MOLPRO's execution is controlled by an input file. In general, each input record begins with a keyword, which may be followed by data or other keywords. Molpro input contains commands, directives, options and data. The commands and directives are sequentially executed in the order they are encountered. Furthermore, procedures can be defined anywhere in the input, which can include any number of commands and directives. They are only executed when called (which may be before or after the definition in the input file).
The input file can be written in free format. The following conversions take place:
Input may be given upper or lower case. The input processor converts all characters to upper case. All integers are appended with “.” (only floating point numbers are read by the program).
Several logical input records can actually be typed on one line and separated by semicolons, i.e., a given input line may contain many actual commands (separated by semicolons), or just one, as you prefer. These basic command units (records) delimited by semicolons are also frequently referred to as cards throughout this manual.
Exception to these general rules are:
A MOLPRO input record (card) contains a number of input fields. Input fields may be up to 256 characters wide and contain either expressions or strings. The fields can be separated by commas or blanks. We recommend the general use of commas in order to avoid unexpected results.
Each line may start with a label. A label is separated from the body of the line by a colon (:). The colon is part of the label. The length of the label must not exceed 6 characters (including the colon) and the labels must be unique. Labels may be useful with GOTO commands. Example:
Here START: is a label, and CCSD(T) is a command.
Strings containing blanks can be entered using quotes. For instance, 'This is a string' is interpreted as one string, but This is a string is a sequence of four strings in four subsequent fields. Strings in quotes are not converted to upper case.
Input lines may be concatenated using at the end of the line(s) to be continued. Any number of lines may be concatenated up to a total length of 1024 characters (only 500 characters are possible on older IBM systems).
Filenames may be up to 31 characters long, provided that long filenames are supported by the Unix system used. An exception are older CRAY systems, which allow only 8 characters for the names of binary MOLPRO files.