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Context: In this paper, the optimum coverage of 4.44% and the optimum adsorption sites were determined for the Be3N2 adsorption system of O atoms at different coverages based on density functional theory. The electronic and optical properties of the model were investigated by applying bending deformation to the model at these coverage and adsorption sites. Adsorption of O atoms disrupts the geometrical symmetry of Be3N2, resulting in orbital rehybridization and lowering its band gap. Bending deformation causes the band gap of the adsorbed O atom structure of Be3N2 to first increase and then decrease, resulting in the modulation of its band gap. With increasing bending deformation, the adsorbed system is redshifts, and the degree of redshift increases with increasing bending deformation. Methods: All calculations in this paper were performed using the first-principles-based CASTEP module of Materials Studio (MS). The generalized gradient approximation (GGA) plane-wave pseudopotential method and the Perdew-Burke-Ernzerhof (PBE) Perdew et al. Phys Rev Lett 77:3865, 1996 generalized functional were used in the geometry optimization and calculation process to calculate the exchange–correlation potential between electrons. The effect of coverage on the electronic and optical properties of the Be3N2-adsorbed O atom system was investigated by adsorbing different numbers of O atoms on a monolayer of Be3N2. The Be3N2 protocell contains two N atoms and three Be atoms with a space community of P6/MMM (No.191). The original cell was expanded 3 times along the direction of the base vectors a and b in the Be3N2 plane to create a 3 × 3 × 1 monolayer Be3N2 supercell system. A vacuum layer of 15 Å is set in the direction of the crystal plane of the vertical monolayer Be3N2 supercell to eliminate interactions between adjacent layers. In the overall energy convergence test of the Be3N2 supercell, the plane wave truncation energy was set to 500 eV, and the energy difference between the calculations given in the literature Reyes-Serrato et al. J Phys Chem Solids 59:743-6, 1998 using 550 eV was less than 0.01 eV, verifying the reliability of the data at a truncation energy of 500 eV. The Monkhorst–Pack special k-point sampling method Monkhorst et al. Phys Rev B 13:5188, 1976 was used in the structural calculations, and the grid was set to 3 × 3 × 1. The geometric optimization parameters are set as follows: the self-consistent field iteration convergence criterion is 2.0 × 10−6 eV, and the iterative accuracy convergence value is not less than 1.0 × 10−5 eV/atom for the total force of each atom and less than 0.03 eV/Å for all atomic forces. In addition the high-symmetry k-point path is taken as Γ(0,0,0) → M(0,0.5,0) → K(− 1/3,2/3,0) → Γ(0,0,0) Chen et al, AIP Adv 8:105105, 2018. [ABSTRACT FROM AUTHOR]

Context: The electronic properties and optical properties of Cr-doped monolayer WS2 under uniaxial compressive deformation have been investigated based on density functional theory. In terms of electronic structure properties, both intrinsic and doped system bandgaps decrease with the increase of compression deformation, and the values of the bandgap under the same compression deformation after Cr doping are reduced compared with the corresponding intrinsic states. When the compressive deformation reaches 10%, both the intrinsic and doped system band gaps are close to zero. New electronic states and impurity energy levels appear in the WS2 system when doped with Cr atoms. For the optical properties, the calculation and analysis of the dielectric function under each deformation regime of monolayer WS2 show that the compression deformation affects the dielectric function, and when the compression deformation is 10%, the un-doped and Cr-doped regimes show a decrease in ε1(ω) compared to the compression deformation of 8%. For each deformation system, the peak reflections occur in the ultraviolet region. Near the position where the second peak of the absorption spectrum appears, it can be seen that the ability of each system to absorb light gradually decreases with the increase of the amount of deformation and appears to be red-shifted to varying degrees. Methods: This study follows the initial principles of the density functional theory framework and is based on the CASTEP module of Materials-Studio software GGA and PBE generalizations are used to perform computations such as geometry optimization of the model. We have calculated the energy band structure of monolayer WS2 with intrinsic and compressive deformations of 2% and 4% using PBE and HSE06, respectively. The band gap values calculated using PBE are 1.802 eV, 1.663 eV, and 1.353 eV, respectively, and the band gap values calculated with HSE06 are 2.267 eV, 2.034 eV, 1.751 eV. The results show that the bandgap values calculated by HSE06 are significantly higher than those calculated by PBE, but the bandgap variations calculated by the two methods have the same trend, and the shape characteristics of the energy band structure are also the same. However, it is worth noting that the computation time required for the HSE06 calculation is much longer than that of the PBE, which is far beyond the capability of our computer hardware, and the purpose of this paper is to investigate the change rule of the effect of deformation on the bandgap value, so to save the computational resources, the next calculations are all calculated using the PBE. The Monkhorst–Pack special K-point sampling method is used in the calculations. The cutoff energy for the plane wave expansion is 400 eV, and the K-point grid is assumed to be 5 × 5 × 1. Following geometric optimization, the iterative precision converges to a value of less than 0.03 eV/Å for all atomic forces and at least 1 × 10−5 eV/atom for the total energy of each atom. The vacuum layer's thickness was selected at 20 Å to mitigate the impact of the interlayer contact force. [ABSTRACT FROM AUTHOR]

