Molecular-orbital calculations for materials design such as alloys, ceramics, and coordination compounds are now possible for experimentalists. Molecuar-orbital calculations for the interpretation of chemical effect of spectra are also possible for experimentalists. The most suitable molecular-orbital calculation method for these purpose is the DV-Xa method, which is robust in such a way that the calculation converges to a result even if the structure of the molecule or solid is impossible in the pressure and temperature ranges on earth. This book specially addresses the methods to design novel materials and to predict the spectrallline shape of unknown materials using the DV-Xa molecular-orbital method, but is also useful for those who want to calculate electronic structures of materials using any kind of method.