Detecting the minimum in argon high-harmonic generation spectrum using Gaussian basis sets

Overview & Synopsis

Coupling the real-time description of the ultrafast electron dynamics in strong laser fields with quantum chemistry techniques still represents an open challenge for theoreticians. In this work, high-harmonic generation (HHG) spectrum of the argon atom has been computed by means of the time-dependent configuration with singly excited configurations approach (TDCIS), using Gaussian basis sets. We show that adding a number of continuum-optimal Gaussian functions to basis sets routinely used in quantum chemistry calculations, provides the expected position of the intensity minimum in the HHG spectrum, for a given selection of laser intensities and ionisation parameters. Advantages and weaknesses of the proposed computational strategy are discussed. We give evidence here that Gaussian-based TDICS simulations are accurate enough to correctly reproduce the features of ultrafast and highly nonlinear optical processes, as HHG. Keywords Nonlinear optics • strong fields • ionisation Electron dynamics in atoms and molecules interacting with an intense and ultrashort laser pulse has becoming an attractive and largely diffused research field since the advent of the attosecond laser pulses [1]. As an example, high-harmonic generation (HHG) [2, 3] spectra are successfully used to explain the attosecond dynamics of electronic wave packets [4]. From a theoretical perspective, achieving a robust understanding of the mechanisms controlling the electron dynamics affected by a strong laser field is still a challenge and several approaches have been proposed [4]. One of them is given by the real-time propagation of the electronic wave function expanded in the basis of field-free eigenstates from configuration interaction with singly excited configurations (TDCIS) [5-10], coupled to Gaussian basis sets. Computation of HHG spectrum of atomic and molecular species using standard quantum-chemistry