arXiv subjects

Mahmood Akbari

Publications and source records attributed to Mahmood Akbari.

7 recordsLinked to original sources

arXiv2024

CO2 capture using boron, nitrogen, and phosphorus-doped C20 in the present electric field: A DFT study

Burning fossil fuels emits a significant amount of CO2, causing climate change concerns. CO2 Capture and Storage (CCS) aims to reduce emissions, with fullerenes showing promise as CO2 adsorbents. Recent research focuses on modifying fullerenes using an electric field. In light of this, we carried out DFT studies on some B, N, and P doped C20 (C20-nXn (n = 0, 1, 2, and 3; X = B, N, and P)) in the absence and presence of an electric field in the range of 0-0.02 a.u.. The cohesive energy was calculated to ensure their thermodynamic stability showing, that despite having lesser cohesive energies than C20, they appear in a favorable range. Moreover, the charge distribution for all structures was depicted using the ESP map. Most importantly, we evaluated the adsorption energy, height, and CO2 angle, demonstrating the B and N-doped fullerenes had the stronger interaction with CO2, which by far exceeded C20's, improving its physisorption to physicochemical adsorption. Although the adsorption energy of P-doped fullerenes was not as satisfactory, in most cases, increasing the electric field led to enhancing CO2 adsorption and incorporating chemical attributes to CO2-fullerene interaction. The HOMO--LUMO plots were obtained by which we discovered that unlike the P-doped C20, the surprising activity of B and N-doped C20s against CO2 originates from a high concentration of the HOMO-LUMO orbitals on B and N atoms. Additionally, the charge distribution for all structures was depicted using the ESP map. In the present article, we attempt to introduce more effective fullerene-based materials for CO2 capture as well as strategies to enhance their efficiency and revealing adsorption nature over B, N, and P-doped fullerenes.

physics.chem-ph↗

arXiv2021

Exclusive robustness of Gegenbauer method to truncated convolution errors

Spectral reconstructions provide rigorous means to remove the Gibbs phenomenon and accelerate the convergence of spectral solutions in non-smooth differential equations. In this paper, we show the concurrent emergence of truncated convolution errors could entirely disrupt the performance of most reconstruction techniques in the vicinity of discontinuities. They arise when the Fourier coefficients of the product of two discontinuous functions, namely $f=gh$, are approximated via truncated convolution of the corresponding Fourier series, i.e. $\hat{f}_k\approx \sum_{|\ell|\leqslant N}{\hat{g}_\ell\hat{h}_{k-\ell}}$. Nonetheless, we numerically illustrate and rigorously prove that the classical Gegenbauer method remains exceptionally robust against this phenomenon, with the reconstruction error still diminishing proportional to $\mathcal{O}(N^{-1})$ for the Fourier order $N$, and exponentially fast regardless of a constant. Finally, as a case study and a problem of interest in grating analysis whence the phenomenon initially was noticed, we demonstrate the emergence and practical resolution of truncated convolution errors in grating modes, which constitute the basis of Fourier modal methods.

physics.comp-ph↗

arXiv2021

Fast estimation of propagation constants in crossed gratings

Fourier-based modal methods are among the most effective numerical tools for the accurate analysis of crossed gratings. However, leading to computationally expensive eigenvalue equations significantly restricts their applicability, particularly when large truncation orders are required. The resultant eigenvalues are the longitudinal propagation constants of the grating and play a key role in applying the boundary conditions, as well as in the convergence and stability analyses. This paper aims to propose simple techniques for the fast estimation of propagation constants in crossed gratings, predominantly with no need to solve an eigenvalue equation. In particular, we show that for regular optical gratings comprised of lossless dielectrics, nearly every propagation constant appears on the main diagonal of the modal matrix.

physics.optics↗

arXiv2020

First Principle Simulation of Coated Hydroxychloroquine on Ag, Au and Pt Nanoparticle as a Potential Candidate for Treatment of SARS-CoV-2 (COVID-19)

The {\it{in vitro}} antiviral activity of Hydroxychloroquine (HCQ) and chloroquine (CQ) against SARS-CoV-2 from the first month of pandemic proposed these drugs as the appropriate therapeutic candidate, although their side effect directed the clinical test toward optimizing the safe utilization strategies. The noble metal nanoparticles (NP) as promising materials with antiviral and antibacterial properties can deliver the drug to the target agent and decrease the side effect. In this work, we have applied quantum mechanical and classical atomistic molecular dynamics computational approaches to demonstrate the adsorption properties of HCQ on Ag, Au, AgAu, and Pt nanoparticles. The adsorption energies (less than -30 kcal/mole) were established for HCQ, and the (non)perturbative effects of this drug on the plasmonic absorption spectra of AgNP and AuNP have characterized with time-dependent density functional theory. The effect of size and compositions of nanoparticle on the coating with HCQ and CQ have obtained and proposed the appropriate candidate for drug delivery. This kind of modeling could help the experimental groups to find the efficient and safe therapies.

physics.med-ph↗

arXiv2019

Uniaxial Strain Effects on Graphene Nanoribbon Resonant Tunneling Transistors

The effect of the uniaxial strain on the current-voltage characteristic of a typical armchair graphene-nanoribbon-hBN heterostructure device is simulated numerically by employing the nearest-neighbor tight-binding model and the non-equilibrium Green's function formalism. Simulations clearly reveal the following notable dependencies: (i) the strain invariably reduces the current; (ii) the strain applied in the armchair direction markedly widens the main peak of the current over a larger region of the bias voltage compared with the unstrained state; (iii) the current decreases faster when the strain is applied in the armchair rather than the zigzag direction.

cond-mat.mes-hall↗

arXiv2005

Propagation of Light in Photonic Crystal Fibre Devices

We describe a semi-analytical approach for three-dimensional analysis of photonic crystal fibre devices. The approach relies on modal transmission-line theory. We offer two examples illustrating the utilization of this approach in photonic crystal fibres: the verification of the coupling action in a photonic crystal fibre coupler and the modal reflectivity in a photonic crystal fibre distributed Bragg reflector.

physics.optics↗

arXiv2005

The radiated fields of the fundamental mode of photonic crystal fibers

The six-fold rotational symmetry of photonic crystal fibers has important manifestations in the radiated fields in terms of i) a focusing phenomena at a finite distance from the end-facet and ii) the formation of low-intensity satellite peaks in the asymptotic far field. For our study, we employ a surface equivalence principle which allows us to rigorously calculate radiated fields starting from fully-vectorial simulations of the near field. Our simulations show that the focusing is maximal at a characteristic distance from the end-facet. For large-mode area fibers the typical distance is of the order 10 Lambda with Lambda being the pitch of the triangular air-hole lattice of the photonic crystal fiber.

physics.optics↗