Organic and organometallic molecules are considered to form most promising nonlinear optical materials of the future. One of the key factors for applications in photonics and biophotonics is to find materials with particular nonlinear optical properties at desirable wavelength regions. Theoretical simulations have played and will continue to play an important role in the design of such materials. Over the years, we have developed and applied various computational methods to compute the dynamic second and third order nonlinear optical properties, as well as one-, two-, and three-photon absorption, of molecules at ab initio and density functional theory levels. Special attention has also been paid to understand the role of factors like electron correlation, vibrational motion, the presence of a solvent, dimensionality and conjugation of charge transfer networks etc. We are involved in several projects with technical applications, for instance optical power limiting and photodynamic therapy (see figure). If you are interested in projects in these areas contact Yi Luo or Hans Ågren.