Computational characterization of novel nanostructured materials: A case study of NiCl2_2

A computational approach combining dispersion-corrected density functional theory (DFT) and classical molecular dynamics is employed to characterize the geometrical and thermo-mechanical properties of a recently proposed 2D transition metal dihalide NiCl$_2$. The characterization is performed using a classical interatomic force field whose parameters are determined and verified through the comparison with the results of DFT calculations. The developed force field is used to study the mechanical response, thermal stability, and melting of a NiCl$_2$ monolayer on the atomistic level of detail. The 2D NiCl$_2$ sheet is found to be thermally stable at temperatures below its melting point of ~695 K. At higher temperatures, several subsequent structural transformations of NiCl$_2$ are observed, namely a transition into a porous 2D sheet and a 1D nanowire. The computational methodology presented through the case study of NiCl$_2$ can also be utilized to characterize other novel 2D materials, including recently synthesized NiO$_2$, NiS$_2$, and NiSe$_2$

Chemical Functionalization Effects on Cubane-Based Chain Electronic Transport

We report electronic structure calculations in chemically functionalized linear cubane-based chains. The effects of covalent chemical attachments on chain transport properties are examined with nonorthogonal tight-binding model (NTBM) considering Landauer-Büttiker formalism. The covalent bonding of even a single-type functional group is shown to considerably alter the conductance of the chain. For similar radical doping density, electronic characteristics are found to range from insulator to narrow-gap semiconductor depending on the nature of the covalent bonding. Therefore it has become possible to tune electronic properties of the cubane-based one-dimensional oligomers by the functionalization for nanoelectronic applications

Theoretical Study of High-Frequency Response of InGaAs/AlAs Double-Barrier Nanostructures

The presented article contains the numerical calculations of the InGaAs/AlAs resonant tunneling diode’s (RTD) response to the AC electric field of a wide range of amplitudes and frequencies. These calculations have been performed within the coherent quantum-mechanical model that is based on the solution of the time-dependent Schrödinger equation with exact open boundary conditions. It is shown that as the field amplitude increases, at high frequencies, where ħω>Γ (Γ is the width of the resonant energy level), the active current can reach high values comparable to the direct current value in resonance. This indicates the implementation of the quantum regime for RTD when radiative transitions are between quasi-energetic levels and the resonant energy level. Moreover, there is an excitement of higher quasi-energetic levels in AC electric fields, which in particular results in a slow droop of the active current as the field amplitude increases. It also results in potentially abrupt changes of the operating point position by the ħω value. This makes it possible to achieve relatively high output powers of InGaAs/AlAs RTD having an order of 105 W/cm2 at high frequencies

Thermal stability of carbon [<i>n</i>,5] prismanes (<i>n</i> = 2–4): a molecular dynamics study

<p>Tight-binding molecular dynamics simulations are carried out to analyse the thermal stability of the carbon [<i>n</i>,5] prismanes with <i>n</i> = 2–4 over a wide temperature range. The results obtained demonstrate that the isomerisation activation energy as well as the frequency factor in the Arrhenius equation of these metastable nanostructures rapidly decreases with an increase of <i>n</i>. Therefore, the increase in the effective length of [<i>n</i>,5] prismane leads to the decrease in its lifetime up to the moment of its isomerisation. Nevertheless, the stability of [<i>n</i>,5] prismanes is confirmed to be sufficient for their existence at the liquid-nitrogen temperature. The main identified mechanism of [<i>n</i>,5] prismanes isomerisation is the interlayer C–C bond breaking leading to their transformation to the hypostrophene-based molecular systems.</p

Energy and Electronic Properties of Nanostructures Based on the CL-20 Framework with the Replacement of the Carbon Atoms by Silicon and Germanium: A Density Functional Theory Study

We consider SinCL-20 and GenCL-20 systems with carbon atoms replaced by silicon/germanium atoms and their dimers. The physicochemical properties of the silicon/germanium analogs of the high-energy molecule CL-20 and its dimers were determined and studied using density functional theory with the B3LYP/6-311G(d,p) level of theory. It was found that the structure and geometry of SinCL-20/GenCL-20 molecules change dramatically with the appearance of Si-/Ge-atoms. The main difference between silicon- or germanium-substituted SinCL-20/GenCL-20 molecules and the pure CL-20 molecule is that the NO2 functional groups make a significant rotation relative to the starting position in the classical molecule, and the effective diameter of the frame of the systems increases with the addition of Si-/Ge-atoms. Thus, the effective framework diameter of a pure CL-20 molecule is 3.208 &Aring;, while the effective diameter of a fully silicon-substituted Si6CL-20 molecule is 4.125 &Aring;, and this parameter for a fully germanium-substituted Ge6CL-20 molecule is 4.357 &Aring;. The addition of silicon/germanium atoms to the system leads to a decrease in the binding energy. In detail, the binding energies for CL-20/Si6CL-20/Ge6CL-20 molecules are 4.026, 3.699, 3.426 eV/atom, respectively. However, it has been established that the framework maintains stability, with an increase in the number of substituting silicon or germanium atoms. In addition, we designed homodesmotic reactions for the CL-20 molecule and its substituted derivatives Si6CL-20/Ge6CL-20, and then determined the strain energy to find out in which case more energy would be released when the framework breaks. Further, we also studied the electronic properties of systems based on CL-20 molecules. It was found that the addition of germanium or silicon atoms instead of carbon leads to a decrease in the size of the HOMO&ndash;LUMO gap. Thus, the HOMO&ndash;LUMO gaps of the CL-20/Si6CL-20/Ge6CL-20 molecules are 5.693, 5.339, and 5.427 eV, respectively. A similar dependence is also observed for CL-20 dimers. So, in this work, we have described in detail the dependence of the physicochemical parameters of CL-20 molecules and their dimers on the types of atoms upon substitution

On the Performances in the Explaining of Chemical Reactivity of Fullerenes of Electronic Structure Rules

Important electronic structure rules like Maximum Hardness Principle, Minimum Polarizability Principle, Minimum Electrophilicity Principle and Minimum Magnetizability Principle found many field of the chemistry. In the present report, we investigated the validity of the mentioned electronic structure rules in the explaining of the chemical reactivity or stability of fullerenes. For this purpose, important quantum chemical parameters like frontier orbital energies, hardness, electronegativity, softness and electrophilicity for carbon fullerenes (from C20 to C240) were calculated and discussed. As a result, it was shown that none of the electronic construction principles mentioned are fully sufficient. To explain the chemical reactivity of fullerenes, new electronic structure rules or new parameters are require