def wavelength_ang(voltage_kV):
    """
    Calculates the relativistic electron wavelength
    in angstroms based on the microscope accelerating 
    voltage
    
    Parameters
    ----------
    voltage_kV: float
                microscope operating voltage in kilo 
                electronVolts
    
    Returns
    -------
    wavelength: float
                relativistic electron wavelength in 
                angstroms
    
    :Authors:
    Debangshu Mukherjee <mukherjeed@ornl.gov>
    """
    m = 9.109383 * 10 ** -31
    e = 1.602177 * 10 ** -19
    c = 299792458
    h = 6.62607 * 10 ** -34
    voltage = voltage_kV * 1000
    numerator = h ** 2 * c ** 2
    denominator = e * voltage * (2 * m * c ** 2 + e * voltage)
    wavelength = 10 ** 10 * (numerator / denominator) ** 0.5
    return wavelength
