First-Principles Investigation On Peristylapolyenes And The Narrow Of Band Gap Of Anatase TiO₂ By N-doping

In this paper, we first introduced computer molecular simulation status and development trend of materials computation with computer molecular simulation. Then molecular simulation software of our laboratory——MS(Materiales Studio), its instruction and modules used in it(CASTEP and Dmol3)were introduced. Following, we described traditional single electron approximation theory(HFA)in condensed physics and its more precise description——modern single electron approximation theory(DFT). We described materials computation methods with first-principles based on DFT. Furthermore, we investigated peristylapolyenes and N-doped anatase TiO₂ with this method combined with experimental work of our laboratory.This work investigated geometrical structures and electrical characteristics of C3nH2n molecules with GGA approximate calculation based on DFT(n is the number of carbon atoms of bottom carbon ring ). The results show that the molecules form basin-structures when n=3～8 and plane-structures when n=9～10 whose symmetry groups are both Cnv. While n=11～12 they form saddle-structures. We also investigated its binding energy, energy gap, HOMO(Highest occupied molecular orbital) and LUMO(Lowest unoccupied molecular orbital)etc, showing that these molecules are stable and plane structures are the most stable form. The results also show that deoxidization capacities become weaker and oxidation capacities become stronger with increase of n.The electronic structures of pure anatase TiO₂ and anatase TiO₂-xNx which can be obtained by different concentrations of N-doping have been investigated by using first-principles ultrasoft- pseudopotential method. The calculation indicates that the band gap of TiO₂ become narrow due to N-doping so-called red-shift. The monotone decrease of band gap of TiO₂-xNx with increasing N concentrations was observed. Our work shows that the top position of the valence band is determined by the O 2p electron state before doping and density of states changed a little with different N-doping. After N doping, top position of the valence band is determined by the N 2p electron state, and it moves to short wavelength with N doping concentration increasing. The bottom position of the conduction band is determined by Ti 3d state, and moves to long wavelength with N doping concentration increasing, leading to narrow energy gap.