Semiclassical on-the-fly computation of the S→S1 absorption spectrum of formaldehyde

Abstract

The anharmonic S0→S1 vibronic absorption spectrum of the formaldehyde molecule is computed on the fly using semiclassical dynamics. This first example of an on-the-fly semiclassical computation of a vibronic spectrum was achieved using a unit prefactor modified frozen Gaussian semiclassical propagator for the excited state. A sample of 6000 trajectories sufficed for obtaining a converged spectrum, which is in reasonable agreement with experiment. Similar agreement is not obtained when using a harmonic approximation for the spectrum, demonstrating the need for a full anharmonic computation. This first example provides a resolution of ∼100 cm−1. Potential ways of improving the methodology and obtaining higher resolution and accuracy are discussed.

First principles semiclassical calculations of vibrational eigenfunctions

“…(17). In the second column, the trajectory used for the eigenfunction calculations for all states is the same, i.e., the ground state harmonic trajectory.…”

“…quantum effects in the nuclear dynamics. [8][9][10][11][12][13][14][15][16][17] Although there has been great development in this field, to our knowledge, calculations of molecular eigenfunctions using on-the-fly approaches have not been explored.…”

“…This is another example of first-principles SC-IVR, as well as it is the work of Pollak and Tatchen on the absorption spectrum of the same molecule. 17 In Sec. II, we will review the expression for computing the eigenfunctions using wavepackets and semiclassical approximations.…”

A correlated-polaron electronic propagator: Open electronic dynamics beyond the Born-Oppenheimer approximation

“…[24][25][26][27][28][29][30] In the latter approach, the electronic degrees of freedom are described as a superposition of a few adiabatic surfaces, and nuclear wave-packets are studied in the dynamics. In our approach, the electronic degrees of freedom are described in all-electron detail, but the dynamics of the nuclei are approximated by the choice of the Holstein Hamiltonian.…”

Relation of exact Gaussian basis methods to the dephasing representation: Theory and application to time-resolved electronic spectra

“…Both approaches benefit from the ultrafast character of the dynamics not only thanks to a lower computational cost, but also because their accuracy deteriorates at longer times. Among these methods, semiclassical initial value representation 7 and methods employing Gaussian bases 6,8 were employed successfully for "direct" dynamics in which the electronic structure is evaluated on the fly.…”