Mopac is a free software for semiempirical calculations.
The home page is
The program can be downloaded from that page.
A manual is available in

The current version is Mopac-2012.
The program is installed in

To run it, you must set
export MOPAC_LICENSE=/temp4/bio/MOPAC/Mopac-2012
export MOPAC_LICENSE=/lunarc/nobackup/projects/bio/MOPAC/Mopac-2012
The executable file is linked to mopac
However, there is also a mopac in Amber, so check which one is really used.

Mopac requires that the program is updated every year. When the program refuses to run,
download a new version from
(no password or anything else required)
unzip the file and copy MOPAC2012.exe to the old position of that file.
27/2-15: got
mopac: error while loading shared libraries: cannot open shared object file: No such file or directory
Copy this file ( from the new installation and put it together with MOPAC2012.exe.
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/temp4/bio/MOPAC/Mopac-2012/
For alarik, the CentOS 6 version had to be used, but not LD_LIBRARY had to be executed.

Input files must end with .mop.

You run the software with
mopac test
using test.mop as the input file and giving the output file test.out.

Input file
Coordinates (one per atom)
Blank line
Extra lines

Comment lines start with a *

The simplest way to specify the geometry is by Cartesian coordinates
O 0.00  0  0.00  0 0.00  0
C 1.21  1  0.00  0 0.00  0
H 1.79  1  0.93  1 0.00  0
H 1.79  1 -0.93  1 0.00  1
The extra 0/1 specifies whether the coordinate should be optimised or not

You can turn off geometry optimisation also by the keyword 1SCF