Lingbiao Meng

Gas Phase Conformations of Selenocysteine and Related Ions: A Comprehensive Theoretical Study

Extensive ab initio molecular calculations have been first performed to thoroughly characterize the gas-phase potential energy surfaces (PES) of the 21th amino acid selenocysteine and related ions (neutral, protonated and deprotonated). A wide range of trial structures generated by considering the combinations of all internal single-bond rotamers was surveyed at the BHandHLYP/6-31G(d) level, and then refined at the BHandHLYP/6-311++G(d,p) level. A total of 76, 23, 38, and 3 unique stable conformers respectively for neutral, protonated, deprotonated, and doubly deprotonated selenocysteine is identified, and neutral zwitterionic forms are found to be as local minima on the gas-phase PES. The properties of the low energy conformers, such as relative energies, dipole moments, rotational constants, and intramolecular hydrogen bonds, were determined and analyzed. The thermochemical properties of proton affinity (PA), gas-phase basicity (GB), proton dissociation energy (PDE), gas-phase acidity (GA), and the vertical ionization energies (VIEs) were computed by the theoretical approaches of BHandHLYP, B3LYP, MP2, and CCSD(T). Moreover, the conformational equilibrium effect (CEE) on thermochemical properties was analyzed. The statistical simulation predicts that the CEE generally yields a physical correction on about a 1 kBT scale in GA/GB calculations for multi-conformer systems.

Unique Zigzag-Shaped Buckling Zn2C Monolayer with Strain-Tunable Band Gap and Negative Poisson Ratio

Designing new materials with reduced dimensionality and distinguished properties has continuously attracted intense interest for materials innovation. Here we report a novel two-dimensional (2D) Zn2C monolayer nanomaterial with exceptional structure and properties by means of first-principles calculations. This new Zn2C monolayer is composed of quasi-tetrahedral tetracoordinate carbon and quasi-linear bicoordinate zinc, featuring a peculiar zigzag-shaped buckling configuration. The unique coordinate topology endows this natural 2D semiconducting monolayer with strongly strain tunable band gap and unusual negative Poisson ratios. The monolayer has good dynamic and thermal stabilities and is also the lowest-energy structure of 2D space indicated by the particle-swarm optimization (PSO) method, implying its synthetic feasibility. With these intriguing properties the material may find applications in nanoelectronics and micromechanics.

Low Energy Conformations and Gas-Phase Acidity and Basicity of Pyrrolysine

The gas-phase conformational potential energy surfaces (PES) of the last, 22nd amino acid pyrrolysine and related derivatives (neutral, deprotonated, and protonated) were extensively searched for the first time. By considering all possible combinations of the single-bond rotational degrees of freedom with a semiempirical and ab initio combined computational approach, a large set of unique low-energy conformers was identified for each pyrrolysine species, and essential properties such as vibrational frequencies, dipole moments, rotational constants, and intramolecular hydrogen bonding configurations were presented and characterized. The conformational electronic energies and thermochemical properties of proton affinity/dissociation energy (PA/PDE) and gas-phase acidity/basicity (GA/GB) were determined by the density functional BHandHLYP, B3LYP, and M062X, and Møller-Plesset MP2 methods. The MP2 and DFT methods are found to predict disparate PES for neutral and protonated conformations and sufficiently different thermochemical data. The measurements of dipole moments and characteristic IR modes at low temperature as well as GA/GB are demonstrated to be feasible approaches to verify the theoretical predictions.

Enhanced quantum interference transport in gold films with random antidot arrays

We report on the quantum interference transport of randomly distributed antidot arrays, which were prepared on gold films via the focused ion beam direct writing method. The temperature dependence of the gold films’ resistances with and without random antidot arrays were described via electron–phonon interaction theory. Compared with the pristine gold films, we observed an unexpected enhancement of the weak localization signature in the random antidot array films. The physical mechanism behind this enhancement may originate from the enhancement of electron–electron interactions or the suppression of electron–phonon interactions; further evidence is required to determine the exact mechanism.

