running-codes-on-linux.md

Running codes on Linux

ECCE does not include a computational chemistry code, and it does not install one for you. On Linux, most of the codes ECCE works with are in the distribution's own package archive, so they install with one command and are updated with the rest of the system. ORCA and Gaussian are not, and come from their makers. ECCE-QM, the small quantum chemistry program that comes with ECCE, needs nothing extra.

The calculations run on your own computer: the machine to choose in the Launcher is localhost. For a cluster, see Register Machines.

From the package archive (Debian, Ubuntu)

Debian 13 has these codes in its archive:

Code	Package	Version in Debian 13
NWChem	nwchem	7.2.3
MOPAC	mopac	23.1.2
GROMACS	gromacs	2025.2
Quantum ESPRESSO	quantum-espresso	6.7
CP2K	cp2k	2025.1

Install the ones you need, for example:

sudo apt install nwchem mopac

The programs are then in /usr/bin, where ECCE's Find button looks. Ubuntu 24.04 has the same packages, some in older versions.

Do not install the package called orca. In Debian and Ubuntu, orca is the GNOME screen reader, not the quantum chemistry program. ORCA comes from its own web site; see below.

The screen reader is often installed with the desktop anyway, so give ORCA's full path in Register Machines rather than the bare name orca. Find looks for ORCA in folders named orca... in your home folder, /opt and /usr/local, and one folder below them (for example /opt/orca/orca_6_1_1_linux_x86-64_.../orca). A job that finds the screen reader instead of ORCA stops and says so in its output.

On Fedora, Rocky Linux and RHEL, some of these codes are in Fedora or EPEL; dnf search nwchem (and so on) shows what your system offers.

ORCA

ORCA is free for academic use but is not in any distribution's archive.

1. Download ORCA from FACCTS (https://www.faccts.de/orca/; you need a free academic account to log in), choosing ORCA for Linux: x86-64 for a PC, arm64 for an ARM machine. For x86-64 there are two archives, orca_6_1_1_linux_x86-64_shared_openmpi418.tar.xz and orca_6_1_1_linux_x86-64_shared_openmpi418_nodmrg.tar.xz; the second leaves out the DMRG module, which ECCE does not use. Either works.

2. Unpack it, for example in your home folder:

   mkdir -p ~/orca && tar xf orca_6_1_1_linux_x86-64_shared_openmpi418_nodmrg.tar.xz -C ~/orca
   

   or, for every user of the computer, under /opt with sudo.

3. The program is the file orca in the unpacked folder. Give ECCE its full path: ORCA finds its helper programs next to itself.

For a calculation on more than one core, ORCA needs the Open MPI version named in the archive's file name (for example, openmpi418 is Open MPI 4.1.8). ORCA's download page and manual describe how to install it if your distribution's openmpi-bin is a different version.

Gaussian

Gaussian is a commercial program. A site with a licence installs it; ask your system administrator for the location of g16 and of its setup file (g16.profile). ECCE needs the full path of g16.

NBO (optional)

NBO 6 or 7 adds natural bond orbital analysis to ORCA and Gaussian jobs. It is licensed separately from the University of Wisconsin. After installing it:

• ORCA: in Register Machines, on the Codes tab, select ORCA and add to Environment variables the line NBOEXE /path/to/nbo7/bin/nbo7.i8.exe.
• Gaussian: add the line PATH /path/to/nbo7/bin for Gaussian 16, and set BINDIR in NBO's own gaunbo7 script to the same folder.

Tell ECCE where the codes are

1. In the Organizer, choose Tools > Register Machines... (see Register Machines) and select localhost.
2. On the Codes tab select a code and press Find. For a code from the package archive this finds the program in /usr/bin. For ORCA and Gaussian, enter the full path of the program in the Program field.
3. Save. ECCE writes your choices to ~/.ECCE/CONFIG.localhost.

Then make a calculation as in Your first calculation and choose localhost in the Launcher.