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

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 TDCIS simulations are accurate enough to correctly reproduce the features of ultrafast and highly nonlinear optical processes, as HHG.