# Ab initio quantum dynamics as a scalable solution to the exoplanet opacity challenge: A case study of CO$_2$ in hydrogen atmosphere

**Authors:** Laurent Wiesenfeld, Prajwal Niraula, Julien de Wit, Nejmeddine Jaïdane, Iouli E. Gordon, Robert J. Hargreaves  
**arXiv:** [2409.04439](https://arxiv.org/abs/2409.04439)  
**Date:** 2024-09-06  
**Summary page:** https://www.summarizepaper.com/en/paper/2409.04439v1/

## Key points

- New-generation framework for ab initio calculations of pressure broadening coefficients
- Importance of pressure broadening in interpreting remote sensing data and understanding light-matter interactions in exoplanetary atmospheres
- Ab initio calculations considered the most accurate method for calculating pressure broadening coefficients
- Introduction of a cost-effective and scalable solution meeting precision requirements within relevant timescales, suitable for missions like JWST
- Method involves computing potential energy surfaces using MOLPRO code and solving the electronic Schrödinger equation with fixed nuclei using quantum chemistry methods
- Results show that even moderate precision potentials can exceed current precision requirements
- Approach provides a computationally affordable way to compute full-dimensional interaction potentials and scattering quantum dynamics, reducing model-limited biases from pressure broadening
- Significance of ab initio calculations in addressing opacity challenges in exoplanetary research and supporting instrument-limited science with JWST and future missions

## Summary

This Letter presents a new-generation framework for ab initio calculations of pressure broadening coefficients to address the opacity challenge in exoplanetary atmospheres for the upcoming James Webb Space Telescope (JWST) mission. Pressure broadening, measured as half-widths at half maximum (HWHM), is crucial for interpreting remote sensing data and understanding light-matter interactions in exoplanetary atmospheres. While various methods exist for calculating these coefficients, ab initio calculations are considered the most accurate. This study introduces a cost-effective and scalable solution that meets precision requirements within relevant timescales, making it suitable for ongoing missions like JWST. The method involves computing potential energy surfaces using MOLPRO code and solving the electronic Schrödinger equation with fixed nuclei using quantum chemistry methods to obtain reliable results for different relative orientations and intermolecular distances of CO2 and H2 molecules. Results show that even moderate precision potentials can meet precision requirements beyond what is currently available. This approach provides a computationally affordable way to compute full-dimensional interaction potentials and scattering quantum dynamics, reducing model-limited biases from pressure broadening. Overall, this study highlights the significance of ab initio calculations in addressing opacity challenges in exoplanetary research and emphasizes their role in supporting instrument-limited science with JWST and future missions.