Fengyu Li

Semiconducting Group 15 Monolayers: A Broad Range of Band Gaps and High Carrier Mobilities

Optoelectronic applications require materials both responsive to objective photons and able to transfer carriers, so new two-dimensional (2D) semiconductors with appropriate band gaps and high mobilities are highly desired. A broad range of band gaps and high mobilities of a 2D semiconductor family, composed of monolayer of Group 15 elements (phosphorene, arsenene, antimonene, bismuthene) is presented. The calculated binding energies and phonon band dispersions of 2D Group 15 allotropes exhibit thermodynamic stability. The energy band gaps of 2D semiconducting Group 15 monolayers cover a wide range from 0.36 to 2.62 eV, which are crucial for broadband photoresponse. Significantly, phosphorene, arsenene, and bismuthene possess carrier mobilities as high as several thousand cm(2)  V(-1)  s(-1) . Combining such broad band gaps and superior carrier mobilities, 2D Group 15 monolayers are promising candidates for nanoelectronics and optoelectronics.

Graphane/Fluorographene Bilayer: Considerable C–H···F–C Hydrogen Bonding and Effective Band Structure Engineering

Systematic density functional theory (DFT) computations revealed the existence of considerable C-H···F-C bonding between the experimentally realized graphane and fluorographene layers. The unique C-H···F-C bonds define the conformation of graphane/fluorographene (G/FG) bilayer and contribute to its stability. Interestingly, G/FG bilayer has an energy gap (0.5 eV) much lower than those of individual graphane and fluorographene. The binding strength of G/FG bilayer can be significantly enhanced by applying appropriate external electric field (E-field). Especially, changing the direction and strength of E-field can effectively modulate the energy gap of G/FG bilayer, and correspondingly causes a semiconductor-metal transition. These findings open new opportunities in fabricating new electronics and opto-electronics devices based on G/FG bilayer, and call for more efforts in using weak interactions for band structure engineering.

Appropriate description of intermolecular interactions in the methane hydrates: An assessment of DFT methods

Accurate description of hydrogen‐bonding energies between water molecules and van der Waals interactions between guest molecules and host water cages is crucial for study of methane hydrates (MHs). Using high‐level ab initio MP2 and CCSD(T) results as the reference, we carefully assessed the performance of a variety of exchange–correlation functionals and various basis sets in describing the noncovalent interactions in MH. The functionals under investigation include the conventional GGA, meta‐GGA, and hybrid functionals (PBE, PW91, TPSS, TPSSh, B3LYP, and X3LYP), long‐range corrected functionals (ωB97X, ωB97, LC‐ωPBE, CAM‐B3LYP, and LC‐TPSS), the newly developed Minnesota class functionals (M06‐L, M06‐HF, M06, and M06‐2X), and the dispersion‐corrected density functional theory (DFT) (DFT‐D) methods (B97‐D, ωB97X‐D, PBE‐TS, PBE‐Grimme, and PW91‐OBS). We found that the conventional functionals are not suitable for MH, notably, the widely used B3LYP functional even predicts repulsive interaction between CH4 and (H2O)6 cluster. M06‐2X is the best among the M06‐Class functionals. The ωB97X‐D outperforms the other DFT‐D methods and is recommended for accurate first‐principles calculations of MH. B97‐D is also acceptable as a compromise of computational cost and precision. Considering both accuracy and efficiency, B97‐D, ωB97X‐D, and M06‐2X functional with 6‐311++G(2d,2p) basis set without basis set superposition error (BSSE) correction are recommended. Though a fairly large basis set (e.g., aug‐cc‐pVTZ) and BSSE correction are necessary for a reliable MP2 calculation, DFT methods are less sensitive to the basis set and BSSE correction if the basis set is sufficient (e.g., 6‐311++G(2d,2p)). These assessments provide useful guidance for choosing appropriate methodology of first‐principles simulation of MH and related systems.

Theoretical design of MoO3-based high-rate lithium ion battery electrodes: the effect of dimensionality reduction

By means of density functional theory computations, we systematically investigated the behavior of lithium (Li) adsorption and diffusion on MoO3 with different dimensions: including three-dimensional (3D) bulk, two-dimensional (2D) double-layer, 2D monolayer and one-dimensional (1D) nanoribbons. The Li binding energies and diffusion barriers are comparable in MoO3 bulk and double-layer. Reducing the dimension to the MoO3 monolayer simultaneously lowers the Li diffusion barrier and the interaction between Li atoms and the MoO3 monolayer. Cutting the MoO3 monolayer into 1D nanoribbons can further facilitate the diffusion of Li atoms, and enhance the Li binding energies. Especially, Li diffusion on nanoribbons is rather facile along both the axial and the transverse directions. These computational results demonstrate that due to the dimensional reduction, MoO3 monolayer nanosheets and nanoribbons have exceptional properties (good electronic conductivity, fast Li diffusion, high operating voltage and high energy density), and thus are promising as high-rate Li ion battery electrodes.

