: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

We examine the magnetic properties of two-dimensional graphene with topological line defect using first-principles calculations and predict a weak ferromagnetic ground state with spin-polarized electrons localized along the extended line defect. Our results show that tensile strain along the zigzag direction can greatly enhance local magnetic moments and ferromagnetic stability of the system. In sharp contrast, tensile strain applied along the armchair direction quickly diminishes these magnetic moments. A detailed analysis reveals that this intriguing magnetism modulation by strain stems from the redistribution of spin-polarized electrons induced by local lattice distortion. It suggests a sensitive and effective way to control magnetic properties of graphene which is critical for its applications in nanoscale devices.

Tunable magnetism in strained graphene with topological line defect

By means of comprehensive first-principles calculations, we investigate the stability, electronic and optical properties of an AlAs/germanene heterostructure. In particular, electric field and strain are used to tailor its electronic band gap and dielectric function. The binding energy and interlayer distance indicate that germanene and AlAs monolayers in the AAI pattern are bound together via van der Waals interaction with a maximum indirect-gap of 0.494 eV, which is expected to have potential application in the field of field-effect transistors. Under a negative E-field and compressive strain, the bandgaps of the AAI-stacking show a near-linear and linear decrease behavior, respectively, whereas the response of the bandgaps to a positive E-field and tensile strain displays a dramatic and monotonous decrease relationship. The work function of the AAI-stacking is calculated to be 4.35 eV smaller than that of individual monolayers. Besides, the optical properties are also calculated. The imaginary parts of the dielectric function of the germanene/AlAs heterobilayer exhibit a significant enhancement in comparison with the considered monolayers, indicating the improvement of the capability of absorbing photons. In particular, the imaginary part of the dielectric function of the heterostructure is enhanced with the increase of E-field and mechanical strain, which suggests that the optical properties of the heterostructure can be improved by E-field and mechanical strain. Simultaneously, a red-shift or blue-shift can be observed with the changes in E-field and mechanical strain. All these nontrivial and tunable properties endow the AlAs/germanene nanocomposite with great potential for FETs, strain sensors, photocatalysis, field emission, energy harvesting, and photonic devices.

An AlAs/germanene heterostructure with tunable electronic and optical properties via external electric field and strain

The structural and electronic properties of a g-C3N4/graphene/g-C3N4 (g-C3N4/SLG/g-C3N4) sandwich heterostructure have been systematically investigated using density functional theory with van der Waals corrections. The results indicate that the band gap of the g-C3N4/SLG/g-C3N4 sandwich heterostructure can be opened to 106 meV without strain. Applying strain is a promising way to tune the electronic properties of a sandwich heterostructure. After applying uniaxial strain, the heterostructure can withstand larger tensile strain than compression strain without damaging the structure and the band gap is more easily increased by the X-direction strain. When the 5% X-direction strain is applied, the band gap could be opened to 525 meV and meanwhile maintain a high carrier mobility. These electronic properties may provide a potential application in nanodevices.

A tunable and sizable bandgap of a g-C3N4/graphene/g-C3N4 sandwich heterostructure: a van der Waals density functional study

Effect of hole doping and strain modulations on electronic structure and magnetic properties in ZnO monolayer

Density-functional theory calculations are performed to investigate the effects of surface modifications and nanosheet thickness on the electronic and magnetic properties of gallium nitride (GaN) nanosheets (NSs). Unlike the bare GaN NSs terminating with polar surfaces, the systems with hydrogenated Ga (H-GaN), fluorinated Ga (F-GaN), and chlorinated Ga (Cl-GaN) preserve their initial wurtzite structures and exhibit ferromagnetic states. The abovementioned three different decorations on Ga atoms are energetically more favorable for thicker GaN NSs. Moreover, as the thickness increases, H-GaN and F-GaN NSs undergo semiconductor to metal and half-metal to metal transition, respectively, while Cl-GaN NSs remain completely metallic. The predicted diverse and tunable electronic and magnetic properties highlight the potential of GaN NSs for novel electronic and spintronic nanodevices.

Tuning electronic and magnetic properties of GaN nanosheets by surface modifications and nanosheet thickness

Superplastic dual-phase nanostructure Mg alloy: A molecular dynamics study

Dual-phase nanostructured amorphous/crystalline (A/C) model is an effective method to improve the mechanical properties of Mg alloys. However, the interaction behavior between A/C interface (ACI) and various defects is still unclear. Here, the interaction mechanisms between the basal/prismatic interface (BPI) and ACI of dual-phase nanoscale A/C MgAl/Mg alloys are investigated by molecular dynamics simulation method. The results indicate that the ACIs have a significant Peach-Koehler (attractive or repulsive) force to govern the activation of interfacial dislocations in BPI. When the spacing between ACI and BPI (SAB) is less than 12.0 nm, it is found that the attractive force plays a dominant role in interfacial dislocation activation. On the contrary, the repulsive force has an effect on the activation of dislocations. The results also show that the maximum peak strain increases almost linearly with increasing SAB, and the maximum peak strain delay is attributed to the strain contributed by BPIs migration.

M.X. Xiao

Papers

Tuning electronic and magnetic properties of GaN nanosheets by surface modifications and nanosheet thickness

Superplastic dual-phase nanostructure Mg alloy: A molecular dynamics study

Atomic simulation of interaction mechanism between basal/prismatic interface and amorphous/crystalline interface of dual-phase magnesium alloys

Atomic simulation of deformation behavior of dual-phase crystalline/amorphous Mg/Mg-Al nanolaminates

Atomic-scale insight into mechanical properties and deformation behavior of crystalline/amorphous dual-phase high entropy alloys