def getReferencesHeader():
    """
    Returns the 'references' part in output file
    """
    str = ''
    str += """-------------------------------------------------------------------------------------------------------
"""
    str += ' References:\n'
    str += '\n'
    str += (
        '   Very Fast Empirical Prediction and Rationalization of Protein pKa Values\n'
        )
    str += '   Hui Li, Andrew D. Robertson and Jan H. Jensen\n'
    str += (
        '   PROTEINS: Structure, Function, and Bioinformatics 61:704-721 (2005)\n'
        )
    str += '   \n'
    str += """   Very Fast Prediction and Rationalization of pKa Values for Protein-Ligand Complexes
"""
    str += '   Delphine C. Bas, David M. Rogers and Jan H. Jensen\n'
    str += (
        '   PROTEINS: Structure, Function, and Bioinformatics 73:765-783 (2008)\n'
        )
    str += '   \n'
    str += """   PROPKA3: Consistent Treatment of Internal and Surface Residues in Empirical pKa predictions
"""
    str += (
        '   Mats H.M. Olsson, Chresten R. Sondergard, Michal Rostkowski, and Jan H. Jensen\n'
        )
    str += (
        '   Journal of Chemical Theory and Computation, 7(2):525-537 (2011)\n')
    str += '   \n'
    str += (
        '   Improved Treatment of Ligands and Coupling Effects in Empirical Calculation\n'
        )
    str += '    and Rationalization of pKa Values\n'
    str += (
        '   Chresten R. Sondergaard, Mats H.M. Olsson, Michal Rostkowski, and Jan H. Jensen\n'
        )
    str += '   Journal of Chemical Theory and Computation, (2011)\n'
    str += '   \n'
    str += """-------------------------------------------------------------------------------------------------------
"""
    return str
