Computational techniques for obtaining the electronic ground state in the ab initio pseudopotential method using a plane-wave basis set have been examined for SiC(110) - Al interfaces as metal - ceramic interfaces. The preconditioned conjugate-gradient (CG) method by Teter, Payne and Allan (TPA) performing direct energy minimization is efficient for an SiC surface as it is a non-metallic large system. However, this method encounters oscillations by charge sloshing in the SiC - Al interface because of its metallic nature. The subspace rotation by Gillan instead of the subspace diagonalization improves the convergence behaviour, although it is not easy to remove small oscillations in the present system. We have found that the CG method by Bylander, Kleinman and Lee is more efficient than the other methods for the SiC - Al interface, where the preconditioned CG techniques are used for minimization of energy expectation values in fixed charge density and potential combined with the mixing scheme of Kerker to prevent the charge sloshing. This method is also more efficient than a similar kind of method such as the block Davidson method for the present system, because the band-by-band scheme is more suitable for metal - ceramic interfaces. From the relaxed configurations of the SiC - Al interfaces, we have found strong attractive interactions between C and Al atoms, which should play a favourable role in the adhesion between SiC and Al.