def DrudeSommerfeld(omega, omegap, gamma):
    """
	The Drude-Sommerfeld model of a metal dielectric.
	Applies when only free-electron contributions need
	to be considered.

	Returns
	----------

	eps:		Drude permittivity
	"""
    frac = omegap ** 2 / (omega ** 2 + 1.0j * gamma * omega)
    eps = 1 - frac
    return eps
