Advantages of DFT in biological chemistry

• Computational demands are much less severe than for ab initio methods of similar quality - hence the method is applicable to much larger molecules.
• Metals are frequently present in active centers of enzymes. Traditional ab initio methods have severe problems with transition metals. In fact, it can be proved that Hartree-Fock equation cannot be solved for the true metalic state. It is related to the fact that there is a difficulty to converge HF when highest occupied orbitals are very close in energy (the situation very popular for transition metals).
• The DFT, similar to ab initio methods, is nonparametric, i.e., applicable to any molecule. While some say that basis sets are parameters for ab initio and DFT methods, this is an exaggeration. Basis sets are easily derived from atomic calculations, and beside, they were derived long time ago for all elements of periodic table.
• The restriction of DFT being applicable to the ground state only is not usually a problem, unless you study interaction of radiation with biological molecules (e.g., UV induced mutations).

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