Hybrid CIS-DFT method to study electric field effects on electronic excited states of ethylene

Abstract

The present work is devoted to the study of the effects of external dipole electric field on the molecular structure of ethylene using a hybrid method which combines the single-excitation configuration interactions (CIS) with density functional theory (DFT), i.e. CIS-DFT(B3LYP). It is found that the effects of electric dipole field on the molecular geometry (D2h, D2d and C2v), dipole moment, transition dipole moment, polarizability and, particularly, excitation energy of ethylene are remarkable. The advantages of the hybrid CIS-DFT method are that it can determine the symmetry of molecule and the correct order of excitation as well as the Molecular Orbital (MO) electron configuration; thereby the electronic excitation states of ethylene are easily derived and most of them are in agreement with those obtained in experiments or references. It may be the first time the effects of external electric field on ethylene molecule have been considered. Compared with other ab initio methods, the CIS-DFT method is relatively accurate and low cost in computation. We expect that it can be used to study other closed-shell molecules.