scholarly journals Potential Application of h-BNC Structures in SERS and SEHRS Spectroscopies: A Theoretical Perspective

Sensors ◽  
2019 ◽  
Vol 19 (8) ◽  
pp. 1896
Author(s):  
Sara Gil-Guerrero ◽  
Nicolás Otero ◽  
Marta Queizán ◽  
Marcos Mandado Alonso
Keyword(s):  
Density Functional ◽  
Laser Excitation ◽  
Signal To Noise Ratio ◽  
Theoretical Perspective ◽  
Resonance Excitation ◽  
Pristine Graphene ◽  
Metallic Surfaces ◽  
Enhancement Factors ◽  
Graphene Nanodisks ◽  
Molecular Affinity

In this work, the electronic and optical properties of hybrid boron-nitrogen-carbon structures (h-BNCs) with embedded graphene nanodisks are investigated. Their molecular affinity is explored using pyridine as model system and comparing the results with the corresponding isolated graphene nanodisks. Time-dependent density functional theory (TDDFT) analysis of the electronic excited states was performed in the complexes in order to characterize possible surface and charge transfer resonances in the UV region. Static and dynamic (hyper)polarizabilities were calculated with coupled-perturbed Kohn-Sham theory (CPKS) and the linear and nonlinear optical responses of the complexes were analyzed in detail using laser excitation wavelengths available for (Hyper)Raman experiments and near-to-resonance excitation wavelengths. Enhancement factors around 103 and 108 were found for the polarizability and first order hyperpolarizability, respectively. The quantum chemical simulations performed in this work point out that nanographenes embedded within hybrid h-BNC structures may serve as good platforms for enhancing the (Hyper)Raman activity of organic molecules immobilized on their surfaces and for being employed as substrates in surface enhanced (Hyper)Raman scattering (SERS and SEHRS). Besides the better selectivity and improved signal-to-noise ratio of pristine graphene with respect to metallic surfaces, the confinement of the optical response in these hybrid h-BNC systems leads to strong localized surface resonances in the UV region. Matching these resonances with laser excitation wavelengths would solve the problem of the small enhancement factors reported in Raman experiments using pristine graphene. This may be achieved by tuning the size/shape of the embedded nanographene structure.

scholarly journals Quantum Chemistry of Cocaine and its Isomers I: Energetics, Reactivity and Solvation

2021 ◽  
Vol 75 ◽  
Author(s):  
Safa Ben Amara ◽  
Thorsten Koslowski ◽  
Ali Zaidi
Keyword(s):  
Dipole Moment ◽  
Solvent Effect ◽  
Density Functional ◽  
Chemical Reactivity ◽  
Theoretical Perspective ◽  
Solvent Polarity ◽  
Stable Conformation ◽  
Functional Theory ◽  
Implicit Solvents ◽  
The Rich

ABSTRACT We investigate the rich stereochemistry of cocaine and its diastereoisomers from a theoretical perspective using density functional theory. The relative stability of the eight considered isomers is discussed, and a comparison of the corresponding internal coordinates is given. Our results reveal that the S-pseudococaine isomer is the most stable conformation, whereas the natural occurring isomer (R-cocaine) lies higher in energy. The different isomers' chemical reactivity is discussed based on the calculation of the hardness, softness, electrophilicity and dipole moment. It was found that the dipole moment varies over a broad range from 0.65 to 4.60 D, whereas the other properties are slightly modified. The solvent effect on the energy stability of the cocaine isomers was studied by considering chloroform, dimethyl-sulfoxide (DMSO) and water as implicit solvents. Our calculations show that the different isomers' energy order and their energy gaps are slightly modified due to solvent effects. However, in all cases, the S-pseudococaine remains the most stable isomer. However, the dipole moment and the chemical reactivity of the cocaine isomers increase with the solvent polarity. Keywords: Cocaine isomers,DFT, stability, solvent effect, chemical reactivity.

scholarly journals 1D Quantum Simulations of Electron Rescattering with Metallic Nanoblades

Instruments ◽  
2019 ◽  
Vol 3 (4) ◽  
pp. 59
Author(s):  
Joshua Mann ◽  
Gerard Lawler ◽  
James Rosenzweig
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Strong Field ◽  
Field Enhancement ◽  
Time Dependent ◽  
High Yield ◽  
Theory Approach ◽  
Full Time ◽  
Metallic Surfaces ◽  
Functional Theory

Electron rescattering has been well studied and simulated for cases with ponderomotive energies of the quasi-free electrons, derived from laser–gas and laser–surface interactions, lower than 50 eV. However, with advents in longer wavelengths and laser field enhancement metallic surfaces, previous simulations no longer suffice to describe more recent strong field and high yield experiments. We present a brief introduction to and some of the theoretical and empirical background of electron rescattering emissions from a metal. We set upon using the Jellium potential with a shielded atomic surface potential to model the metal. We then explore how the electron energy spectra are obtained in the quantum simulation, which is performed using a custom computationally intensive time-dependent Schrödinger equation solver via the Crank–Nicolson method. Finally, we discuss the results of the simulation and examine the effects of the incident laser’s wavelength, peak electric field strength, and field penetration on electron spectra and yields. Future simulations will investigate a more accurate density functional theory metallic model with a system of several non-interacting electrons. Eventually, we will move to a full time-dependent density functional theory approach.

