The MOLCAS 5.0 suite of quantum chemical programs is modular in design. The desired calculation is achieved by executing a list of MOLCAS program modules in succession, occasionally manipulating the program information files. If the information files from a previous calculation are saved then a subsequent calculation need not recompute them. This is dependent on the correct information being preserved in the information files for the subsequent calculations. Each module has keywords to specify the functions to be carried out and many modules are reliant on the specification of keywords in previous modules.
The following sections describe the use of the MOLCAS modules and their interelationships. Each module is introduced in the approximate order of a calculation. The flow charts in each section show diagrammatically the dependencies of the module. A complete flowchart for the MOLCAS 5.0 suite of codes appears in Section 3.29.