استقصاء الخصائص التركيبية والبصرية اللاخطية للبوليمايد باستخدام نظرية دالة الكثافة الوظيفية

Polyimide Structural and Non - Linear Optical Properties Investigation Utilizing the Density Functional Theory

Abstract
In this study, density functional theory (DFT) calculations were performed to investigate the structural, nonlinear optical (NLO), and spectroscopy properties for the pristine Polyimide (PI) monomer. The potential energy surface (PES) scan was performed using the semi-empirical method PM6 to predict the best conformer. The B3LYP functional, which employs Beck’s three-parameters hybrid exchange functional and the Lee-Yang-Parr correlation functional, and 6-311G(d,p) were used effectively to optimize the monomer and assess the properties. The calculated average value of bond lengths was found to be 1.392 in Angstrom units, while the average value of the bond angles was 119.8 in Degree units. The bond lengths and bond angles from DFT were in good agreement with the experimental data.
The charge distribution by natural bond orbitals (NBO) methode, and NLO properties as dipole moment, polarizability, first-order hyperpolarizability, and susceptibility were also studied. The observation of an uneven distribution of charges led to a non-zero dipole moment of 1.52 Debye.
Finally, the infrared spectrum was obtained and examined after being adjusted by a scaling factor of 0.9679. The UV absorption spectrum was investigated using the TD-B3LYP method with the same basis set. The maximum wavelength at the oscillator strength (f = 0.0007) was found to be 513 nm, which is in good agreement with the experimental value of 500 nm.