# 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.

$ADFBIN/adf <<eor TITLE C2H2 nrel BASIS Type TZ2P Core None END ATOMS C 0.0 0.0 0.0 C 0.0 0.0 1.20692 H 0.0 0.0 2.26672 H 0.0 0.0 -1.0598 END XC GGA Becke Perdew END BeckeGrid Quality good end SYMMETRY NOSYM SAVE TAPE10 eor rm logfile cp TAPE10 t10 cp TAPE21 t21 # The CPL program can run in parallel. # The specification of what needs to be calculated is given in the nmrcoupling # block key. # coupling without the SD term$ADFBIN/cpl <<eor
nmrcoupling
dso
pso
scf converge=1e-7
nuclei 1 2 3 4
nuclei 3 4
end
eor
rm logfile
cp t10 TAPE10
cp t21 TAPE21

# 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

$ADFBIN/cpl <<eor nmrcoupling dso pso sd scf converge=1e-7 nuclei 1 2 3 4 nuclei 3 4 end eor rm logfile mv TAPE21 C2H2_1.t21 # redo the same set of calculations, but with a different orientation # of the molecule this time. Only the CPL calculation without the SD # term is carried out in order to keep the execution time for this example # within reasonable limits rm logfile rm TAPE10$ADFBIN/adf <<eor
TITLE C2H2 nrel

BASIS
Type TZ2P
Core None
CreateOutput None
END

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

XC
GGA Becke Perdew
END

BeckeGrid
Quality good
end
SAVE TAPE10

SYMMETRY NOSYM

eor
rm logfile

# coupling without the SD term