"On-the-fly ab initio semiclassical evaluation of vibrationally resolved electronic spectra"

Vibrationally resolved electronic spectra pose a challenge to the theory of chemical dynamics because an accurate description of such spectra depends both on the quality of the electronic potential energy surfaces and on the inclusion of nuclear quantum effects. On-the-fly ab initio semiclassical dynamics addresses both issues simultaneously. I will present an on-the-fly ab initio implementation [1,2] of the thawed Gaussian approximation [3], a very simple semiclassical method, which, nevertheless, goes far beyond the standard approaches by including vibrational mode distortion, Duschinsky rotation, and anharmonicity. I will demonstrate the utility of the ab initio thawed Gaussian approximation on several examples of vibrationally resolved electronic absorption, emission, and photoelectron spectra of both floppy (ammonia [2]) and large molecules (oligothiophenes with up to 105 vibrational degrees of freedom [1]). To describe electronic spectra beyond the Condon approximation, we have also implemented an extension [4] by considering the Herzberg-Teller contribution due to the dependence of the electronic transition dipole moment on nuclear coordinates; the electronically forbidden transition in benzene provides a beautiful extreme example because the Condon approximation yields a “zero” spectrum (see figure). I will also mention how the ab initio thawed Gaussian approximation can describe time-resolved and two-dimensional spectroscopy [5, 6] and help understand the ultrafast decay of electronic coherence due to nuclear motion [7]. Finally, I will discuss two extensions: the single-Hessian approximation [8], which conserves energy and speeds up calculations, and the thermofield dynamics [9], which allows treating finite-temperature effects at zero additional cost.

 

[1] M. Wehrle, M. Šulc, and J. Vaníček, J. Chem. Phys. 140, 244114 (2014).

[2] M. Wehrle, S. Oberli, and J. Vaníček, J. Phys. Chem. A 119, 5685 (2015).

[3] E. J. Heller, J. Chem. Phys. 62, 1544 (1975). 

[4] A. Patoz, T. Begušić, and J. Vaníček, J. Phys. Chem. Lett. 9, 2367 (2018).

[5] T. Begušić, J. Roulet, and J. Vaníček, J. Chem. Phys. 149, 244115 (2018).

[6] T. Begušić and J. Vaníček, J. Chem. Phys. 153, 184110 (2020). 

[7] N. V. Golubev, T. Begušić, and J. Vaníček, Phys. Rev. Lett. 125, 083001 (2020).

[8] T. Begušić, M. Cordova, J. Vaníček, J. Chem. Phys. 150, 154117 (2019).

[9] T. Begušić and J. Vaníček, J. Chem. Phys. 153, 024105 (2020), editor’s pick and featured article.

Transmisión en vivo de la videoconferencia vía YouTube: bit.ly/YouTube_ICF 

Participante: Dr. Jiri Vanicek

Institución: École Polytechnique Fédérale de Lausanne, Switzerland

Fecha y hora: Este evento terminó el Miércoles, 02 de Diciembre de 2020