Tutorials
### Example 1 - Ethene C

### Example 2 - Ethyne C

# Jcoupling

Start by copying the input files into your home directory ie

`cp /home/jr_yates/jryates/WORKSHOP/workshop_nmr_jc.tgz ./ `

### Example 1 - Ethene C_{2}H_{4}

FILES:

- c2h4.cell
- c2h4.param

OBJECTIVES:

- Compute C-C C-H and H-H couplings
- Compare to experiment.

INSTRUCTIONS:

- Look at the param file.
`task = magres`

and`magres_task = jcoupling`

. - Look at the cell file. Note the line
`jcoupling_site : C 1`

. This sets the perturbing atom. We will be computing the J-couplings between this site and all others in the calculation. - Run castep. (
`castepsub ethanol`

) Look at the output file. At the end the isotropic J-coupling is reported, listed in order of distance from the perturbing atom. - Change the perturbing atom and re-run the calculation. How many calculations are needed to compute all the coupling? Some couplings can be computed in two ways - how do they compare?
- Compare with experiment - J(C1-C1)=67.5Hz, J(C1-H1)=156.3Hz, J(C1-H3)=2.4Hz, J(H1-H2)=2.2Hz , J(H1-H2)=11.6Hz, J(H1-H2)=19Hz
- What is the effect of using a GGA functional?

### Example 2 - Ethyne C_{2}H_{2}

Repeat the above calculations for C_{2}H_{2}

%block POSITIONS_ABS bohr C -0.001000 -0.001000 -0.001000 C 2.266671 -0.001000 -0.001000 H 4.269781 -0.001000 -0.001000 H -2.004110 -0.001000 -0.001000 %endblock POSITIONS_ABS

- Compare with experiment. J(C1-C2)=184Hz, , J(C1-H2)=242Hz, , J(C1-H1)=53, , J(H1-H2)=10Hz.

### Example 3 - Alanine

Look at J-couplings in the molecular crystal Alanine (take the cell file from the shielding example).

A calculation on the primitive cell is too small to give converged results - but you can get an idea of the couplings. Note any spurious couplings which arise from interactions of periodic images (eg when the 1st and 2nd distances are roughly equal).