Ab initio packages for starters

	PCGamess: Ab initio code for your Windows PC
	MacMolplt: Nice visualization of Gamess output
	Arguslab: Visualize or draw molecules, optimize with molecular dynamics, useful to generate starting geometries
	Mopac: Molecular dynamics and semiempirical methods

 

Suggested sequence for simple structure calculations:

(1) Draw your molecule in CHEMSKETCH and push the ‘optimize 3D’ button, save it in .mol format

(2) I used OPENBABEL to convert the .mol coordinates to Gamess input format.

(3) Perform a PM3 calculation in Gamess Firefly to get a better structure (fast calculation). A sample input file is here: Toluene_PM3_geometry.

(4) Use the PM3 structure result to start a DFT (B3LYP) calculation with the Gaussian 6-31 basis set (fraction of a minute calculation). A sample input file is here: Toluene_B3LYP-6-31G_geometry.

(5) Use the DFT-6-31 structure result to start a DFT B3LYP calculation with a larger basis set (e.g.,Dunnings augmented correlation-consistent valence-triple-zeta basis set. This basis is about as good as it gets, so this will be the final structure.) A sample input file is here: Toluene_B3LYP-accpVTZ_geometry.