The Spartan Computational Methods. Spartan'06 Essential provides a well documented range of computational approaches, including Molecular Mechanics, Semi-Empirical and Hartree-Fock Molecular Orbital Theory. All methods are easily accessed via Spartan's seamless graphical interface.
  Molecular Mechanics Molecular mechanics is presently the only practical method for calculations on very large molecules or for conformational searching on highly flexible molecules. MMFF94, in particular, has proven to be a reliable and fast tool for conformational analysis. There are no atom limits for molecular mechanics calculations.

Both the SYBYL and MMFF94 force fields are supported. SYBYL extends throughout the entire Periodic Table while MMFF94 has been specifically parameterized to reproduce geometries and conformations of organic molecules and biopolymers. Additionally, an MMFFaq option applies an aqueous solvent energy correction to energy data, of special utility in ranking conformers.
Molecular Orbital

Semi-empirical models are the simplest of the quantum chemical schemes, and are useful for equilibrium and transition-state structure calculations. PM3, in particular, has proven to be a reliable tool for geometry calculations on transition metal inorganic and organometallic compounds.

MNDO, AM1, RM1 and PM3 methods are supported. MNDO/d extensions for heavy main-group elements have been implemented and PM3 parameters for most transition metals are available.

The RM1 (Recife Model 1) reparameterization of AM1 is new in Spartan'06. In most cases RM1 yields superior results to both AM1 an PM3 (for organic molecules), comparisons to MNDO were not available at the time of Spartan'06 release.

Molecular Orbital
Hartree-Fock models useful for predicting structure, energy and property calculations, in particular for organic molecules.

A variety of standard basis sets are supported: STO-3G, 3-21G, 6-31G*, 6-311G*, with extensions including (d), (d,p), (2d), (2d,2p), (2df, 2dp), (3d, 3p), (3df, 3dp) and diffuse functions and/or additional polarization functions.