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Molecular Orbital Calculations of Water


	Molecular geometry of water.

The image to right is a picture of the best geometry optimization. The best geometry optimization was found to be the DZV level of theory. It was determined to be the best optimization because it gave values that were closest to the experimental values.


	HOMO diagram of water.

The HOMO (highest occupied molecular orbital) diagram of water is the image to the left. There are 10 electrons present in water and therefore the 5th molecular orbital will have an electron pair present in it. The best geometry optimization was used to calculate the HOMO diagram. The 5th molecular orbital is a bonding orbital. This is represented in the diagram to the left because the red and blue molecular orbitals do not repel each other.


	LUMO diagram of water.

The image to the right is of the LUMO (lowest unoccupied molecular orbital) diagram of water. This is the 6th orbital because there are 10 electrons present in water and therefore there are two electrons in the 5ht orbital and none in the 6th. The 6th orbital is an antibonding orbital. This is represented because the red and blue regions of the molecular orbital diagram to the right do not interact.


	Electrostatic potential of water

The image to the left is a live display of the electrostatic potential of water on the molecular surface. The best geometry optimization level of theory was used for this calculation, which was the DZV level of theory.


	Dipole moments of water.

The image to the right is the calculated dipole moments of water. These dipole moments were found using the DVZ level of calculations from the GAMESS package. The experimental dipoles found were as follows:

Level of calculation:    PM3        21G         31G
Dipole moment¹:       -1.738    -2.388    -2.501
Dipole moment:        -1.779      -2.360      -2.572

The unis for all of the dipole moments are debeyes. The dipole moments that we calculated, the second row, are very similar to those found in the literature.

¹ Calculated Electric Dipole Moments for Water, http://cccbdb.nist.gov/dipole2.asp accessed Mar 5 2011.

IR of Water²

The above link is to an IR spectrum of water. The stretching observed is probably due to a combination of different vibrational modes as the same time; however, the stretching of water, where the hydrogens are moving in unison away from and back towards the oxygen molecule (stretching the bond length) may be observed around 800-600(1/cm). The bending of water, where the hydrogens are moving in unison away from and back towards the oxygen molecule (stretching the bond angle) may be observed around 1700 (1/cm). Finally, the stretching of water where the bond lengths of the hydrogens and being shortened and lengthened opposite one another may be observed around 3400 (1/cm).

² Coblentz Society, Inc. IR Spectrum of Water, http://webbook.nist.gov/cgi/cbook.cgi?ID=C7732185&Units=SI&Type=IR-SPEC&Index=1#IR-SPEC

Based on template by A. Herráez as modified by J. Gutow

Page skeleton and JavaScript generated by export to web function using Jmol 12.0.26 2010-11-06 14:33 on Mar 1, 2011.

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