Time-dependent Density Functional Response Research Articles

Enhanced optical nonlinearity based on silicon ring

ABSTRACTThe time-dependent density functional cubic response calculations show that silicon analogues of polycyclic aromatic hydrocarbons have much larger non-resonant second-order optical hyperpolarisabilities (γ) than corresponding hydrocarbons. An analysis of fuzzy atom bond order quantitatively reveals that these silicon analogues have a very similar π-electron delocalisation to corresponding hydrocarbons. The enhanced optical nonlinearity of these silicon analogues is attributed to the higher (hyper)polarisabilities of the silicon atom and a significant decrease in transition energies of silicon analogues compared with corresponding hydrocarbons. The silicon analogues of polycyclic aromatic hydrocarbons would be good candidates as infrared nonlinear optical materials due to their enhanced non-resonant nonlinear optical polarisabilities in the infrared range.

Accurate Intermolecular Interaction Energies from a Combination of MP2 and TDDFT Response Theory.

A new method is presented that improves the supermolecular second-order Møller-Plesset (MP2) method for dimer systems with strong dispersion interactions while preserving the generally good performance of MP2 for other types of intermolecular interactions, e.g., hydrogen-bonded systems. This is achieved by adding a correction term to the supermolecular MP2 energy that is determined using time-dependent density functional (TDDFT) response theory and that accounts for the error of the dispersion energy contained in the supermolecular MP2 method. It is shown for the S22 database set of noncovalent complexes and some potential energy curves of noncovalent bound aromatic dimers that the approach gives strong improvements over MP2 if compared to coupled-cluster singles, doubles, and perturbative triples (CCSD(T)) reference energies. An efficient computer implementation of the method is presented that is shown to scale only with the fourth power of the system size and thus leads only to a slightly higher computational cost than that of the supermolecular MP2 itself.

Time Dependent Density Functional Response Theory Calculation of Optical Rotation as a Method for the Assignment of Absolute Configuration of Camphor-Derived Furyl Hydroperoxide and Alcohol

The absolute configuration of (R)-(+)-camphor-derived furyl hydroperoxide and alcohol, which exhibit a number of stable conformations, has been successfully accomplished on the basis of time dependent density functional response theory (TDDFT) calculations of optical rotation. Assuming standard approximations, it has been found that the results are improved by using populations for the conformers derived from free energy differences instead of the commonly used PES minimum differences. This represents the first computational study devoted to the direct determination of absolute configuration of an optically pure hydroperoxide, without any need of its further chemical derivatization.

Synthesis, spectral and redox properties of tetraammine dioxolene ruthenium complexes †

A series of species [RuIII(NH3)4(Cat-R)]n+ have been synthesized where Cat-R is a catecholate dianion having the substituent R = CO2−, CO2H, OMe or H. These so-called parent species were characterized by their electronic spectra, FTIR, mass spectrum, cyclic voltammetry and EPR. Controlled potential reduction yields [RuII(NH3)4(Cat-R)](n − 1)+ while controlled potential oxidation yields [RuII(NH3)4(Q-R)](n + 1)+ (Q-R = substituted quinone). Density Functional Theory (DFT) was primarily used to explore the electronic structures of these complexes. Application of the INDO semi-empirical model proved less useful. Time dependent density functional response theory was used to calculate the electronic spectra of the species with R = H. The electronic spectra of the closed shell species are well reproduced by the calculations. The physical properties of these complexes indicate a charge delocalized system reminiscent of a delocalized organic molecule. The simple valence descriptions noted above are convenient to use but do not reflect the actual electronic structure. The electronic spectra of the parent species are temperature dependent. The visible region charge transfer band shifts by about 1500 cm−1 to higher energy in acidic media at liquid nitrogen temperature. This is interpreted in terms of solvent effects rather than valence tautomerism. The electrochemical properties of [RuIII(NH3)4(Cat-R)], in aqueous solution, reveal the first example of a reversible and stable Ru–quinone species in that medium. The pKa values for several dioxolene species, with R = CO2−, are derived from a Pourbaix diagram.