MOLCAS manual:

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2.1 Prerequisites

2.1.1 Prerequisite hardware

In general, MOLCAS can be built on any hardware that runs under a UNIX operating system. Some of these variants of hardware and software have been tested by us, and you should not have any problems to install MOLCAS on any of these. For other platforms you will most likely need to put some extra effort into the installation. In many cases the only effort on your part is setting some compiler flags, paths to system software etc. For a list of the platforms where we have successfully installed MOLCAS see our homepage:

To load the executables resident, sufficient memory is required. In addition, the programs are enabled to allocate work space dynamically. To avoid excessive paging we recommend that your machine should be equipped with at least 2 GB of memory per running application. Note, that MOLCAS will run faster with more memory.

To build MOLCAS you may need up to 2 GB of free disk space depending on what you choose to install and how (e.g. CMake keeps the object files around). The actual size of a MOLCAS installation is around 300-600 MB. To run the verification tests of MOLCAS you should have a scratch disk with up to 1 GB of free disk space, depending on the suite you run. For the ``small'' set about 400 MB will suffice. To perform larger calculations, ample amount of scratch disk space is necessary. The exact amount varies with the type of systems studied, but a general recommendation is at least 4 GB of disk space, per production run.

2.1.2 Prerequisite software

If you obtain the source code of MOLCAS, then you need to make certain that the necessary software is available to build MOLCAS. The minimum requirements are:

  • A Fortran compiler (with support for Fortran 2003 and later)
  • A C compiler
  • GNU make See URL and navigate to the gnumake page or go directly to
  • Perl (version 5.008 or higher)

Also, you can benefit from following optional dependencies:

  • CMake (version 2.8.11 or higher)
  • an optimized BLAS/LAPACK library (alternative for the slow built-in library based on Netlib)
  • NVBLAS to utilise usage of GPU for some BLAS operations
  • MPI-2 (to enable parallelization features of MOLCAS)
  • Global Arrays (version 5 or higher, an alternative to the built-in DGA library)

The Graphical User Interface codes used in MOLCAS can be downloaded from the following pages: LUSCUS version >= 0.8.3 (, and GV (

MOLCAS can be interfaced to other Quantum chemical software such as Columbus, QCMaquis, Block. However at the moment there is no out-of-the-box installation tools. Windows

To install MOLCAS under MS Windows (98/NT/XP/7/8) one should install Cygwin (freeware from RedHat Inc., which can be downloaded from ). The minimal installation of Cygwin to run MOLCAS includes:

  • check that user name (under Windows) does not contain spaces
  • select a disk, which has enough space for installation of Cygwin and MOLCAS
  • install Cygwin to the root of selected disk with all defaults
  • run setup again and install the following packages: Devel$\rightarrow$gcc-fortran, Devel$\rightarrow$make, Devel$\rightarrow$gcc-gcc, Utils$\rightarrow$time, Perl$\rightarrow$perl
  • optionally install editors: Editors$\rightarrow$mc, Editors$\rightarrow$vim
  • run cygwin.bat to create Cygwin environment for the user
  • copy MOLCAS tar file into your home directory in Cygwin, and proceed with installation in the same way as under Linux. MacOS

Installation of MOLCAS under MacOS requires installation of the Apple Developer Tools (Xcode) and a Fortran compiler. These programs could be downloaded from:

However, if you are looking for an out of the box solution, you can download a Free PGI for Mac OS X distribution available at

2.1.3 Preparing the installation

In order to install MOLCAS you need to choose a directory where the MOLCAS driver script is to be installed. The driver executes scripts and programs form the MOLCAS package and must be located in a directory included into the PATH variable. Usually this will be /usr/bin when installing as root, and  /bin when installing as an unprivileged user.

The driver script molcas uses the value of the environment variable MOLCAS to identify which version to use. The major advantage with this mechanism is that it is easy to switch between different versions of MOLCAS by simply changing the environment variable MOLCAS. However if the current directory is a subdirectory (up to 3rd level) of a MOLCAS tree, the latter will be used regardless of the value of the MOLCAS variable.

MOLCAS itself can be located in any place on the disk. The installation can be done by root, or by an unprivileged user. In the later case you can copy the molcas driver script to an appropriate location, e.g. /usr/local/bin, after the installation.

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Next: 2.2 Configuring MOLCAS Up: 2. Installation Previous: 2. Installation