We have simulated the effect of changing the end groups in BTP core with five organic units of 1,3-Indandione (IN), 2-thioxothiazolidin-4-one (Rhodanine), propanedinitrile (Malononitrile), (2-(6-oxo-5,6-dihydro-4H-cyclopenta[c]thiophen-4-ylidene)malononitrile) (CPTCN) and 2-(3-oxo-2,3-dihydroinden-1-ylidene (IC), and two halogenated units of (4F) IC and (4Cl) IC on the optical and photovoltaic properties of the BTP DA'D core molecular unit. Thus modified, seven molecular structures are considered and their optical properties, including HOMO and LUMO energies and absorption spectra are simulated in this paper. On the basis of HOMO and LUMO energies, it is found that two of the seven molecules, BTP-IN and BTP-Rhodanine, can act as donors and the other four, BTP-(4F) IC, BTP-(4Cl) IC, BTP-CPTCN and BTP-IC, as acceptors in designing bulk heterojunction (BHJ) organic solar cells (OSCs). Using these combinations of donors and acceptors in the active layer, eight BHJ OSCs, such as BTP-IN: BTP-(4F) IC, BTP-IN: BTP-(4Cl) IC, BTP-IN: BTP-CPTCN, BTP-IN: BTP-IC, BTP-Rhodanine: BTP-(4F) IC, BTP-Rhodanine: BTP-(4Cl) IC, BTP-Rhodanine: BTP-CPTCN and BTP-Rhodanine: BTP-IC, are designed, and their photovoltaic performance is simulated. The photovoltaic parameters J s c , V o c and FF for all eight BHJ OSCs and their power conversion efficiency (PCE) are simulated. It is found that the BHJ OSC of the BTP-IN: BTP-CPTCN donor–acceptor blend gives the highest PCE (14.73%) and that of BTP-Rhodanine: BTP-(4F) IC gives the lowest PCE (12.07%). These results offer promising prospects for the fabrication of high-efficiency BHJ OSCs with the blend of both donor and acceptor based on the same core structure. [ABSTRACT FROM AUTHOR]

Context: Cubic boron arsenide (c-BAs), a semiconducting material with ultra-high thermal conductivity and carrier mobilities, has been studied using first-principles calculation. This study examined the elastic and optoelectronic properties of c-BAs. The challenge of subphase boron (B) formation in bulk form owing to the volatile nature of arsenic (As) makes it mandatory to calculate its optoelectronic properties, by producing vacancies and antisite defects with BAs (As atom on a B site) and AsB (B atom on an As site). The mechanical properties including bulk (B), shear (G) moduli, and Poison's ratio of all the systems were studied. It was found that mechanical instability of the structure is observed for the overall vacancy creation, arsenic substitution, and mutual antisite defects. Further, pristine c-BAs showed an indirect bandgap of 1.48 eV. Defect formation reduces the bandgap and shifts the absorption peaks, which improves the overall optoelectronic properties of the host material. In addition, B vacancy formation shows the maximum optical absorption and reflectivity and low energy loss, suggesting its potential applications for optoelectronic devices. The obtained anticipated data from this study is for the optoelectronic and elastic properties of c-BAs, for the device applications in photonics and electronics. Method: In this paper, the elastic and optoelectronic properties of the pristine and defected c-BAs were systematically investigated using the Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA). The SIESTA program uses pseudopotentials in the norm-conserving nonlocal forms and pseudo-atomic orbital (PAO) basis set with a double-zeta potential (DZP) which are fundamental for calculating the Hamiltonian and overlap matrices in O(N) operations. [ABSTRACT FROM AUTHOR]

Iron impurities are believed to act as deep acceptors that can compensate for the n-type conductivity in as-grown Ga2O3, but several scientific issues, such as the site occupation of the Fe heteroatom and the complexes of Fe-doped β-Ga2O3 with native defects, are still lacking. In this paper, based on first-principle density functional theory calculations with the generalized gradient approximation approach, the controversy regarding the preferential Fe incorporation on the Ga site in the β-Ga2O3 crystal has been addressed, and our result demonstrates that Fe dopant is energetically favored on the octahedrally coordinated Ga site. The structural stabilities are confirmed by the formation energy calculations, the phonon dispersion relationships, and the strain-dependent analyses. The thermodynamic transition level Fe3+/Fe2+ is located at 0.52 eV below the conduction band minimum, which is consistent with Ingebrigtsen's theoretical conclusion, but slightly smaller than some experimental values between 0.78 eV and 1.2 eV. In order to provide direct guidance for material synthesis and property design in Fe-doped β-Ga2O3, the defect formation energies, charge transitional levels, and optical properties of the defective complexes with different kinds of native defects are investigated. Our results show that VGa and Oi can be easily formed for the Fe-doped β-Ga2O3 crystals under O-rich conditions, where the +3 charge state FeGaGai and −2 charge state FeGaOi are energetically favorable when the Fermi level approaches the valence and conduction band edges, respectively. Optical absorption shows that the complexes of FeGaGai and FeGaVGa can significantly enhance the optical absorption in the visible-infrared region, while the energy-loss function in the β-Ga2O3 material is almost negligible after the extra introduction of various intrinsic defects. [ABSTRACT FROM AUTHOR]

The influence of pressure on the optical properties of nanostructured tetragonal Cu 2 Sb has been investigated jointly by experimental Raman spectroscopy (RS) and theoretical first-principles calculation based on density functional theory (DFT) varying pressure from zero (ambient condition) to 45 GPa. The DFT determined pressure dependence of the Raman active modes and the mode-Grüneisen parameters for each Raman mode are found to be in excellent agreement with those experimentally determined. Comparison of the pressure evolution of the experimental Raman data with those of DFT has allowed us to make the proper assignment of optical phonon modes. Image 1 • The Raman modes of the Cu 2 Sb were observed under high-pressures conditions. • The high-pressure in-situ data were supported by ab initio calculations. • The compressibility parameter of the Cu2Sb were obtained. • In-situ high-pressure Raman scattering and ab-initio studies in Cu2Sb up to 45 GPa. [ABSTRACT FROM AUTHOR]

