Trial Run and Exercises

As a starting example, you should construct and run a simple water molecule. We're going to make it very simple, not many options requested, and we're going to use a Z-matrix as the molecular geometry specification format. The entire file looks like this (and don't forget the blank lines!):

-don't forget a blank line here!
# HF/STO-3G Test
-don't forget a blank line here!
Single point energy calc of water
-don't forget a blank line here!
0 1
O
H  1  0.956
H  1  0.956  2 104.5
-don't forget a blank line here!

This file says these things:

We are requesting an ab initio calculation, using the Hartree-Fock approximation with an STO-3G (Slater-type orbitals, three gaussians) as the initial guess for the mathematical engine. "Test" tells Gaussian94 not to archive the results to some directory.
Gives a title of "single point energy calc of water". A single point energy is the energy of the molecule at a given, specific geometry (bond distances, angles, and dihedrals). We are not asking for the software to optimize the geometry, just calculate what we have given it!
Charge is zero, and multiplicity is 1, since all the electrons are paired
Internal coordinates gives a O-H bond distance of 0.956 angstroms, with an H-O-H bond angle of 104.5 degrees. We need no dihedrals here since we only have three atoms.
Don't forget the blank lines (what a nag!)

Other Exercises

Benzene Specs for an optimization
Butane Specs for an optimization with a fixed dihedral angle

Developed by
Graphic of Shodor Logo