Effect of basis set¶
We are going to compare the effects of the basis set on the energy of a RHF calculation on water.
Running GAMESS¶
To speed things up, we are going to use the geometry we found for RHF/3-21G and use that for our calculations.
In Avogadro, open the output file from the RHF/3-21G geometry optimisation of water (remember to rename the file to .gamout
), and create several input files for a single-point RHF calculations with increasing basis set size.
The notation for calculations of this type uses the //
notation; for example, RHF/6-31G//RHF/3-21G
.
When they have all been created, run each of them in turn.
(Note to self: Is there time to run an MP2/3-21G calculation?)
Analyse¶
For each calculation, note the final RHF energy and also the wall clock time (found at the end of the output file).
- What is the effect of the basis set size on the energy? Based on this, does it make sense to compare the results of calculations with different basis set sizes?
- What is the effect of the basis set size on the computation speed?