MoO3 and MoO2 systems have attracted particular attention for many widespread applications thanks to their electronic and optical peculiarities; from the crystallographic point of view, MoO3 adopts a thermodynamically stable orthorhombic phase (α-MoO3) belonging to the space group Pbmn, while MoO2 assumes a monoclinic arrangement characterized by space group P21/c. In the present paper, we investigated the electronic and optical properties of both MoO3 and MoO2 by using Density Functional Theory calculations, in particular, the Meta Generalized Gradient Approximation (MGGA) SCAN functional together with the PseudoDojo pseudopotential, which were used for the first time to obtain a deeper insight into the nature of different Mo–O bonds in these materials. The calculated density of states, the band gap, and the band structure were confirmed and validated by comparison with already available experimental results, while the optical properties were validated by recording optical spectra. Furthermore, the calculated band-gap energy value for the orthorhombic MoO3 showed the best match to the experimental value reported in the literature. All these findings suggest that the newly proposed theoretical techniques reproduce the experimental evidence of both MoO2 and MoO3 systems with high accuracy. [ABSTRACT FROM AUTHOR]

Context: Based on the first-principles calculations, this paper investigates the structural, elastic, electronic, and optical properties of albite and kaolinite, respectively. It is determined that both of them show structural stability, mechanical stability, and brittleness by calculating formation enthalpy, phonon dispersion, elastic, and mechanically relevant properties. Both materials are insulators with an indirect bandgap. By calculating the TDOS and PDOS, the main characteristics of the electronic structure of NaAlSi3O8 come from O-2p and Si-3p states, O-2p, and Al-3p states hybridization, similar to Al4[Si4O10](OH)8. The covalence of Si–O bonds in NaAlSi3O8 is greater than Al–O bonds, and the covalent property sequence of Si–O bands in NaAlSi3O8 is Si2-O3 > Si1-O4 > Si2-O2 > Si1-O8 > Si1-O6 > Si3-O2 > Si3-O4. The optical anisotropy of NaAlSi3O8 and Al4[Si4O10](OH)8 is analyzed. Methods: First-principles density functional theory (DFT) calculation was carried out by the CASTEP computer program. The GGA-PW91 exchange–correlation was used. The energy convergence tolerance, the maximum force, and the maximum displacement were set in the calculation. [ABSTRACT FROM AUTHOR]

The Dirac cone in the single-layer graphene limits its application in electronic devices such as Schottky barrier diodes and field-effect transistors. Thus, we make the novel heterostructures based on graphene to solve this problem. The electronic and optical properties of pristine and Ag/Au/Cu-doped graphene/MoS 2 heterostructures are investigated by using the density functional theory. For the Ag/Au/Cu-doped MoS 2 monolayer, the results show that they are magnetic. Their bands across the Fermi level, which indicates these systems are metallic. For the Ag/Au/Cu-doped graphene/MoS 2 heterostructures, they are metallic and nonmagnetic. Especially in the Au-doped graphene/MoS 2 , the Dirac cone opens about 66 meV. It means that Au-doped graphene/MoS 2 has the potential to be a candidate material for high speed electronic devices. Compared with pristine heterostructure, the probability of electron transition in the low energy region is the enhanced in Ag/Au/Cu-doped systems. The optical absorption coefficient of doped heterostructure is enhanced in the range of 0–0.4 eV and 1.7–2.7 eV. This work indicates that these heterostructures have a certain potential in the application of nanodevices. [Display omitted] • This paper confirms that the graphene can adsorb on Ag/Au/Cu-doped MoS 2 monolayer stably. • This paper finds that the Dirac cone in the Au-doped graphene/MoS 2 heterostructure opens about 66 meV. • The introduction of Ag/Au/Cu atoms in graphene/MoS 2 heterostructure can make the electron transfer at low energy. • The optical absorption coefficient is improved in these doped heterostructures. [ABSTRACT FROM AUTHOR]

HfO2 can assume different crystalline structures, such as monoclinic, orthorhombic, and cubic polymorphs, each one characterized by unical properties. The peculiarities of this material are also strongly related to the presence of doping elements in the unit cell. Thus, the present paper has the main purpose of studying and comparing twelve different systems characterized by diverse polymorphs and doping percentages. In particular, three different crystalline structures were considered: the monoclinic P21/c, the orthorhombic Pca21, and the cubic Fm 3 ¯ m phases of HfO2. Each one has been studied by using Y as a doping agent with three different contents: 0% Y:HfO2, 8% Y:HfO2, 12% Y:HfO2, and 16% Y:HfO2. For all the systems, density functional theory (DFT) methods based on PBE/GGA, and on the HSE hybrid functionals were used to optimize the geometry as well as to study their optical properties. Depending on the polymorphs, Y affects the formation energy in different ways and causes changes in the optical properties. When the percentage of Y did not exceed 12%, a stabilization of the cubic phase fraction and an increase of the dielectric constant was observed. Additionally, the calculated optical bandgap energies and the refractive index are examined to provide an overview of the systems and are compared with experimental data. The bandgaps obtained are in perfect agreement with the experimental values and show a slight increase as the doping percentage grows, while only minor differences are found between the three polymorphs in terms of both refractive index and optical band gap. The adopted first principles study generates a reasonable prediction of the physical-chemical properties of all the systems, thus identifying the effects of doping phenomena. [ABSTRACT FROM AUTHOR]

