@article{vanHoof:2111,
      author        = "van Hoof, P. A. M. and  Ferland, G. J. and  Williams, R.
                       J. R. and  Volk, K. and  Chatzikos, M. and  Lykins, M. and 
                       Porter, R. L.",
      title         = "{Accurate determination of the free-free Gaunt factor -
                       II. Relativistic Gaunt factors}",
      year          = "2015",
}