PyStructureFactor: A Python code for the molecular structure factor in tunneling ionization rates

Abstract

Tunneling ionization is at the core of strong-field and attosecond science. In this paper, we present PyStructureFactor — a general Python code towards the calculation of the structure factor in the tunneling ionization rate of common molecules under intense laser fields. The numerical implementation is based on the well-developed weak-field asymptotic theory in the integral representation. The information of the electronic structure of the molecules is obtained via the PySCF quantum chemistry package. PyStructureFactor is a general computational framework that can be utilized to compute the molecular structure factor of various types of molecules, including polar and nonpolar diatomic molecules, degenerate molecules, and open-shell molecules. Examples are given that are benchmarked against known results with good agreements. The present PyStructureFactor is implemented in an efficient manner and is easily applicable towards larger molecules. Program summaryProgram title: PyStructureFactorCPC Library link to program files:https://doi.org/10.17632/td88mhw2sg.1Developer's repository link:https://github.com/TheStarAlight/PyStructureFactorLicensing provisions: Apache-2.0Programming language: Python 3Nature of problem: The structure factor of a molecule in intense laser fields determines its orientation-dependent tunneling ionization rate, which is crucial for the studies of ultrafast molecular dynamics and its control. However, the strong-field community lacks an open-source code to calculate the molecular structure factor, and can only resort to known results of a few molecules.Solution method: We developed the PyStructureFactor program with the structure factor of arbitrary molecules calculated using the weak-field asymptotic theory in the integral representation. The underlying electronic structure necessary for the calculation is obtained using the PySCF quantum chemistry package.Additional comments including restrictions and unusual features: The accuracy of the molecular structure factor calculated by PyStructureFactor is restricted by the level of precision of the electronic structure information extracted from the PySCF package.The running time depends on the size of the molecule, the basis set of the calculation, the level of precision of the electronic structure calculations, and other parameters passed to the program. The example in Fig. 2 took 1.2 seconds to finish on an AMD Ryzen 9 7950X CPU on the WSL Ubuntu 22.04 LTS.