This paper employs the Heyd-Scuseria-Ernzerhof (HSE) function to research electronic structures of monolayer InxAl1-xN with different compositions (x = 0, 0.25, 0.5, 0.75, 1) based on the first-principles, and the optical properties of singlelayer InxAl1-xN are calculated by Generalized Gradient Approximation-Perdew Burke Ernzerhof (GGA-PBE) function. The influence of the electronic structure on the properties has been analyzed. Then the influence of doping quantity on the characteristics has been summarized, which also indicates the trend of the complex dielectric function and absorption spectrum. The calculation results show that with the increase of x, the static dielectric constant increases, the electron transition ability increases, and the absorption peak intensity in the light absorption spectrum increases. It can conclude that the InxAl1-xN compound can theoretically achieve the adjustable Eg and photoelectric performance with x, which will apply in making various optoelectronic devices, including solar cells and sensors. [ABSTRACT FROM AUTHOR]

This paper explains our first-principle computational investigation regarding the structural, optical, elastic, and electrical characteristics of gallium-based GaMF3 (M = Be and Ge) perovskite-type (halide-perovskite) compounds. Our current computation is based on density functional theory (DFT) and is achieved with the help of the WIEN2k code. We used the Birch–Murnaghan equation for optimization; in both compounds, we found that both GaBeF3 and GaGeF3 compounds are structurally stable. For the computation of elastic characteristics, the IRelast package for calculating elastic constants (ECs) is utilized. These compounds are mechanically ductile, scratch-resistant, anisotropic, and mechanically stable, showing huge opposition to plastic strain. The modified Becke–Johnson (TB-mBJ) potential approximation method is used to calculate different physical characteristics and shows that GaGeF3 behaves as a metal, whereas the GaBeF3 compound is insulating in nature. The involvement of various electronic states in band structures is calculated using the theory of the density of states. The different optical properties of these compounds can be studied easily using their band gap energy. At high energy ranges, these substances demonstrate strong absorption. At low energies, the GaGeF3 compound is transparent, while the GaBeF3 compound is opaque to incoming photons. Investigation of the optical characteristics has led us to the conclusion that both GaGeF3 and GaBeF3 compounds can be used for high-frequency ultraviolet device applications. This computational work is considered to be the first time that we can study these compounds, which to our knowledge have not previously been experimentally validated. [ABSTRACT FROM AUTHOR]

This paper reports, the electronic and optical properties of Ca 6-x Na 2 Y 2 (SiO 4) 6 F 2 :xEu3+ (x = 0–0.05 mol%) fluorapatite ceramic prepared by solution combustion method. The electronic properties such as energy band gap, total density of states, partial density of states, frontier molecular orbitals and mulliken population analysis were investigated with B3LYP hybrid GGA function by density functional theory (DFT). The lattice parameters value of Ca 6 Na 2 Y 2 (SiO 4) 6 F 2 fluorapatite ceramic calculated by DFT shows a good agreement with experimental crystallographic (XRD) analysis. The least square approach was used for computation of crystallographic parameters through Rietveld refinement analysis of XRD patterns. Fourier transform infrared (FTIR) spectra show four different symmetric stretching and bending modes due to the presence of (PO 4), (CO 2) and (OH) groups in Ca 6-x Na 2 Y 2 (SiO 4) 6 F 2 :xEu3+ fluorapatite ceramic. The band gap value calculated by DFT was 5eV whereas calculated by UV–visible spectroscopy was 4.1 eV, which shows the insulating behaviour of Ca 6 Na 2 Y 2 (SiO 4) 6 F 2 ceramic. From frontier molecular orbital calculations the energy band gap between HOMO and LUMO states was found to be 5.194 eV. Mulliken population analysis shows that Ca1, Na1, Si1 and F1 are main electron donors whereas Y1 and O1 are main electron acceptor atoms in Ca 6 Na 2 Y 2 (SiO 4) 6 F 2 ceramic. It also confirms that Y bonds are more covalent in nature than Na and Ca bonds. Photoluminescence (PL) spectroscopy of Ca 6-x Na 2 Y 2 (SiO 4) 6 F 2 :xEu3+fluorapatite ceramic shows three intense peaks at 600 nm, 623 nm and 698 nm perceiving 5D 0 – 7F 1 , 5D 0 – 7F 2 and 5D 0 – 7F 4 transitions in orange and red regions under 250 nm UV excitation. The CIE chromaticity diagram shows cool emission in red and orange region with an application in optical and electronic devices. [ABSTRACT FROM AUTHOR]

In this paper, a new type of Ba 2 La 8 (SiO 4) 6 O 2 : Sm3+ phosphor was synthesized by solid-phase reaction, and the hydrophobic agent was used to restrain the hydrolysis of silicate phosphor. The microstructure, optical properties and electroluminescence properties of the samples were systematically analyzed. The results show that the Ba 2 La 8 (SiO 4) 6 O 2 : x Sm3+ phosphors have a strong orange-red emission at 600 nm, which corresponds to the 6G 5/2 →6H 7/2 energy level transition of Sm3+ ions. The optimal luminescence intensity was achieved at the dopant concentration of 10 mol%. The prepared phosphor has good thermal stability, the luminescence intensity at 423 K is still 85% of that at 298 K, and the internal quantum efficiency (IQE) is 22.59%. The ultraviolet-visible-near-infrared (UV–VIS–NIR) spectrum and the density functional theory reveal that the Ba 2 La 8 (SiO 4) 6 O 2 host can provide an excellent band-gap environment for the luminescent center. In addition, the modified Ba 2 La 8 (SiO 4) 6 O 2 : 0.10Sm3+ phosphor showed excellent hydrophobicity and luminescent properties, with a contact angle of 140.315°, and the luminescent intensity remained 75% of the pre-modified level. The Ba 2 La 8 (SiO 4) 6 O 2 : Sm3+ phosphor has good dispersion in PVA solution and emits bright red light. The above properties indicate that Ba 2 La 8 (SiO 4) 6 O 2 : Sm3+ phosphor has excellent luminescence properties and has broad application prospects. [ABSTRACT FROM AUTHOR]

Using the density functional theory (DFT) of the first principle and Generalized gradient approximation method, the electronic structures and optical properties of the InxGa1-xN crystals with different x (x = 0.25, 0.5, 0.75, 1) have been calculated in this paper. The influence of the electronic structure on the properties has been analyzed. Then the influence of doping quantity on the characteristics has been summarized, which also indicates the trend of complex dielectric function, absorption spectrum and transitivity. With the increase of x, the computational result shows that the optical band gap (i.e.Eg) of the InxGa1-xN crystal tends to be narrow, then the absorption spectrum shifts to the low-energy direction. And the Fermi energy slightly moves to the bottom of conduction band which would cause the growth of conductivity by increasing x. In a word, the InxGa1-xN compound can be achieved theoretically the adjustable Eg and photoelectric performance with x, which will be used in making various optoelectronic devices including solar cell and sensors. [ABSTRACT FROM AUTHOR]

• Structures in transition states were computed by QST2 option. • Calculated hydrogen bond parameters on ILs were compared with crystallographic data in the literature. • Theoretical non-linear optical properties were investigated by DFT method, statically and dynamically. • Interaction energies were calculated by CP approach and Grimme's dispersion model. This paper includes the structural properties, transition state analysis and NLO properties of the ionic liquids in quantum chemical calculations. Hydrogen bond geometries calculated by B3LYP and ωB97XD approaches have been compared with the crystallographic data in the literature. Transition state analysis have been carried out using Synchronous Transit-Guided Quasi-Newton (STQN) method with QST2 option and Density Functional Theory. Forms according to the positions of the proton on hydrogen bond axes and transition states have been evaluated by relative energy scanning. Interactions between anions and cations in ionic liquids optimizations have been studied by CP approach with D2 and D3 versions of Grimme's dispersion correction. Electric dipole moments, dipole polarizability, first and second dipole hyper polarizability and important components have been calculated, statically and dynamically for ionic liquids. Effective and stable structures in terms of NLO have been evaluated. In addition, B3LYP and ωB97XD functionals approaches have been tested considering Grimme's D2/D3 dispersion models for lithium interactions with bis(trifluoromethanesulfonyl)amide and methylsulfonate anions. [ABSTRACT FROM AUTHOR]

Abstract On the basis of great diverse applications of nonlinear optical (NLO) materials, organometallic complexes have attracted considerable attention. In this paper, we present a detailed investigation on a series of Pt(II) dithienylcyclopentene(DTE)-based complexes via density functional theory method with the aim of evaluating their structures, electronic absorption spectra and first hyperpolarizabilities. The calculations demonstrate that the first hyperpolarizabilities can be enhanced by the introduction of quinolone into the complexes because of the enlarged spatial separation of electron density. However, Pt(II) complexes containing perfluorocyclopentene ring exhibit decreasing NLO response attributed to lower amount of charge transferred and short effective CT distance. The static first hyperpolarizabilities (β tot) of monometallic Pt(II) complexes are larger than those of bimetallic Pt(II) complexes due to correlative mixed charge-transfer patterns. More importantly, the closed-ring (1c) complex comprising DTE unit exhibits the largest β tot value approaching 144 × 10−30 esu, with the contrast over five times compared to corresponding open-ring due to the better π-conjugated delocalization and smaller HOMO and LUMO energy gap. In general, we envision our work will be beneficial for further rational design of DTE-containing Pt(II) complexes as high performance NLO materials. Graphical abstract Image 1 Highlights • Monometallic Pt(II) DTE-based complexes exhibit the largest β tot values. • The second-order NLO response of bimetallic Pt(II) complexes can be altered by various ligands. • The switching of NLO properties has been achieved by photoisomerization. [ABSTRACT FROM AUTHOR]

The theoretical applications of hyperbolic metamaterials have generated excitement in multiple fields, particularly in super-resolution optics. In practice, however, the potential of HMMs has been limited by the shortcomings of their constituent parts. Primarily, these are high losses and instabilities in the metal component, which is typically gold or silver, and excessive thickness in both types of layers. In this paper, we use density functional theory to investigate BaMoO 3 -SrHfO 3 metamaterials. We predict that these are hyperbolic throughout the visible range and have the potential to mitigate many of these limitations, including a significant loss reduction. We also examine the accuracy of the effective-medium theory, which is used to predict the bulk optical properties of multilayered HMMs. [Display omitted] • New class of hyperbolic metamaterials based on a layered perovskite/perovskite structure. • Lower losses compared to current metal plasmonic materials like gold and silver. • Comparison of the results of first-principles calculations with those of the effective-medium theory for layered metamaterials. [ABSTRACT FROM AUTHOR]

