Maryam Momeni Feili and  Mahvash Zandy Navgaran,  Calculation of Wave Function at the Origin (WFO) for the Ground State of Doubly Heavy Mesons Based On the Variational Method.   journal   = {International Journal of Physical and Mathematical Sciences}, [online]. World Academy of Science, Engineering and Technology.
    September 2011, vol. 57(9). 1465 - 1468
    [viewed 21 October 2019]. Available from: https://publications.waset.org/pdf/1173.