MOLCAS manual: Subsections 1.2.1 Manual in Four Parts 1.2.2 Notation 1.2 The MOLCAS Manual 1.2.1 Manual in Four Parts This manual is designed for use with the ab initio Quantum chemistry software package MOLCAS 8.1 developed at the by the world-wide MOLCAS team where its base and origin is the Department of Theoretical Chemistry, Lund University, Sweden. MOLCAS is designed for use by Theoretical Chemists and requires knowledge of the Chemistry involved in the calculations in order to produce and interpret the results correctly. The package can be moderately difficult to use because of this `knowledge requirement', but the results are often more meaningful than those produced by blackbox packages which may not be sufficiently chemically precise in either input or output. The MOLCAS manual is divided in four parts to facilitate its use. The MOLCAS Installation Guide describes simple and more complex aspects on how to install, tailor, and control the MOLCAS package. The Short Guide to MOLCAS is a brief introductory guide which addresses the needs of the novice and intermediate users and is designed for all those who want to start using MOLCAS as soon as possible. Only basic environment definitions, simple input examples, and minimal description of output results are included in the short guide. Two types of introductory tutorials are given in the short guide: problem-based and program-specific. Problem-based tutorials are exercises focused on solving a simple Quantum Chemical project and contain all the required input files. Examples include computing electronic energy of a molecule at different levels of theory, optimizing the geometry of a molecule, calculating the transition state in the ground state of a chemical system, and computing an excited state. The input files for this section can be found in the directory $MOLCAS/doc/samples/problem_based_tutorials. These examples are also employed in MOLCAS workshops that the MOLCAS team has organized in recent years. Another type of tutorial is designed for the first-time user to provide an understanding of program modules contained in MOLCAS include simple, easy-to-follow examples for many of these modules. The systems covered in the short guide are not necessarily calculated with most suitable methods or produce highly significant results, but provide both several tips for the beginner and actual input file formats. The Short Guide to MOLCAS can be independently printed as a booklet. The MOLCAS User's Guide contains a complete listing of the input keywords for each of the program modules and a information regarding files used in each calculation. Here the user will find all keywords that can be used together with a specific program and thus how to set up the input for a MOLCAS run. Advanced Examples and Annexes include outlines of actual research performed using MOLCAS. The approach to a research project is outlined including input files and shell scripts. More importantly, however, the value of the calculations is evaluated and advanced features of 8.1 are used and explained to improve the value of the results. The complete manual is available on the net in HTML and PDF formats (http://www.molcas.org/). 1.2.2 Notation For clarity, some words are printed using special typefaces. Keywords, i.e. words used in input files, are typeset in the small-caps typeface, for example EndOfInput. Programs (or modules) are typeset in the teletype typeface. This will eliminate some potential confusion. For example, when discussing the RASSCF method, regular uppercase letters are used, while the program will look like RASSCF. Files are typeset in the slanted teletype typeface, like InpOrb. Commands, unix or other, are typeset in a sans serif typeface, like ln -fs. Complete examples, like input files, shell scripts, etc, are typeset in the teletype typeface.