Ultrafast nonadiabatic electron dynamics in photoexcited C60: A comparative study among DFT exchange-correlation functionals

The non-radiative electron-relaxation dynamics in C$_{60}$ molecule is studied after selective initial photoexcitations. The methodology includes nonadibabtic molecular simulation combined with time-dependent density functional theory (DFT) and semi-classical surface hopping approach. Results of treating the DFT exchange-correlation (xc) interaction by the non-empirical Perdew-Burke-Ernzerhof (PBE), hybrid PBE0, and hybrid Becke 3-parameter Lee-Yang-Parr (B3LYP) functional are compared. Even though some differences in the details are found, all three functionals produce qualitatively similar unoccupied band structures in the ground state. The model-dependent differences in the ultrafast population dynamics, including the occurrences of transient entrapment of population, are studied systematically. The trend of the results demonstrates a universal dependence on the structure of unoccupied band offering a spectroscopic route to probe this structure. Results can be verified, as well as the best xc model for quantitative accuracy can be determined, by comparing with ultrafast transient absorption or time-resolved photoelectron spectroscopy measurements. From the computational standpoint, the study facilitates method optimization to simulate nonadiabatic relaxation dynamics in technologically important fullerene derivatives.Comment: 9 pages, 5 figures, Submitted to the journal and currently in the peer-review proces

A tool for determination of the three-dimensional orientation of electronic transition dipole moments and identification of configurational isomers

A method is presented that combines femtosecondpolarization resolved UV/visible pump–IR probe spectroscopy and density functional theory calculations in determining the three-dimensional orientation of an electronic transition dipole moment (tdm) within the molecular structure. The method is demonstrated on the approximately planar molecule coumarin 314 (C314) dissolved in acetonitrile, which can exist in two ground state configurations: the E- and the Z-isomer. Based on an exhaustive search analysis on polarization resolved measurement data for four different vibrational modes, it is concluded that C314 in acetonitrile is the E-isomer. The electronic tdm vector for the electronic S0→S1 transition is determined and the analysis shows that performing the procedure for four vibrational modes instead of the minimally required three reduces the 1σ probability area from 2.34% to 2.24% of the solution space. Moreover, the fastest rotational correlation timeτc for the C314 E-isomer is determined to be 26±2 ps

Time Delay in the Recoiling Valence Photoemission of Ar Endohedrally Confined in C60\mathrm{C_{60}}

Effects of confinement and electron correlations on the relative time delay between the 3s and 3p photoemissions of Ar confined endohedrally in C₆₀ are investigated using the time dependent local density approximation - a method that is also found to mostly agree with recent time delay measurements between the 3s and 3p subshells in atomic Ar. At energies in the neighborhood of 3p Cooper minimum, correlations with C₆₀ electrons are found to induce opposite temporal effects in the emission of Ar 3p hybridized symmetrically versus that of Ar 3p hybridized antisymmetrically with C₆₀. A recoil-type interaction model mediated by the confinement is found to best describe the phenomenon

Ultrafast Dynamics of Photoionized Acetylene

Acetylene cations [HCCH]$^+$ produced in the A$^{2}Σ^{+}_g$ state by extreme ultraviolet (XUV) photoionization are investigated theoretically, based on a mixed quantum-classical approach. We show that the decay of the A$^{2}Σ^{+}_g$ state occurs via both ultrafast isomerization and nonradiative electronic relaxation. We find a time scale for hydrogen migration and electronic decay of about 60 fs, in good agreement with recent XUV-pump/XUV-probe time-resolved experiments on the same system [Phys. Rev. Lett. 105, 263002 (2010)]. Moreover, we predict an efficient vibrational energy redistribution mechanism that quickly transfers excess energy from the isomerization coordinates to slower modes in a few hundred femtoseconds, leading to a partial regeneration of acetylenelike conformations