Density Functional Theory Study Of The Organic Molecules-PTCDA/ME-PTCDI And Molecular-dynamics Simulation With The EAM

Novel materials are the base of New Scientific & Technical Revolution in matters. With the rapid developments of organic optoelectronic devices, such as organic solar cells, organic light-emitting diodes (OLEDs) and organic field-effect transistors (OFETs), et al. organic materials with high mobility, good stability and facile processability are in impending need. The organic semiconductor materials made of the PTCDA or ME-PTCDI have many advantages, such as a simple fabrication process, low cost, flexibility, and the realization of large-area planer processes .so they can be widely applied in the process of prepareing the OFETs,OLEDs and so on .In this dissertation, it is include three parts. the electronic spectra and energy level structure of the PTCDA molecule were investigated by quantum mechanics calculation in the first part. The results suggest theoretical basis and direction for design of novel organic materials. The geometry structure of PTCDA molecule was optimized by means of DFT with B3LYP methods at 6-31G* basis set level. From optimized geometry, PTCDA is a planner molecule; it consists of 38 atoms (C₂₄H₈O₆), the point symmetry group of the molecule being D_2h. from the energy level structure, PTCDA has good stabilization. Vibrational modes of the PTCDA molecule were researched by means of the Group Theory. The results can be good compared with DFT.there are 108 internal molecular vibrational modes, among them, 46 are IR active, 54 are Raman active, 8 are silent.the optical properties of the PTCDA molecule have been investigated by using time-dependent density functional theory with B3LYP methods at 6-31+G(d,p) basis set level. The calculated results indicate the optical spectra of the PTCDA molecule mainly localize at the visible region.the most wavelength is 516.5nm. the electronic transition mostly take place between HOMO and LUMO.The electronic spectra and energy level structure of the ME-PTCDI molecule were investigated by quantum mechanics calculation in the second part. The point symmetry group of the molecule being Cs. The optical properties of the ME-PTCDI molecule have been systematically investigated by using time-dependent density functional theory with B3LYP methods at 6-31+G(d,p) basis set level. The calculated results indicated the energy of the HOMO.-LUMO gap of the excited states is smaller than that in the ground states.The most wavelength is 526.lnm.the electronic transition mostly take place between HOMO and LUMO.Structural and electronic properties of the Si clusters have been investigated computationally by means of the Molecular-dynamics Simulation Study with the Embedded-atom method. The procedure was compiled by the FORTRAN languages. The procedure has been completed, and can be run normally. For the results can't be good compared with the other results, so we are debugging the procedure now.