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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]

In this paper, based on the first-principle calculations of hybrid density functional theory, the MoSTe/g-GeC of the Z-scheme heterostructure is constructed. The stability, electronic properties, optical absorption properties, and photocatalytic mechanism of the heterostructure is investigated. The band structure of MoSTe/g-GeC heterostructure is staggered, and the bandgap is 0.47 eV. The built-in electric field from g-GeC to MoSTe, with a size of 1.03 eV. The optical absorption coefficient of MoSTe/g-GeC heterostructures is significantly higher than that of MoSTe and g-GeC layer. When pH ranges from 0 to 7, the reduction reaction occurs in g-GeC layer, and the oxidation reaction occurs in the MoSTe layer. In the MoSTe/g-GeC heterostructure under different stresses, the band structure is arranged in a staggered manner. Importantly, under tensile strain, the bandgap of MoSTe/g-GeC heterostructure can be changed from the indirect into a direct bandgap. The bandgap of heterostructure decreases under the strain. In addition, the analysis of the photocatalytic mechanism shows that the redox reaction of the MoSTe/g-GeC heterostructure occurs on the layer with strong redox ability, and their light absorption ability is significantly enhanced compared to single-layers, which effectively improves the photocatalytic properties. It's a potential high-efficiency photocatalytic materials for direct Z-scheme heterostructure. In this paper, the stability, electronic properties, optical absorption properties, and photocatalytic mechanism of the MoSTe/g-GeC heterostructure is systematically studied. The results show that the heterostructure is a direct z-scheme heterostructure, and the photocatalytic performance is better than that of MoSTe and GeC monolayers. [Display omitted] • MoSTe/g-GeC heterostructure is a direct Z-scheme heterostructure, which is suitable for photocatalytic water splitting. • MoSTe/g-GeC heterostructure has excellent absorption coefficient (9.8 × 104 cm−1) in the visible and ultraviolet ranges. • The bandgap of MoSTe/g-GeC heterostructure can change from indirect bandgap to direct bandgap under partial strain. [ABSTRACT FROM AUTHOR]

Cyclo[18]carbon has received considerable attention thanks to its novel geometric configuration and special electronic structure. Superalkalis have low ionization energy. Doping a superalkali in cyclo[18]carbon is an effective method to improve the optical properties of the system because considerable electron transfer occurs. In this paper, the geometry, bonding properties, electronic structure, absorption spectrum, and nonlinear optical (NLO) properties of superalkaline M 3O (M = Li, Na)-doped cyclo[18]carbon were studied by using density functional theory. M 3O and the C18 rings are not coplanar. The C18 ring still exhibits alternating long and short bonds. The charge transfer between M 3O and C18 forms stable [ M 3O]+[C18]− ionic complexes. C18 M 3O (M = Li, Na) shows striking optical nonlinearity, i.e., their first- and second-order hyperpolarizability (β vec and γ ||) increase considerably at λ = 1907 nm and 1460 nm. [ABSTRACT FROM AUTHOR]

Fluoroperovskites, a subgroup of perovskite materials, have gained substantial scientific interest due to their outstanding optoelectronic properties and potential applications in electronic devices, such as solar cells, LEDs, and transistors. These unique properties originate from the crystal structure, enabling adaptable bandgap engineering. This paper investigates the structural, elastic, electronic, and optical properties of LiXF3 (X = Cd, Hg) using Density Functional Theory in WIEN2K. The stable cubic nature of LiCdF3 and LiHgF3 with lattice constants of 4.396 Å and 4.560 Å, respectively, is revealed. Elastic property analysis confirms mechanical equilibrium and ductility, while band structure calculations indicate indirect band gaps of 2.64 eV and 3.38 eV for LiCdF3 and LiHgF3, respectively, from (M − Γ). Optical properties within a 15 eV range are correlated with the electronic structure, providing a comprehensive understanding of Li-based fluoroperovskites' physical attributes. [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]

In this paper, we have performed a study on the optical properties of single crystals ZnGa2S4 by method of density functional theory (DFT) and ellipsometry measurements. The calculated results for the real ε r and imaginary ε i parts of the dielectric function are compared with the measured experimental spectroscopic ellipsometry (SE) spectra in the 0.7–6.5 eV spectral region. Absorption coefficient-photon energy dependency revealed the existence of direct bandgap transitions with energy 3.5 eV. This result is very close to bandgap obtained from our theoretical 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]

With the development of industrialization, the use of mercury in industry has become more and more widespread, causing serious impacts on the environment. It is therefore urgent to find new effective ways to combat mercury pollution. In this paper, The effect of C, O, P, Ni and Au doping on the adsorption of Hg atoms by WS 2 has been investigated based on the first nature principle of density functional theory. The electronic structures and optical properties of the adsorbed systems were calculated after atomic doping. The results show that the absolute value of the adsorption energy of the intrinsic adsorption system is small and does not favour the adsorption of Hg on WS 2. However, after C, P, Ni and Au doping, the adsorption energy of the system is significantly increased and a strong charge transfer between WS 2 and Hg atoms occurs, as well as a significant change in the band gap of the structure. This suggests that atomic doping favors the adsorption of Hg by WS 2. The effect of O doping on the adsorption system is not significant. In addition, a study of the optical properties revealed that the static dielectric constants of the system appeared to increase to varying degrees after the doping of the atoms. The doping of P, Ni and Au atoms increases the light absorption coefficient and contributes to the photocatalytic efficiency of the structures. The doped atoms cause a red shift in the reflectivity peak of the adsorbed system. In summary, the doping of C, P, Ni and Au enhances the adsorption of Hg atoms on WS 2. O doping has less effect on the adsorption of Hg on WS 2. • In this paper, the effect of C, O, P, Ni and Au doping on the adsorption of Hg atoms by WS2 was investigated. • The results show that atomic doping favors the adsorption of Hg by WS2. • Atomic doping alters the electronic properties of the structure. • Atomic doping alters the optical properties of the structure. [ABSTRACT FROM AUTHOR]

