This project forms part of a joint CASKNAW PSA programme of the Non-linear Optics group of the FJIRSM Institute in Fuzhou, China and our Theoretical Chemistry Group. It focuses on the development and application of time-dependent density functional theory (TDDFT) for the calculation and analysis of nonlinear optical (NLO) properties of organo-metallic compounds. The common interests are:
The theoretical development and implementation have predominantly been done at our group in Groningen, with prof. dr. R. Broer and dr. ir. P. L. de Boeij project leaders. First, we have developed a TDDFT-SOS method for computing the frequency-dependent hyperpolarizability tensors, which represent the second harmonic generation (SHG) phenomena. Our TDDFT-SOS method is formulated in such a way that we can easily perform the analysis of the NLO phenomena. The method also leads to reduced computational cost. It offers a decomposition of the response functions into contributions from individual states. The main complication to solve in TDDFT-SOS approach is the calculation of transition dipole moments, which relies on the knowledge of the wave-functions of excited states. The resulting TDDFT-SOS method is implemented in the ADF code. This new extension of the code describes not only SHG, but also the other nonlinear optical processes such as optical rectification (OR), sum-frequency generation (SFG), difference-frequency generation (DFG), third harmonic generation (THG), etc. The TDDFT-SOS method also forms a good starting point to do a fragment analysis. In this way, detailed information on the chemical and structural origins of the nonlinear optical responses can be obtained.
The TDDFT-SOS method has been applied to a variety of organo-metallic compounds. The aim is to search for new materials with enhance nonlinear optical properties. These calculations have mostly been done at FJIRSM in Fuzhou China with prof. dr. K. Wu as project leader. The Fuzhou group has also developed a new single-parameter hybrid exchange-correlation (XC) density functional, which has been shown to be suitable for the study of NLO properties, and in particular for the organo-metallic compounds. In addition, they also extended the basis sets used by the ADF program by adding diffuse functions, which turn out to be essential for the convergence of hyperpolarizability calculations. These new developments make it possible to perform a large-scale screening and simulation of large organo-metallic compounds with effective and affordable computations. The FJIRSM group has studied a large number of non-centro-symmetric organo-metallic and transition metal cluster compounds in order to explore and understand the relationship between the microscopic structure and nonlinear optical properties. On the basis of these systematic studies, the origin of the nonlinear optical activity of organo-metallic compounds could be related to charge transfer between the organic ligands and the transition metal core. The FJIRSM group also made progress in the synthesis of novel organo-metallic materials with potential nonlinear optical functionality.