The use of computers in chemical research. With the increase in processing power of computers, calculations on individual molecules and on chemical systems have become important tools for research and industrial development. With simple molecules, predictions can be made about electronic structure and properties using ab-initio calculations. For more complex molecules semiempirical calculations are used. The field has been particularly expanded by the density-functional method of treating large molecules and by the availability of software for analysing molecular behaviour and structure. See also molecular modelling.