# An Open-Source Framework for $N$-Electron Dynamics: II. Hybrid Density Functional Theory/Configuration Interaction Methodology

## TL;DR

This paper introduces an open-source framework combining TDDFT and CIS methods to analyze and visualize correlated many-electron dynamics efficiently, enabling detailed insights into electron behavior in complex molecules.

## Contribution

It extends existing tools by integrating hybrid TDDFT/CIS methodology into an open-source Python package for scalable, detailed electron dynamics analysis.

## Key findings

- Good quantitative agreement with higher-level wave function methods.
- Demonstrated scalability on medium-sized organic molecules.
- Revealed mechanistic details of charge migration via flux densities.

## Abstract

In this contribution, we extend our framework for analyzing and visualizing correlated many-electron dynamics to non-variational, highly scalable electronic structure method. Specifically, an explicitly time-dependent electronic wave packet is written as a linear combination of $N$-electron wave functions at the configuration interaction singles (CIS) level, which are obtained from a reference time-dependent density functional theory (TDDFT) calculation. The procedure is implemented in the open-source Python program detCI@ORBKIT, which extends the capabilities of our recently published post-processing toolbox [J. Comput. Chem. 37 (2016) 1511]. From the output of standard quantum chemistry packages using atom-centered Gaussian-type basis functions, the framework exploits the multi-determinental structure of the hybrid TDDFT/CIS wave packet to compute fundamental one-electron quantities such as difference electronic densities, transient electronic flux densities, and transition dipole moments. The hybrid scheme is benchmarked against wave function data for the laser-driven state selective excitation in LiH. It is shown that all features of the electron dynamics are in good quantitative agreement with the higher-level method provided a judicious choice of functional is made. Broadband excitation of a medium-sized organic chromophore further demonstrates the scalability of the method. In addition, the time-dependent flux densities unravel the mechanistic details of the simulated charge migration process at a glance.