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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 1 1 , C 1 2 and C 4 4 of Fm-3m structure of HgF2 have been explored using thermo_pw package. The ductile nature of HgF2 is evidenced by its B ∕ G H 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 (F) , internal energy (E) , specific heat at constant volume (Cv), and Debye temperature ( Θ D). 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 "s", "p", and "d" 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. [ABSTRACT FROM AUTHOR]

In this research, the adsorption of targeted noxious gases like H2S, HF and H2 on penta-PdAs2 monolayer are deeply studied by means of the density functional theory (DFT). After the capturing of three kind of pollutant gases (H2S, HF and H2), it is observed that, the electronic properties are slightly affected from the pristine one. In all cases, the physisorption interaction found with adsorption energy of − 0.49, − 0.39 and − 0.16 eV for H2S, HF and H2 gases, respectively. Which is exposed that H2S gas strongly absorbed on penta-PdAs2 nanosheet. In case of HF (H2) gas adsorbed systems, the obtained charge transfer is + 0.111 e (+ 0.037 e), revealed that the electrons are going to PdAs2 nanosheet from the HF (H2) molecules. Further, under the non-equilibrium Green's function (NEGF) theory, the IV response and sensitivity of absorbed H2S, HF and H2 have been discussed. The results demonstrate that the H2S molecules on PdAs2 has suitable adsorption strength and explicit charge transfer compared with other targeted molecules. Hence, our novel findings of H2S, HF and H2 targeted gas sensing on penta-PdAs2 nanosheet might provide reference-line to design modern gas sensor device at the nano-scale. [ABSTRACT FROM AUTHOR]

We studied the physical, electronic transport and optical properties of a unique pentagonal PdQ2 (Q = S, Se) monolayers. The dynamic stability of 2Dwrinkle 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. [ABSTRACT FROM AUTHOR]

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/Å) 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. [ABSTRACT FROM AUTHOR]

The density functional theory (DFT) based analysis of cubic phase cesium lead chloride (CsPbCl 3 ) perovskite is reported. Here the absence of imaginary frequencies in the phonon dispersion curves of unit cell of bulk and monolayer CsPbCl 3 showed that both the structures are dynamically stable. The pristine CsPbCl 3 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 CsPbCl 3 monolayers, intermediate states were generated in both the cases due to Mn-3 d and Nb-4 d 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 CsPbCl 3 monolayers indicated that their absorption edges get shifted toward low photon energy, i.e. red shifted compared to the pristine CsPbCl 3 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 ( J sc ) of the Nb-doped CsPbCl 3 monolayer was obtained around 655.45 A/m 2 , and the efficiency of this material came out to be around 15.68%. For the Mn-doped CsPbCl 3 monolayer the value of J sc came to be around 525.68 A/m 2 and showed strikingly high efficiency of 26.88% thus being a suitable candidate for its application as an absorber layer in solar cells.