The interaction of methanol (CH3OH) molecules with the Al(100) surface is investigated in the framework of the density-functional theory. Numerical parameters, such as the decrease in the kinetic energy, number of special points used for integration over the Brillouin zone, broadening of the filling function, and number of atomic metal layers, are determined. The density-functional theory calculations with these parameters offer reliable data on the total energy and structural optimization of the system under consideration. The geometric characteristics of a methanol molecule in both isolated and adsorbed states on the metal surface are calculated. It is shown that the electron pseudodensity at the metal surface changes in the presence of an adsorbed molecule. The influence of the orientation of the methanol molecule (with respect to the metal surface and nearest neighbor methanol molecules) on the total energy of the system is analyzed. It is found that the total energy of the system is affected by the metal deformation and the interaction of adsorbed molecules with each other.