returns the maximum pairwise electronegativity difference

def max_electronegativity(self):
        '''
        returns the maximum pairwise electronegativity difference
        '''
        maximum = 0
        for e1, e2 in combinations(self.elements, 2):
            if abs(Element(e1).X - Element(e2).X) > maximum:
                maximum = abs(Element(e1).X - Element(e2).X)
        return maximum