Molecular structure and spectrum of P-xylene under external electric field

We optimize the P-xylene molecule under different external electric fields (-0.025 ∼ 0.025 a. u) on the 6-311 G + + (d, p) basis using the method of B3LYP of density functional theory (DFT). In this way, we can get the bond lengths, energies, electric dipole moments and frontier orbital energies, which are configuration parameters of P-xylene. Besides of these, we also analyze how the parameters change with the change of external electric field. On the basis of optimized ground state, we calculate the UV-visible absorption spectra under different external electric fields on the 6-311 G + + (d, p) basis using the method of TDDFT/B3LYP. Based on the above results, we discuss the change rule of excited energies, wavelengths, oscillator strengths of the first 9 excited states with the change of external electric field (0 ∼ 0.020 a.u). The computing results offer useful theoretical bases for the degradation of P-xylene under external electric field. (authors)