returns shrage transfer as string

def charge_transfer_to_string(self):
        """returns shrage transfer as string"""
        ch = self.charge_transfer
        chts = ['\nCharge Transfer\n\nabsorbing atom']
        for i in range(len(ch)):
            for atom, v2 in ch[str(i)].items():
                a = ['\n', atom, '\n', 's   ', str(v2['s']), '\n',
                     'p   ', str(v2['p']), '\n',
                     'd   ', str(v2['d']), '\n',
                     'f   ', str(v2['f']), '\n',
                     'tot ', str(v2['tot']), '\n']
                chts.extend(a)
        return ''.join(chts)