@classmethod
def hexagonal(cls, a, c):
    """
        Initializes a Box in standard hexagonal setting using only hexagonal lattice
        parameters.  

        a = b != c, alpha = beta = 90, gamma = 120

        Parameters
        ----------
        - a : float
            The a lattice constant
        - c : float
            The c lattice constant

        Returns
        -------
        atomman.Box
        """
    if a == c:
        raise ValueError('hexagonal lattice constants must be different')
    return cls(a=a, b=a, c=c, alpha=90, beta=90, gamma=120)
