---
abstract: 'We present quantum dynamics of collisions between two para-H$_2$ molecules from low (10$^{-3}$ K) to high collision energies (1 eV). The calculations are carried out using a quantum scattering code that solves the time-independent Schrödinger equation in its full dimensionality without any decoupling approximations. The six-dimensional potential energy surface for the H$_4$ system developed by Boothroyd et al. \[J. Chem. Phys. [**116**]{}, 666 (2002)\] is used in the calculations. Elastic, inelastic and state-to-state cross sections as well as rate coefficients from $T = 1$ K to 400 K obtained from our calculations are compared with available experimental and theoretical results. Overall, good agreement is obtained with previous studies.'
author:
- 'Goulven Qu[é]{}m[é]{}ner, Naduvalath Balakrishnan'
title: 'Quantum calculations of H$_2$–H$_2$ collisions: from ultracold to thermal energies'
---

=cmr7

Introduction
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Collisions between molecules are fundamental processes which take place in many areas of physics and chemistry. Molecular collisions are prevalent in the interstellar medium, in the atmospheres of planets, in combustion chemistry and and in many other chemical and industrial processes. Being the simplest neutral molecule - molecule system, the H$_2-$H$_2$ system has served as a prototype for accurate calculations of tetratomic potential energy surfaces (PESs) as well as 