The performance of density functional based methods in the description of selected biological systems and processes.

The catalytic mechanism of the purple acid phosphatase enzyme, electronic and structural properties of AT(GC)Zn(2)(OH)(2)(H(2)O)(2), a metal mediated DNA dimer, and UV-vis spectroscopic features of the chlorophyll-a (Chl-a) system, a potential photosensitizer, are the three different and interesting topics chosen to verify how the oldest and the most recent density functional methods work in the description of biological systems. Reported data indicate that good results can be obtained provided that computational strategies, exchange-correlation functionals and basis sets are carefully selected and applied.