# Example: NMR Spin-spin coupling constants: C2H2¶

```
#!/bin/sh
# Non-relativistic calculation
# ============================
# A calculation of NMR nuclear spin-spin coupling constants (NSCCs).
# As explained in the ADF manual, the quality of a calculation for spin-spin
# coupling constants, using the program 'CPL', depends largely on the preceding
# ADF calculation, which produces the Kohn-Sham orbitals and orbital energies,
# used as a starting point.
# One of the quality-determining factors is the chosen basis set. It should be
# sufficiently flexible near the nucleus. Although the all-electron basis TZ2P
# is chosen in this example, it is recommendable to add more functions to the
# basis sets near the nucleus in case of heavy elements. One could start from a
# ZORA/QZ4P basis for example.
# The NOSYM symmetry currently needs to be specified in ADF to enable the CPL
# program to work correctly.
AMS_JOBNAME=first $AMSBIN/ams <<eor
System
atoms
C 0.0 0.0 0.0
C 0.0 0.0 1.20692
H 0.0 0.0 2.26672
H 0.0 0.0 -1.0598
end
end
Task SinglePoint
Engine ADF
title C2H2 nrel
beckegrid
quality good
end
basis
type TZ2P
core None
end
save TAPE10
symmetry NOSYM
xc
gga Becke Perdew
end
Relativity
Level None
End
EndEngine
eor
# The CPL program can run in parallel.
# The specification of what needs to be calculated is given in the nmrcoupling
# block key.
# coupling without the SD term
$AMSBIN/cpl <<eor
adffile first.results/adf.rkf
tape10file first.results/TAPE10
nmrcoupling
dso
pso
scf converge=1e-7
nuclei 1 2 3 4
nuclei 3 4
end
eor
rm logfile
# In this first example, the SD subkey is left out, as this would lead to a very
# strong increase in the required CPU time. The SD subkey is included in the
# second CPL run. That subkey controls the calculation of the so-called spin-
# dipole term.
# The subkeys dso and pso specify that, respectively, the diamagnetic and
# paramagnetic orbital terms will be calculated. The often dominant Fermi
# contact term (FC) is calculated by default and therefore does not have to be
# specified explicitly.
# The scf convergence subkey, in this context, refers to the convergence for the
# solution of the coupled-perturbed Kohn-sham equations which need to be solved
# to obtain to spin-spin couplings.
# The following lines
# nuclei 1 2 3 4
# nuclei 3 4
# specify that one coupled-perturbed Kohn-Sham calculation is performed where
# nucleus number 1 (according to the ordering in the ADF output) is the
# perturbing nucleus, and nuclei 2, 3, and 4 are the perturbed nuclei, and
# another coupled-perturbed Kohn-Sham calculation is performed where nucleus 3
# is the perturbing nucleus and nucleus 4 is the perturbed nucleus.
# The second CPL run also includes the spin-dipole (SD) term, through the SD
# subkey.
# The output of the CPL program first contains a lot of general information, a
# summary of the specified input, and then produces the desired numbers:
# It prints separately the different contributions (FC, DSO, PSO, SD) if
# specified in input and sums them up to a total number. Experimental NSCCs
# between two nuclei A and B are usually reported as J(A,B) in Hertz. From a
# computational point of view, the so-called reduced NSCCs K(A,B) are more
# convenient for comparisons. CPL outputs both. In this example, the Fermi-
# contact term is indeed dominant.
# The first part of the output refers to the line
# nuclei 1 2 3 4
# then the same thing is done for the second similar line where nucleus 3 is the
# perturbing nucleus.
# The output for the second CPL run looks very similar, but now the SD term is
# added to the Fermi contact term, resulting in much longer execution times.
# == Scalar relativistic and spin-orbit calculations ==
# The CPL program also enables calculations using scalar relativistic effects
# (ZORA) and/or spin-orbit effects.
# Schematically, this requires the following changes to the input file with
# respect to a regular spin-orbit calculation and a non-relativistic CPL
# calculation:
# steep (1s) functions may need to be added to the standard basis sets. the
# full-potential option for ZORA is needed in the create runs and all further
# runs: relativistic zora scalar full the molecular ADF calculation should
# contain the line relativistic zora full spinorbit the CPL input is unmodified
# with respect to the example given here. Please check the ADF manual for
# details on relativistic input options.
# coupling including the SD term
$AMSBIN/cpl <<eor
adffile first.results/adf.rkf
tape10file first.results/TAPE10
nmrcoupling
dso
pso
sd
scf converge=1e-7
nuclei 1 2 3 4
nuclei 3 4
end
eor
rm logfile
# redo the same set of calculations, but with a different orientation
# of the molecule this time. Only the CPL calculation without the SD
# term is carried out in order to keep the execution time for this example
# within reasonable limits
AMS_JOBNAME=second $AMSBIN/ams <<eor
System
atoms
C 0.0 0.0 0.0
C 0.0 1.20692 0.0
H 0.0 2.26672 0.0
H 0.0 -1.0598 0.0
end
end
Task SinglePoint
Engine ADF
title C2H2 nrel
beckegrid
quality good
end
basis
core None
type TZ2P
end
save TAPE10
symmetry NOSYM
xc
gga Becke Perdew
end
Relativity
Level None
End
EndEngine
eor
# coupling without the SD term
$AMSBIN/cpl <<eor
adffile second.results/adf.rkf
tape10file second.results/TAPE10
nmrcoupling
dso
pso
scf converge=1e-7
nuclei 1 2 3 4
nuclei 3 4
end
eor
rm logfile
```