With first-principles plane-wave ultrasoft pseudopotential method based on density functional(DFT) system, we analyze properties of optical gas sensor materials anatase TiO₂(101) surfaces with NO₂ adsorption. Cu and Cr atoms are easily doped on TiO₂(101) surface. Cu and Cr doped TiO₂(101) surfaces could absorbed NO₂ molecules steadily. After adsorption, material optical properties changed obviously. Cu doped TiO₂(101) surfaces have the highest adsorption energy and the shortest distance between surface and molecule. Analyzing charge density difference and charge population we found that charge transfer occurs between NO₂ molecule and material surface. Electron transfer number is as follows:Cu-doped surface > Cr-doped surface > Undoped surface. Comparing absorption and reflection spectra we found that Cu-doped surface optical properties changed obviously. Redox capacity between surfaces and molecules decided optical gas sensing propertiess. Cu and Cr has 4s valence electron structure which could reduce materials oxygen vacancies oxidative properties. For oxidizing gases, 4s electron could increase surfaces and molecules redox effect. Cu 4s electron is more active. It indicates that Cu doped TiO₂ is a good optical gas sensor material for oxidizing gases.

With first-principles plane-wave ultrasoft pseudopotential method based on density functional theory (DFT), we studied acceptor level characreristics of anatase titanium dioxide doped and co-doped with 3d metal impurities Cu and non-metallic impurities C, N and F.It shows that Cu-N co-doping system and Cu, N single-doped system are better for visible light.Cu-N co-doping system, compared with Cu, N single-doped system, has a smaller band gap and greater density distribution on shallow acceptor level.It also shows that Cu-N co-doping system has highest absorption and reflectivity.Therefore, this system is the best for visible light.Cu and N acceptor level cooperative action results in the best visible light effect.

Fast evaluation of frequency domain free surface Green Function with sufficient accuracy is the key of frequency domain approach for solving hydrodynamic problems.In this paper,the fast caculation of free surface Green Function and its derivatives (frequency domain,infinite depth) is investigated and discussed.This approach is shown to be applicable and efficient.

The spherical aberration of electron lens is always the principal factor which limits the resolution of electron microscope.An analysis and computation of magretic sextupole corrector to correct spherical aberration in a round lens is presented.The numerical results show that resolution of electron microscope can be improved by using the present system.