  The large discrepancy between the values of the free energy for DNA
dinucleotides (or dimers) measured by different teams has raised a yet
unsettled debate. Here the free energy is fitted by a three parameter empiric
formula derived in the framework of the crystal basis model of genetic code.
Sum rules are derived and compared satisfactorily with the data. On the basis
of theoretical and phenomenological arguments, a relation between the
correlation functions of dimer distribution and the free energy is assumed.
  From consistency conditions, sum rules are derived. A check of these
conditions with different samples of experimental data is performed, allowing
us to argue on the reliability of the different sets of experimental data.
