Simulation of a tetramer form of 5-iodouracil: The vibrational spectra and molecular structure in the isolated and in the solid state by using DFT calculations

The unit cell found in the crystal was simulated as a tetramer form by density functional calculations (DFT). They were performed to clarify wavenumber assignments of the experimental observed bands in the biomolecule 2,4-dihydroxy-5-iodopyrimidine (5-iodouracil). Comparisons with the gas phase data were also carried out. Correlations with the molecule of uracil were made, and specific scale factors were deduced and employed in the predicted wavenumbers of 5-iodouracil. The scaled wavenumbers were used in the assignment of the IR and Raman experimental spectra. Good reproduction of the experimental wavenumbers is obtained and the % error is very small in the majority of cases. Comparisons were also performed with other 5-substituted uracil derivatives. The NBO atomic charges and several thermodynamic parameters were also calculated. Several linear relationships were established.