Molecular geometries of molecules can be determined using software Gamess, and multiple basis sets were used to determine the best geometry optimization of the molecule Formaldehyde. Ab Initio was the preferred level of theory because it calculated all integrals instead of simple approximations. The basis sets were set up in Ab Initio. The input files for Ab Initio were AM1/PM3 files created in MacMolPlt and the generated files were, in increasing order of size, 6-21G, 6-31G, and DZV basis sets. As the basis set size increased, more options for electrons were available for calculations. Therefore, it is assumed that the best geometry optimization is given by the DZV basis set. All of the basis sets showed a bond length for C-O to be 0.129 nm. The generic length of this bond is 0.121 nm. The basis sets showed the bond length for C-H to be 0.109 nm. The generic length of this bond is 0.109nm. The percent error in the calculation are: 6.6% for C-O, 0.0% for C-H.

The values for the RHF calculations and UHF calculations were -113.83 and -113.77, respectively. Since the RHF values resulted in a lower energy, the RHF SCF Type gave better results than the UHF SCF Type. This means that the oxygen in formaldehyde had a pair of electrons and had not formed a radical.

To view the Potential Energy, Molecular Orbital, and Vibrational Frequency of Formaldehyde click the link.

 

Using directory /Users/student/Desktop/IEAR/Formaldehyde_Geometry
  adding JmolPopIn.js
  ...jmolApplet0
      ...adding Formaldehyde6-21G_Geometry.png
copying and unzipping jsmol.zip directory into /Users/student/Desktop/IEAR/Formaldehyde_Geometry
      ...copying
file:/Volumes/ROWLEY2/Ilenia&Andy Molecules/Formaldehyde/Formaldehyde-6-21G-RHF.log
         to
/Users/student/Desktop/IEAR/Formaldehyde_Geometry/Formaldehyde-6-21G-RHF.log
      ...adding Formaldehyde6-21G_Geometry.spt
  ...jmolApplet1
      ...adding Formaldehyde6-31G_Geometry.png
copying and unzipping jsmol.zip directory into /Users/student/Desktop/IEAR/Formaldehyde_Geometry
      ...copying
file:/Volumes/ROWLEY2/Ilenia&Andy Molecules/Formaldehyde/Formaldehyde-6-31G-RHF.log
         to
/Users/student/Desktop/IEAR/Formaldehyde_Geometry/Formaldehyde-6-31G-RHF.log
      ...adding Formaldehyde6-31G_Geometry.spt
  ...jmolApplet2
      ...adding FormaldehydeDZV_Geometry.png
copying and unzipping jsmol.zip directory into /Users/student/Desktop/IEAR/Formaldehyde_Geometry
      ...copying
file:/Volumes/ROWLEY2/Ilenia&Andy Molecules/Formaldehyde/Formaldehyde-DZV-RHF.log
         to
/Users/student/Desktop/IEAR/Formaldehyde_Geometry/Formaldehyde-DZV-RHF.log
      ...adding FormaldehydeDZV_Geometry.spt