Single Point Energy Calculations

1
Single Point Energy Calculations

2
Two Main Type of Basis Functions

• Plane Wave - Sine and Cosine Functions - Not used
  in Gaussian
• Atomic/Slater/Contracted Gaussian Orbitals - Used
  in Gaussian

3
Why atomic like orbitals?

• Two atoms far away almost exactly the same as two
  individual atoms.
• Two atoms close together can be thought of in
  pieces.
• Sum of potentials should lead to sum of density.

4
What is a Contracted Gaussian?
5
Flexible Valence - Zeta

• Most Basis Sets are double or triple zeta in
  valuence - allows breathing
• Possible basis sets exists that are 4,5 6 zeta.
• Single Zeta falling out of use.
• Density Fitting Basis Sets have multiple Zeta
  Core - DZVP, TZVP

6
Basis Set Interpretation

• What does 6-31G(d,p) mean?
• 6 is the contraction of core orbitals.
• 31 means that valence orbitals are represented by
  two orbitals one contracted 3 times, one not
  contracted.
• First sign means 3s orbitals on heavies
• Second sign means 2s on H
• (d,p) are polarization on heavies and lights
  respectively

7
Effective Core Potentials

• Necessary Evil
• LANL2DZ one of many
• Takes into account relativistic effects

8
For More Information

• Http//staff.science.nus.edu.sg/chmbrpa/Basis20S
  ets.ppt

9
Homework

• Pick and important molecule from your research.
  Build it and perform a single point energy
  calculation. Consider carefully Basis Set and
  Method. Take time to look through the results.
  What insight do you gain?
• Work on problems from Ch2.
• Read Ch 2/3.