Quantumchemistry, NWI-MOL406, Computer exercises, Assignment 1
In this exerise we study a simple chemical reaction of the
SN2 type:
Cl− + CH3Br → CH3Cl + Br−
This includes:
- Structure of reactants and products
- Pre/post-reactive complex
- Transition state
Note that this system has a very simple reaction coordinate. You can use the appropriate tool in NWCHEM and constrain your search so that the system has three-fold symmetry, e.g., by using a "hand-written" z-matrix. You could also use xyz-format but take care that C3v symmetry is present in you initial configuration.
Look in the NWChem manual (
https://github.com/nwchemgit/nwchem/wiki or
https://nwchemgit.github.io)
, e.g., at "saddle", on how to do a transition state (TS) search.
You may have to start the NWCHEM TS search with an initial guessed configuration already close to the TS.
Also, you may want to do a frequency calculation first, in order to select the mode that is most similar to the reaction coordinate. But with a judicious choice of starting structure, you might be able to avoid that.
For this exercise use B3LYP and investigate the effect of basis set (in)completeness:
- 3-21++G* for H and C, 3-21g for Br and Cl
- 6-311++G** for H and C, 6-311G** for Br and Cl
Compare your result with accurate quantum chemical calculations from the litterature.
Please also see the checklist.
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