On-the-fly ab initio semiclassical evaluation of electronic coherences in polyatomic molecules reveals a simple mechanism of decoherence

TL;DR

This paper introduces a simple semiclassical method that accurately predicts electronic coherence decay in polyatomic molecules, revealing the physical mechanism behind decoherence and avoiding computational complexity of full quantum calculations.

Contribution

A single-trajectory semiclassical scheme is demonstrated to evaluate electronic coherence times accurately, providing physical insights and computational efficiency for polyatomic molecules.

Findings

Semiclassical method agrees well with quantum calculations.

Decoherence is explained by phase space distance and trajectory area.

Method avoids the curse of dimensionality, enabling efficient predictions.

Abstract

Irradiation of a molecular system by an intense laser field can trigger dynamics of both electronic and nuclear subsystems. The lighter electrons usually move on much faster, attosecond time scale but the slow nuclear rearrangement damps ultrafast electronic oscillations, leading to the decoherence of the electronic dynamics within a few femtoseconds. We show that a simple, single-trajectory semiclassical scheme can evaluate the electronic coherence time in polyatomic molecules accurately by demonstrating an excellent agreement with full-dimensional quantum calculations. In contrast to numerical quantum methods, the semiclassical one reveals the physical mechanism of decoherence beyond the general blame on nuclear motion. In the propiolic acid, the rate of decoherence and the large deviation from the static frequency of electronic oscillations are quantitatively described with just two semiclassical parameters---the phase space distance and signed area between the trajectories moving on two electronic surfaces. Because it evaluates the electronic structure on the fly, the semiclassical technique avoids the "curse of dimensionality" and should be useful for preselecting molecules for experimental studies.