ACD/ChemSketch
From NMR Wiki
Overview:
The 3D optimization is based on modified molecular mechanics which take into account bond stretching, angle bending, internal rotation, and Van der Waals non-bonded interactions.
References:
Cedric Mumford. School Science Review, June 2003, 84 (309)
Sadanand Pathre. Analytical Chemistry, 1996, 68, 740A-741A
Gary O. Spessard. J. Chem. Inf. Comput. Sci., Vol. 38, No. 6, 1998
Pavel Simakov. Science, 2001, Vol. 291, No. 5511, Page 2179