On the optimal basis set for electron dynamics in strong laser fields: The case of molecular ion H$^{+}_2$

TL;DR

This paper compares different basis sets for solving the time-dependent Schrödinger equation to accurately model electron dynamics in strong laser fields for the molecular ion H$^{+}_2$, focusing on high-harmonic generation and ionization.

Contribution

It evaluates the numerical performance of real-space grid, B-spline, and Gaussian bases, including optimized Gaussian functions, for modeling strong-field electron dynamics in H$^{+}_2$.

Findings

B-spline basis provides high accuracy for continuum states.

Optimized Gaussian basis effectively reproduces two-center interference.

Real-space grid is computationally intensive but accurate.

Abstract

A clear understanding of the mechanisms that control the electron dynamics in strong laser field is still a challenge that requires to be interpreted by advanced theory. Development of accurate theoretical and computational methods, able to provide a precise treatment of the fundamental processes generated in the strong field regime, is therefore crucial. A central aspect is the choice of the basis for the wave-function expansion. Accuracy in describing multiphoton processes is strictly related to the intrinsic properties of the basis, such as numerical convergence, computational cost, and representation of the continuum. By explicitly solving the 1D and 3D time-dependent Schr\"odinger equation for H$^{+}_{2}$ in presence of an intense electric field, we explore the numerical performance of using a real-space grid, a B-spline basis, and a Gaussian basis (improved by optimal Gaussian functions for the continuum). We analyze the performance of the three bases for high-harmonic generation and above-threshold ionization for H$^{+}_{2}$. In particular, for high-harmonic generation, the capability of the basis to reproduce the two-center interference and the hyper-Raman phenomena is investigated.