Application of the density functional theory: from biomolecules to transition metal complexes

Density functional theory (DFT), as the most popular method in the modern quantum chemistry field, has been applied to two molecular systems. The first work performs a systematic structure optimization and vibronic analysis of hydrogenated DNA bases (cytosine tautomers and guanine) and base pair (guanine cytosine base pair). A reliable approach combined B3LYP functional with DZP++ basis sets was applied consistently to all structures. The electron affinities of each hydrogenated structure were also predicted. The results have been reported from the Chapter 2 to Chapter 4. In the second work, the heterometallic binuclear cyclopentadienylironnickel carbonyls 5Cp2FeNi(CO)n (n = 3, 2, 1; Cp = -C5H5) have been studied by DFT BP86 functional for comparison with the isoelectronic homometallic dicobalt derivatives Cp2Co2(CO)n. A high spin open-shell structure was found for Cp2FeNi(CO) to have lower total energy than closed-shell structure with multiple Fe-Ni bond, while homometallic Cp2Co2(CO) prefers closed-shell structure with multiple Co-Co bond.