Cost-Efficient High-Resolution Linear Absorption Spectra Through Extrapolating the Dipole Moment from Real-Time Time-Dependent Electronic-Structure Theory

TL;DR

This paper introduces a function fitting approach to extrapolate high-resolution absorption spectra from short real-time electronic structure calculations, significantly reducing computational costs while maintaining spectral accuracy.

Contribution

The authors develop a novel fitting method that extrapolates spectra from shorter dipole trajectories, enabling high-resolution spectra with less computational effort.

Findings

High-resolution spectra can be reproduced from short dipole trajectories.

The method converges with as little as 100 a.u. of dipole data for some systems.

An error estimate reliably assesses the fit quality and convergence.

Abstract

We present a novel function fitting method for approximating the propagation of the time-dependent electric dipole moment from real-time electronic structure calculations. Real-time calculations of the electronic absorption spectrum require discrete Fourier transforms of the electric dipole moment. The spectral resolution is determined by the total propagation time, i.e. the trajectory length of the dipole moment, causing a high computational cost. Our developed method uses function fitting on shorter trajectories of the dipole moment, achieving arbitrary spectral resolution through extrapolation. Numerical testing shows that the fitting method can reproduce high-resolution spectra using short dipole trajectories. The method converges with as little as 100 a.u. dipole trajectories for some systems, though the difficulty converging increases with the spectral density. We also introduce an error estimate of the fit, reliably assessing its convergence and hence the quality of the approximated spectrum.