Liquids Quantum Chemistry Lab

Outline

Core

• starting gaussview
• building a molecule of H₂O
• optimising a molecule of H₂O
• understanding the output file
• editing input files directly and submitting to a queue
• confirming a minimium = carrying out a frequency analysis
• determining the ESP based CHELPG and density based NBO charges
• adding a continium solvation environment

keywords section from the Gaussian online-manual

A Project

at the end of the first lab session you should decide on a project to work on together.

This is a chance for you to explore for yourselves. In your group decide on a "project" and split the work into parts each carried out by individuals, however the results should be brought together to make whole argument/hypothesis/invesitgation in the presentation.

Studying one thing which you compare across a range of examples is a good idea. Keep it small and simple.

You should spend about 3hrs out of lab time and 3 hours in lab time on this.

Larger molecules take longer to compute, so you will want to spend time setting up calculations, submitting them to the queue and then coming back to look at them later. You will not be able to sit-down and do all the calculations in a 3hr block. I find split it up into 1/2hr morning and night very useful. Then get together in the second lab session to write the presentation and interpret the results together.

please read this on Energies and accuracy

If you choose something outside of those below you MUST clear your project with me (as you are infants when it comes to QM calculations I want to avoid you picking someting too challening for your new skills).

Some ideas:

• examine the effect of forming a H-bond on the MOs and charges, take water and form a dimer, add a Cl anion, or a Na cation what effect do these have?
• expand your explicit water "cluster" to 2 waters, 3 waters, 4 waters ... (each person does a different cluster and then you can compare results). Warning the more molecules you have the more possible conformations you need to check.
• examine a solvent like ammonia or methanol in a similar way
• highly polar solutes are solvated much better in polar solvents, pick a very polar small molecule (HF or HCl) and examine the stability and properties in various solvents.
• non-polar solutes are solvated much better in non-polar solvents, pick a non-polar small molecule (CH₄,CCl₄) and examine the stability and properties in various solvents.
• or pick one solvent and look at how a range of solutes from non-polar to polar are solvated
• compare a range of similar solvents, say water, methanol, and ethanol. What is the effect of the lengthening alkyl chain?

Need Help

• contact me, I'm very happy to revceive questions via e-mail: