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.

Band structures,density of states and optical properties of pure,N-doped,S-doped and N-S co-doped rutile TiO₂ are studied with plane-wave ultrasoft pseudopotential method based on first-principles density functional theory.It shows that the gap of N-doped TiO₂ reduces to 1.43 eV,and there is an impurity band on top of the valence band.S-doped TiO₂ results in Fermi level moves to the conduction band,and the gap decreases to 0.32 eV.N-S co-doped TiO₂ results in two impurity bands located in the band gap.One impurity band is apart from the bottom of conduction band by 0.35 eV,the other is apart from the top of valence band by 0.85 eV,which is mainly formed by N-atom 2p orbital and S-atom 3p orbital.It causes a red-shift in absorption wavelength,and gives rise to extremely great absorption coefficient in visible-light region,which shows a strong photocatalytic activity.