1. A computer-implemented method of identifying candidate molecules having a known biological activity or physicochemical property, the method comprising: providing a set of field points representing field extrema of a first molecule, wherein each field point has a position and a field size value, the molecule having a known biological activity or physicochemical property; using a processor to determine at the position of each of the field points of the first molecule the field of a second molecule to obtain a set of field sample values; combining the field sample values of the second molecule with the field size values of the first molecule to provide a score indicative of the field similarity of the first molecule to the second molecule, wherein the field is an electrostatic field; and providing a measure of the second molecule to have the known biological activity or physicochemical property based on the score.