Mn monolayer modified Rh for syngas-to-ethanol conversion: a first-principles study

Rh is unique in its ability to convert syngas to ethanol with the help of promoters. We performed systematic first-principles computations to examine the catalytic performance of pure and Mn modified Rh(100) surfaces for ethanol formation from syngas. CO dissociation on the surface as well as CO insertion between the chemisorbed CH(3) and the surface are the two key steps. The CO dissociation barrier on the Mn monolayer modified Rh(100) surface is remarkably lowered by ~1.5 eV compared to that on Rh(100). Moreover, the reaction barrier of CO insertion into the chemisorbed CH(3) group on the Mn monolayer modified Rh(100) surface is 0.34 eV lower than that of methane formation. Thus the present work provides new mechanistic insight into the role of Mn promoters in improving Rhs selectivity to convert syngas to ethanol.

Theoretical design of novel trinuclear sandwich complexes with central M3 triangles (M = Ni, Pd, Pt).

On the basis of the 18-electron rule, we theoretically designed a series of sandwich complexes [M(3)L(2)(CO)(3)](q) (M = Ni, Pd, Pt; L = C(7)H(7), P(5), P(6), As(5), As(6); q = 2+, 0, or 2-) by means of density functional theory computations. These sandwich structures are of high stability, revealed by their strong donating and back-donating metal-ligand interactions, considerable aromatic characters as well as sizable energy gaps. All these proposed sandwich structures might serve as promising building blocks for new nanomaterials.

Improved stability of water clusters (H2O)30–48: a Monte Carlo search coupled with DFT computations

The growing structural patterns of water clusters with 30–48 water molecules were investigated by means of a combined Monte Carlo search algorithm and density functional theory computations. The (H2O)30–48 clusters with amorphous core–shell structures are lower in energy than the previously reported fused cage and the tubular configurations. The significant differences in infrared spectra of these three different structural patterns provide some clues to identify the structural properties of these medium-sized water clusters in experiments.

High-Performance Ru1/CeO2 Single-Atom Catalyst for CO Oxidation: A Computational Exploration

By means of density functional theory computations, we examine the stability and CO oxidation activity of single Ru on CeO2 (111), TiO2 (110) and Al2 O3 (001) surfaces. The heterogeneous system Ru1 /CeO2 has very high stability, as indicated by the strong binding energies and high diffusion barriers of a single Ru atom on the ceria support, while the Ru atom is rather mobile on TiO2 (110) and Al2 O3 (001) surfaces and tends to form clusters, excluding these systems from having a high efficiency per Ru atom. The Ru1 /CeO2 exhibits good catalytic activity for CO oxidation via the Langmuir-Hinshelwood mechanism, thus is a promising single-atom catalyst.

What is the preferred structure of the Meisenheimer-Wheland complex between sym-triaminobenzene and 4,6-dinitrobenzofuroxan?

The geometries, energies, and electronic properties of possible configurations of Meisenheimer-Wheland (M-W) complexes of sym-triaminobenzenes and 4,6-dinitrobenzofuroxan (DNBF) were investigated theoretically by MP2 and a variety of DFT methods. The pi-pi complex is preferred thermodynamically by more than 15 kcal/mol over the sigma-complexes for the unsubstituted species. However, the N-substituents of the 1,3,5-triaminobenzenes influence the relative stabilities of the alternative configurations significantly. The sigma-syn configuration of the M-W complex of 1,3,5-tris(N-piperidyl)benzene and DNBF has the lowest energy, followed closely by the sigma-anti and pi-pi forms. The small energy differences between different configurations are consistent with the dynamic interconversion of three homomeric structures observed experimentally by NMR. The ca. 1.63 A C-C interring bond exchanges among three equivalent sites. Quantum theory of atoms in molecules (QTAIM) analysis provided insights into the nature of the intermonomer interactions. Charge transfer and sigma bonding account for the stability and remarkably large binding energies of the M-W complexes.

First total synthesis of the (±)-2-methoxy-6-heptadecynoic acid and related 2-methoxylated analogs as effective inhibitors of the leishmania topoisomerase IB enzyme

The fatty acids (±)-2-methoxy-6Z-heptadecenoic acid, (±)-2-methoxy-6-hepta-decynoic acid, and (±)-2-methoxyheptadecanoic acid were synthesized and their inhibitory activity against the Leishmania DNA topoisomerase IB enzyme (LdTopIB) determined. Both 2-OMe-17:1 fatty acids were synthesized from 4-bromo-1-pentanol, the olefinic fatty acid in 10 steps and in 7 % overall yield, while the acetylenic fatty acid in 7 steps and in 14 % overall yield. The 2-OMe-17:0 acid was prepared in 6 steps and in 42 % yield from 1-hexa-decanol. The 2-OMe-17:1 acids inhibited LdTopIB, with the acetylenic acid displaying an EC50 = 16.6 ± 1.1 μM, but the 2-OMe-17:0 acid did not inhibit LdTopIB. The (±)-2-methoxy-6Z-heptadecenoic acid preferentially inhibited LdTopIB over the human TopIB enzyme. Unsaturation seems to be a prerequisite for effective inhibition, rationalized in terms of weak intermolecular interactions between the active site of LdTopIB and either the double or triple bonds of the fatty acids. Toxicity toward Leishmania donovani promastigotes was also investigated, resulting in the order acetylenic > olefinic > saturated with the (±)-2-methoxy-6-heptadecynoic acid displaying an EC50 = 74.0 ± 17.1 μM. Our results indicate that α-methoxylation decreases the toxicity of C17:1 fatty acids toward L. donovani promastigotes, but improves their selectivity index.