2.1 Introduction

When the program has been installed properly on your machine, you should be able to run it by supplying appropriate input. This document describes how input is organized. A few sample runs are contained in the distribution, see the Examples document on the SCM website for a description.

Input is structured by keywords, or keys. A key is a string of letters, dollar signs ($), and digits. It must not start with a digit. It must not contain any other character, in particular not any blank.

Key-controlled input occurs in two forms: either one record (which contains both the key and/or associated data) or a sequence of records, collectively denoted as a key block. The first record of the block specifies the key (and may supply additional information); the block is closed by the 'end-key' code: a record containing only the word 'End'. The other records in the block provide data associated with the key.

The form to be used for a key is not optional: each admissible key corresponds to a particular form. The block form is used for keys that relate to 'lists' of data, such as atomic coordinates or basis functions.

As is the case in the molecular code, the 'title' must be specified explicitly with the key 'Title' and may be put on any record of the input file. The input file should end with a record End Input, that is, the program reads input until such a record is encountered or until the Fortran end-of-file condition becomes true, whichever comes first.

End Input is not a key.

Summarizing, the input file must have the following format: