First-principles investigation on the thermoelectric performance of half-Heusler compound CuLiX(X = Se, Te).

The remarkable thermoelectric performance is predicted for half-Heusler (HH) compounds of CuLiX (X = Se, Te) based on the first-principles calculation, the deformation potential (DP) theory, and semi-classical Boltzmann theory. The Slack model is employed to evaluate the lattice thermal conductivity and the result is in good agreement with the previously reported data. The results of mechanical properties demonstrate that CuLiSe is ductile but CuLiTe is brittle. The relaxation time and the carrier mobility are calculated with DP theory. The electrical and thermal conductivities are obtained by using the semi-classical Boltzmann theory based on the relaxation approximation. The Seebeck coefficient and power factor are obtained and their characters are analyzed. The dimensionless figure of merits (ZT) is obtained for the p- and n-type CuLiX. The maximum ZT of 2.65 can be achieved for n-type CuLiTe at the carrier concentration of 3.19 × 1019 cm-3 and 900 K, which indicates that this compound is a very promising candidate for the highly efficient thermoelectric materials.

Group-IVA element-doped SrIn2O4 as potential materials for hydrogen production from water splitting with solar energy.

Band gap engineering can efficiently improve the photocatalytic activity of semiconductors for hydrogen generation from water splitting. Herein, we present a comprehensive investigation on the geometrical structures, electronic, optical, and potential photocatalytic properties and charge carrier mobility of pristine and group-IVA element-doped SrIn2O4 using first-principles density functional theory with the meta-GGA+MBJ potential. The calculated formation energies are moderate, indicating that the synthesis of the doped structures is experimentally feasible. In addition, the energy band gaps of the group-IVA element-doped SrIn2O4 range from 1.67 to 3.07 eV, which satisfy the requirements for photocatalytic water splitting, except for that of the Si mono-doped structure. Based on the deformation potential theory, a high charge carrier mobility of 2093 cm2 V-1 s-1 is obtained for the pristine SrIn2O4 and those of the doped-structures are also large, although a decrease in the values of some are observed. The optical absorption coefficient of the doped structures in the near ultraviolet (UV) and visible light range significantly increases. Therefore, group-IVA element-doped SrIn2O4 are potential candidates as photocatalysts for hydrogen generation from water splitting driven by visible light.

Discrete Dipole Approximation Simulation of Nearly Touching Plasmonic Au Dimers and Influence of Particle Shape Assembly on Optical Response.

The method Discrete Dipole Approximation (DDA) is used to calculate the extinction spectra and field distribution of three types of dimers. In the paper we provide a systematic analysis of the optical response of different nanoscopic dimer structures with relatively small gap distances. A description is given about how the energy and excitation cross sections of dimer plasmons depend on nanoparticle separation. Resonance peaks of dimers show red-shift compared with single nanoparticle. Dimers formed by different single particle display distinct optical response. Interaction junctions in dimers can serve as hot spots for field enhancement. Field distribution in gaps made of two flat planes is nearly continuous. Changing gaps between two particles in dimers can tune the resonance wavelength effectively as well as different particle ensembles. Existence of sharp corners can attract and change field distribution. It is not effective volume but the effective cross-section that dominates the extinction efficiency.

The influence of edge and corner evolution on plasmon properties and resonant edge effect in gold nanoplatelets.

In this paper a simulation of the properties of surface plasmons on gold nanoplatelets with various cross-sections inscribed in a circle and an investigation of their field distributions to assign multiple SPRs are described. The manipulated propagation can be obtained through the evolution of edges and corners. Furthermore, the particle morphology and the associated spectral positions alone do not uniquely reflect the important details of the local field distribution or the resonance modes. The plasmon modes were investigated and found to be mainly excited along the edges and in the side and sloped side surfaces. The strong field distributions can generally be found around the corners and how the plasmons transmit through the corners to adjacent edges was also investigated. Besides the plasmons excited along the edges as were found for the triangular nanoplatelets, plasmons were excited in the interior region of the triangular surfaces and were also investigated. Despite this in the infrared region, plasmon modes were found to be along the edges for the hexagonal nanoplatelets. Also, it can be seen that the change of nanoplatelet thickness can support different plasmon modes ranging from dipolar resonance mode to quadrupole resonance mode. The thickness far below the skin depth can display complex plasmon modes along the edges and on the side and sloping side surfaces as well as the strong coupling between the top and bottom surfaces. The observed plasmon resonance modes in this simulation reflect the interference of all these contributions including the plasmons along the edges and on the side surfaces. This is an essential step towards a thorough understanding of plasmon modes and the effect of edge and corner evolution in polygonous nanoplatelets.

[Study of density functional theory for surface-enhanced Raman spectra of furfural].

In the present paper, DFT method at the B3LYP/6-31+G* * (C, H, O)/LANL2DZ(Ag) level was used to optimize molecular configurations of furfural. Based on the optimized structure, the normal Raman spectrum (NRS) of FUR and the surface-enhanced Raman spectrum (SERS) of FUR adsorbed on Ag, Ag2 and Ag4 were all calculated, which were compared with the experimental values. The calculation results indicated that a good conformity was found between the computed and the experimental results. The results of furfural adsorbed on Ag4 were more approximate to the ever reported experimental date than those of furfural adsorbed on Ag and Ag2. At the end, detailed analysis of the Raman spectrum and more comprehensive assignments of the vibration mode for furfural were studied by the software of GaussView. The data of the SERS by comparing with the one of NRS show that furfural molecule and Ag atoms interact with each other. And we suppose that the molecular plane with the ring of adsorbed furfural molecule is vertically orientated to the silver surface. The work in this paper offers a theory evidence for detection and trace analysis of drinks containing furfural.

[Study of density functional theory for surface-enhanced Raman spectra of p-aminothiophenol].

In the present paper, DFT method at the B3LYP/6-31++G** (C, H, N, S)/LANL2DZ(Ag) level was used to optimize molecular configurations of p-aminothiophenol. Based on the optimized structure, the normal Raman scattering (NRS) spectrum of PATP and the surface-enhanced Raman scattering(SERS) spectrum of PATP adsorbed on Ag and Ag2 were both calculated, and were compared with the results of other literatures values. The calculation results indicated that a good conformity was found between the computed and experimental results. The results of PATP adsorbed on Ag2 were more approximate to the ever reported experimental data than those of PATP adsorbed on Ag. At the end, detailed analysis of the Raman spectrum and more comprehensive assignments of the vibration mode for p-aminothiophenol were studied by the software of GaussView. In comparison with SERS spectrum and NRS spectrum of PATP molecule, the authors observed the stretching vibration bands in the SERS spectrum at about 213 cm(-1), which is due to Ag-S stretching vibration mode. The work in this paper has greatly directive value in understanding and explaining some experiment phenomenon, and helps to study the mechanism of surface-enhanced Raman scattering of PATP.