The I2-II-IV-VI4 series of quaternary chalcogenides semiconductors have drawn wide interest for their potential application as solar-cell absorbers. In this paper, we present a study of electronic and optical properties of the equilibrium kesterite structure (KS) of Cu2ZnGeS4 (CZGS) calculated by means of the full potential linearized augmented plane wave method. For this purpose, we used the Wien2k code based on the density functional theory with the generalized gradient approximation (GGA), modified Becke-Johnson exchange potential (mBJ) and the Hubbard potential U. The TB-mBJ is used alone or combined with U (TB-mBJ, and TB-mBJ+U). The results are compared with other theoretical results and the available experimental ones. The obtained results show that the top of the valence band is mainly composed by the Cu d orbital while the bottom of the conduction band is a mixture of Ge s and S p states. It was found that KS-CZGS has a direct band gap of 0.3, 1.8 and 2.0 eV using GGA, GGA+TB-mBJ and GGA+TB-mBJ+U, respectively. It is observed that states exist above the Fermi level (0 eV) with a width of 0.3 and 0.2 eV when we use GGA and GGA+TB-mBJ, while these states come down under the Fermi level when using GGA+TB-mBJ+U. The optical properties are calculated and an almost isotropic behavior is found in contrast to the reported properties of the stannite phase. This behavior can be linked to the charge density and the structure. [ABSTRACT FROM AUTHOR]

In this paper, structural, spectroscopic and optical properties of a new synthesized of Iron complex Difluoro(oxalato)borate salt with 1,10-phenanthroline ligand have been discussed. The optimized molecular structure, vibrational frequencies and corresponding vibrational assignments of Fe(phen) 3 (BF 4 )(C 2 O 4 BF 2 )·H 2 O have been investigated experimentally and theoretically using Gaussian 09 software package. The optical band gap has been determined from UV–vis spectroscopy by the Tauc model, the obtained band gap values are equal to 2.25 and 2.05 eV for direct and indirect allowed transition respectively. The HOMO and LUMO analysis have been used to determine the energy band gap of the complex and to confirm that charge transfer occurs in the complex. Moreover, the electronegativity, hardness and softness have been calculated to get predictions about chemical behavior for the complex. The stability of the molecule arising from the hyper-conjugative interaction and the charge delocalization has been analyzed using NBO analysis. [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]

In this paper, the effects of biaxial [110] strain synergistic vacancy defects on the binding energy, electronic structure, and optical properties of monolayer MoS 2 were investigated using first-principles based on density functional theory. The results show that the monolayer MoS 2 is the most stable in the unstressed state, when it has vacancy defects, the stability decreases slightly, and the binding energy decreases with the increase of the absolute value of the strain. Monolayer MoS 2 is a semiconductor with a direct band gap of 1.73 ​eV. When Mo-vacancy appears, the band gap decreases significantly and the metallicity increases. When S-vacancy appears, the direct band gap transforms into an indirect band gap and the forbidden bandwidth decreases. The optical properties of the material are red-shifted by tensile strain, and blue-shifted by compressive strain. The strain coordinated vacancy defects have a significant effect on the regulation of the optical properties of monolayer MoS 2. The synergistic strain effect of vacancy provides some theoretical support for the application of monolayer MoS 2 in optics and other fields. The first principle calculation method based on density functional theory is used to study the electronic structure of monolayer MoS 2 and its vacancy structure. Different strains are applied to three different systems to improve the optical properties. The optical properties of materials can be significantly improved by strain synergetic vacancy. [Display omitted] • Effects of strain and vacancy defects on monolayer MoS 2 were investigated. • Using first principles based on density functional theory. • Results show that the synergistic strain of vacancy can effectively tune the optical properties of monolayer MoS 2. • Band gap of monolayer MoS 2 decreases when vacancy defects appear. • The strain will make the optical parameters of the material red shift or blue shift. [ABSTRACT FROM AUTHOR]

The electronic, magnetic, optical and thermoelectric properties of delafossites XMnO 2 (X ​= ​Au, Ag, Cu) have been calculated by DFT approach. The monoclinic phase of crystal structures with space group C2/m (12) are taken for the investigation. The band structures and density of states analysis show CuMnO 2 , AuMnO 2 are ferromagnetic materials. The bandgap values of AuMnO 2 , AgMnO 2 and CuMnO 2 for up spin channel are 1.67 ​eV, 2.43 ​eV and 1.32 ​eV, respectively. The optical properties are determined in terms of dielectric constants, refractive index, absorption, and other dependent parameters. The absorption of light energy was found from visible to ultraviolet regions which increases their importance for optoelectric applications. In the end, thermoelectric properties are calculated by BoltzTrape Code. The power facter ascertain thermoelectric efficiency which is measured in terms of Seebeck coefficient and electrical conducitivity. The specific heat capacity and other thermodynamic papers are described. Therefore, the transition metals based delafossites are suitable for thermoelectric and optoelectronic applications. Crystal structures of XMnO 2 (X ​= ​Ag, Au, Cu) in monoclinic phase (top), and temperature-dependent thermoelectric parameters; Seebeck coefficient and Power factor (bottom). [Display omitted] • Above room temperature ferromagnetism, and spintronic applications. • Quantum spin of electrons dominant the charge with multifunctional properties. • Exchange mechanism certifies the ferromagnetism by electron spin instead of magnetic ion clustering. • Half metallic ferromagnetism and 100% spin polarization. • Large value of electrical conductivity and ultralow low values of thermal conductivity. [ABSTRACT FROM AUTHOR]

In this paper, we report the electrostatic potential and nonlinear optical properties of meta-nitroacetanilide. Molecular properties were calculated by Hatree Fock (HF) and density functional theory (DFT) methods with the 6-31+G (d) basis set. The molecular electrostatic potential map indicates that the negative potential sites are on oxygen atoms as well as the positive potential sites are around the hydrogen atoms. The second-order nonlinear optical properties based on the first static hyperpolarizability (β) have been investigated. The calculated results show that the title molecule might have nonlinear optical behavior. The thermodynamic functions (entropy, heat capacity and enthalpy) were obtained from spectroscopic data by statistical methods for the range of temperature 100-1000 K. [ABSTRACT FROM AUTHOR]

