![\fbox{
\parbox[h][\height][l]{12cm}{
\small
\noindent
{\bf Reference literature:...
...\newblock {\em J.Chem.Phys.}, {\bf 121},\hspace{0.25em} 7614 (2004)
\end{list}}}](img45.png)
The calculation of hyperfine coupling tensors (in vacuum or in solution) is invoked by the keyword *ESR in the **RESPONSE input module. Thus a complete input file for the calculation of hyperfine coupling tensors will be:
**DALTON INPUT .RUN RESPONSE **INTEGRALS .FC .SD **WAVE FUNCTIONS .HF **RESPON .TRPFLG *ESR .ATOMS 2 1 2 .FCCALC .SDCALC .MAXIT 30 **END OF DALTON INPUT
This will invoke the calculation of hyperfine coupling tensors using the Restricted-Unrestricted methodology [76]. In this approach, the unperturbed molecular system is described with a spin-restricted MCSCF wave function or spin-restricted Kohn-Sham DFT, and when the perturbation--Fermi Contact or Spin Dipole operators--is turned on, the wave function spin relaxes and all first-order molecular properties are evaluated as the sum of the conventional average value term and a relaxation term that includes the response of the wave function to the perturbations.
The selection of a flexible atomic orbital basis set is decisive
in these calculations. Dunning's cc-pVTZ or Widmark's basis sets with some
functions uncontracted, and one or two sets of diffuse functions and
several tight 
functions added have been shown to provide accurate
hyperfine coupling tensors [77].
If more close control of the different parts of the calculation of hyperfine coupling tensors is wanted, we refer the reader to the sections describing the options available.