Optical limiting (OL) and dynamical two-photon absorption (TPA) of 4,4'-bis(di-n-butylamino)stilbene (BDBAS) molecules in chirped femtosecond laser pulses are studied by solving Maxwell-Bloch equations with an iterative predictor-corrector finitedifference time-domain (FDTD) method.It shows that both sign and magnitude of chirp rate influence greatly spectrum evolution and OL behavior.Spectra exhibit obvious carrier frequency shifts depending on sign of chirp rate,blue shift for positive chirp rate and red shift for negative chirp rate.As absolute chirp rate increases,shift becomes more obvious,OL window gets narrower and saturation of output intensity becomes greater.Interestingly,self-induced transparency (SIT) appears as a negative chirp rate reduces to a certain value (-0.025 fs^-2).Dynamical TPA cross section is reduced as chirp effect is considered.It provides a method for controlling nonlinear optical absorptions.

With density functional theory(DFT) and elastic scattering Green's function method,electronic transport of alkanemonothiol molecular membranes were simulated theoretically.It shows that conductive ability of molecular membranes increased 2 to 3 orders of magnitude than that of a single molecule due to interaction between molecules.Conductive ability of a molecular junction increases with increasing external force.Increase of current is mainly due to increased probability of tunneling within and between chains in a molecular junction.The increased probability is caused by coupling enhancement between molecule and electrode and between molecules.

With ab initio theory and elastic scatering Green's function method,current and conductance of heterocyclic molecular isomers are investigated.It shows that expending orbits and coupling coefficients have dominant influence on electronic transport of molecular systems.Positions of nitrogen atoms and terminal atoms in molecules affect expending of molecular orbits and coupling degree,which results in difference in electronic transport.

With first principle and hybrid density functional theory,electronic structrue of an organic molecule bis-(4-mercaptophenyl)-ether is calculated.Electronic transport is studied by elastic scattering Green function method.It shows that electronic field has obvious influence on electronic structrue of molecular system.The current and conductance exhibit nonlinear changes.They are close to experimental results.