Utilities.py 文件源码

def berry_phase(H,path,ns):
    '''
    Calculate the Berry phase of some bands of a Hamiltonian along a certain path.

    Parameters
    ----------
    H : callable
        Input function which returns the Hamiltonian as a 2D array.
    path : iterable
        The path along which to calculate the Berry phase.
    ns : iterable of int
        The sequences of bands whose Berry phases are wanted.

    Returns
    -------
    1d ndarray
        The wanted Berry phase of the selected bands.
    '''
    ns=np.array(ns)
    for i,parameters in enumerate(path):
        new=eigh(H(**parameters))[1][:,ns]
        if i==0:
            result=np.ones(len(ns),new.dtype)
            evs=new
        else:
            for j in xrange(len(ns)):
                result[j]*=np.vdot(old[:,j],new[:,j])
        old=new
    else:
        for j in xrange(len(ns)):
            result[j]*=np.vdot(old[:,j],evs[:,j])
    return np.angle(result)/np.pi