Rubidium cations (Rb+) significantly improve the overall performance of organic-inorganic hybrid perovskite based devices and have gained exceptional attention due to their good thermal and structural stability. In this paper, we have evaluated the physical attributes of rubidium based Rb 2 TlRhF 6 via DFT code using TB-mBJ potential. Structural stability has been confirmed through negative formation energy and calculated tolerance factor. Band structure and TDOS profile confirm semiconductor nature with 3.2 eV direct bandgap at (L-L) symmetry points. A ductile nature with metallic bonding is observed through the investigation of elastic attributes. Optical analysis of Rb 2 TlRhF 6 indicates great absorption in the UV region. Low thermal conductivity and electrical resistivity, along with a high value for power factor, resulted in high ZT value of 0.8 and 800 K. The combined qualities provide a stunning and exciting picture of this compound for use in thermoelectric advanced technologies. [ABSTRACT FROM AUTHOR]

A new type of copper cysteamine photosensitizer, Cu-Cy: Cu 3 Cl (SR) 2 (R = CH 2 CH 2 NH 2), was reported and later, there was another experimental report of Cu-Cy synthesis with other halogen elements (Cu-Cy-X, X = F, Br, and I), these later group of cysteamines contained Cl as an impurity. To realize the full potential applications of these cysteamines as photosensitizers, it is imperative to fundamentally understand the effect of Cl on the stability and optical properties of Cu-Cy-F/Br/I. In this paper, the stability of Cl-doped Cu-Cy-X (X = F, Br, and I) and their electronic and optical properties pertaining to their application as photosensitizers were investigated by using density functional theory (DFT). It was found that mixing Cu-Cy-Br and Cu-Cy-I with Cl increased their thermodynamic stability as well as made the materials mechanically harder. In addition, mixing halogens in Cu-Cy rendered a significant impact on their optical properties, namely the mixing affected Cu-Cy's deexcitation to their ground states during the photosensitizing process. In addition, it was found that after the initial photoexcitation within these Cu-cysteamines, the intersystem crossing can take place due to spin–orbit coupling from the Cu atoms. [Display omitted] • Mixing Cl with Br and I in Cu-Cy increases the thermodynamic stability of Cu-Cy. • Cl in Cu-Cy-X2 (X2 = F, Br, and I) makes the material mechanically hard. • Çu-Cy structures with higher contents of I are kinetically more stable. • Intersystem crossing occurs due to spin-orbit coupling. • Cu-Cy-X is initiated at a lower UV region comparing to mixed halogen Cu-Cy. [ABSTRACT FROM AUTHOR]

Based on the superior properties of g-CN and GaGePS monolayers, this paper investigates the optoelectronic properties of the g-CN/GaGePS van der Waals heterostructure under strain and external electric field modulation using density functional theory. The results show that g-CN/GaGePS heterostructure has a type II band alignment and possesses an indirect band gap of 0.986eV, which exhibits enhanced absorption in the visible and ultraviolet range. Under the application of a biaxial strain of 7 %, the g-CN/GaGePS heterostructure undergoes a transition from type II to type I. Furthermore, the electric field not only modulates the g-CN/GaGePS band gap, but also induces band alignment (type II to type Ⅰ) and an indirect gap to direct gap transition. The absorption in the visible range is enhanced by a positive electric field, whereas a negative electric field exerts the opposite effect. A negative electric field enhances UV range absorption. These results suggest that the g-CN/GaGePS heterostructure has prospective applications in optoelectronic devices. [ABSTRACT FROM AUTHOR]

In this paper, we prepared an innovative heterogeneous structure by stacking monolayers of Sc 2 CF 2 on isolated WSSe. Base on the first principles and density functional theory, the interface stability, electronic properties, optical properties of the two-dimensional Sc 2 CF 2 /WSSe heterostructure are discussed by calculation and further verification. The results show that the heterostructure has a indirect band gap of 1.00 eV (GGA-PBE), and has a direct-Z band arrangement profitable for water splitting. The heterostructure shows greater capability of the segregation of photogenerated electron-hole pairs directly. The optical properties was studied for further consideration. Moreover the associated edge positions also satisfy the thermodynamic requirements of water spitting when pH = 7. The heterostructure of Sc 2 CF 2 /WSSe shows reinforced optical properties relative to monolayers and feasibility in photocatalysis. • Electronic and optical properties of Sc 2 CF 2 /WSSe heterostructure. • The Sc 2 CF 2 /WSSe heterostructure exhibits Z-scheme band alignment. • The compatibility of spontaneous OER on Sc 2 CF 2 /WSSe heterostructure under mild circumstance. [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]