# User Manual for MOLSCAT, BOUND and FIELD, Version 2025.0: programs for quantum scattering properties and bound states of interacting pairs of atoms and molecules

## TL;DR

This paper introduces MOLSCAT, BOUND, and FIELD, software packages for quantum scattering and bound state calculations of atomic and molecular systems, supporting plug-in routines for complex interactions and external fields.

## Contribution

It provides a comprehensive, flexible suite of programs for quantum scattering and bound state calculations, including handling external fields and complex interactions with plug-in routines.

## Key findings

- Supports various collision types and external fields.
- Handles simple and complex interaction potentials.
- Locates Feshbach resonances in ultracold collisions.

## Abstract

MOLSCAT is a general-purpose package for performing non-reactive quantum scattering calculations for atomic and molecular collisions using coupled-channel methods. Simple atom-molecule and molecule-molecule collision types are coded internally and additional ones may be handled with plug-in routines. Plug-in routines may include external magnetic, electric or photon fields (and combinations of them). Simple interaction potentials are coded internally and more complicated ones may be handled with plug-in routines. BOUND is a general-purpose package for performing calculations of bound-state energies in weakly bound atomic and molecular systems using coupled-channel methods. It solves the same sets of coupled equations as MOLSCAT, and can use the same plug-in routines if desired, but with different boundary conditions. FIELD is a development of BOUND that locates external fields at which a bound state exists with a specified energy. One important use is to locate the positions of magnetically tunable Feshbach resonance positions in ultracold collisions. The program source code is available from https://github.com/molscat/molscat