Time-dependent density functional theory study of absorption spectra of metallocenes

Extensive TDDFT calculations with various combinations of functionals are carried out to compute low-lying excited states of ferrocene. The combined functional and basis set approach TD-PBE0/6-311++G(d,p) is found to be well-behaved in the calculation of excited states. This choice of functional/basis set can give correct ground-state geometries, excitation energies, absorption spectra, and correct symmetry sequence of low level unoccupied molecular orbitals. This method is applied to the calculation of excitation energies of bis(benzene)chromium and four derivatives of ferrocene and the results are accurate within 0.3 eV. The current study implies that the combination TD-PBE0/6-311++G(d,p) can be used to compute excited state properties of other transition metal complexes.