Quantum Calculations for Cl2

The images that are displayed below show the optimized geometries for the basis sets AM1, PM3, 6-21G, 6-31G, and DZV. The PM3 basis set gives the best result for bond length when comparing it to literature values, however the optimized basis set DZV was used for the other properties such as HOMO/LUMO and vibration frequencies.



Literature values for Cl2:
Bond length (nm)
Vibrational frequencies (cm^-1)
0.1988
554



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Optimized Geometry for Cl2_AM1
This diagram displays the optimized geometry for the basis set AM1. It displays the bond length of the Cl2 diatomic molecule, which is 0.192 nm.

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Optimized Geometry for Cl2_PM3
This image here shows the optimized geometry under the basis set of PM3. The bond length is 0.204 nm, which is the closest calculated value when compared to the experimental value of 0.1988 nm2.
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Optimized Geometry for Cl2_6-21G
The image here displays the optimized geometry for the 6-21G basis set. The bond length for Cl2 is 0.218 nm.
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Optimized Geometry for Cl2_6-31G
This image in the optimized geometry of Cl2 for 6-31G which actually has a shorter bond length than the 6-21G basis set.
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Optimized Geometry for Cl2_DZV
The basis set DZV had the furthest calculated value from the experimental value at 0.219 nm. However, because DZV is the largest basis set, this optimized geometry was used for the calculations of properties of the Cl2 diatomic molecule.
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HOMO for DZV of Cl2
As stated above, this HOMO is using the basis set DZV. Because the HOMO is determined by the total electrons in a molecule divided by two, molecular orbital 17 was used to display the HOMO of Cl2.
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HOMO degenerate for DZV of Cl2
This image displays the HOMO degenerate, which is another molecular orbital that shares the same energy as a different molecular orbital. 
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LUMO for DZV of Cl2
LUMO is the lowest unoccupied molecular orbital, which is simply one molecular orbital higher than the HOMO. Because the HOMO is molecular orbital 17, the LUMO must be molecular orbital 18.
Page skeleton and JavaScript generated by the Export to Web module of Jmol 14.29.46 2019-06-03 12:50 on Oct 3, 2019.
Based on a template by A. Herráez and J. Gutow
This image displays the bond length in angstroms vs the
      potential energy in hartrees
This figure was generated in IGOR and displays the potential energy (hartrees) of Cl2 vs. the bond length (angstroms). It shows that the energy is the lowest for the 6-31G basis set, while the energy for the DZV is actually the second lowest.


Molecular Orbitals:

The image above shows the molecular orbital diagram for Cl2 with the corresponding molecular orbital images.




The one calculated vibrational frequency for Cl2 came out to be roughly 516.81 cm^-1. The CCCBDB website has one vibrational frequency of 554 cm^-12.