We have carried out a numerical study of the structural, thermodynamic, and motional properties of ultra-thin smectic films deposited in vacuo on a solid surface and subjected to external electric field E. A molecular model based upon the random walk theory is applied for calculating the rotational self-diffusion (RSD) coefficient D-perpendicular to both in the bulk of the smectic film, as well as in the vicinity of the bounding surfaces. Calculations of D-perpendicular to require the orientational distribution function or the set of the orientational order parameters (OPs) which has been obtained by using the mean-field approach. The effects both of surface enhanced pair interactions in the bounding LC/solid and LC/vacuum layers and of E on the orientational and translational OPs, as well as on the RSD coefficient of smectic films have been investigated. A reasonable agreement between the theoretically predicted and the experimentally obtained data on the RSD coefficient in the bulk of 4-n-octyl-40-cyanobiphenyl phase has been obtained. (c) 2013 Elsevier B.V. All rights reserved.