def collisions(distance_list, distance_cutoff):
    """
        Determine if there are any collisions between non-bonded
        particles, where a "collision" is defined as a distance shorter than 'distance_cutoff'.

        :param distance_list: A list of distances.
        :type distance_list: List( `Quantity() <https://docs.openmm.org/development/api-python/generated/simtk.unit.quantity.Quantity.html>`_ )

        :param distance_cutoff: The distance below which particles will be considered to have "collisions".
        :type distance_cutoff: `Quantity() <https://docs.openmm.org/development/api-python/generated/simtk.unit.quantity.Quantity.html>`_

        :returns:
          - collision (Logical) - A variable indicating whether or not the model contains particle collisions.

        """

    collision = False

    if len(distance_list) > 0:
        for distance in distance_list:
            if distance < distance_cutoff:
                collision = True

    return collision