Abstract: The electronic structure evolution of adipate ester insulating oil molecules were systematically investigated under external electric fields using quantum chemical computational methods. Based on B3LYP density functional theory, we calculated and analyzed changes in key parameters including molecular ground-state geometries, frontier orbitals, electron density, surface electrostatic potential, dipole moments and molecular polarity indexunder varying electric field intensities. The findings reveal that the vertical ionization potential of adipate ester molecules exhibits length-dependent variations of carbon chains under zero-field conditions. Enhanced external electric fields induce directional polarization in adipate ester molecules, leading to a reduction in the energy gap, intensified charge transfer effects, and nonlinear increases in dipole moment and molecular polarity index.At critical field strengths, polarization triggers charge separation in adipate ester molecules,the molecular chain breaks and result in breakdowm.

Key words: ester oil, electronic structure, density functional theory, electric field response, computational simulation