Theoretical Study on Dissociation Mechanisms of Di-ethyl Berylliums and Di-t-butyl Berylliums

The potential energy surfaces (PES) of unimolecular dissociation reactions for di-ethyl beryllium and di-t-butyl beryllium are investigated by B3LYP, CCSD(T), and G3B3 approaches. Possible reaction pathways through either the radical or transition state (TS) of the molecules are considered. The geometries, vibrational frequencies and relative energies for various stationary points are determined. From the study of energetics, the TS pathways arising from concerted molecular eliminations are indicated to be the main dissociation pathways for both molecules. The PES differences of the dissociation reactions are investigated. The activation energies and rate constants will be helpful for investigating the predictive ability of the reaction in further theoretical and experimental research.

Two-dimensional zigzag-shaped Cd2C monolayer with a desirable bandgap and high carrier mobility

Through purposive atomic transmutation and extensive density functional calculations, we design and predict a novel zigzag-shaped Cd2C monolayer exhibiting distinguished structure and properties. The zigzag-shape structure, buckled with two adjacent rows of atoms shifted oppositely with respect to the plane, is formed by tetracoordinate carbon and bicoordinate cadmium. The unique structure topology and resulting electronic hybridizations render the Cd2C monolayer with robust stability and distinctive electronic properties: it is a natural 2D semiconductor with high and anisotropic acoustic-phonon-limited carrier mobilities (∼103–105 cm2 V−1 s−1); its fundamental bandgap is moderate ∼1.7 eV and meanwhile, it can be flexibly tuned in a large range of more than 1 eV by external strains. Additionally, as the lowest-energy structure of 2D space, the monolayer exhibits excellent thermal and kinetic stabilities. These outstanding properties indicate that the Cd2C monolayer is a promising nanomaterial for future electronic applications.

Linear magnetoresistance in gold foams

The electrical transport properties of metal foams may not only be of fundamental research interest but can also lead to wide application in sensors. We report the magnetotransport properties of gold foams prepared by a chemical template–dealloying method. The temperature dependence of the resistivity of gold foams represents a metallic behavior with zero magnetic field. With increasing magnetic field, a crossover from quadratic to linear dependence of the magnetoresistance in gold foams is observed in the studied temperature range (2–50 K). The physical mechanisms resulting in this observation may be ascribed to the classical linear magnetoresistance theory based on the spatial mobility fluctuations or current distribution effect. However, further evidence is required to determine the exact mechanism.

Anomalous magnetotransport behaviours in PtSe2 microflakes

Platinum diselenide (PtSe2) is a newly discovered 2D transition metal dichalcogenide, and is further theoretically identified as a candidate of type-II Dirac semimetals. The electrical transport study of PtSe2 microflakes may provide great potential not only in fundamental physics, but also for future electronic applications. We report the anomalous magnetotransport properties of PtSe2 microflakes. The anisotropic magnetoresistance of PtSe2 microflakes can be normalized by introducing a 3D scaling factor [Formula: see text], where θ is the magnetic field angle with respect to the c axis of the crystal and γ is the mass anisotropic constant of electrons. Additionally, the non-monotonic temperature-dependent magnetoresistance of PtSe2 microflakes is observed both in the perpendicular and in-plane magnetic field orientations. This anomalous magnetotransport behaviour may be ascribed to the novel features of type-II Dirac fermions; however, the exact physical mechanism deserves further investigation.

Electrical transport properties of nickel chromium alloy films

The effect of the electron–phonon interactions on the electrical transport properties of NiCr alloy films is studied. The resistivity of the NiCr films is measured between 2 and 300 K, and reveals an overall metallic conduction behavior. The resistivity–temperature curves of NiCr films are successfully interpreted using the traditional electron–phonon coupling theory. The results reveal that the electrons coupling with the acoustic-mode phonons dominate the electrical properties of NiCr films over the entire temperature range investigated, and weak corrections by the electron–optical–phonon interactions are present in the high temperature regime. The dominance of the electron–phonon interactions on the transport behavior of NiCr films is further confirmed by the magnetotransport analysis. The electron–phonon interaction constant of NiCr films is also discussed.