Dielectric properties of ultra-thin films

A novel evaluation method of a dielectric constant is proposed with the use of first-principles calculations for the ground states in external eletrostatic fields, which is applicable to ultrathin films. The optical dielectric constant evaluated at the innermost region of the film approaches a constant value near to the experimental bulk dielectric constant with increasing the thickness of Si(111) ultra-thin films up to only 8 bi-layers, while the energy gap of the film is much larger than that of bulk Si. The theoretical value of the optical dielectric constant for the Si (111) film, which is converged at a large thickness, well reproduces the experimental one for bulk Si.