Problems installing MOPAC

While most users install MOPAC without problems, some users have difficulties getting MOPAC to work.

If you are experiencing difficulties, please carry out  the following instructions before asking for help

Using MOPAC with Chem3D


Problems getting the license key to install

Make sure you have permission to write to the folder that contains the MOPAC executable.
This issue affects Windows, Linux, and Mac computers. 
The default location of the folder that holds MOPAC depends on your operating system.
If you cannot set the permissions to read and write to files in the default folder, then change the location of the MOPAC folder by using an Environmental Variable.
A suitable place is your home directory, in a folder called, e.g., <your_name>/mopac

Even with a new copy of MOPAC, the message that the program has expired still appears

The expiry date for academic versions is stored in the MOPAC executable, not in the license key. Please delete all MOPAC executables, then try to run MOPAC again - obviously this attempt should fail because you've already deleted the executables. If MOPAC tries to run, continue deleting MOPAC executables.

Once MOPAC does not try to run, download and install a new MOPAC executable.

If MOPAC still will not work, then do the following:

Completely empty the folder that contains the MOPAC executable.
Carry out the instructions for installing MOPAC.
Make a note of each instruction that you do, and also make a note of what the computer response is.
When the problem occurs, stop, and send your notes to

Missing libraries in Linux systems

CentOS 6.3 (a RedHat derivative) does not install 32-bit libraries, which normally reside in the directory /lib , nor does it even offer the opportunity to do so at installation time.
However, these libraries can be easily obtained by doing two steps:
# yum install glibc.i686 and after that is done,
# yum install
The folder /lib now contains the libraries and links that were originally missing.

Then run
# /installdirectory/MOPAC2016.exe {license}
without a hitch.

Libraries exist, but are not "seen" by MOPAC, in Linux systems

If MOPAC will not run because it needs the library, and you find that the library exists as:  /opt/intel/fc/9.0/lib/, the adding this to the .bashrc file might help:


Linux gives the message "FATAL: kernel too old, Segmentation fault."

The version of Linux is out-of-date.  Either update the version of Linux or create a virtual machine that will run an up-to-date operating system.  Versions of MOPAC for old OS are not supported.

Error message "error while loading shared libraries: cannot open shared object file: No such file or directory"

You will need to install the shared library. To do this, proceed as follows:
(A) Copy from the MOPAC distribution zip file to the folder /opt/mopac/
(B) Edit your .bashrc or .cshrc to include the line:
export LD_LIBRARY_PATH=/opt/mopac
(C) Run the start-up script, that is, run the command: "source .bashrc" This will export the library.

MOPAC does not run on Leopard, Snow Leopard, or Lion.

 MOPAC2016 for Mac computers run on Mountain Lion (OS X 10.8) and higher.