def grep_PAW_order(fpot):
    """ 
      helper-function to extract order of PAW potential
    
    """
    with open(fpot, 'r') as pfile:
        lines = pfile.readlines()
    order = []
    for l in range(len(lines)):
        if len(lines[l].split()) > 0 and lines[l].split()[0] == 'PAW_PBE':
            order.append(lines[l].split()[1])
    return(order)