ORCA Program Installation Guide

ORCA is a powerful and versatile quantum chemistry software package developed by the group of Prof. Frank Neese. The ORCA program is free for academic use.

Step 1: Go to https://www.faccts.de/orca/. Navigate to the “DOWNLOADS” tab. In the window that opens, register on the ORCA website using an academic email address. Then, complete the registration using the link sent to your academic email, and log in to the website again with your email address and password.

Figure 1. ORCA Download Page.

On this download page, different ORCA versions are listed for macOS, Linux, and Windows operating systems, respectively. The file ending with “...macosx_intel_openmpi411” corresponds to the version for Intel-based Macs running macOS and includes the OpenMPI 4.1.1 library. The file ending with “...macosx_arm64_openmpi411” is optimized for macOS systems with ARM-based Apple M1/M2/M3 processors. The file labeled “...linux_arm64_shared…” is intended for ARM-based Linux servers (e.g., AWS Graviton). The file ending with “...linux_x86-64_...nodmrg” represents the version for standard Linux servers with x86_64 architecture.

Here, the “nodmrg” suffix indicates that the DMRG module is not included. The file starting with “Orca...Win64_msmpi.zip” contains the standard ORCA installation for Windows x86_64 systems and supports Microsoft MPI (parallel computing). The “Orca...Win64_autoci.zip” file is also intended for Windows systems and includes the AutoCI module. This module is very large and contains additional data for complex quantum chemical calculations; therefore, its size is quite large (7.3 GB).

The SHA256 file is a checksum used to verify the integrity and authenticity of the downloaded files.

Step 2:

ORCA Installation for Windows

To install ORCA on Windows, download the file starting with “Orca...Win64_msmpi.zip”. Extract the ZIP file into a folder using WinRAR or any other extraction tool. Then, double-click on “Orca6.1.0.Win64.exe”. Follow the installation steps as in a standard software setup. In a typical installation, only the serial modules of ORCA are installed. To also install the parallel components, select the Custom or Full installation option. The default installation directory for ORCA is C:\Orca_6.1.0, but a different folder can be selected if desired. The required environment variables are configured accordingly during installation.

ORCA Installation for Linux

Download the ORCA file for Linux. Extract the archive using the command tar -xf filename.tar.xz, rename the directory to “orca”, and move the folder to the user’s home directory (~). Then, navigate into the folder, where a .run file such as filename.run should be present. Grant execution permission to this file using the command chmod a+x filename.run. After that, run the file in the terminal with the command ./filename.run.

The installation program will install ORCA in the user directory and configure the system path to include the ORCA directory. The installer also provides options such as extracting only, and interactively or non-interactively specifying the extraction path.

-i : Specify an alternative installation path interactively

-p <path> : Specify an alternative installation path

-x : Extract only

Example usage:

./filename.run -- -p /my/home/orca/dir

After installing ORCA, to add the program to the PATH variable:

> echo 'export PATH="$HOME/orca:$PATH"; export LD_LIBRARY_PATH="$HOME/orca:$LD_LIBRARY_PATH"'  >> ~/.bash_profile; source

> ~/.bash_profile

This command should be entered in the terminal. In this code, $HOME/orca must correspond to the directory where ORCA is installed. Essentially, the command adds the installation directory and the library path to the PATH variable.

Installation for macOS

The ORCA installation for macOS is similar to the Linux installation. The .run file is executed as in Linux, and the PATH variable is set accordingly.

In the terminal, enter:

echo 'export PATH="/Applications/orca:$PATH"; export LD_LIBRARY_PATH="/Applications/orca:$LD_LIBRARY_PATH"'  >> ~/.zshrc; source ~/.zshrc