Key Points for Geometry Optimizations:

Geometry Optimization Lab Activity

Students

• Scientists use three measurements to define a molecule's geometry:
  1. Bond Angles (measured in degrees)
  2. Bond Lengths (measured in angstroms)
  3. Dihedral Angles (measured in degrees)
• The optimal geometry of a molecule is the geometry that corresponds to the lowest single point energy calculation of the molecule.
• Potential Energy Surfaces (PES) are mathematical representations of various geometries and their corresponding single point energies.
• PES can be used to find quick estimates of the optimal molecular geometry by locating the minimum point on the graph.
• Computer programs that calculate optimal molecular geometries use three types of calculations:
  1. Molecular Mechanics
  2. Semi-Empirical
  3. ab initio
• In order to run a geometry optimization on the computer, you must enter an initial set of cartesian coordinates and a basis set.