# The Chronus Quantum (ChronusQ) Software Package

## TL;DR

ChronusQ is an open-source, parallel C++ software package designed for advanced ab initio electronic structure calculations, emphasizing time dependence, spin, relativistic effects, and magnetic field inclusion.

## Contribution

It introduces a modern, parallel C++ framework with comprehensive features for electronic structure theory, including relativistic and magnetic field treatments, advancing computational chemistry tools.

## Key findings

- Supports time-dependent and spin-dependent electronic structure calculations
- Includes relativistic effects and magnetic field perturbations
- Utilizes MPI and OpenMP for efficient parallel performance

## Abstract

The Chronus Quantum (ChronusQ) software package is an open source (under the GNU General Public License v2) software infrastructure which targets the solution of challenging problems that arise in ab initio electronic structure theory. Special emphasis is placed on the consistent treatment of time dependence and spin in the electronic wave function, as well as the inclusion of relativistic effects in said treatments. In addition, ChronusQ provides support for the inclusion of uniform finite magnetic fields as external perturbations through the use of gauge-including atomic orbitals (GIAO). ChronusQ is a parallel electronic structure code written in modern C++ which utilizes both message passing (MPI) and shared memory (OpenMP) parallelism. In addition to the examination of the current state of code base itself, a discussion regarding ongoing developments and developer contributions will also be provided.