scholarly journals Non Perturbative Time-Dependent Density Functional Theory, TDDFT: Study of Ionization and Harmonic Generation in Linear Di-(N₂) and Tri-(CO₂, OCS, CS₂) Atomic Molecules with Ultrashort Intense Laser Pulses-Orientational Effects

10.5772/13227 ◽  
2010 ◽  
Author(s):  
Andre D ◽  
Emmanuel Penka
Keyword(s):  
Density Functional Theory ◽  
Harmonic Generation ◽  
Density Functional ◽  
Laser Pulses ◽  
Time Dependent ◽  
Intense Laser ◽  
Functional Theory ◽  
Intense Laser Pulses ◽  
Dependent Density

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

2010 ◽  
Vol 88 (11) ◽  
pp. 1186-1194
Author(s):  
Emmanuel Penka Fowe ◽  
André Dieter Bandrauk
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Laser Pulses ◽  
Time Dependent ◽  
Intense Laser ◽  
Functional Theory ◽  
Intense Laser Pulses ◽  
Highest Occupied Molecular Orbital ◽  
Analysis Of The Images ◽  
Dependent Density

Time-dependent density functional theory (TDDFT) studies of the ionization of CO2 by intense laser pulses Io ≥ 1 × 1014 W/cm2, at 800 nm are presented using the LB94 and the LDA potentials. Results reveal that for lower laser peak intensity, Io = 3.5 × 1014 W/cm2, 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.

Nonlinear time-dependent density functional theory studies of the ionization of CO2 by ultrashort intense laser pulses

2009 ◽  
Vol 87 (7) ◽  
pp. 1081-1089
Author(s):  
Emmanuel Penka Fowe ◽  
André Dieter Bandrauk
Keyword(s):  
Density Functional Theory ◽  
Molecular Orbital ◽  
Density Functional ◽  
Laser Pulses ◽  
Time Dependent ◽  
Intense Laser ◽  
Functional Theory ◽  
Intense Laser Pulses ◽  
Highest Occupied Molecular Orbital ◽  
Dependent Density

Time-dependent density functional theory (TDDFT) studies of the ionization of CO2 by intense laser pulses (3.50 × 1014, 1.40 × 1015, 2.99 × 1015, and 1.25 × 1016 W/cm2) at 800 nm (ω = 0.0584 au) are presented in the nonlinear nonpertubative regime. Special emphasis is placed on elucidating molecular orbital orientation and various peak-intensities effects on the ionization processes. The results reveal that molecular orbital ionizations are strongly sensitive to their symmetry and the laser intensities. Most notably, we found that with a proper choice of the laser intensity (3.5 × 1014 W/cm2), the sensitivity is strong enough such that the nature and symmetry of the highest occupied molecular orbital (HOMO) can be directly probed and visualized from the angular dependence of laser-induced ionization. At higher intensities, ionization is found to occur also from inner orbitals, thus complicating the imaging of simple orbitals. A time-dependent electron-localization function (TDELF) is used to get a visual insight on the time evolution process of the electron density.

Nonperturbative time-dependent density functional theory (TDDFT) and time-dependent electron localization function (TDELF) study of the ionization of OCS and CS2 with ultrashort intense laser pulses — Orientational effects

2012 ◽  
Vol 90 (7) ◽  
pp. 616-624 ◽  
Author(s):  
Emmanuel Fowe Penka ◽  
André Dieter Bandrauk
Keyword(s):  
Density Functional Theory ◽  
Laser Pulse ◽  
Density Functional ◽  
Laser Pulses ◽  
Time Dependent ◽  
Intense Laser ◽  
Electron Localization ◽  
Functional Theory ◽  
Intense Laser Pulses ◽  
Dependent Density

The nonlinear nonperturbative response of OCS and CS2 to ultrashort (few cycles) intense laser pulses was studied numerically by time-dependent density functional theory (TDDFT) methods to understand molecular ionization as a function of laser–molecule orientation. A time-dependent electron localization function(TDELF) was used to visualize the nonlinear nonperturbative electron transfer occurring during the laser pulse. It was found that, for intensities I > 3.5 × 1014 W/cm2, the inner shell Kohn–Sham (KS) molecular orbitals contribute significantly to the ionization, whereas for the intensity I < 3.5 × 1014 W/cm2, the highest occupied molecular orbital (HOMO) shows the dominant response to the field. In general, the ionization rate maxima correspond to the alignment of maximum KS orbital densities with the laser pulse polarization instead of orbital ionization potentials (IP). These findings are corroborated through analysis of the TDELF images, where the ionization occurs from the lone pair or bond regions of the corresponding molecules.

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