**Assignment
CompChem4: Model Chemistries**

1. Basis Set Effects on Hydrogen Fluoride.

Perform Optimize+Vib Freq calculations at the MP2 level for hydrogen fluoride (HF) using the following basis sets: STO-3G, 3-21G, 6-31G(d), and 6-311+G(d,p).

Make a table with columns for basis set, bond length,
dipole moment, vibrational frequency, energy, and CPU time. Also include the experimental values
(0.9171Ĺ, 1.91 D, and 4139 cm^{-1}) in the table.

Comment on the effect of basis set on the calculation.

2. Theoretical Method Effects on Hydrogen Fluoride.

Perform Optimize+Vib Freq calculations using the 6-311+G(d,p) basis set for hydrogen fluoride (HF) using the following methods: HF, MP2, MP4, B3LYP. (Note that you already did the MP2 calculation in the previous problem.)

Make a table with columns for method, bond length,
dipole moment, vibrational frequency, energy, and CPU time. Also include the experimental values
(0.9171Ĺ, 1.91 D, and 4139 cm^{-1}) in the table.

Comment on the effect of theoretical method on the calculation.

3. Compound Method Calculation of Ozone Destruction by Atomic Chlorine.

Perform CBS-4M calculations on atomic Cl (doublet), O_{3}
(bent geometry, singlet), OCl (doublet), and O_{2} (triplet). [It has been observed that OCl must be built
with oxygen as the first atom; otherwise, the CBS-4M portion of the calculation
fails.] When configuring Gaussian job
options, set Calculation = “Other(CBS-4M)”, Theory = “Other()”, and Basis Set =
“Other()”.

Make a table with columns for molecule, energy, and enthalpy. Use your results to calculate the enthalpy change of the reaction

Cl + O_{3}
®
ClO + O_{2}

Compare your results to the experimental value of DH = -39.1 kcal/mol.

Is the difference between calculation and experiment
in line with what can be expected from compound methods? How does your result compare to Hartree-Fock
calculations (such as the previously calculated decomposition of CH_{3}CHO
into CO and CH_{4})?

4. CBS-4M Compound Method

The CBS-4M compound method represents a good compromise between computational accuracy and speed.

View the raw output of a CBS-4M calculation for a molecule (not an atom). Copy all the route lines in the output file and paste them into your homework. Use these lines to explain how the CBS-4M compound method actually works.

5. Software Packages

Locate freely available, non-commercial software packages that implement the following chemical models:

· Extended Huckel Molecular Orbital Theory

· Molecular Mechanics (often included in Molecular Dynamics)

They should be compatible with unix (or Linux) operating systems. Some of these programs will likely form the basis of our upcoming Software Program project.

Provide the URL to the site describing the software and where it can be downloaded.

6. How could WebMO be improved to assist you with your calculations? Please be even more imaginative and thorough with your suggestions and constructive criticism than you have been in the past. Thank you in advance!