Intelligent software: The OpenMol program

The case is argued that the rigorous use of expert systems and abstract data types for quantum chemical calculations can lead to a more open, more flexible program, which is easier for a novice to use but also, through the possibility of rapid prototyping and symbolic manipulation, for an expert to exploit as an important working tool. The ideas behind this program are, however, quite general and apply equally to many other scientific areas where experience and different numerical techniques have to be combined in a flexible way to produce useful results.