强外电场作用下二甲基硅酮的分子结构和激发态

The Molecular Structure and Excited States for Dimethyl Siloxane under the Strong Electric Field

The ground states of dimethyl siloxane under different intense electric fields ranging from - 0. 04 to 0. 04 a. u. are optimized using density functional theory DFT / B3P86 at 6-311 ++ G（d，p）level. The excitation energies and oscillator strengths under the same intense applied electric fields are calculated employing the revised hybrid CIS-DFT method. The result shows that the electronic state，molecular geometry，total energy，dipole moment and excitation energy are strongly dependent on the field strength and behave asymmetry to the direction of the applied electric field. As the electric field changes from - 0. 04 to 0. 04 a. u. ，the bond length of Si-O increases whereas the bond length of Si-C decreases because of the charge transfer induced by the applied electric field. The dipole moment of the ground state decreases linearly with the applied field strength. However，the dipole moment of molecule changes from positive to negative as the inverse electric field increase to - 0. 03 a. u. Further increase of the inverse electric field results in an increase of the total energy of the molecule. The dependence of the calculated excitation energies on the applied electric field strength is fitting well to the relationship proposed by Grozema. The excitation energies of the first five excited states of dimethyl siloxane decrease as the applied electric filed increases because the energy gap between the HOMO and LUMO become close with the field，which shows that the molecule is easy to be excited under electric field and hence can be easily dissociated.