Nonlinear time-dependent density functional theory investigation and visualization of ionizations in CO2 - Effects of laser intensities and molecular orientations

Time-dependent density functional theory (TDDFT) studies of the ionization of CO2 by intense laser pulses I-o >= 1 x 1014 W/cm(2), at 800 nm are presented using the LB94 and the LDA potentials. Results reveal that for lower laser peak intensity, I-o = 3.5 x 10(14) W/cm(2), the highest occupied molecular orbital (HOMO) contributes significantly to ionization owing to its lower ionization potential (IP), whereas the inner orbitals play the important role for higher laser peak intensities. Even though such lower orbitals have higher IP, the ionization process occurs when orbital densities are maximum along the direction of the laser field polarization. These findings are confirmed through the analysis of the images from the time-dependent electron localization function (TDELF) and the spectra of higher order harmonic generation (HOHG). Additionally, in spite of the IP difference between Kohn-Sham orbitals from LDA and LB94 potentials, our results show almost the same trend for both.