and dynamics of dynamics of the excited electronic states. The data also provide information peridinin.     

Plasmon Spectroscopy for Subnanometric Copper Particles: Dielectric Function and Core–Shell Sizing

In the last years, there has been a growing interest in the study of transition metal nanoparticles (Nps) due to their potential applications in several fields of science and technology. In particular, their optical properties are governed by the characteristics of the dielectric function of the metal, its size and environment. This work analyses the separated contribution of free and bound electrons on the optical properties of copper Nps. Usually, the contribution of free electrons to the dielectric function is corrected for particle size through the modification of the damping constant, which is changed as usual introducing a term inversely proportional to the particle’s radius to account for the extra collisions with the boundary when the size approaches the electronic mean free path limit (about 10 nm). For bound electron contribution, the interband transitions from the d-band to the conduction band are considered together with the fact that the electronic density of states in the conduction band must be made size-dependent to account for the larger spacing between electronic energy levels as the particle decreases in size below 2 nm. Taking into account these specific modifications of free and bound electron contributions to the dielectric function, it was possible to fit the bulk complex dielectric function, and consequently, determine optical parameters and band energy values such as the coefficient for bound electron contribution Q _bulk?=?2?×?10²⁴, gap energy E _g?=?1.95 eV, Fermi energy E _F?=?2.15 eV, and damping constant for bound electrons γ _b?=?1.15?×?10¹⁴ Hz. With both size-dependent contributions to the dielectric function, extinction spectra of copper Nps in the subnanometer radius range can be calculated using Mie’s theory and its behaviour with size can be analysed. These studies are applied to fit experimental extinction spectra of very small spherical core–shell Cu–Cu₂O Nps generated by ultrafast laser ablation of a solid target in water. Theoretical calculations for subnanometric core radius are in excellent agreement with experimental results obtained from core–shell colloidal Nps. From the fitting, it is possible determining core radius and shell thickness of the Nps, showing that optical extinction spectroscopy is a good complementary technique to standard high-resolution electron microscopy for sizing spherical nanometric-subnanometric Nps.     

Electronic and optical properties of functionalized zigzag ZnO nanotubes

The present paper reports the analysis of surface decoration on the structural, electronic, and optical properties of (n,0) ZnO nanotubes, performed by means of a density function theory based ab-initio approach. Fe functionalization induced buckling in ZnO nanotubes affects its electronic and optical properties. Increase in Fe functionalization leads to better stability of ZnO nanotube and shows enhanced metallic character. The possibility of its use in optoelectronics has been analyzed in terms of dielectric constant, absorption coefficient, and refractive index. In another observation, the high sensitivity of the HCN molecule for the Fe-incorporated ZnO nanotube suggests it as a potential gas sensor.

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Graphical abstract HCN-adsorbed Fe-ZnO nanotube, electron difference density, and PDOS analysis of different orbitals.