First Principles Calculations of Graphene Doped with Al, P and Si Heteroatoms

2017 ◽  
Vol 16 ◽  
pp. 52-55 ◽  
Author(s):  
Maria Teresa Romero ◽  
Yuliana Avila Alvarado ◽  
Reyes Garcia-Diaz ◽  
Carlos Rodriguez Garcia ◽  
Raul Ochoa Valiente ◽  
...  
Keyword(s):  
Band Structure ◽  
Fermi Level ◽  
Density Functional ◽  
Pristine Graphene ◽  
High Symmetry ◽  
Linear Dispersion ◽  
Graphene Layers ◽  
Doping Effects ◽  
Semiconductor Behavior ◽  
Quantum Espresso

In this work, studies of the doping effects on the electronic and structural properties of graphene were performed. Calculations have been done within the periodic density functional theory (DFT) as implemented in PWscf code of the Quantum Espresso Package. Graphene layers have been modeled using the 4x4 periodic supercells. The doping is explored considering phosphorus (P), aluminum (Al) and silicon (Si) heteroatoms. One heteroatom per supercell was considered. Electronic structure results show that the pristine graphene has a linear dispersion at high symmetry K point and zero gap. Band structure of graphene doped with Al atoms exhibit a metal behavior since a valence band crosses the Fermi level. Graphene doped with P also presents a metal behavior but in this case a conduction band crosses the Fermi level. In addition, when the dopant is Si the band structure shows a semiconductor behavior with a 0.3 eV gap. In all cases, the zero gap energy characteristic of graphene was changed by dopant heteroatom. The Dirac lineal dispersion relation is preserved only in the pristine graphene.

scholarly journals Adsorption of Transition Metal Catalysts on Carbon Supports: A Theoretical Perspective

2021 ◽  
Author(s):  
Arunabhiram Chutia
Keyword(s):  
Transition Metal ◽  
Density Functional ◽  
Carbon Materials ◽  
Catalyst Surface ◽  
Theoretical Perspective ◽  
Short Review ◽  
Metal Catalysts ◽  
Transition Metal Catalysts ◽  
Carbon Supports ◽  
Adsorbed Species

Adsorption is a fundamental process, which takes place on a catalyst surface before it dissociates, diffuses over the surface and recombines with other adsorbed species to form the final product. Therefore, in theoretical chemistry understanding of the local geometrical and electronic properties of the adsorbed species on the catalyst surface has been a topic of core focus. In this short review we briefly summarise some of the important developments on theoretical studies related to the adsorption properties of transition metal catalysts on graphene and graphene-related carbon materials. Prior to this, we will present a discussion on various forms of carbon materials used as catalyst supports, which will be followed by a brief discussion of the fundamentals of the density functional theory.

scholarly journals Direct light–induced spin transfer between different elements in a spintronic Heusler material via femtosecond laser excitation

2020 ◽  
Vol 6 (3) ◽  
pp. eaaz1100 ◽  
Author(s):  
Phoebe Tengdin ◽  
Christian Gentry ◽  
Adam Blonsky ◽  
Dmitriy Zusin ◽  
Michael Gerrity ◽  
...  
Keyword(s):  
Femtosecond Laser ◽  
Time Scales ◽  
Density Functional ◽  
Laser Excitation ◽  
High Harmonic ◽  
Density Functional Theory Calculations ◽  
Spin Transfer ◽  
Magnetic Interactions ◽  
Magnetic Sublattice ◽  
Wide Range

Heusler compounds are exciting materials for future spintronics applications because they display a wide range of tunable electronic and magnetic interactions. Here, we use a femtosecond laser to directly transfer spin polarization from one element to another in a half-metallic Heusler material, Co2MnGe. This spin transfer initiates as soon as light is incident on the material, demonstrating spatial transfer of angular momentum between neighboring atomic sites on time scales < 10 fs. Using ultrafast high harmonic pulses to simultaneously and independently probe the magnetic state of two elements during laser excitation, we find that the magnetization of Co is enhanced, while that of Mn rapidly quenches. Density functional theory calculations show that the optical excitation directly transfers spin from one magnetic sublattice to another through preferred spin-polarized excitation pathways. This direct manipulation of spins via light provides a path toward spintronic devices that can operate on few-femtosecond or faster time scales.

B(OH)2-functionalized graphene nanoflake as a promising nanocarrier for letrozole delivery: A DFT study

2021 ◽  
Author(s):  
Malakehsadat Seyedmousavi ◽  
Morteza Rouhani ◽  
Zohreh Mirjafary
Keyword(s):  
Adsorption Energy ◽  
Density Functional ◽  
Anticancer Agent ◽  
Density Functional Theory Calculations ◽  
Pristine Graphene ◽  
Physical Interaction ◽  
Functionalized Graphene ◽  
Functional Theory ◽  
Graphene Nanoflakes ◽  
Graphene Nanoflake

Abstract We studied the capability of pristine, Al-doped and B(OH)2-functionalized graphene nanoflakes for delivery of Letrozole (LT) anticancer agent using density functional theory calculations. It was shown that LT/pristine graphene complex includes very weak physical interaction with Ead = -2.447 kcal.mol-1 which is so weak to be applied in drug delivery purposes. So, graphene nanoflake was doped by Al atom and the calculations demonstrated the LT adsorption energy was increased significantly (Ead = -33.571 kcal.mol-1). However, the LT release study showed that the adsorption energy did not change efficiently upon protonation in acidic environment (Ead = -31.857 kcal.mol-1). Finally, the LT adsorption was investigated on B(OH)2-functionalized graphene. The calculations represented that the adsorption energy was -9.607 kcal.mol-1 which can be attributed to the possible hydrogen bonding between LT molecule and B(OH)2 functional group. The adsorption energy was changed to -1.015 kcal.mol-1 during protonation process. It can be concluded that the protonation of LT/B(OH)2-functionalized graphene complex in carcinogenic cells area, separates the LT from the nanocarrier. Thus, B(OH)2-functionalized graphene nanoflakes can be considered as a promising nanocarrier candidate for LT delivery.

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