# ORCA¶

Some users have requested an installation of the ORCA quantum chemistry program on Stallo. Unfortunately, ORCA does not come with a computer center license, which basically means that we cannot easily install it globally on Stallo. However, the code is free of charge and available for single users or at research group level, provided compliance with the ORCA End User License Agreement. This means that interested users can download the precompiled executables from the ORCA web page themselves, and run the code on Stallo.

## Installation¶

2. Download the Linux x86-64 complete archive and place it somewhere in your home folder
3. Extract the tarball
$tar xjvf orca_4_0_0_2_linux_x86-64_openmpi202.tbz  1. The orca executable is located in the extracted archive and should work out of the box ## Usage¶ In order to run ORCA in parallel the OpenMPI module must be loaded, and it is important to use the full path to the executable $ module load OpenMPI/2.0.2-GCC-6.3.0-2.27
\$ /full/path/to/orca orca.inp >orca.out


A very simple example input file is provided below. Please refer to the ORCA manual for details on how to run the code for your application.

### ORCA input example¶

! HF def2-TZVP

%pal
nprocs 4    # parallel execution
end

* xyz 0 1
C  0.0  0.0  0.0
O  0.0  0.0  1.13
*