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In this paper, Fm-3m structure of HgF2 has been studied using the density functional theorem (DFT). The stability of this structure is revealed by the positive phonon frequencies of the phonon dispersion curves and by satisfying Born Huang criteria concerned with elasticity of the structure. For the very first time, the elastic constants C[Formula: see text], C[Formula: see text] and C[Formula: see text] of Fm-3m structure of HgF2 have been explored using thermo_pw package. The ductile nature of HgF2 is evidenced by its [Formula: see text] ratio of 2.56. The linear response approach has been used to evaluate the intrinsic thermodynamic characteristics of HgF2 while examining the temperature fluctuations of the Helmholtz free energy ([Formula: see text], internal energy ([Formula: see text], specific heat at constant volume (Cv), and Debye temperature ([Formula: see text]. The ionic behavior of HgF2 is demonstrated by the broad valence bandgap that is present in the electronic band structure and density of states. Moreover, the hybridization between “[Formula: see text]”, “[Formula: see text]”, and “[Formula: see text]” orbitals in HgF2 is defined by the charge density along the [110] plane. The static refractive index of HgF2 is 1.26. The broad optical investigation demonstrates Fm-3m HgF2’s transparency in the UV and visible spectrums. Additionally, it exhibits considerable UV absorption throughout its range as well as with absorption tail that continues into the visible spectrum. The overall optical parameters of Fm-3m HgF2 show non-linear optical behavior which makes the material to be useful in ultraviolet (UV) photo-sensing devices.

With an inspiration of sensing toxic gases, this study is aimed at exploring the potential of a Janus MoSSe monolayer as a gas sensor. Here, we focused on the adsorption mechanism after the exposure to NH

The density functional theory (DFT) based analysis of cubic phase cesium lead chloride (CsPbCl3) perovskite is reported. Here the absence of imaginary frequencies in the phonon dispersion curves of unit cell of bulk and monolayer CsPbCl3 showed that both the structures are dynamically stable. The pristine CsPbCl3 monolayer is a wide bandgap semiconductor with an energy gap of 3.24 eV; therefore, an approach to alter its properties was adopted by doping Mn at the Pb-site and Nb at the Cs-site, respectively. In these Mn- and Nb-doped CsPbCl3 monolayers, intermediate states were generated in both the cases due to Mn-3d and Nb-4d orbitals, respectively, which makes the transfer of excited photoelectrons easier from the valence band to the conduction band. The absorption coefficient plots of Mn-doped and Nb-doped CsPbCl3 monolayers indicated that their absorption edges get shifted toward low photon energy, i.e. red shifted compared to the pristine CsPbCl3 monolayer. As both the impurity atoms considered are transition metals, we have also taken into account the effect of spin polarization on electronic and optical properties of doped monolayers. Solar cell parameters of all of these monolayers have been calculated using the Shockley-Queisser (SQ) limit. The short-circuit current density (Jsc) of the Nb-doped CsPbCl3 monolayer was obtained around 655.45 A/m2, and the efficiency of this material came out to be around 15.68%. For the Mn-doped CsPbCl3 monolayer the value of Jsc came to be around 525.68 A/m2 and showed strikingly high efficiency of 26.88% thus being a suitable candidate for its application as an absorber layer in solar cells.

Recently, group-V two-dimensional (2D) monolayer elements, notably the novel allotropes of antimonene and phosphorene have fascinated emergent attention. Motivated by this, first principles calculations have been employed to investigate electronic, vibrational and optical properties of blue phosphorene (BP). Unlike graphene and black phosphorene, blue phosphorene demonstrates a wide fundamental indirect band gap of 2.07 eV between M to K point. The phonon dispersion curve shows dynamical stability of the monolayer. We have also calculated optical properties of blue phosphorene. Our observations suggest that absorption process begins in visible (VIS) region, but peaks in ultraviolet (UV) region at the energy range of 7.39–9.33 eV. The maximum reflectivity arises up to 35% at 9.57 eV. The outcome concludes that blue phosphorene is a prominent material for optoelectronic applications.

In this study, we have examined the geometrical, electronic and optical properties of penta-PdX2 (X = As,P) using density functional calculation. The electronic structure calculations show that the penta-PdAs2 and PdP2 are semiconductors with direct band gaps of 0.34 eV and 0.30 eV, respectively. The dynamical stability of penta-PdX2 monolayer is proved by the absence of imaginary frequencies in the phonon dispersion curve. By applying a biaxial strain (for PdAs2: − 6% to + 6% and for PdP2: − 5.5% to + 5.5%) on the monolayer, the effective mass and band edges are tuned effectively. Remarkably, the range of penta-PdX2 carrier mobility was obtained in an extremely high order of 105 cm2 V−1 s−1 for holes and 104 cm2 V−1 s−1 for electrons. The optical properties of penta-PdX2 were also strained-tunable and exhibit outstanding absorption of infrared, visible and ultraviolet light. More importantly, the band edges alignment has tunable with implemented external electric field (V/A) along the z-direction. Our work would stimulate the fabrication of penta-PdX2 monolayer, and it is envisioned that it is an appropriate future candidate for optoelectronic and ultra-fast electronic applications.

Using first principles total energy calculation with the approach of density functional theory (DFT) and DFT + U calculations, the structural and electronic properties of erbium copper (ErCu) intermetallic compound were studied. In the present work, we used the local density approximation for the exchange and correlation potential for the spin polarized case. The structural optimization shows that ErCu is stable in the cubic structure. The obtained ground state properties viz; lattice constant ao (a.u), bulk modulus B (GPa) and magnetic moment (μB), which show good comparison with the available experimental data. We have also investigated the electronic properties such as electronic band structure, density of states, Fermi surfaces and charge density of states for spin-polarized case. In the band structure, majority spins energies contributions are higher than the minority spins energies contribution. The total density of states (TDOS) show that near the Fermi level, is mostly dominated by Er ‘f’ orbital electrons and below the Fermi level, are due to Cu ‘3d’ orbital electrons. The charge distributions of ErCu are ranging between +0.0003 e/A3 to +0.0693 e/A3 for majority channels and +0.0003 e/A3 to +0.0715 e/A3 for the minority spin channels.