The present paper reports six distinctive doping effects of γ-Si 3 N 4 resulted with C, O and F dopants. Based on density functional calculations, 15 doped structures from different doping method are appreciated with formation and binding energies. Six of them, which are considered to be more easily to synthesize, are put into investigations of electronic and optical properties. The successively reduced energy gap, transformation of semiconductor to conductor and enhanced visible-light absorption coefficient are found. The mechanisms for six doping effects are explored with four concentrations and elucidated on the basis of the electronic structure. [ABSTRACT FROM AUTHOR]

A systematic investigation into electronic and optical properties of ReN at ambient and high pressure by density functional theory with the generalized gradient approximation has been presented in this paper. Optical properties such as the dielectric function, refractive index, absorption, reflectivity, and electron energy-loss spectrum are obtained successfully. The features in the spectra of the optical parameters are analyzed in detail. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga2O3) is a promising wide-band-gap semiconductor material for UV optical detectors and high-power transistor applications. The fabrication of p-type Ga2O3 is a key problem that hinders its potential for realistic power applications. In this paper, pure α-Ga2O3 and Ca-doped α-Ga2O3 band structure, the density of states, charge density distribution, and optical properties were determined by a first-principles generalized gradient approximation plane-wave pseudopotential method based on density functional theory. It was found that calcium (Ca) doping decreases the bandgap by introducing deep acceptor energy levels as the intermediate band above the valence band maximum. This intermediate valence band mainly consists of Ca 3p and O 2p orbitals and is adequately high in energy to provide an opportunity for p-type conductivity. Moreover, Ca doping enhances the absorptivity and reflectivity become low in the visible region. Aside, transparency decreases compared to the pure material. The optical properties were studied and clarified by electrons-photons interband transitions along with the complex dielectric function's imaginary function. [ABSTRACT FROM AUTHOR]

In this paper we study the complexation of Al3+ and several transition metals (Cr3+, Fe3+, Mn2+, Ni2+) in the ionic liquid 1-butyl-3-methylimidazolium thiocyanate. New insights into the structure, single-particle dynamics and electronic properties (optical absorption spectra) of these bulk mixtures are provided by molecular dynamics and density functional theory calculations, and our results are successfully compared with available experimental data. Our theoretical results reveal the existence of a bridging coordination mode between neighboring metal-ligand complexes in the polar nanoregions, and a scarce influence of the apolar nanoregions in the single-particle dynamics of the species in the mixture. Moreover, most part of the relevant features of the UV–Vis optical absorption spectra of these systems is properly explained by our density functional theory calculations for isolated complexes in the gas phase, evidencing that ionic liquid cations play only a limited role in the complex electronic properties. • Transition metal doped [BMIM][SCN] ionic liquid • Structure and single-particle dynamics of the transition metal-SCN− complexes in the bulk • Coordination mode by bridging of neighboring metal-SCN− complexes • UV–Vis absorption spectra dominated by metal-ligand complexes [ABSTRACT FROM AUTHOR]

Pyrite is a mineral often associated with coal in coal seams and is a major source of sulfur in coal. Coal–pyrite is widely distributed, easily available, low-cost, and non-toxic, and has high light absorption coefficient. So, it shows potential for various applications. In this paper, the density-functional theory (DFT + U) is used to construct coal–pyrite with carbon doped in the sulfur and iron vacancies of pyrite. The effects of different carbon defects, different carbon doping concentrations, and different doping distributions in the same concentration on the electronic structure and optical properties of coal–pyrite were studied. The results show that the absorption coefficient and reflectivity of coal–pyrite, when its carbon atom substitutes the iron and sulfur atoms in the sulfur and iron vacancies, are significantly higher than those of the perfect pyrite, indicating that coal–pyrite has potential for application in the field of photovoltaic materials. When carbon is doped in the sulfur vacancy, this impurity state reduces the width of the forbidden band; with the increase in the doping concentration, the width of the forbidden band decreases and the visible-light absorption coefficient increases. The distribution of carbon impurities impacts the band gap but has almost no effect on the light absorption coefficient, complex dielectric function, and reflectivity, indicating that the application of coal–pyrite to photovoltaic materials should mainly consider the carbon doping concentration instead of the distribution of carbon impurities. The research results provide a theoretical reference for the application of coal–pyrite in the field of photoelectric materials. [ABSTRACT FROM AUTHOR]

A detailed theoretical investigation on the structural, electronic, optical and thermoelectric properties of the quaternary BaAg 2 GeS 4 compound is presented in this paper. Within the framework of density functional theory (DFT), calculations based on the full-potential linearized augmented plane wave (FP-LAPW) method are performed. The band gap obtained using the Tran-Blaha modified Becke-Johnson exchange potential shows improved values as compared with the generalized gradient approximations with the Wu-Cohen version (GGA-WC). Therefore these results are used to determine the optical and thermoelectric properties. Results show that the BaAg 2 GeS 4 compound is an indirect gap semiconductor. It can be used as effective ultraviolet absorber provided that it exhibits a wide absorption band and high absorption coefficient up to 182.820 (104/cm). Thermoelectric properties results show promising characteristics of the studied compound, with the best doping being in the range of 1.1 × 10 18 and 1.3 × 10 19 (cm−3) depending on the working temperature. Image 1 [ABSTRACT FROM AUTHOR]

