Computational Chemistry, Short talk
CC-016

On-the-fly ab initio semiclassical evaluation of vibronic spectra at finite temperature

T. Begušić1, J. Vaníček1*
1Laboratory of Theoretical Physical Chemistry, Institute of Chemical Sciences and Engineering, EPFL

To compute and analyze vibrationally resolved electronic spectra at zero temperature, we have recently implemented the on-the-fly ab initio extended thawed Gaussian approximation [1], which accounts for anharmonicity, mode-mode coupling, and Herzberg-Teller effects. Here, we generalize this method in order to evaluate spectra at non-zero temperature [2]. In line with thermo-field dynamics [3, 4], we transform the von Neumann evolution of the density matrix to the Schrödinger evolution of a wavefunction in an augmented space with twice as many degrees of freedom. Due to efficiency of the extended thawed Gaussian approximation, this increase in the number of coordinates results in nearly no additional computational cost. More specifically, compared to the original, zero-temperature approach, the finite-temperature method requires no additional ab initio electronic structure calculations. At the same time, the new approach allows for a clear distinction among finite-temperature, anharmonicity, and Herzberg-Teller effects on spectra. We show, on a model Morse system, the advantages of the finite-temperature thawed Gaussian approximation over the commonly used global harmonic methods and apply it to evaluate the symmetry-forbidden absorption spectrum of benzene (see graphic), where all of the aforementioned effects contribute.

 

 

[1] Aurélien Patoz, Tomislav Begušić, Jiří Vaníček, Journal of Physical Chemistry Letters, 2018, 9, 2367-2372.
[2] Tomislav Begušić, Jiří Vaníček, Submitted (available at arXiv:2005.09126 [physics.chem-ph]).
[3] Masuo Suzuki, Journal of the Physical Society of Japan, 1985, 54, 4483.
[4] Raffaele Borrelli, Maxim F. Gelin, Scientific Reports, 2017, 7, 1-9.