We studied the physical, electronic transport and optical properties of a unique pentagonal PdQ2 (Q= S, Se) monolayers. The dynamic stability of 2D - wrinkle like - PdQ2 is proven by positive phonon frequencies in the phonon dispersion curve. The optimized structural parameters of wrinkled pentagonal PdQ2 are in good agreement with the available experimental results. The ultimate tensile strength (UTHS) was calculated and found that, penta-PdS2 monolayer can withstand up to 16% (18%) strain along x (y) direction with 3.44 GPa (3.43 GPa). While, penta-PdSe2 monolayer can withstand up to 17% (19%) strain along x (y) dirrection with 3.46 GPa (3.40 GPa). It is found that, the penta-PdQ2 monolayers has the semiconducting behavior with indirect band gap of 0.94 and 1.26 eV for 2D-PdS2 and 2D-PdSe2, respectively. More interestingly, at room temperacture, the hole mobilty (electron mobility) obtained for 2D-PdS2 and PdSe2 are 67.43 (258.06) cm2 V-1 s-1 and 1518.81 (442.49) cm2 V-1 s-1, respectively. In addition, I-V characteristics of PdSe2 monolayer show strong negative differential conductance (NDC) region near the 3.57 V. The Shockly-Queisser (SQ) effeciency prameters of PdQ2 monolayers are also explored and the highest SQ efficeinciy obtained for PdS2 is 33.93% at -5% strain and for PdSe2 is 33.94% at -2% strain. The penta-PdQ2 exhibits high optical absorption intensity in the UV region, up to 4.04 × 105 (for PdS2) and 5.28 × 105 (for PdSe2), which is suitable for applications in optoelectronic devices. Thus, the ultrathin PdQ2 monolayers could be potential material for next-generation solar-cell applications and high performance nanodevices.

We studied the physical, electronic transport and optical properties of a unique pentagonal PdQ

In the present work, the cubic structure of HgF2 has been studied using generalized gradient approximation within the framework of density functional theory. Here, the positive phonon frequencies in the phonon dispersion curves show stability of the structure. The elastic constants also satisfy criteria of being kinetically stable material. The B/GH ratio 2.56 of HgF2 indicates its ductile nature. The thermodynamic intrinsic parameters of HgF2 have been calculated using linear response method where the temperature variations of Helmholtz free energy (F), internal energy (E), specific heat at constant volume (Cv) and Debay temperature (ϴD) have been studied. The explanation of the bonding nature is discussed using electronic band structure, density of states and charge density. Here, the presence of the wide valence band gap in electronic band structure and density of states displays the ionic behaviors of HgF2. In addition, the charge density along the [111] plane defines hybridization in between ‘s’, ‘p’ and ‘d’ orbitals in HgF2. The optical parameters of Fm3m-HgF2 were calculated using Random Phase Approximation. Here, the found static refractive index is 1.26. The general optical study showing the trend of being transparent in most of the UV region and fully transparent in the visible region by ionic Fm3m HgF2. Also, it shows significant absorption in the entire UV region and a long absorption tail which extends into the visible region.

The density functional theory (DFT) based analysis of cubic phase cesium lead chloride (CsPbCl

The elastic and thermal properties of TbH2 compound were studied using the density functional theory (DFT) for temperature ranges from 0 to 800 K within the local density approximation (LDA) pseudopotential. The elastic constants and mechanical properties such as bulk modulus B, Young's modulus E, shear modulus GH, Poisson's ratio σ, Debye temperature (ϴD), and sound velocities (vm) of TbH2 compound were investigated. Moreover, the first principles density functional perturbation theory (DFPT) as implemented in the quasi-harmonic approximation (QHA) was used for the calculation of the thermal properties like vibrational energy ΔF, entropy S, internal energy ΔE and constant-volume specific heat CV of the TbH2. The obtained B/G ratio is 2.51, which reveals the good ductility of the TbH2 compound.

Motivated by the fascinating behavior of monolayer MoX2 (X = S, Se, Te), we have reported the structural, phonon dispersions relations, electronic and optical properties for monolayer to quadlayer of MoX2 (X = S, Se, Te) by employing ab-initio calculations. The optimized lattice parameters, bond angle and bond length of layered MoX2 (X = S, Se, Te) increases in the order of MoS2

The First principle study of structural, elastic, electronic and thermal properties for B2–HgMg amalgam has been carried out using Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA) exchange correlation functionals. The presently ground state properties; lattice constant, bulk modulus, elastic constants, ductility and enthalpy show good agreement with available experimental results. The ductility of B2–HgMg is proven from Pugh's relation; the obtained B/GH values are 4.17 and 3.61 for LDA and GGA, respectively. The dynamical stability of B2–HgMg at 0 K and 900 K is confirmed from the positive frequency in the phonon spectra. The electronic band structure and density of states reveal the metallic nature of B2–HgMg and major contribution of Hg-d electrons for core configuration. The electron like Fermi surfaces and charge density along [111] and [100] planes illustrate strong bonding between Hg–Hg atoms compare to Hg–Mg atoms. The Grunesian parameter and Bulk modulus at 900 K decreases to less than half of its value at 0 K indicates compressible nature of B2– HgMg.