There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

: 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

The stability of two-dimensional (2D) layers and membranes is subject of a long standing theoretical debate. According to the so called Mermin-Wagner theorem, long wavelength fluctuations destroy the long-range order for 2D crystals. Similarly, 2D membranes embedded in a 3D space have a tendency to be crumpled. These dangerous fluctuations can, however, be suppressed by anharmonic coupling between bending and stretching modes making that a two-dimensional membrane can exist but should present strong height fluctuations. The discovery of graphene, the first truly 2D crystal and the recent experimental observation of ripples in freely hanging graphene makes these issues especially important. Beside the academic interest, understanding the mechanisms of stability of graphene is crucial for understanding electronic transport in this material that is attracting so much interest for its unusual Dirac spectrum and electronic properties. Here we address the nature of these height fluctuations by means of straightforward atomistic Monte Carlo simulations based on a very accurate many-body interatomic potential for carbon. We find that ripples spontaneously appear due to thermal fluctuations with a size distribution peaked around 70 \AA which is compatible with experimental findings (50-100 \AA) but not with the current understanding of stability of flexible membranes. This unexpected result seems to be due to the multiplicity of chemical bonding in carbon.

Intrinsic ripples in graphene

Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

Lithium–sulfur (Li–S) batteries have attracted considerable attention due to high theoretical specific energy and environmental friendliness. However, the shuttle of lithium polysulfides (LiPSs) has become a major obstacle for developing Li–S batteries. In this work, we explored a new C4N4 monolayer, which could be easily prepared from its bulk form using a similar mechanical exfoliation approach to that of graphene due to its smaller exfoliation energy. The C4N4 monolayer could suppress the shuttling of LiPSs and produce significant improvement in the cycling performance of Li–S batteries. Moreover, adsorption calculations revealed that polysulfide captured by C4N4 was chemisorbed with a suitable range of adsorption energies from −1.931 to −3.119 eV. Furthermore, excellent surface diffusions of LiPSs on C4N4 resulted in a fast charge/discharge rate. Moreover, to improve the electrical conductivity of C4N4, graphyne was selected to construct a C4N4/graphyne heterostructure. Based on these remarkable results, we conclude that C4N4 is a highly promising anchoring material for Li–S batteries. We hope that our studies will inspire more experimental and theoretical studies on exploring the potential of other 2D nanostructures as lithium–sulfur battery hosts.

A novel porous C4N4 monolayer as a potential anchoring material for lithium–sulfur battery design

Two-dimensional Porous Transition Metal Organic Framework Materials with Strongly Anchoring Ability as Lithium-Sulfur Cathode

Metallic phase (1T) MoS2 has been regarded as an appealing material for hydrogen evolution reaction. In this work, a novel interface-induced strategy is reported to achieve stable and high-percentage 1T MoS2 through highly active 1T-MoS2 /CoS2 hetero-nanostructure. Herein, a large number of heterointerfaces can be obtained by interlinked 1T-MoS2 and CoS2 nanosheets in situ grown from the molybdate cobalt oxide nanorod under moderate conditions. Owing to the strong interaction between MoS2 and CoS2 , high-percentage of metallic-phase (1T) MoS2 of 76.6% can be achieved, leading to high electroconductivity and abundant active sites compared to 2H MoS2 . Furthermore, the interlinked MoS2 and CoS2 nanosheets can effectively disperse the nanosheets so as to enlarge the exposed active surface area. The near zero free energy of hydrogen adsorption at the heterointerface can also be achieved, indicating the fast kinetics and excellent catalytic activity induced by heterojunction. Therefore, when applied in hydrogen evolution reaction (HER), 1T-MoS2 /CoS2 heterostructure delivers low overpotential of 71 and 26 mV at the current density of 10 mA cm-2 with low Tafel slops of 60 and 43 mV dec-1 , respectively in alkaline and acidic conditions.

3D 1T-MoS 2 /CoS 2 Heterostructure via Interface Engineering for Ultrafast Hydrogen Evolution Reaction

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.

Cheng He

Papers

A novel porous C4N4 monolayer as a potential anchoring material for lithium–sulfur battery design

Two-dimensional Porous Transition Metal Organic Framework Materials with Strongly Anchoring Ability as Lithium-Sulfur Cathode

3D 1T-MoS 2 /CoS 2 Heterostructure via Interface Engineering for Ultrafast Hydrogen Evolution Reaction

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

Rational design of porous carbon allotropes as anchoring materials for lithium sulfur batteries