Guo-Zhong He

Band gap narrowing of TiO2 by compensated codoping for enhanced photocatalytic activity

In this study, we have performed first-principles screened exchanged hybrid density function theory with the HSE06 function calculations of the C-Mo, C-W, N-Nb and N-Ta codoped anatase TiO2 systems to investigate the effect of codoping on the electronic structure of TiO2. The calculated results demonstrate that (W(s)+C(s)) codoped TiO2 narrows the band gap significantly, and have little influence on the position of conduction band edges, therefore, enhances the efficiency of the photocatalytic hydrogen generation from water and the photodegradation of organic pollutants. Moreover, the proper oxygen pressure and temperature are two key factors during synthesis which should be carefully under control so that the desired (W(s)+C(s)) codoped TiO2 can be obtained.

Time-dependent Density Functional-based Tight-bind Method Efficiently Implemented with OpenMP Parallel and GPU Acceleration

The time‐dependent density functional‐based tight‐bind (TD‐DFTB) method is implemented on the multi‐core and the graphical processing unit (GPU) system for excited state calculations of large system with hundreds or thousands of atoms. Sparse matrix and OpenMP multithreaded are used for building the Hamiltonian matrix. The diagonal of the eigenvalue problem in the ground state is implemented on the GPUs with double precision. The GPU‐based acceleration fully preserves all the properties, and a considerable total speedup of 8.73 can be achieved. A Krylov‐space‐based algorithm with the OpenMP parallel and GPU acceleration is used for finding the lowest eigenvalue and eigenvector of the large TDDFT matrix, which greatly reduces the iterations taken and the time spent on the excited states eigenvalue problem. The Krylov solver with the GPU acceleration of matrix‐vector product can converge quickly to obtain the final result and a notable speed‐up of 206 times can be observed for system size of 812 atoms. The ...

ENHANCEMENT AND EXTENSION OF HIGH-ORDER HARMONIC EMISSION AND AN ISOLATED SUB-100 AS PULSE GENERATION FROM TWO-COLOR LASER FIELDS

We theoretically propose a method to generate a coherent and ultrabroad extreme ultraviolet supercontinuum using Ar+ ions. When the medium is exposed to a two-color laser field, which is synthesized by a few-cycle fundamental laser pulse and its second-harmonics pulse, the harmonics spectrum presents a two-plateau structure. For the selection of the short quantum path utilizing the two-color scheme, the supercontinuum in the second plateau is almost synchronously emitted and a single 58 attosecond (as) pulse can be directly obtained. By increasing the intensity of the controlling field or adjusting the delay time of the two laser fields, a more intense isolated as pulse will be generated.

A Theoretical Investigation of the Structural Properties of Chemically Modified Mo-S-I Nanowires

Abstract Molybdenum-based materials are good catalysts. The structural properties of a chemically modified MoSI nanowire were investigated by density functional theory calculations. The structural simulation showed that MoSI nanowires have good flexibility and showed hysteresis in its structural evolution. The formation energy, projected density of states, and charge density showed that the chemical modification of MoSI nanowires is possible without losing useful structural and electronic properties useful for applications in catalysis. We suggest potential applications for MoSI nanowire materials in nanoelectronics, nanoelectromechanical, catalysis, and nano-confinement investigations.