4 How to run MOLPRO

In order to run MOLPRO you have first to write an input file. This can be done in any directory of your choice. Input files can have any name, but it is best to avoid using a file name with extension .out. It is often convenient to name the input file as h2o.inp, benzene.inp, depending on the molecule, or whatever you like.

Simple examples for input files will be given in the following sections. Once the input file is ready, a MOLPRO calculation can be started using the molpro command. Assume the input file is called h2o.inp. The command to run MOLPRO is then simply

molpro h2o.inp &

This will create an output file h2o.out, i.e. the extension .inp is replaced by .out. The same would happen with any other extension, e.g., h2o.com, h2o.input, h2o.test would all produce the output in h2o.out. If h2o.out already exists, the old output will be moved to h2o.out_1, or, if this already exists as well, appended to it. In this way old outputs are not lost. This mechanism can be disabled using the -s option:

molpro -s h2o.inp &

would not save an existing output file but simply overwrite it. If you want to give your output a different name than the default one, you can use the -o option, for instance

molpro -o water.output h2o.inp &

There are many other options for the molpro command, which, however, need rarely to be specified. You can find a full description in the MOLPRO reference manual.

The amount of memory MOLPRO is allowed to use can be specified using the -m option, e.g.,

molpro -m 4M h2o.inp &

This means that 4 megawords (MW) of memory are allocated by molpro (see also memory input card, section 12.1.