Extensive studies have demonstrated that all-inorganic lead-free halide perovskite solar cells as promising photoelectric devices are receiving great attention. In this paper, we have investigated the structures, electronical and optical properties of perovskite Cs 2 Ti(Br 1-x Y x) 6 (Y = Cl, I, x ​= ​0, 0.25, 0.5, 0.75, 1). When x ​= ​0.25, the system Cs 2 Ti(Br 0.75 Cl 0.25) 6 has the suitable band gap value. With the increase of Cl content, the absorption coefficients showing blue shift which lead to the optical performance slightly decreased. But the systems become more stable. For the substitution of I to Br, the band gap values are lower than the optimal one. As to optical calculations, we find that the systems show obvious red shift, which result in the optical performance enhanced. However, the systems become unstable and not easy to be prepared. All calculations reveal that these excellent properties make Cs 2 Ti(Br 0.75 Cl 0.25) 6 as an ideal candidate material for perovskite solar cells. Cs 2 Ti(Br 0.75 Cl 0.25) 6 is chose as the most potential photoelectric material. Image 1 • Different Br-site substitution contents are considered in Cs 2 Ti(Br 1-x Y x) 6. • Obvious redshift implies enhancement of optical properties in Cs 2 Ti(Br 1-x I x) 6. • The stability is improved signally due to the doping of Cl atoms. • Cs 2 Ti(Br 0.75 Cl 0.25) 6 is chose as the most potential photoelectric material. [ABSTRACT FROM AUTHOR]

Using the first-principle calculation that is based on the density functional theory (DFT), our group gains some insights of the structural, electronic and optical properties of two brand new types of BiOI/TiO2 heterojunctions: 1I-terminated BiOI {001} surface/TiO2 (1I-BiOI/TiO2) and BiO-terminated BiOI {001} surface/TiO2 (BiO-BiOI/TiO2). The calculation illustrates that BiOI/TiO2 heterojunction has excellent mechanical stability, and it shows that there is a great possibility for the BiOI/TiO2 heterojunction to be used in visible-light range, hence the photocatalytic ability can be enhanced dramatically. Especially, from the calculation, we discovered that there are two specific properties: the band-gap of 1I-BiOI/TiO2 heterojunction reduces to 0.28 eV, and the BiO-BiOI/TiO2 semiconductor material changes to n-type. The calculated band offset (BOs) for 1I-BiOI/TiO2 heterojunction indicates that the interfacial structure contributes a lot to a suitable band alignment which can disperse the photo-generated carriers into the opposite sides of the interface, so this could effectively weaken the electron-hole recombination. Meanwhile, the built-in potential around the interface accelerates the movement of the photo-generated electron-hole pairs. We believe this is the reason that the BiOI/TiO2 material shows perfect photocatalytic performance. This paper can provide theoretical support for the related research, especially the further research of the BiOI-based material. [ABSTRACT FROM AUTHOR]

The paper reports the results on first-principles investigation of energy band spectrum and optical properties of bulk and nanoporous silicon. We present the evolution of energy band-gap, refractive indices and extinction coefficients going from the bulk Si of cubic symmetry to porous Si with periodically ordered square-shaped pores of 7.34, 11.26 and 15.40 Å width. We consider two natural processes observed in practice, the hydroxylation of Si pores (introduction of OH groups into pores) and the penetration of water molecules into Si pores, as well as their impact on the electronic spectrum and optical properties of Si superstructures. The penetration of OH groups into the pores of the smallest 7.34 Å width causes a disintegration of hydroxyl groups and forms non-bonded protons which might be a reason for proton conductivity of porous Si. The porosity of silicon increases the extinction coefficient, k, in the visible range of the spectrum. The water structuring in pores of various diameters is analysed in detail. By using the bond valence sum approach we demonstrate that the types and geometry of most of hydrogen bonds created within the pores manifest a structural evolution from distorted hydrogen bonds inherent to small pores (∼7 Å) to typical hydrogen bonds observed by us in larger pores (∼15 Å) which are consistent with those observed in a wide database of inorganic crystals. [ABSTRACT FROM AUTHOR]

In this paper, we report the results of theoretical calculation on the structural, electronic, optical and thermoelectric properties of 2T-Al 2 MgC 2 compound. These properties are investigated through the calculations based on the density functional theory and Boltzmann transport theory. Our calculated structural parameters are in very good agreement with other experimental and theoretical values available in the literature. Studied material has an indirect band gap K Γ − L of 2.579 eV calculated with the Tran-Blaha modified Becke-Johnson exchange (mBJ) potential, which is higher than those obtained with the standard functionals. 2T-Al 2 MgC 2 compound has a wide absorption band from the high energy zone of visible to ultraviolet region. While it shows the transparent properties when the photon energy is lower than 2.579 eV and beyond 25 eV. Considered ternary is a good thermoelectric material with high thermopower and the figure of merit close to unity. At the hole (electron)-doping level of 1 × 10 17 (cm−3), the calculated figure of merit is 0.98 (0.97). Image 1 [ABSTRACT FROM AUTHOR]

In this paper, we investigate the effect of conduction band non-parabolicity (NPBE) on the third harmonic generation(THG), the linear and nonlinear intersub-band optical absorption coefficients (OACs) related with electronic states of double semi-V-shaped GaAs/Ga1−xAlxAs quantum wells(QWs) by using the compact-density-matrix approach. Simultaneously, the work is performed in the position dependent effective mass in order to compute the electronic structure for the system by the finite difference and self-consistent techniques. We also compare the results with and without considering NPBE. It is found that: (1) the NPBE has a significant influence on the sub-band energy levels of double semi-V-shaped QWs, and (2) the amplitude and position of the resonant peaks of the THG and nonlinear OACs in the case of considering NPBE show complicated behavior due to the energy dependent effective mass m*(E) where the energy value was chosen self-consistently. [ABSTRACT FROM AUTHOR]