Theoretical molecular science, which predicts the properties and functions of large complex molecules such as nano-materials and biological molecules via molecular theoretical calculations, is steadily increasing in importance. However, the current theoretical underpinnings are not wholly satisfactory. Consequently, we aim to realize an updated theoretical molecular science by developing a molecular theory and calculation methods that can handle large complex molecules with high precision under a variety of conditions. Moreover, to utilize these achievements, we are developing software, named NTChem, that can run on the K computer. By making full use of the performance power of the K computer, we expect this software will be useful for creating new drugs and designing new materials.