Quick And Dirty Optimizations With Pm6

Unfortunately, while Gaussian 09 has a PM6 implementation, it cannot be applied to solids. So instead, use MOPAC. The input file should end in the extension ".mop", and has the following format.

PM6 
COMMENT1: 
COMMENT2: 
Ga      4.50297 1       0.06638 1       6.71660 1
Ga      4.37828 1       15.02062        1       2.20639 1
P       2.98738 1       1.29386 1       4.48112 1
P       5.89387 1       13.79314        1       4.44186 1
....
H       3.07010 1       5.59124 1       9.86614 1
Tv      8.8990001678    0       0.0000000000    0       0.0000000000    0
Tv      0.0000000000    0       15.0869998932   0       0.0000000000    0
Tv      -0.0355072299   0       0.0000000000    0       17.8459653479   0

Atom positions are specified are in cartesian coordinates in angstroms. the "Tv" atoms specify the translation vectors of the system (also in angstroms). The "1"s following the coordinates say that this particular coordinate is optimizable. Obviously you can put some important human-readable comments in the comment line. You also don't want to optimize the translation vectors, so make these zero.

The perl program "molden2mopac.pl" will help you take an arbitrary xyz file and convert it to the above format. Be careful, as you probably don't want to optimize the translation vectors.

Install MOPAC on your computer as described on the MOPAC website, then run the program. I find that for our compounds each geometry step takes less than a minute.

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