1. A molecular information providing system having a terminal unit including a molecular structure input/output means, and a molecular information providing apparatus connected via a network to said terminal unit and including a database storing a molecular structure, an intermediate representation generated from said molecular structure, and a characteristic decided depending on said molecular structure, said molecular information providing apparatus comprising: means for calculating principal axes of inertia from an atomic arrangement notation specifying said molecular structure; means for registering in said database said intermediate representation, wherein said intermediate representation is a coordinate transformation of atomic coordinates of said molecular structure into a coordinate system in directions of said principal axes of inertia; means for computing a molecular orbital corresponding to said molecular structure, when an estimated computation time for said computing does not exceed a threshold value; and means for retrieving the molecular structure from said database, employing said intermediate representation, when said estimated computation time exceeds said threshold value.